Spintronics [1] is a developmental technology in which carrier spin rather than charge is the relevant physical property for transport and storage. Organic materials may have special advantages for long range coherent spin tranport since spin-orbit interactions in these materials are weak. This possibility has lead to a flurry of research aimed at "organic spintronics" [2]. So far, intriguing results have been obtained [3] but the spintronic properties of organics are still controversial [4].

Our group is trying to establish the basic surface science of organic spintronic molecules adsorbed on magnetic surfaces. In collaboration with the Electronic and Magnetic Materials Group at Argonne National Lab's Center for Nanoscale Materials, we have been working to apply Spin Polarized Scanning Tunneling Microscopy [5] to single organic molecules like rubrene (see Figure 1) which has been shown to have a long spin diffusion length in TMR spin valves [6]. These measurements will help determine how molecular orbitals become spin polarized and how organic tunnel barriers transmit spin polarized currents.

Figure 1. STM image of a single Rubrene

molecule adsorbed on a Cr(001) surface.

In addition to our collaboration at Argonne, we have also developed spin polarized STM capabilities in our STM labs at NC State where we have applied it understand the spin dependent interfacial electronic structure of Alq3 on Cr(001). Figure 2a shows an STM image of a disordered monolayer of Alq3 on Cr(001) using ordinary STM imaging [7]. Figure 2b shows a spin polarized conductance map of the clean Cr(001) surface [5] and Figure 2b shows a similar map of the same surface with a submonolayer coverage of Alq3 molecules. Current efforts are mapping the energy-dependent spin asymmetry in this important model system. Since this molecule represents the most famous case of organic "GMR" [3], we are interested in determining the role of metal-molecule hybridization, which has recently been shown to be operative in metallophthalocyanines [8,9], on spin injection into Alq3 films.

Figure 2. a)STM image of ~ 1ML of Alq3/Cr(001); b)SPSTM of clean Cr(001); c) SPSTM of submonolayer Alq3 (single molecule circled) on Cr(001).

References

[1] Wolf et al., Science 294, 1488 (2001).

[2] Naber et al., J. Phys. D: Appl. Phys. 40, R205 (2007).

[3] Xiong et al., Nature 427, 821 (2004).

[4] Jiang et al., Phys. Rev. B 77, 035303 (2008).

[5] M. Bode, Rep. Prog. Phys. 66, 523 (2003).

[6] Shim et al., Phys. Rev. Lett 100, 226603 (2008).

[7] Wang et al. Org. Electron. 12, 1920 (2011).

[8] Iacovita et al., Phys. Rev. Lett. 101, 116602 (2008).

[9] Atodiresei et al., Phys. rev. Lett. 105, 066601 (2010).