Search

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]

V1−xCrxO2 (0 ≤ x ≤ 0.3) (VCO) thin films were deposited onto r-sapphire substrates using a pulsed laser deposition method. The electronic structures of these compounds were investigated by x-ray photoemission spectroscopy (XPS), and the electrical transport measurements by four-probe electrical resistivity along with the Hall effect measurements. The XPS study shows that the valency of the Cr ions in the VCO films is 3 + and the V ions are in mixed states of 4 + and 5 +. From the resistivity-temperature measurements, the metal–insulator transition (MIT) temperature (TC) of Vanadium dioxide (VO2) increases significantly upon Cr doping, while the hysteresis width and resistivity follow a gradual decrease. These findings will pave the way for the usage of VO2 films in solar and electrical device applications where larger critical temperatures than pristine VO2 are required. [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]

A Cu(II)–salen complex encapsulated in MWW-framework as an efficient chiral organocatalyst was developed for the synthesis of 3,4-dihydropyrimidin-2-(1H)-one (DHPMs) derivatives via an asymmetric pathway. In order to confirm its structural properties, single-crystal X-ray diffraction, powder XRD, BET, XPS, FE-SEM, EDX, UV-Vis, and FTIR spectra were used. Using computer-assisted DFT calculations, the Cu(II)–salen complex has been fine-tuned to fit into the pocket of the porous MWW support while keeping its chirality. This organocatalyst was shown to be a potent catalyst for the formation of the desired DHPMs product under short reaction times. Furthermore, this green protocol allows rapid and simple isolation of active MWW-trapped Cu(II)–salen scaffolds and its reusability in at least five consecutive runs without losing much of its activity. [ABSTRACT FROM AUTHOR]

An ilmenite structure was maintained with better crystalline characteristics which were determined from structural examinations employing x-ray diffraction of thermally evaporated NiTiO3 (NTO) thin films on Si (100) substrates. NiO6 and TiO6 octahedra are arranged in alternating layers in the lattice structure of NTO. Atomic force microscopy, which highlights the structure of the film surface, was used to assess the thin film microstructure and surface roughness. NTO preferentially absorbs ultraviolet radiation below 360 nm, visible light in the wavelength range from 420 nm to 540 nm and above 700 nm. NTO displays a band gap of 2.17 eV and exhibits direct band gap semiconductor characteristics. Corresponding to photon energy of 2.7 eV, 2.5 eV and 1.5 eV, NTO shows clear absorbance peaks at 448 nm, 502 nm and 743 nm, respectively. It is hypothesized that the peaks of NTO's visible light absorbance result mostly from the charge transfer transitions d → d of Ni inside its valence band. The films have been further characterized by x-ray photoemission spectroscopy and valence band spectroscopy, with a range of photonic energy resulting in the phenomenon of resonance photoemission spectroscopy (RPES) in accordance to find out the electronic spectra of NTO which eliminates the possibility of metal clusters in NTO films. The RPES spectra indicate that the Ti 3d (Ti3+ defect states) and O 2s are strongly hybridized. The magnetic hysteresis loop demonstrated that the NTO films may exhibit superparamagnetic behavior at 300 K. These characterization techniques help to understand its electronic and magnetic properties, which are important in photocatalytic devices. [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]

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]

Considering the excellent tunability of electrical and dielectric properties in binary metal oxide based multi-layered nanolaminate structures, a thermal atomic layer deposition system is carefully optimized for the synthesis of device grade Al 2 O 3 /TiO 2 nanolaminates with well-defined artificial periodicity and distinct interfaces, and the role of process temperature in the structural, interfacial, dielectric and electrical properties is systematically investigated. A marginal increase in interfacial interdiffusion in these nanolaminates, at elevated temperatures, is validated using X-ray reflectivity and secondary ion mass spectrometry studies. With an increase in deposition temperature from 150 to 300 °C, the impedance spectroscopy measurements of these nanolaminates exhibited a monotonic increment in dielectric constant from ∼95 to 186, and a decrement in dielectric loss from ∼0.48 to 0.21, while the current-voltage measurements revealed a subsequent reduction in leakage current density from ∼2.24 × 10 -5 to 3.45 × 10 -7 A cm -2 at 1 V applied bias and an improvement in nanobattery polarization voltage from 100 mV to 700 mV, respectively. This improvement in dielectric and electrical properties at elevated processing temperature is attributed to the reduction in impurity content along with the significant enhancement in sublayer densities and the conductivity contrast driven Maxwell-Wagner interfacial polarisation. Additionally, the devices fabricated at 300 °C exhibited a higher capacitance density of ∼22.87 fF μm -2 , a low equivalent oxide thickness of ∼1.51 nm, and a low leakage current density of ∼10 -7 A cm -2 (at 1 V bias), making this nanolaminate a promising material for high-density energy storage applications. These findings highlight the ALD process temperature assisted growth chemistry of Al 2 O 3 /TiO 2 nanolaminates for superior dielectric performance and multifaceted applications.

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, Y 3+ , Eu 3+ and La 3+ , using combustion techniques. Positron annihilation lifetime spectroscopy (PALS) suggested enhanced defect density with doping in general and higher concentration of oxygen vacancies in La 3+ doped ceria compared to Y 3+ and Eu 3+ counterparts. X-ray photoelectron spectroscopy (XPS) suggested the existence of both Ce 3+ and Ce 4+ , with the former having higher fraction in CeO 2 :La 3+ compared to CeO 2 :Y 3+ . The electron transfer resistance ( R ct ) 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 R ct was seen in the 5% La doped sample owing to the very high concentration of oxygen vacancies and Ce 3+ /Ce 4+ ratio and CeO 2 :5.0% La 3+ 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 Ce 3+ /Ce 4+ ratio and see its implication in both catalytic and magnetic applications.