QUANTITATIVE ELECTRON-PROBE MICROANALYSIS OF NITROGEN

Quantitative electron probe microanalysis of nitrogen has been performed on 18 nitride specimens in the voltage range of 4-30 kV. A conventional lead stearate and a new W/Si multilayer analyzer crystal (2d = 5.98 nm) were used simultaneously. The net peak count rates on the latter crystal were approximately 2.8 times higher than on the lead stearate crystal. In addition, significant improvements in the peak to background ratios were achieved, which proved critical when dealing with difficult nitrides such as ZrN, Nb2N, and Mo2N. A most conspicuous feature of the new crystal, however, is its effective suppression of higher-order reflections in the wavelength range of N-K-alpha. As a result, backgrounds are free of interfering lines and spectral artifacts, which facilitates accurate background determination. Two procedures for the analysis of nitrogen in the presence of titanium are also discussed. One procedure is based on the assumption that the area-peak factor (APF, integral k-ratio/peak k-ratio) of the N-K-alpha peak in Ti-N compounds relative to a nitrogen standard (Cr2N) has a fixed value which can be used in order to separate the Ti-iota-iota peak from the N-K-alpha peak. Extensive tests on a number of compositions in the Ti-N system have shown that it is possible to do quantitative analysis of nitrogen in Ti-N compounds with a relative accuracy of better than 5%. For very low levels of nitrogen (below 15 at%) the APF method was found unsuitable. In such cases, however, the well-known multiple least-squares digital-fitting techniques appeared to do an excellent job. In order to account for the effects of peak shape alterations in the N-K-alpha peak, all nitrogen spectra were recorded in integral fashion and compared with those of the Cr2N standard. The shape alterations for the N-K-alpha peak were much smaller than for B-K-alpha and C-K-alpha radiations: The observed values for the area-peak factor relative to Cr2N differed less than 5% from unity. The present work has resulted in a database containing 144 integral k-ratios for N-K-alpha and 149 peak k-ratios for the x-ray lines of the metal partners in the nitrides. Our own Gaussian phi(rho-z) matrix correction procedure "PROZA," used in conjunction with a set of improved mass absorption coefficients, yielded excellent results for the nitrogen data: An average value of k(calc)/K(meas) of 1.0051 and a relative root mean square deviation of 3.99%.