Spin injection and spin dynamics in organic spintronics interfaces
Final Report Abstract
The objective of the proposed experimental program was to resolve fundamental questions regarding spin relaxation, spin-dependent transport, spin injection, and magnetic phenomena at interfaces with organic semiconductors (OSC). The proposal was motivated by the fact that OSC may represent a major opportunity for application in the growing field of spintronics, since they are expected to possess very low spin-orbit coupling and thus extremely long spin relaxation times. We proposed to study representative OSC materials and to focus mainly on spin injection across the interface between such OSC and an inorganic solid, serving as source for spin polarized electrons. Since the low spin-orbit coupling in OSC makes the standard characterization methods successfully used for inorganic semiconductors practically useless, we proposed to achieve the proposed objective by applying the spin- and time-resolved two-photon photoemission (STR- 2PPE) technique, combined with a systematic approach of materials and surface/interface analysis. The STR-2PPE studies were performed mainly on the OSC copper phthalocyanine (CuPc), which was grown on three different spin-injector substrates: ferromagnetic Co(001) thin films, ptype GaAs(001) and thin films of the halfmetallic ferromagnet Heusler alloy Co2MnSi(001). Regarding the Co-CuPc system, we started with the characterization of epitaxial Co(001) thin films. This was followed by a careful and systematic study of the growth, electronic and spindependent properties of CuPc on Co(001) by means of Auger spectroscopy, near edge x-ray adsorption spectroscopy (NEXAFS), STM and UPS. Finally we applied the STR-2PPE and found that injection into unoccupied molecular orbitals of CuPc can take place from a cobalt substrate with a spin injection efficiency of 85%-90%. Moreover, we estimated an electron inelastic mean free path in CuPc in the range of 1nm and a ten to thirty times higher quasi-elastic spin-flip length. We demonstrated that quasi-elastic spin-flip processes are the dominant microscopic mechanism limiting the spin diffusion length in CuPc. Similar experiments were performed on the GaAs-CuPc system, demonstrating that spinpolarized electrons originating from the GaAs substrate can be injected into CuPc without any substantial spin-flip scattering at the interface. Furthermore, we could follow the temporal evolution of the spin polarization injected into the organic layer in the range up to 1 ps after injection from the GaAs substrate. The results show that the degree of spin polarization of electrons injected through the GaAs/CuPc interface into molecular orbitals just above the lowest unoccupied molecular orbital onset of CuPc is preserved longer than the spin polarization of electrons injected in energetically higher lying states. Concerning the Co2MnSi-CuPc system, we observed an unexpected behaviour of the static spin dependent properties of the Co2MnSi surface after deposition of less than 1ML CuPc that is still under investigation. After publication of our article in Nature Materials, describing the results of our studies on the Co-CuPc system, a few press releases about our research in the field of organic spintronics appeared in the local press. Moreover, a news & views article and two editorials in Nature materials was partly dedicated to our experimental achievements: Z. Valy Vardeny “Organics strike back”, Nature Materials 8, 91-93 (2009) “Why going organic is good”, Nature materials 8, 691 (2009) G. Szulczewski, S. Sanvito, M. Coey, “A spin of their own” Nature Materials 8, 693-695 (2009)
Publications
- Electron spin dynamics and spin-flip processes in solids and at semiconductor/metal interfaces. Festkörper Seminar, RWTH Aachen, Oktober 23, 2006
Mirko Cinchetti
- Epitaxial film growth and magnetic properties of Co2FeSi. Phys. Rev. B 74, 174426 (2006)
H. Schneider, G. Jakob, M. Kallmayer, H.J. Elmers, M. Cinchetti, B. Balke, S. Wurmehl, C. Felser, M. Aeschlimann, and H. Adrian
- PhD thesis. “Spin- and Time-Resolved Two Photon Photoemission Study of a CuPc/Co Junction for Spin-Based Applications”. TU Kaiserslautern, 10.02.2006
Oleksiy Andreyev
- Spin-resolved two-photon photoemission study of the surface resonance state on Co/Cu(001). Phys. Rev. B 74, 195416 (2006)
O. Andreyev, Yu.M. Koroteev, M. Sánchez Albaneda, M. Cinchetti, G. Bihlmayer, E.V. Chulkov, J. Lange, F. Steeb, M. Bauer, P.M. Echenique, S. Blügel, and M. Aeschlimann
- Towards a full Heusler alloy showing room temperature half-metalicity at the surface. J. Phys. D: Appl. Phys. 40, 1 (2007)
M. Cinchetti, J.-P. Wüstenberg, M. Sánchez Albaneda, F. Steeb, A. Conca, M. Jourdan , M. Aeschlimann
- Electron spin dynamics and spin-flip processes in ferromagnets and at interfaces with organic semiconductors. Seminarvortrag KOMET, Fachbereich Physik, Johannes Gutenberg-Universität Mainz, April 29, 2008
Mirko Cinchetti
- Energy resolved spin dynamics at semiconductor surfaces. SPIE Photonics West, San Jose, USA, January 22, 2008
Martin Aeschlimann
- Hot-electron dynamics in thin films of sodium-doped perylene-3,4,9,10-tetracarboxylic dianhydride. Phys. Rev. B 78, 195326 (2008)
J. Wüsten, S. Berger, M. Salomo, A. Mönnich, M. Bauer, M. Aeschlimann, Ch. Ziegler
- PhD thesis. “Elektronische Eigenschaften der Grenzfläche zwischen Me-Phthalocyanin (Me=Cu, Fe) und Kobalt”. 30.06.2008
Kathrin Goedel (geb. Heimer)
- Spin injection and spin dynamics at the CuPc/GaAs interface studied with ultraviolet photoemission spectroscopy and two-photon photoemission spectroscopy. Phys. Rev. B 78, 075311 (2008)
Huanjung Ding, Yongli Gao, Mirko Cinchetti, Jan-Peter Wüstenberg, Marina Sánchez Albaneda, Oleksiy Andreyev, Michael Bauer, Martin Aeschlimann
- Determination of spin injection and transport in a ferromagnet/organic semiconductor heterojunction by two-photon photoemission. Nature Materials, Vol. 8, 115-119 (2009)
Mirko Cinchetti, Kathrin Heimer, Jan-Peter Wüstenberg, Oleksiy Andreyev, Michael Bauer, Stefan Lach, Christiane Ziegler, Yongli Gao, Martin Aeschlimann
- Determination of spin injection and transport in ferromagnet/organic semiconductor heterojunctions. SPINOS 09: 2nd Topical Meeting on Spins in Organic Semiconductors, February 4-7, 2009, Salt Lake City, Utah (USA)
Mirko Cinchetti
- Determination of spin injection and transport in organic semiconductor heterojunctions with ferromagnets including Heusler Alloys. 3Königstreffen: Magnetism meets semiconductors – Novel Spin Phenomena in Heterostructures and Novel Materials, Bad Honnef, January 5-7, 2009
Mirko Cinchetti
- Effects of post-growth annealing on structural and compositional properties of the Co2Cr0.6Fe0.4Al surface and its relevance for the surface electron spin polarization. J. Phys. D: Appl. Phys. 42, 084016 (2009)
J.-P. Wüstenberg, J. Fischer, C. Herbort, M. Jourdan, M. Aeschlimann, M. Cinchetti
- Investigations of metallo-phthalocyanines grown on ferromagnetic Co(001) thin films. E-MRS Spring Meeting 2009, Strasbourg, France, June 8-12, 2009
Martin Aeschlimann
- Tailoring the spin properties of metal/organic interfaces by alkali metal doping. EMRS Fall meeting, September 14-18, 2009, Warsaw
Mirko Cinchetti
- Unraveling the fundamental issues of organic spintronics with spin-resolved two-photon photoemission. SFB 668 – Kolloquium, University of Hamburg, October 20, 2009, Hamburg
Mirko Cinchetti
- Tailoring the spin functionality of a hybrid metal-organic interface by means of alkali metal doping. DPG Spring Meeting 2010, 21-26 March, Regensburg
Mirko Cinchetti
