Study of deposit associated with discharge in micro-pixel gas chamber

We found some deposits associated with discharge on dielectric (polyimide) substrates in “Micro-Pixel Gas Chambers” (μ-PIC) operating with Ar/C2H690/10. Secondary electron images taken with a scanning electron microscope (SEM) revealed that they were a conductive material. Auger electron spectroscopy clearly showed that their main component was carbon (98%). Their origin was clarified using spark tests in which a single pixel was sparked a specific number of times. Secondary electron images clearly showed that discharge occurred in the narrow gaps between the electrodes. With a Ar/C2H650/50 gas mixture, the amount of carbon deposited depended on the number of sparks. The drop in the applied voltage after the test depended on the number of sparks. With pure N2 gas, no deposits were clearly found, however, a decrease in the applied voltage after the tests was observed. This can be attributed to carbonization of the polyimide surface. Although the SEM images did not show clear proof of this, this carbonization could contribute much less than the ethane dissociation.