Collision of hyperthermal atoms with a solid surface. I. Energy dissipation in the solid

It is well established that when a hyperthermal atom collides with a solid surface, a large fraction of the atom's translational energy may be transferred to the solid in a single collision. The energy transferred to the solid may be channeled into two modes, which are electronic excitation and energy transfer to phonons. In the present work, electronic excitation in the solid was not considered. Thus, it was assumed that energy is transferred during the scattering event from the projectile to the solid vibrational modes only. Since the gas particle interacts with a limited small number of surface atoms, a "hot spot" is formed on the surface. We found that the excitation of the vibrational modes of the solid decays initially with a decay constant of less than 0.5 ps and then more slowly with a decay constant of 2.5-3.5 ps. A discussion of which vibrational modes are excited is also given.