Coverage-dependent adsorption and stability of functionalized Ge(1 0 0) and (1 1 1) surfaces

Abstract The coverage-dependent adsorption and stability of functionalized Ge(1 0 0) and (1 1 1) surfaces terminated with X and XH (X = –F, –Cl, –Br, -I, –CH3, and –OH) are systematically investigated by employing density functional theory calculations. The chemical bond Ge-X slightly decreases with the increase of surface coverage for Ge(1 0 0) and Ge(1 1 1) surfaces and much less depends on the surface crystal orientation. The adsorption energy indicates that different chemical species adsorption on Ge surface are favorable thermodynamically. Ge(1 1 1) surface shows stronger adsorption stability over the entire coverage range compared with Ge(1 0 0) surface. The Bader population analysis shows that the charge transfer from the Ge atoms to the chemical species X results in local dipole moment at the surfaces. The surface reconstruction and the electronegativity difference between the adsorbate and substrate atoms lead to the charge redistribution, which give rise to a significant influence on the surface or interface properties. The study of coverage-dependent adsorption and stability of functionalized Ge surfaces terminated with different chemical groups may pave the way for Ge device application in the fields of optoelectronics, bioelectronics, and electronics.