Final Report Summary - ENSEMBLE (Engineered Self-organized Multi-component structures with novel controllable Electromagnetic functionalities)
Executive Summary:
Research and industrial development depends on novel materials, on their associated novel properties and enabled by them functionalities. That is why the overall objective of ENSEMBLE project was to design, manufacture, and characterize self-organised multi-component and multi-scale structures, which display: controlled geometrical motifs, controlled composition and physico-chemical structure, controllable size of structuring ranging from micro- to nano, novel predictable and controllable electromagnetic properties and metamaterials capabilities.
In order to achieve the main objective ENSEMBLE Project developed:
(i) new modelling tools in order to gain insight into eutectic self-organization and the control mechanisms behind,
(ii) new modelling tools enabling design of composite materials with special electromagnetic properties as well as comparing the experimental results for obtained materials with theory,
(iii) novel technologies and novel materials which were characterized by often specially designed characterization set-ups (iv), as well as finally we demonstrated new materials exhibiting special electromagnetic properties (v).
To understand the self-organization processes in eutectic growth we have developed multi-scale modeling tools. These tools all working in 3D are:
(i) an atomistic phase-field theory [the phase-field crystal (PFC) approach] for unary and binary solidification;
(ii) a quantitative phase-field model working on the submicron to micron scale;
(iii) a quantitative phase-field model coupled with hydrodynamics (with the Navier-Stokes equation) in three dimensions relying of spectral methods combined with operator splitting; and
(iv) a quantitative multi-phase-field theory working above the micron scale, obtained by combining the quantitative multi-phase-field theory of Folch and Plapp with Kim's model.
To understand the electromagnetic properties of the manufactured materials and to be able to design materials with special electromagnetic properties on-demand we generated simple models and numerical methods that allowed electromagnetic modelling and simulations of eutectic self-organised micro and nanostructures, and enabled assistance in the design and characterization.
Project Context and Objectives:
MATERIALS: The materials investigated in this project were self-organised eutectic or eutectic-like submicron and nanostructures. A eutectic is characterized by the formation of two or more non-mixable crystals from a completely mixable melt. Directionally solidified eutectics (DSE) have excellent potential for use in different types of light/electromagnetic waves manipulation. DSE may be defined as composite materials with a complex and homogeneous micro- or nanostructure which controls their properties. Eutectics exhibit the unusual characteristic of being both monolith and multicomponent/multiphase in nature with sharp, clean and strong interfaces. Eutectic composites may have multiple functionalities arising from the constituent phases of the eutectic (additive properties) as well as new functionalities which do not exist in the component phases but which uniquely derive from their combination and appropriate structuring on the nano- or micro-scale (product properties). The product properties are particularly important, as they promise metamaterial-like behaviour of appropriately-designed and engineered eutectic materials.
NEW PROPERTIES/FUNCTIONALITIES: The collaborative project did foresee research for the development of nanostructures by self-organisation aimed at motifs capable of generating new functionalities. The focus was on generating new knowledge of self-organisation principles in eutectic materials with potential cutting-edge electromagnetic properties/functionalities.
General CONCEPT: Growth of eutectics is recognized as a paradigm for pattern-forming or 'self-organising systems'. Self-organised structures on size scales reaching down to the submicron and nanoscale regime emerge due to the interplay of chemical diffusion and capillarity. The fundamentally novel CONCEPT of the project was to utilize - for the first time - eutectic self-organisation for the preparation of multi-component and multi-scale structures with controlled physicochemical and structural properties, with geometrical motifs capable of generating novel, predictable and controllable electromagnetic functionalities. This required a deeper understanding of factors influencing eutectic self-organisation mechanisms on the submicron/nanoscale. Accordingly, the main topic and activity of the project was to generate new knowledge of eutectic self-organisation on this scale, by combining state-of-the-art experimental and modelling techniques. Further the objective was to predict and design self-organised multi-component and multi-scale structures with so far unseen physicochemical and structural properties. This was combined with the electromagnetic design of complex structures which can generate unusual electromagnetic functionalities.
The following results of the project were expected:
a) the ability to predict the occurrence of specific patterns in eutectic systems,
b) knowledge of how to design nanopatterned materials with controlled physicochemical and structural properties,
c) methodologies for the design and fabrication of self-organised multi-component and multi-scale structures with unusual electromagnetic functionalities, and
d) experimental realisation of these self-organised systems.
The planned programme of research was expected to open new horizons for utilizing self-organised structures in various fields.
The advantage of using eutectic solidification on the submicron/nanometer scale is the availability of monolithic composite materials with clean and strong interfaces and a broad range of possible components with the possibility to realize a broad variety of geometrical motifs. In order to achieve controlled physicochemical and structural properties capable of generating novel, beyond the state-of-the-art electromagnetic properties, it was necessary to investigate the combination of various component materials with diverse types of structuring. Due to the extreme conditions needed to realize eutectic solidification on the nanoscale, fairly little is known about the mechanisms operating in this regime, including: diffusion on the nanoscale; the effect of substrate/seed materials; underlying anisotropies; and surface nucleation.
The TASKS of this project were:
a) to develop new knowledge of the control parameters/material properties that govern eutectic pattern formation on the nanoscale via phase field modelling;
b) to develop new tools for control of self-organisation in eutectics, leading to the ability to achieve desired structural properties (geometrical motifs) and desired, controlled physico-chemical properties;
c) to combine a knowledge of self-organisation and materials chemistry with the ability to design and discover new physical phenomena in such media;
d) to develop analytical and numerical techniques for designing and modelling self-organised materials with novel and advanced electromagnetic properties;
e) to develop and master the necessary nano- and submicron fabrication techniques;
f) to analyze the potential of self-organised eutectic materials for practical applications in photonic devices;
g) to examine the possibilities of combining eutectic self-organisation with other means of controlled structuring, for the generation of even more advanced materials.
The execution of the above tasks was planned to lead to achievement of the following objective:
The OBJECTIVE of this project was to design, manufacture, and characterize self-organised multi-component and multi-scale structures, which display:
O1: Controlled geometrical motifs, including rod-like, lamellar, globular and percolating patterns, which can provide the expected electromagnetic functionalities;
O2: Controlled composition and physico-chemical structure, realized by combining materials with different refractive indices or different optical properties, which can provide the theoretically-predicted electromagnetic functionalities;
O3: Controllable size of structuring ranging from micro- to nano scale following the theoretical predictions;
O4: Novel predictable and controllable electromagnetic properties. At least one of the following properties can be obtained: controlled effective refractive index,; artificial magnetism; controlled dispersion; controlled sub-wavelength field generation and enhancement.
O5: Metamaterials capabilities which extend to applications such as: imaging, high compact optoelectronic devices, efficient photovoltaics and active devices.
Project Results:
In the theory/modeling domain of eutectic growth we have developed multi-scale modeling tools in order to gain further insight into eutectic self-organization. These tools all working in 3D are:
Model I - an atomistic phase-field theory [termed the phase-field crystal (PFC) approach] for unary and binary solidification. We have worked out an efficient method to solve numerically the binary phase-field crystal (PFC) model. Using the operator splitting method, the problem has been decomposed into sub-problems that can be solved more efficiently. It has been shown that our method speeds up the computations by orders of magnitude relative to the conventional explicit finite difference scheme, while the costs of the pointwise implicit solution per time step remains low. We have also demonstrated that our method can efficiently be parallelized for distributed memory systems, where an excellent scalability with the number of CPUs has been observed.
We have performed a systematic study of crystallization using the PFC approach, leading to the following results:
(a) determination of the unary and binary phase diagrams,
(b) a demonstration that dendrites can be grown in both unary (bcc and fcc) and binary systems,
(c) the identification of new homogeneous and heterogeneous nucleation modes;
(d) a discovery that the competition between diffusion controlled and diffusionless growth modes yield fractallike growth forms,
(e) determination of the anisotropies of the growth rate and the interfacial free energy,
(f) extension of the PFC approach to the modeling of colloid patterning experiments,
(g) the observation that - owing to a particle diffusion controlled relaxation dynamics of the particle density - the PFC model predicts eutectic cells in a binary system;
(h) a demonstration that both in 2D and 3D, the eutectic structures forming on the nanoscale relax on the timescale of solidification.
Model II - a quantitative phase-field model working on the submicron to micron scale. Via comparing the simulations directly to experiments, we have demonstrated on test systems of known properties (Ag-Cu) that Models II is indeed quantitative down to the nanoscale. We have explored the relationship between the nanoscale eutectic patterns and model parameters (anisotropies of the solid-liquid and solid-solid interfaces)/technological conditions (undercooling, temperature gradients, composition, pulling velocity, misorientation of growth relative to pulling). It has been shown, e.g. that the roughness of the solid-liquid interfaces due to the anisotropy of the interfacial free energies, the cross-sectional temperature gradients, crystal misorientation relative to pulling direction, and the anisotropy of the interface energies play essential roles in determining the eutectic pattern forming on the nanoscale.
Model III - Model II coupled with hydrodynamics in three dimensions relying of spectral methods combined with operator splitting. Using Model III, we have confirmed for the Ag-Cu system that the osmotic flow destabilizes the planar interface, yielding dendritic humps of concentric ring pattern (similar to the ternary two-phase dendritic dendrites, however, now in a binary system).
Model IV - a quantitative multi-phase-field theory working above the micron scale. In the case the of Al-Al2Cu system, we have demonstrated that our multi-phase-field model is indeed quantitative. Model IV has predicted a so far unknown morphological transition between cylindrical rods to rods of hexagonal cross-section, when dynamically increasing the volume fraction of the 'rod-phase'. Furthermore, incorporating cubic anisotropies for the solid-solid and solid-liquid interfacial free energies, we have obtained rectangular morphologies akin to those seen in the respective experiments on eutectic Al-Al2Cu. Finally, Model IV has been adopted for quasi-biner eutectic systems, where the solid phases are line compounds. In the case of LiF-NaCl system, we have observed a quantitative agreement between parameter free predictions and experimental data from experiments done within the Project.
Highlights of significant results
- First demonstration that the phase-field crystal method can handle multiple crystalline phases and their anisotropies;
- Systematic exploration of the abilities of the PFC model for describing crystalline freezing;
- Identification of new modes for homogeneous/heterogeneous crystal nucleation and growth on the basis of atomistic simulations;
- Demonstration that osmotic-pressure-induced flow destabilizes the eutectic growth front, leading to the formation of eutectic cells;
- Development of a quantitative multi-phase-field theory (Model IV) that can accommodate data from thermodynamic databases and its application to the Al-Al2Cu eutectic system, where an excellent agreement has been seen with experients;
- Extension of our quantitative multi-phase-field theory to eutectic systems of stoichiometric solids and its application to the quasi-binary LiF-NaCl system, where a good agreement has been found with experiments;
- Exploration of spiralling two-phase eutectic dendrites in ternary systems;
- First systematic mapping of the effect of anisotropic phase-boundary on nanoscale eutectic self-organization.
Examples of the main results of WP1 are given below:
Comparison of quantitative Phase-Field (PF) predictions with experiments: Model II (and Model III in the no hydrodynamics limit) solved with a combination of a spectral method and operator splitting has been used to predict the eutectic wavelength vs. velocity relationship for the eutectic Ag-Cu binary alloy, whereas Model IV has been tested in the case of the Al-Al2Cu system. In both cases values for all the model parameters have been taken from experiments. In both cases, an excellent agreement can be seen between experiments and simulations without adjustable parameters.
Atomistic modeling of eutectic self-organization on the nanoscale: Many of the important features of eutectic self-organization such as anisotropic growth, effects of crystal defects and elasticity can only be understood within an atomistic description of solidification. We have developed, implemented, and numerically validated a semi-implicit fully spectral scheme to solve the binary phase-field-crystal equations in two dimensions. Being a simple dynamical density functional theory this is an atomistic model, in which the atomic positions, the crystal structure, the elastic properties, and the anisotropies of the solid-liquid interface and the growth kinetics are predicted.
The ability to model various crystal structures is an important prerequisite of describing eutectic solidification. After extending Model I to 3D, first for a single component case, we have proven that besides the stable bcc structure, metastable fcc and hcp crystalline structures may also form in this model. Investigating the orientation dependence of the growth rate we have obtained quantitative information on the anisotropy of the kinetic coefficient. Subsequently, we have performed a systematic evaluation of the phase-field crystal model (Model I) in 2D and 3D, to see how far it can be applied for describing solidification in undercooled liquids. In this, we were advancing from simpler to more complex cases: We started with single component 2D and 3D systems, and turned then to the binary 2D and 3D systems. We have determined the respective phase-diagrams (in 3D bcc, fcc, and hcp stability domains have been identified), the dependence of the interface properties on the model parameters, and demonstrated that dendritic and eutectic structures develop in 2D and 3D, and that an amorphous precursor precedes crystal nucleation.
It has also been shown that in the single component limit the PFC can also be regarded a reasonable model of colloidal crystal aggregation. At large driving forces, a transition from diffusion-controlled to diffusionless growth mechanism has been observed in even the single component limit.
Remarkably, we have observed eutectic solidification on the nanometer scale, and the formation of eutectic cells in large-scale 2D simulations. The mobility of the phase boundaries in the nanoscale eutectics seems to be fairly high both in 2D and 3D.
Snapshots of eutectic solidification on the atomistic scale in the binary phase-field crystal model in three dimensions. Time elapses from left to right. The size of the simulation window is 450 - 300 - 300. Simulation has been started by placing two supercritical clusters of different compositions into the simulation window. Note the perfect structure initially, which breaks up to grains at later stages of the simulation. Remarkably, on this nanoscale the eutectic pattern evolves on a timescale comparable with the time of solidification. The brown and grey colours denote the terminal solutions of the two crystalline phases.
Exploration of trends in a quantitative phase-field modeling of eutectic soldification (Models II and III): Quantitative phase-field theoretical Model II has been used to investigate the trends obtained via a simple qualitative model of eutectic solidification during the previous reporting period. Simulations performed with Model II confirmed the tendencies obtained with the simpler model.
The relationships so far identified are as follows:
a. comparable volume fractions ? enhanced propensity toward lamellar structures
b. increasing crystal misorientation relative to pulling direction ? enhances propensity to form lamellae and regularizes the eutectic pattern
c. misoriented anisotropies of cubic or octahedral equilibrium shapes ? helps the formation of lamellar structures that have perpendicular orientations to each other
d. temperature gradient perpendicular to pulling ? regularizes the eutectic pattern
e. reducing the solid-liquid interfacial free energy of one of the constituents? enhances propensity of tubular structures
f. increasing the anisotropy of the solid-liquid interface free energy ? increases the roughness of the solid-liquid interface
g. increasing roughness of the solid-liquid interface ? enhances correlation between eutectic pattern and surface morphology
h. increasing the temperature gradient in the pulling direction ? reduces the roughness of the solid-liquid interface
i. the value for C = 2v remains reasonably constant even at high undercoolings
Relying on the identified trends, we have performed a systematic search for the SRR and fishnet structures. In this we have varied simultaneously such (usually unknown) properties as the magnitude and anisotropy of the solid-liquid interface free energy and the anisotropy of the solid-solid interface free energy. Other parameters, we changed, were the temperature and its gradient. Temperature gradient in the pulling direction usually stabilizes the cross-sectional pattern. We have been able to produce patterns that show resemblance to the experimental SSR and fishnet structures, although the agreement is not fully satisfactory.
Approximants of SRR (upper row) and fishnet (lower row) structures (side and cross-sectionals views are shown): The interplay of the anisotropies of the solid-liquid and solid-solid interface free energies have been utilized to produce these structures.
Model III: It has been shown that the solid-liquid interface is destabilized by osmotic pressure driven flow, yielding eutectic cells resembling to the early stage of 'eutectic dendrites' recently discovered experimentally, and may lead to concentric ring structures.
Spiraling two-phase eutectic dendrites in ternary systems: To model the formation of spiraling eutectic patterns shown in Amended Annex I of the ENSEMBLE project has been studied experimentally recently, we have adopted Model II to a symmetric model ternary system. Starting from a random solid-phase pattern and with a perturbation of wavelength in the range of the Mullins-Sekerka instability, humps form that evolve into full scale dendritic structures composed of A-rich and B-rich solid solutions. The eutectic pattern on the dendrites has been observed to be one of the four possibilities: concentric rings, and single, double and triple spiraling structures, the latter appearing at late stage on the largest dendrite. Of nine peaks, five shows the ring structure and four the single-spiral pattern (one rotating clockwise and three counter-clockwise). Some of the dendrites disappear others grow on their expense. This is the first successful modeling of two-phase eutectic dendrites.
Comparison of predicted solidification morphology with experiment for Al-Al2Cu: In this system rectangular motives have been observed experimentally that resemble to the SRR-type motifs seen in TiO2-SrTiO3. Unfortunately, neither experimental nor molecular dynamics data are available for the anisotropies of the interfacial free energies in this system. Therefore, we have attempted reverse engineering: We have adjusted of the anisotropies of the solid-solid and solid-liquid interface energies in Model IV until the forming eutectic pattern matched reasonably with the experimentally observed patterns.
The resemblance needs yet to be improved. We wish to note in this respect that we do not know the true anisotropies, and that stress-induced growth anisotropy, which has been neglected in this study, may also influence the growth morphology.
The same model has been adopted to systems consisting of two line compounds as the solid phases, and has been applied for the LiF-NaCl system, leading to growth rate that are consistent with those found experimentally by the experimental partners in the project.
In the theory/modelling domain of electromagnetic properties we generated simple models and numerical methods that allowed electromagnetic modelling and simulations of eutectic self-organised micro and nanostructures, and enabled assistance in the design and characterization.
(i) A powerful and fast quasianalytical multiple scattering of multipolar expansions method and numerical boundary element method that solves the full Maxwell equations have been developed. These methods have been applied to investigate the electromagnetic properties of a variety complex eutectic systems and structures.
(ii) Investigation of validity of homogeneous effective medium descriptions in alkali-halide systems has been provided by comparison of numerical results obtained by FDTD and finite element method with analytical effective medium models, for the eutectic systems of LiF in NaCl and LiF in KCl in the frequency regime of the polaritonic resonances of the samples (1-12 THz).
(iii) We have explained the scattering characteristics of eutectic structures made of polaritonic rods in a host material and showed that these structures could lead to negative refractive index and focusing.
(iv) We have demonstrated a new kind of waveguides involving eutectics composed of alkali-halide wires embedded in an alkali-halide matrix (LiF in NaCl and KCl). These samples can be used to propagate signals through electromagnetic (polaritonic) resonances confined to the gap region between two adjacent wires, which can be potentially useful for near-field imaging.
(v) The electromagnetic response of the self-organized microstructure of terbium-scandium-aluminium garnet-terbium-scandium perovskite eutectic (Tb3Sc2Al3O12-TbScO3) suggests a possibility to guide a signal through the sample along the wires by means of the individual TbScO3 wires electromagnetic modes. The possibility to obtain super-resolution imaging has been studied.
(vi) We have proposed a system made from arrays of silver wires separated by dielectric material as a compact waveguide at optical frequencies that presents highly-confined plasmon gap modes concentrated in the regions between the wires.
(vii) We have demonstrated a possibility of broadband magnetic response, negative permittivity and permeability in designed prototype of split-ring resonator-like structures based on SrTiO3-TiO2 eutectic.
(viii) We have shown that chiral structures can exhibit negative refractive index and can be more promising candidates for eutectic-based negative refractive index metamaterials than traditional based on SRRs.
(ix) Ability of doping the eutectic materials with plasmonic (metal) nanoparticles has been demonstrated. This enables a possibility to move the electromagnetic excitations from mid infrared frequency to visible and near infrared and use eutectic in a large range of applications. We have modelled and characterized the plasmonic properties (localized surface plasmons) of the metal nanoparticles with different sizes and shapes and that can be potentially used for doping of complex eutectic.
In the fabrication domain of self-organized materials we have successfully grown eutectic and eutectic-like materials with controlled geometrical motifs including rodlike, lamellar, or with such unusual geometries like eutectics containing TiO2 phase where we did obtain geometries resembling working metamaterial structures (split-ring-resonator and fishet-like structures). We presented an anisotropic split-tube structure with fractal multiscale character. We have demonstrated control of eutectic structures, from fibrous to lammelar, according to the growth rate used. We have successfully grown materials with controlled composition and physico-chemical structure, realized by combining materials with different refractive indices or different optical properties aiming at specific electromagnetic functionalities. We have successfully obtained metallodielectric materials incorporating metals at the melt extraction step or after subsequent treatment or by producing templates for subsequent metalization. We succeeded in pushing the refinement of the structure down to the nanoscale utilizing various methodologies such as increasing the solidification rate of the materials, adding additional phase, doping with nanoparticles. By combining the controllable composition, geometrical motifs and size of structuring we demonstrated materials with predictable and controllable electromagnetic properties.
Metallodielectric materials for plasmonic applications: Most of currently, made materials with extraordinary electromagnetic properties (eg. metamaterials) are made with the use of one component material being metal which provides negative electric permittivity. There were not many experiments done in which metal-oxide eutectics were investigated. The most interesting metals are metals with high conductivity, like silver and gold. We employed several metodologies for manufacturing of metallodielectric materials: Direct growth from the melt was applied for Bi2O3-Ag and Cu2O/CuO-Ag eutectics were grown directly from the melt. The Bi2O3-Ag eutectic exhibits 3D multiscale micro/nanostructure microstructure of Ag precipitates embedded in Bi2O3 matrix while Cu2O/CuO-Ag eutectic exhibits micron-scale structure. Growth of eutectics where one phase can be easily reduced to metal and subsequent thermochemical reduction was applied and lead to formation of following composites Co-CeO2, Co-GDC, Ni-TiO2, Ni-YSZ alternate lamellae stacks. Further, experiments to infiltrate templates prepared by etching away one of the phases of the dielectric-dielectric with metals as silver and gold eutectic were performed. They lead to manufacturing metallodielectric surfaces such as Ag- NaMgF3, Ag-LiF, Ag-CaF2-LiF, Ag-Tb3Sc2Al3O12, Ag-TbScO3, Au-TiO2, Ag-SrTiO3-TO2, Au- PrAlO3-PrAl11O18 with various surface geometries as pillars, double pillars, arrays of holes, elongated holes. Finally to enter the nanosize regime we developed a new method of manufacturing nanometallodielectric materials by doping dielectric matrices as single crystalline matrices, glasses and eutectic matrices by doping with metallic nanoparticles. Nanoparticles tend to agglomerate as their surface-to-volume ratio is high, leading to strong attractive electrostatic forces. A distinct advantage of the -PD method was discovered that it helps de-agglomerate the nanoparticles, as they are transported through the nozzle at the centre of the crucible die. During the flow of liquid through the capillary, bubble formation (cavitation) and collapsing of formed bubbles (implosion) can occur. Previous investigations of liquid flows through capillaries have suggested that this phenomenon can lead to separation of nanoparticles originally present as larger agglomerates, as the shock waves are created at the locations of the collapsed bubbles.
De-agglomeration of Ag nanoparticles during directional solidification using the micro-pulling-down method. (a) Scheme of the micro-pulling-down method and of the de-agglomeration process occurring. (b) SEM image of the agglomerated Ag nanopowder used for doping the NBP matrix. (c, d) SEM images of small (c) and large (d) nanoparticles embedded in the NBP matrix after the solidification process. (e), Comparison of coloration of three solutions (left to right): (i) pure NBP glass dissolved in HCl (aq); (ii) Ag nanopowder mixed in an ultrasonic mixer in isopropanol; the black colour is due to Ag agglomerates; (iii) NBP:nAg glass dissolved in HCl (aq), the yellow coloration is due to dispersed Ag nanoparticles.
Towards nanosize: Nanosize scale materials can provide electromagnetic responses in the visible frequencies. That is it was important to develop methodologies to enter the nanosize regime with the investigated materials. Several approaches were taken. The most straightforward was applying high growth rates which enabled manufacturing of PrAlO3-PrAl11O18 rodlike eutectic with rods with diameter beyond 200 nm, with the growth rate of 1200 mm/h. Other submicron rodlike microstructures obtained in this way included Al2O3-EuAlO3, Al2O3-GdAlO3 and MnOx-YSZ eutectics. Another example of grown in this way of submicron scale lamellar, ordered microstructures were Ni-YSZ, CeO2 CoO, GDC-CoO eutectics. Adding a third phase into eutectic - ternary eutectic led down to 50 nm achievable sizes of the precipitates. Manufacturing eutectic-like composites were the growth led to growth of one phase in-between the grains of the other phase as in Bi2O3-Ag eutectic led to multiscale structure with smallest silver precipitates getting down to below 10 nm. Annealing of NiTiO3-TiO2 eutectic with reducing atmospheres led to formation of Ni particles attached to TiO2 microstructure. Depending on the time and temperature of annealing nanoscale Ni particles could be formed.
One of the proposed ways to get to the nano-regime was the use of nanoparticles especially metallic nanoparticles, which could be incorporated both in dielectric material and in the eutectic itself. Experiments were performed using single crystalline matrices as Bi12GeO20 (melting point (mp) = 1203 K) and nanoparticles of Ni (mp=1726 K) 20 nm, Co (mp=1768 K) 28 nm, and Mo (mp=2896 K) 70 nm. The crystals with up to 10 wt% of the nanoparticles were obtained. All of them had metallic lustre. In the obtained crystals the nanoparticles enlarged a little but stayed in the nano-range, and they oxidized or formed other compounds. The glass matrices were used. The most successful one was Na5B2P3O13 (NBP). It has been successfully doped with: (i) Ag spherical nanoparticles, (ii) antimony-tin oxide spherical nanoparticles, (iii) Ag wires, (iv) Ag spherical nanoparticles and erbium ions. The manufacturing of composites including nanoparticles of various composition, specific shape and size was enabled by the described above method which allowed for non-chemical doping of the dielectric matrices by the metallic nanoparticles. Also eutectics including Na5B2P3O13 phase were grown doped with Ag spherical nanoparticles.
Further we focused on manufacturing controlled composition and physico-chemical structure, realized by combining materials with different refractive indices or different optical properties, which can provide the theoretically-predicted electromagnetic functionalities.
Eutectic materials for subwavelength waveguiding and subwavelength focusing based on phonon polaritons: Anisotropic materials (rodlike or layered structures) with anisotropic permittivity (rods of metal embedded in dielectric or alternating metal-dielectric layers) can exhibit subwavelength waveguiding and subwavelength focusing as well as negative refraction. Regular eutectics exhibit rodlike and lamellar microstructures. It has been demonstrated that dielectric materials may have behaviour similar to plasmonic metals, and rods or layers made of such materials (polaritonic materials) may provide the above described properties. One of the important results of this project was the identification of suitable polaritonic eutectics, that is to say, eutectics with coupled fibrous microstructures where strong refractive index contrast among the component phases arise in the phonon-polariton dispersion region (FIR or THz range), as potential subwavelength guiding and focusing structures. Eutectics with fibrous structure include alkali-halides, where long LiF single crystal fibres are embedded in NaCl or KCl matrices.
The optical properties of these structures are highly anisotropic. In the medium and far infrared regions of the electromagnetic spectrum the phonon dispersion bands have wavelengths similar to the scale of phase interspacing; then unconventional optical effects can be expected. We especially concentrated on fibrous microstructures at the wavelength ranges, where the rods exhibit negative dielectric permittivity and the matrix positive permittivity. The alkali halide eutectics NaCl-LiF (25 vol% LiF fiber) and KCl-LiF (7 vol% LiF fibers) present phonon-polariton resonances at 33 μm (LiF), 70 μm (KCl) and 61 μm (NaCl) (9.18 THz, 4.13 THz and 4.83 THz respectively). We solidified ingots of 1 cm2 section achieving inter-rod spacing from 25 to 3 μm (and LiF rod diameters from 11 to 0.8 μm). In those systems anisotropic dielectric constant is obtained in various spectral windows. The rods have negative dielectric constant in the 16 to 32 μm wavelength range. Thin slices to achieve transparency have been prepared. We have also grown alkali halide eutectics with ternary composition NaCl-LiF-CaF2, in an effort to diminish the microstructure size and consequently expand the range where effective medium models describe the system and, more importantly, the resolution of devices based on self-focusing in the material is increased. Other fluoride eutectics of LiYF4-LiF (with larger vol% of LiF) have also been prepared in a wide range of solidification rates. Other investigated materials include Tb3Sc2Al3O12-TbScO3 system, where the operation wavelengths are shorter (16-18 μm) and the operation temperatures may be higher. Microstructures of examples of polaritonic materials grown within the project are shown above.
Materials with excitonic resonances: Except of plasmonic and phononic resonances we also investigated materials with excitonic resonances, which appear in the UV region. ZnO is a semiconductor with a wide energy gap (approximately 3.3 eV). It is very interesting and intensively investigated material for applications in optoelectronics. Theoretical calculations also show that ZnO doped with magnetic ions, can be semimagnetic semiconductor at room temperature. ZnO-ZnWO4 eutectic system was obtained from the liquid phase by the micro-pulling down method. The microstructure of ZnO-ZnWO4 eutectic forms the broken-lamellar structure, where ZnWO4 is a matrix and ZnO are broken lamellas. Despite the excitonic peak additional peak is observed in transmission which is strongly nanostructure-dependent. Its origin is not yet clear but it could be due to magnetic resonance due to excitons.
Systems for active change of dielectric-metallic behaviour: The eutectic systems with large difference in the bandgaps between the two components phases were sought and grown, since they can provide the possibility of an active change of such a composite material with applied electromagnetic radiation from a dielectric-dielectric system to a metallo-dielectric system. GdCrO3-Gd2O3, GdFeO3-Gd2O3 and MnOx-YSZ eutectics were grown. The GdFeO3-Gd2O3 eutectic has rod-like microstructure with GdFeO3 matrix and Gd2O3 rods (see picture on the right). It was shown that the green coloration comes from the GdCrO3 phase, which absorption edge is approximately at 500nm. The large difference in the bandgaps of GdCrO3 and Gd2O3 can provide the possibility of an active change of this material with applied electromagnetic radiation from a dielectric-dielectric system to a dielectric system with metallic wires. The eutectic possesses a distinct resonance at 2.16 THz (red line). Although, the s-polarized THz electric field is propagating along the GdCrO3 rods in the Gd2O3 matrix, a slight blueshift of this peak and the appearance of a second one at 1.57 THz are observed when the sample is rotated 90 degrees in respect to its initial position (black line). The measurements are being continued in order to demonstrate a switch on/switch off metamaterial where the dielectric-dielectric material will be changed to metal-dielectric material dynamically.
Eutectics for solar energy harvesting applications: To our knowledge, eutectics have not yet been implemented in any other type of energy system than solid oxide fuel cells, SOFC. However they seem to have a lot of potential, since (i) hybrid semiconducting materials of various component phases can be obtained; (ii) component phases are characterized with high crystallinity; and (iii) the micro/nanostructure refinement can be controlled using the growth rate. One of the proposed in the project demonstrators was an efficient photovoltaic device. The first of the ideas how to use the eutectics for solar energy harvesting appeared with the example of SrTiO3-TiO2 eutectic, which contains two phases (SrTiO3 and TiO2) which are investigated as photoanodes in photoelectrochemical cell (PEC), for utilizing the solar energy for production of hydrogen. The eutectic bi-crystals have been prepared by the micro-pulling down method, with special type of crucible with rectangular shaper enabling manufacturing of bigger samples of 2x10x40 mm. This has been necessary for proper electrodes preparation. The electrodes have been prepared out of this material and the first experiments of photocurrent have been performed on polished to 15-30 micrometers samples. Than further processed samples were introduced on fluor doped tin oxide glass (FTO) and electrical contact was made using silver paste. Photoelectrochemical properties were measured with 150W Xenon lamp with water filter. Measurements were done in 1M H2SO4. Density of photocurrents was about 8mA/cm2 in the case of SrTiO3-TiO2. Because of the surprisingly good results in the observed photocurrents other eutectics containing titanium oxide and a titanate have been investigated. One of them is NiTiO3-TiO2 eutectic. Eutectic rods with different pulling rates have been obtained by the micro-pulling down method with the inductive heating. The observed structure was not very homogenous, however in many places an interesting microstructure exists, where TiO2 ellipsoidal rods are embedded in matrix of NiTiO3. Some precipitates of metallic Ni are also observed. The first trials of growth of the eutectic plates have also been performed. The observed photocurrent for this material was 3mA/cm2.
In the demonstration domain, where the aim was to demonstrate the potential metamaterial-based applications of self-organized eutectics, we demonstrated:
(i) Photoactive eutectics as photoanodes in photoelectrochemical cells (PECs) experimental demonstration;
(ii) Localized surface plasmon resonance (LSPR) in visible and infrared, as well as enhanced photoluminescence due to LSPR in manufactured nanoplasmonic materials experimental demonstration,
(iii) Subwavelength resolution imaging (superlensing) and subwavelength propagation and transmission in polaritonic eutectics, due to four different phenomena (all numerically demonstrated):
- Hyperbolic dispersion relation
- Backward radiation in negative permittivity materials
- Subwavelength Mie resonances in permittivity near zero materials
- Surface phonon-polariton modes and gap-phonon polariton modes.
Below we describe in some detail the above mentioned demonstrated phenomena.
Photoactive eutectics as photoanodes in photoelectrochemical cells (PEC): Photoelectrochemical cells utilize solar energy for water splitting and generation of hydrogen. The solar energy is absorbed by photoanode and produces a current flow between photoanode and cathode, this splits water into hydrogen and oxygen. In the project, the potential use of eutectics containing TiO2 phase as photoanodes in photoelectrochemical cell has been demonstrated. The main systems employed wer SrTiO3-TiO2 and NiTiO3-TiO2 eutectics. Eutectic materials with new macroscopic geometry have been obtained for this aim plate-like geometry. Semiconductor materials with big enough band gap (for TiO2 rutile is 3.0 eV) are stable during photoelectrolysis. The grown eutectic structures were of high crystallinity, interconnected and with a big surface area. Photocurrent density up to 8 mA/cm2 at 600 mW/cm2 illumination has been demonstrated for SrTiO3-TiO2 eutectic, not only at UV but also at visible wavelengths. The NiTiO3-TiO2 has shown highest density of photocurrent of 3mA/cm2. Most probably the photocurrents in both cases can be still improved by various processing of the material (annealing, different material thickness, eutectics grown with different pulling rate, various dopants, plasmonic effects). The advantage of eutectics as photoanodes is that they are multiphase materials, so they posses multiple bandgaps which may allow for absorption of broad range of solar energy without necessity of making the multijunctions. Moreover, numerous interfaces allow moving the created charges without recombination to the surface. These are the first demonstrations of photocurrents in eutectic crystals used as photoanodes in photoelectrochemical cells.
Demonstration of localized surface plasmon resonance (LSPR) and enhanced photoluminescence in manufactured nanoplasmonic materials (potential application solid state lasers in UV, Si solar cell with up-conversion enhanced performance): Plasmonic behaviour has been demonstrated in two kinds of materials: (i) dielectric materials doped with plasmonic nanoparticles and (ii) metallodielectric eutectics. Plasmonic behaviour has been demonstrated both in visible and infrared wavelengths. Also anisotropic plasmonic behaviour has been demonstrated. Additionally ability to dope the nanoplasmonic materials with active ions has been shown and subsequent 7-fold enhancement of photoluminescence has been demonstrated.
Nanoplasmonic rod made by doping dielectric matrix with silver nanoparticles
demonstrating different colurs while being placed at different coulr backgrounds due to LSPR.
LSPR in the visible wavelength range:
(i) The localized surface plasmon resonance phenomenon was demonstrated in Na5B2P3O13 (NBP) as a matrix doped with 0.15 wt.% of silver nanoparticles. The NBP:nAg system exhibited a resonance at visible wavelengths, which was manifested as a sharp extinction peak of Lerenzian shape with a maximum at 404 nm. The Lorentzian shape of this peak indicates a homogenous broadening of the band, which is of high importance for many applications. The LSPR quality factor, defined as the ratio between the LSPR energy and the LSPR full-width-at-half-maximum (FWHM), was 20.5. Narrower plasmon resonances, thus larger quality factors result from smaller damping. This is important for applications where large field enhancement is necessary, such as photoluminescence.
(ii) The LSPR phenomenon has been also demonstrated in the bulk Bi2O3-Ag eutectic which exhibits three-dimensional structure of silver micro and nanoprecipitates. The Ag-Bi2O3 eutectic microstructure is formed of Ag precipitates in the form of triangular shapes with sharp corners embedded in Bi2O3 matrix. The microprecipitates are partially interconnected with tens of micrometer long, nanometer-scale precipitates. The Ag-Bi2O3 eutectic in the transmitted mode showed a localized surface plasmon resonance at 590 nm.
LSPR in the infrared wavelength range: The localized surface plasmon resonance has been demonstrated in infrared wavelength in NBP doped with ATO (antimony-tin oxide) and CuO-Ag eutectic. Transparent conductive oxides, such as antimonytin oxide or indiumtin oxide, are active in the near-infrared region and constitute attractive plasmonic materials, owing to the small negative values of the real part of the permittivity and to low losses. These features make them promising candidates for example for transformation-optics and superlens applications.
Enhancement of photoluminescence.
The enhancement of photoluminescence in the manufactured nanoplasmonic materials co-doped with rare earth ions has been demonstrated (NBP rods co-doped with Ag nanoparticles and erbium ions, NBP:nAg,Er3). In NBP:nAg,Er3+, we observed, relative to the NBP:Er3+ sample, a seven-fold increase of the 1534-nm Er3+ photoluminescence (PL) at room temperature upon excitation with a 325-nm continuous wave He-Cd laser. Potential application of these materials are: solid state lasers in UV, Si solar cells with up-conversion enhanced performance.
Subwavelength resolution imaging (superlensing) and subwavelength propagation and transmission in polaritonic eutectics: Using polaritonic alkalide-halide systems we were able to demonstrate subwavelength resolution imaging (superlensing) and subwavelength propagation in the THz regime, exploiting a variety of different phenomena and principles which (as we discovered during the project) are realizable there. The particular systems that we used to demonstrate most of the subwavelength imaging and transmission possibilities are LiF circular rods periodically placed (in a nearly hexagonal lattice) either in NaCl or in KCl. In some cases we employed also TbScO3 rods in Tb3Sc2Al3O12 matrix. Below we describe in more detail each of the phenomena that leaded to sub-wavelength propagation.
THz superlensing in hyperbolic dispersion relation metamaterials: Structures with hyperbolic dispersion relation (i.e. anisotropic structures with permittivity tensor components of different sign) have been proven a very important category of metamaterials, as they give the ability of sub-wavelength resolution imaging without the need of any resonant response (which implies high losses), or magnetic response (which is not easy to be achieved), and are relatively simple structures which can be easily fabricated. The ability of hyperbolic metamaterials (HMM) for subwavelength resolution imaging is based on the fact the HMM do not have an upper limit to the magnitude of wave vectors that they can support, so they can transmit arbitrarily large (in principle) parallel (to the air-HMM interface) wave vector components, which in free space are evanescent components and carry the subwavelength details of a source object. Moreover, the hyperbolic dispersion is associated with high density of electromagnetic (EM) modes, which can greatly affect the performance of EM sources placed in such a medium. In the framework of the project we showed that hyperbolic dispersion relation leading to subwavelength resolution imaging can be observed in the THz and IR regimes using rods made of a polaritonic material, and exploiting the negative permittivity response of the rods in combination with the structure geometry. Analogous results can be obtained also in other systems that we have examined, like LiF rods in NaCl with larger lattice constant and rod radius, or systems of LiF rods in KCl.
THz superlensing based on backward radiation in polaritonic waveguides: It has been shown recently that in waveguides with small negative permittivity values (-1less thaneless than0) there is the possibility of backward guided modes (i.e. modes of opposite phase and group velocity) which show quite strong 'attenuation' (leakage) leading to backward radiation from the side-walls of the guide. Exploiting such modes one can achieve subwavelength propagation and imaging of electromagnetic waves in a system of parallel waveguides; such a system can be a two-dimensional periodic system of rods (guides) in a host, where the rods have small negative permittivity values (also in a binary layered system with one material having small negative permitivity). In the framework of the project we showed that this phenomenon can be realized in the THz regime in systems of polaritonic LiF rods (acting as waveguides with small negative permittivity) in NaCl host.
Epsilon near zero based phenomena in polaritonic systems: total transmission, total reflection and subwavelength propagation: Besides metamaterial effects based on negative permittivity materials (like metals or polaritonic materials) it has been shown that interesting effects and possibilities can also be achieved in systems with high index dielectric inclusions. In such systems, sub-wavelength Mie-resonances can be excited, leading to phenomena like negative permeability and/or permittivity, subwavelength guiding etc. As we discovered during the project, the presence of permittivity near zero regimes in polaritonic materials allows the observation of the same phenomena in systems of dielectric rods in a polaritonic host with e approximately 0, without the need of very high index values for the rods. In such systems we can achieve subwavelength and strongly confined Mie resonances. Exploiting the coupling among those resonances in arrangements of closely placed rods we showed that one can achieve, under certain conditions, phenomena like total transmission, total reflection, negative permittivity and permeability and subwavelength propagation, guiding and imaging.
Subwavelength transmission due to surface phonon-polariton modes and gap-phonon polariton modes: Subwavelength transmission has been demonstrated in Tb3Sc2Al3O12-TbScO3 eutectic with rodlike structure, where TbScO3 rods are embedded in Tb3Sc2Al3O12 matrix. It has been shown that both component materials exhibit many wavelength ranges where Re less than 0. In some of the wavelength ranges the rods demonstrate Re less than 0 at Im small, and the matrix has Re greater than 0 and Im also small. And especially for the range ca. 16 - 18 μm the quality factor (Q=-Re/Im) is enough high to enable the subwavelength transmission along the rods. This material could be applied for directional emissivity control, especially that the material can stand very high temperatures (melting point approximately 1900μC).
Potential Impact:
Impact on the Scientific Community
In order to have an impact on the scientific community ENSEMBLE project broadly disseminated the project results through publications, talks at international conferences, workshops and institutions, and organization/co-organization of conferences and sessions at international conferences. We published around 95 papers, and 2 book chapters, more papers are still coming. We had 4 journal covers, approximately130 invited (including plenary and keynote) talks at conferences and workshops, approximately 30 seminars at Universities and Institutes, approximately160 contributed and poster presentations and we participated in the organization of several conferences.
We organized an internal workshop where we invited interested industry representatives and we organized a topical meeting within META12 Conference session 'Bottom-up approach towards metamaterials and plasmonics' where the most important representative from all over the world were invited.
Meeting with representatives of Saint Gobain (France), Umicore (Belgium)
and Cemat-Silicon (Poland)
Impact on wider community
We disseminated the information about the project and connected research in media such as in television, radio and newspapers.
TV broadcasts:
1. Teleexpress daily programme - PL, 2 March 2009
Institute of Electronic Materials Technology in Warsaw coordinates european research on metamaterials
http://www.youtube.com/watch?feature=player_embedded&v=3l0NAwDovvI
Radio:
1. Program 1 Polish Radio - PL, 27 November 2010
Program "Evening of discovery" with the participation of scientists from the Institute of Electronic Materials Technology in Warsaw. http://www.polskieradio.pl/23/266/Artykul/267472,Grafen-z-Polski
2. Radio dla Ciebie - PL, November 2011
The eight women honored in the competition organized in honor of Marie Curie http://www.rdc.pl/index.php?/pol/aktualnosci/aktualnosci/osiem_kobiet_wyrozniono_w_konkursie_zorganizowanym_w_holdzie_marii_sklodowskiej_curie
Press:
1. Nasz Dziennik daily newspaper - PL, 16-17 June 2012, No 139 (4374)
Scientists reach out forinvisibility http://www.naszdziennik.pl/index.php?dat=20120616&typ=my&id=my05.txt
2. Przeglad Techniczny - newspaper for engineers - PL, 2011
Wynalazczyni 2011 Dorota A. Pawlak
http://www.przeglad-techniczny.pl/index.php?option=com_content&view=article&Itemid=44&id=946
Other (internet):
1. Summary of the fourth edition of the "inventor" competition organized by FSNT-NOT, UP RP and SPWiR (16 December 2011) - PL
http://www.przeglad-techniczny.pl/index.php?option=com_content&view=article&Itemid=44&id=1167
2. "Forum Akademickie" magazine V contest on the popular science article under the title 'Complex and simple young scholars about their research'
K. Sadecka http://forumakademickie.pl/aktualnosci/2010/6/15/555/v-edycja-konkursu-rozstrzygnieta/
3. Ministry of Science and Higher Eduction in Poland, 14 September 2011
'Scientists from ITME obtained ribbon shape SrTiO-3-TiO2 eutectic'
http://www.nauka.gov.pl/nauka/sukcesy-uczonych/sukcesy-uczonych/artykul/naukowcy-itme-otrzymali-eutektyk-srtio3-tio2-w-postaci-wstazki/
4. The Polish National Contact Point for Research Programmes of the European Union (KPK), Success stories - the website which has been designed to highlight Polish successful projects financed under Fifth Framework Programme (FP5), Sixth Framework Programme (FP6) , Seventh Framework Programme (FP7) and the CIP programme.
http://en.kpk.gov.pl/index.php?option=com_sobi2&sobi2Task=sobi2Details&catid=2&sobi2Id=111&Itemid=142&lang=pl
5. Euro Nano Forum http://www.euronanoforum2011.eu/dorota-anna-pawlak
6. Press releases of Fundation for Polish Science - dr hab. Dorota Pawlak - Inventor Wynalazczyni 2011 (Wynalazczyni 2011) http://www.fnp.org.pl/biuro_prasowe/informacje_prasowe/informacje_prasowe_fundacji_na_rzecz_nauki_polskiej_2011_rok/dr_hab
7. ORC Seminar Series
'Materials for Metamaterials: self-organized eutectic micro- and nanostructures'
http://www.orc.soton.ac.uk/448.html
Potential impact:
The project has developed novel materials, such as
(i) bulk 3D nanoplasmonic materials which demonstrate localized surface plasmon resonance at visible and IR wavelengths,
(ii) bulk anisotropic nanoplasmonic materials with anisotropic optical behaviour at visible frequencies,
(iii) bulk eutectic-based nanostructured anisotropic materials exhibiting excitonic resonances at UV region as well as additional unusual behaviour strongly structure-dependent,
(iv) bulk 3D nanoplasmonic materials co-doped with erbium exhibiting 7-fold plasmonic enhancement of photoluminescence at telecommunication 1.5 μm wavelength,
(iv) materials with subwavelength guiding in THz regime.
The potential application we foresee in solid state lasers, optical fiber amplifiers, Si solar cells with plasmonic and up-conversion enhanced efficiency, filters, directional emissivity control, sources of IR and THz radiation, imaging systems.
Most important points of the potential impact:
(1) New modelling tools for self-organization processes - useful for further research and materials analysis.Developed models can be applied to various kinds of materials not only eutectics. Can be used in basic and applied research and in industry.
(2) New tools for modelling electromagnetic properties of complex materials useful for various complex materials:
(i) boundary element method (BEM, 2D and 3D),
(ii) multiple elastic scattering of multipole expansions (MESME),
(iii) effective medium description for polaritonic materials.
Can be used in basic and applied research and in industry.
(3) Novel technologies developed such as:
(i) 3D bulk nanoplasmonic materials (doping with NPs),
(ii) metallodielectric materials,
(iii) nanosized multiphase materials.
Can be used in basic and applied research and potentially further industralized.
(4) Novel materials developed and investigated, as: novel nanoplasmonic materials, novel polaritonic materials, novel materials with excitonic resonance, materials for dynamic change of the dielectric-metallic properties, materials for photoelectrochemistry, and others. Can be used in further basic and applied research.
(5) Novel complex materials with demonstrated special electromagnetic properties:
(i) photoactive eutectics for photoanodes in photoelectrochemical cells,
(ii) nanoplasmonic materials with LSPR at visible and IR for (enhancement of properties as photoluminescence, nonlinear processes) nonlinear absorbers,
(iii) materials with LSPR and RE demonstrating enhanced PL for photovoltaics (via up-conversion processes) novel efficient light sources,
(iv) polaritonic materials with subwavelength transmission for subwavelength resolution imaging (superlensing) directional emissivity control.
Can be used in basic and applied research and potentially further industralized
Patents applied for:
1. The way of manufacturing nanoplasmonic composites made of dielectric matrices doped with plasmonic nanoparticles (metallic and/or semiconducting) as plasmonic rods. (ITME)
2. Manufacturing of photoanodes for photoelectrochemical cells made of eutectic materials. (ITME)
Educational impact:
During the project the students and PhD students had the chance to work with the world-class scientists in this multidisciplinary team. They had the chance to perform experiments and learn at the partners laboratories. The map below illustrates the temporary 'migration' of students during the project duration. Despite the end of the project this continues. In July a student from ITME will visit FORTH for continuation of the measurements.
Additionally the knowledge generated by RISSPO/WIGNER in the framework of WP1 will be used in a compact teaching module entitled 'Introduction to phase-field modeling of solidification' consisting of 15 h lectures + 15 h computational practices; a course offered to PhD students and posdoctoral fellows. (It has been successfully tested in April 2011 as an invited teaching module of the Rolls-Royce Doctoral Training Course at the Cambridge University, UK).
Collaboration between Partners and integration with other programmes: During the project we collaborated with COST Action MP0803 and COST Action MP0702 using short term scientific missions. Most of the Partners are/were involved in at least one of these two COST Actions, as well as some Partners are members of Metamorphose VI. Most of the Partners are actively involved also in other research programs, this helped to disseminate the knowledge more efficiently and all the involved research programs benefited from those activities. The coordinator of the project and one other representative took part in a meeting of Seventh Framework Programme (FP7) coordinators (for Seventh Framework Programme (FP7) NMP call on self-organization and self-assembly) in Brussels, Belgium (February 2012) for the networking, and presentation of the project results.
Exploitation and use of foreground in research:
The models worked out by RISSPO/WIGNER will be used in the following research projects WIGNER participates in:
1. EU Seventh Framework Programme (FP7) 'EXOMET' (status: under signing the Grant Agreement). Models I and IV will be adopted for the actual tasks and further used.
2. ESA PECS project 'GRADECET' (status: signed contract). Models III and IV will be adopted for the actual tasks and further used.
3. ESA PECS project 'MAGNEPHAS III' (status: signed contract). Models III and IV will be adopted for the actual tasks and further used.
The latter two projects are related to microgravity experiments on board of sounding rockets and the International Space Station.
The technologies and materials developed by ITME will be used in the following research projects ITME participates in:
1. NATIONAL SCIENCE CENTRE Project Maestro New generation of plasmonic metamaterials (started May 2012) technology of manufacturing dielectric matrices with plasmonic nanoparticles will be utilized there.
2. Swiss-Polish Cooperation Programme - Hybrid semiconducting materials for solar energy conversion (started October 2011) the technology of manufacturing eutectic materials with big areas, the technology of electrodes preparation and the idea of utilizing the eutectic systems for generation hydrogen using solar energy will be used there.
The technologies and materials developed by ICMA will be used in the following research collaborations/potential projects ICMA will participate in:
1. Collaboration with IMEDA Materiales use of sc-micropilars for micromechanics
2. Project on metal-dielectric materials (potential)
3. Project on effect of nanosize on photoluminescence
Impact on the world-wide research initiatives:
Additionally we did strongly influence the world-wide research because after disseminating our results at various conferences the subject of the project has been noticed by the US Air Force and the Air Force Office for Scientific Research (AFOSR) opened a call for Multidisciplinary University Research Initiative (MURI) for a subject of research very similar to the subject of research of ENSEMBLE project: 'Directional Eutectic Structures: Self-Assembly for Metamaterials and Photonics'. AFOSR will fund the winning consortium with 7.5 mln USD. This will certainly help in spreading the research starting within the ENSEMBLE project and will cause high impact of this research in the future.
Networking:
Achieving the objectives of the project took a lot of effort from all the partners, which required often different understanding of the subject. This after undertaken effort created an invaluable platform of understanding which in future hopefully will be further used and will result in many new developments.
List of Websites:
http://www.ensemble-fp7.eu
Research and industrial development depends on novel materials, on their associated novel properties and enabled by them functionalities. That is why the overall objective of ENSEMBLE project was to design, manufacture, and characterize self-organised multi-component and multi-scale structures, which display: controlled geometrical motifs, controlled composition and physico-chemical structure, controllable size of structuring ranging from micro- to nano, novel predictable and controllable electromagnetic properties and metamaterials capabilities.
In order to achieve the main objective ENSEMBLE Project developed:
(i) new modelling tools in order to gain insight into eutectic self-organization and the control mechanisms behind,
(ii) new modelling tools enabling design of composite materials with special electromagnetic properties as well as comparing the experimental results for obtained materials with theory,
(iii) novel technologies and novel materials which were characterized by often specially designed characterization set-ups (iv), as well as finally we demonstrated new materials exhibiting special electromagnetic properties (v).
To understand the self-organization processes in eutectic growth we have developed multi-scale modeling tools. These tools all working in 3D are:
(i) an atomistic phase-field theory [the phase-field crystal (PFC) approach] for unary and binary solidification;
(ii) a quantitative phase-field model working on the submicron to micron scale;
(iii) a quantitative phase-field model coupled with hydrodynamics (with the Navier-Stokes equation) in three dimensions relying of spectral methods combined with operator splitting; and
(iv) a quantitative multi-phase-field theory working above the micron scale, obtained by combining the quantitative multi-phase-field theory of Folch and Plapp with Kim's model.
To understand the electromagnetic properties of the manufactured materials and to be able to design materials with special electromagnetic properties on-demand we generated simple models and numerical methods that allowed electromagnetic modelling and simulations of eutectic self-organised micro and nanostructures, and enabled assistance in the design and characterization.
Project Context and Objectives:
MATERIALS: The materials investigated in this project were self-organised eutectic or eutectic-like submicron and nanostructures. A eutectic is characterized by the formation of two or more non-mixable crystals from a completely mixable melt. Directionally solidified eutectics (DSE) have excellent potential for use in different types of light/electromagnetic waves manipulation. DSE may be defined as composite materials with a complex and homogeneous micro- or nanostructure which controls their properties. Eutectics exhibit the unusual characteristic of being both monolith and multicomponent/multiphase in nature with sharp, clean and strong interfaces. Eutectic composites may have multiple functionalities arising from the constituent phases of the eutectic (additive properties) as well as new functionalities which do not exist in the component phases but which uniquely derive from their combination and appropriate structuring on the nano- or micro-scale (product properties). The product properties are particularly important, as they promise metamaterial-like behaviour of appropriately-designed and engineered eutectic materials.
NEW PROPERTIES/FUNCTIONALITIES: The collaborative project did foresee research for the development of nanostructures by self-organisation aimed at motifs capable of generating new functionalities. The focus was on generating new knowledge of self-organisation principles in eutectic materials with potential cutting-edge electromagnetic properties/functionalities.
General CONCEPT: Growth of eutectics is recognized as a paradigm for pattern-forming or 'self-organising systems'. Self-organised structures on size scales reaching down to the submicron and nanoscale regime emerge due to the interplay of chemical diffusion and capillarity. The fundamentally novel CONCEPT of the project was to utilize - for the first time - eutectic self-organisation for the preparation of multi-component and multi-scale structures with controlled physicochemical and structural properties, with geometrical motifs capable of generating novel, predictable and controllable electromagnetic functionalities. This required a deeper understanding of factors influencing eutectic self-organisation mechanisms on the submicron/nanoscale. Accordingly, the main topic and activity of the project was to generate new knowledge of eutectic self-organisation on this scale, by combining state-of-the-art experimental and modelling techniques. Further the objective was to predict and design self-organised multi-component and multi-scale structures with so far unseen physicochemical and structural properties. This was combined with the electromagnetic design of complex structures which can generate unusual electromagnetic functionalities.
The following results of the project were expected:
a) the ability to predict the occurrence of specific patterns in eutectic systems,
b) knowledge of how to design nanopatterned materials with controlled physicochemical and structural properties,
c) methodologies for the design and fabrication of self-organised multi-component and multi-scale structures with unusual electromagnetic functionalities, and
d) experimental realisation of these self-organised systems.
The planned programme of research was expected to open new horizons for utilizing self-organised structures in various fields.
The advantage of using eutectic solidification on the submicron/nanometer scale is the availability of monolithic composite materials with clean and strong interfaces and a broad range of possible components with the possibility to realize a broad variety of geometrical motifs. In order to achieve controlled physicochemical and structural properties capable of generating novel, beyond the state-of-the-art electromagnetic properties, it was necessary to investigate the combination of various component materials with diverse types of structuring. Due to the extreme conditions needed to realize eutectic solidification on the nanoscale, fairly little is known about the mechanisms operating in this regime, including: diffusion on the nanoscale; the effect of substrate/seed materials; underlying anisotropies; and surface nucleation.
The TASKS of this project were:
a) to develop new knowledge of the control parameters/material properties that govern eutectic pattern formation on the nanoscale via phase field modelling;
b) to develop new tools for control of self-organisation in eutectics, leading to the ability to achieve desired structural properties (geometrical motifs) and desired, controlled physico-chemical properties;
c) to combine a knowledge of self-organisation and materials chemistry with the ability to design and discover new physical phenomena in such media;
d) to develop analytical and numerical techniques for designing and modelling self-organised materials with novel and advanced electromagnetic properties;
e) to develop and master the necessary nano- and submicron fabrication techniques;
f) to analyze the potential of self-organised eutectic materials for practical applications in photonic devices;
g) to examine the possibilities of combining eutectic self-organisation with other means of controlled structuring, for the generation of even more advanced materials.
The execution of the above tasks was planned to lead to achievement of the following objective:
The OBJECTIVE of this project was to design, manufacture, and characterize self-organised multi-component and multi-scale structures, which display:
O1: Controlled geometrical motifs, including rod-like, lamellar, globular and percolating patterns, which can provide the expected electromagnetic functionalities;
O2: Controlled composition and physico-chemical structure, realized by combining materials with different refractive indices or different optical properties, which can provide the theoretically-predicted electromagnetic functionalities;
O3: Controllable size of structuring ranging from micro- to nano scale following the theoretical predictions;
O4: Novel predictable and controllable electromagnetic properties. At least one of the following properties can be obtained: controlled effective refractive index,; artificial magnetism; controlled dispersion; controlled sub-wavelength field generation and enhancement.
O5: Metamaterials capabilities which extend to applications such as: imaging, high compact optoelectronic devices, efficient photovoltaics and active devices.
Project Results:
In the theory/modeling domain of eutectic growth we have developed multi-scale modeling tools in order to gain further insight into eutectic self-organization. These tools all working in 3D are:
Model I - an atomistic phase-field theory [termed the phase-field crystal (PFC) approach] for unary and binary solidification. We have worked out an efficient method to solve numerically the binary phase-field crystal (PFC) model. Using the operator splitting method, the problem has been decomposed into sub-problems that can be solved more efficiently. It has been shown that our method speeds up the computations by orders of magnitude relative to the conventional explicit finite difference scheme, while the costs of the pointwise implicit solution per time step remains low. We have also demonstrated that our method can efficiently be parallelized for distributed memory systems, where an excellent scalability with the number of CPUs has been observed.
We have performed a systematic study of crystallization using the PFC approach, leading to the following results:
(a) determination of the unary and binary phase diagrams,
(b) a demonstration that dendrites can be grown in both unary (bcc and fcc) and binary systems,
(c) the identification of new homogeneous and heterogeneous nucleation modes;
(d) a discovery that the competition between diffusion controlled and diffusionless growth modes yield fractallike growth forms,
(e) determination of the anisotropies of the growth rate and the interfacial free energy,
(f) extension of the PFC approach to the modeling of colloid patterning experiments,
(g) the observation that - owing to a particle diffusion controlled relaxation dynamics of the particle density - the PFC model predicts eutectic cells in a binary system;
(h) a demonstration that both in 2D and 3D, the eutectic structures forming on the nanoscale relax on the timescale of solidification.
Model II - a quantitative phase-field model working on the submicron to micron scale. Via comparing the simulations directly to experiments, we have demonstrated on test systems of known properties (Ag-Cu) that Models II is indeed quantitative down to the nanoscale. We have explored the relationship between the nanoscale eutectic patterns and model parameters (anisotropies of the solid-liquid and solid-solid interfaces)/technological conditions (undercooling, temperature gradients, composition, pulling velocity, misorientation of growth relative to pulling). It has been shown, e.g. that the roughness of the solid-liquid interfaces due to the anisotropy of the interfacial free energies, the cross-sectional temperature gradients, crystal misorientation relative to pulling direction, and the anisotropy of the interface energies play essential roles in determining the eutectic pattern forming on the nanoscale.
Model III - Model II coupled with hydrodynamics in three dimensions relying of spectral methods combined with operator splitting. Using Model III, we have confirmed for the Ag-Cu system that the osmotic flow destabilizes the planar interface, yielding dendritic humps of concentric ring pattern (similar to the ternary two-phase dendritic dendrites, however, now in a binary system).
Model IV - a quantitative multi-phase-field theory working above the micron scale. In the case the of Al-Al2Cu system, we have demonstrated that our multi-phase-field model is indeed quantitative. Model IV has predicted a so far unknown morphological transition between cylindrical rods to rods of hexagonal cross-section, when dynamically increasing the volume fraction of the 'rod-phase'. Furthermore, incorporating cubic anisotropies for the solid-solid and solid-liquid interfacial free energies, we have obtained rectangular morphologies akin to those seen in the respective experiments on eutectic Al-Al2Cu. Finally, Model IV has been adopted for quasi-biner eutectic systems, where the solid phases are line compounds. In the case of LiF-NaCl system, we have observed a quantitative agreement between parameter free predictions and experimental data from experiments done within the Project.
Highlights of significant results
- First demonstration that the phase-field crystal method can handle multiple crystalline phases and their anisotropies;
- Systematic exploration of the abilities of the PFC model for describing crystalline freezing;
- Identification of new modes for homogeneous/heterogeneous crystal nucleation and growth on the basis of atomistic simulations;
- Demonstration that osmotic-pressure-induced flow destabilizes the eutectic growth front, leading to the formation of eutectic cells;
- Development of a quantitative multi-phase-field theory (Model IV) that can accommodate data from thermodynamic databases and its application to the Al-Al2Cu eutectic system, where an excellent agreement has been seen with experients;
- Extension of our quantitative multi-phase-field theory to eutectic systems of stoichiometric solids and its application to the quasi-binary LiF-NaCl system, where a good agreement has been found with experiments;
- Exploration of spiralling two-phase eutectic dendrites in ternary systems;
- First systematic mapping of the effect of anisotropic phase-boundary on nanoscale eutectic self-organization.
Examples of the main results of WP1 are given below:
Comparison of quantitative Phase-Field (PF) predictions with experiments: Model II (and Model III in the no hydrodynamics limit) solved with a combination of a spectral method and operator splitting has been used to predict the eutectic wavelength vs. velocity relationship for the eutectic Ag-Cu binary alloy, whereas Model IV has been tested in the case of the Al-Al2Cu system. In both cases values for all the model parameters have been taken from experiments. In both cases, an excellent agreement can be seen between experiments and simulations without adjustable parameters.
Atomistic modeling of eutectic self-organization on the nanoscale: Many of the important features of eutectic self-organization such as anisotropic growth, effects of crystal defects and elasticity can only be understood within an atomistic description of solidification. We have developed, implemented, and numerically validated a semi-implicit fully spectral scheme to solve the binary phase-field-crystal equations in two dimensions. Being a simple dynamical density functional theory this is an atomistic model, in which the atomic positions, the crystal structure, the elastic properties, and the anisotropies of the solid-liquid interface and the growth kinetics are predicted.
The ability to model various crystal structures is an important prerequisite of describing eutectic solidification. After extending Model I to 3D, first for a single component case, we have proven that besides the stable bcc structure, metastable fcc and hcp crystalline structures may also form in this model. Investigating the orientation dependence of the growth rate we have obtained quantitative information on the anisotropy of the kinetic coefficient. Subsequently, we have performed a systematic evaluation of the phase-field crystal model (Model I) in 2D and 3D, to see how far it can be applied for describing solidification in undercooled liquids. In this, we were advancing from simpler to more complex cases: We started with single component 2D and 3D systems, and turned then to the binary 2D and 3D systems. We have determined the respective phase-diagrams (in 3D bcc, fcc, and hcp stability domains have been identified), the dependence of the interface properties on the model parameters, and demonstrated that dendritic and eutectic structures develop in 2D and 3D, and that an amorphous precursor precedes crystal nucleation.
It has also been shown that in the single component limit the PFC can also be regarded a reasonable model of colloidal crystal aggregation. At large driving forces, a transition from diffusion-controlled to diffusionless growth mechanism has been observed in even the single component limit.
Remarkably, we have observed eutectic solidification on the nanometer scale, and the formation of eutectic cells in large-scale 2D simulations. The mobility of the phase boundaries in the nanoscale eutectics seems to be fairly high both in 2D and 3D.
Snapshots of eutectic solidification on the atomistic scale in the binary phase-field crystal model in three dimensions. Time elapses from left to right. The size of the simulation window is 450 - 300 - 300. Simulation has been started by placing two supercritical clusters of different compositions into the simulation window. Note the perfect structure initially, which breaks up to grains at later stages of the simulation. Remarkably, on this nanoscale the eutectic pattern evolves on a timescale comparable with the time of solidification. The brown and grey colours denote the terminal solutions of the two crystalline phases.
Exploration of trends in a quantitative phase-field modeling of eutectic soldification (Models II and III): Quantitative phase-field theoretical Model II has been used to investigate the trends obtained via a simple qualitative model of eutectic solidification during the previous reporting period. Simulations performed with Model II confirmed the tendencies obtained with the simpler model.
The relationships so far identified are as follows:
a. comparable volume fractions ? enhanced propensity toward lamellar structures
b. increasing crystal misorientation relative to pulling direction ? enhances propensity to form lamellae and regularizes the eutectic pattern
c. misoriented anisotropies of cubic or octahedral equilibrium shapes ? helps the formation of lamellar structures that have perpendicular orientations to each other
d. temperature gradient perpendicular to pulling ? regularizes the eutectic pattern
e. reducing the solid-liquid interfacial free energy of one of the constituents? enhances propensity of tubular structures
f. increasing the anisotropy of the solid-liquid interface free energy ? increases the roughness of the solid-liquid interface
g. increasing roughness of the solid-liquid interface ? enhances correlation between eutectic pattern and surface morphology
h. increasing the temperature gradient in the pulling direction ? reduces the roughness of the solid-liquid interface
i. the value for C = 2v remains reasonably constant even at high undercoolings
Relying on the identified trends, we have performed a systematic search for the SRR and fishnet structures. In this we have varied simultaneously such (usually unknown) properties as the magnitude and anisotropy of the solid-liquid interface free energy and the anisotropy of the solid-solid interface free energy. Other parameters, we changed, were the temperature and its gradient. Temperature gradient in the pulling direction usually stabilizes the cross-sectional pattern. We have been able to produce patterns that show resemblance to the experimental SSR and fishnet structures, although the agreement is not fully satisfactory.
Approximants of SRR (upper row) and fishnet (lower row) structures (side and cross-sectionals views are shown): The interplay of the anisotropies of the solid-liquid and solid-solid interface free energies have been utilized to produce these structures.
Model III: It has been shown that the solid-liquid interface is destabilized by osmotic pressure driven flow, yielding eutectic cells resembling to the early stage of 'eutectic dendrites' recently discovered experimentally, and may lead to concentric ring structures.
Spiraling two-phase eutectic dendrites in ternary systems: To model the formation of spiraling eutectic patterns shown in Amended Annex I of the ENSEMBLE project has been studied experimentally recently, we have adopted Model II to a symmetric model ternary system. Starting from a random solid-phase pattern and with a perturbation of wavelength in the range of the Mullins-Sekerka instability, humps form that evolve into full scale dendritic structures composed of A-rich and B-rich solid solutions. The eutectic pattern on the dendrites has been observed to be one of the four possibilities: concentric rings, and single, double and triple spiraling structures, the latter appearing at late stage on the largest dendrite. Of nine peaks, five shows the ring structure and four the single-spiral pattern (one rotating clockwise and three counter-clockwise). Some of the dendrites disappear others grow on their expense. This is the first successful modeling of two-phase eutectic dendrites.
Comparison of predicted solidification morphology with experiment for Al-Al2Cu: In this system rectangular motives have been observed experimentally that resemble to the SRR-type motifs seen in TiO2-SrTiO3. Unfortunately, neither experimental nor molecular dynamics data are available for the anisotropies of the interfacial free energies in this system. Therefore, we have attempted reverse engineering: We have adjusted of the anisotropies of the solid-solid and solid-liquid interface energies in Model IV until the forming eutectic pattern matched reasonably with the experimentally observed patterns.
The resemblance needs yet to be improved. We wish to note in this respect that we do not know the true anisotropies, and that stress-induced growth anisotropy, which has been neglected in this study, may also influence the growth morphology.
The same model has been adopted to systems consisting of two line compounds as the solid phases, and has been applied for the LiF-NaCl system, leading to growth rate that are consistent with those found experimentally by the experimental partners in the project.
In the theory/modelling domain of electromagnetic properties we generated simple models and numerical methods that allowed electromagnetic modelling and simulations of eutectic self-organised micro and nanostructures, and enabled assistance in the design and characterization.
(i) A powerful and fast quasianalytical multiple scattering of multipolar expansions method and numerical boundary element method that solves the full Maxwell equations have been developed. These methods have been applied to investigate the electromagnetic properties of a variety complex eutectic systems and structures.
(ii) Investigation of validity of homogeneous effective medium descriptions in alkali-halide systems has been provided by comparison of numerical results obtained by FDTD and finite element method with analytical effective medium models, for the eutectic systems of LiF in NaCl and LiF in KCl in the frequency regime of the polaritonic resonances of the samples (1-12 THz).
(iii) We have explained the scattering characteristics of eutectic structures made of polaritonic rods in a host material and showed that these structures could lead to negative refractive index and focusing.
(iv) We have demonstrated a new kind of waveguides involving eutectics composed of alkali-halide wires embedded in an alkali-halide matrix (LiF in NaCl and KCl). These samples can be used to propagate signals through electromagnetic (polaritonic) resonances confined to the gap region between two adjacent wires, which can be potentially useful for near-field imaging.
(v) The electromagnetic response of the self-organized microstructure of terbium-scandium-aluminium garnet-terbium-scandium perovskite eutectic (Tb3Sc2Al3O12-TbScO3) suggests a possibility to guide a signal through the sample along the wires by means of the individual TbScO3 wires electromagnetic modes. The possibility to obtain super-resolution imaging has been studied.
(vi) We have proposed a system made from arrays of silver wires separated by dielectric material as a compact waveguide at optical frequencies that presents highly-confined plasmon gap modes concentrated in the regions between the wires.
(vii) We have demonstrated a possibility of broadband magnetic response, negative permittivity and permeability in designed prototype of split-ring resonator-like structures based on SrTiO3-TiO2 eutectic.
(viii) We have shown that chiral structures can exhibit negative refractive index and can be more promising candidates for eutectic-based negative refractive index metamaterials than traditional based on SRRs.
(ix) Ability of doping the eutectic materials with plasmonic (metal) nanoparticles has been demonstrated. This enables a possibility to move the electromagnetic excitations from mid infrared frequency to visible and near infrared and use eutectic in a large range of applications. We have modelled and characterized the plasmonic properties (localized surface plasmons) of the metal nanoparticles with different sizes and shapes and that can be potentially used for doping of complex eutectic.
In the fabrication domain of self-organized materials we have successfully grown eutectic and eutectic-like materials with controlled geometrical motifs including rodlike, lamellar, or with such unusual geometries like eutectics containing TiO2 phase where we did obtain geometries resembling working metamaterial structures (split-ring-resonator and fishet-like structures). We presented an anisotropic split-tube structure with fractal multiscale character. We have demonstrated control of eutectic structures, from fibrous to lammelar, according to the growth rate used. We have successfully grown materials with controlled composition and physico-chemical structure, realized by combining materials with different refractive indices or different optical properties aiming at specific electromagnetic functionalities. We have successfully obtained metallodielectric materials incorporating metals at the melt extraction step or after subsequent treatment or by producing templates for subsequent metalization. We succeeded in pushing the refinement of the structure down to the nanoscale utilizing various methodologies such as increasing the solidification rate of the materials, adding additional phase, doping with nanoparticles. By combining the controllable composition, geometrical motifs and size of structuring we demonstrated materials with predictable and controllable electromagnetic properties.
Metallodielectric materials for plasmonic applications: Most of currently, made materials with extraordinary electromagnetic properties (eg. metamaterials) are made with the use of one component material being metal which provides negative electric permittivity. There were not many experiments done in which metal-oxide eutectics were investigated. The most interesting metals are metals with high conductivity, like silver and gold. We employed several metodologies for manufacturing of metallodielectric materials: Direct growth from the melt was applied for Bi2O3-Ag and Cu2O/CuO-Ag eutectics were grown directly from the melt. The Bi2O3-Ag eutectic exhibits 3D multiscale micro/nanostructure microstructure of Ag precipitates embedded in Bi2O3 matrix while Cu2O/CuO-Ag eutectic exhibits micron-scale structure. Growth of eutectics where one phase can be easily reduced to metal and subsequent thermochemical reduction was applied and lead to formation of following composites Co-CeO2, Co-GDC, Ni-TiO2, Ni-YSZ alternate lamellae stacks. Further, experiments to infiltrate templates prepared by etching away one of the phases of the dielectric-dielectric with metals as silver and gold eutectic were performed. They lead to manufacturing metallodielectric surfaces such as Ag- NaMgF3, Ag-LiF, Ag-CaF2-LiF, Ag-Tb3Sc2Al3O12, Ag-TbScO3, Au-TiO2, Ag-SrTiO3-TO2, Au- PrAlO3-PrAl11O18 with various surface geometries as pillars, double pillars, arrays of holes, elongated holes. Finally to enter the nanosize regime we developed a new method of manufacturing nanometallodielectric materials by doping dielectric matrices as single crystalline matrices, glasses and eutectic matrices by doping with metallic nanoparticles. Nanoparticles tend to agglomerate as their surface-to-volume ratio is high, leading to strong attractive electrostatic forces. A distinct advantage of the -PD method was discovered that it helps de-agglomerate the nanoparticles, as they are transported through the nozzle at the centre of the crucible die. During the flow of liquid through the capillary, bubble formation (cavitation) and collapsing of formed bubbles (implosion) can occur. Previous investigations of liquid flows through capillaries have suggested that this phenomenon can lead to separation of nanoparticles originally present as larger agglomerates, as the shock waves are created at the locations of the collapsed bubbles.
De-agglomeration of Ag nanoparticles during directional solidification using the micro-pulling-down method. (a) Scheme of the micro-pulling-down method and of the de-agglomeration process occurring. (b) SEM image of the agglomerated Ag nanopowder used for doping the NBP matrix. (c, d) SEM images of small (c) and large (d) nanoparticles embedded in the NBP matrix after the solidification process. (e), Comparison of coloration of three solutions (left to right): (i) pure NBP glass dissolved in HCl (aq); (ii) Ag nanopowder mixed in an ultrasonic mixer in isopropanol; the black colour is due to Ag agglomerates; (iii) NBP:nAg glass dissolved in HCl (aq), the yellow coloration is due to dispersed Ag nanoparticles.
Towards nanosize: Nanosize scale materials can provide electromagnetic responses in the visible frequencies. That is it was important to develop methodologies to enter the nanosize regime with the investigated materials. Several approaches were taken. The most straightforward was applying high growth rates which enabled manufacturing of PrAlO3-PrAl11O18 rodlike eutectic with rods with diameter beyond 200 nm, with the growth rate of 1200 mm/h. Other submicron rodlike microstructures obtained in this way included Al2O3-EuAlO3, Al2O3-GdAlO3 and MnOx-YSZ eutectics. Another example of grown in this way of submicron scale lamellar, ordered microstructures were Ni-YSZ, CeO2 CoO, GDC-CoO eutectics. Adding a third phase into eutectic - ternary eutectic led down to 50 nm achievable sizes of the precipitates. Manufacturing eutectic-like composites were the growth led to growth of one phase in-between the grains of the other phase as in Bi2O3-Ag eutectic led to multiscale structure with smallest silver precipitates getting down to below 10 nm. Annealing of NiTiO3-TiO2 eutectic with reducing atmospheres led to formation of Ni particles attached to TiO2 microstructure. Depending on the time and temperature of annealing nanoscale Ni particles could be formed.
One of the proposed ways to get to the nano-regime was the use of nanoparticles especially metallic nanoparticles, which could be incorporated both in dielectric material and in the eutectic itself. Experiments were performed using single crystalline matrices as Bi12GeO20 (melting point (mp) = 1203 K) and nanoparticles of Ni (mp=1726 K) 20 nm, Co (mp=1768 K) 28 nm, and Mo (mp=2896 K) 70 nm. The crystals with up to 10 wt% of the nanoparticles were obtained. All of them had metallic lustre. In the obtained crystals the nanoparticles enlarged a little but stayed in the nano-range, and they oxidized or formed other compounds. The glass matrices were used. The most successful one was Na5B2P3O13 (NBP). It has been successfully doped with: (i) Ag spherical nanoparticles, (ii) antimony-tin oxide spherical nanoparticles, (iii) Ag wires, (iv) Ag spherical nanoparticles and erbium ions. The manufacturing of composites including nanoparticles of various composition, specific shape and size was enabled by the described above method which allowed for non-chemical doping of the dielectric matrices by the metallic nanoparticles. Also eutectics including Na5B2P3O13 phase were grown doped with Ag spherical nanoparticles.
Further we focused on manufacturing controlled composition and physico-chemical structure, realized by combining materials with different refractive indices or different optical properties, which can provide the theoretically-predicted electromagnetic functionalities.
Eutectic materials for subwavelength waveguiding and subwavelength focusing based on phonon polaritons: Anisotropic materials (rodlike or layered structures) with anisotropic permittivity (rods of metal embedded in dielectric or alternating metal-dielectric layers) can exhibit subwavelength waveguiding and subwavelength focusing as well as negative refraction. Regular eutectics exhibit rodlike and lamellar microstructures. It has been demonstrated that dielectric materials may have behaviour similar to plasmonic metals, and rods or layers made of such materials (polaritonic materials) may provide the above described properties. One of the important results of this project was the identification of suitable polaritonic eutectics, that is to say, eutectics with coupled fibrous microstructures where strong refractive index contrast among the component phases arise in the phonon-polariton dispersion region (FIR or THz range), as potential subwavelength guiding and focusing structures. Eutectics with fibrous structure include alkali-halides, where long LiF single crystal fibres are embedded in NaCl or KCl matrices.
The optical properties of these structures are highly anisotropic. In the medium and far infrared regions of the electromagnetic spectrum the phonon dispersion bands have wavelengths similar to the scale of phase interspacing; then unconventional optical effects can be expected. We especially concentrated on fibrous microstructures at the wavelength ranges, where the rods exhibit negative dielectric permittivity and the matrix positive permittivity. The alkali halide eutectics NaCl-LiF (25 vol% LiF fiber) and KCl-LiF (7 vol% LiF fibers) present phonon-polariton resonances at 33 μm (LiF), 70 μm (KCl) and 61 μm (NaCl) (9.18 THz, 4.13 THz and 4.83 THz respectively). We solidified ingots of 1 cm2 section achieving inter-rod spacing from 25 to 3 μm (and LiF rod diameters from 11 to 0.8 μm). In those systems anisotropic dielectric constant is obtained in various spectral windows. The rods have negative dielectric constant in the 16 to 32 μm wavelength range. Thin slices to achieve transparency have been prepared. We have also grown alkali halide eutectics with ternary composition NaCl-LiF-CaF2, in an effort to diminish the microstructure size and consequently expand the range where effective medium models describe the system and, more importantly, the resolution of devices based on self-focusing in the material is increased. Other fluoride eutectics of LiYF4-LiF (with larger vol% of LiF) have also been prepared in a wide range of solidification rates. Other investigated materials include Tb3Sc2Al3O12-TbScO3 system, where the operation wavelengths are shorter (16-18 μm) and the operation temperatures may be higher. Microstructures of examples of polaritonic materials grown within the project are shown above.
Materials with excitonic resonances: Except of plasmonic and phononic resonances we also investigated materials with excitonic resonances, which appear in the UV region. ZnO is a semiconductor with a wide energy gap (approximately 3.3 eV). It is very interesting and intensively investigated material for applications in optoelectronics. Theoretical calculations also show that ZnO doped with magnetic ions, can be semimagnetic semiconductor at room temperature. ZnO-ZnWO4 eutectic system was obtained from the liquid phase by the micro-pulling down method. The microstructure of ZnO-ZnWO4 eutectic forms the broken-lamellar structure, where ZnWO4 is a matrix and ZnO are broken lamellas. Despite the excitonic peak additional peak is observed in transmission which is strongly nanostructure-dependent. Its origin is not yet clear but it could be due to magnetic resonance due to excitons.
Systems for active change of dielectric-metallic behaviour: The eutectic systems with large difference in the bandgaps between the two components phases were sought and grown, since they can provide the possibility of an active change of such a composite material with applied electromagnetic radiation from a dielectric-dielectric system to a metallo-dielectric system. GdCrO3-Gd2O3, GdFeO3-Gd2O3 and MnOx-YSZ eutectics were grown. The GdFeO3-Gd2O3 eutectic has rod-like microstructure with GdFeO3 matrix and Gd2O3 rods (see picture on the right). It was shown that the green coloration comes from the GdCrO3 phase, which absorption edge is approximately at 500nm. The large difference in the bandgaps of GdCrO3 and Gd2O3 can provide the possibility of an active change of this material with applied electromagnetic radiation from a dielectric-dielectric system to a dielectric system with metallic wires. The eutectic possesses a distinct resonance at 2.16 THz (red line). Although, the s-polarized THz electric field is propagating along the GdCrO3 rods in the Gd2O3 matrix, a slight blueshift of this peak and the appearance of a second one at 1.57 THz are observed when the sample is rotated 90 degrees in respect to its initial position (black line). The measurements are being continued in order to demonstrate a switch on/switch off metamaterial where the dielectric-dielectric material will be changed to metal-dielectric material dynamically.
Eutectics for solar energy harvesting applications: To our knowledge, eutectics have not yet been implemented in any other type of energy system than solid oxide fuel cells, SOFC. However they seem to have a lot of potential, since (i) hybrid semiconducting materials of various component phases can be obtained; (ii) component phases are characterized with high crystallinity; and (iii) the micro/nanostructure refinement can be controlled using the growth rate. One of the proposed in the project demonstrators was an efficient photovoltaic device. The first of the ideas how to use the eutectics for solar energy harvesting appeared with the example of SrTiO3-TiO2 eutectic, which contains two phases (SrTiO3 and TiO2) which are investigated as photoanodes in photoelectrochemical cell (PEC), for utilizing the solar energy for production of hydrogen. The eutectic bi-crystals have been prepared by the micro-pulling down method, with special type of crucible with rectangular shaper enabling manufacturing of bigger samples of 2x10x40 mm. This has been necessary for proper electrodes preparation. The electrodes have been prepared out of this material and the first experiments of photocurrent have been performed on polished to 15-30 micrometers samples. Than further processed samples were introduced on fluor doped tin oxide glass (FTO) and electrical contact was made using silver paste. Photoelectrochemical properties were measured with 150W Xenon lamp with water filter. Measurements were done in 1M H2SO4. Density of photocurrents was about 8mA/cm2 in the case of SrTiO3-TiO2. Because of the surprisingly good results in the observed photocurrents other eutectics containing titanium oxide and a titanate have been investigated. One of them is NiTiO3-TiO2 eutectic. Eutectic rods with different pulling rates have been obtained by the micro-pulling down method with the inductive heating. The observed structure was not very homogenous, however in many places an interesting microstructure exists, where TiO2 ellipsoidal rods are embedded in matrix of NiTiO3. Some precipitates of metallic Ni are also observed. The first trials of growth of the eutectic plates have also been performed. The observed photocurrent for this material was 3mA/cm2.
In the demonstration domain, where the aim was to demonstrate the potential metamaterial-based applications of self-organized eutectics, we demonstrated:
(i) Photoactive eutectics as photoanodes in photoelectrochemical cells (PECs) experimental demonstration;
(ii) Localized surface plasmon resonance (LSPR) in visible and infrared, as well as enhanced photoluminescence due to LSPR in manufactured nanoplasmonic materials experimental demonstration,
(iii) Subwavelength resolution imaging (superlensing) and subwavelength propagation and transmission in polaritonic eutectics, due to four different phenomena (all numerically demonstrated):
- Hyperbolic dispersion relation
- Backward radiation in negative permittivity materials
- Subwavelength Mie resonances in permittivity near zero materials
- Surface phonon-polariton modes and gap-phonon polariton modes.
Below we describe in some detail the above mentioned demonstrated phenomena.
Photoactive eutectics as photoanodes in photoelectrochemical cells (PEC): Photoelectrochemical cells utilize solar energy for water splitting and generation of hydrogen. The solar energy is absorbed by photoanode and produces a current flow between photoanode and cathode, this splits water into hydrogen and oxygen. In the project, the potential use of eutectics containing TiO2 phase as photoanodes in photoelectrochemical cell has been demonstrated. The main systems employed wer SrTiO3-TiO2 and NiTiO3-TiO2 eutectics. Eutectic materials with new macroscopic geometry have been obtained for this aim plate-like geometry. Semiconductor materials with big enough band gap (for TiO2 rutile is 3.0 eV) are stable during photoelectrolysis. The grown eutectic structures were of high crystallinity, interconnected and with a big surface area. Photocurrent density up to 8 mA/cm2 at 600 mW/cm2 illumination has been demonstrated for SrTiO3-TiO2 eutectic, not only at UV but also at visible wavelengths. The NiTiO3-TiO2 has shown highest density of photocurrent of 3mA/cm2. Most probably the photocurrents in both cases can be still improved by various processing of the material (annealing, different material thickness, eutectics grown with different pulling rate, various dopants, plasmonic effects). The advantage of eutectics as photoanodes is that they are multiphase materials, so they posses multiple bandgaps which may allow for absorption of broad range of solar energy without necessity of making the multijunctions. Moreover, numerous interfaces allow moving the created charges without recombination to the surface. These are the first demonstrations of photocurrents in eutectic crystals used as photoanodes in photoelectrochemical cells.
Demonstration of localized surface plasmon resonance (LSPR) and enhanced photoluminescence in manufactured nanoplasmonic materials (potential application solid state lasers in UV, Si solar cell with up-conversion enhanced performance): Plasmonic behaviour has been demonstrated in two kinds of materials: (i) dielectric materials doped with plasmonic nanoparticles and (ii) metallodielectric eutectics. Plasmonic behaviour has been demonstrated both in visible and infrared wavelengths. Also anisotropic plasmonic behaviour has been demonstrated. Additionally ability to dope the nanoplasmonic materials with active ions has been shown and subsequent 7-fold enhancement of photoluminescence has been demonstrated.
Nanoplasmonic rod made by doping dielectric matrix with silver nanoparticles
demonstrating different colurs while being placed at different coulr backgrounds due to LSPR.
LSPR in the visible wavelength range:
(i) The localized surface plasmon resonance phenomenon was demonstrated in Na5B2P3O13 (NBP) as a matrix doped with 0.15 wt.% of silver nanoparticles. The NBP:nAg system exhibited a resonance at visible wavelengths, which was manifested as a sharp extinction peak of Lerenzian shape with a maximum at 404 nm. The Lorentzian shape of this peak indicates a homogenous broadening of the band, which is of high importance for many applications. The LSPR quality factor, defined as the ratio between the LSPR energy and the LSPR full-width-at-half-maximum (FWHM), was 20.5. Narrower plasmon resonances, thus larger quality factors result from smaller damping. This is important for applications where large field enhancement is necessary, such as photoluminescence.
(ii) The LSPR phenomenon has been also demonstrated in the bulk Bi2O3-Ag eutectic which exhibits three-dimensional structure of silver micro and nanoprecipitates. The Ag-Bi2O3 eutectic microstructure is formed of Ag precipitates in the form of triangular shapes with sharp corners embedded in Bi2O3 matrix. The microprecipitates are partially interconnected with tens of micrometer long, nanometer-scale precipitates. The Ag-Bi2O3 eutectic in the transmitted mode showed a localized surface plasmon resonance at 590 nm.
LSPR in the infrared wavelength range: The localized surface plasmon resonance has been demonstrated in infrared wavelength in NBP doped with ATO (antimony-tin oxide) and CuO-Ag eutectic. Transparent conductive oxides, such as antimonytin oxide or indiumtin oxide, are active in the near-infrared region and constitute attractive plasmonic materials, owing to the small negative values of the real part of the permittivity and to low losses. These features make them promising candidates for example for transformation-optics and superlens applications.
Enhancement of photoluminescence.
The enhancement of photoluminescence in the manufactured nanoplasmonic materials co-doped with rare earth ions has been demonstrated (NBP rods co-doped with Ag nanoparticles and erbium ions, NBP:nAg,Er3). In NBP:nAg,Er3+, we observed, relative to the NBP:Er3+ sample, a seven-fold increase of the 1534-nm Er3+ photoluminescence (PL) at room temperature upon excitation with a 325-nm continuous wave He-Cd laser. Potential application of these materials are: solid state lasers in UV, Si solar cells with up-conversion enhanced performance.
Subwavelength resolution imaging (superlensing) and subwavelength propagation and transmission in polaritonic eutectics: Using polaritonic alkalide-halide systems we were able to demonstrate subwavelength resolution imaging (superlensing) and subwavelength propagation in the THz regime, exploiting a variety of different phenomena and principles which (as we discovered during the project) are realizable there. The particular systems that we used to demonstrate most of the subwavelength imaging and transmission possibilities are LiF circular rods periodically placed (in a nearly hexagonal lattice) either in NaCl or in KCl. In some cases we employed also TbScO3 rods in Tb3Sc2Al3O12 matrix. Below we describe in more detail each of the phenomena that leaded to sub-wavelength propagation.
THz superlensing in hyperbolic dispersion relation metamaterials: Structures with hyperbolic dispersion relation (i.e. anisotropic structures with permittivity tensor components of different sign) have been proven a very important category of metamaterials, as they give the ability of sub-wavelength resolution imaging without the need of any resonant response (which implies high losses), or magnetic response (which is not easy to be achieved), and are relatively simple structures which can be easily fabricated. The ability of hyperbolic metamaterials (HMM) for subwavelength resolution imaging is based on the fact the HMM do not have an upper limit to the magnitude of wave vectors that they can support, so they can transmit arbitrarily large (in principle) parallel (to the air-HMM interface) wave vector components, which in free space are evanescent components and carry the subwavelength details of a source object. Moreover, the hyperbolic dispersion is associated with high density of electromagnetic (EM) modes, which can greatly affect the performance of EM sources placed in such a medium. In the framework of the project we showed that hyperbolic dispersion relation leading to subwavelength resolution imaging can be observed in the THz and IR regimes using rods made of a polaritonic material, and exploiting the negative permittivity response of the rods in combination with the structure geometry. Analogous results can be obtained also in other systems that we have examined, like LiF rods in NaCl with larger lattice constant and rod radius, or systems of LiF rods in KCl.
THz superlensing based on backward radiation in polaritonic waveguides: It has been shown recently that in waveguides with small negative permittivity values (-1less thaneless than0) there is the possibility of backward guided modes (i.e. modes of opposite phase and group velocity) which show quite strong 'attenuation' (leakage) leading to backward radiation from the side-walls of the guide. Exploiting such modes one can achieve subwavelength propagation and imaging of electromagnetic waves in a system of parallel waveguides; such a system can be a two-dimensional periodic system of rods (guides) in a host, where the rods have small negative permittivity values (also in a binary layered system with one material having small negative permitivity). In the framework of the project we showed that this phenomenon can be realized in the THz regime in systems of polaritonic LiF rods (acting as waveguides with small negative permittivity) in NaCl host.
Epsilon near zero based phenomena in polaritonic systems: total transmission, total reflection and subwavelength propagation: Besides metamaterial effects based on negative permittivity materials (like metals or polaritonic materials) it has been shown that interesting effects and possibilities can also be achieved in systems with high index dielectric inclusions. In such systems, sub-wavelength Mie-resonances can be excited, leading to phenomena like negative permeability and/or permittivity, subwavelength guiding etc. As we discovered during the project, the presence of permittivity near zero regimes in polaritonic materials allows the observation of the same phenomena in systems of dielectric rods in a polaritonic host with e approximately 0, without the need of very high index values for the rods. In such systems we can achieve subwavelength and strongly confined Mie resonances. Exploiting the coupling among those resonances in arrangements of closely placed rods we showed that one can achieve, under certain conditions, phenomena like total transmission, total reflection, negative permittivity and permeability and subwavelength propagation, guiding and imaging.
Subwavelength transmission due to surface phonon-polariton modes and gap-phonon polariton modes: Subwavelength transmission has been demonstrated in Tb3Sc2Al3O12-TbScO3 eutectic with rodlike structure, where TbScO3 rods are embedded in Tb3Sc2Al3O12 matrix. It has been shown that both component materials exhibit many wavelength ranges where Re less than 0. In some of the wavelength ranges the rods demonstrate Re less than 0 at Im small, and the matrix has Re greater than 0 and Im also small. And especially for the range ca. 16 - 18 μm the quality factor (Q=-Re/Im) is enough high to enable the subwavelength transmission along the rods. This material could be applied for directional emissivity control, especially that the material can stand very high temperatures (melting point approximately 1900μC).
Potential Impact:
Impact on the Scientific Community
In order to have an impact on the scientific community ENSEMBLE project broadly disseminated the project results through publications, talks at international conferences, workshops and institutions, and organization/co-organization of conferences and sessions at international conferences. We published around 95 papers, and 2 book chapters, more papers are still coming. We had 4 journal covers, approximately130 invited (including plenary and keynote) talks at conferences and workshops, approximately 30 seminars at Universities and Institutes, approximately160 contributed and poster presentations and we participated in the organization of several conferences.
We organized an internal workshop where we invited interested industry representatives and we organized a topical meeting within META12 Conference session 'Bottom-up approach towards metamaterials and plasmonics' where the most important representative from all over the world were invited.
Meeting with representatives of Saint Gobain (France), Umicore (Belgium)
and Cemat-Silicon (Poland)
Impact on wider community
We disseminated the information about the project and connected research in media such as in television, radio and newspapers.
TV broadcasts:
1. Teleexpress daily programme - PL, 2 March 2009
Institute of Electronic Materials Technology in Warsaw coordinates european research on metamaterials
http://www.youtube.com/watch?feature=player_embedded&v=3l0NAwDovvI
Radio:
1. Program 1 Polish Radio - PL, 27 November 2010
Program "Evening of discovery" with the participation of scientists from the Institute of Electronic Materials Technology in Warsaw. http://www.polskieradio.pl/23/266/Artykul/267472,Grafen-z-Polski
2. Radio dla Ciebie - PL, November 2011
The eight women honored in the competition organized in honor of Marie Curie http://www.rdc.pl/index.php?/pol/aktualnosci/aktualnosci/osiem_kobiet_wyrozniono_w_konkursie_zorganizowanym_w_holdzie_marii_sklodowskiej_curie
Press:
1. Nasz Dziennik daily newspaper - PL, 16-17 June 2012, No 139 (4374)
Scientists reach out forinvisibility http://www.naszdziennik.pl/index.php?dat=20120616&typ=my&id=my05.txt
2. Przeglad Techniczny - newspaper for engineers - PL, 2011
Wynalazczyni 2011 Dorota A. Pawlak
http://www.przeglad-techniczny.pl/index.php?option=com_content&view=article&Itemid=44&id=946
Other (internet):
1. Summary of the fourth edition of the "inventor" competition organized by FSNT-NOT, UP RP and SPWiR (16 December 2011) - PL
http://www.przeglad-techniczny.pl/index.php?option=com_content&view=article&Itemid=44&id=1167
2. "Forum Akademickie" magazine V contest on the popular science article under the title 'Complex and simple young scholars about their research'
K. Sadecka http://forumakademickie.pl/aktualnosci/2010/6/15/555/v-edycja-konkursu-rozstrzygnieta/
3. Ministry of Science and Higher Eduction in Poland, 14 September 2011
'Scientists from ITME obtained ribbon shape SrTiO-3-TiO2 eutectic'
http://www.nauka.gov.pl/nauka/sukcesy-uczonych/sukcesy-uczonych/artykul/naukowcy-itme-otrzymali-eutektyk-srtio3-tio2-w-postaci-wstazki/
4. The Polish National Contact Point for Research Programmes of the European Union (KPK), Success stories - the website which has been designed to highlight Polish successful projects financed under Fifth Framework Programme (FP5), Sixth Framework Programme (FP6) , Seventh Framework Programme (FP7) and the CIP programme.
http://en.kpk.gov.pl/index.php?option=com_sobi2&sobi2Task=sobi2Details&catid=2&sobi2Id=111&Itemid=142&lang=pl
5. Euro Nano Forum http://www.euronanoforum2011.eu/dorota-anna-pawlak
6. Press releases of Fundation for Polish Science - dr hab. Dorota Pawlak - Inventor Wynalazczyni 2011 (Wynalazczyni 2011) http://www.fnp.org.pl/biuro_prasowe/informacje_prasowe/informacje_prasowe_fundacji_na_rzecz_nauki_polskiej_2011_rok/dr_hab
7. ORC Seminar Series
'Materials for Metamaterials: self-organized eutectic micro- and nanostructures'
http://www.orc.soton.ac.uk/448.html
Potential impact:
The project has developed novel materials, such as
(i) bulk 3D nanoplasmonic materials which demonstrate localized surface plasmon resonance at visible and IR wavelengths,
(ii) bulk anisotropic nanoplasmonic materials with anisotropic optical behaviour at visible frequencies,
(iii) bulk eutectic-based nanostructured anisotropic materials exhibiting excitonic resonances at UV region as well as additional unusual behaviour strongly structure-dependent,
(iv) bulk 3D nanoplasmonic materials co-doped with erbium exhibiting 7-fold plasmonic enhancement of photoluminescence at telecommunication 1.5 μm wavelength,
(iv) materials with subwavelength guiding in THz regime.
The potential application we foresee in solid state lasers, optical fiber amplifiers, Si solar cells with plasmonic and up-conversion enhanced efficiency, filters, directional emissivity control, sources of IR and THz radiation, imaging systems.
Most important points of the potential impact:
(1) New modelling tools for self-organization processes - useful for further research and materials analysis.Developed models can be applied to various kinds of materials not only eutectics. Can be used in basic and applied research and in industry.
(2) New tools for modelling electromagnetic properties of complex materials useful for various complex materials:
(i) boundary element method (BEM, 2D and 3D),
(ii) multiple elastic scattering of multipole expansions (MESME),
(iii) effective medium description for polaritonic materials.
Can be used in basic and applied research and in industry.
(3) Novel technologies developed such as:
(i) 3D bulk nanoplasmonic materials (doping with NPs),
(ii) metallodielectric materials,
(iii) nanosized multiphase materials.
Can be used in basic and applied research and potentially further industralized.
(4) Novel materials developed and investigated, as: novel nanoplasmonic materials, novel polaritonic materials, novel materials with excitonic resonance, materials for dynamic change of the dielectric-metallic properties, materials for photoelectrochemistry, and others. Can be used in further basic and applied research.
(5) Novel complex materials with demonstrated special electromagnetic properties:
(i) photoactive eutectics for photoanodes in photoelectrochemical cells,
(ii) nanoplasmonic materials with LSPR at visible and IR for (enhancement of properties as photoluminescence, nonlinear processes) nonlinear absorbers,
(iii) materials with LSPR and RE demonstrating enhanced PL for photovoltaics (via up-conversion processes) novel efficient light sources,
(iv) polaritonic materials with subwavelength transmission for subwavelength resolution imaging (superlensing) directional emissivity control.
Can be used in basic and applied research and potentially further industralized
Patents applied for:
1. The way of manufacturing nanoplasmonic composites made of dielectric matrices doped with plasmonic nanoparticles (metallic and/or semiconducting) as plasmonic rods. (ITME)
2. Manufacturing of photoanodes for photoelectrochemical cells made of eutectic materials. (ITME)
Educational impact:
During the project the students and PhD students had the chance to work with the world-class scientists in this multidisciplinary team. They had the chance to perform experiments and learn at the partners laboratories. The map below illustrates the temporary 'migration' of students during the project duration. Despite the end of the project this continues. In July a student from ITME will visit FORTH for continuation of the measurements.
Additionally the knowledge generated by RISSPO/WIGNER in the framework of WP1 will be used in a compact teaching module entitled 'Introduction to phase-field modeling of solidification' consisting of 15 h lectures + 15 h computational practices; a course offered to PhD students and posdoctoral fellows. (It has been successfully tested in April 2011 as an invited teaching module of the Rolls-Royce Doctoral Training Course at the Cambridge University, UK).
Collaboration between Partners and integration with other programmes: During the project we collaborated with COST Action MP0803 and COST Action MP0702 using short term scientific missions. Most of the Partners are/were involved in at least one of these two COST Actions, as well as some Partners are members of Metamorphose VI. Most of the Partners are actively involved also in other research programs, this helped to disseminate the knowledge more efficiently and all the involved research programs benefited from those activities. The coordinator of the project and one other representative took part in a meeting of Seventh Framework Programme (FP7) coordinators (for Seventh Framework Programme (FP7) NMP call on self-organization and self-assembly) in Brussels, Belgium (February 2012) for the networking, and presentation of the project results.
Exploitation and use of foreground in research:
The models worked out by RISSPO/WIGNER will be used in the following research projects WIGNER participates in:
1. EU Seventh Framework Programme (FP7) 'EXOMET' (status: under signing the Grant Agreement). Models I and IV will be adopted for the actual tasks and further used.
2. ESA PECS project 'GRADECET' (status: signed contract). Models III and IV will be adopted for the actual tasks and further used.
3. ESA PECS project 'MAGNEPHAS III' (status: signed contract). Models III and IV will be adopted for the actual tasks and further used.
The latter two projects are related to microgravity experiments on board of sounding rockets and the International Space Station.
The technologies and materials developed by ITME will be used in the following research projects ITME participates in:
1. NATIONAL SCIENCE CENTRE Project Maestro New generation of plasmonic metamaterials (started May 2012) technology of manufacturing dielectric matrices with plasmonic nanoparticles will be utilized there.
2. Swiss-Polish Cooperation Programme - Hybrid semiconducting materials for solar energy conversion (started October 2011) the technology of manufacturing eutectic materials with big areas, the technology of electrodes preparation and the idea of utilizing the eutectic systems for generation hydrogen using solar energy will be used there.
The technologies and materials developed by ICMA will be used in the following research collaborations/potential projects ICMA will participate in:
1. Collaboration with IMEDA Materiales use of sc-micropilars for micromechanics
2. Project on metal-dielectric materials (potential)
3. Project on effect of nanosize on photoluminescence
Impact on the world-wide research initiatives:
Additionally we did strongly influence the world-wide research because after disseminating our results at various conferences the subject of the project has been noticed by the US Air Force and the Air Force Office for Scientific Research (AFOSR) opened a call for Multidisciplinary University Research Initiative (MURI) for a subject of research very similar to the subject of research of ENSEMBLE project: 'Directional Eutectic Structures: Self-Assembly for Metamaterials and Photonics'. AFOSR will fund the winning consortium with 7.5 mln USD. This will certainly help in spreading the research starting within the ENSEMBLE project and will cause high impact of this research in the future.
Networking:
Achieving the objectives of the project took a lot of effort from all the partners, which required often different understanding of the subject. This after undertaken effort created an invaluable platform of understanding which in future hopefully will be further used and will result in many new developments.
List of Websites:
http://www.ensemble-fp7.eu