An apparatus for determining the secondary electron emission properties of nonconductors
The apparatus described allows the measurement of the secondary emission coefficient and the secondary electron energy distribution from nonconducting surfaces. The potential of the nonconducting surface is stabilized by a cathode very close to it. The use of an oscillatory primary beam allows a measurement of the secondary emission coefficient. The application of a sinusoidally modulated voltage sawtooth allows the determination of the emitted electron energy distribution and measures the potential of the emitting surface. The performance of the apparatus is demonstrated by results obtained from an amorphous magnesium oxide coating.
AC Methods for the Determination of Photoelectron Energy Distributions
The sensitivity of the Spicer‐Berglund retarding‐potential method for the determination of photoelectron energy distributions may be improved by an order of magnitude by a more effective cancellation of the capacitative component of the signal. A double modulation technique, in which energy distributions can be traced from saturated photocurrents of the order of 10−11 A, is also described. This method can be employed to eliminate steady thermionic or photoelectric currents many orders of magnitude greater than that under investigation.
Measurement of Photoemitted Electron Energy Distributions by an ac Method
By means of the ac retarding potential method, the energy distribution of photoemitted electrons can be measured much more rapidly and conveniently than is possible by conventional dc methods. In the ac method, a small (about 20 mV) ac voltage (24 cps) is added to a slowly varying (about 1 V/min) retarding potential and the in‐phase ac component of the photoemission signal is measured. For the conventional dc techniques, it is necessary to impose very stringent stability conditions on the light source and measuring equipment. Since, in the ac method, the derivative of the I‐V characteristic is taken electronically (to give the energy distribution) and is averaged over many cycles, the stability requirements are relaxed by a large amount and data may be obtained much more quickly and conveniently. With the complete system described, resolutions of about 0.1 eV have been attained and small signal conductances (ΔI/ΔV) smaller than 10−11 mhos have been measured.