Electronic effects induced by single hydrogen atoms on the Ge(001) surface

The properties of an isolated dangling bond formed by the chemisorption of a single hydrogen atom on a dimer of the Ge(001) surface are investigated by first-principles density functional theory (DFT) calculations, and scanning tunneling microscopy (STM) measurements. Two stable atomic configurations of the Ge-Ge-H hemihydride with respect to the neighboring bare Ge-Ge dimers are predicted by DFT. For both configurations, the unpaired electron of the HGe(001) system is found to be delocalized over the surface, rendering the isolated dangling bond of the hemihydride unoccupied. However, local surface charge accumulation, such as may occur during STM imaging, leads to the localization of two electrons onto the hemihydride dangling bond. The calculated surface densities of states for one of the charged Ge-Ge-H hemihydride configurations are found to be in good agreement with atomic-resolution STM measurements on n-type Ge(001). Comparison with a Si-Si-H hemihydride of the Si(001) surface shows similarities in structural properties, but substantial differences in electronic properties.