Preferential epitaxy of evaporated thin films produced by charged particles on NaCl substrates

Abstract

Thin films of Sn, Fe, Cr, Au, and cadmium and zinc chalcogenides (several tens to 600 å in thickness) were evaporated onto air-cleaved and vacuum-cleaved (001)NaCl substrates at temperatures ranging from 25 to 400°C, except that the upper limit for Sn was 150°C, in vacuums of 10 −6 and ∼10 −8 Torr. In the absence of charged particles or an electric field, two or more epitaxial orientations generally coexisted in the films. However, when the substrate was subjected to electron bombardment (∼10 12 electrons cm 2 ·sec, at 200–500 V) or a lateral electric field (dc 100–300 V cm ) during the evaporation, preference of a single orientation (preferential epitaxy) was observed in the films. Similar effects were observed also when the electron bombardment was applied to the substrate surface immediately before or in the very early stages of the deposition, or to the incident evaporation vapor. These results indicate that lattice defects of the substrate surface, produced by charged particles or an electric field, play very important roles in determining epitaxial orientation during the very early stages of film growth.