Ion desorption of surface-oriented methyl-ester compounds using a self-assembled monolayer by core-electron excitations: Polarization-dependence measurements

Polarization dependence of photodesorbing ions by carbon and oxygen core-electron excitations of methyl-ester terminated self-assembled monolayers have been investigated using existing time-of-flight mass spectrometer combined with additional correction electrodes at both sides of the sample holder, which apply an appropriate potential gradient for desorbing ions. Ions which desorb site selectively indicate significant polarization dependence. On the other hand, non-selective ions rarely show the dependence. These findings indicate that site-selective ion desorption takes place only within the functional group where core electron is excited and the initial memory of the core excitation is effectively conserved during desorption. Trends of the polarization dependence differ in desorbing ions as well as resonant excitations. Variation of the dependence can be understood by the different superiority of dissociation/desorption mechanisms: direct dissociation induced by core excitation and indirect dissociation caused by rapid energy relaxation and X-ray-induced electron stimulated desorption.