Interface Chemistry of Contact Metals and Ferromagnets on the Topological Insulator Bi2Se3

5 years ago

Interface Chemistry of Contact Metals and Ferromagnets on the Topological Insulator Bi2Se3

Zifan Che, Christopher L. Hinkle, Jiyoung Kim, Qingxiao Wang, Christopher M. Smyth, Lee A. Walsh, Moon J. Kim, Robert M. Wallace, Ruoyu Yue, Adam T. Barton

The interface between the topological insulator (TI) Bi₂Se₃ and deposited metal films is investigated using X-ray photoelectron spectroscopy including conventional contact metals (Au, Pd, Cr, and Ir) and magnetic materials (Co, Fe, Ni, Co_0.8Fe_0.2, and Ni_0.8Fe_0.2). Au is the only metal to show little or no interaction with the Bi₂Se₃, with no interfacial layer between the metal and the surface of the TI. The other metals show a range of reaction behaviors with the relative strength of reaction (obtained from the amount of Bi₂Se₃ consumed during reaction) ordered as Au < Pd < Ir < Co ≤ CoFe < Ni < Cr < NiFe < Fe, in approximate agreement with the behavior expected from the Gibbs free energies of formation for the alloys formed. Post metallization anneals at 300 °C in vacuum were also performed for each interface. Several of the metal films were not stable upon anneal and desorbed from the surface (Au, Pd, Ni, and Ni_0.8Fe_0.2), while Cr, Fe, Co, and Co_0.8Fe_0.2 showed accelerated reactions with the underlying Bi₂Se₃, including interdiffusion between the metal and Se. Ir was the only metal to remain stable following anneal, showing no significant increase in reaction with the Bi₂Se₃. This study reveals the nature of the metal–Bi₂Se₃ interface for a range of metals. The reactions observed must be considered when designing Bi₂Se₃-based devices.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b08480

DOI: 10.1021/acs.jpcc.7b08480