Nand Lal Misra

Total reflection X-ray fluorescence: A technique for trace element analysis in materials

Total Reflection X-ray Fluorescence (TXRF) is a variant of Energy dispersive X-ray Fluorescence (EDXRF). It is a comparatively new method of trace element analysis and finds its application in various research areas of material development and processing. The versatility of TXRF is due to (i.) requirement of very less amount of sample (ii.) its capability to analyse very low concentrations and (iii.) capability of analysing surface and shallow layers up to a depth of few nanometers profiling up to few nanometers depth in materials. Presence of impurities in semiconductor wafers affects the quality of the wafer significantly. Analysis of thin wafers is one of the several applications of TXRF where no other technique can compete with it. In the present paper the principle, advantages and some applications of this technique are briefly summarised.

Galvanic reactions involving silver nanoparticles embedded in cation-exchange membrane.

Galvanic reactions of Hg(2+), Rh(3+), and AuCl(4)(-) ions with Ag nanoparticles positioned near the surface and throughout the matrix of host poly(perfluorosulfonic) acid membrane have been studied.

A novel vacuum spectrometer for total reflection x-ray fluorescence analysis with two exchangeable low power x-ray sources for the analysis of low, medium, and high Z elements in sequence.

The extension of the detectable elemental range with Total Reflection X-ray Fluorescence (TXRF) analysis is a challenging task. In this paper, it is demonstrated how a TXRF spectrometer is modified to analyze elements from carbon to uranium. Based on the existing design of a vacuum TXRF spectrometer with a 12 specimen sample changer, the following components were renewed: the silicon drift detector with 20 mm(2) active area and having a special ultra-thin polymer window allowing the detection of elements from carbon upwards. Two exchangeable X-ray sources guarantee the efficient excitation of both low and high Z elements. These X-ray sources were two light-weighted easily mountable 35 W air-cooled low-power tubes with Cr and Rh anodes, respectively. The air cooled tubes and the Peltier-cooled detector allowed to construct a transportable tabletop spectrometer with compact dimensions, as neither liquid nitrogen cooling for the detector nor a water cooling circuit and a bulky high voltage generator for the X-ray tubes are required. Due to the excellent background conditions as a result of the TXRF geometry, detection limits of 150 ng for C, 12 ng for F, and 3.3 ng for Na have been obtained using Cr excitation in vacuum. For Rh excitation, the detection limits of 90 pg could be achieved for Sr. Taking 10 to 20 μl of sample volume, extrapolated detection limits in the ng/g (ppb) range are resulting in terms of concentration.

New thorium–bismuth oxide solid solutions with oxygen vacancy induced tunable ferromagnetism

A combined X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) spectroscopy, and magnetic and electron paramagnetic resonance (EPR) study on defect-induced magnetism in Th1−xBixO2−δ (0 ≤ x ≤ 0.3) solid solutions is presented in this paper. The solid solutions were prepared through a solid-state reaction route. The XRD patterns of the solid solutions suggest Bi dissolution up to 30 at% in the ThO2 matrix. The EXAFS study at the Bi and Th L3 edges indicates the formation of oxygen vacancies near Bi sites with an increasing trend with the Bi at% in the solid solutions. The magnetic measurements in field cooled (FC) and zero field cooled (ZFC) mode indicate an interesting observation involving ferromagnetic ordering with Curie temperature at around 70 K. The possibility of a spin glass-like phase was conclusively ruled out by a memory effect test experiment. The EPR studies revealed the presence of two different signals at g ∼ 2.05 and 2.25 due to the paramagnetic oxygen vacancy () and ferromagnetic resonance (FMR). The constant increase in intensity of the FMR signal with increasing doping level corroborates well with the increasing saturation magnetization value in magnetic measurements. By lowering the measurement temperature, this FMR signal showed an increase in its intensity along with continuous broadening and shift of the resonance field position to the lower field, which further signifies the presence of ferromagnetic ordering due to the paramagnetic oxygen vacancy in the Th1−xBixO2−δ solid solution.

Preparation, characterization and thermal behavior of K2U4O13-Rb2U4O13 solid solutions

Abstract The preparation and characterization of (K1−xRbx)2U4O13 solid solutions has been studied for the x values in the range of 0u2009−u20091. The solid solutions were prepared by heating K2U4O13 and Rb2U4O13 in required stoichiometry at about 600–700u202f℃ for about 50u2009h in air atmosphere. The XRD patterns of the products suggest formation of the solid solutions in full composition range of Rb2U4O13 and K2U4O13. The cell volume of the crystal unit cell of solid solutions changes linearly with Rb atom % in (Rbu2009+u2009K) present in the solid solutions and follows Vegards law. The solid solutions when heated in Ar/He atmospheres at 900u2009℃ produce corresponding low valent uranate solid solutions (K1−xRbx)2U4O12 or their mixtures.