The valence band offset value of 2.3 ± 0.2 eV at epitaxial NiO/Al2O3 heterojunction is determined from photoelectron spectroscopy experiments. Pulsed laser deposited thin film of NiO on Al2O3 substrate is epitaxially grown along [111] direction with two domain structures, which are in-plane rotated by 60° with respect to each other. Observation of Pendellosung oscillations around Bragg peak confirms high interfacial and crystalline quality of NiO layer deposited on Al2O3 substrate. Surface related feature in Ni 2p3/2 core level spectra along with oxygen K-edge soft X-ray absorption spectroscopy results indicates that the initial growth of NiO on Al2O3 substrate is in the form of islands, which merge to form NiO layer for the larger coverage. The value of conduction band offset is also evaluated from the measured values of band gaps of NiO and Al2O3 layers. A type-I band alignment at NiO and Al2O3 heterojunction is also obtained. The determined values of band offsets can be useful in heterojunction based light emitting devices.

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For small samples, the modification of the X-ray reflectivity (XRR) profile by the geometric factors due to the profile and size of the beam and the size of the sample is significant. These geometric factors extend the spill-over angle, which is often greater than the critical angle for small samples. To separate the geometric factors, it is necessary to know the spill-over angle. Since the geometric factors are smoothly varying functions and extend beyond the critical angle, it is impossible to determine the spill-over angle from the XRR profile of small samples. It is shown that the spill-over angle can be determined by comparing the normal XRR profile of a small sample with the XRR profile taken with a surface-contact knife edge on the same sample. Thus, a procedure has been developed for data reduction for small samples and validated with suitable experiments. Unlike the methods used hitherto, which have drawbacks, this is a self-consistent method for data reduction.

We hereby report detailed structural and morphological studies for an ultrathin NiO/ZnO bilayer structure grown on sapphire (001) substrate using pulsed laser deposition technique. The combined X‐ray reflectivity (XRR) and grazing incidence X‐ray fluorescence (GIXRF) studies revealed formation of a low‐density defective ZnO interfacial layer of thickness ~32 Å at the ZnO/sapphire interface prior to growth of main ZnO layer. Our results further indicate that the variation of electron density across the NiO/ZnO bilayer structure is smooth and we do not observe presence of any interface layer between them. X‐ray diffraction measurements show that deposited ZnO layer is epitaxial in nature whereas NiO is highly oriented along (100) direction. The angle dependent X‐ray absorption near edge fine structure (XANES) measurements at Ni–K edge has been utilized to determine depth‐resolved oxidation state of Ni and the results have been correlated with the depth‐resolved electron density of NiO layer. The method described here offers nondestructive determination of the microstructural parameters as well as depth‐resolved mapping of oxidation state of a thin film‐based heterojunction device. It extends several advantages over destructive methods which are abundantly reported in literature.

Uranium is reported to be present in phosphate fertilizers. The recovery of uranium from the fertilizers is important because it can be used as fuel in nuclear reactors and also because of environmental concerns. For both these activities suitable method of uranium determinations at trace levels in these fertilizers are required. Studies have been initiated for such TXRF determination of uranium and the results are reported in the present paper. For TXRF determinations the fertilizer samples were processed with nitric acid and the uranium present in it was removed by solvent extraction using tri-n-butyl phosphate as the extractant. The organic phase containing uranium was equilibrated with 1.5% suprapure nitric acid to bring out uranium in aqueous phase. This aqueous phase was mixed with internal standard Y and the TXRF spectra were measured by depositing samples on float glass supports. The amounts of uranium in four fertilizer samples of Hungarian origin were determined by processing these TXRF spectra. Uranium concentrations in two fertilizer samples were found to be in the range of 4-6 μg/g, whereas two fertilizer samples did not show the presence of uranium. The precision of the TXRF determination of uranium was found to be better than 8% (1σ ).