Valence Band Spectroscopy in the Ultrasoft X-Ray Region (50 to 100 A)

Transitions from the valence electron levels into the first relatively sharp inner sub-shell levels result in characteristic x-ray emissions in the 100-200 eV region. These spectra sensitively reflect the chemical state of the atoms which are representative of the submicron thickness of the sample surface under low energy x-ray excitation and of the first few molecular layers of the sample under electron excitation.An optimized measurement method for this 50-100 A spectral region is “based upon single crystal spectrometry using a lead stearate analyzer which has high dispersion and efficiency and an energy width of about one eV in this wavelength range. Spectra are recorded using “tuned” proportional counter detection. In the work reported here, low energy x-ray excitation is used in order to minimize the possibility of radiation damage of the sample.Each spectrum is calibrated for both energy and instrument transmission using known, sharp M lines of elements such as molybdenum, zirconium and yttrium which will bracket the spectraj. range under measurement. A simple method has been developed for "stripping" from the measured spectra the Lorentzian crystal width and the Gaussian collimation width in order to allow an estimation to be made of the actual emission line widths as well as the relative intensities.In this report, as an illustrative application example, S-LII, III spectra are presented for a series of sulfur compounds in "both solid, and gas states. Manne's approximate molecular orbital interpretation of the x-ray emission spectra has been adopted and extended to apply to the LII, III spectra for second row elements.