Dynamical study of Cl2 interaction with clean and Cs-covered Si(100) at 200 K

Abstract

Abstract Cs adatom effects in Cl 2 beam scattering from Si(100) at 200 K have been studied by changing the incident energies E i from 0.055 to 0.86 eV. The observed influences of the Cs adatoms to scattering yield are quite opposite in nature between low and high Cl coverage regimes: For low Cl coverage regime, the direct-inelastic (DI) scattering yield is much larger on the cesiated surface than on the Cs-free surface at E i = 0.055 eV, suggesting that the Cs adatoms play a role in making the physisorption potential shallow. For the origin of this potential shallowing, Pauli repulsion is proposed to play a role. The DI scattering yield from the cesiated surfaces decreases with increasing E i , i.e. sticking is activated by E i . This E i -activated sticking is interpreted in terms of competition between harpooning and Pauli repulsion. For high Cl coverage regime, on the other hand, intense trapping-desorption (TD) scattering is observed on the Cs-free surface. However, for the cesiated surfaces, no TD scattering is observed at all. The occurrence of the Cl 2 temperature programmed desorptions around 220 K indicates that the Cl 2 physisorption is stable at 200 K on the cesiated surface. This implies that the Cs adatoms, presumably in the form of Cs + Cl − ionic bonds, play a role in deepening the physisorption potential further.