Mixed oxides of Ti-V-O were co-precipitated by wet process using TiCl₄ and VOCl₃ as starting materials. As-precipitated gels were calcinated at 800°C for 4 hours in oxygen atmosphere. Effects of vanadium content on the structural evolution, morphology, and band gap of Ti-V-O oxides were investigated. Calcination has produced mixtures of TiO₂/VO₂/V₂O₅ oxides and has allowed formation of Ti_{1-x}V_{x}O₂. Lattice parameters of rutile TiO₂ were precisely measured to investigate vanadium substitution into single rutile phase of Ti_{1-x}V_{x}O₂ with varying vanadium content. As vanadium addition was increased, particles were coarsening rapidly during calcination. Band gap of the Ti-V-O oxides was measured using ultraviolet visible light spectrometer. A decrease of band gap down to 1.7 eV with the addition of maximum of 10 at.% of vanadium was measured, which is due to the formation of single phase of Ti_{1-x}V_{x}O₂ as well as the formation of metallic VO₂ or V₂O₅ particles.
In 4H-SiC PiN diodes, Shockley-type stacking faults expand from basal plane dislocations under conducting forward current. We report for the first time overlapped single Shockley-type stacking faults in a 4H-SiC PiN diode after forward conduction. In photoluminescence measurements, we observed not only an emission peak at 425 nm, which corresponds to the single Shockley-type stacking fault, but also one at 432 nm. In cross-sectional cathode luminescence images, emission lines at 425 nm and 432 nm merge and become straight. Transmission electron microscope images showed that the structure at the position with the 432 nm emission overlapped the single Shockley-type stacking faults.
High-energy milling of sulphides with a reactive metal in so-called mechanochemical reduction mode can lead to products in nanorange and to composition which simplifies the following metallurgical processing. Chalcopyrite CuFeS₂, a ternary semiconductor with antiferromagnetic properties represents promising candidate as an advanced material for use in inexpensive nanoelectronics (solar cells, magnetic area), as well as copper ore source in metallurgical operations. In this work, the process of mechanochemical reduction of chalcopyrite with elemental iron is studied. The composition and properties of nanopowder prepared by high-energy milling were analyzed by X-ray diffraction and magnetic measurements. Most of the reaction takes place during 30 min with chalcocite Cu₂S and troilite FeS as the only reaction products. The magnetic investigations reveal significant increase of saturation magnetization as a result of milling. Unlike the conventional high-temperature reduction of chalcopyrite, the mechanochemical reduction is fast and ambient temperature and atmospheric pressure are sufficient for its propagation.
We synthesized the uniform monoclinic gallium oxide (Ga_2O_3) nanobelts by a simple thermal annealing of GaN powders. The as-syn-thesized nanobelts were rectangular in cross-sectional shape with width ranging from 100 to 700 nm. The length direction of the nanobelt was along [010]. Photoluminescence measurement under excitation at 325 nm showed that the Ga_ 2O_3 nanobelts had a blue emission at around 454 nm.
Nanocrystalline Sb_2S_3 particles have been synthesized from Sb and S powders by high-energy milling in a planetary mill using argon protective atmosphere. X-ray diffraction, particle size analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, electron diffraction, high resolution transmission electron microscopy, UV-VIS, and differential scanning calorimetry methods for characterization of the prepared particles were applied. The powder X-ray diffraction pattern shows that Sb_2S_3 nanocrystals belong to the orthorhombic phase with calculated crystallite size of about 36 nm. The nanocrystalline Sb_2S_3 particles are constituted by randomly distributed crystalline nanodomains (20 nm) and then these particles are forming aggregates. The monomodal distribution of Sb_2S_3 particles with the average hydrodynamic parameter 210 nm was obtained. The quantification of energy dispersive X-ray spectroscopy analysis peaks give an atomic ratio of 2:3 for Sb:S. The optical band gap determined from the absorption spectrum is 4.9 eV, indicating a considerable blue shift relative to the bulk Sb_2S_3. Differential scanning calorimetry curves exhibit a broad exothermic peak between 200 and 300°C, suggesting recovery processes. This interpretation is supported by X-ray diffraction measurements that indicate a 23-fold increase of the crystallite size to about 827 nm as a consequence of application of high temperature process. The controlled mechanochemical synthesis of Sb_2S_3 nanoparticles at ambient temperature and atmospheric pressure remains a great challenge.
In this paper we propose a method of intercalation of layered single crystals with atoms of 3d-metals in a magnetic-field gradient. We report on structure properties of Co_{x}InSe and Co_{x}In₂Se₃ layered crystals intercalated by cobalt. It was established that ferromagnetic ordering at room temperature is observed in the intercalated crystals. The crystals are a nanocomposite material that consists of a layered matrix and arrays of Co nanoformations on the van der Waals surfaces of InSe and In₂Se₃ layers.
Different optical energy gaps in ferroelectric and paraelectric phases as well as light scattering on domain walls allow to observe ferroelectric domains in antimony sulfoiodide (SbSI) near the Curie temperature. Mobility 8.11(44)× 10^{-8} m^2/(Vs) of ferroelectric domain walls under external electric field has been determined along c-axis of SbSI single crystals using optical transmittance microscopy.
In this study we demonstrate the use of elemental precursors (Cu, Fe, Sn, S) to obtain stannite forms by a solid-state one-pot mechanochemical synthesis. In the processing route, we report the kinetics of the synthesis. For the characterization of the unique nanostructures, X-ray diffraction, specific surface area measurements and SQUID magnetometry methods were applied. CFTS polymorphs with the tetragonal body-centered structure with the average crystallite size 18-19 nm were obtained. The weak ferromagnetic properties of the quaternary nanocrystals after maximum milling time were also documented.
The mechanochemical synthesis of nanocrystalline CuFeSe₂ particles prepared by high-energy milling in a planetary mill in an argon atmosphere from copper, iron, and selenium for 60 min is reported for the first time. The CuFeSe₂ nanoparticles crystallize in tetragonal structure with mean crystallite size of about 32±1 nm. High resolution transmission electron microscopy measurements confirmed the presence of agglomerates which are formed by small nanocrystalline domains (5-40 nm). The magnetic data revealed that paramagnetic CuFeSe₂ nanoparticles coexist with a small amount of ferromagnetic impurities at room temperature. The magnetic transition towards a weak ferromagnetic or ferrimagnetic behavior occurs in CuFeSe₂ at approximately 79 K. The band gap of the CuFeSe₂ particles is 0.95 eV which is wider than the band gap in bulk materials (0.16 eV), which could be in many aspects of application more beneficial.
AlGaN/GaN heterostructure field effect transistors were investigated in terms of microwave and sensor applications. Heterostructure layers grown on sapphire substrates were evaluated using impedance spectroscopy measurements. The 2DEG sheet concentration of 8× 10^{12} cm^{-2} and mobility of 1600 cm^{2}/(Vs) were obtained. The measured I-V characteristics of the heterostructure field effect transistors devices revealed the saturated drain current 180 mA/mm and the gate pinch-off voltage -2.0 V with the transconductance 200 mS/mm. The structures have been characterized in microwave frequency range with the measured cut-off frequency of 6 GHz for 1 μm gate device. Studies of an AlGaN/GaN heterostructure Schottky diode with a catalytic Pt electrode as a hydrogen gas sensor confirmed high sensitivity of the Schottky barrier on hydrogen adsorption. Differential conductance of the Schottky diode was found to be a convenient parameter to estimate changes of the Schottky barrier height.
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