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Photochromic properties in silver-doped titania nanoparticles
摘要： The Ag-doped TiO2 nanoparticles were synthesized at room temperature using a solution of titanium isopropoxide and silver nitrate as precursors. The inclusion of Ag in the nanocrystalline TiO2 lattice was systematically analyzed both from a morphological and a structural point of view. Raman spectroscopy, electron microscopy, electronic diffraction and x-rays allow us to testify that the dopant Ag does not modify the nanocrystalline anatase tetragonal structure of the nanoparticles, but causes a small distortion of the structure. UV–vis spectroscopy allowed to analyze the optical properties of the obtained nanoparticles. Kubelka Munk’s model allowed the interpretation of diffuse reflectance spectra. We have obtained a very different system from the hetero-system Ag-TiO2 described in the literature, but it shows an interesting photochromic behaviour. Ag-doped TiO2 nanoparticles darken and whiten under UV light and visible light, respectively, in a very fast way. A simple kinetic model has been used to process experimental data and describe the observed photochromic process and to determine the darkening and whitening constants.
关键词： photochromism,electron diffraction,nanoparticles,optical properties,Raman spectroscopy
更新于2025-09-23 15:22:29
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Constructing CH <sub/>3</sub> NH <sub/>3</sub> PbI <sub/>3</sub> and CH <sub/>3</sub> NH <sub/>3</sub> PbBr <sub/>3</sub> Perovskite Thin Film Electronic Structure from Single Crystal Band Structure Measurements
摘要： Photovoltaic cells based on halide perovskites and possessing remarkably high power conversion efficiencies have been reported. To push the development of such devices further, a comprehensive and reliable understanding of their electronic properties is essential, but presently not available. To provide a solid foundation for understanding the electronic properties of polycrystalline thin films, we employ single crystal band structure data from angle-resolved photoemission measurements. For two prototypical perovskites (CH3NH3PbBr3 and CH3NH3PbI3) we reveal the band dispersion in two high symmetry directions, and identify the global valence band maxima. With these benchmark data, we construct 'standard' photoemission spectra from polycrystalline thin film samples and resolve challenges discussed in the literature of determining the valence band onset with high reliability. Within the framework laid out here, the consistency of relating the energy level alignment in perovskite-based photovoltaic and optoelectronic devices with their functional parameters is substantially enhanced.
关键词： single crystal and thin film perovskites,angle-resolved photoemission,low-energy electron diffraction and density functional theory
更新于2025-09-23 15:22:29
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Coulomb interaction-induced jitter amplification in RF-compressed high-brightness electron source ultrafast electron diffraction
摘要： We have theoretically and experimentally demonstrated an RF compression-based jitter-amplification effect in high-brightness electron source ultrafast electron diffraction (UED), which degrades the temporal resolution significantly. A detailed analysis and simulations reveal the crucial role of the longitudinal and transverse Coulomb interaction for this jitter-amplification effect, which accord very well with experimental results. An optimized compact UED structure for full compression has been proposed, which can suppress the jitter by half and improve the temporal resolution to sub-100 fs. This Coulomb interaction-induced jitter amplification exists in nearly the whole ultrafast physics field where laser-electron synchronization is required. Moreover, it cannot be suppressed completely. The quantified explanation for the mechanism and optimization provides important guidance for photocathode accelerators and other compression-based ultrashort electron pulse generation and precise control.
关键词： system optimization,jitter amplification,RF compression,high-brightness electron source,ultrafast electron diffraction,Coulomb interaction
更新于2025-09-23 15:21:21
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Self-assembled indium nanostructures formation on InSe (0001) surface
摘要： The surfaces of 2D layered crystals are one among most perspective templates for self-assembling of metal nanostructures due to the dewetting. The initial InSe (0001) surface as topological template was characterized by means of scanning tunneling microscopy/spectroscopy (STM/STS) and low electron energy diffraction. InSe (0001) surface used in the process of formation of nanostructures found to be a template covered with array of triangular-shaped cites. The results of STM/STS studies on the formation of indium nanostructures on (0001) surface of InSe layered semiconductor crystal are presented. Indium was thermally deposited on structurally perfect InSe crystal cleavages obtained in situ. Geometrically heterogeneous (in height) initial (0001) InSe surface is used to activate the dewetting phenomenon in a manner that leads to the formation of 0D triangular-shaped nucleus of deposited indium nanostructures. STS acquired spatially averaged I–V curves changes their dependence from semiconductor one to almost metallic due to dewetting process. Moreover, the spatial arrangement of formed indium nanostructures is powered by hexagonal lattice symmetry of InSe surface on macroscale.
关键词： Hetero nanostructures,Nanostructures template-directed assembly,Layered crystals,Scanning tunneling microscopy/spectroscopy,Indium selenide,Low energy electron diffraction
更新于2025-09-23 15:21:01
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Determination of 60° polarization nanodomains in a relaxor-based ferroelectric single crystal
摘要： Here, we report a determination of monoclinic nanodomains in PMN-xPT with x ? 31%PT by using scanning convergent beam electron diffraction (SCBED). We show the presence of 60 6 a degree nanodomains with Cm-like symmetry as well as signi?cant variations (a) in local polarization directions across lengths of (cid:3)10 nm. The principle of our technique is general and can be applied for the determination of polarization domains in other ferroelectric materials of different symmetry. VC 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4932955]
关键词： ferroelectric materials,scanning convergent beam electron diffraction,monoclinic nanodomains,PMN-xPT,SCBED
更新于2025-09-23 15:21:01
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Ultrathin films of L1 <sub/>0</sub> -MnAl on GaAs (001): A hard magnetic MnAl layer onto a soft Mn-Ga-As-Al interface
摘要： Ferromagnetic MnAl (L10-MnAl phase) ultrathin films with thickness varying from 1 to 5 nm have been epitaxially grown on a GaAs (001) substrate. A coercivity above 8 kOe has been obtained with no need of a buffer layer by tuning the sample preparation and the growth parameters. Surface and interface analysis carried out by in situ characterization techniques (x-ray photoelectron spectroscopy and low energy electron diffraction), available in the molecular beam epitaxy chamber, has shown the formation of a ferromagnetic interface consisting of Mn-Ga-As-Al, which contribution competes with the MnAl alloyed film. The appearance of this interface provides important information to understand the growth mechanism of MnAl-based films reported in the literature.
关键词： x-ray photoelectron spectroscopy,ferromagnetic,GaAs,molecular beam epitaxy,low energy electron diffraction,ultrathin films,L10-MnAl
更新于2025-09-23 15:21:01
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p+ polycrystalline silicon growth via hot wire chemical vapour deposition for silicon solar cells
摘要： Hot wire chemical vapour deposition (HWCVD) is explored as a way of growing boron-doped silicon for photovoltaic devices. Deposition temperatures are measured using a custom-built monitoring system for two different filament configurations within the HWCVD tool. A refined fabrication process is presented, using an altered filament arrangement, that currently provides a maximum deposition temperature of 535 oC, for growing boron-doped silicon films via HWCVD, with the inclusion of a short post-deposition anneal at 800 oC for 2 minutes. Transmission electron microscopy reveals improvements in interfacial quality, as well as larger grains present after post-annealing treatments. In addition, re-crystallisation of as-deposited amorphous Si films under a short anneal is confirmed using Raman spectroscopy. The enhancements in morphology translate to a boost in current rectification based on our dark current-voltage measurements. This is further supported by secondary-ion mass spectrometry analysis, presenting p+ properties with uniform doping in the 1021 cm-3 region.
关键词： Selective area electron diffraction,Crystallisation,Emitter,Hot wire chemical vapour deposition,Silicon solar cells,Transmission electron microscopy
更新于2025-09-23 15:19:57
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Precession Electron Diffraction and Orientation Phase Mapping of Assembled Ag/ZnO Nanoantennas
摘要： The manipulation of the geometrical and structural arrangement of the constituent’s elements on devices at nanoscale level is highly desirable for a precise monitoring of the opto-electrical properties exhibited for these nanomaterials. In fact, a great effort has being made to understand the coupling mechanisms on metal-semiconductors systems, most precisely at interfaces nanoscale level. For instance, it is well known that the multidirectional radiation pattern generated by the active elements on nanoantenna applications is highly dependent on both the structural and orientation distribution of the receiver elements as well as the passive element on the nanoscale device. For example, Wang, et al [1] have synthesized high order nanostructures in a hierarchical configuration to study the photo-induced optical properties of these systems in function of the ZnO concentration distributed along the silver nanowires. However, few is known about the structural coupling mechanisms between this metal-semiconductor heterojunctions. Thus, to understand the dynamic coupling at the interface level in the Ag/ZnO metal-semiconductor heterojunctions we report the epitaxial growing of zinc oxide nanorods on the pentagonal exposes faces of Ag nanowires resembling a hierarchal nanoantenna. Moreover, the studied of the growth mechanism in the active/contact faces of the metal-semiconductor heterojunction has been done by mapping simultaneously the dynamical electron diffraction pattern under in-situ precession electron diffraction at the heterojunction interface Ag/ ZnO nanosystem. Indeed, by indexing the dynamical diffraction patterns using orientational/phase mapping from the precessed electron diffraction data collected an orientational mapping has been retrieved showing the interfacial growing polar planes (0002) of ZnO nanorods on the pentagonal planes of silver nanowires with a mismatch between planes along the coupling interface. For completeness, grazing angle x-ray diffraction measurements on prepared substrates Ag/ZnO systems shown well-defined peaks associated to the main phases of ZnO nanorods and Ag nanowires respectively. A full understanding of the fit faces mechanism between Ag/ZnO along the mismatch direction undoubtedly will allow elucidating the mechanism through which the contact metal-semiconductor behaves at the heterojunction interface.
关键词： Nanoscale Devices,Ag/ZnO Nanoantennas,Metal-Semiconductor Heterojunctions,Orientation Phase Mapping,Precession Electron Diffraction
更新于2025-09-23 15:19:57
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Growth of Ag(1?1?1) on Si(1?1?1) with nearly flat band and abrupt interface
摘要： Growth of Ag films of up to 30 nm thickness on Si(1 1 1) 7 × 7 at room temperature is investigated by low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). LEED revealed the coexistence of Ag and Si spots starting with 1 monolayer (ML) of Ag deposited. The Ag lattice constant, starting with 25 ML, is slightly higher than for bulk Ag and increase linearly with Ag thickness, reaching about 4.2 nm for the thickest films. The average terrace widths detected from LEED spot profile analysis are about 30 nm for clean Si(1 1 1) 7 × 7 and about 5.5 nm for the thickest Ag(1 1 1) film, in agreement with STM observations. The intensity variation of core levels analyzed by XPS is taken into account by a model assuming the initial formation of Ag islands with linear variation of coverage vs. the amount of Ag deposited, followed by growth in a quasi layer-by-layer mode. The interface barrier is in the range of 0.4 eV, lower than all values reported previously. Ag deposited on Si(1 1 1) 7 × 7 at room temperature provides flat Ag(1 1 1) for synthesis of 2D materials, and may be used for low barrier Schottky diodes.
关键词： Scanning tunneling microscopy,Low energy electron diffraction,X-ray photoelectron spectroscopy,Ag/Si(1 1 1),Molecular beam epitaxy,Surface barrier height
更新于2025-09-23 15:19:57
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European Microscopy Congress 2016: Proceedings || Analysis of GaAs compound semiconductors and the semiconductor laser diode using electron holography, Lorentz microscopy, electron diffraction microscopy and differential phase contrast STEM
摘要： The content within the paper discusses the development and application of semiconductor devices and their semiconductor layers using electron holography, electron microscopy, electron diffraction microscopy, and different phase contrast methods. It highlights the importance of these techniques in understanding the structural and electronic properties of semiconductor materials.
关键词： semiconductor devices,phase contrast,electron diffraction,electron microscopy,electron holography
更新于2025-09-11 14:15:04