Structure of Films Formed During the Deposition of Lubrication Molecules on Iron and Silicon Carbide

Abstract

The structure of films formed on iron foil and silicon carbide wafers during high temperature (700 degrees C) deposition of two lubricants, tricresol phosphate (TCP) and poly phenyl ether (PPE), were studied using scanning and transmission electron microscopy, energy dispersive x-ray analysis, x-ray diffraction, and rate measurements. It was found that on iron foils, TCP decomposes and some of the molecular fragments which remain interact chemically with the iron. A two-layer structure forms. The bottom layer apparently consists of fairly large oriented cementite (Fe3C) crystals. The top layer contains particles of iron phosphide structures. In thicker films, other iron carbides, iron phosphides, and iron-phosphate crystals are also present. The size, chemical content, and degree of crystallinity of the particle structures was found to change with depth of deposit. The rate of deposition declined with time, and this correlated with a decline in the iron concentration near the surface, suggesting that iron plays a catalytic role in film formation. In contrast, the deposition of PPE resulted in the formation of cone-shaped structures, which were primarily carbonaceous but had some iron-containing crystals on their outer surfaces along with evidence of Fe5C2. The rate of deposition remained constant. Finally, on silicon carbide it was found that the rate of deposition was slow (non-catalytic), and that only amorphous particles, rich in phosphorus, formed.