Implications of specimen preparation and of surface contamination for the measurement of the grain boundary carbon concentration of steels using x-ray microanalysis in an UHVFESTEM

The purpose of the present investigation was to gain an understanding of th e nature of the carbon contamination on the surface of standard steel trans mission electron spectroscopy (TEM) specimens, the effect of exposure of a clean specimen to normal laboratory air, and the efficacy of plasma-cleanin g treatments. This knowledge is a necessary prerequisite to the development of appropriate specimen preparation and/or specimen cleaning methods. X-ra y photoelectron spectroscopy in combination with argon ion beam profiling w as used to characterize the specimen surfaces of X65 steel and 316 stainles s steel. The only clean carbon-free surface obtained was that during argon etching of the sample in the surface analysis chamber. Any exposure of a pr eviously cleaned sample to laboratory air resulted in a rapid carbon (hydro carbon) contamination of the sample surface and the development of surface oxidation, Plasma cleaning with subsequent exposure of the specimen to the laboratory air also resulted in a carbon-contaminated surface. This suggest s that procedures of preparation of TEM specimens of steels outside an ultr ahigh vacuum chamber are unlikely to result in the lowering of contaminatio n rates on specimens to levels where measurements for carbon in the grain b oundaries are possible. What is needed is a cleaning system as an integral part of the specimen insertion system into the field-emission scanning tran smission electron microscope. This cleaning could be carried out by argon i on etching. Copyright (C) 2000 John Wiley & Sons, Ltd.