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Ge 2 Sb 2 Te 5 (GST), a phase change material, generally exhibits two-step crystallization (amorphous → fcc → hcp) to store and process data. The present study reports the crystallization behavior and bonding mechanism of Ga-doped GST thin films with thermal annealing. Ga doping results in the formation of Ga–Te bonds and shows no bonding with other host elements (Ge and Sb), which changes the bonding mechanism and leads to one-step crystallization (amorphous → fcc). The optical transmission contrast confirmed the thermal stabilization of the fcc phase with thermal annealing. These findings suggest that Ga doping into GST thin films has thermally stabilized the metastable fcc phase and suppressed the hcp phase, hence posing it as a potential candidate for phase change memory applications with fast processing speed and low power consumption. [ABSTRACT FROM AUTHOR]

W/B4C multilayers (MLs) consisting of ten layer pairs with varying boron carbide layer thicknesses have been investigated. The ML structures were characterized using grazing‐incidence hard X‐ray reflectivity (GIXR), resonant soft X‐ray reflectivity (RSXR), hard X‐ray photoelectron spectroscopy (HAXPES) and X‐ray absorption near‐edge spectroscopy (XANES). Depth‐resolved spectroscopic information on the boron carbide layer in W/B4C MLs was extracted with sub‐nanometre resolution using reflectivity performed in the vicinity of the B K‐edge. Interestingly, these results show that the composition of boron carbide films is strongly dependent on layer thicknesses. HAXPES measurements suggest that most of the boron is in the chemical state of B4C in the multilayer structures. XANES measurements suggest an increase in boron content and C—B—C bonding with increase in boron carbide layer thickness. [ABSTRACT FROM AUTHOR]

The Hard X‐ray Photo‐Electron Spectroscopy (HAXPES) beamline (PES‐BL14), installed at the 1.5 T bending‐magnet port at the Indian synchrotron (Indus‐2), is now available to users. The beamline can be used for X‐ray photo‐emission electron spectroscopy measurements on solid samples. The PES beamline has an excitation energy range from 3 keV to 15 keV for increased bulk sensitivity. An in‐house‐developed double‐crystal monochromator [Si (111)] and a platinum‐coated X‐ray mirror are used for the beam monochromatization and manipulation, respectively. This beamline is equipped with a high‐energy (up to 15 keV) high‐resolution (meV) hemispherical analyzer with a microchannel plate and CCD detector system with SpecsLab Prodigy and CasaXPS software. Additional user facilities include a thin‐film laboratory for sample preparation and a workstation for on‐site data processing. In this article, the design details of the beamline, other facilities and some recent scientific results are described. [ABSTRACT FROM AUTHOR]

The effects of disorder on the magnetic phases as well as on the conduction process are extensively studied in LaFeO3 nanoparticles in a wide field and temperature ranges. The disorder induced by Na in LaFeO3 alters its robust magnetic phase to the coexistence of distinctly different magnetic orders. The phase purity of the samples, which plays an important role, is detected by synchrotron x-ray diffraction. Detailed magnetic measurements are carried out to investigate the evolution of phases due to substitutions. The samples show the coexistence of a superparamagnetic phase along with a weak ferromagnetic phase, and the ratio of the two distinct phases varies with substitutions. The Mössbauer measurement supported the said magnetic phases in the samples. The X-ray photoelectron spectroscopy analysis clarifies the simultaneous presence of Fe3+ and Fe4+ due to Na+ incorporation. Furthermore, the electrical conduction is found to be greatly influenced by such substitutional disorder. From the dielectric measurement, a p-type polaronic conduction mechanism is found in 25% Na incorporation, which is mainly due to the hole hopping between Fe4+ and Fe3+ states. The semicircles in the whole temperature range in the Cole–Cole plots of impedance and modulus spectra are the co-contribution of the grain and the grain boundary effect in the conduction process. [ABSTRACT FROM AUTHOR]

Defect tuning in ceria to enhance its catalytic properties is a subject of great interest for the scientific community owing to the growing demand for catalytic materials in drug, automobile and chemical industries. Doping induced defect engineering was found to be one of the most sought out strategies particularly in oxides for achieving multifunctionality. Here, in this study, we have doped ceria with distinct sized trivalent rare-earth ions, namely, Y3+, Eu3+ and La3+, using combustion techniques. Positron annihilation lifetime spectroscopy (PALS) suggested enhanced defect density with doping in general and higher concentration of oxygen vacancies in La3+ doped ceria compared to Y3+ and Eu3+ counterparts. X-ray photoelectron spectroscopy (XPS) suggested the existence of both Ce3+ and Ce4+, with the former having higher fraction in CeO2:La3+ compared to CeO2:Y3+. The electron transfer resistance (Rct) reduced in all the doped samples when compared to undoped ceria and they demonstrated improved catalytic activity towards the oxygen reduction reaction (ORR). The highest reduction in Rct was seen in the 5% La doped sample owing to the very high concentration of oxygen vacancies and Ce3+/Ce4+ ratio and CeO2:5.0% La3+ showed the best performance towards ORR electrocatalysis. The studies are expected to help in further tuning the catalysts in terms of dopant concentrations, and in future work, the strategy will be to control the Ce3+/Ce4+ ratio and see its implication in both catalytic and magnetic applications. [ABSTRACT FROM AUTHOR]

Co-doped SnO2 nanowires were grown by thermal evaporation of a mixture of Tin metal powder and CoCl2 · 6H2O in a tubular furnace. The growth occurs by vapor-solid growth mechanism. Nanowires grew along the sidewall of the alumina boat placed in the tubular furnace and the diameter of these nanowires (as was evident from scanning electron microscopy), was found to be in the range of 50 nm to 200 nm. Co was successfully doped in SnO2 lattice as revealed by X-ray diffraction data and was found to be in Co2+ state in the nanowires as detected by X-ray Photoelectron Spectroscopy measurements. Room temperature magnetic measurements, carried out using Vibrating Sample Magnetometer, indicated ferromagnetic behavior of the nanowires indicating their potential for spintronics applications. With increasing Co doping (upto 1%), the lattice parameters of SnO2 decreased and the saturation magnetization increased, suggesting a strong structure-magnetic property relationship. [ABSTRACT FROM AUTHOR]

Spintronics-based studies have produced significant attention in the last decade while claiming the observation of room temperature ferromagnetism (RTFM). Nevertheless, there is a lack of consensus on a mechanism responsible for this phenomenon. In this study, we focus on Cu-doped ZnO (ZCO) to understand the microscopic origin of RTFM and the role of different oxidation states of Cu in RTFM. We have performed different spectroscopic techniques using synchrotron facilities. The values of spin-moment obtained from x-ray magnetic circular dichroism sum-rule truly exhibit a ferromagnetic interaction in the nanocrystalline powder of ZCO with ∼0.58 μB for 5% of Cu concentration in the total fluorescence yield mode. Such an enhanced magnetization is attributed to the presence of Cu2+, which is mainly localized in the bulk region. Cu in ZCO is mostly dominated by the presence of Cu2+. This is clearly reflected by the profiles of x-ray photoemission spectroscopy. Consequently, the weakly magnetized total electron yield mode is attributed to a state of magnetic frustration as the majority of Cu3+ is found on the surface. Some of these Cu3+ when come in the vicinity of Cu2+ ions result in a highly correlated state of double exchange mechanism, which is the microscopic origin of RTFM in ZCO. The coupling between Cu2+-Cu3+ is mediated via oxygen vacancies (VO), the presence of which is confirmed through the features of electron energy loss spectroscopy over different edges. The confirmation of VO is also supported by the deconvolution of E2high-phonon in the Raman spectra. Moreover, the defects in the local electronic structures of ZCO are demonstrated by the deconvoluted spectra of Cu L3 x-ray absorption spectroscopy. The images obtained from high-resolution transmission electron microscopy confirm the incorporation of Cu into the wurtzite crystal of ZnO. A clear enhancement in magnetization upon an increase in carriers of Cu in ZCO indicates carrier-induced ferromagnetism. Cu2+ and VO are the two attributes of RTFM in ZCO. [ABSTRACT FROM AUTHOR]

The scientific community has shown a growing interest in relating to the lanthanide based luminescent materials and it has made an effort to develop them. Among these several luminescent materials, we have proposed to developed (Y,Gd)F3 nanophosphors doped with distinct of Eu3+ concentrations using modified hydrothermal process. The effect of co-doping of rare earth activators to the host lattice structure and morphology are investigated using different analytical techniques. The diffuse reflectance spectra reveal a tuning of optical band gap due to substitutions. From the extensive XPS analysis, Gd and Eu are found to be in a stable ionic state of +3 which is replacing Y3+ in YF3 host. Photoluminescence emission spectra of the nanophosphors are excited by near ultraviolet (UV, 393 nm) excitation. From photoluminescence study, the intensity variation is observed for emission peak at 591 nm and fluorescence quenching occurs at higher doping level. This effect subsequently explained on the frame work of local symmetry and nonradiative transfer among multipole-multipole interaction. At 393 nm excitation Eu3+ (2, 3, 5, 7, 10 at %) doped (Y, Gd) F3 show CIE chromaticity coordinates shifted to red regions with increase in Eu doping levels. Because of the longer decay time these phosphors can be used for bio-labeling and other similar applications. [ABSTRACT FROM AUTHOR]

In this work, we fabricated peculiar and highly cogent iron-doped graphitic carbon nitride (Fe@g-C3N4) nanocatalysts with varying ratios of g-C3N4 nanosheets to Fe-dopant in 1 : 1, 1 : 3, and 1 : 5, respectively. Numerous physicochemical techniques, including high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR), powder X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to validate the as-synthesized catalysts to explain their morphology and chemical structure. In addition, it was revealed that Fe metal ions were well disseminated with no alteration in the layered stacking structures of the g-C3N4 nanosheet and/or might interact with N atoms of the graphitic plane, forming intercalation compounds, thereupon influencing the energy band structure, augmenting visible light absorption, and electron–hole rupture rate. Under visible light (12 W) conditions, Fe@g-C3N4 (1 : 1) has shown superior performance for selective Baeyer–Villiger oxidation reaction, giving 100% cyclohexanone conversion and an admirable product selectivity of 2-oxepanone, i.e., 99.85%. Besides, the main advantages of the present catalyst include its excellent reusability up to five repeated cycles with no significant loss of activity. [ABSTRACT FROM AUTHOR]

Rare earth activated nanofluorides have attracted attention due to their interesting optical properties and diverse applications endowed by their low phonon energy. In this study, a series of (Y0.95−x, Gd0.05) F3:xTb3+ (x = 0, 0.01, 0.03, 0.05, 0.07, 0.10) nanophosphors were fabricated via a hydrothermal synthesis route. The structures, morphologies, and optical properties of the synthesized nanophosphors were analyzed in detail using X-ray diffractometry, vibrational spectroscopies, transmission electron microscopy, X-ray photoelectron spectroscopy, and diffuse reflectance spectroscopy. The characteristic emissions of both the Gd3+ (6P7/2 → 8S7/2) and Tb3+ (5D4 → 7Fj) ions can be observed in the photoluminescence spectra at the 272 nm excitation of Gd3+ ions and the Gd3+ → Tb3+ energy transfer leading to 15-fold enhancement in the green emission of the trivalent terbium ion is discussed thoroughly. The possible energy transfer mechanism from Gd3+ to Tb3+ is presented schematically and 88.92% energy transfer efficiency was achieved, which is dominated by electric dipole–dipole interactions. The calculated branching ratio (for 5D4 → 7F5), quantum efficiency of 89% and obtained colorimetric parameters suggest the applicability of the synthesized nanophosphors in ultraviolet excitable phosphors for white light-emitting diodes and solid-state green lasers. [ABSTRACT FROM AUTHOR]