EPITAXIAL GROWTH OF SiO₂ ON Mo(112)

Abstract

A new preparation is reported which, for the first time, results in a thin, crystalline SiO2 film on a Mo(112) single crystal. The procedure consists of repeated cycles of silicon deposition and subsequent oxidation, followed by a final annealing procedure. AES and XPS have been used to control film stoichiometry. LEED pictures of high contrast show a hexagonal, crystalline SiO2 overlayer with a commensurate relationship to the Mo(112) substrate. The wetting of the substrate by the film has been investigated by LEED, XPS and TDS, revealing that the film covers the substrate completely.

On the geometrical and electronic structure of an ultra-thin crystalline silica film grown on Mo(112)

“…1d). Therefore, the preparations reported by Schroeder et al [15] and Chen et al [28], which include annealing in oxygen ambient, must have resulted in the "Orich" films in our notation.…”

“…Originally, Schroeder et al [15] used four cycles of Si deposition at 300 K and oxidation at 800 K in 5x10 -6 mbar O 2 . Subsequently, the film was annealed stepwise up to 1100 -1250 K in 10 -5 mbar of O 2 until the films exhibited a c(2x2)-Mo(112) structure by LEED.…”

“…Although the first attempts to synthesize crystalline silica films can be traced back to the early 90's [13,14], the preparation of well-ordered thin silica films was reported only recently by Schroeder et al [15][16][17][18] using a Mo(112) substrate, who basically modified a recipe originally applied to the Mo(100) and Mo(110) substrates by Goodman and coworkers [13,14]. The film exhibited a c(2x2) diffraction pattern with respect to Mo(112), and showed at least two oxygen species in X-ray photoelectron spectra (XPS) and a strong phonon absorption band centered at 1048 cm -1 observed by infrared reflection absorption spectroscopy (IRAS).…”

“…Based on attenuation of the substrate signals in Auger electron spectroscopy (AES) and angular-resolved XPS spectra, Schroeder et al [15] came to the conclusion that the well ordered films are 5-8 Å in thickness. Based on AES data Kim et al [24] also reported on the film thickness of 7-8 Å.…”

Realization of an atomic sieve: Silica on Mo(112)

“…As pore diameters in zeolites and silicates are adjustable between 5-100 Å, size-selective adsorption and reaction schemes can be realized. 4,5 The system consists of an ultra-thin silicon-dioxide film that is prepared on a Mo(112) surface. 6,7,8 The fundamental building blocks of the oxide layer are six-membered -Si-O-rings, enclosing a hole of 3-4 Å diameter.…”