Sputtered Co is investigated as a suitable contact metal for bulk Bi 2 ͑Te,Se͒ 3 , and the results are compared to sputtered Ni. The coefficient of thermal expansion of Co matches that of bulk Bi 2 ͑Te,Se͒ 3 used in our study, and the compatible interface favors the selection of Co as a contact metal. Significant Ni diffusion into Bi 2 ͑Te,Se͒ 3 was observed. In contrast, Co on Bi 2 ͑Te,Se͒ 3 shows significantly less diffusion, even at anneal temperatures as high as 200°C. CoTe 2 is the

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... d phase that is formed. First principles calculations for Bi 2 Te 3 support the experimental observation. Figure 1. XRD spectra for the as-deposited 90 nm sputtered Co film taken at an X-ray incidence angle of = 2°and annealed film at 200°C for = 0.5, 1.0, and 2.0°. Electrochemical and Solid-State Letters, 12 ͑10͒ H395-H397 ͑2009͒ 1099-0062/2009/12͑10͒/H395/3/$25.00 © The Electrochemical Society H395 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 109.171.137.210 Downloaded on 2015-05-19 to IP