时间: 2014年4月29日 星期二 下午4:00

地点: 四川大学(望江校区)物理馆1楼103室

报告人：张洪滔博士，Queen Mary University of London

报告题目： Hole injection from ferromagnetic material to tris (8-hydroxyquinoline) aluminium (Alq3) in the presents of interfacial states

报告内容: Previously it has been argued that transition metal ferromagnetic metals (FM) such as NiFe and Co are inefficient electron injectors due to their unfavourable work functions (e.g. ~2eV barriers between LUMO of Alq3 and work function of NiFe) [1, 2]. However, others claim that Alq3 is poor hole transporter as it is often labelled as an electron transport material because of primary role it performs in OLEDs [3]. Recently, it has been shown that the inclusion of a thin layer LiF between a NiFe cathode and Alq3 in a spin valve resulted in a change in sign of magnetoresistence (MR) [4]. It was interpreted by reversing the sign of the spin-polarization of the charge carriers in Alq3 [5]. Using the charge mobility measurements by Time of Flight (ToF) and dark injection (DI) transients on single organic layer devices consisting of: ITO or NiFe, Alq3, Al or Au, we explicitly show that the inclusion of a FM electrode introduces trap-like states with an energy between the HOMO and LUMO, previously termed hybrid interface states which is accompanied by a spin-dependent broadening and a spin-dependent energy shift of the density of states in the molecular monolayer [6]. Conclusively, it is holes not electrons been injected from NiFe and Alq3 is not a bad hole transporter. Therefore transition metal FM/Alq3 based organic spin valves have their charge carrier transport dominated by holes.

References

[1] Z.H. Xiong et al, Nat. 427, 821-824 (2004).

[2] R. Lin, et al, Phy. Rev. B, 81, 1-6 (2010).

[3] V.A. Dediu et al, Nat. Mat. 8, 707-716 (2009).

[4] D. Dhandapani et al, Magnetics, IEEE Transactions, 46, 1307-1310 (2010).

[5] L. Schulz, et al, Nat. Mat. 10, 39-44 (2010).

[6] C. Barraud, et al, Nat. Phys. 6, 615-620 (2010)

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