Electrostatic Charge Distribution on Ultrahigh Vacuum Cleaved Silicates

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Abstract
Recent measurements of relatively strong long-range electrostatic attractive forces, produced by ultrahigh vacuum cleavage of silicates, prompted the design and fabrication of a special UHV system to measure the charge distributions. The system is described in this paper, together with preliminary results from the experiment. Charge distributions found to date have varied from dipolar to octapolar shapes on the face of cylindrical samples in excess of 1 esu/cm2. A relationship appears to exist between the orientation of the multipolar distributions and the crystallographic axes. Results from the first cleavages of orthoclase (nominally, KAlSi3O8) at 10−10 Torr indicate that there are at least two discharging mechanisms: first, the charge decays to one half its initial (extrapolated to zero) value in 1.5 h due to gas adsorption; second, it then decays very slowly with a half-life of at least 76 days. Irradiation with uv light causes discharge. When the pressure in the system is raised towards atmospheric with dry nitrogen, the charge is stable (to a first order of approximation) up to pressures in the 10-μ range. Discharge in bursts, as the pressure is raised, is readily explained by the Paschen sparking potential relation for gaseous discharges.

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