CONTAMINATION IN ANALYTICAL ELECTRON-MICROSCOPY AND IN ALCHEMI

The amount of contamination was characterised quantitatively by the nu mber of emitted carbon K-alpha X-ray photons. The magnitude of the cha nnelling effect was plotted as a function of contamination. The Al/Si ratio varied by 80%, while the O/Si ratio only changed by 10%, ruling out x-ray absorption as the major cause of the observed variation. The randomised direction of bombarding electrons (caused by the contamina tion hill) was identified as the origin of the decreasing channelling effect as contamination increased. Dependence of contamination on the method of sample preparation and experimental condition were measured. Contamination affects a disc-shaped area of the sample with a diamete r 10 times larger than that of the visible contamination hill. Floodin g with a high dose of electrons was found to produce a 2 minute interv al almost free from contamination for subsequent analysis. Reduced con tamination facilitated the identification of a carbide inclusion in a steel matrix.