Energy calibration work function measurement

Figure 13 shows a photocell used recently for work-function measurements (43). A metal coating inside the cell serves as the anode, and B is the cathode, which may be a metal foil or a film previously evaporated from a filament at C. Also provided at C are a W emitter for bombarding the cathode surface and a Pt electrode for thermally dissociating gas molecules. The monochromatic light which passes through the quartz window Q strikes the cathode B, and its energy can be measured by a calibrated photocell. 

There are two practical difficulties. One is the measurement of the very small photocurrent, which may be as low as 10" amp, requiring the use of a vibrating reed electrometer or similar instrument. The second is that, for work functions above 5 eV, Vq lies in the far ultraviolet. This makes the study of some adsorptions very difficult and 6 eV is about the practical limit of such measurements. A suitable light source is the quartz mercury arc. The energy of the incident beam can be measured with a calibrated photocell, a vacuum thermopile or a radiometer. A suitable cell for adsorption studies is shown in Fig. 11. The sample being studied forms the cathode B. It can be a metal foil or a film formed by evaporation from the filament E. A wire C is fused through the glass to make contact with the... 

Because the work function of a particular spectrometer is an instrumental constant, it can readily be determined either by direct measurement or by reference to some standard electron energy. For example, the well known 83.8-eV binding energy of the 4/7,2 level of gold is often used to calibrate the spectrometer work-function. The work function can then be subtracted from the right side of Equation 15.1 to give... 

MCA emulators are concerned mainly with the acquisition of the spectrum data. They emulate the functions of the hardwired multichannel analyser. Examples are the Canberra System 100 (no longer available) and ORTEC Maestro-32. These programs will provide for energy calibration but not necessarily width or efficiency calibration. Peak area measurement and peak search may be provided but this is unlikely to be as complex as a dedicated off-line analysis package. In our context, I will define online as being work done interactively with data held and displayed in the MCA emulator. Off-line would then be work done with spectra stored on computer disk. 

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