Glass, a Disturbing Factor in Physical Electronics Measurements

Abstract

Evidence has been obtained that Pyrex and other glasses are not desirable construction materials in certain types of physical investigations such as clean surface experiments and measurements involving small ion or electron currents produced at low pressures. Pyrex appears to decompose at temperatures above about 350°C liberating water vapor and decomposition products which are not readily pumped out of a vacuum system. Pyrex also appears to chemically sputter in the presence of gaseous ions such as nitrogen or oxygen, thus liberating contamination into the system which is not readily removed. Sodium and potassium have been identified among the decomposition products and it is well known that these atoms are desorbed as ions from many metal surfaces when the surface is heated. Thus decomposition and sputtering of glass can produce spurious ion currents under certain conditions. The decomposition products can possibly account for insulating films on metal electrodes which charge up or polarize under charge bombardment.