Features of the X-ray microanalysis (electron probe microanalysis) of nitrogen-containing compounds

The goal of this study is development of the method for studying the chemical composition of natural and synthetic nitrogen-containing compounds using electron probe microanalysis (EPMA) and the use of EPMA for identification of the form of occurrence of light elements (C, N, O) in complex anions and cations. The analysis was performed using Kα lines attributed to electronic transitions from valence 2p states to internal 1s states. The characteristic features of the Kα spectra of C, N, O, which affect the correctness of the EPMA results were revealed to introduce the corrections that take into account the integrated line intensity, the effect of self-absorption of the nitrogen line and absorption of the background by nitrogen.

The method is intended for studying different nitrogen-contained samples including diamonds obtained by detonation synthesis. The surface of these samples is usually covered with a layer oxygen- and nitrogen-containing functional groups. The main problem associated with the experiment is determination of optimal conditions for excitation and registration of Kα lines. The accelerating voltage used is 10 kV, the beam current is 50 – 120 nA. In the analysis in the differential mode of recording the signal amplitude we use the same (for all samples) empirical formula to describe the shape of the background intensity curve in the vicinity of the nitrogen line. The resistance of the samples to the impact of the electron beam is increased when using a raster mode with a linear size of 20 – 40 μm and sample movement within the area ~100 × 100 μm² (if possible with allowance for the sample size). The concentrations of the determined elements were calculated using the PAP program with B. L. Henke absorption coefficients. The detection limits of carbon, oxygen and nitrogen at a current of 80 nA were 0.33, 0.46 and 0.86 wt.%, respectively.

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