Vibrational dynamics of the Si–H stretching modes of the Si(100)/H:2×1 surface

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Abstract
The lifetime T 1 of the symmetric Si–H stretching mode for the Si(100)/H:2×1 surface is significantly longer (T 1≳6 ns at 100 K) than for Si(111)/H:1×1. T 1 is strongly sample dependent and temperature dependent. Samples with the longest lifetimes also show the smallest inhomogeneous width. The difficulty in reproducing the longer lifetimes at low temperature indicates that the measuredT 1 may not be intrinsic and may by due to defects. The deuterated surface has a lifetime of 250±30 ps with little variation from sample to sample and a weak temperature dependence. It is expected to be the intrinsic lifetime. On the hydrogenated surface, the energy transfer time between the symmetric and asymmetric mode is measured to be 90±15 ps at 100 K. From photon‐echo measurement, the measureddephasing time at 100 K is 75±5 ps. We propose that the dephasing on that surface is induced by a low‐energy siliconphonon (200–300 cm−1) as for the Si(111)/H:1×1 surface. We derive an expression relating the dephasing time and the energy transfer time for the general case of two coupled oscillators and discuss its application to this system.