The cluster expansion (CE) method [1] coupled with first-principles calculations have been widely used for exploring phase stability in bulk and surface alloys. More recently, attempts are made to address nano-scale alloy systems, including bimetallic nanoparticles [2]. In this work [3], we demonstrate the use of the CE method to identify groundstates in C-Si, Ge-Si and Sn-Si alloy nanowires. The CE Hamiltonian is first constructed by fitting to the energies of various alloy NW configurations calculated using density functional theory. A converged CE Hamiltonian is used with simulated annealing to search for groundstates across compositions. While stable configurations for Ge-Si and Sn-Si NWs are core-shell like (segregation), those for C-Si are ordered. We next compute the band gaps of these NW groundstates versus composition, showing the composition range where the band gap varies linearly and where it does not. We further predict composition ranges where the spatial separation of near-band gap states are imminent, making it possible for electron�hole charge separation.[1] Sanchez, J.M., Ducastelle, F., and Gratias, D., Physica 128A, 334 (1984).[2] Tan, T.L., Wang, L.-L., Johnson, D.D., and Bai, K., Nano Lett 12, 4875 (2012).[3] Ng, M.-F. and Tan, T.L, Nano Lett, accepted (2013).

Stable alloy nanowire configurations and their electronic band characteristics via first-principles

247th National Meeting (2014)

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