Quantification of carbon contamination resulting from sample preparation in transmission electron microscopy

Transmission electron microscopy (TEM) is a powerful technique for high resolution investigations of specimens that is of much current research interest. Often, TEM measurements are impaired by carbon contamination, which arises when volatile organic components (VOCs) are reduced by the electron probe and form amorphous carbon on the studied sample. This results in a layer of contamination that increases the overall thickness of the sample and therefore decreases the quality of images and spectroscopic data obtainable from TEM investigations. In the course of the work reported here, carbon contamination in TEM experiments resulting from the processes involved in sample preparation was investigated.

One aim of this work is the analysis of solvent contamination resulting from outgassing at environmental TEM pressure, which is studied by proton-transfer-reaction mass spectrometry. In addition, the adsorption of contaminating species to the surfaces of the octagon and removal of these VOCs by applying high vacuum and plasma cleaning is discussed.

Another part of this thesis focuses on carbon contamination accumulated by electron beam exposure, which was quantified by electron energy loss spectroscopy thickness measurements. Here, specimens were prepared with different solvents that are commonly used either in chemical synthesis or in the sample preparation process by electron microscopists. The resulting contamination was compared as a function of the drying time and the time a sample remains in the microscope. The efficiency of several established mitigation strategies addressing carbon contamination was studied. Furthermore, utilizing a self designed and built sample cleaning station for the removal of hydrocarbon contaminants by vacuum is discussed as an additional approach for mitigating carbon contamination.


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