Nondestructive analysis of single crystals of selenide spinels by X-ray spectrometry techniques

The paper presents possibilities and difficulties in nondestructive analysis of small multielement single crystals performed by means of X-ray spectrometry techniques: micro-X-ray fluorescence spectrometry (μ-XRF), energy-dispersive electron probe microanalysis (ED-EPMA), and X-ray photoelectron spectroscopy (XPS). The capability of the X-ray spectroscopy techniques in elemental analysis is demonstrated with the single crystals of selenide spinels of the general formula M(x)N(y)Cr(z)Se(4) (M(+2) and N(+3) are, for example, Zn(+2), V(+3), Ga(+3), Cd(+2), In(+3), and Sb(+3)). The results of the nondestructive analyses (μ-XRF, ED-EPMA, and XPS) are compared with those obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) and wavelength-dispersive X-ray spectrometry (WDXRF) following sample digestion. The present study shows satisfactory agreement between the results of μ-XRF analysis performed using the standardless fundamental parameter method and the results obtained with the WDXRF and ICP-OES analyses. If the measured single crystal is precisely positioned, the difference between μ-XRF and wet analysis (WDXRF and ICP-OES) does not exceed 5% rel. The reliable results of ED-EPMA can be obtained only if the measured area is sufficiently large, i.e., of 200 × 300 μm. Even if this condition is fulfilled, the relative difference between the ED-EPMA and the wet analysis may reach 10% rel. In case of the XPS analysis, the accuracy of results depends on the proper preparation of the sample surface. It should be free of contamination that can be obtained by scraping in situ in ultrahigh vacuum. The ion etching, commonly used for cleaning the surface, leads to preferential sputtering; therefore, the reliable results cannot be obtained.