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Surface characterization of clean SrTiO <sub/>3</sub> (100) substrates by x-ray photoelectron spectroscopy
摘要： The authors analyze the x-ray photoelectron spectra of SrTiO3(100) (STO) substrates to clarify the electronic structure characteristics induced by a sputter–anneal procedure. The survey spectra, the valence band spectra, and the relevant core level spectra, i.e., Sr 3s, Sr 3p, Sr 3d, Sr 4s, Sr 4p, Ti 2p, Ti 3s, Ti 3p, O 1s, and O 2s along with their satellite structures, of both pristine and sputtered and annealed STO have been measured. A comparison of spectra reveals the appearance of new features in the Ti 2p spectra of sputtered and annealed STO, corresponding to Ti3+ states and gap states near the Fermi energy. The presence of Ti3+ states points to the formation of a two-dimensional electron system at the STO surface generated by Ar+ sputtering and annealing in vacuum. Furthermore, the sputter-annealed surface shows only minor carbon contamination as compared to that of the pristine substrate.
关键词： XPS,transition metal oxide,sputtering,2DES,strontium titanium oxide,core level,single crystal
更新于2025-09-23 15:21:01
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Ferromagnetic Properties of N-Doped and Undoped TiO2 Rutile Single-Crystal Wafers with Addition of Tungsten Trioxide
摘要： In this work, undoped, N-doped, WO3-loaded undoped, and WO3-loaded with N-doped TiO2 rutile single-crystal wafers were fabricated by direct current (DC) magnetron sputtering. N-doping into TiO2 and WO3 loading onto TiO2 surface were used to increase and decrease oxygen vacancies. Various measurements were conducted to analyze the structural and magnetic properties of the samples. X-ray diffraction results showed that the N-doping and WO3 loading did not change the phase of all samples. X-ray photoelectron spectroscopy results revealed that W element loaded onto rutile single-crystal wafers existed in the form of WO3. UV-Vis spectrometer results showed that the absorption edge of WO3-loaded undoped and WO3-loaded with N-doped TiO2 rutile single-crystal wafers had red shift, resulting in a slight decrease in the corresponding band gap. Photoluminescence spectra indicated that oxygen vacancies existed in all samples due to the postannealing atmosphere, and oxygen vacancies density increased with N-doping, while decreasing with WO3 loading onto TiO2 surface. The magnetic properties of the samples were investigated, and the saturation magnetization values were in the order N-doped > WO3-loaded with N-doped > undoped > WO3-loaded undoped rutile single-crystal wafers, which was the same order as the oxygen vacancy densities of these samples. N-doping improved the saturation magnetization values, while WO3-loaded decreased the saturation magnetization values. This paper reveals that the magnetic properties of WO3-loaded with N-doped rutile single-crystal wafers originate from oxygen vacancies.
关键词： rutile TiO2 single-crystal wafers,WO3-loaded,oxygen vacancy,ferromagnetic properties
更新于2025-09-23 15:21:01
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Spectroscopy, Crystal and Molecular Structures of New 4-Acylpyrazolone Dinitrophenylhydrazones
摘要： Still looking at the development of new materials with unique properties and taking advantage of the nucleophilic properties of amines to form stable azomethines, dinitrophenylhydrazine was reacted with 4-ethyl-5-methyl-2-phenyl-pyrazol-3-one and then with 4-propyl-5-methyl-2-phenyl-pyrazol-3-one to get and respectively, 4-propyl-5-methyl-2-phenyl-pyrazol-3-one dinitrophenylhydrazone (Pmpp-Dh), via a simple condensation reaction in a one-pot synthesis system. Careful interpretations of results from elemental analysis, mass and NMR spectroscopy were in agreement with single-crystal X-ray diffraction data. Reported Schiff bases in their single-crystal solid state exist in imine keto tautomer form, each crystallizing in a monoclinic crystal system, with a space group of C2/c (No. 15) in Empp-Dh and P21/c (No. 14) in Pmpp-Dh. They have extensive intra- and inter-molecular hydrogen as well as C–H···π-ring interactions.
关键词： Schiff base,monoclinic,spectroscopy,dinitrophenylhydrazone,chemical shift,acylpyrazolone,single crystal
更新于2025-09-23 15:21:01
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Epitaxial lateral overgrowth of GaN on nano-cavity patterned sapphire substrates
摘要： The epitaxial lateral overgrowth of GaN by metal-organic chemical vapor deposition using a nano-cavity patterned sapphire substrate (NCPSS) was investigated. The NCPSS, with a hexagonal non-close-packed nano-cavity pattern on the sapphire substrate, was fabricated by polystyrene sphere coating and size reduction by reactive ion etching, followed by deposition of alumina and thermal oxidation. The coalescence of GaN on the NCPSS was achieved by the formation of relatively large GaN islands and enhanced lateral overgrowth of the GaN islands over several nano-cavity pattern areas. The threading dislocation density (TDD) measured by cathodoluminescence measurement was significantly reduced from 2.4 108 cm-2 to 6.9 107 cm-2 by using the NCPSS. Dislocation behaviors that contribute to the reduction of TDD of the GaN layer were observed by transmission electron microscopy. Raman spectroscopy revealed that the compressive stress in the GaN layer was reduced by 21% due to the embedded nano-cavities. In addition, the diffuse reflectance of GaN on the NCPSS was enhanced by 54% ~ 62%, which is attributed to the increased probability of light extraction through effective light scattering by nano-cavities.
关键词： A1. Nanostructures,B1. Nitrides,A2. Single crystal growth,A3. Metalorganic chemical vapor deposition,A3. Nanoscale epitaxial lateral overgrowth
更新于2025-09-23 15:21:01
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Crystal size improvement of Bi-based superconducting whiskers under stress-controlled condition
摘要： Using stress-controlled amorphous precursors, we have successfully grown Bi2Sr2Ca n-1CunOy (Bi-based) high-transition temperature superconducting whiskers with large crystal-size. Especially, under a high compressive stress attained by 1 GPa pelletizing, the crystal size of a whisker was significantly enhanced up to 9.5 mm length (growth period: 96 h) which is 2.4 times larger than that of the conventional amorphous-precursors method when using similar growth conditions and substrate compositions. In addition, by using the stress-controlled precursors, the number of the obtained Bi-based whiskers were also increased by a factor of 1.8.
关键词： A2. Single crystal growth,A1. Stresses,B2. Superconducting materials,A1. Growth models
更新于2025-09-23 15:19:57
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Raman scattering obtained from laser excitation of MAPbI3 single crystal
摘要： Finding renewable energy sources is of paramount importance to meet the increasing global energy demand whilst minimizing the impact on the environment. The research community has focused on solar energy as it is endlessly available, and have ranked the methylammonium lead iodide (MAPbI3) as one of the most promising candidate amongst perovskite solar cells. Despite its high efficiency, the MAPbI3 is sensitive to humidity, light, and temperature, its instability affects primarily on the crystalline structure and eventually leads to degradation. Three crystalline structures are known for this material, orthorhombic, tetragonal, and cubic which exist in different temperatures. Here we report on several processes detected from laser excitation of MAPbI3 single crystal at ambient conditions. A phase transition from tetragonal to cubic phase was induced by excitation of over 15 mW laser power. The phases were characterized by LF-Raman and photoluminescence, taken simultaneously with the increase of exciting laser power and the spectral changes were assigned to the structural differences. In addition, Raman stimulation of iodine vapors signal was observed, those vapors were generated from the core of the focus wherein the highest temperature led to degradation. The stimulated Raman phenomenon was enabled due to the unique properties of the MAPbI3 single crystal and revealed viability to use this material for additional applications in other research fields.
关键词： Methylammonium lead iodide,Stimulated Raman,Low frequency Raman,Phase transition,Single crystal
更新于2025-09-23 15:19:57
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Growth of Single-Crystal Cd0.9Zn0.1Te Ingots Using Pressure Controlled Bridgman Method
摘要： We report growth of single-crystal Cd0.9Zn0.1Te ingots while using the pressure-controlled Bridgman method. The Cd pressure was controlled during growth to suppress its evaporation from the melt and reduce the size of Te inclusions in the as-grown crystals. The accelerated crucible rotation technique (ACRT) was used to suppress constitutional supercooling. The fast accelerating and slow decelerating rotation speeds were optimized. Two-inch Cd0.9Zn0.1Te single-crystal ingots without grain boundaries or twins were grown reproducibly. Glow discharge mass spectrometry results indicate the e?ective segregation coe?cients of Zn and In dopants are 1.24 and 0.18, respectively. The full width half maximum (FWHM) of X-ray rocking curve was approximately 22.5 ”, and the IR transmittance was approximately 61%, indicating high crystallinity. The mean size of the Te inclusions was approximately 13.4 μm. Single-crystal wafers were cut into 5 × 5 × 2 mm3 slices and then used to fabricate gamma ray detectors. The energy resolution and peak-to-valley ratio maps were constructed while using 59.5 keV gamma ray measurements, which proved the high uniformity of detection performance.
关键词： ACRT,CZT single-crystal ingot,pressure control,Bridgman method
更新于2025-09-23 15:19:57
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Efficient photodiode-type photodetectors with perovskite thin films derived from MAPbI3 single-crystal precursor
摘要： Perovskite photosensitive layer plays an important role on the photoelectric properties of photodetector (PD). Here, precursor solution comprising methylammonium lead iodide (MAPbI3) single-crystal is applied to prepare perovskite film to enlarge the grain size of perovskite photosensitive layer and improve the detectivity of PD device. Compared with the traditional precursor solution composed of raw-materials (MAI+PbI2), perovskite film derived from MAPbI3 single-crystal precursor possesses high crystalline quality with large grain sizes, enhanced light absorption intensity and long carrier lifetime. Thus, the PD device based on perovskite photosensitive layer derived from MAPbI3 single-crystal precursor achieves an improved responsivity of 0.633 A W?1 and an optimized detectivity of 2.502×1011 Jones under 660 nm illumination with a light intensity of 1.25 mW cm?2 at ?0.4 V. This research highlights an innovative application of perovskite single-crystal for thin film devices.
关键词： perovskite,photosensitive layer,single-crystal precursor,photodetector
更新于2025-09-23 15:19:57
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Monolayer single crystal two-dimensional quantum dots via ultrathin cutting and exfoliating; è??è?????????????￥?|?????¤?????±????????o???′é???-???1;
摘要： Two-dimensional (2D) atomically thin quantum dots (QDs) possess extraordinary electrical and optical properties. However, fabricating high quality 2D QDs via a universal and reliable technique remains a challenge. Here, we report a simple strategy to prepare high quality, monolayer single crystal 2D QDs via ultrathin cutting 2D bulk single crystals by ultramicrotome, followed by an exfoliation process. The as-prepared 2D QDs have pristine surface, high quality, high monolayer yield and high photoluminescence quantum yield (the highest photoluminescence quantum yield of WS2 is 18%), which can be used as promising, low toxic, biocompatible, and good cell-permeability fluorescent labeling agents for in vitro imaging.
关键词： photoluminescence quantum yield,ultra-thin cutting,single crystal,two-dimension,quantum dots
更新于2025-09-23 15:19:57
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Single-crystalline-like stainless steel 316L with different geometries fabricated by laser powder bed fusion
摘要： In this study, we explored the feasibility of fabricating single-crystalline or single-crystalline-like stainless steel 316L (SS316L) with different geometries (thin struts, cubes, walls and a simulated pump impeller) using laser powder bed fusion (LPBF). The LPBF-fabricated SS316L thin struts possessed a single-crystalline core featuring a ?110? ∥ building direction (BD) crystallographic texture. The cubes, walls and the pump impeller preserved this ?110? ∥ BD texture and also exhibited a well-defined single-crystalline-like {110}?001? Goss texture. Cellular sub-grain structures with their primary dendrite arm spacing (PDAS) values smaller than 1 μm were discovered in all the samples with their growth directions showing a 45° angular deviation from the BD. Nanoscale precipitates and dislocations were also found in the cellular sub-grain structures of the thin struts. The mechanical properties of different geometries (the thin struts, the walls, and the simulated pump impeller) were studied and compared. The anisotropic mechanical responses of the walls and the simulated pump impeller were correlated with their crystallographic textures.
关键词： Single crystal,Geometries,Crystallographic texture,Laser powder bed fusion,Mechanical properties,Stainless steel 316L
更新于2025-09-23 15:19:57