Breaking relaxing bonds at a H:Si(100)-(2 x 1) surface with infrared laser pulses

The time-dependent self-consistent field (TDSCF) approach is developed and applied to study the free relaxation and the infrared-laser-driven desorption of H atoms from a H:Si(100)-(2 x 1) surface. The method has made it possible to treat, by means of computer simulation within the Schrodinger wave function formalism, as many as 536 degrees of freedom of a H-Si cluster. The model used includes the H-Si stretching and the Si-Si-H bending motion of the adsorbed H atom, coupled nonlinearly to 534 degrees of freedom of the substrate, which are represented by the corresponding normal modes. It is shown that the bending vibrations relax on a picosecond time scale due to vibration-phonon coupling, in agreement with a previous perturbative study. It is also found that almost complete desorption of H atoms can be accomplished by optimally chosen, strong infrared (IR) laser pulses of 0.5 ps duration. The desorption rate is systematically studied as a function of the laser field strength for the case of plateau-type IR laser fields of 10 ps duration.