Sputtered Co is investigated as a suitable contact metal for bulk Bi-2(Te,Se)(3), and the results are compared to sputtered Ni. The coefficient of thermal expansion of Co matches that of bulk Bi-2(Te,Se)(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,Se)(3) was observed. In contrast, Co on Bi-2(Te,Se)(3) shows significantly less diffusion, even at anneal temperatures as high as 200 degrees C. CoTe2 is the preferred phase that is formed. First principles calculations for Bi2Te3 support the experimental observation. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3196237] All rights reserved.