Zheng Zhihong

Synthesis of silicon nitride films by ion-beam-enhanced deposition and their protective properties against oxidation☆

Abstract Silicon nitride films were synthesized on cold-rolled nickel coupons by concurrent electron beam evaporation of silicon and bombardment with nitrogen ions (ion-beam-enhanced deposition). IR, Rutherford backscattering, Auger electron spectroscopy, transmission electron spectroscopy, scanning electron microscopy, energy dispersive ellipsometry and spreading resistance measurements were performed for investigating the properties, composition, and structure of the films. Isothermal and cyclic oxidation tests were carried out on the uncoated nickel coupons and those coated with films of thicknesses up to 10 000 A at 1300 K in a flow of pure oxygen at atmospheric pressure. The films decrease the isothermal oxidation rates, the thicker films having a larger effect. However, films of thicknesses up to 3000 A are not effective for cyclic oxidation. The scanning electron microscopy observation and energy dispersive X-ray analysis revealed that thin films rich in silicon remained in the NiO scale near the scale-substrate interface after both isothermal and cyclic oxidation. Further, much thinner films containing silicon were present on the outer surface of the NiO scales formed on the specimens coated with nitride films of thickness 10 000 A. The oxidation mode initially follows an approximately linear law and approaches a parabolic law later.

SYNTHESIS OF SILICON-NITRIDE FILMS BY ION-BEAM ENHANCED DEPOSITION

Abstract Silicon nitride films with stoichiometric ratio of Si3N4 have been synthesized by concurrent electron beam evaporation of silicon and bombardment with nitrogen ions. The results show that the component ratio of nitrogen to silicon in IBED silicon nitride films can be controlled and predicted by the atomic arrival rate ratio of nitrogen to silicon. IR measurement shows that the characteristic absorption peak of IBED Si3N4 is located at a wavenumber of 840 cm−1. The refractive index ranges from 2.2 to 2.6. RBS, AES, TEM, SEM, ED and spreading resistance measurement were used for investigation of the depth profiles of composition and structure of silicon nitride films synthesized by IBED. An intermixed layer is formed at the interface by the knock on effect, and a silicon enriched layer is observed at the surface region of the film. Normally the films were found to be amorphous, but electron diffraction patterns taken from deposited layer showed a certain crystallinity. The silicon nitride films prepared by IBED have dramatically less oxygen content than that formed by non-ion-assisted deposition.

Properties and structure of silicon nitride films synthesized by ion-beam-enhanced deposition

Abstract Silicon nitride films with a stoichiometric ratio of Si 3 N 4 were synthesized by ion-beam- enhanced deposition (IBED). It was observed that a silicon nitride film formed by IBED is composed of a thin silicon-enriched top layer, a stoichiometric Si 3 N 4 layer and a smooth transition layer at the interface next to the substrate. By detailed theoretical analysis and computer simulation of IR reflection interference spectra, refractive index profiles of the films were obtained. Composition profiles and refractive index profiles were correlated using the Lorentz-Lorenz equation. The fatigue and high temperature oxidation behaviour of metals can be improved using Si 3 N 4 coatings made by means of IBED, and the mechanisms of these are discussed.