Dw. Sloan et al., INTERACTION OF 50 EV ELECTRONS WITH D2O ON GAAS(100), Journal of vacuum science & technology. A. Vacuum, surfaces, and films, 14(1), 1996, pp. 216-222
Citations number
38
Categorie Soggetti
Physics, Applied","Materials Science, Coatings & Films
The interaction of 50 eV electrons with D2O, dosed on GaAs (100) at 10
0 K, has been investigated using temperature programmed desorption (TP
D), x-ray photoelectron spectroscopy, and high resolution electron ene
rgy loss spectroscopy. There is good evidence that water adsorbs molec
ularly and does not dissociate thermally in TPD. The TPD spectra chang
e with coverage. At the lowest exposures, the desorption is broad, pea
ked near 200 K, and exhibits a long tail extending to 600 K, the latte
r a characteristic of every exposure. As the exposure increases, this
peak moves slightly to lower temperatures (196 K) and a second peak ap
pears at 156 K; these two then merge to an unresolved peak at 176 K wh
ich moves downward to as low as 169 K. Dissociation and desorption are
induced by electron irradiation at 100 K; the O (1s) binding energy s
hifts downward (533.2-531 eV) and broadens and the vibrational spectra
take on characteristics expected for O-D formation and the desorption
of molecular water. Electron-induced O-D bond breaking is limited to
D2O molecules located at the GaAs interface. During heating (up to 600
K) after electron irradiation, there is (1) some D2O and D-2 desorpti
on, (2) depending on the annealing temperature, a lower O(1s) binding
energy (530 eV at 400 K, 529 eV at 600 K), and (3) loss of all vibrati
onal features attributable to D. These facts are all consistent with f
orming a small amount of surface oxide, possibly at defect sites. The
D2O removal process is adequately described as first order with an upp
er bound for the cross section, sigma(D2O), of 1.16 X 10(-17) cm(2). T
he measured isotope effect, sigma(H2O)/sigma(D2O), was 2.57. (C) 1996
American Vacuum Society.