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Research on the defect types transformation induced by growth temperature of vertical graphene nanosheets
摘要： The in?uence factors on the defect types in vertical graphene nanosheets (VGNs) are widely researched while few systematic research has been reported on the growth temperature, which should play an important role in the transformation of defects types. In this work, VGNs were grown via plasma enhanced chemical vapor deposition (PECVD) method in the atmosphere of CH4, H2 and Ar. Based on SEM, Raman, XPS, NEXAFS and UPS spectrum analysis, we found that the types of defects in VGNs have clearly transformed from vacancy-like to boundary-like, corresponding to the rising growth temperature. Moreover, NEXAFS suggests that features near 7.7 eV are attributed to boundary-like defects, as well as (cid:1)6.7 eV in UPS, providing an intuitive and half-quantitative direction to characterize boundary-like defects in VGNs. Additionally, the sheet resistance (from 1386 to 175 Ohm/Sq) and the wetting angle (from 148(cid:3) to 121(cid:3)) decrease as the temperature rises. It shows that changing the growth temperature, as the easy and effective method, is crucial of modulating the properties of VGNs owning to the transition of defects types from vacancy-like to boundary-like.
关键词： Vertical graphene nanosheets,Near-edge X-ray absorption ?ne structure,Defects type,Ultraviolet photoemission spectroscopy,Modulate properties
更新于2025-09-23 15:22:29
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Constituent substitution in hot wall deposition of Bi2S3 films by reaction with substrates
摘要： Replacement of a constituent in the overgrown layers with the materials provided by the substrates is investigated when Bi2S3 films are deposited on III-V compound semiconductors and transition metals using a hot wall epitaxy method. The substitution caused by the S atoms is stronger than that by the Se and Te atoms in deposition of Bi2Se3 and Bi2Te3 films. Mere exposure to Bi2S3 vapor of In-containing compounds (InP and InAs) and Ga-containing compounds (GaAs and GaSb) at epitaxial growth temperatures results in a capping of their surfaces by In2S3 and GaS, respectively. A temperature window is revealed to exist for the GaAs case where growth of Bi2S3 microcrystals occurs within the temperature range for the sulfide formation. The sulfurization by the material substitution is thus demonstrated to be not always identical with that using elemental sulphur. We examine furthermore the sulfides synthesized on the surfaces of Cu, Ag, Ni, Mo, and W. The sulfides produced on Cu and Ag undergo material alterations when they are irradiated by a laser light.
关键词： X-ray crystallography,Hot wall epitaxy,Material substitution,Raman spectroscopy,Bi2S3,Sulfides
更新于2025-09-23 15:22:29
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Optimized chemical cleaning procedure for enhancing photoemission from GaAs photocathode
摘要： To obtain cleaner GaAs photocathode surface, various wet chemical cleaning methods to remove the oxides and carbon contaminations from the surface of GaAs photocathode are investigated, and an improved chemical etching method is presented to further enhance the cathode photoemission performance. By means of X-ray photoelectron spectroscopy analysis, characteristics of these methods are summarized. HF solution can effectively reduce surface oxides, but it does not effectively act on the absorbed carbon contaminations. The mixed solution of HCl and isopropanol scores well in removing carbon contaminations, but the ability of removing oxides is relatively weaker. The mixed solution of HCl and deionized water right after the mixed solution of H2SO4, H2O2 and deionized water is unfavorable to reduce Ga oxides. The improved chemical etching method, which uses HF solution followed by the mixture of HCl and isopropanol has more advantages in removing oxides and carbon contaminations at the same time. Moreover, a hydrophobic surface is obtained by using the improved method, which also plays a role in the contaminations removal. The quantum efficiencies of GaAs photocathode undergoing various wet chemical cleaning procedures are compared after subsequent heat treatment and activation. The results show that the chemical treatment of HF solution followed by the mixture of HCl and isopropanol can help GaAs photocathode obtain higher activated photocurrent and quantum efficiency.
关键词： Chemical cleaning,GaAs photocathode,Quantum efficiency,X-ray photoelectron spectroscopy
更新于2025-09-23 15:22:29
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Molecular and excited state properties of photostable anthraquinone blue dyes for hydrophobic fibers
摘要： Synthetic dyes having high photostability on hydrophobic fibers such as poly(ethylene terephthalate) (PET) are of interest for use on textile substrates for outdoor applications. While much is known about photostable dyes developed for PET in the 1980s, owing to their viability for use in automobile interiors, little has been published on currently viable photostable disperse dyes. As part of an effort to help fill this void and to facilitate future photostable disperse dye design, the present study involved the use of experimental measurements and modelling studies to help characterize the molecular structures of commercially viable dyes for producing photostable colors on PET fibers, beginning with a pair of blue dyes. With the aid of HR-MS, 500 MHz 1H NMR, and X-ray crystallography, it was established that the two dyes are structural isomers having 1,5-(OH)2-anthraquinone (AQ) and 1,8-(OH)2-AQ base structures. It is proposed that the photostability of these dyes arises from the presence of multiple OH/NH groups ortho to the AQ C]O groups which enables them to dissipate excited state energy through intramolecular proton transfer. Further, using DFT-based molecular modelling studies, it was shown that the dye having the 1,5-(OH)2-AQ base structure has a lower ESOP than the isomeric dye having the 1,8-(OH)2-AQ base structure. Similarly, results from calculating Frontier HOMO and LUMO isosurfaces indicated that the LUMO lobes of the latter dye are larger, suggesting that this dye undergoes excitation faster than the 1,5-(OH)2-AQ isomer.
关键词： Molecular modelling,Anthraquinone disperse dyes,X-ray crystallography,Intramolecular H-bonding,Structural analysis
更新于2025-09-23 15:22:29
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Study on the measurement error and scope of analytical gradient model in phase measuring deflectometry
摘要： The existing analytical gradient models in phase measuring de?ectometry (PMD) usually su?er in the ambiguous problem. To solve this problem, simpli?cation/assumption is often given to the surface shape, which causes non-ignorable measurement error in certain situations. In order to analyze the relation between the surface shape and measurement error when simpli?cation/assumption is used, a ray tracing simulation model is developed in this paper. For any given PMD system setup, the relation between the height/slope variations of test surface and measurement accuracy can be carried out. The corresponding experiment work proves the correctness of this simulation model. The increasing of either the height or slope of object will lead to the exponential aggravating of measurement error. For our experiment setup, the measurement gradient error will be less than 0.5% if the ratio of the distance between the LCD (Liquid Crystal Display) screen and the reference plane and the STD (standard derivation) of object height is larger than 200.
关键词： Phase measuring de?ectometry,Error analysis,Ray tracing model,Optical 3D measurement
更新于2025-09-23 15:22:29
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Enhanced luminescent properties of Tb3+-doped transparent oxyfluoride glass-ceramics containing YF3 nanocrystals
摘要： Tb3+-doped transparent oxyfluoride glass-ceramics (GC) containing YF3 nanocrystals have been fabricated via a traditional melt-quenching route with appropriate thermal-treatment. The microstructural, luminescent and optical properties of the synthesized material were investigated systematically. The precipitated particles in the glass phase of GC540 are YF3 nanocrystals with a mean size of around 20 nm, which has been confirmed and estimated by XRD and TEM. Compared with the precursor glass (PG), the emission intensity at 545 nm (5D4→7F5) of YF3: Tb3+-doped GC is significantly enhanced (under ultraviolet and X-rays excitation) and the lifetime of GC is longer. It can be confirmed that the preferential enrichment of Tb3+ in the precipitated low-phonon-energy YF3 nanocrystals can effectively reduce non-radiative transitions. The obtained results confirm that such Tb3+-doped YF3 GC might be useful as a novel X-ray scintillating material for slow event detection.
关键词： X-ray excited luminescence spectra,luminescent properties,YF3,Glass-ceramics
更新于2025-09-23 15:22:29
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Multi-layered WO3 nano-platelets for efficient photoelectrochemical water splitting: the role of the annealing ramp
摘要： Multi-layered WO3 nano-square platelets films were successfully grown on transparent TCO substrates by spray-coating of WO3 nanoparticles aqueous suspension prepared by the sol-gel method. This work assesses the influence of two annealing schemes in the photo-response of WO3 photoelectrodes with different film thicknesses. The photoelectrochemical characterization reveals that the slow-heating ramp produces a photoelectrode with an improved photocurrent density of 1.6 mA·cm-2 at 1.23 V vs RHE. Comparing photoelectrodes with the same film thickness, the slow-heating ramp yield higher photocurrent densities; 80 % more than the conventional fast-heating ramp. The effect of the annealing ramp on the morphology and crystalline-phase structure of WO3 photoelectrodes is correlated with the photocurrent density. The slow-heating ramp annealing unveils film morphology with both, higher porosity degree and higher nano-square platelets dimensions. DRX structural analyses disclose that the films grow in monoclinic crystalline phase with a textural preferential direction [002], often related to improved photocurrent performances. The crystallite sizes and lattice microstrain are estimated using a simple X-ray diffraction broadening method, the Williamson-Hall analysis. A quantified correlation between the WO3 lattice defects, intergrains strain and performance is performed. The proposed deposition method paves the way for producing efficient and scalable photoelectrodes of WO3 for photoelectrochemical water splitting by using low-cost and simple manufacturing processes.
关键词： annealing ramp,X-ray peak broadening,tungsten trioxide,nano-platelets,photoelectrochemical cells,photoelectrodes
更新于2025-09-23 15:22:29
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Laguerre–Gauss and Hermite–Gauss soft X-ray states generated using diffractive optics
摘要： Light’s capacity to carry angular momentum is integral to our knowledge of physics and ability to probe matter. In addition to spin, photons can occupy free-space orbital angular momentum eigenstates. Visible light orbital angular momentum is used in quantum information experiments, super-resolution microscopy, optical tweezers and angular momentum transfer to atoms in optical lattices. Soft X-ray orbital angular momentum applications, slowed by the lack of suitable optics and the rarity of coherent X-ray sources, could enable the direct alteration of atomic states through orbital angular momentum exchange, and methods to study the electronic properties of quantum materials. We have made soft X-ray diffractive optics that generate single Laguerre–Gauss modes, observed carrying up to 30? angular momentum per photon, or their superpositions. We also present Hermite–Gauss diffractive optics and a soft X-ray orbital angular momentum analyser. These tools could enable both the manipulation and finer characterization of topologically complex electronic matter, such as magnetic skyrmions.
关键词： Hermite–Gauss modes,Diffractive optics,Laguerre–Gauss modes,Soft X-ray,Orbital angular momentum
更新于2025-09-23 15:22:29
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Layer by layer deposition of alternate carbon nanotubes and Ni films for efficient multilayer thin film temperature gauges
摘要： This study reports a novel approach for growing multilayer thin films consisting of alternate layers of carbon nanotubes (CNT) and nickel on Si (1 0 0) substrates and justifies their use in thin film temperature sensors. A low pressure chemical vapor deposition system was employed for synthesizing CNT films, while Ni films were deposited by electrodeposition. Porous-Si was used as substrate to increase adhesion between the layers of the multilayer structure. The structure of the multilayer films and the quality of the CNT grown were analyzed using several characterization methods, including scanning electron microscopy, x-ray photoelectron spectroscopy, x-ray auger electron spectroscopy and Raman spectroscopy. The electrical characteristics were investigated using a van der Pauw setup and the effect of the increasing number of CNT layers in the multilayer structure was studied. The sensitivity of the multilayer film was found to increase with increasing number of CNT layers, despite the decrease of the temperature coefficient of resistance. On the other hand, the initial resistance was found to increase. Results indicated that these multilayer structures are appropriate for fabricating highly sensitive thin film gauges that can detect lower heat fluxes with more accuracy.
关键词： carbon nanotubes,thin film gauges,surface and interface chemistry,porous silicon,adhesion sensing,x-ray photoelectron spectroscopy
更新于2025-09-23 15:22:29
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Additional phase transition in a PbZr <sub/>0.87</sub> Ti <sub/>0.13</sub> O <sub/>3</sub> single crystal
摘要： PbZr1-xTixO3 (PZT) ceramics are one of the most known and widely used piezoelectric materials. In order to understand the origin of the high piezoelectricity it is essential to also understand its phase diagram. Many recent papers reported on the modification of PZT phase diagram based on ceramic experimental data. This is due to difficulties to get good quality single crystal samples. We have succeeded in getting a good quality single crystal with x= 0.13. Based on temperature changes of elastic properties we confirmed the existence of additional phase transition appearing in the PbZr0.87Ti0.13O3. The temperature dependence of the elastic properties was investigated by means of piezoelectric measurements and Brillouin light scattering. We discussed the correlation between anomalies of the elastic properties found in these measurements, and suggested that, except for the two well-known phase transitions, these anomalies point to another phase transition below Tc. The structure and symmetry of this crystal have been tested with use of the x-ray diffraction at the room temperature.
关键词： x-ray diffraction,phase transitions,elastic properties,piezoelectricity,PZT single crystals
更新于2025-09-23 15:22:29