The effect of Al3+, Na+ and Li+ impurities on the charging ability of single-crystalline quartz under electron beam irradiation

Quartz crystals which are either natural or synthetic, always contain some impurities in the ppm range. Of the possible impurities that may be present, most notable is the trivalent substitutional cation Al3+ for Si4+ and interstitial alkali ions (M+) such as Na+ and Li+. In the present paper, the charging ability of the quartz samples with impurities under electron beam irradiation was investigated by a time-resolved current method and a mirror image method employing a scanning electron microscope (SEM). The experimental results obtained by both methods are consistent and reveal that the quartz sample with least concentration of free-interstitial alkali ions (M+) has highest charging ability. An analysis reveals that the defects due to electron beam irradiation play an important role in electron trapping, while the free-interstitial alkali ions contribute to the sample conductivity and release the trapped charge.