MEASUREMENT OF LOCALIZED SURFACE POTENTIAL DIFFERENCES

There is considerable current interest in the detection and measurement of surface potential difference and charge density on metal oxide layers and on dielectrics. The Kelvin vibrating capacitor method has been developed so as to give a high degree of localization in the measurement of surface potential. This apparatus was designed and used to measure the potential distribution left on a cathode or anode surface by the track of a 1000 A electric arc. A vibrating gold wire probe senses an area of about 0·4 mm2 as against the more usual few square centimetres employed in surface potential measurement. A MOST is the detector, and a d.c. backing-off potential enables a null measurement to be made on a cathode-ray oscilloscope after frequency-selective amplification. A sensitivity in measurement of about 0·01 v on the surface under examination is obtained.