HOMOEPITAXIAL GROWTH INVESTIGATED BY HIGH-RESOLUTION HE ATOM SCATTERING - NACL ONTO NACL(001)

The homoepitaxial growth of NaCl vapor deposited onto the cleaved (001) surface of NaCl was studied with a nearly monoenergetic (DELTA-E/E congruent-to 2%) He atom beam. In comparison with reflection high-energy electron diffraction, the He atom is unique for epitaxial studies in that it is uncharged, nondestructive, and sensitive only to the outer surface layer. The oscillations in the scattered intensities of the specular and Bragg peaks due to the layer-by-layer growth were examined by measuring the angular distributions as a function of coverage, surface temperature (150-400 K) and incident He atom wave vector (6-8 angstrom-1). The periodic variation in the relative heights of the specular and Bragg peaks with DELTA-k(z) = \k(fz) - k(iz)\ showed that under these conditions the growth is two-dimensional with a terrace height of 2.8 angstrom or half the bulk face-centered-cubic lattice spacing. In addition, scattering cross sections for adsorbed NaCl at low coverages were determined with respect to these same parameters. The cross sections for substrate temperatures above 250 K decline rapidly, which suggests that surface diffusion becomes much more rapid above, this point. Previous studies had reported high mobilities down to temperatures considerably lower.