Final Report Summary - HINTS (Next Generation Hybrid Interfaces for Spintronic Applications)
Executive Summary:
The Consortium has succeeded to fulfil all the most important and ambitious objectives of the project. The extremely challenging objective of controlling the sign of the spin transfer at the interface (objective still critical in inorganic spintronics) has been achieved even in two different ways: by chemical tailoring of the interface (foreseen in the workplan) and by electric interfacial tuning (discovered by HINTS). While the former allows to select the sign during sample fabrication, the latter, attributable to a smart multifunctional interface behaviour, allows to change the sign during the device operation (reconfigurable operation). HINTS succeeded to bring to 11V the voltage interval where the magnetoresistance is detected, while the workplan objective was 3-5V. While highest voltage operation was detected at low T (<50 K), some materials maintained these properties up to 200-250K close to room temperature operation. This achievement paves the way for future detailed investigation of spin polarized effects on OLED behaviour, considering such parameters as efficiency, colour and other. Indeed, HINTS anticipated this by showing unequivocal and strong effect of spin polarization of driving currents on OLEDs (HyLEDs) electroluminescence.
Realization of continuous interfacial tailoring layers and realization of HOI interfaces with sharpness of 1 nm (approximately one molecule size) have been achieved. This achievement exceeds the state-of –the art quality of interfaces in OLED and OFET devices and could be applied beyond organic spintronic applications.
Interfacial proximity effect was found to embody the most powerful tailoring method for the control of spin transfer across HOI interfaces. The energy of this effect exceed room temperature promoting routes for conceptually new device paradigms. Innovative devices based on rich linear and nonlinear interface effects will definitely represent most proficient application and research line on the short and short-medium terms.
The modification of interfacial spin transfer by insertion of magnetic molecules (high spin) was also achieved. While this fulfils the objectives of the project, the modification was generally negative. Revealing the full potential of merging together the fields of spintronics and molecular magnetism would represent the topic for a fully dedicated project or even number of projects and will for sure constitute one of the most advantageous future research lines. A disruptive progress was achieved by a joint experimental-theoretical effort concerning the basic rules governing the spin transfer at HOI interfaces. HINTS looked “inside the interface” revealing how the spin dependent residence time is distributed in the first 2-3 monolayers of the organic semiconductor. The spin dependent residence time at the interface was proposed as a key parameter for the spin filtering capability. The model, based on spin dependent band broadening and energy shifts, was strongly upgraded by HINTS. Both approaches indicate robust room temperature spin transfer and spin selectivity outcomes.
On the theoretical side it has been revealed for the first time the enormous role in spin injection and transport of the resistance non-linearity in organic semiconductors. The built model defines the set of parameters, such as interface resistance, organic resistance, voltage and others, able to provide the detection of the magnetoresistance (similarly to conductivity mismatch effect in inorganic spintronic devices).
The involvement of industrial partners in the main project objectives has further grown up. Thus, two equipment producing partners succeeded to develop useful modifications to their commercial products as stimulated by the needs of HINTS requirements to the interface.
HINTS was funded with 3,874,360.00 € granted by the European Commission in the 7th Framework Programme, coordinated by Dr. Valentin Dediu of the Institute for the Study of Nanostructured Materials - ISMN (Italy), and carried out by a consortium of 14 leading research institutions.
Project Context and Objectives:
HINTS main goal was to advance new solutions for spintronic devices via the control and the tunability of the interface spin-transfer efficiency. It was the first time a research program addressed so methodically this subject, aiming essentially at putting the basis of a new generation of spintronic devices able to go beyond current GMR and TMR (commercial) achievements. Hybrid organic-inorganic (HOI) materials and interfaces were the materials of choice, featuring such advantage as the low-cost processing and the greatest choice of molecules.
All the main objectives of the project have been successfully fulfilled.
HINTS OBJECTIVES and HINTS SOLUTIONS
• Develop innovative HOI materials with interfaces exhibiting binding interactions specifically tailored for targeted spin transfer properties => Various combinations of materials have been fabricated and investigated along three tailoring approaches: proximity effect, dipole tailoring, magnetic molecule tailoring.
• Establish the basic rules governing the spin transfer behaviour at HOI Interfaces with different chemical bonds => Disruptive success achieved in joint experimental-theoretical work: proposed both a DFT based description and a phenomenological model able to describe both interfacial spin injection and spin transport inside the organic medium.
• As a consequence of the newly developed knowledge: fabricate a set of HOI materials with interfaces that allow for enhanced control of spin-selectivity => Chemical and electric interfacial tailoring have lead to a selectivity control exceeding 100% (sign reversal achieved).
• Design a set of HOI materials with tunable interfaces featuring a high (above 90%) spin transfer efficiency => Some interfaces showed spin transfer close to 100%.
• Develop HOI Interfaces with efficient spin injection at high bias voltages compatible with new ICT applications for hybrid Spintronics materials (3-5 V electrical bias) => Achieved spin injection at 11 V, outstanding achievement opening the door for applying spintronic effects in OLEDs and OFETs.
• Develop new processing technologies and protocols able to maintain the Spintronics parameters of HOI interfaces on large area (3-inches standard) wafers in UHV conditions => demonstrated evaporation of HOI materials on 3” substrates with thickness homogeneity exceeding 95 % and a material utilisation efficiency of 15%.
• Develop new processing technologies and protocols allowing for decreased material consumption for both UHV and solution processing methods => High TRL value achieve introducing (low) consumption modifications to prototypes of commercial effusion cells (UHV). Breakthrough research performed for the utilization of solution processing in organic spintronics.
• Select HOI materials with interfaces able to maintain high spin-charge transfer efficiency under conditions compatible with flexible electronics requirements => while representing a secondary objective by dedicated effort, excellent compatibility between selected HOI materials and flexible substrates demonstrated.
• Assessment of the innovative HOI materials with regard to selected ICT applications => HINTS dedicated significant efforts to these aspects under the guidance of industrial partners.
• Assessment of the innovative HOI materials towards roadmapping trends and development of a set of proposals for the update of ICT roadmaps => A set of roadmapping recommendations developed.
Project Results:
WP1
Molecular driven magnetism on reactive metal surfaces.
The outcome of this study provides an alternative way to create spin-polarized interfaces, relying on the interaction between high-spin quinoline molecules (Tb3q9) and non-magnetic metallic surfaces. The molecules preserve their structural, chemical and magnetic properties when deposited onto noble metal (Au) and passivated (SiO2) surfaces; while the adsorption on reactive metals such as Cu induces a magnetic phase at the interface involving molecular Tb-atoms, as measured via SQUID magnetometry and element-specific X-ray magnetic circular dichroism (XMCD). Remarkably, the magnetic ordering at the hybrid interface persists up to room-temperature for the Tb3q9/Cu system and is linked to a chemically-triggered change in structure and stoichiometry of the interfacial species. On the one hand, our work provides a route towards a controllable “magnetic doping” of a metal surface through molecular adsorption, while on the other hand, the creation of a magnetically active interface between a non-magnetic metal and a high-spin molecular layer opens new avenues for the design of a new class of molecular-based spintronic devices.
Paper submitted 2014.
Partners involved: NANOG (leader), UVEG, TCD, UNIKL, LiU
Scientific Impact:
Fully innovative knowledge concerning proximity effects.
Application Impact:
Possibly innovative technological approach for tailoring interafces
Dipole-layer: tuning work function and spin polarization.
We use strong donor and acceptor molecules with p-orbitals to tune energy level alignment and magnetic properties of the FM-based (Fe, Co, Ni) HIS
Utilizing the acceptor molecules (TCNE, TNAP and TCNQ) we can achieve high work function HIS with effective WF in the tunable range of 5.0 to 5.7 eV, suitable for hole injection
The donor molecule, AOB, allows us to create low work function HIS with an effective WF ~3.4 eV
Organic Electronics, 15 (2104) 1951; Advanced Functional Materials, 24 (2014) 4812; Manuscript in preparation.
Partners involved: LiU, UNIKL, CNRS, NANOG
Scientific Impact:
Fully innovative knowledge concerning proximity effects.
Application Impact:
Possibly innovative technological approach for tailoring interfaces.
Growth of Self-assembled monolayer of dipolar molecules on LSMO surfaces.
(La,Sr)MnO3 manganite (LSMO) has emerged is widely used in organic spintronic devices due to its highly spin-polarized character and air stability. Whereas organic semiconductors and polymers have been mainly envisaged to propagate spin information, self-assembled monolayers (SAMs) have been overlooked and should be considered as promising materials for molecular engineering of HOI interfaces. Surprisingly, up to now the first key step of SAM grafting protocols over LSMO surface thin films is still missing.
Demonstrated that alkylphosphonic acid groups can be used as the preferred anchoring group when dealing with the self-assembled monolayer functionalization of the standard ferromagnetic electrode material LSMO. Hence alkylphosphonic acid based SAMs are suitable to design HOI interfaces with an indirect contact between spin injector (SI) and spin collector (SC).
ACS Nano 6, 8753 (2012)
Partners involved: CNRS, Thales, UVEG
Scientific Impact:
First ever grafting of SAM on LSMO surface. Efficient spin injection achieved.
Application Impact:
Compatibility of most advanced spintronic interfaces with cheap solution processes demonstrated.
A new concept of fabricating organic spin valve (OSV), concretely fabrication of organic semiconductor from solution methods instead of expensive and complicated evaporation techniques besides we introduced the use of ionic molecular monolayer in the fabrication of a light-emitted OSV. It was established for the first time an OSV and a spin-polarized electroluminescent device with ferromagnetic electrodes that acts as a bipolar OSV, based in solution and low cost methods. Our OSV shows a spin valve magneto electroluminescence (MEL) effect of around 1%.
Partners involved: UVEG, CNR
Scientific Impact:
High efficient light emission at conditions compatible with spin polarized injection
Application Impact:
Enables the possibility to control light emission in OLEDs by magnetic field (efficiency, read –write options etc)
Growth of Self-Assembled Monolayer of dipolar molecules on Permalloy and Cobalt surfaces
The fact the LSMO’s surface Curie temperature (Tc) is close to room temperature, implies that spintronic effects in LSMO-based devices are expected only at low temperature. Hence, after the interesting results obtained using self-assembled monolayers (SAMs) on LSMO as interfaces between spin injector and spin collector in basic spintronic devices, it will be desirable to substitute LSMO by a ferromagnet of higher Tc, as for example ferromagnetic (FM) metals or alloys, like cobalt (Co) or permalloy (Py). Unlike LSMO, FM metals readily oxidize and it is not surprising that SAM grafting protocols over FM electrodes are almost non-existing. We have developed the grafting protocols necessary for the integration of SAMs on 3d FM metals with solution approaches. The formation of SAMs on Co and Py both under ambient conditions and in inert atmosphere, after removing the oxide with a simple wet etching process, have been achieved. We have observed that comparing with oxidized Py or Co, the ferromagnetic behaviour of the substrate can be improved during the solution processes. By standard characterizations it is probed that only thiol group can be successfully grafted on ferromagnetic surfaces whereas phoshonic acids group works with oxidized metal surfaces.
Partners involved: UVEG, CNRS, Thales
Scientific Impact:
Grafting protocols of SAM on clean and oxidized ferromagnetic metallic surfaces in glove box conditions.
Application Impact:
Compatibility of most advanced spintronic interfaces with cheap solution processes demonstrated.
WP2
Determination of the metal-molecule energy-level aligment by in-device spectroscopy
In this study, we have shown that the energy alignment at metal/molecule interfaces can be measured in a chip by the fabrication of a simple 3-terminal device. As a proof of principle, we measured the energy barriers at the interfaces between C60 and different metals. Furthermore, such a device can be used to inject carriers in the organic layer overcoming the contact resistance. This property allows the injection of a highly spin-polarized current into a molecular layer and to study its conduction properties at very low temperatures, in a range where the contact resistance usually prevents any carrier injection. We anticipate that this scheme for charge injection free from the contact resistance is not limited to bulk semiconductors, but can be extended in principle to any semiconductor, including solution-processable semiconductors and monolayer dichalcogenides.
Nature Communications 4, 2794 (2014)
Partner involved: NANOG
Scientific Impact:
New HOI interface characterized
Application Impact:
Innovative and cheap approach for interface energetics in HOI based devices
A 1/2 ML of oxygen on the Co(001) surface acts as a „wetting“ layer. STM measurements show that MPc’s generally form self-assembled layers on such a ultrathin oxygen layer. We found that oxidation of the cobalt going from ½ ML to higher thickness leads to a gradual suppression of hybrid interface states, and moreover to a progressive change in the work function as also seen for the Co-Mq3 interface.
Partner involved: UNIKL
Scientific Impact:
Oxygen layer effect on interface hybridization.
Application Impact:
Possible tailoring approach.
STM measurements show that for MPc’s on Co there is no “real” ordering as seen for the self-assembled layers on the MPc/CoOx/Co system. No decoration on the edge of the surface terraces indicates the high reactivity found for all the MPcs on the native Co surface. The surface dipole saturates for all the MPc systems including H2Pc when reaching 1 monolayer (ML) indicating the interaction with the substrate is related to the first monolayer. UPS measurements (He I and He II) clearly show that the H2Pc-MnPc molecules bind strongly to the Co surface and are forming HIS near/at the Fermi level.
Advanced Functional Materials, 22, 989 (2012)
Partner involved: UNIKL
Scientific Impact:
Confirming the role of the oxygen layer
Application Impact:
Possible tailoring approach.
Key improvements of the Interface Co/AlOx/Alq3
It was demonstrated by Hard X ray photoemission spectroscopy and TEM analysis that exposure of Alq3 to O2 before the deposition of metal provides a much better top electrode/organic interface characterized by higher morphological and chemical sharpness (1-2 nm interface width).
Paper in preparation 2014.
Partner involved: CNR
Scientific Impact:
Burried interface investigated
Application Impact:
New routes for direct deposition of reactive metals on Alq3.
WP3
Static characterization of the Co-Mq3 interface.
We have used spin-resolved photoemission spectroscopy to study the static spin-dependent electronic properties of the interface formed between cobalt as ferromagnetic electrode and three metal quinolines: Alq3, Gaq3 and Inq3. By combining ultra-violet-photoemission spectroscopy (UPS), spin-resolved near-threshold photoemission spectroscopy (NT-PS), spin-resolved two-photon photoemission (2PPE) spectroscopy and state-of-art density functional theory (DFT) calculations (performed in WP1), our study unequivocally shows that all three Mq3 molecules bind so strongly to the surface that spin-polarised interface states are formed. Interestingly, the interface electronic structure is very similar in all cases. This is a consequence of the fact that for all the three molecules, the HOMOs are localised on the phenoxide moiety of the ligands, while the three LUMOs on the pyridyl moiety: thus almost no charge is localised on the metal centres.
PRB 89, 094412 (2014)
Partners involved: UNIKL, TCD
Scientific Impact:
Accurate detection of proximity induced purely interface spin polarized states.
Application Impact:
Enable conceptually new device paradigms based on non-linear interface behaviour.
Formation of hybrid interfaces.
We have studied the formation of hybrid interfaces by two complementary spectroscopic methods: spin-polarized STS (scanning tunneling spectroscopy) and spin-polarized NT-PS (near threshold- photoemission spectroscopy).
Both methods give evidence for the formation of spin polarized hybrid interface states in the energetic region close to the Fermi level.
PRB 84, 224403 (2011)
Partner involved: UNIKL
Scientific Impact:
Definition of the energetics of the proximity induced interface states.
Application Impact:
Enable conceptually new device paradigms based on non-linear interface behaviour.
Chemical tailoring of the spin properties of the Co-Mq3 interface.
We have created different experimental molecules to tailor the spin-dependent properties of the interface by modifying chemisorption with cobalt. For example, Al(OP)3 was developed to produce a ligand that has more extended p-systems than Alq3. We expect a modification of the chemisorption on cobalt, and thus different spin-dependent properties of the Co/Al(OP)3 interface with respect to Co/Alq3. Using spin-resolved photoemission methods, we have indeed identified two hybrid interface-states in the energy window of 2 eV below the Fermi energy, in contrast to the Co/Alq3 interface where only one hybrid state is present.
NJP 15, 113054 (2013)
Partners involved: UNIKL, TCD
Scientific Impact:
New (HINTS developed) molecules show modified interface hybridization.
Application Impact:
Enable conceptually new device paradigms based on non-linear interface behaviour.
Physical tailoring of the spin properties of the Co-Alq3 interface.
We have used oxidation of the Co/Alq3 interface to control its electronic properties. Oxidation of cobalt is expected to dramatically influence the strength of hybridization with the deposited molecules, and as a consequence the spin-dependent electronic properties of the interface. By UPS, NT-PS and 2PPE we found indeed that oxidation of the cobalt leads to a gradual suppression of hybrid interface states, and moreover to a progressive change in the work function and to a continuous energetic shift of the molecular orbitals towards higher binding energies. Based on our spectroscopic observations, we have suggested controlled oxidation of the ferromagnetic electrode as an easy and effective possibility to tune the spin-properties of metal/organic interfaces.
APL 103, 251603 (2013)
Partner involved: UNIKL
Scientific Impact:
Defined the role of superficial oxygen on spin polarization.
Application Impact:
Enable soft interface modifications in future HOI devices.
Microscopic understanding of hybrid metal-organic interfaces.
We have used spin- and time-resolved two-photon photoemission to study the spin-dependent electron relaxation across hybrid interfaces. We found that electrons injected across hybrid interfaces are trapped into hybrid interface states in a spin-dependent manner for a surprisingly long time of the order of 0.5–1 ps. This is the microscopic origin of the spin-filtering properties of hybrid interfaces. The achieved microscopic understanding of the spin-dependent dynamics at hybrid interfaces lays the foundation for designing advanced actively controlled spintronics devices.
Nature Phys. 9, 242–247 (2013)
Nature Phys. 9, 210–211 (2013)
Partners involved: UNIKL, CNR
Scientific Impact:
Outstanding achievement – first look “inside” the interface.
Application Impact:
Promotes new ways to describe key device parameters. Room temperature operation.
Coherent excitation of hybrid interface states.
We have performed phase-stabilized two-photon photoemission experiments at the Co-Alq3 interface to probe the coherence of the optical excitation across hybrid interfaces. We have found long-lived excitations with coherence times of up to 110fs. This demonstration of coherent control of spin polarized hybrid interface states opens the way to ultrafast spin control at the molecular scale.
Partner involved: UNIKL
Scientific Impact:
found long-lived excitations with coherence times of up to 110fs
Application Impact:
opens the way to ultrafast spin control at the molecular scale.
Spin-polarization loss at insulator/organic interfaces.
We have investigate the influence of the tunnel barrier MgO inserted at the interface between the spin injector CoFe and the organic semiconductor C60 by spin-resolved photoemission spectroscopy. At the CoFe/C60 interface the spin polarization persist up to 15nm C60 thickness and decrease linearly with C60 thickness. At the CoFe/MgO/C60 interface, however, we observe a drastic reduction of the spin polarization directly at the interface between C60 and MgO, indicating an enhanced spin-scattering rate at the insulator/organic interface.
Partner involved: UNIKL
Scientific Impact:
MgO barrier strongly reduce the spin transfer efficiency
Application Impact:
Nearly 100% spin transfer – CoFe/ C60 interface is among best candidates for device applications.
A nonlinear behavior of a logarithmic plot of the PES intensities in the region below EF show the existence of HIS formed by the hybridization reaction. Using a modified Lambert-Beer law, SP-UPS measurements clearly show differences in the spin down channel just below EF for the different MPc’s and the pure organic system H2Pc. By using a very recently published model describing the interaction of the carbon pz orbitals with a FM, the main structures in the spin down channel at 1.1 eV and the structure at 0.3 eV in the spin up channel are attributed to the interaction of the phenyl-ring system with the metal substrate d orbitals. These structures are consistent with calculations which were also made by the partner TCD for the system MPc/Co. The differences for the spin down channel just below EF are therefore density of states which must be attributed to the metal atom d-states changing the DOS at the Fermi level and still reflects the importance of the geometry of the open shell frontier orbitals in MPc’s for the discussion of spin polarization effects at the interface.
Partner involved: UNIKL
Scientific Impact: quantitative description of hybridized interface states
Application Impact:
Important as characterization method for device interfaces.
In SP-UPS spectra a 1/2 ML of oxygen on the Co(001) surface clearly shows a strong majority polarization vanishing rapidly going to higher oxygen layers. This polarization is also described in DFT GGA+U calculations for a ½ ML on Co. This clearly shows that a very small amount of oxygen is not “magnetically dead”. Measurements of the spin polarization for the two archetypical MPc’s, CuPc and FePc, show slight differences. The SP-UPS spectra we measure were then correlated with some DFT calculations of the system MPc/CoOx/Co(001) indicating that the differences we investigate matches with two separate interaction mechanisms which were caused by the differences in the geometry of the open shell frontier orbitals of the MPc’s central atom and therefor the interaction path. Therefore the results on the MPc/CoOx/Co(001) also reflect the importance of the geometry of the open shell frontier orbitals in MPc’s for the discussion of spin polarization effects at the interface.
Partner involved: UNIKL
Scientific Impact:
The strong interfacial effect of oxygen on spin polarization of the injecting surface. Also revealed the importance of the geometry of the frontier orbitals in metal phthalocyanines.
Application Impact:
Important tailoring issues in vertical spintronic devices.
UPS measurements in cooperation with partner LiU clearly show a charge redistribution seen by the enhancement of work function and a asymmetric behavior of the HOMO and HOMO-1 levels up to the first monolayer. SP-UPS measurements clearly show a spin-splitting of this two MO’s. A nonlinear behavior of a logarithmic plot of the PES intensity’s in the region below EF clearly show the existence of HIS formed at the interface. A remaining high intensity in the spin DOS just below EF furthermore indicates differences in the interaction mechanism with the Co substrate compared to one suggested for the MPc systems.
These observations are important comparing them with C60 spin valves experiments which have been done.
Partners involved: UNIKL, LiU, NANOG
Scientific Impact:
quantitative description of hybridized interface states
Application Impact:
Important tailoring issues in vertical spintronic devices.
Multifunctional magnetic&electric memory and logic gate
Resistive bistability effect in organic (LSMO-Alq3-Co) spintronic devices was put at the basis of new device paradigm featuring both electric and magnetic memory (magnetically enhanced memristor). The device could be set in 32 different and reversible resistive states. The excellent control of the resistance is very promising for memory applications.
In addition to memory capability, the device performs as logic gate – two logic gates, AND and IMP, have been experimentally demonstrated.
Advanced Materials 2013, 25, 534–538
Partners involved: CNR, QMUL
Scientific Impact:
Full electrical control of the magnetoresistance achieved.
Application Impact:
Important input for device paradigms conceptually different from inorganic spintronic devices.
The absence of Hanle effect in prototypical devices.
We investigated the Hanle effect, one of the main outstanding issues in organic spintronics. We have investigated it by measuring the GMR of a prototypical organic spintronic device at different angles between the device’s plane and the magnetic field, and we found no sign of its presence. Although we have no definitive explanation for this finding, an exceptionally high mobility (30 cm2V-1 s-1) would be sufficient to justify the present data. Altogether, these results strongly suggest that the current understanding of transport in organic GMR devices is not sufficiently developed to explain the absence of the observation of spin precession and supports the framework of transport occurring via high mobility, high conductivity channels.
Appl. Phys. Lett. 102, 092407 (2013)
Partners involved: CNR, MLU
Scientific Impact:
Crucial achievement questioning most of previously adopted concepts for spin transport in organic materials. Immediately stimulated an intense discussion.
Application Impact:
Allows to distinguish tunnelling and injection devices.
Defect role in prototypical Alq3 based devices
From the comparison of the electrical resistance of the hundreds of spintronic devices fabricated over the course of the project, two regimes in the Resistance vs Thickness curve could be observed. The high resistance one, with a resistance that is proportional to the thickness of the organic layer, shows no MR; in this case we suppose that transport occurs via the LUMO and/or HOMO levels. Instead, the low resistance regime, highly variable between nominally identical samples, shows MR ; in this case the transport presumably occurs through defects. A meta-anlisys of the data available from the literature for comparable devices, follows the same pattern.
Commented in Nature Nanotechnology 8, 885 (2013)
Partner involved: CNR
Scientific Impact:
Acquired significant indications for the key role of defects and impurities in the detection of MR in Alq3 based devices.
Application Impact:
Definition of optimal devices resistances and transport modes.
Dipole layer HIS: work function and spin-polarization.
We used X-ray Magnetic Circular Dichroism to confirm spin-polarized hybridized -orbitals for TNAP/FM and TCBE/FM HOI. The spin-polarized occupied density of states of a particular TCNE/FM HOI, TCNE/Co, was then explored using spin-polarized ultraviolet photoelectron spectroscopy. According to the XMCD results and sum rules, TCNQ and TNAP adlayers have no detrimental influence on the spin polarization of the FM surface whereas AOB adlayers reduce the spin polarization of the FM surface. The results demonstrate that high and low effective work function FM-OS HIS with spin-polarized -orbitals at the interface can be achieved but also demonstrates that the OS-FM interaction can negatively impact on the surface spin-polarization of the FM. Nevertheless, the wide range of work functions achievable and the in general favorable magnetic properties make these HOI potentially useful as spin injecting / spin detecting contacts.
Partners involved: LiU, UNIKL
Scientific Impact:
Revealed that TCNQ and TNAP adlayers have no detrimental influence on the spin polarization, while changing significantly the current injection. Vice versa, the AOB adlayers reduce the spin polarization
Application Impact:
Crucial technological information for devise fabrication.
Spin transfer through self-assembled monolayers in a nanocontact.
A lithography process has been developed to fabricate nano-scale vertical systems where molecules are connected to ferromagnetic leads. This technique allows probing HOI interfaces at the nanoscale. Nanolithography based on real time electrically controlled nano-indentation has been used to fabricate LSMO/SAMs/Co magnetic tunnel junctions where SAMs are alkyl-acid phosphonic Self-Assembled Monolayers. Lateral size of the devices can vary from few nm to few tenth nm. Electrical characterizations show that not short-circuited nano-junctions can be achieved. This technique is quite versatile since different kind of ferromagnetic electrodes and molecules can be used.
Magnetoresistance signal up to 40% has been measured and is comparable to the best organic spin valves. Hence spin dependent transport reveals an efficient spin transfer at HOI interfaces using Self-assembled monolayers grafted on a ferromagnetic electrode.
This shows the potential of SAMs for future chemically tailored and engineered spintronics applications while opening the door to additional molecular electronics functionalities.
Advanced Materials 24, 6429 (2012)
Partner involved: CNRS, Thales, UVEG
Scientific Impact:
Efficient spin transfer at HOI interfaces using Self-assembled monolayers grafted on a ferromagnetic electrode
Application Impact:
This shows the potential of SAMs for future chemically tailored and engineered spintronics applications while opening the door to additional molecular electronics functionalities.
HOIMs featuring efficient spin transfer at high operation bias voltages.
Spin transfer at hybrid inorganic/organic interface has been probed by tunnelling magnetoresistance experiments in Self-Assembled Monolayers (SAMs) based magnetic tunnel junctions. The self-assembled monolayers are alkyl phosphonic acids grafted on a half metallic LSMO electrode (D1.2). LSMO/C12PO3H2/Co magnetic tunnel junctions have been fabricated using the nano-indentation technique (D1.6). Figures a-b represent the bias voltage dependence of the tunnel magnetoresistance and two examples of magnetoresistance curves recorded at low (10 mV) and high (4 V) bias voltage. A striking point is the very weak decrease (~25 %) of the tunnel magnetoresistance with the bias voltage. Actually at a voltage as large as 4 V the tunnel magnetoresistance is still about 22%. The high tunnel magnetoresistance ratio at such high bias voltage is a unique feature of these HOI based magnetic tunnel junctions where molecular vibrations plays a crucial and beneficial role since they can short-circuit magnon excitations that usually affect inorganic systems.
These measurements demonstrate an efficient spin transfer at these hybrid inorganic/organic interfaces and reveal the potential of SAMs as spin injector working at high bias voltage. This could be a key enabler for future applications such as spin-OLEDs where the spin current is expected to drastically improve the OLED efficiency.
Advanced Materials 24, 6429 (2012)
Partners involved: CNRS, Thales, UVEG
Scientific Impact:
Efficient spin transfer at HOI interfaces: revealed the potential of SAMs as spin injector working at high bias voltage.
Application Impact:
Possible key enabler for future applications such as spin-OLEDs where the spin current is expected to drastically improve the OLED efficiency.
Magnetoresistance at high bias voltage in H2PC-based organic spin-valves
Magnetoresistance (MR) is observed in vertical organic spin valves consisting of a LSMO and a Co electrode and the metal-free phthalocyanine H2PC. The devices undergo a strong resistance increase (approximately 3 orders of magnitude) during cool down to 4.2K (see Fig. a) indicating that the resistance is dominated by the charge transfer through the H2PC-layer. In addition to the spin-valve signal (see Fig. b) which has a magnitude of ≈8% at low bias and is persistent to bias voltages of up to ±8 V (see Fig. c) we also have identified a sizeable contribution of tunneling anisotropic magnetoresistance (TAMR) to the MR effect (see phiscan measurement in Fig. d). The bias dependence of the TAMR is comparable to this of the spin-valve signal with a maximum of ≈2.5% at 0V. The observation of TAMR suggests that, despite the strong temperature dependence of R, tunneling processes still have a measureable influence on the device resistance and the magnetotransport behaviour in the low bias regime.
Partner involved: MLU
Scientific Impact:
Innovative, very important for the further understanding of the physics behind MR in organic spin valves
Application Impact:
The realization of structures exhibiting MR at bias voltages in the >±3V regime basically is mandatory for a successful implementation in applications.
Magnetoresistance up to 3-4 percent was established at voltages as high as 11 V, exceeding by far the HINTS objective of 3-5 V. Noteworthy this magnetoresistance was detected in OLED devices at currents and voltages corresponding to light emission. The result opens the possibility to promote efficient studies of the capability to modify light emission in organic based LEDs by spin polarized injection.
Partners involved: UVEG, CNR
Scientific Impact:
A different type of multifunctional devices: magneto- optical. HOI with high voltage operation demonstrated.
Application Impact:
Spin polarised injection is expected to improve OLEDs efficiency (double for singlet emission).
Outstanding magnetic modulation of the electroluminescence was achieved in OLEDs with two spin polarized electrodes.
Partners involved: UVEG, CNR
Scientific Impact:
Hints for both light emission physics and spintronic effects.
Application Impact:
Possibility to combine magnetic and optical writing and reading of information. Increased OLED efficiency (see above).
Lateral organic spin-valves fabricated by shadow evaporation
A novel fabrication process has been developed, improved and established that allows for the in-situ fabrication of lateral organic spin valves with a channel length in the sub-100nm regime. The process’ key step is a shadow evaporation process which is illustrated in Fig. a and b. Preliminary experiments have been undertaken in order to verify that all requirements for spin-valve functionality are met, e.g. different coercive fields of the two electrodes (see MOKE measurements in Fig. c). The contacts’ separation has been checked by imaging methods (see Fig. d) and indirectly by transport measurements. In devices employing the organic semiconductor N,N'-bis(Heptafluorobutyl)-3,4:9,10-Perylene Diimide (PTCDI-C4F7) we have measured a spin-valve-like magnetoresistance effect of up to ≈50% (see Fig. e and f) at room temperature which can be explained by lateral tunneling.
Organic Electronics 14, 2082 (2013)
Partner involved: MLU
Scientific Impact:
devices which do not suffer from side effects like a reduction of the organic interlayer’s thickness.
Application Impact:
realization of lateral spin-valve structures is an important step towards the implementation of non-volatile switching to the established organic field effect transistor technology.
Resistive switching in AlQ3-based TAMR devices.
A resistive switching (RS) effect going beyond common bipolar switching has been observed in AlQ3-based single-sided vertical spin valves (tunneling anisotropic magnetoresistance, TAMR, structures with only one ferromagnetic LSMO electrode). The RS (see Fig. a) is initiated by short voltage pulses and allows for setting the device resistance in the range between ≈1kΩ (base resistance state, BRS) and a maximum of ≈120kΩ (high resistance state, HRS). Magnetotransport measurements have been performed in this resistance range revealing a strong increase of the TAMR magnitude when the device resistance is increased (Fig. b). Based on the results of further studies (Simmons analysis of I/V characteristics, see Fig. c and d) a modification of the tunnel barrier which is located between the LSMO electrode and the AlQ3-layer can be identified as the origin of the MR effect’s enhancement. Furthermore, among other experiments, a similar analysis has been undertaken for a complete RS cycle in order to investigate the barrier parameters’ dynamics caused by the applied voltage pulses (Fig. e). In all results of I/V curve analysis an increase/decrease in barrier thickness/height (dbarrier/Φ0) with increasing device resistance (and vice versa) can be discerned suggesting very basic mechanisms behind the RS, which very likely are creation, motion and removal of oxygen vacancies at the LSMO electrode’s surface.
Partner involved: MLU
Scientific Impact:
TAMR can be employed as a powerful tool for the investigation of interfaces and interface-related effects.
Application Impact:
realization of another class of promising multifunctional devices.
Spin transfer sign modification at a selected tailored HOI interface at room temperature
We developed organic spin valves relying on conventional metallic ferromagnetic electrodes (Co, Fe,Ni…) having high Curie temperature well above room temperature. Co/Alq3/Co organic spin valves were fabricated in-situ by shadow mask. Inverse magnetoresistance was obtained at room temperature. This was ascribed to a strong hybridization (HOI) sustaining up to room temperature as an inverse magnetoresistance in spin valves with identical ferromagnetic electrodes implies that the spin polarization is inverted at one of the two interfaces. This was further confirmed as, by inserting a tunnel barrier at the bottom interface to suppress the hybridization (HOI), normal magnetoresistance was then observed.
This demonstrates that the hybridization is strong enough to be observed at room temperature and unveils the potential of HOI for room temperature applications.
Partners involved: CNRS, Thales
Scientific Impact:
Demonstrated that the hybridization is strong enough at room temperature
Application Impact:
Potential of HOI for room temperature applications.
Control spin polarisation of extracted holes by inclusion of interfacial layers
VLS modifies the energy of the HOMO/LUMO with respect to the ferromagnet.
This changes the spin polarisation of extracted charge carriers at that interface
Phys. St. Sol. B 2012
Partner involved: QMUL
Scientific Impact:
Revealed the role of interface energetics on spin transfer at HOI.
Application Impact:
Provides strong indications for the most efficient interfacial engineering of devices.
Direct evidence that transition metal FMs are hole injectors/extractors and that the lower hole mobility isn't the limiting factor in organic spin valves
- Mobility of holes ~50 times smaller than electrons.
- Not limiting factor in spintronic devices, if it is possible to inject only holes at FM-Alq3 interfaces.
APL 2014
Partner involved: QMUL
Scientific Impact:
Most deep investigation on the mobility effects in HOI based spintronic devices.
Application Impact:
Key information for the control of mobility in devices.
Room temperature spin transport in organic molecules with hopping charge transport and air stability
Produced and characterized spin valves based on the organic semiconductor Bathocuproine (BCP). In two sets of devices, different AlOx seed layers have been employed, that we distinguish between “leaky” and “non-leaky” on the basis of the temperature dependence of their resistance. For the devices with non-leaky seed layer, the main charge transport mechanism is tunneling, and consequently MR is measured only for extremely thin BCP films (5 nm). By contrast, for devices with leaky AlOx layer, the transport takes place into the BCP film, featuring an exponential increase of the resistance characteristic of hopping transport. In these devices, a sizable MR is measured up to a thickness of 60 nm. Finally the BCP-based SVs have shown excellent air-condition stability in terms of device performance even after long time (more than 70 days), outperforming most of the reported organic spin valves.
Nature Communications 4, 2794 (2014)
Partner involved: NANOG
Scientific Impact:
Modification of the tailoring oxide layer allows to modify internal interfacial structure.
Application Impact:
The observation of air-stable room-temperature spin transport in BCP-based SVs is of great importance for the future industrial interest in organic spintronics considering cheap (non UHV) technologies.
WP4
Enhanced spin-orbit coupling in molecules at the interface with a ferromagnetic metal.
For the interface between fcc Co(001) and Alq3, we have found (through density functional theory calculations) a small, but still non-zero, spin-polarization induced even on molecules very weakly coupled to the surface. This is shown in the left panel of the picture, where the spin-resolved density of states (DOS) for the LUMO of an Alq3 molecule is displayed. Therefore, we infer that spinterface effects are non-negligible also for molecules in the second layer of an organic film deposited on a ferromagnetic metal. Even more interestingly, we have found that the DOS presents comparable non-collinear components when the spin-orbit coupling is explicitly included in the calculation (right panel of the picture). As the Co(001) is a surface with a relatively large spin-orbit coupling strength (in fact spin hot spots have been extensively studied for this surface), the small hybridization is able to enhances the spin-orbit coupling strength in the molecule itself (we note that the intrinsic spin-orbit coupling strength of gas-phase Alq3 is so small that cannot even be numerically resolved in calculations).
In future, more systematic studies for different class of molecules may be performed.
Partners involved: TCD, UNIKL
Scientific Impact:
Elucidates the enormous role of the spin-orbit coupling at HOI interfaces.
Application Impact:
Promotes routes for the modification of magnetic anisotropy and other magnetic parameters in thin ferromagnetic films by deposing top organic layers- mild engineering of key magnetic properties.
A multiscale theoretical scheme to compute material-specific charge and spin transport properties of organic semiconductors has been developed. This scheme has been extensively applied in order to study crystalline rubrene. Highly anisotropic transport properties have been found (left panel of the picture) and, moreover, the obtained value for the charge carrier mobility is in good agreement with the highest estimate, which was reported in experiments. Furthermore, we could compute the spin-relaxation length (right panel of the picture). By including both the spin-orbit and the hyperfine interaction, a good agreement between our computed value and the experimental estimate has been achieved. More importantly, the spin-diffusion length ls is found to be independent on the temperature for zero-spin orbit coupling. In contrast ls decreases with the temperature when the spin-orbit coupling is not neglected. Our results then suggest that the analysis of the temperature dependence of the spin-diffusion length can be used as a mean to investigate the relative importance of the spin-orbit coupling and of the hyperfine interaction in the spin transport properties of (crystalline) organic semiconductors. This would finally help to address the long-debated issue about the origin of spin-relaxation in organic materials.
Partner involved: TCD
Scientific Impact:
Developed the most advanced multiscale theoretical scheme able to compute charge and spin transport properties in HOI and organic materials.
Application Impact:
Important step towards the “on need” developed and fabricated materials for Spintronics.
Moving beyond the ferromagnetic electrodes’ age: exploring novel materials
Until recently, most of the studies in organic spintronics have investigated hybrid interfaces between ferromagnetic metal and organic semiconductors. Usually, a hybrid interface is engineered through a careful selection of the organic molecules. Here, instead, we have investigated theoretically (by mean of density functional theory calculations) the impact of different classes of inorganic materials. For example, we have considered the interface formed by absorbing different molecules on the 3D topological insulator, Bi2Se3. We have found three different physical scenarios, exemplified in the picture by plotting the (molecule and surface) density of states (DOS) resolved in reciprocal space. For weakly coupled molecules (top panel), no change in the electronic structure neither of Bi2Se3 nor of the molecule is seen. For molecules in an intermediate coupling regime (central panel), the electronic structure of Bi2Se3 is unchanged, while a hybrid interface state appears. Finally, for the case of strongly coupled molecules, Bi2Se3 still preserves its topological nature although the electronic structure changes visibly. Furthermore, and more importantly, the typical features of the topological insulator are seen also on the molecule DOS.
The first two scenarios (weak and intermediate coupling) have been observed also experimentally by UNIKL. For the third case, an experimental proof is not available yet.
Finally, we think that, if a suitable molecule able to form a strong chemical bond with Bi2Se3 was identified, a novel hybrid interface could be made thus opening the route to completely unexplored applications for spin-injection /detection .
Partners involved: TCD, UNIKL
Scientific Impact:
Extremely innovative knowledge on the use of topological insulators in spintronics.
Application Impact:
Step towards new, naturally cheaper electrodes (rare earth free)
Hopping Magnetotransport via Nonzero Orbital Momentum States and Organic Magnetoresistance
The theory of hopping magnetoresistance was extended to states with nonzero orbital momenta. Different from s states, a weak magnetic field expands the electron (hole) wave functions with positive magnetic quantum numbers, m>0, and shrinks the states with negative m in a wide region outside the point defect. This together with a magnetic-field dependence of injection/ionization rates results in a negative weak-field magnetoresistance, which is linear in B when the orbital degeneracy is lifted. The theory provides a possible explanation of a large low field magnetoresistance in disordered conjugated organic materials.
PRL 108, 186601 (2012)
Partners involved: JSI, CNR
Scientific Impact:
Revealing the presence of magnetoresistance in hopping transport in general.
Application Impact:
Enabling possible field dependent correction in devices based on hopping conductivity.
Magnetoresistance in organic spintronic devices: the role of nonlinear effects.
A full set of kinetic equations was derived describing injection and transport of spin polarized carriers in organic semiconductors with hopping conductivity via an impurity level. The model predicts a strongly voltage dependent magnetoresistance defined as resistance variation between devices with parallel and antiparallel electrode magnetizations (spin valve effect). Namely, the voltage dependence of the magnetoresistance splits into three distinct regimes. The first regime matches well known inorganic spintronic regimes, corresponding to barrier controlled spin injection or the conductivity mismatch case. The second regime at the intermediate voltages corresponds to strongly suppressed magnetoresistance. The third regime develops at higher voltages and accounts for a novel and purely organic paradigm. It is promoted by strongly non-linear effects in organic semiconductor which strength is characterized by the dimensionless parameter eU/kBT. This nonlinearity, depending on device conditions, can lead to both significant enhancement or to exponential suppression of the spin-valve effect in organic devices.
Paper submitted 2014
Partners involved: JSI, CNR
Scientific Impact:
Conceptually new approach proposed to circumvent conductivity mismatch problem in spintronics by making use of non-linear carrier transport. Fully applicable to organic and HOI cases.
Provides explanation of high voltage magnetoresistance.
Application Impact:
Significant step towards a quantitative description of HOI spintronic devices with electrical injection.
WP5
Two flanges dedicated to the efficient evaporation of organics
The flanges are easy to implement in an existing UHV system.
Both provide a film thickness uniformity better than ± 2 % on 3 inch substrates. One flange is dedicated for the evaporation of organics only and has an outstanding material utilization efficiency of 15 %. Using this flange for the evaporation of metals, which usually have a higher evaporation temperature, increases the temperature of the substrate. This increase might destroy organic films, which were prior evaporated to the substrate. Hence the second flange has a larger crucible-substrate distance and thus is also suitable for the evaporation of metals. Due to larger crucible-substrate distance the material utilization efficiency is only 6.5 % on 3 inch substrates.
Partners involved: MBE-K, CNR, NANOG
Application Impact:
Significant improvements to available commercial solutions.
OME 100 Effusion Cell
The OME 100 Effusion Cell is an advancement of the OME evaporators. It dedicated to the evaporation of sensitive organic materials on large spherical calottes (Ø ~ 1 m) which are often used in the industrial environment. Due to the large substrates the orifice of the evaporator needs to be large.
Besides evaporating the organics from a quartz liner it is possible to evaporate it directly from the copper crucible. The copper crucible can be plated with nickel, gold or silver. Evaporating directly from the copper crucible increases the thermal flow into the organic material. An additional thermocouple positioned in crucible makes it possible to directly measure the temperature of the organic material.
Partner involved: MBE-K
Application Impact:
The development of the effusion cell is finished and some evaporators are already in use.
TRL 6-7
OME 63 Effusion Cell
Like the OME 100 the OME 63 is an advancement of the OME evaporators. It has been developed and build for customers, who evaporate sensitive organics to large substrates (diameter of a few cm) and need a large amount of organics. The effusion cell can be used both for research purposes and industrial applications.
The development of the effusion cell is finished and some evaporators are already in use.
Partner involved: MBE-K
Application Impact:
The development of the effusion cell is finished and some evaporators are already in use.
TRL 6-7
Thermostar
A big difference between the evaporation of organics and metals is the usually much lower thermal conductivity of the organic material. In combination with a large orifice this might lead to a strong temperature gradient within the organic material. While the outer molecules in direct contact with the crucible evaporate with an acceptable rate the rate strongly decreases for molecules in the inner part of the crucible. Therefore the total rate is much lower as possible and also the danger of decomposition of the organics is much higher due to the high gradient of the temperature within the crucible.
To increase the thermal conductivity within the organic material the Thermostar was invented. The Thermostar is build of copper sheets arranged in a star shape. The copper sheets can be plated with different materials like gold, nickel and silver. The Thermostar needs to fit to the inner shape of the crucible and the normally used maximum filling level.
Partners involved: MBE-K, MLU
Application Impact:
Fabricated an insert to standard commercial crucibles allowing to decrease internal temperature gradients and enhance effusion homogeneity.
TRL 5-6
Customized OME 40 effusion cells for CNR-ISMN
To optimize the evaporation setup the CNR-ISMN is using for the evaporation to 1 x 1 cm² substrates several simulations were carried out. Based on the results two customized OME 40 effusion cells were built for the CNR-ISMN. By reducing the crucible-substrate distance and using a conical crucible the film thickness uniformity could be kept at 95% while increasing the material utilization efficiency from 0.34% to 1.07%.
The development of the customized OME 40 is finished and the CNR-ISMN is using the two build evaporators.
Partners involved: MBE-K, CNR
Application Impact:
Performed the customisation of the commercial cell OME40 aiming at more efficient use of the filling material. Applicable for the case of low amounts of starting material.
TRL 4-5
Simulation: selection of the setup used for the evaporation on 3” substrates
For the evaporation of organics on 3” substrates the partner nanoGUNE had to choose between two evaporation setups. With the help of the simulation of these two setups it was possible to choose the evaporation process suitable for their application without performing time-consuming experimental tests.
Using the chosen evaporation setup three 3” substrates were coated with C60 and subsequently analyzed with ellipsometry. Simulation and experiment were in very good agreement.
Partners involved: MBE-K, NANOG
Application Impact:
Brings high quality HOI interface protocols to 3” substrate growth setups.
As part of the HINTS project M-Solv has focused on developing a machine for depositing solution based OSC molecules in an inert environment. The MGB-601 has been built and tested using ink jet and ultrasonic spraying methods for solution deposition.
Novel material handling methods have been developed to enable the use of ink jet print heads inside a glove box. And as a consequence the tool offering capability of M-Solv has been increased.
Partner involved: M-SOLV
Application Impact:
M-Solv has increased the TRL of the tehcnology to 7 and above and this has lead to a sale worth EUR 500k to a top 4 world ranking university, of a mulit-head spray deposition system in a glove box.
By demonstrating that it is possible to pattern sub micron films and stop on a specified layer, it is possible to pattern thin film devices through laser processing only. This is industrially relevant as it reduces the number of masks required and associated alignment for each subsequent layer. Therefore manufacturing costs are reduced.
Partners involved: M-SOLV, MLU
Application Impact:
By reducing the manufacturing costs the TRL of this process has moved to TRL 5/6 from 2.
Ink jet printing:
As part of the project M-Solv developed methods for using ink jet printing processes for precise deposition of materials. Both for discreet formation and also for uniformity of deposited films. Novel process regimes had to be developed so that a thin layer <100nm could be achieved over a 10um x 10um area that would be suitable for device fabrication.
It has been shown that ±3um in dimensional accuracy can be achieved along with thickness regimes of <20nm with a sub nm roughness. Therefore ink jet has the potential to make functional layers with the required surface roughness and thickness uniformity.
The process relies heavily on the ink – surface interaction and how it wets.
Partners involved: M-SOLV, UVEG
Scientific Impact:
Found the wetting requirements for achieving the high uniformity
Application Impact:
Compatibility between some spintronics materials and ink jet technology demonstrated.
Organic spin valve with lateral dimensions in the sub-500nm regime
A fabrication process for vertical organic spin-valve devices was developed and tested to achieve active device areas of less than 100x100 nm² and which is flexible in terms of material choice for the active layers. The fabricated samples consist of the layer stack LSMO/AlQ3/MgO/Co and the active area is defined by insulating Al2O3 (Fig. a).
Several samples with an active area of about 500x500nm² have been fabricated and in Fig. b) a SEM image of the active area is shown. Along more than 10 samples each with 7 devices a variety of MR results has been measured. Two examples are shown in Fig. c) and d) where a negative MR effect of about -170% and a positive effect of about +95% has been observed in two different samples with an AlQ3 thickness of 12 nm.
Partner involved: MLU
Scientific Impact:
Reveals the physics in vertical organic spin-valves as, for instance, the occurrence of pinholes gets less probable in smaller devices.
Application Impact:
development of a fabrication process employing lithography is an important step towards the ‘mass production’ of organic spintronics devices.
WP6
The investigation on the assessment of new processing technologies has been performed.
The main HINTS scientific achievements during the whole project duration and the best materials to fabricate the hybrid interfaces have been collected.
Partners involved: Thales, CNR
Potential Impact:
The potential impact of the HINTS achievements can be evaluated as extremely high.
One of the main achievements of the proposal is the control of the sign of spin transferred polarization. The strength and especially the versatility of this effect in HOI is by far higher than analogue effect detected in inorganic spintronics. The sign inversion gives a magnetoresistance modification >100%, what is clearly appealing for device applications. Furthermore, the electrical modulation of the sign has no precedents in inorganic spintronics, and can be at the basis of innovative reconfigurable logic elements.
It can be expected that the extremely efficient control of the spin polarization sign at HOI interfaces may be transferred even into inorganic device area. The rationale for this is supported by the high structural, temperature and chemical stability of the first 1-2 monolayers of organic materials grown on metals or oxides. This option, on the other hand, would not be compatible with inorganic devices requiring epitaxial growth conditions.
The advancement of the spin dependent residence time at the interface and “inside” it (HINTS knowledge and know-how) represents a new way to quantify the spin filtering capability. It has the potential to become the parameter of the future devices based on HOI as well as it can be used in recent close-to-market inorganic devices.
HINTS has established the phenomenological criteria for the detection of the magnetoresistance in HOI based devices, providing thus means for the fabrication of laboratory and industrial devices with desired values of magnetoresistance.
One of the highest impact results is the realization of high voltage operated magnetoresistance. This opens the possibility to use spin polarized carriers at the light emitting voltages in OLEDs or at the operating voltages of OFETs. Thus the organic spintronics can enter for the first time in these two ICT applications, widely employed in display and lightening industries.
Moreover, the achievement of first promising results for the transfer of spintronic achievements on flexible substrates promotes the application of most or part of HINTS results in Large Area Flexible Organic electronics (TOLAE).
Finally, high TRL values have been reached in the tasks involving both research and industrial partners. Two equipment producing partners succeeded to develop useful modifications to their commercial products (at least TRL 6) as stimulated by the needs of HINTS requirements to the interface.
List of Websites:
www.hintsproject.eu
The Consortium has succeeded to fulfil all the most important and ambitious objectives of the project. The extremely challenging objective of controlling the sign of the spin transfer at the interface (objective still critical in inorganic spintronics) has been achieved even in two different ways: by chemical tailoring of the interface (foreseen in the workplan) and by electric interfacial tuning (discovered by HINTS). While the former allows to select the sign during sample fabrication, the latter, attributable to a smart multifunctional interface behaviour, allows to change the sign during the device operation (reconfigurable operation). HINTS succeeded to bring to 11V the voltage interval where the magnetoresistance is detected, while the workplan objective was 3-5V. While highest voltage operation was detected at low T (<50 K), some materials maintained these properties up to 200-250K close to room temperature operation. This achievement paves the way for future detailed investigation of spin polarized effects on OLED behaviour, considering such parameters as efficiency, colour and other. Indeed, HINTS anticipated this by showing unequivocal and strong effect of spin polarization of driving currents on OLEDs (HyLEDs) electroluminescence.
Realization of continuous interfacial tailoring layers and realization of HOI interfaces with sharpness of 1 nm (approximately one molecule size) have been achieved. This achievement exceeds the state-of –the art quality of interfaces in OLED and OFET devices and could be applied beyond organic spintronic applications.
Interfacial proximity effect was found to embody the most powerful tailoring method for the control of spin transfer across HOI interfaces. The energy of this effect exceed room temperature promoting routes for conceptually new device paradigms. Innovative devices based on rich linear and nonlinear interface effects will definitely represent most proficient application and research line on the short and short-medium terms.
The modification of interfacial spin transfer by insertion of magnetic molecules (high spin) was also achieved. While this fulfils the objectives of the project, the modification was generally negative. Revealing the full potential of merging together the fields of spintronics and molecular magnetism would represent the topic for a fully dedicated project or even number of projects and will for sure constitute one of the most advantageous future research lines. A disruptive progress was achieved by a joint experimental-theoretical effort concerning the basic rules governing the spin transfer at HOI interfaces. HINTS looked “inside the interface” revealing how the spin dependent residence time is distributed in the first 2-3 monolayers of the organic semiconductor. The spin dependent residence time at the interface was proposed as a key parameter for the spin filtering capability. The model, based on spin dependent band broadening and energy shifts, was strongly upgraded by HINTS. Both approaches indicate robust room temperature spin transfer and spin selectivity outcomes.
On the theoretical side it has been revealed for the first time the enormous role in spin injection and transport of the resistance non-linearity in organic semiconductors. The built model defines the set of parameters, such as interface resistance, organic resistance, voltage and others, able to provide the detection of the magnetoresistance (similarly to conductivity mismatch effect in inorganic spintronic devices).
The involvement of industrial partners in the main project objectives has further grown up. Thus, two equipment producing partners succeeded to develop useful modifications to their commercial products as stimulated by the needs of HINTS requirements to the interface.
HINTS was funded with 3,874,360.00 € granted by the European Commission in the 7th Framework Programme, coordinated by Dr. Valentin Dediu of the Institute for the Study of Nanostructured Materials - ISMN (Italy), and carried out by a consortium of 14 leading research institutions.
Project Context and Objectives:
HINTS main goal was to advance new solutions for spintronic devices via the control and the tunability of the interface spin-transfer efficiency. It was the first time a research program addressed so methodically this subject, aiming essentially at putting the basis of a new generation of spintronic devices able to go beyond current GMR and TMR (commercial) achievements. Hybrid organic-inorganic (HOI) materials and interfaces were the materials of choice, featuring such advantage as the low-cost processing and the greatest choice of molecules.
All the main objectives of the project have been successfully fulfilled.
HINTS OBJECTIVES and HINTS SOLUTIONS
• Develop innovative HOI materials with interfaces exhibiting binding interactions specifically tailored for targeted spin transfer properties => Various combinations of materials have been fabricated and investigated along three tailoring approaches: proximity effect, dipole tailoring, magnetic molecule tailoring.
• Establish the basic rules governing the spin transfer behaviour at HOI Interfaces with different chemical bonds => Disruptive success achieved in joint experimental-theoretical work: proposed both a DFT based description and a phenomenological model able to describe both interfacial spin injection and spin transport inside the organic medium.
• As a consequence of the newly developed knowledge: fabricate a set of HOI materials with interfaces that allow for enhanced control of spin-selectivity => Chemical and electric interfacial tailoring have lead to a selectivity control exceeding 100% (sign reversal achieved).
• Design a set of HOI materials with tunable interfaces featuring a high (above 90%) spin transfer efficiency => Some interfaces showed spin transfer close to 100%.
• Develop HOI Interfaces with efficient spin injection at high bias voltages compatible with new ICT applications for hybrid Spintronics materials (3-5 V electrical bias) => Achieved spin injection at 11 V, outstanding achievement opening the door for applying spintronic effects in OLEDs and OFETs.
• Develop new processing technologies and protocols able to maintain the Spintronics parameters of HOI interfaces on large area (3-inches standard) wafers in UHV conditions => demonstrated evaporation of HOI materials on 3” substrates with thickness homogeneity exceeding 95 % and a material utilisation efficiency of 15%.
• Develop new processing technologies and protocols allowing for decreased material consumption for both UHV and solution processing methods => High TRL value achieve introducing (low) consumption modifications to prototypes of commercial effusion cells (UHV). Breakthrough research performed for the utilization of solution processing in organic spintronics.
• Select HOI materials with interfaces able to maintain high spin-charge transfer efficiency under conditions compatible with flexible electronics requirements => while representing a secondary objective by dedicated effort, excellent compatibility between selected HOI materials and flexible substrates demonstrated.
• Assessment of the innovative HOI materials with regard to selected ICT applications => HINTS dedicated significant efforts to these aspects under the guidance of industrial partners.
• Assessment of the innovative HOI materials towards roadmapping trends and development of a set of proposals for the update of ICT roadmaps => A set of roadmapping recommendations developed.
Project Results:
WP1
Molecular driven magnetism on reactive metal surfaces.
The outcome of this study provides an alternative way to create spin-polarized interfaces, relying on the interaction between high-spin quinoline molecules (Tb3q9) and non-magnetic metallic surfaces. The molecules preserve their structural, chemical and magnetic properties when deposited onto noble metal (Au) and passivated (SiO2) surfaces; while the adsorption on reactive metals such as Cu induces a magnetic phase at the interface involving molecular Tb-atoms, as measured via SQUID magnetometry and element-specific X-ray magnetic circular dichroism (XMCD). Remarkably, the magnetic ordering at the hybrid interface persists up to room-temperature for the Tb3q9/Cu system and is linked to a chemically-triggered change in structure and stoichiometry of the interfacial species. On the one hand, our work provides a route towards a controllable “magnetic doping” of a metal surface through molecular adsorption, while on the other hand, the creation of a magnetically active interface between a non-magnetic metal and a high-spin molecular layer opens new avenues for the design of a new class of molecular-based spintronic devices.
Paper submitted 2014.
Partners involved: NANOG (leader), UVEG, TCD, UNIKL, LiU
Scientific Impact:
Fully innovative knowledge concerning proximity effects.
Application Impact:
Possibly innovative technological approach for tailoring interafces
Dipole-layer: tuning work function and spin polarization.
We use strong donor and acceptor molecules with p-orbitals to tune energy level alignment and magnetic properties of the FM-based (Fe, Co, Ni) HIS
Utilizing the acceptor molecules (TCNE, TNAP and TCNQ) we can achieve high work function HIS with effective WF in the tunable range of 5.0 to 5.7 eV, suitable for hole injection
The donor molecule, AOB, allows us to create low work function HIS with an effective WF ~3.4 eV
Organic Electronics, 15 (2104) 1951; Advanced Functional Materials, 24 (2014) 4812; Manuscript in preparation.
Partners involved: LiU, UNIKL, CNRS, NANOG
Scientific Impact:
Fully innovative knowledge concerning proximity effects.
Application Impact:
Possibly innovative technological approach for tailoring interfaces.
Growth of Self-assembled monolayer of dipolar molecules on LSMO surfaces.
(La,Sr)MnO3 manganite (LSMO) has emerged is widely used in organic spintronic devices due to its highly spin-polarized character and air stability. Whereas organic semiconductors and polymers have been mainly envisaged to propagate spin information, self-assembled monolayers (SAMs) have been overlooked and should be considered as promising materials for molecular engineering of HOI interfaces. Surprisingly, up to now the first key step of SAM grafting protocols over LSMO surface thin films is still missing.
Demonstrated that alkylphosphonic acid groups can be used as the preferred anchoring group when dealing with the self-assembled monolayer functionalization of the standard ferromagnetic electrode material LSMO. Hence alkylphosphonic acid based SAMs are suitable to design HOI interfaces with an indirect contact between spin injector (SI) and spin collector (SC).
ACS Nano 6, 8753 (2012)
Partners involved: CNRS, Thales, UVEG
Scientific Impact:
First ever grafting of SAM on LSMO surface. Efficient spin injection achieved.
Application Impact:
Compatibility of most advanced spintronic interfaces with cheap solution processes demonstrated.
A new concept of fabricating organic spin valve (OSV), concretely fabrication of organic semiconductor from solution methods instead of expensive and complicated evaporation techniques besides we introduced the use of ionic molecular monolayer in the fabrication of a light-emitted OSV. It was established for the first time an OSV and a spin-polarized electroluminescent device with ferromagnetic electrodes that acts as a bipolar OSV, based in solution and low cost methods. Our OSV shows a spin valve magneto electroluminescence (MEL) effect of around 1%.
Partners involved: UVEG, CNR
Scientific Impact:
High efficient light emission at conditions compatible with spin polarized injection
Application Impact:
Enables the possibility to control light emission in OLEDs by magnetic field (efficiency, read –write options etc)
Growth of Self-Assembled Monolayer of dipolar molecules on Permalloy and Cobalt surfaces
The fact the LSMO’s surface Curie temperature (Tc) is close to room temperature, implies that spintronic effects in LSMO-based devices are expected only at low temperature. Hence, after the interesting results obtained using self-assembled monolayers (SAMs) on LSMO as interfaces between spin injector and spin collector in basic spintronic devices, it will be desirable to substitute LSMO by a ferromagnet of higher Tc, as for example ferromagnetic (FM) metals or alloys, like cobalt (Co) or permalloy (Py). Unlike LSMO, FM metals readily oxidize and it is not surprising that SAM grafting protocols over FM electrodes are almost non-existing. We have developed the grafting protocols necessary for the integration of SAMs on 3d FM metals with solution approaches. The formation of SAMs on Co and Py both under ambient conditions and in inert atmosphere, after removing the oxide with a simple wet etching process, have been achieved. We have observed that comparing with oxidized Py or Co, the ferromagnetic behaviour of the substrate can be improved during the solution processes. By standard characterizations it is probed that only thiol group can be successfully grafted on ferromagnetic surfaces whereas phoshonic acids group works with oxidized metal surfaces.
Partners involved: UVEG, CNRS, Thales
Scientific Impact:
Grafting protocols of SAM on clean and oxidized ferromagnetic metallic surfaces in glove box conditions.
Application Impact:
Compatibility of most advanced spintronic interfaces with cheap solution processes demonstrated.
WP2
Determination of the metal-molecule energy-level aligment by in-device spectroscopy
In this study, we have shown that the energy alignment at metal/molecule interfaces can be measured in a chip by the fabrication of a simple 3-terminal device. As a proof of principle, we measured the energy barriers at the interfaces between C60 and different metals. Furthermore, such a device can be used to inject carriers in the organic layer overcoming the contact resistance. This property allows the injection of a highly spin-polarized current into a molecular layer and to study its conduction properties at very low temperatures, in a range where the contact resistance usually prevents any carrier injection. We anticipate that this scheme for charge injection free from the contact resistance is not limited to bulk semiconductors, but can be extended in principle to any semiconductor, including solution-processable semiconductors and monolayer dichalcogenides.
Nature Communications 4, 2794 (2014)
Partner involved: NANOG
Scientific Impact:
New HOI interface characterized
Application Impact:
Innovative and cheap approach for interface energetics in HOI based devices
A 1/2 ML of oxygen on the Co(001) surface acts as a „wetting“ layer. STM measurements show that MPc’s generally form self-assembled layers on such a ultrathin oxygen layer. We found that oxidation of the cobalt going from ½ ML to higher thickness leads to a gradual suppression of hybrid interface states, and moreover to a progressive change in the work function as also seen for the Co-Mq3 interface.
Partner involved: UNIKL
Scientific Impact:
Oxygen layer effect on interface hybridization.
Application Impact:
Possible tailoring approach.
STM measurements show that for MPc’s on Co there is no “real” ordering as seen for the self-assembled layers on the MPc/CoOx/Co system. No decoration on the edge of the surface terraces indicates the high reactivity found for all the MPcs on the native Co surface. The surface dipole saturates for all the MPc systems including H2Pc when reaching 1 monolayer (ML) indicating the interaction with the substrate is related to the first monolayer. UPS measurements (He I and He II) clearly show that the H2Pc-MnPc molecules bind strongly to the Co surface and are forming HIS near/at the Fermi level.
Advanced Functional Materials, 22, 989 (2012)
Partner involved: UNIKL
Scientific Impact:
Confirming the role of the oxygen layer
Application Impact:
Possible tailoring approach.
Key improvements of the Interface Co/AlOx/Alq3
It was demonstrated by Hard X ray photoemission spectroscopy and TEM analysis that exposure of Alq3 to O2 before the deposition of metal provides a much better top electrode/organic interface characterized by higher morphological and chemical sharpness (1-2 nm interface width).
Paper in preparation 2014.
Partner involved: CNR
Scientific Impact:
Burried interface investigated
Application Impact:
New routes for direct deposition of reactive metals on Alq3.
WP3
Static characterization of the Co-Mq3 interface.
We have used spin-resolved photoemission spectroscopy to study the static spin-dependent electronic properties of the interface formed between cobalt as ferromagnetic electrode and three metal quinolines: Alq3, Gaq3 and Inq3. By combining ultra-violet-photoemission spectroscopy (UPS), spin-resolved near-threshold photoemission spectroscopy (NT-PS), spin-resolved two-photon photoemission (2PPE) spectroscopy and state-of-art density functional theory (DFT) calculations (performed in WP1), our study unequivocally shows that all three Mq3 molecules bind so strongly to the surface that spin-polarised interface states are formed. Interestingly, the interface electronic structure is very similar in all cases. This is a consequence of the fact that for all the three molecules, the HOMOs are localised on the phenoxide moiety of the ligands, while the three LUMOs on the pyridyl moiety: thus almost no charge is localised on the metal centres.
PRB 89, 094412 (2014)
Partners involved: UNIKL, TCD
Scientific Impact:
Accurate detection of proximity induced purely interface spin polarized states.
Application Impact:
Enable conceptually new device paradigms based on non-linear interface behaviour.
Formation of hybrid interfaces.
We have studied the formation of hybrid interfaces by two complementary spectroscopic methods: spin-polarized STS (scanning tunneling spectroscopy) and spin-polarized NT-PS (near threshold- photoemission spectroscopy).
Both methods give evidence for the formation of spin polarized hybrid interface states in the energetic region close to the Fermi level.
PRB 84, 224403 (2011)
Partner involved: UNIKL
Scientific Impact:
Definition of the energetics of the proximity induced interface states.
Application Impact:
Enable conceptually new device paradigms based on non-linear interface behaviour.
Chemical tailoring of the spin properties of the Co-Mq3 interface.
We have created different experimental molecules to tailor the spin-dependent properties of the interface by modifying chemisorption with cobalt. For example, Al(OP)3 was developed to produce a ligand that has more extended p-systems than Alq3. We expect a modification of the chemisorption on cobalt, and thus different spin-dependent properties of the Co/Al(OP)3 interface with respect to Co/Alq3. Using spin-resolved photoemission methods, we have indeed identified two hybrid interface-states in the energy window of 2 eV below the Fermi energy, in contrast to the Co/Alq3 interface where only one hybrid state is present.
NJP 15, 113054 (2013)
Partners involved: UNIKL, TCD
Scientific Impact:
New (HINTS developed) molecules show modified interface hybridization.
Application Impact:
Enable conceptually new device paradigms based on non-linear interface behaviour.
Physical tailoring of the spin properties of the Co-Alq3 interface.
We have used oxidation of the Co/Alq3 interface to control its electronic properties. Oxidation of cobalt is expected to dramatically influence the strength of hybridization with the deposited molecules, and as a consequence the spin-dependent electronic properties of the interface. By UPS, NT-PS and 2PPE we found indeed that oxidation of the cobalt leads to a gradual suppression of hybrid interface states, and moreover to a progressive change in the work function and to a continuous energetic shift of the molecular orbitals towards higher binding energies. Based on our spectroscopic observations, we have suggested controlled oxidation of the ferromagnetic electrode as an easy and effective possibility to tune the spin-properties of metal/organic interfaces.
APL 103, 251603 (2013)
Partner involved: UNIKL
Scientific Impact:
Defined the role of superficial oxygen on spin polarization.
Application Impact:
Enable soft interface modifications in future HOI devices.
Microscopic understanding of hybrid metal-organic interfaces.
We have used spin- and time-resolved two-photon photoemission to study the spin-dependent electron relaxation across hybrid interfaces. We found that electrons injected across hybrid interfaces are trapped into hybrid interface states in a spin-dependent manner for a surprisingly long time of the order of 0.5–1 ps. This is the microscopic origin of the spin-filtering properties of hybrid interfaces. The achieved microscopic understanding of the spin-dependent dynamics at hybrid interfaces lays the foundation for designing advanced actively controlled spintronics devices.
Nature Phys. 9, 242–247 (2013)
Nature Phys. 9, 210–211 (2013)
Partners involved: UNIKL, CNR
Scientific Impact:
Outstanding achievement – first look “inside” the interface.
Application Impact:
Promotes new ways to describe key device parameters. Room temperature operation.
Coherent excitation of hybrid interface states.
We have performed phase-stabilized two-photon photoemission experiments at the Co-Alq3 interface to probe the coherence of the optical excitation across hybrid interfaces. We have found long-lived excitations with coherence times of up to 110fs. This demonstration of coherent control of spin polarized hybrid interface states opens the way to ultrafast spin control at the molecular scale.
Partner involved: UNIKL
Scientific Impact:
found long-lived excitations with coherence times of up to 110fs
Application Impact:
opens the way to ultrafast spin control at the molecular scale.
Spin-polarization loss at insulator/organic interfaces.
We have investigate the influence of the tunnel barrier MgO inserted at the interface between the spin injector CoFe and the organic semiconductor C60 by spin-resolved photoemission spectroscopy. At the CoFe/C60 interface the spin polarization persist up to 15nm C60 thickness and decrease linearly with C60 thickness. At the CoFe/MgO/C60 interface, however, we observe a drastic reduction of the spin polarization directly at the interface between C60 and MgO, indicating an enhanced spin-scattering rate at the insulator/organic interface.
Partner involved: UNIKL
Scientific Impact:
MgO barrier strongly reduce the spin transfer efficiency
Application Impact:
Nearly 100% spin transfer – CoFe/ C60 interface is among best candidates for device applications.
A nonlinear behavior of a logarithmic plot of the PES intensities in the region below EF show the existence of HIS formed by the hybridization reaction. Using a modified Lambert-Beer law, SP-UPS measurements clearly show differences in the spin down channel just below EF for the different MPc’s and the pure organic system H2Pc. By using a very recently published model describing the interaction of the carbon pz orbitals with a FM, the main structures in the spin down channel at 1.1 eV and the structure at 0.3 eV in the spin up channel are attributed to the interaction of the phenyl-ring system with the metal substrate d orbitals. These structures are consistent with calculations which were also made by the partner TCD for the system MPc/Co. The differences for the spin down channel just below EF are therefore density of states which must be attributed to the metal atom d-states changing the DOS at the Fermi level and still reflects the importance of the geometry of the open shell frontier orbitals in MPc’s for the discussion of spin polarization effects at the interface.
Partner involved: UNIKL
Scientific Impact: quantitative description of hybridized interface states
Application Impact:
Important as characterization method for device interfaces.
In SP-UPS spectra a 1/2 ML of oxygen on the Co(001) surface clearly shows a strong majority polarization vanishing rapidly going to higher oxygen layers. This polarization is also described in DFT GGA+U calculations for a ½ ML on Co. This clearly shows that a very small amount of oxygen is not “magnetically dead”. Measurements of the spin polarization for the two archetypical MPc’s, CuPc and FePc, show slight differences. The SP-UPS spectra we measure were then correlated with some DFT calculations of the system MPc/CoOx/Co(001) indicating that the differences we investigate matches with two separate interaction mechanisms which were caused by the differences in the geometry of the open shell frontier orbitals of the MPc’s central atom and therefor the interaction path. Therefore the results on the MPc/CoOx/Co(001) also reflect the importance of the geometry of the open shell frontier orbitals in MPc’s for the discussion of spin polarization effects at the interface.
Partner involved: UNIKL
Scientific Impact:
The strong interfacial effect of oxygen on spin polarization of the injecting surface. Also revealed the importance of the geometry of the frontier orbitals in metal phthalocyanines.
Application Impact:
Important tailoring issues in vertical spintronic devices.
UPS measurements in cooperation with partner LiU clearly show a charge redistribution seen by the enhancement of work function and a asymmetric behavior of the HOMO and HOMO-1 levels up to the first monolayer. SP-UPS measurements clearly show a spin-splitting of this two MO’s. A nonlinear behavior of a logarithmic plot of the PES intensity’s in the region below EF clearly show the existence of HIS formed at the interface. A remaining high intensity in the spin DOS just below EF furthermore indicates differences in the interaction mechanism with the Co substrate compared to one suggested for the MPc systems.
These observations are important comparing them with C60 spin valves experiments which have been done.
Partners involved: UNIKL, LiU, NANOG
Scientific Impact:
quantitative description of hybridized interface states
Application Impact:
Important tailoring issues in vertical spintronic devices.
Multifunctional magnetic&electric memory and logic gate
Resistive bistability effect in organic (LSMO-Alq3-Co) spintronic devices was put at the basis of new device paradigm featuring both electric and magnetic memory (magnetically enhanced memristor). The device could be set in 32 different and reversible resistive states. The excellent control of the resistance is very promising for memory applications.
In addition to memory capability, the device performs as logic gate – two logic gates, AND and IMP, have been experimentally demonstrated.
Advanced Materials 2013, 25, 534–538
Partners involved: CNR, QMUL
Scientific Impact:
Full electrical control of the magnetoresistance achieved.
Application Impact:
Important input for device paradigms conceptually different from inorganic spintronic devices.
The absence of Hanle effect in prototypical devices.
We investigated the Hanle effect, one of the main outstanding issues in organic spintronics. We have investigated it by measuring the GMR of a prototypical organic spintronic device at different angles between the device’s plane and the magnetic field, and we found no sign of its presence. Although we have no definitive explanation for this finding, an exceptionally high mobility (30 cm2V-1 s-1) would be sufficient to justify the present data. Altogether, these results strongly suggest that the current understanding of transport in organic GMR devices is not sufficiently developed to explain the absence of the observation of spin precession and supports the framework of transport occurring via high mobility, high conductivity channels.
Appl. Phys. Lett. 102, 092407 (2013)
Partners involved: CNR, MLU
Scientific Impact:
Crucial achievement questioning most of previously adopted concepts for spin transport in organic materials. Immediately stimulated an intense discussion.
Application Impact:
Allows to distinguish tunnelling and injection devices.
Defect role in prototypical Alq3 based devices
From the comparison of the electrical resistance of the hundreds of spintronic devices fabricated over the course of the project, two regimes in the Resistance vs Thickness curve could be observed. The high resistance one, with a resistance that is proportional to the thickness of the organic layer, shows no MR; in this case we suppose that transport occurs via the LUMO and/or HOMO levels. Instead, the low resistance regime, highly variable between nominally identical samples, shows MR ; in this case the transport presumably occurs through defects. A meta-anlisys of the data available from the literature for comparable devices, follows the same pattern.
Commented in Nature Nanotechnology 8, 885 (2013)
Partner involved: CNR
Scientific Impact:
Acquired significant indications for the key role of defects and impurities in the detection of MR in Alq3 based devices.
Application Impact:
Definition of optimal devices resistances and transport modes.
Dipole layer HIS: work function and spin-polarization.
We used X-ray Magnetic Circular Dichroism to confirm spin-polarized hybridized -orbitals for TNAP/FM and TCBE/FM HOI. The spin-polarized occupied density of states of a particular TCNE/FM HOI, TCNE/Co, was then explored using spin-polarized ultraviolet photoelectron spectroscopy. According to the XMCD results and sum rules, TCNQ and TNAP adlayers have no detrimental influence on the spin polarization of the FM surface whereas AOB adlayers reduce the spin polarization of the FM surface. The results demonstrate that high and low effective work function FM-OS HIS with spin-polarized -orbitals at the interface can be achieved but also demonstrates that the OS-FM interaction can negatively impact on the surface spin-polarization of the FM. Nevertheless, the wide range of work functions achievable and the in general favorable magnetic properties make these HOI potentially useful as spin injecting / spin detecting contacts.
Partners involved: LiU, UNIKL
Scientific Impact:
Revealed that TCNQ and TNAP adlayers have no detrimental influence on the spin polarization, while changing significantly the current injection. Vice versa, the AOB adlayers reduce the spin polarization
Application Impact:
Crucial technological information for devise fabrication.
Spin transfer through self-assembled monolayers in a nanocontact.
A lithography process has been developed to fabricate nano-scale vertical systems where molecules are connected to ferromagnetic leads. This technique allows probing HOI interfaces at the nanoscale. Nanolithography based on real time electrically controlled nano-indentation has been used to fabricate LSMO/SAMs/Co magnetic tunnel junctions where SAMs are alkyl-acid phosphonic Self-Assembled Monolayers. Lateral size of the devices can vary from few nm to few tenth nm. Electrical characterizations show that not short-circuited nano-junctions can be achieved. This technique is quite versatile since different kind of ferromagnetic electrodes and molecules can be used.
Magnetoresistance signal up to 40% has been measured and is comparable to the best organic spin valves. Hence spin dependent transport reveals an efficient spin transfer at HOI interfaces using Self-assembled monolayers grafted on a ferromagnetic electrode.
This shows the potential of SAMs for future chemically tailored and engineered spintronics applications while opening the door to additional molecular electronics functionalities.
Advanced Materials 24, 6429 (2012)
Partner involved: CNRS, Thales, UVEG
Scientific Impact:
Efficient spin transfer at HOI interfaces using Self-assembled monolayers grafted on a ferromagnetic electrode
Application Impact:
This shows the potential of SAMs for future chemically tailored and engineered spintronics applications while opening the door to additional molecular electronics functionalities.
HOIMs featuring efficient spin transfer at high operation bias voltages.
Spin transfer at hybrid inorganic/organic interface has been probed by tunnelling magnetoresistance experiments in Self-Assembled Monolayers (SAMs) based magnetic tunnel junctions. The self-assembled monolayers are alkyl phosphonic acids grafted on a half metallic LSMO electrode (D1.2). LSMO/C12PO3H2/Co magnetic tunnel junctions have been fabricated using the nano-indentation technique (D1.6). Figures a-b represent the bias voltage dependence of the tunnel magnetoresistance and two examples of magnetoresistance curves recorded at low (10 mV) and high (4 V) bias voltage. A striking point is the very weak decrease (~25 %) of the tunnel magnetoresistance with the bias voltage. Actually at a voltage as large as 4 V the tunnel magnetoresistance is still about 22%. The high tunnel magnetoresistance ratio at such high bias voltage is a unique feature of these HOI based magnetic tunnel junctions where molecular vibrations plays a crucial and beneficial role since they can short-circuit magnon excitations that usually affect inorganic systems.
These measurements demonstrate an efficient spin transfer at these hybrid inorganic/organic interfaces and reveal the potential of SAMs as spin injector working at high bias voltage. This could be a key enabler for future applications such as spin-OLEDs where the spin current is expected to drastically improve the OLED efficiency.
Advanced Materials 24, 6429 (2012)
Partners involved: CNRS, Thales, UVEG
Scientific Impact:
Efficient spin transfer at HOI interfaces: revealed the potential of SAMs as spin injector working at high bias voltage.
Application Impact:
Possible key enabler for future applications such as spin-OLEDs where the spin current is expected to drastically improve the OLED efficiency.
Magnetoresistance at high bias voltage in H2PC-based organic spin-valves
Magnetoresistance (MR) is observed in vertical organic spin valves consisting of a LSMO and a Co electrode and the metal-free phthalocyanine H2PC. The devices undergo a strong resistance increase (approximately 3 orders of magnitude) during cool down to 4.2K (see Fig. a) indicating that the resistance is dominated by the charge transfer through the H2PC-layer. In addition to the spin-valve signal (see Fig. b) which has a magnitude of ≈8% at low bias and is persistent to bias voltages of up to ±8 V (see Fig. c) we also have identified a sizeable contribution of tunneling anisotropic magnetoresistance (TAMR) to the MR effect (see phiscan measurement in Fig. d). The bias dependence of the TAMR is comparable to this of the spin-valve signal with a maximum of ≈2.5% at 0V. The observation of TAMR suggests that, despite the strong temperature dependence of R, tunneling processes still have a measureable influence on the device resistance and the magnetotransport behaviour in the low bias regime.
Partner involved: MLU
Scientific Impact:
Innovative, very important for the further understanding of the physics behind MR in organic spin valves
Application Impact:
The realization of structures exhibiting MR at bias voltages in the >±3V regime basically is mandatory for a successful implementation in applications.
Magnetoresistance up to 3-4 percent was established at voltages as high as 11 V, exceeding by far the HINTS objective of 3-5 V. Noteworthy this magnetoresistance was detected in OLED devices at currents and voltages corresponding to light emission. The result opens the possibility to promote efficient studies of the capability to modify light emission in organic based LEDs by spin polarized injection.
Partners involved: UVEG, CNR
Scientific Impact:
A different type of multifunctional devices: magneto- optical. HOI with high voltage operation demonstrated.
Application Impact:
Spin polarised injection is expected to improve OLEDs efficiency (double for singlet emission).
Outstanding magnetic modulation of the electroluminescence was achieved in OLEDs with two spin polarized electrodes.
Partners involved: UVEG, CNR
Scientific Impact:
Hints for both light emission physics and spintronic effects.
Application Impact:
Possibility to combine magnetic and optical writing and reading of information. Increased OLED efficiency (see above).
Lateral organic spin-valves fabricated by shadow evaporation
A novel fabrication process has been developed, improved and established that allows for the in-situ fabrication of lateral organic spin valves with a channel length in the sub-100nm regime. The process’ key step is a shadow evaporation process which is illustrated in Fig. a and b. Preliminary experiments have been undertaken in order to verify that all requirements for spin-valve functionality are met, e.g. different coercive fields of the two electrodes (see MOKE measurements in Fig. c). The contacts’ separation has been checked by imaging methods (see Fig. d) and indirectly by transport measurements. In devices employing the organic semiconductor N,N'-bis(Heptafluorobutyl)-3,4:9,10-Perylene Diimide (PTCDI-C4F7) we have measured a spin-valve-like magnetoresistance effect of up to ≈50% (see Fig. e and f) at room temperature which can be explained by lateral tunneling.
Organic Electronics 14, 2082 (2013)
Partner involved: MLU
Scientific Impact:
devices which do not suffer from side effects like a reduction of the organic interlayer’s thickness.
Application Impact:
realization of lateral spin-valve structures is an important step towards the implementation of non-volatile switching to the established organic field effect transistor technology.
Resistive switching in AlQ3-based TAMR devices.
A resistive switching (RS) effect going beyond common bipolar switching has been observed in AlQ3-based single-sided vertical spin valves (tunneling anisotropic magnetoresistance, TAMR, structures with only one ferromagnetic LSMO electrode). The RS (see Fig. a) is initiated by short voltage pulses and allows for setting the device resistance in the range between ≈1kΩ (base resistance state, BRS) and a maximum of ≈120kΩ (high resistance state, HRS). Magnetotransport measurements have been performed in this resistance range revealing a strong increase of the TAMR magnitude when the device resistance is increased (Fig. b). Based on the results of further studies (Simmons analysis of I/V characteristics, see Fig. c and d) a modification of the tunnel barrier which is located between the LSMO electrode and the AlQ3-layer can be identified as the origin of the MR effect’s enhancement. Furthermore, among other experiments, a similar analysis has been undertaken for a complete RS cycle in order to investigate the barrier parameters’ dynamics caused by the applied voltage pulses (Fig. e). In all results of I/V curve analysis an increase/decrease in barrier thickness/height (dbarrier/Φ0) with increasing device resistance (and vice versa) can be discerned suggesting very basic mechanisms behind the RS, which very likely are creation, motion and removal of oxygen vacancies at the LSMO electrode’s surface.
Partner involved: MLU
Scientific Impact:
TAMR can be employed as a powerful tool for the investigation of interfaces and interface-related effects.
Application Impact:
realization of another class of promising multifunctional devices.
Spin transfer sign modification at a selected tailored HOI interface at room temperature
We developed organic spin valves relying on conventional metallic ferromagnetic electrodes (Co, Fe,Ni…) having high Curie temperature well above room temperature. Co/Alq3/Co organic spin valves were fabricated in-situ by shadow mask. Inverse magnetoresistance was obtained at room temperature. This was ascribed to a strong hybridization (HOI) sustaining up to room temperature as an inverse magnetoresistance in spin valves with identical ferromagnetic electrodes implies that the spin polarization is inverted at one of the two interfaces. This was further confirmed as, by inserting a tunnel barrier at the bottom interface to suppress the hybridization (HOI), normal magnetoresistance was then observed.
This demonstrates that the hybridization is strong enough to be observed at room temperature and unveils the potential of HOI for room temperature applications.
Partners involved: CNRS, Thales
Scientific Impact:
Demonstrated that the hybridization is strong enough at room temperature
Application Impact:
Potential of HOI for room temperature applications.
Control spin polarisation of extracted holes by inclusion of interfacial layers
VLS modifies the energy of the HOMO/LUMO with respect to the ferromagnet.
This changes the spin polarisation of extracted charge carriers at that interface
Phys. St. Sol. B 2012
Partner involved: QMUL
Scientific Impact:
Revealed the role of interface energetics on spin transfer at HOI.
Application Impact:
Provides strong indications for the most efficient interfacial engineering of devices.
Direct evidence that transition metal FMs are hole injectors/extractors and that the lower hole mobility isn't the limiting factor in organic spin valves
- Mobility of holes ~50 times smaller than electrons.
- Not limiting factor in spintronic devices, if it is possible to inject only holes at FM-Alq3 interfaces.
APL 2014
Partner involved: QMUL
Scientific Impact:
Most deep investigation on the mobility effects in HOI based spintronic devices.
Application Impact:
Key information for the control of mobility in devices.
Room temperature spin transport in organic molecules with hopping charge transport and air stability
Produced and characterized spin valves based on the organic semiconductor Bathocuproine (BCP). In two sets of devices, different AlOx seed layers have been employed, that we distinguish between “leaky” and “non-leaky” on the basis of the temperature dependence of their resistance. For the devices with non-leaky seed layer, the main charge transport mechanism is tunneling, and consequently MR is measured only for extremely thin BCP films (5 nm). By contrast, for devices with leaky AlOx layer, the transport takes place into the BCP film, featuring an exponential increase of the resistance characteristic of hopping transport. In these devices, a sizable MR is measured up to a thickness of 60 nm. Finally the BCP-based SVs have shown excellent air-condition stability in terms of device performance even after long time (more than 70 days), outperforming most of the reported organic spin valves.
Nature Communications 4, 2794 (2014)
Partner involved: NANOG
Scientific Impact:
Modification of the tailoring oxide layer allows to modify internal interfacial structure.
Application Impact:
The observation of air-stable room-temperature spin transport in BCP-based SVs is of great importance for the future industrial interest in organic spintronics considering cheap (non UHV) technologies.
WP4
Enhanced spin-orbit coupling in molecules at the interface with a ferromagnetic metal.
For the interface between fcc Co(001) and Alq3, we have found (through density functional theory calculations) a small, but still non-zero, spin-polarization induced even on molecules very weakly coupled to the surface. This is shown in the left panel of the picture, where the spin-resolved density of states (DOS) for the LUMO of an Alq3 molecule is displayed. Therefore, we infer that spinterface effects are non-negligible also for molecules in the second layer of an organic film deposited on a ferromagnetic metal. Even more interestingly, we have found that the DOS presents comparable non-collinear components when the spin-orbit coupling is explicitly included in the calculation (right panel of the picture). As the Co(001) is a surface with a relatively large spin-orbit coupling strength (in fact spin hot spots have been extensively studied for this surface), the small hybridization is able to enhances the spin-orbit coupling strength in the molecule itself (we note that the intrinsic spin-orbit coupling strength of gas-phase Alq3 is so small that cannot even be numerically resolved in calculations).
In future, more systematic studies for different class of molecules may be performed.
Partners involved: TCD, UNIKL
Scientific Impact:
Elucidates the enormous role of the spin-orbit coupling at HOI interfaces.
Application Impact:
Promotes routes for the modification of magnetic anisotropy and other magnetic parameters in thin ferromagnetic films by deposing top organic layers- mild engineering of key magnetic properties.
A multiscale theoretical scheme to compute material-specific charge and spin transport properties of organic semiconductors has been developed. This scheme has been extensively applied in order to study crystalline rubrene. Highly anisotropic transport properties have been found (left panel of the picture) and, moreover, the obtained value for the charge carrier mobility is in good agreement with the highest estimate, which was reported in experiments. Furthermore, we could compute the spin-relaxation length (right panel of the picture). By including both the spin-orbit and the hyperfine interaction, a good agreement between our computed value and the experimental estimate has been achieved. More importantly, the spin-diffusion length ls is found to be independent on the temperature for zero-spin orbit coupling. In contrast ls decreases with the temperature when the spin-orbit coupling is not neglected. Our results then suggest that the analysis of the temperature dependence of the spin-diffusion length can be used as a mean to investigate the relative importance of the spin-orbit coupling and of the hyperfine interaction in the spin transport properties of (crystalline) organic semiconductors. This would finally help to address the long-debated issue about the origin of spin-relaxation in organic materials.
Partner involved: TCD
Scientific Impact:
Developed the most advanced multiscale theoretical scheme able to compute charge and spin transport properties in HOI and organic materials.
Application Impact:
Important step towards the “on need” developed and fabricated materials for Spintronics.
Moving beyond the ferromagnetic electrodes’ age: exploring novel materials
Until recently, most of the studies in organic spintronics have investigated hybrid interfaces between ferromagnetic metal and organic semiconductors. Usually, a hybrid interface is engineered through a careful selection of the organic molecules. Here, instead, we have investigated theoretically (by mean of density functional theory calculations) the impact of different classes of inorganic materials. For example, we have considered the interface formed by absorbing different molecules on the 3D topological insulator, Bi2Se3. We have found three different physical scenarios, exemplified in the picture by plotting the (molecule and surface) density of states (DOS) resolved in reciprocal space. For weakly coupled molecules (top panel), no change in the electronic structure neither of Bi2Se3 nor of the molecule is seen. For molecules in an intermediate coupling regime (central panel), the electronic structure of Bi2Se3 is unchanged, while a hybrid interface state appears. Finally, for the case of strongly coupled molecules, Bi2Se3 still preserves its topological nature although the electronic structure changes visibly. Furthermore, and more importantly, the typical features of the topological insulator are seen also on the molecule DOS.
The first two scenarios (weak and intermediate coupling) have been observed also experimentally by UNIKL. For the third case, an experimental proof is not available yet.
Finally, we think that, if a suitable molecule able to form a strong chemical bond with Bi2Se3 was identified, a novel hybrid interface could be made thus opening the route to completely unexplored applications for spin-injection /detection .
Partners involved: TCD, UNIKL
Scientific Impact:
Extremely innovative knowledge on the use of topological insulators in spintronics.
Application Impact:
Step towards new, naturally cheaper electrodes (rare earth free)
Hopping Magnetotransport via Nonzero Orbital Momentum States and Organic Magnetoresistance
The theory of hopping magnetoresistance was extended to states with nonzero orbital momenta. Different from s states, a weak magnetic field expands the electron (hole) wave functions with positive magnetic quantum numbers, m>0, and shrinks the states with negative m in a wide region outside the point defect. This together with a magnetic-field dependence of injection/ionization rates results in a negative weak-field magnetoresistance, which is linear in B when the orbital degeneracy is lifted. The theory provides a possible explanation of a large low field magnetoresistance in disordered conjugated organic materials.
PRL 108, 186601 (2012)
Partners involved: JSI, CNR
Scientific Impact:
Revealing the presence of magnetoresistance in hopping transport in general.
Application Impact:
Enabling possible field dependent correction in devices based on hopping conductivity.
Magnetoresistance in organic spintronic devices: the role of nonlinear effects.
A full set of kinetic equations was derived describing injection and transport of spin polarized carriers in organic semiconductors with hopping conductivity via an impurity level. The model predicts a strongly voltage dependent magnetoresistance defined as resistance variation between devices with parallel and antiparallel electrode magnetizations (spin valve effect). Namely, the voltage dependence of the magnetoresistance splits into three distinct regimes. The first regime matches well known inorganic spintronic regimes, corresponding to barrier controlled spin injection or the conductivity mismatch case. The second regime at the intermediate voltages corresponds to strongly suppressed magnetoresistance. The third regime develops at higher voltages and accounts for a novel and purely organic paradigm. It is promoted by strongly non-linear effects in organic semiconductor which strength is characterized by the dimensionless parameter eU/kBT. This nonlinearity, depending on device conditions, can lead to both significant enhancement or to exponential suppression of the spin-valve effect in organic devices.
Paper submitted 2014
Partners involved: JSI, CNR
Scientific Impact:
Conceptually new approach proposed to circumvent conductivity mismatch problem in spintronics by making use of non-linear carrier transport. Fully applicable to organic and HOI cases.
Provides explanation of high voltage magnetoresistance.
Application Impact:
Significant step towards a quantitative description of HOI spintronic devices with electrical injection.
WP5
Two flanges dedicated to the efficient evaporation of organics
The flanges are easy to implement in an existing UHV system.
Both provide a film thickness uniformity better than ± 2 % on 3 inch substrates. One flange is dedicated for the evaporation of organics only and has an outstanding material utilization efficiency of 15 %. Using this flange for the evaporation of metals, which usually have a higher evaporation temperature, increases the temperature of the substrate. This increase might destroy organic films, which were prior evaporated to the substrate. Hence the second flange has a larger crucible-substrate distance and thus is also suitable for the evaporation of metals. Due to larger crucible-substrate distance the material utilization efficiency is only 6.5 % on 3 inch substrates.
Partners involved: MBE-K, CNR, NANOG
Application Impact:
Significant improvements to available commercial solutions.
OME 100 Effusion Cell
The OME 100 Effusion Cell is an advancement of the OME evaporators. It dedicated to the evaporation of sensitive organic materials on large spherical calottes (Ø ~ 1 m) which are often used in the industrial environment. Due to the large substrates the orifice of the evaporator needs to be large.
Besides evaporating the organics from a quartz liner it is possible to evaporate it directly from the copper crucible. The copper crucible can be plated with nickel, gold or silver. Evaporating directly from the copper crucible increases the thermal flow into the organic material. An additional thermocouple positioned in crucible makes it possible to directly measure the temperature of the organic material.
Partner involved: MBE-K
Application Impact:
The development of the effusion cell is finished and some evaporators are already in use.
TRL 6-7
OME 63 Effusion Cell
Like the OME 100 the OME 63 is an advancement of the OME evaporators. It has been developed and build for customers, who evaporate sensitive organics to large substrates (diameter of a few cm) and need a large amount of organics. The effusion cell can be used both for research purposes and industrial applications.
The development of the effusion cell is finished and some evaporators are already in use.
Partner involved: MBE-K
Application Impact:
The development of the effusion cell is finished and some evaporators are already in use.
TRL 6-7
Thermostar
A big difference between the evaporation of organics and metals is the usually much lower thermal conductivity of the organic material. In combination with a large orifice this might lead to a strong temperature gradient within the organic material. While the outer molecules in direct contact with the crucible evaporate with an acceptable rate the rate strongly decreases for molecules in the inner part of the crucible. Therefore the total rate is much lower as possible and also the danger of decomposition of the organics is much higher due to the high gradient of the temperature within the crucible.
To increase the thermal conductivity within the organic material the Thermostar was invented. The Thermostar is build of copper sheets arranged in a star shape. The copper sheets can be plated with different materials like gold, nickel and silver. The Thermostar needs to fit to the inner shape of the crucible and the normally used maximum filling level.
Partners involved: MBE-K, MLU
Application Impact:
Fabricated an insert to standard commercial crucibles allowing to decrease internal temperature gradients and enhance effusion homogeneity.
TRL 5-6
Customized OME 40 effusion cells for CNR-ISMN
To optimize the evaporation setup the CNR-ISMN is using for the evaporation to 1 x 1 cm² substrates several simulations were carried out. Based on the results two customized OME 40 effusion cells were built for the CNR-ISMN. By reducing the crucible-substrate distance and using a conical crucible the film thickness uniformity could be kept at 95% while increasing the material utilization efficiency from 0.34% to 1.07%.
The development of the customized OME 40 is finished and the CNR-ISMN is using the two build evaporators.
Partners involved: MBE-K, CNR
Application Impact:
Performed the customisation of the commercial cell OME40 aiming at more efficient use of the filling material. Applicable for the case of low amounts of starting material.
TRL 4-5
Simulation: selection of the setup used for the evaporation on 3” substrates
For the evaporation of organics on 3” substrates the partner nanoGUNE had to choose between two evaporation setups. With the help of the simulation of these two setups it was possible to choose the evaporation process suitable for their application without performing time-consuming experimental tests.
Using the chosen evaporation setup three 3” substrates were coated with C60 and subsequently analyzed with ellipsometry. Simulation and experiment were in very good agreement.
Partners involved: MBE-K, NANOG
Application Impact:
Brings high quality HOI interface protocols to 3” substrate growth setups.
As part of the HINTS project M-Solv has focused on developing a machine for depositing solution based OSC molecules in an inert environment. The MGB-601 has been built and tested using ink jet and ultrasonic spraying methods for solution deposition.
Novel material handling methods have been developed to enable the use of ink jet print heads inside a glove box. And as a consequence the tool offering capability of M-Solv has been increased.
Partner involved: M-SOLV
Application Impact:
M-Solv has increased the TRL of the tehcnology to 7 and above and this has lead to a sale worth EUR 500k to a top 4 world ranking university, of a mulit-head spray deposition system in a glove box.
By demonstrating that it is possible to pattern sub micron films and stop on a specified layer, it is possible to pattern thin film devices through laser processing only. This is industrially relevant as it reduces the number of masks required and associated alignment for each subsequent layer. Therefore manufacturing costs are reduced.
Partners involved: M-SOLV, MLU
Application Impact:
By reducing the manufacturing costs the TRL of this process has moved to TRL 5/6 from 2.
Ink jet printing:
As part of the project M-Solv developed methods for using ink jet printing processes for precise deposition of materials. Both for discreet formation and also for uniformity of deposited films. Novel process regimes had to be developed so that a thin layer <100nm could be achieved over a 10um x 10um area that would be suitable for device fabrication.
It has been shown that ±3um in dimensional accuracy can be achieved along with thickness regimes of <20nm with a sub nm roughness. Therefore ink jet has the potential to make functional layers with the required surface roughness and thickness uniformity.
The process relies heavily on the ink – surface interaction and how it wets.
Partners involved: M-SOLV, UVEG
Scientific Impact:
Found the wetting requirements for achieving the high uniformity
Application Impact:
Compatibility between some spintronics materials and ink jet technology demonstrated.
Organic spin valve with lateral dimensions in the sub-500nm regime
A fabrication process for vertical organic spin-valve devices was developed and tested to achieve active device areas of less than 100x100 nm² and which is flexible in terms of material choice for the active layers. The fabricated samples consist of the layer stack LSMO/AlQ3/MgO/Co and the active area is defined by insulating Al2O3 (Fig. a).
Several samples with an active area of about 500x500nm² have been fabricated and in Fig. b) a SEM image of the active area is shown. Along more than 10 samples each with 7 devices a variety of MR results has been measured. Two examples are shown in Fig. c) and d) where a negative MR effect of about -170% and a positive effect of about +95% has been observed in two different samples with an AlQ3 thickness of 12 nm.
Partner involved: MLU
Scientific Impact:
Reveals the physics in vertical organic spin-valves as, for instance, the occurrence of pinholes gets less probable in smaller devices.
Application Impact:
development of a fabrication process employing lithography is an important step towards the ‘mass production’ of organic spintronics devices.
WP6
The investigation on the assessment of new processing technologies has been performed.
The main HINTS scientific achievements during the whole project duration and the best materials to fabricate the hybrid interfaces have been collected.
Partners involved: Thales, CNR
Potential Impact:
The potential impact of the HINTS achievements can be evaluated as extremely high.
One of the main achievements of the proposal is the control of the sign of spin transferred polarization. The strength and especially the versatility of this effect in HOI is by far higher than analogue effect detected in inorganic spintronics. The sign inversion gives a magnetoresistance modification >100%, what is clearly appealing for device applications. Furthermore, the electrical modulation of the sign has no precedents in inorganic spintronics, and can be at the basis of innovative reconfigurable logic elements.
It can be expected that the extremely efficient control of the spin polarization sign at HOI interfaces may be transferred even into inorganic device area. The rationale for this is supported by the high structural, temperature and chemical stability of the first 1-2 monolayers of organic materials grown on metals or oxides. This option, on the other hand, would not be compatible with inorganic devices requiring epitaxial growth conditions.
The advancement of the spin dependent residence time at the interface and “inside” it (HINTS knowledge and know-how) represents a new way to quantify the spin filtering capability. It has the potential to become the parameter of the future devices based on HOI as well as it can be used in recent close-to-market inorganic devices.
HINTS has established the phenomenological criteria for the detection of the magnetoresistance in HOI based devices, providing thus means for the fabrication of laboratory and industrial devices with desired values of magnetoresistance.
One of the highest impact results is the realization of high voltage operated magnetoresistance. This opens the possibility to use spin polarized carriers at the light emitting voltages in OLEDs or at the operating voltages of OFETs. Thus the organic spintronics can enter for the first time in these two ICT applications, widely employed in display and lightening industries.
Moreover, the achievement of first promising results for the transfer of spintronic achievements on flexible substrates promotes the application of most or part of HINTS results in Large Area Flexible Organic electronics (TOLAE).
Finally, high TRL values have been reached in the tasks involving both research and industrial partners. Two equipment producing partners succeeded to develop useful modifications to their commercial products (at least TRL 6) as stimulated by the needs of HINTS requirements to the interface.
List of Websites:
www.hintsproject.eu
