Detection and Localization of Eu on Biosilica by Analytical Scanning Electron Microscopy

Algae like diatoms are widely studied as a means to remediate anthropogenically contaminated sites. In the present study, CL (cathodoluminescence) and EDX (energy-dispersive X-ray) spectroscopy in an SEM (scanning electron microscope) were optimized for the detection of Eu(III) sorbed on diatom biosilica. The required stability of biosilica under a focused electron beam was extensively investigated. Using experimentally determined data of thermal properties, the temperature increase within biosilica exposed to an electron beam was simulated by finite element calculations based on results from Monte Carlo simulations of electron scattering. Complementary thermogravimetric studies substantiated a chemical stability of biosilica in a wide temperature range, confirming its suitability for long-lasting SEM investigations. In subsequent EDX measurements, characteristic Eu lines were detected. Eu was found to preferentially accumulate and aggregate on silica fragments. CL spectra were obtained for the Eu(III) reference material, EuCl3. For Eu-loaded biosilica, even parts without detectable Eu signal in the EDX spectra show significant Eu(III) signals in the CL spectra. This highlights the sensitivity of CL in studying f-element sorption. CL data showed that Eu(III) was distributed on the entire surface. In conclusion, this work demonstrates the merit of CL and EDX methods for sorption studies on biogenic materials.

AUTIGENIC MINERAL FORMATION AS AN OBJECTIVE FACTOR OF TRANSFORMATION OF TECHNOGENIC PLACERS

The paper presents the data of analytical scanning electron microscopy and mineralogical methods for studying the morphology and chemical composition of spiral man-induced products, metal spheroids and native gold from the alluvial mining waste. In all samples, including the tungsten “spiral”, mercurous gold was found. The spheroids were diagnosed as lead ones with a fine impregnation of alumina-silicate substance, antimony and copper ones with autigenic isometric and xenomorphic mineral deposits on the surface, etc. The inclusion of carbon in many newly formed minerals confirms the leading role of this element in the process of technogenic mineral formation as a reducing agent. The identified chemical diversity of numerous ore and rock phases is explained by complex physico-chemical processes occurring in the technogenic system, in which not only the residual gold is transformed, but also new ore-mineral complexes, including gold-containing ones, arise.

Nanotube Formation on Ti-15Zr-4Nb-4Ta by Anodic Oxidation

Surface morphology and composition of anodized Ti-15Zr-4Nb-4Ta alloys with nanotube were examined by using X-ray diffractometry and analytical scanning electron microscopy. The Ti alloy consisted of α and β phases. Anodizing to form nanotube on the Ti alloy was carried out using electrolyte of 0.2 wt.% NH4F and 2 Vol.% H2O in ethylene glycol under different potential at from 30 to 60V. SEM observation showed that nanotubes were vertically aligned on surface of the Ti alloy. Inner diameter of these nanotubes varied from 45 to 127 nm with increasing applied potential to the specimen from 30 to 60 V. Surface of the Ti alloy with nanotube was ragged due to the difference in dissolution rate of the internal structure of α and β phases.

Investigations of Critical Structural Defects in Active Layers of GaN-on-Si for Power Electronic Devices

The influence of structural defects in the active layer of GaN-on-Si substrates on the vertical leakage current was studied. The structural defects were analyzed by analytical scanning electron microscopy by means of cathodoluminescence (CL). The leakage current was determined by vertical I-V measurements.Two possibilities were found, which give potential explanations for the variations of the vertical leakage current: i) Threading dislocations, which may partially form leakage paths, were detected by CL imaging. ii) Variations of the carbon doping, which is used to tune GaN to a semi insulating material were revealed by CL spectroscopy.