Electron stimulated desorption of the metallic substrate at monolayer coverage: Sensitive detection via 193 nm laser photoionization of neutral aluminum desorbed from CH3O/Al(111)

A fortuitous overlap between the gain profile of the 193 nm ArF excimer laser and the Al autoionizing transition 2S1/2 (512753 cm-1) left-arrow 2P0J has been exploited in the direct observation of substrate metal atoms in an electron simulated desorption (ESD) process from the monolayer adsorbate system CH3O/Al(111). The identity of the mass 27 photoion was established as Al+ by (1) isotopic substitution of 13C in the methanol employed for methoxy formation, and (2) tunable laser scans utilizing the 2DJ (J=3/2, 5/2) intermediate levels at ∼32436 cm-1 and a 248 nm ionization step. An ESD yield of ∼x10-6 Al atoms/(electron at 1 keV) was established by comparison with a sputtering experiment in the same apparatus. Velocity distributions measured for the desorbed Al species showed some differences in comparison with methoxy velocity data: a slightly lower peak velocity and a significantly less prominent high-velocity component. 10 refs., 4 figs