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NANOstructured active MAGneto-plasmonic MAterials

Final Report Summary - NANOMAGMA (NANOstructured active MAGneto-plasmonic MAterials)

Executive Summary:

The goal of this project has been the study, development and application of a novel concept of nanostructured materials formed by the combination of components with plasmonic and magneto-optic (MO) activity. This combination produces "magneto-plasmonic" nanomaterials tailored on the nanoscale, in which the application of an external magnetic field allows controlling the plasmonic properties of the system, and the excitation of Plasmon resonances gives rise to enhanced magneto-optical performances. Thanks to these facts, magneto-plasmonic nanostructures will become key active material elements in future tunable nano-optical devices and in biosensors with enhanced sensitivity (in particular, in novel surface magneto-plasmon resonance (SMPR) sensors). In addition, the identification of relevant applications of magneto-plasmonic materials for microelectronics and information technology has also been carried out.
In short the S&T objectives can be regarded as four:
(a) Development of nanomaterials that combine plasmons and magnetic properties (films, nanoparticles, core-shell structures).
(b) Investigate the correlation between the optical, magnetic, magneto-optical and magneto-plasmonic properties.
(c) Carry out theoretical calculations of the optical response considering the magneto-optical contribution.
(d) Perform proof of concepts based in the magneto-plasmonic activity and testing for specific applications in the field of chemical sensors and biosensors. Identification of applications for microelectronics and information technology.

The objectives of this project have been realized by a coordinated action involving theoretical calculations, nanofabrication and characterization, achieving as a consequence magnetoplasmonic systems whose properties have been designed, tested, and optimized, with proven outstanding performance. The main S&T results are:
* Development of theoretical tools for magnetoplasmonic modeling.
* Development of a Near-field Scanning Optical Microscope to be able to operate under the application of external magnetic fields.
* Fabrication of magnetoplasmonic trilayered structures with a 200 enhancement factor of the MO activity upon excitation of Plasmon resonance.
* Identification of interface roughness as key parameter for enhanced MO performance and surface Plasmon wavevector modulation.
* Use of a ferromagnetic layer as a probe for the electromagnetic field distribution within a resonant nanostructure, allowing the identification of the optimum position of the ferromagnetic layer in the nanostructure for maximum MO performance.
* Proof of concept of the sensing potential of magnetoplasmonic nanodisks.
* Development of novel mangetoplasmonic nanostructures by chemical routes.
* Development of two surface magneto-plasmon resonance (SMPR) platforms with demonstrated enhanced gas sensing and biosensing sensitivity and potential combination with impedimetric measurements.
* Identification of non-reciprocal components for photonic integrated circuits at 1.55 µm wavelength as a potential application of magneto-plasmonic (MP) materials


Project Context and Objectives:

The goal of this project is the study, development and application of a novel concept of nanostructured materials formed by the combination of components with plasmonic and magneto-optic (MO) activity. This smart combination allows producing "magneto-plasmonic" nanomaterials tailored on the nanoscale. While noble metals exhibiting plasmon resonances have no magneto-optical activity and ferromagnetic materials suffer from strong plasmon damping, metallic heterostructures made of noble metals and ferromagnetic materials may sustain surface plasmons and have at the same time magneto-optical activity. The nanoscale here is crucial since the base is the interaction between the magneto-optically active material and the electromagnetic field of the plasmon, whose extension is precisely on the nm scale. In addition, the nanoscale is be needed to effectively excite the localized plasmon resonances, either in continuous materials with corrugations or topographical features of nm dimensions that will exhibit resonances associated to propagating plasmons, and nanoparticles, i.e. isolated nanostructures that will exhibit localized plasmons. The ferromagnetic material broadens the plasmon resonance of the structure, but it introduces a magneto-optical activity in the system, absent in pure noble metal layers. This way, to achieve the control of light transmission and guiding with subwavelength elements and sensing applications that plasmonic materials make possible, we propose that in magneto-plasmonic materials the action of an external magnetic field will allow controlling externally these guiding properties and enhancing the sensitivity of plasmonic sensors by magnetic field modulation. Therefore, these materials will be applicable in a broad spectrum of research and industrial areas. In particular, we believe that they could become key elements in future tunable nano-optical devices and in biosensors with enhanced sensitivity. The novel magneto-plasmonic materials offer the unique ability to control their properties in more than one way, since the magneto-optical activity is affected by the alteration of the plasmonic characteristics and the optical response depends on the magnetic ones. The latter puts an additional advantage over conventional materials, since the optical response can be actively tuned by means of an external agent: a magnetic field.
The project has two main goals; the first is to prepare active magneto-plasmonic materials with tailored properties in the nanoscale and understanding the interactions of the magnetic properties with the plasmonic and optical ones, linked to electric charge oscillations.
The second goal is to propose devices for applications that can benefit of this coupling. Since the optical properties of these materials can be driven by using a magnetic field, this allows designing and developing novel magneto-plasmonic devices. In particular, we have performed a proof concept of a new kind of surface plasmon resonance (SPR) sensor with MO elements, i.e. a surface magneto-plasmon resonance (SMPR) sensor, comparing its performance against standard sensors.
The project also includes prospective tasks for silicon-oriented uses. This part includes the identification of relevant applications of magneto-plasmonic materials for microelectronics and information technology. Depending on the materials properties several application routes may be proposed in either opto-electronic, spin-tronic, spin-photonic domains, with the corresponding electromagnetic simulation and integration analysis being performed. Preliminary manufacturing flows are proposed based on 200-to-300mm silicon standards for microelectronic (CMOS) and microsystem (System On Chip SOC) uses.
In short the S&T objectives can be regarded as four, in which we consider both bottom-up and top-down approaches to obtain the desired magneto-plasmonic materials:

(e) Development of nanomaterials that combine plasmons and magnetic properties (films, nanoparticles, core-shell structures).
(f) Investigate the correlation between the optical, magnetic, magneto-optical and magneto-plasmonic properties.
(g) Carry out theoretical calculations of the optical response considering the magneto-optical contribution.
(h) Perform proof of concepts based in the magneto-plasmonic activity and testing for specific applications in the field of chemical sensors and biosensors. Identification of applications for microelectronics and information technology.

Therefore we design novel active (thus "smart") materials tailored in the nanoscale, in particular we will use nanostructures such as alternate layers of noble metal/MO material (a ferromagnet in this case), magnetic nanoparticles as well as core-shell structures and heterodimer structures; the materials will find a space for enhanced and innovative applications (in the areas of photonics and sensors). The final target is to apply the concept to obtain chemical sensors and biosensors with enhanced sensitivity, but to that end it is necessary to investigate thoroughly the magnetic behavior of the material in the nanoscale and the interaction with the optical response. Results from these developments help defining the other applications in the information technologies area.

Along these lines, in the NANOMAGMA project we want to explore a novel magneto-plasmonic sensing concept by using as transducers the sensing MO layers developed within the project and use as detection parameter not only the optical properties of the system but also the magneto-optical properties of a nanostructured layer or of the nanoparticles. This novel sensing concept has been already tested in continuous MO films4 showing an improvement of the sensitivity of standard SPR biosensor. The use of nanostructured material and optimized layer geometries should further increase this sensitivity with respect to the already obtained ones. In the case of chemical gas sensor we want to test how the interaction mechanism taking place between chemical species in vapor phase (oxidizing or reducing gases and alcohol molecules of different steric hindrance), can be modified and amplified by the presence of a thin and well calibrated layer of nanoparticles with MO properties deposited by different physical and chemical deposition methods onto the calibrated substrate responsible of the SPR phenomena.
Moreover, taking into account that,(a) impedance/electrochemical assays are established detection avenues due to automation, real time measurements, sensitivity, and suitable for miniaturization, and (b) the combination of SPR with electrochemical measurements has been demonstrated as a powerful technique for the simultaneous characterization and manipulation of electrode/electrolyte interfaces, a novel approach proposed within NANOMAGMA consists in the achievement of high performance detection device by combining SMPR and Impedance in an unitary analytical platform with micro flow injection capabilities to address novel magneto-optical surfaces.

Our proposed approach progresses the current state of the art in that it combines the capabilities of the two powerful techniques in a differential, multichannel module with simultaneous SMPR and impedance assessment of the same sensing surface with integrated microfluidics and improved design of the measurement channel(s) to:
- Provide inner control; to test consistency of the two recordings, SMPR and electric, in order to check and to eliminate false positive/negative results; to demonstrate a prerequisite for a future "in field" system.
- Extend the range of addressable sensing platforms, i.e cellular or "cell-like", where SPR and in principle SMPR alone lacks the necessary sensitivity enabling development and addressing of cellular or "cell like" sensing platforms (e.g. lipid sensors with embedded receptors).
- Ensure a controlled environment and efficient mass transfer of the target analyte towards the sensing surface: Improved mass transfer coefficients are achieved through optimal micro flow cell design and operational flow rate.

On the other hand, identifying relevant applications being silicon-compatible is challenging and it is an important issue in terms of industrial prospects. Indeed, mobile phone and particularly CMOS sensor drive an important part of the semiconductor industry. This very competitive field could benefit from technology that can increase the optical functionalities or performance of the chip. Other industrial issues may concern on chip photonic devices, ultra high density data storage where plasmonic, near field magneto-optic and spin photonics are emerging technologies. However, it is not straightforward defining such applications, especially as it strongly depends on the materials properties that are a scientific target of the project. An important goal of this project is to identify potential applications in these fields and investigate the benefit of magnetoplasmonic structures numerically (using electromagnetic simulation tools). Basic research on the magneto plasmonic properties done during the project has been used as an input for this prospective work.

Project Results:
The description of the main S&T results comes accompanied with many illustrations. The complete Summary report is included in the attached pdf.