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The Role of Secondary Electron Emission in the Charging of Thin-Film Phase Plates
摘要： In the past few years, physical phase plates (PP) have become a viable tool to enhance the contrast of weak-phase objects in transmission electron microscopy (TEM). Thin-film PPs, such as the Zernike and Hilbert PP, are based on the mean inner potential of microstructured thin films [1,2]. Typically, a thin amorphous carbon (aC)-film is applied, whose thickness is adjusted to induce a well-defined phase shift between unscattered and scattered electrons. However, the illumination with high-energy electrons initiates an irreversible degeneration of the aC-film, which causes electrostatic charging and affects the phase-shifting properties. Taking even advantage of charging, hole-free PPs were recently developed [3,4]. Electrostatic charging plays a central role in the application of thin-film PPs. However, the mechanisms of charging are not well-understood. This work shows that charging is dominated by secondary electron emission. For this purpose, Hilbert PPs were fabricated from different materials to study their charging behavior under electron beam illumination. Besides aC-films, thin films of the metallic glass alloy Pd77.5Cu6.0Si16.5 (PCS) were used for PP fabrication. The PCS-alloy is characterized by an amorphous structure and a high electrical conductivity, which is three orders of magnitude higher than that of aC [5,6]. Moreover, the PCS-alloy exhibits a strong resistance towards oxidation, which suggests less charging of PCS-films.
关键词： transmission electron microscopy,thin-film,secondary electron emission,charging,phase plates
更新于2025-11-21 11:20:48
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Site-controlled formation of single Si nanocrystals in a buried SiO <sub/>2</sub> matrix using ion beam mixing
摘要： For future nanoelectronic devices – such as room-temperature single electron transistors – the site-controlled formation of single Si nanocrystals (NCs) is a crucial prerequisite. Here, we report an approach to fabricate single Si NCs via medium-energy Si+ or Ne+ ion beam mixing of Si into a buried SiO2 layer followed by thermally activated phase separation. Binary collision approximation and kinetic Monte Carlo methods are conducted to gain atomistic insight into the influence of relevant experimental parameters on the Si NC formation process. Energy-filtered transmission electron microscopy is performed to obtain quantitative values on the Si NC size and distribution in dependence of the layer stack geometry, ion fluence and thermal budget. Employing a focused Ne+ beam from a helium ion microscope, we demonstrate site-controlled self-assembly of single Si NCs. Line irradiation with a fluence of 3000 Ne+/nm2 and a line width of 4 nm leads to the formation of a chain of Si NCs, and a single NC with 2.2 nm diameter is subsequently isolated and visualized in a few nanometer thin lamella prepared by a focused ion beam (FIB). The Si NC is centered between the SiO2 layers and perpendicular to the incident Ne+ beam.
关键词： phase separation,Monte Carlo simulations,single electron transistor,ion beam mixing,helium ion microscopy
更新于2025-11-21 11:20:48
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Morphology Phase Diagram of Slot‐Die Printed TiO <sub/>2</sub> Films Based on Sol–Gel Synthesis
摘要： Mesoporous titania films with tailored nanostructures are fabricated via slot-die printing, which is a simple and cost-effective thin-film deposition technique with the possibility of a large-scale manufacturing. Based on this technique, which is favorable in industry, TiO2 films possess the similar advantage with polymer semiconducting devices like ease of large-scale production. The titania morphologies, including foam-like nanostructures, nanowire aggregates, collapsed vesicles and nanogranules, are achieved via a so-called block-copolymer-assisted sol–gel synthesis. By adjusting the weight fraction of reactants, the ternary morphology phase diagram of the printed titania films is probed after template removal. The surface and inner morphology evolutions are explored with scanning electron microscopy and grazing incidence small-angle X-ray scattering, respectively. Special focus is set on foam-like titania nanostructures as they are of especial interest for, e.g., solar cell applications. At a low weight fraction of the titania precursor titanium(IV)isopropoxide (TTIP), foam-like titania films are achieved, which exhibit a high uniformity and possess large pore sizes. The anatase phase of the highly crystalline titania films is verified with X-ray diffraction and transmission electron microscopy.
关键词： TiO2 films,crystallinity,morphology phase diagram,printing,GISAXS
更新于2025-11-21 11:20:42
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Microstructure modelling of laser metal powder directed energy deposition of Alloy 718
摘要： A multi-component and multi-phase-field modelling approach, combined with transformation kinetics modelling, was used to model microstructure evolution during laser metal powder directed energy deposition of Alloy 718 and subsequent heat treatments. Experimental temperature measurements were utilised to predict microstructural evolution during successive addition of layers. Segregation of alloying elements as well as formation of Laves and δ phase was specifically modelled. The predicted elemental concentrations were then used in transformation kinetics to estimate changes in Continuous Cooling Transformation (CCT) and Time Temperature Transformation (TTT) diagrams for Alloy 718. Modelling results showed good agreement with experimentally observed phase evolution within the microstructure. The results indicate that the approach can be a valuable tool, both for improving process understanding and for process development including subsequent heat treatment.
关键词： Modelling,Heat Treatment,Phase-field,Thermal Cycle,DED
更新于2025-11-21 11:18:25
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Study on the element segregation and Laves phase formation in the laser metal deposited IN718 superalloy by flat top laser and gaussian distribution laser
摘要： The element segregation, Laves phase formation, and mechanical properties of the laser metal deposited IN718 superalloy by the flat top laser beam (FTLB) and gaussian distribution laser beam (GDLB) are studied. It is found that the Laves phase formation in the gaussian distribution laser deposited IN718 (GDLD-IN718) is substantially higher than that in the flat top laser deposited IN718 (FTLD-IN718). The higher production of the Laves phase in the GDLD-IN718 contributes to the higher microhardness and lower tensile strength (about 20% reduction) of the as-deposited IN718 than that of the FTLD-IN718. The element redistribution behavior in the laser rapid solidification under both of the lasers are also studied through the finite element simulation. The results show that the severe laser energy concentration in the center of the GDLB produces higher molten pool temperature, lower horizontal thermal gradient to vertical thermal gradient ratio (GX/GZ) of the solid-liquid interface. These typical thermal characteristic of the GDLB generated molten pool eventually results in a lower redistribution coefficient of the alloying elements and as a result, the interdendritic element segregation and Laves phase formation are dramatically improved in the GDLD-IN718. The present comparative study proves that the FTLB is more superior for the laser additive manufacturing than that of the GDLB.
关键词： Dendritic growth,Laser metal deposition,Element segregation,Redistribution coefficient,Laves phase
更新于2025-11-21 11:18:25
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Unraveling the electrical properties of solution-processed copper iodide thin films for CuI/n-Si solar cells
摘要： The effects of temperature and liquid-phase iodination on the electrical property of spin coated CuI thin films have been investigated in details. The XRD study indicates that CuI thin films are polycrystalline in nature and I-doping enhances the crystal quality and size of the films. The SEM images show that the surface uniformity of the CuI thin films increases due to I-doping. The doping of iodine increases the conductivity as well as carrier concentration and mobility of the films as confirmed by Hall study. The temperature dependent resistivity of CuI film shows a sharp fall of resistivity at ~80 °C for un-doped films whereas this behavior disappears for I-doped films. The optical transmittance and band gap of the I-doped films also increases indicating high degeneracy of the films. These findings imply that I-doped spin coated CuI thin films are potential candidate for the solution-processed CuI/n-Si solar cells.
关键词： liquid-phase I-doped,spin coat,CuI thin films,switching-behavior,electrical properties
更新于2025-11-21 11:18:25
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Cr3+ doped nanoporous anodic alumina: Facile microwave assisted doping to realize nanoporous ruby and phase dependent photoluminescence
摘要： Microwave-assisted solution technique (MAST) was used for the homogeneous doping of Cr3+ in nanoporous anodic alumina (NAA) which when heat-treated transforms into nanoporous ruby. The rise in annealing temperature led to the phase transition in the sequence: amorphous- δ- θ- α-alumina as evidenced by XRD. The dopant was homogenously distributed as seen from the elemental mapping and the Cr3+ content was 0.5 at%. Di?use re?ectance spectroscopy (DRS) displayed the characteristic blue and green absorption bands and the color-tone varied from light-green at 700 °C to the pink appearance at 1350 °C owing to the dopant di?usion. Two broad photoluminescence (PL) excitation bands centered at ～550 nm and ～400 nm were observed whose intensity increased with the annealing temperature. All the alumina phases exhibited characteristic phase dependent PL showing variation in the luminescence intensity and peak position. The characteristic R-line for α-phase was intense and observed at 694 nm with 4 m s lifetime in accordance with that expected for Ruby. Crystal ?eld parameters were obtained from the PL excitation spectra and Dq/B values were found to be higher than 2.3 for all the phases of NAA con?rming the presence of Cr3+ ions in the strong crystal ?eld. With annealing, the CIE coordinates moved towards the red region. The presented work shows a promising easy and inexpensive method for dopant incorporation into alumina and explores the understanding of phase-dependent emission of Cr3+ doped NAA for their potential applications in the areas of nano-optics and composite luminescent nanomaterials.
关键词： Nanoporous anodic alumina,Cr3+ doping,Photoluminescence,Phase transition
更新于2025-11-21 11:18:25
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Multifunctional Thermosensitive Liposomes Based on Natural Phase Change Material: Near-Infrared Light-Triggered Drug Release and Multimodal Imaging Guided Cancer Combination Therapy
摘要： Multifunctional theranostic nanoplatforms (NPs) in response to environment stimulations for on-demand drug release are highly desirable. Herein, the near-infrared (NIR)-absorbing dye, indocyanine green (ICG) and the antitumor drug, doxorubicin (DOX) were efficiently co-encapsulated into the thermosensitive liposomes based on natural phase change material (PCM). Folate and conjugated gadolinium chelate-modified liposome shells enhance active targeting and magnetic resonance (MR) performance of the NPs while maintaining the size of the NPs. The ICG/DOX loaded and gadolinium chelates conjugated temperature-sensitive liposomes nanoplatforms (ID@TSL-Gd NPs) exhibited NIR-triggered drug release and prominent chemo-, photothermal, photodynamic therapy properties. With the co-encapsulated ICG, DOX and the conjugated gadolinium chelates, the ID@TSL-Gd NPs can be used for triple-modal imaging (fluorescence/photoacoustic/magnetic resonance imaging, FL/PAI/MRI) guided combination tumor therapy (chemotherapy, photothermotherapy and photodynamic therapy, Chemo/PTT/PDT). After tail vein injection, the ID@TSL-Gd NPs accumulated effectively in subcutaneous HeLa tumor of mice. The tumor was effectively suppressed by accurate imaging guided NIR triggered phototherapy and chemotherapy, and no tumor regression and side effects were observed. In summary, the prepared ID@TSL-Gd NPs achieved multimodal imaging-guided cancer combination therapy, providing a promising platform for improving diagnosis and treatment of cancer.
关键词： Multimodal imaging,Liposomes,Thermosensitive,Combination therapy,Phase change material
更新于2025-11-21 11:08:12
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Chemically exfoliated 1T-phase transition metal dichalcogenide nanosheets for transparent antibacterial applications
摘要： Two-dimensional transition metal dichalcogenides (TMDs) are promising materials for a range of applications owing to their intriguing properties including the excellent electrical performance and biocompatibility. Strikingly, 1T-phase TMDs have attracted significant interest based on their metallic properties with octahedral metal coordination where the phase transition can occur from the semiconducting 2H-phase to metallic 1T-phase by chemical intercalation-induced exfoliation process. In this regard, 1T-phase TMDs have great potential in antibacterial agents in terms of effective charge transfer between the bacterial membrane and TMD nanosheets while their biological interactions have been underexplored. To bridge this gap, we herein investigate the antibacterial activities of various 1T-phase TMDs including molybdenum disulfide (MoS2), tungsten disulfide (WS2), and molybdenum diselenide (MoSe2) toward Gram-negative bacteria Escherichia coli that exhibit the reduction of bacterial viability caused by the production of reactive oxygen species, oxidation of glutathione and other chemical functionalities. The effective antibacterial capacity of metallic 1T-phase TMDs is observed and their bactericidal mechanisms are investigated in terms of their electrical conductivity and chemical oxidation property that induce the charge transfer from bacterial membrane to TMDs leading to the continuous disruption of bacteria and loss of cellular components. Furthermore, we demonstrated the transparent antibacterial films consisting of 1T-phase TMDs in which TMD nanosheets are immobilized on the surfaces and their basal planes play an important role in antibacterial actions for practical biomedical applications. Thus, our findings provide new insights into the great potential of 1T-phase TMDs as promising building blocks for antibacterial surfaces and contribute to the widespread use of 1T-phase TMDs for practical biomedical applications.
关键词： 1T-phase,charge transfer,antibacterial activity,oxidative stress,transition metal dichalcogenide
更新于2025-11-21 11:08:12
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Selective Growth of Ordered Hexagonal InN Nanorods
摘要： Well-ordered and vertically aligned InN nanorods with high aspect ratio are synthetized by hydride vapor phase epitaxy (HVPE) using the selective area growth (SAG) approach. The growth occurs through the apertures of a SiNx masked Ga-polar GaN/c-Al2O3 template for adjusted growth temperature and V/III ratio. The nanorods exhibit a hexagonal shape without any rotation around the growth axis. The wurtzite structure and the high crystalline quality of InN nanorods are confirmed by X-ray diffraction (XRD) as well as by high-resolution transmission electron microscopy (HR-TEM). Only few stacking faults are identified at the bottom part of the nanorods. Photoluminescence (PL) displays an emission peak centered at 0.77 eV which agrees with the band gap of InN. These promising achievements, which go far beyond the existing InN growth limitations, pave the way towards the integration of pure InN in future devices
关键词： Selective Area Growth,Hydride Vapor Phase Epitaxy,Indium Nitride,Nanorods
更新于2025-11-21 11:03:13