Spin Injection and Spin Dynamics at CuPC/GaAs(100) Interface
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Spin Injection and Spin Dynamics at CuPC/GaAs(100) Interface Huanjun Ding1, Yongli Gao1, Marina Sanchez-Albaneda2, Jan-Peter Wüstenberg2, Mirko Cinchetti2, Oleksiy Andreyev2, Michael Bauer2, and Martin Aeschlimann2 1 Department of Physics and Astronomy, University of Rochester, Bausch and Lomb Hall, University of Rochester, Rochester, NY, 14627 2 University of Kaiserslautern, Kaiserslautern, 67663, Germany
ABSTRACT Spin injection from GaAs(100) to organic semiconductor copper phthalocyanine (CuPc) has been investigated experimentally with spin-resolved two-photon photoemission (SR-2PPE) spectroscopy. With SR-2PPE, the dynamics of both electron and spin relaxation have been studied with femtosecond time resolution. The spin-polarized electrons are originally generated in GaAs through optical pumping and injected into CuPc. We observed an enhancement in spin polarization at the interface after initial CuPc deposition. This demonstrates that interface spin scattering is insignificant, which is similar to our previous result of spin injection at CuPc/Co interface. The spin polarization dropped when the CuPc film became thick, an effect attributed to bulk attenuation in CuPc. The lifetime of the unoccupied orbits in CuPc was also studied with red-blue excitation of photon energy 1.56 eV and 3.12 eV, respectively. There was a strong asymmetry in the time-resolved spectra, and an unexpected long lifetime when the lower unoccupied orbital was excited. A simple explanation of this phenomenon will be discussed. INTRODUCTION Common electronic devices generally make use of the electrical charge of the carriers, electrons or holes, in the functional material. However, a new approach, whose operation depends on the spin of the electrons, has recently been intensively investigated. The so-called spintronics is built upon active manipulation and control of the spin degree of freedom, and has already made a major impact on the information technology. Most conventional spintronics devices are based on transition-metal and rare-earth elements and their oxides. The first advance about utilizing organic-based magnets was reported in mid-80s [1,2]. The application of the organic semiconductor in the spintronics provides great opportunities for tuning the magnetic properties by molecular design. In the organic-based spintronic devices, spin-polarized electrons, which are naturally generated in the ferromagnetic materials, can be injected through the organic/inorganic interface. Therefore, the electron-scattering rate during the spin-injection at these interfaces becomes a key factor of the device performance. Direct electrical spininjection has been demonstrated in organic semiconductor by Dediu et al. [3]. More recently, Xiong et al. observed an impressive spin-valve effect with a sandwich structure of ferromagnet/organic semiconductor/ferromagnet [4]. A similar observation on carbon nanotubes has also been reported by Tsukagoshi et al. [5]. At the same time, theoretical calculations of ferromagnetic metal/conjugated polyme
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