Probing the mechanism of infrared resonant desorption of hydrogen from Si(111): anharmonicity and energy pooling

Desorption of hydrogen from a Si(111) surface by resonant infrared excitation of the Si--H vibrational stretch mode requires vibrational ladder climbing of a Si--H bond to a high level leading to associative desorption. We report recent experiments probing the mechanism of ladder climbing. H$_2$ desorption is observed when the excitation linewidths are narrower than the anharmonicity of the Si--H bond, favoring energy pooling over multiphoton absorption. The resonance width of H$_2$ desorption with an excitation linewidth of 8.7~cm$^{-1}$ is measured to be 39~cm$^{-1}$, opening a new opportunity for site--selective modification on the Si(111) surface. The desorption yield decreases when the sample temperature increases, consistent with an energy pooling process.