Hydrogen adsorption on phosphorus-rich(2×1)indium phosphide (001)

Hydrogen adsorption on the InP $\mathrm{}\left(001\right)-(2\mathrm{}\times 1)$ reconstruction has been characterized by vibrational spectroscopy and ab initio calculations with density functional theory. The $(2\mathrm{}\times 1)$ surface is covered with a complete layer of phosphorus dimers. The clean and hydrogen-terminated dimers have been modeled by ${\mathrm{In}}_5{\mathrm{P}}_4{\mathrm{H}}_x$ clusters with the proper number of covalent and dative bonds to accurately represent the surface of interest. The optimized molecular cluster of the unreacted dimer reveals that it has one filled and one partially filled dangling bond. Hydrogen atoms attack the P-P dimers forming terminal and coupled phosphorus-hydrogen bonds, and the predicted vibrational frequencies of these species are in excellent agreement with the infrared spectra. All the observed vibrational modes can be assigned to species containing one, two, and three hydrogen bonds (i.e., PH, HP-PH, and $\mathrm{PH}+{\mathrm{PH}}_2)$ per surface dimer.