Ab initio study of platinum induced reconstructions on Ge(001)-(1 x 2) surface with dimerization

We present first principle total energy calculation of Pt induced reconstructions on Ge(001)-(1 x 2) surface with dimerization. Study was undertaken using localized orbitals basis set DFT using SIESTA to compare pure Ge dimerized Ge(001)-(1 x 2) surface with 0.5 and 1.0 Pt covered dimerized Ge(001)( 1 x 2) surface with the possibility of homo (Ge-Ge and Pt-Pt) and hetro (Pt-Ge) dimers. From total energy calculation results we calculated dimer bond lengths, buckling angles and formation energy of dimers on Ge(001)-(1 x 2) surface. By calculating the formation energy of different configurations we find that Ge-Ge buckled dimerized surface has least (-1.23 eV/dimer) and Pt-Pt symmetric dimerized surface has largest (+0.09 eV/dimer) formation energy with respect to unreconstructed surface. We further calculated the electronic DOS and band structure of Ge dimerized as well as Pt dimerized surface to see the change in semiconducting behavior on dimerization. By comparing the DOS and electronic band structure of homo Ge dimerized surface, we found metallicity of Ge(001)-(1 x 2) surface results from dimer formation. Also by comparing the electronic band structure of homo Ge dimerized surface with unreconstructed surface we find that less number of bands crossing the Fermi level which is perhaps due to the saturation of one dangling bond per Ge surface atom. By introducing Pt at 0.5 and 1.0 coverage in place of Ge, except for homo Pt buckled dimerized surface having 1.0 coverage of Pt, we find in all other cases increase in number of bands are crossing the Fermi level, indicating strong metallic behavior of Ge(001)-(1 x 2) surface. (C) 2011 Elsevier B.V. All rights reserved.