Spinterface Engineering for Efficient Device Operation (SPEEDO)

Lead Research Organisation: University of York
Department Name: Physics

Abstract

Molecular spintronics is an emerging research field that seeks to build on the enormous successes of conventional spintronics (e.g. read-heads in all modern hard disk drives) and organic electronics (e.g. flexible displays) to produce devices such as organic spin transistors, flexible memory elements, and spin LEDs. Organic semiconducting molecules (OSCs) are mainly composed of light elements such as C, H, N, and O which means that they interact very weakly with an electron's spin--this is the fundamental property that spintronic technologies manipulate in addition to electronic charge. As such, OSCs are considered promising materials for use in devices in which it is desirable to pass spin-polarised electrons across an interface with a ferromagnetic material (spin injection) or to transport them from one ferromagnetic electrode to another (spin transport). Other beneficial properties of OSCs include their physical and chemical flexibility and the ability to produce them at low cost in large quantities.

To overcome the poor and irreproducible performance demonstrated by first-generation organic devices, it has become increasingly clear that a much better understanding of the interaction between OSCs and the ferromagnetic substrates that support them is needed. The chemical interaction at this organic/ferromagnetic interface, or 'spinterface', can lead to undesirable effects such as molecular distortion, a reduction in spin polarisation, and the appearance of hybridised electronic states. The aim of this project is to provide this missing knowledge by using a beam of excited helium atoms as a very sensitive probe of surface electronic and magnetic properties. The surface sensitivity of this approach means that it is ideal for studying the adsorption of molecules on surfaces making its application to organic spintronics both novel and timely. In addition to common OSCs such as C60 and the metal phthalocyanines, more exotic 'double-decker' molecules that have a two-layer structure will also be investigated. Theory predicts that these molecules could act as very efficient spin filters however this needs confirming experimentally.

The helium technique will also enable spinterfaces to be engineered with properties that are beneficial to device performance. For example, as we have shown before, the adsorption of simple atoms such as H and B can passivate the electronic states found at the surface of a ferromagnetic material such as Fe3O4 and recover desirable bulk properties such as half-metallicity. Based on these optimised spinterfaces, prototypical devices such as organic spin valves and magnetic tunnel junctions will be fabricated with the aim of demonstrating enhanced device performance. A novel method vacuum bonding process will also be developed to allow high-quality interfaces to be incorporated at both device electrodes. This opens up the possibility of preparing organic devices in which both the top and bottom electrodes consist of ferromagnetic oxides, a concept that has not been satisfactorily demonstrated to date.

Planned Impact

Spintronics is the most active research area currently being pursued worldwide in the field of magnetism, evidenced through representative papers at the leading magnetism conferences (MMM, Intermag, and JEMS) and the level of industrial and institutional funding (it is already a multibillion-dollar industry). Molecular spintronics is a subfield that has emerged more recently but also has enormous potential. One only has to look at the success of the related field of organic electronics, which has led to such device technologies as flexible OLED flat-panel displays and is now an industry also worth billions of dollars per year, to get an idea of the impact this field could have on the economy, society, and science base of the U.K.

The above successes have been built on decades of fundamental physical science research, most notably leading to the award of the Novel Prize for Physics to Albert Fert and Peter Grünberg "for the discovery of Giant Magnetoresistance'. The read-heads of all modern hard drives are based on spintronic principles of magnetoresistance, as are MRAM elements which have moved into the second-generation through the use of thermally-assisted switching and spin transfer torque. The massive increase in data storage, speed-of-access and display quality that these technologies have enabled have clearly led to a huge impact on the society and economy of the U.K., bringing benefits at both an individual and institutional level.

Although at a much earlier stage, organic spintronics also has significant promise in delivering real-world applications such as improved electronic devices and flexible memory elements. For this to happen, a much clearer understanding of the interplay between fundamental material properties and device performance is needed and this is where the proposed project will have the biggest scientific impact. Studying and optimising the interfaces that are central to the performance of an organic device will ultimately lead to faster, ore efficient, and low-power operation. Already, it has been demonstrated that using a spin-polarised current in an organic light-emitting diode (OLED) leads to an increase in light-generation efficiency and a consequent saving in power. Further improvements in device efficiency based on a better understanding of material properties, coupled with the low-cost production methods of organic semiconductors, will ultimately lead to environmental benefits to U.K and a 'greener' society.

As a burgeoning field, there is a lot of potential to commercialise and exploit the scientific knowledge generated as a result of the fundamental research taking place in organic spintronics. For example, if the device fabrication concept proposed in this project works as as expected, it will lead to patentable technology. In the medium-to-long term, it is highly possible that spin-out companies will be developed, creating jobs and wealth. Much of the success of the organic electronics industry can be attributed to fundamental research conducted in the U.K., for example, at world-leading groups at Imperial College London and Cambridge University. This led to the creation of Cambridge Display Technologies, a spin-out company that was floated on the NASDAQ stock exchange in 2004 for $230 million.

Larger, multinational magnetism companies such as Seagate Technologies, whose European operations are based in Londonderry, will also benefit from a better understanding of the materials and processes they incorporate into their products. In turn, this will lead to increased R&D investment. For example, HGST (formerly Hitachi Global Storage Technologies) are investing in significant R&D resources to develop an organic spin transistor. Looking to more blue skies research, single molecule magnets are currently being explored as potential pathways to quantum technologies with simple qubit operations already demonstrated in the TbPc2 molecules that are involved in this proposal.
 
Description PhD Studentship
Amount £210,000 (GBP)
Organisation University of York 
Sector Academic/University
Country United Kingdom
Start 09/2016 
End 03/2020
 
Description University of York Research Priming Fund
Amount £61,712 (GBP)
Organisation University of York 
Sector Academic/University
Country United Kingdom
Start 08/2016 
End 07/2017
 
Description CNR Bologna 
Organisation National Research Council
Department Bologna Research Area
Country Italy 
Sector Public 
PI Contribution I collaborate closely with the group of Prof. Alek Dediu at CNR Bologna. I provide expertise, facilities, and intellectual input to our joint studies of organic semiconductor/ferromagnetic interfaces and devices, mainly based on my experience and interest in using a beam of spin-polarised metastable helium atoms to analyse and subsequently engineer surface magnetic properties. I have published a paper based on our joint work and several more are in preparation. I have presented our work at many conferences. I will host a research visit by Dr. Ilaria Bergenti to York in June 2017.
Collaborator Contribution The group of Prof. Dediu provides their extensive knowledge in the area of organic spintronics along with access to their growth facilities and the provision of samples. They have presented our work at several conferences including the landmark ECMOLS conference in 2016.
Impact Pratt, A, Graziosi, P, Bergenti, I, Prezioso, M, Dediu, A & Yamauchi, Y 2014, 'Ultrahigh vacuum and low-temperature cleaning of oxide surfaces using a low-concentration ozone beam' Review of Scientific Instruments, vol 85, no. 7, 075116. DOI: 10.1063/1.4890208
Start Year 2012
 
Description EWHA Womans University 
Organisation Ewha Womans University, Seoul
Country Korea, Republic of 
Sector Academic/University 
PI Contribution I collaborate with the group of Professor Tae Hee Kim at EWHA who specialises in fabricating and characterisation organic devices. I contribute to improving their devices by providing expertise on organic interface formation and characterisation, using various techniques of surface and interface analysis. I have also jointly hosted a PhD student from this group at the National Institute for Materials Science (NIMS) in Tsukuba, Japan who worked with me for one month on the above studies. Several papers have been published or are in preparation as a result of this collaboration and the work has also been presented at various international conferences. I usually take a leading intellectual role in preparing this dissemination.
Collaborator Contribution Prof. Kim's group at EWHA provides expertise in organic device fabrication and characterisation allowing me to determine the effectiveness of spinterface engineering. As such, I have access to state-of-the-art electrical and spin transport measurement equipment in addition to growth facilities that complement my own. She also hosted my visit to EWHA where I gave an invited seminar and where this collaboration was instigated (in 2012). Her group regularly prepares, submits, and presents conference contributions based on our joint work.
Impact Bae, YJ, Lee, NJ, Kim, TH, Pratt, A & Yamauchi, Y 2014, 'Interface control of spin transport in magnetic tunnel junctions with MgO\Cu-Phthalocyanine hybrid barrier' Bulletin of the American Physical Society, vol 59, no. 1.
Start Year 2012
 
Description National Institute for Materials Science 
Organisation National Institute for Materials Sciences
Country Japan 
Sector Academic/University 
PI Contribution I have a long-standing collaboration with the Spin Characterization Group at the National Institute for Materials Science (NIMS) in Tsukuba, Japan. Headed by Dr. Yasushi Yamauchi and part of the Research Centre for Advanced Measurement and Characterization, this partnership was established in 2009 after I was awarded a JSPS Fellowship to spend 15 months working at NIMS. Following this, I have spent many three month stays there as a visiting researcher and, prior to my appointment as a lecturer at York, I held a tenure-track fellowship in the International Centre for Young Scientists. During these stays, I have secured significant grant income from both Japanese and UK funding sources as well as disseminating our joint research in many publications, invited talks and conference papers.
Collaborator Contribution Hosting my stay as a JSPS Fellow for 15 months. Inviting me to return as a visiting researcher for three months on four separate occasions and covering all associated travel and subsistence expenses. Providing funding to allow me to perform experiments during these visits. Donating a large and unused piece of research equipment--a Mott detector plus accessories such as high voltage power supplies and vacuum components--to my lab in York. To purchase such an item in the UK would cost at least £70000. Hosting and funding three month research visits for two of my PhD students. Hosting and funding summer internships for four final year undergraduate students from York. Hosting research visits from mutual collaborators from EWHA Womans University in Seoul, Korea.
Impact Publications: Sun, X, Pratt, A & Yamauchi, Y 2015, 'Half-Metallicity Induced by Boron Adsorption on an Fe3O4(100) Surface' Physical Chemistry Chemical Physics, vol 17, pp. 15386-15391. DOI: 10.1039/C5CP02466H Sun, X, Wang, B, Pratt, A & Yamauchi, Y 2014, 'Magnetic moment enhancement and spin polarization switch of the manganese phthalocyanine molecule on an IrMn (100) surface' Journal of Chemical Physics, vol 141, no. 3, 034703. DOI: 10.1063/1.4889934 Pratt, A, Graziosi, P, Bergenti, I, Prezioso, M, Dediu, A & Yamauchi, Y 2014, 'Ultrahigh vacuum and low-temperature cleaning of oxide surfaces using a low-concentration ozone beam' Review of Scientific Instruments, vol 85, no. 7, 075116. DOI: 10.1063/1.4890208 Sun, X, Pratt, A, Li, ZY, Ohtomo, M, Sakai, S & Yamauchi, Y 2014, 'The adsorption of h-BN monolayer on the Ni(111) surface studied by density functional theory calculations with a semiempirical long-range dispersion correction' Journal of Applied Physics, vol 115, no. 17, 17C117. DOI: 10.1063/1.4866237 Pratt, A, Kurahashi, M, Sun, X & Yamauchi, Y 2014, 'Characterizing ferromagnetic oxide/organic semiconductor interfaces using a spin-polarized metastable helium beam' Journal of the Magnetics Society of Japan, vol 38, no. 2-2, pp. 71-74. DOI: 10.3379/msjmag.1402R007 Bae, YJ, Lee, NJ, Kim, TH, Pratt, A & Yamauchi, Y 2014, 'Interface control of spin transport in magnetic tunnel junctions with MgO\Cu-Phthalocyanine hybrid barrier' Bulletin of the American Physical Society, vol 59, no. 1. Sun, X, Li, SD, Wang, B, Kurahashi, M, Pratt, A & Yamauchi, Y 2014, 'Significant variation of surface spin polarization through group IV atom (C, Si, Ge, Sn) adsorption on Fe3O4(100)' Physical Chemistry Chemical Physics, vol 16, pp. 95-102. DOI: 10.1039/C3CP53272K Sun, X, Entani, S, Yamauchi, Y, Pratt, A & Kurahashi, M 2013, 'Spin polarization study of graphene on the Ni(111) surface by density functional theory calculations with a semiempirical long-range dispersion correction' Journal of Applied Physics, vol 114, no. 14, 143713. DOI: 10.1063/1.4824186 Kuwabara, H, Yamauchi, Y & Pratt, A 2013, 'Spin behavior in a quarter rotation of the magnetic field' Journal of the Korean Physical Society, vol 62, no. 9, pp. 1286-1290. DOI: 10.3938/jkps.62.1286 Pratt, A, Kurahashi, M, Sun, X, Gilks, D & Yamauchi, Y 2012, 'Direct observation of a positive spin polarization at the (111) surface of magnetite' Physical Review B (Rapid Communications), vol 85, no. 18, 180409(R). DOI: 10.1103/PhysRevB.85.180409 Pratt, A, Dunne, L, Sun, X, Kurahashi, M & Yamauchi, Y 2012, 'Energy-level alignment at the Alq 3/Fe 3O 4(001) interface' Journal of Applied Physics, vol 111, no. 7, 07C114. DOI: 10.1063/1.3677768 Sun, X, Kurahashi, M, Pratt, A & Yamauchi, Y 2011, 'First-principles study of atomic hydrogen adsorption on Fe3O4(100)' Surface Science, vol 605, no. 11-12, pp. 1067-1073. DOI: 10.1016/j.susc.2011.03.006 Pratt, A, Kurahashi, M & Yamauchi, Y 2011, 'Spin-polarized metastable He study of surface magnetic order in Ho thin films' Journal of Applied Physics, vol 109, no. 7, 07C111. DOI: 10.1063/1.3556958 Kurahashi, M, Pratt, A & Yamauchi, Y 2011, 'Spin polarization of the Si(111)-7 × 7 surface: A study with a spin-polarized metastable helium atom beam' Surface Science, vol 605, no. 5-6, pp. 612-615. DOI: 10.1016/j.susc.2010.12.027 Pratt, A, Kurahashi, M, Sun, X & Yamauchi, Y 2011, 'Adsorbate-induced spin-polarization enhancement of Fe3O 4(0 0 1)' Journal of Physics D: Applied Physics, vol 44, no. 6, 064010. DOI: 10.1088/0022-3727/44/6/064010 Sun, X, Pratt, A & Yamauchi, Y 2010, 'First-principles study of the structural and magnetic properties of graphene on a Fe/Ni(111) surface' Journal of Physics D: Applied Physics, vol 43, no. 38, 385002, pp. -. DOI: 10.1088/0022-3727/43/38/385002
Start Year 2009
 
Description Rahul Nair in Manchester 
Organisation University of Manchester
Department National Graphene Institute
Country United Kingdom 
Sector Academic/University 
PI Contribution This is a collaboration with Prof. Rahul Nair of the National Graphene Institute in Manchester who is working on developing and applying graphene oxide membranes and other 2D materials to, for example, water and organic filtration technologies. Much of this work relies on a detailed understanding of the sample chemistry, for example, the carbon bonding environment in graphene oxide and the Mo and S environments in MoS2. We provide this understand to Prof. Nair and his group using our expertise and facility for electron spectroscopy (particularly in this case, X-ray photoelectron spectroscopy). As well as collecting experimental data, I lead the analysis and interpretation of the results and help to write the papers which to-date include a publication in Nature Materials (2017) with another on the verge of being accepted in Nature. With the emergence of graphene spintronics and van der Waals materials, this collaboration overlaps very well with my EPSRC First Grant.
Collaborator Contribution The group of Prof. Nair contributes to the collaboration by providing 2D material membranes for analysis. They also perform a significant amount of additional characterisation of these samples and lead the write up of the results.
Impact The following publications have resulted from this collaboration: (1) Q. Yang, A. Pratt, R. Nair et al., Ultrathin graphene-based membrane with precise molecular sieving and ultrafast solvent permeation, Nature Mater. 16, 1198 (2017); (2) K. G. Zhao, A. Pratt, R. Nair et al., Electrically controlled water permeation through graphene oxide membranes, Nature, article with referees (after responding to favourable initial reviews); (3) C. Hu, A. Pratt, R. Nair et al., Controlling water permeation through MoS2 membranes by phase engineering, article in preparation. This work is multidisciplinary involving: Physics, Chemical Engineering, Materials Science. Publication (1) above resulted in the following press release: http://www.manchester.ac.uk/discover/news/graphene-water-filter-turns-whisky-clear/
Start Year 2016