Surface Science Aspects of Contamination in Tem Sample Preparation

Abstract

AbstractWith the advent of the modem analytical electron microscope with its ultrahigh vacuum conditions, extremely high current density in a very small probe, and its light element analysis capability, it is imperative that contamination of the TEM sample, particularly by hydrocarbons, is eliminated. The degree of cleanliness required for analysis using surface sensitive techniques is also much greater than for other forms of analysis. Contamination of samples can occur (a) prior to analysis, due to the way samples are prepared or handled, or (b) during analysis. Examples of surface contamination prior to analysis and during analysis will be given, in order to illustrate their effect on an analysis.Polished Si, Ni, and Ti bulk samples and pre-thinned TEM Ni and Ti samples were intentionally contaminated by two methods. One set of samples was put on a liquid nitrogen cooled stage for one hour in a diffusion pumped Gatan Duomill in which the liquid nitrogen cold trap above the diffusion pump was intentionally left warm. The other set was contaminated by dipping them into a 100 ml solution of acetone containing 0.04 g of an acetone-soluble low temperature wax. Two commercially available plasma cleaners, specifically designed for eliminating hydrocarbon contamination, were used to clean the samples. The bulk samples were examined with x-ray photoelectron spectroscopy and the TEM samples were examined in a 200 keV analytical TEM. The results from these experiments will be discussed.