Analysis and reduction of low-Z contaminants on thin carbon films

Thin, self-supporting foils prepared from arc-evaporated carbon films have been examined for low-Z contaminants ranging from oxygen to calcium. The foils were analyzed with a windowless Si(Li) X-ray detector using the PIXE technique. Foils from different commercial vendors and foils made in-house using different parting agents have been compared, as well as several different solutions for floating the foils from their glass substrates. A technique of treating foils in ultrasonic baths of weak acetic acid has been developed, and is shown to be at least modestly successful at reducing contaminant levels. Evidence of particulate contamination was observed for some of the foils. For additional strength, most of the foils analyzed were coated with collodion, the most dramatic influence of which was to increase the amount of oxygen seen on the foils. (orig.)