Photon-Stimulated Desorption Mechanism of Cl+Ions from Cl/Si(111) Surface

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Abstract
Photon-stimulated desorption (PSD) of Cl+ions from a Cl/Si(111) surface was studied using synchrotron radiation. The kinetic energy distribution of Cl+ions in PSD agreed with our previous results of electron-stimulated desorption (ESD). The excitation energy threshold of Cl+desorption also agreed within the experimental error. Hence, the desorption mechanisms in both PSD and ESD were considered to be the same. We studied the excitation (photon) energy dependence of the Cl+yield more precisely than ESD to elucidate the excitation mechanism for ion desorption. We found that the lower threshold photon energy was 17eV. Comparison with the ultraviolet photoelectron spectroscopy (UPS) spectrum showed that this energy corresponded to the excitation from the Cl 3s state to the Fermi level. Hence, this PSD process was explained by the KF model, where the Cl 3s core hole was filled by electrons of the Cl-Si bond through the Auger-like process, and then Cl+ions desorbed by repulsive Coulomb force from the adjacent Si+.