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The role of synthesis conditions for structural defects and lattice strain in β-TaON and their effect on photo- and photoelectrocatalysis
摘要： The importance of the synthesis conditions on the structural and photocatalytic properties of tantalum oxide nitride was investigated by comparing two variants of phase-pure β-TaON obtained from application of two different synthesis routes, leading to one unstrained and one heavily anisotropically microstrained β-TaON as shown by XRD-based Rietveld refinement. HRTEM images reveal the origin of the strain to be lattice defects such as stacking faults. The strained β-TaON was found to be the clearly less active semiconductor in photochemical and photoelectrochemical water oxidation. The lattice defects are assumed to act as charge carrier traps hindering the photo-generated holes to be displaced to the reaction sites at the surface.
关键词： tantalum oxide nitride,photocatalysis,photoelectrochemistry,water splitting,structural defects
更新于2025-09-23 15:22:29
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Topologically non-equivalent textures generated by the nematic electrohydrodynamics
摘要： Some classes of nematic liquid crystals can be driven through turbulent regimes when forced by an external electric field. In contrast to isotropic fluids, a turbulent nematic exhibits a transition to a stochastic regime that is characterised by a network of topological defects. We study the deformations arising after the electric field has been switched-off. In contrast to the turbulent regime, the relaxation of this topological-defect regime involves the annihilation of an interlacement of defect lines. We show that these defect lines separate regions of the nematic having topologically non-equivalent textures.
关键词： Nematic liquid crystals,electrohydrodynamics,twist deformation,topological defects
更新于2025-09-23 15:22:29
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Optical and Microstructural Investigation of Heavy B-Doping Effects in Sublimation-Grown 3C-SiC
摘要： In this work, a complementary microstructural and optical approach is used to define processing conditions favorable for the formation of deep boron-related acceptor centers that may provide a pathway for achieving an intermediate band behavior in highly B-doped 3C-SiC. The crystallinity, boron solubility and precipitation mechanisms in sublimation-grown 3C-SiC crystals implanted to 1-3 at.% B concentrations were investigated by STEM. The revealed defect formation and boron precipitation trends upon thermal treatment in the range 1100-2000oC have been cross-correlated with the optical characterization results provided by imaging PL spectroscopy. We discuss optical activity of the implanted B ions in terms of both shallow acceptors and deep D-centers, a complex formed by a boron atom and a carbon vacancy, and associate the observed spectral developments upon annealing with the strong temperature dependence of the D-center formation efficiency, which is further enhanced by the presence of implantation-induced defects.
关键词： photoluminescence,defects,3C-SiC,STEM,implantation,boron doping
更新于2025-09-23 15:22:29
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Time-order Phonon Scattering Processes are Responsible for the Asymmetric G* Raman Band in Graphene
摘要： Background: While most of the prominent features in the Raman spectrum of graphene are well understood as mentioned in patents within the Double Resonance (DR) picture, the origin of the peak at 2450 cm-1 (also called the G* band) still remains unclear. Method and Objective: In this work, we performed detailed Raman studies of single- and few-layer graphene using multiple laser excitations to unravel the origin of G* band. Results: Based on our analyses, we conclude that the G* band arises from a combination of Transverse Optical (iTO) and Longitudinal Acoustic (LA) phonons, and exhibits an asymmetric peak structure due to the presence of two different time-order phonon processes. The lower (higher) frequency sub-peak is ascribed to an LA-first (iTO-first) process. We provide three strong experimental evidences for the time-ordered scattering processes: the dependence of the G* band sub-peaks with (i) increasing laser energy, (ii) increasing defects, and (iii) increasing temperature. Finally, we attribute the enhanced asymmetry of the G* band in multi-layer graphene to multiple processes between electronic sub-bands, similar to the G’ band in multi-layer graphene. Conclusion: Our study uncovered the origin and nature of the G* peak in the Raman spectrum of graphene. We believe our results have important implications for processes such as graphene-enhanced Raman scattering, where the time-ordered scattering of optical and acoustic phonons can be very useful for sensing analytes.
关键词： second order,layer stacking,G* band,defects,graphene,Raman spectroscopy
更新于2025-09-23 15:22:29
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Defect formation in AlN after irradiation with He2+ ions
摘要： The paper presents results of studies on defect formation processes, radiation resistance, amd changes in the conductive and insulating characteristics of AlN ceramics under irradiation with 40 keV He2+ ions. The radiation fluence ranged from 1015 to 5x1017 ion/cm2. Using the method of X-ray structural analysis, it has been established that an increase in the irradiation fluence leads to a decrease in intensities of diffraction peaks and a change in lines shape, which indicates an increase in the concentration of distortions and stresses in the crystal structure. The change in concentration of deformation in the structure is due to the increase in the content of introduced helium and the formation of cascades of secondary defects and vacancies. At large fluences of irradiation (above 1017 ions/cm2), diffraction patterns show the formation of a halo characteristic of X-ray amorphous or highly disordered impurity inclusions and the formation of spherical inclusions in the surface layer, the average size of which varies from 50 to 100 nm. The decrease in resistance and thermal conductivity as a result of irradiation and the formation of helium inclusions in the structure indicates a degradation of the structural characteristics, as well as a decrease in radiation resistance, which is caused by a drop in strength characteristics.
关键词： ceramics,swelling,radiation embrittlement,defects,structural materials
更新于2025-09-23 15:22:29
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Compact integrated magnetometer based on nitrogen-vacancy centres in diamond
摘要： We demonstrate an integrated and miniaturised magnetic field sensor based on the negatively charged nitrogen-vacancy centres (NV-) in diamond. The compact device includes all optical components, both for the optical excitation path and for the detection of the emitted fluorescence signal. We experimentally verify that it enables optically detected magnetic resonance (ODMR) measurements and we specify noise and sensitivity of the magnetometer. The minimal detectable magnetic field of the device is ≈ 1 μT for a given integration time of 1 ms, which is approximately one order of magnitude larger than its photon shot-noise limit. It has the significant advantage over traditional setups using NV- centres (including a laser and a complex optical system) that the specific construction volume is about 2.9 cm3 with a total power consumption of ≈ 1.5 W, which enables the device for a wide range of industrial sensing applications.
关键词： synthetic diamond,defects,optical properties,high pressure high temperature (HPHT),sensors
更新于2025-09-23 15:22:29
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Investigation of local geometrical structure, electronic state and magnetic properties of PLD grown Ni doped SnO2 thin films
摘要： We have investigated the ferromagnetic behavior, electronic states and local geometrical structure of Ni (2 and 10 at %) doped SnO2 thin films. The films were successfully fabricated with the help of pulsed laser deposition (PLD) technique on Si (100) substrate under ultrahigh vacuum (UHV) condition. X-ray diffraction (XRD) results revealed the single phase character of SnO2 rutile lattice structure with P42/mnm space group. The inclusion of Ni ions into SnO2 matrix induced oxygen vacancy (Vo), enhanced the distortion in octahedral local symmetry and reduced the oxidation state of the host Sn4+ (SnO2) to Sn3+ (Sn2O3) these details have been estimated by Raman scattering, Near edge X-ray absorption fine structure (NEXAFS) spectra at Ni L3,2 and O K edges. Further quantitative details on the local geometrical structure around Ni ions were obtained via fitting the experimental Fourier transforms EXAFS spectra |X(R)| with FEFF6 code. The magnetization measurements performed at room temperature (RT) infers that the observed magnetic behavior of the films seems to be relevant to the same crystal growth condition (UHV) and might not be limited directly to the Ni dopant concentrations. The FM signal and the role of surface defects have been discussed based spin-split impurity band difference in the saturation moments even with increase the Ni content. Hence, the similarity in Ni doped SnO2 films displayed ferromagnetic (FM) signal, and there was no significant Ferromagnetism etc. percolation mechanism.
关键词： surface defects,XANES spectra,SnO2 nanostructured thin film,PLD,local symmetry,XRD,NEXAFS
更新于2025-09-23 15:22:29
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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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On the anomaly in the electrical characteristics of thin film transistors with multi-layered sol-gel processed ZnO
摘要： A set of bottom-gate Zinc Oxide (ZnO) thin film transistors (TFTs) with active layers containing 1, 4 and 8 layers of spin-coated ZnO were fabricated and their electrical characteristics such as transistor transfer and capacitance-voltage characteristics were analyzed. The transconductance of the single-layered ZnO transistor shows a single peak. On the other hand, multiple peaks and humps were observed in the transconductance and capacitance-voltage characteristics of multi-layered ZnO transistors. The multi-layers were grown by reiteration of the spin-coating process, producing ZnO-ZnO interlayer-interfaces. The surface of the ZnO layer in contact with the ambient contains active sites, resulting in chemisorption of ambient gases such as oxygen prior to the deposition of subsequent layers. The chemisorbed species become negatively-charged and form charge sheets, depleting the surface/interface region. It was proposed that the formation of depletion layers at ZnO-ZnO interlayer-interfaces is the main cause for the observed anomaly.
关键词： Sol-gel,Zinc oxide,Spin-coating,Thin-film transistors,Electrical Properties,Interface Defects
更新于2025-09-23 15:22:29
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Self-assembly of fractal liquid crystal colloids
摘要： Nematic liquid crystals are anisotropic fluids that self-assemble into vector fields, which are governed by geometrical and topological laws. Consequently, particulate or droplet inclusions self-assemble in nematic domains through a balance of topological defects. Here, we use double emulsions of water droplets inside radial nematic liquid crystal droplets to form various structures, ranging from linear chains to three-dimensional fractal structures. The system is modeled as a formation of satellite droplets, distributed around a larger, central core droplet and we extend the problem to explain the formation of fractal structures. We show that a distribution of droplet sizes plays a key role in determining the symmetry properties of the resulting geometric structures. The results are relevant to a variety of inclusions, ranging from colloids suspensions to multi-emulsion systems. Such systems have potential applications for novel switchable photonic structures as well as providing wider insights into the packing of self-assembled structures.
关键词： Self-assembly,Fractal structures,Topological defects,Colloids,Liquid crystals
更新于2025-09-23 15:22:29