Molecular dynamics simulation of hydrogen-covered reconstructed Si( [formula omitted]):H-2×1 silicon surface: calculation of vibrational energy relaxation rates of hydrogen stretching modes

Abstract

Molecular dynamics simulation for hydrogen-covered Si(1 0 0):H-2×1 silicon surface was carried out to calculate the vibrational energy relaxation rates of Si–H stretches based on the Bloch–Redfield theory. The calculation gave a lifetime of 0.35 ns at 300 K, about three times shorter than the experimental result of 1.2 ns. With a reduction of force constants for the first layer reconstructed silicon dimer Si–Si stretches and Si–Si–Si bends by multiplying with 0.9 in this molecular mechanics force field, the calculation gave a lifetime of 0.51 ns, closer to the experimental result than the calculated result above. This suggests that the vibrational frequencies of first layer silicon dimers should be lower than the bulk modes. In addition, it is noted that the Si–Si–H bending frequency of 625 cm −1 on this Si(1 0 0):H-2×1 surface is lower than the 640 cm −1 on the Si(1 1 1):H-1×1 surface but the lifetime of Si–H stretches on (1 0 0) surface is shorter than (1 1 1) surface. This is in contrast to a result in a previous study for (1 1 1) surface in which the higher Si–Si–H bending frequency should result in a shorter lifetime. These results indicate that the couplings between Si–H stretches and Si–Si–H bends on the Si(1 0 0):H-2×1 surface differ significantly from the Si(1 1 1):H-1×1 surface. Besides discussion of this coupling, the isotope and thermal effects in the calculated lifetimes are reported and discussed as well.