Kazuhiko Mase, Mitsuru Nagasono, Tsuneo Urisu, and Yoshitada
Murata
[Bull. Chem. Soc. Jpn., 69, 1829-1832 (1996)]
Electron-ion coincidence (EICO) spectroscopy for studying surface dynamics has been developed. The apparatus consists of an electron gun, a cylindrical mirror analyzer (CMA), and a time-of-flight ion mass spectrometer (TOF-MS). A sample surface is excited with an electron beam, and the energy of the emitted electrons is analyzed by the CMA. The TOF spectra of desorbed ions are measured with the TOF-MS and a multichannel scaler, taking the energy-analyzed electron signal as the starting trigger. Those ions coincidently desorbed with electrons give a characteristic peak in the TOF spectrum. The apparatus has been evaluated on the basis of electron-ion coincidence measurements of an F/SrTiO3(100) surface. The F+ coincidence signal was observed to be enhanced at electron kinetic energies of 650-655 eV, corresponding to the F(KL23L23) Auger transition. The result provides direct evidence of the Auger-stimulated ion-desorption mechanism for an ionically bonded surface (the Knotek-Feibelman (KF) mechanism).
Mitsuru Nagasono, Kazuhiko Mase, and Tsuneo Urisu
[Surface Sci., 363, 342-346 (1996)]
Electron stimulated ion desorption induced by core level excitations is studied for H2O condensed on a SiO2/Si(111) surface at 80 K (H2O/SiO2/Si(111)) by using Auger electron-ion coincidence spectroscopy. The coincidence H+ yield from the H2O/SiO2/Si(111) is found to be enhanced at the electron kinetic energies corresponding to O(KVV) Auger transitions. This result presents a direct and clear evidence of Auger stimulated ion desorption mechanism accompanied by the cleavage of a covalent bond. A KVNBVNB Auger process is concluded to lead to ion desorption less efficiently than KVBVNB and KVBVB processes (VNB and VB represent the non-bonding and bonding valence orbitals, respectively).