Growth and Characterization of Crystalline Silica Films on Pd(100)

Abstract

Silica films grown on Pd(100) were characterized by Auger electron spectroscopy, low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). While no evidence of long-range order could be detected for films grown below 600 K, STM images of these films nevertheless revealed flat surfaces through which the step-terrace structure of the substrate could be seen. Annealing the films in 10–6 Torr of O2 above 975 K resulted in crystalline bilayers that produced hexagonal LEED patterns with a periodicity twice that of the substrate and with one of the overlayer close-packed directions paralleling Pd[011]. The extent of the crystalline domains was limited to typically five repeat units along two of the three close-packed directions of the film but was tens of repeat units long along the third. The lattice matching to the substrate expands the spacing in the bilayer on Pd(100) compared to bulk crystalline SiO2 and bilayers observed on other substrates; as a consequence, it is suggested that the...