AES electron beam induced fragmentation of molecular water adsorbed on copper

Abstract

The effect of electron beam irradiation with energies ranging between 1000 and 2000 eV on adsorbed water molecules was studied in an Auger spectrometer with a single pass CMA. The M₂₃ VV transitions doublet of Cu at 59–61 eV and the LMM transitions between 600 and 940 eV were monitored simultaneously while exposing the Cu sample at 170 or 300 K to water, until the oxygen KLL signal took a steady value. The target current was also monitored intercalating a picoammeter between sample and ground. Both, polycrystalline and Cu(100) samples were studied.

As the water exposure progressed, the M₂₃VV doublet became unresolvable and the sample current took even more negative values. A fairly good correlation was found between the oxygen signal and the sample current, or the doublet resolution independently of the sample temperature. The kinetics of the changes suggest, however, that the water molecule must be adsorbed to be dissociated. Annealing at 673 K restores the original doublet resolution. A lateral composition profile taken after annealing (14 h at 300 K or 5–10 min at 573 K) indicated that the oxygen concentration is maximum at the beam incidence point, dramatically decreasing at 0·4 mm all around. With XPS the formation of a Cu₂O layer only in the beam damaged region was established, beyond any doubt.