Investigation of Carbon Contamination of Mirror Surfaces Exposed to Synchrotron Radiation

摘要

In a systematic investigation gold coated silicon substrates were irradiated with filtered synchrotron radiation under varying conditions. The thickness of the contaminant was measured with a VUV reflectometer through the observation of interference structures. In addition the overall photocurrent which varies with the thickness of the contaminant could be measured. All results show that the cracking process is caused predominantly by the photoelectrons emitted and not by the primary photons. This is specifically supported by the observation of two different growth rates: an initial fast rate up to about 50 A thickness due to the high photoyield of gold and an asymptotic growth rate of about 10% the initial rate due to the much smaller yield of carbon. A rate equation deduced from a simple model describes the dependence of the growth rate on residual gas pressure and temperature in good qualitative agreement with the experimental results. (ERA citation 11:006077)