Electron energy-analyzer broadening

The resolution of overlapping spectral peaks depends on their separations, intensities, and widths. Whereas separation and intensity are predominantly functions of the sample, peak width is strongly influenced by the instrument s design. The observed line is a convolution of the natural line, a function characteristic of inelastically scattered electrons that produces a skewed base line, and the instrument function. The instrument function is, in turn, the convolution of the x-ray excitation line shape, the broadening inherent in the electron energy analyzer, and the effect of electrical filtering. This description is summarized in Table I. 

Still higher resolution studies of evaporated films of y-Ce and a-Ce were carried out very recently by Patthey et al. (1985). They used the inherently sharp He resonance lines at 21.2 and 40.8 eV and a very low pass energy in their electron energy analyzer to achieve an overall resolution of 20meV. To reduce thermal broadening of the spectra of y-Ce, they cooled their samples to 150 K. (The p phase should be the stable phase at this temperature, but its spectrum is similar to that of y-Ce, based on lower energy resolution results of Wieliczka and Olson (1983).) The results of fig. 15 show that a-Ce has a structured peak at the Fermi level, while y-Ce has a peak at the Fermi level and another peak about 350 meV lower. These two were unresolved in earlier measurements and they were ascribed to spin-orbit-split 4f5 2 4f7/2 levels (see later). 

The precise nature of broadening due to the energy analyzer depends on analyzer design and may not be easy to compute, even in the ideal case. Measurement may also be difficult. The determination of the broadening function sM(x) may be attempted with the aid of narrow spectral lines or spectral lines of known shape, or by supplying the analyzer with electrons from a thermionic source (Lee, 1973). 

The broadening due to the analyzer depends on the energy at which the electrons travel through the analyzer and the width of the slits between the energy filter and the actual detector. The analyzer contribution to the line width becomes irrelevant at low pass energies, however, at the cost of intensity. 

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