We found some deposits associated with discharge on dielectric (polyimide) substrates in "Micro-PixelGas Chambers" (μ-PIC) operating with Ar/C_2H_690/10.Secondary electron images taken with ascanning electron microscope (SEM) revealed that they were a conductive material. Auger electronspectroscopy clearly showed that their main component was carbon (98). Their origin was clarifiedusing spark tests in which a single pixel was sparked a specific number of times. Secondary electronimages clearly showed that discharge occurred in the narrow gaps between the electrodes. With aAr/C_2H_650/50gas mixture, the amount of carbon deposited depended on the number of sparks. Thedrop in the applied voltage after the test depended on the number of sparks. With pure N2 gas, nodeposits 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 showclear proof of this, this carbonization could contribute much less than the ethane dissociation.
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