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Vortex beam generation with variable topological charge based on a spiral slit
摘要： We propose a vortex beam generator based on a nanometer spiral slit and explore the propagation rule of the topological charge. Compared to the common methods of generation of a vortex beam with a fixed topological charge, the optical vortex generated by the proposed vortex beam generator has the topological charge varying with the propagation distance. The value of topological charge can be modulated by the geometric charge of the spiral slit and the propagation distance. Theoretical analysis predicts the variation rule of the topological charge of vortex beam in the near field, and numerical simulations and experimental measurement verify the proposed scheme. Discussion on the shape and structure of the spiral slit is also presented. This work provides the theoretical foundation for the generation of a vortex field with variable topological charge. The simple geometry of the vortex beam generator and the flexible modulation of the topological charge must inspire applications of the vortex beam.
关键词： optical vortex,near-field diffraction,variable topological charge
更新于2025-09-23 15:22:29
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European Microscopy Congress 2016: Proceedings || Structure solution of the complex λ-La6W2O15
摘要： The structure solution of the complex β-Ga2O3 (β-Ga2O3) phase has been studied by a number of groups [1-3], but little detailed information has been reported due to the lack of good single crystals. The β-Ga2O3 phase has a monoclinic structure with space group C2/m and lattice parameters a = 12.23 ?, b = 3.04 ?, c = 5.80 ?, β = 103.7°. Recently, the structures of La2Ga2O7, La1.8Sr0.2Ga2O6.9 and La0.9Sr0.1Ga0.9Mg0.1O2.9 have been solved using X-ray powder diffraction (XRPD) [4-7]. The β-Ga2O3 phase has been studied by a number of groups [8-11], but little detailed information has been reported due to the lack of good single crystals. The β-Ga2O3 phase has a monoclinic structure with space group C2/m and lattice parameters a = 12.23 ?, b = 3.04 ?, c = 5.80 ?, β = 103.7°. Recently, the structures of La2Ga2O7, La1.8Sr0.2Ga2O6.9 and La0.9Sr0.1Ga0.9Mg0.1O2.9 have been solved using X-ray powder diffraction (XRPD) [4-7].
关键词： structure solution,β-Ga2O3,X-ray powder diffraction,monoclinic,lattice parameters
更新于2025-09-23 15:22:29
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CoGe surface oxidation studied using X-ray photoelectron spectroscopy
摘要： Cobalt germanides have been widely studied as semiconductor contact materials, but recent theoretical studies suggest that they may also be excellent catalysts for methane steam reforming with stabilities and activities comparable to more expensive noble metal catalysts. We have sputter deposited CoGe alloy films and characterized their structure and morphology after post-deposition annealing in high vacuum up to 1000 °C. We used X-ray photoelectron spectroscopy to study the initial oxidation of amorphous and crystalline CoGe alloy surfaces under low pressures of O2 and H2O. The oxidation rate in O2 was found to be faster for an amorphous CoGe surface compared to a crystalline surface. We also found that there was little difference in the oxidation rate in H2O for either amorphous or crystalline surfaces. During O2 oxidation, the crystalline surface preferentially forms GeO and the amorphous surface preferentially forms GeO2. We have also observed preferential oxidation of Ge in the CoGe thin films. During temperature programmed desorption studies, we found that GeO desorption begins near 350 °C and that GeO2 decomposes to GeO and desorbs near 700 °C. More studies of CoGe catalysts are warranted, however GeO desorption may be a concern under reaction conditions when the film is subjected to an oxidizing environment.
关键词： Oxidation,Cobalt germanium,Temperature programmed desorption,Atomic force microscopy,X-ray photoelectron spectroscopy,X-ray diffraction
更新于2025-09-23 15:21:21
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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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Dielectric and piezoelectric properties of Sm3+ doped lead barium niobate (PBN) ceramics
摘要： Rhombohedral samarium doped Lead based ceramic materials were fabricated by a high temperature conventional solid state mixed oxide ceramic process. The ceramic composition Pb1-x-3y/2Bax Re3+ y Nb2O6 (x = 0.35 and y=0.00, 0.02, 0.04 and 0.06, Re3+ = Sm3+). The pure and Sm3+ doped lead barium niobate ceramic materials are single phase with rhombohedral(hexagonal) symmetry obtained from powder x-ray diffraction (XRD). The grain size has been measured for all the compositions and lying between 1.60-2.90μm. Broad dielectric peak phase transitions observed with temperature in pure and Sm3+ ion modified lead barium niobate ceramic materials. It is observed that the high values of piezoelectric charge coefficients in d31 and d33 in Sm3+ doped lead barium niobate ceramics. The mechanical quality factor Qm and d33 increases with increase of Sm3+ ion concentration and indicating a highly polarisable lead ion contributing to high Curie temperature dielectric constant.
关键词： SEM,Piezoelectric properties,Rhombohedral,Synthesis of ceramic compositions,dielectric,X-Ray diffraction
更新于2025-09-23 15:21:21
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Anisotropic nano-scale resolution in 3D Bragg coherent diffraction imaging
摘要： We demonstrate that the resolution of three-dimensional (3D) real-space images obtained from Bragg coherent x-ray diffraction measurements is direction dependent. We propose and demonstrate the effectiveness of a metric to determine the spatial resolution of images that accounts for the directional dependence. The measured direction dependent resolution of (cid:2)4–9 nm is higher than the best previously obtained 3D measurements. Finally, we quantify the relationship between the resolution of recovered real-space images and dosage and discuss its implications in the light of next generation synchrotrons.
关键词： synchrotrons,resolution,Bragg coherent x-ray diffraction imaging,dosage,direction dependent
更新于2025-09-23 15:21:21
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Specialty probes give super-res imaging that special blink
摘要： Fluorescent probes light the way to cellular detail, but light can also get in the way. Because of the diffraction limit, structures closer to one another than 200 nanometers (nm) or so cannot be discerned. Unless you use probes with super-resolution imaging. These techniques, such as reversible saturable optical linear fluorescence transitions (RESOLFT) or photoactivated localization microscopy (PALM)/stochastic optical reconstruction microscopy (STORM), use specialty probes, dyes and fluorescent proteins (FPs) that can switch from dark to light and from one color to another. 'We need the labels in combination with the microscope to overcome the diffraction barrier,' says Stefan Jakobs, who develops probes at University Medical Center G?ttingen and the Max Planck Institute for Biophysical Chemistry. In structured illumination microscopy (SIM), labs routinely achieve 100-nm resolution, he says. Scientists using stimulated emission depletion microscopy (STED), RESOLFT, PALM or STORM reach beyond 50-nm resolution. In principle, he says, the methods are diffraction unlimited.
关键词： STORM,STED,RESOLFT,super-resolution imaging,SIM,fluorescent probes,diffraction limit,PALM
更新于2025-09-23 15:21:21
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Coherent Tabletop EUV Ptychography of Nanopatterns
摘要： Coherent diffraction imaging (CDI) or lensless X-ray microscopy has become of great interest for high spatial resolution imaging of, e.g., nanostructures and biological specimens. There is no optics required in between an object and a detector, because the object can be fully recovered from its far-field diffraction pattern with an iterative phase retrieval algorithm. Hence, in principle, a sub-wavelength spatial resolution could be achieved in a high-numerical aperture configuration. With the advances of ultrafast laser technology, high photon flux tabletop Extreme Ultraviolet (EUV) sources based on the high-order harmonic generation (HHG) have become available to small-scale laboratories. In this study, we report on a newly established high photon flux and highly monochromatic 30 nm HHG beamline. Furthermore, we applied ptychography, a scanning CDI version, to probe a nearly periodic nanopattern with the tabletop EUV source. A wide-field view of about 15 × 15 μm was probed with a 2.5 μm?diameter illumination beam at 30 nm. From a set of hundreds of far-field diffraction patterns recorded for different adjacent positions of the object, both the object and the illumination beams were successfully reconstructed with the extended ptychographical iterative engine. By investigating the phase retrieval transfer function, a diffraction-limited resolution of reconstruction of about 32 nm is obtained.
关键词： high-order harmonic generation,ptychography,lensless X-ray microscopy,Extreme Ultraviolet,Coherent diffraction imaging
更新于2025-09-23 15:21:21
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Preferred orientation of 2,7-dioctyl[1]benzothieno[3,2- <i>b</i> ][1]benzothiophene molecules on inorganic single-crystal substrates with various orientations
摘要： The organic molecule 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) was deposited on quartz glass, e11 (cid:2)20T A-, (0001) C-, and e1 (cid:2)102T R-single-crystal Al2O3 (sapphire), and (100)-, and (111)-single-crystal MgO substrates by vacuum thermal evaporation, and structural characterizations were carried out by X-ray di?raction analysis and atomic force microscopy (AFM) observation. The (001) out-of-plane orientation with a similar in-plane orientation was obtained irrespective of the substrate material and orientation, and its formation was governed by π–π-stacking-induced molecular ordering. The degree of orientation was re?ected by the grain structure related to the substrate material. The growth model of the oriented C8-BTBT layer was speculated on the basis of experimental results.
关键词： π–π-stacking,vacuum thermal evaporation,X-ray diffraction,C8-BTBT,atomic force microscopy
更新于2025-09-23 15:21:21
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Effect of low-energy ion impact on the structure of hexagonal boron nitride films studied in surface-wave plasma
摘要： A high‐density surface‐wave plasma source is used to deposit hexagonal boron nitride (hBN) films in a gas mixture of He, H2, N2, Ar, and BF3 under a high ion flux condition using low‐energy ion irradiation. The ion energy is controlled between around zero and 100 eV by applying a negative or positive bias voltage to a substrate, while the ion flux is increased by locating a substrate upstream in the diffusive plasma. For ion energies above ～37 eV, the structure of the films depends upon ion energy more than substrate temperature, typical of subplantation processes. As a result, the structural order and crystallinity of sp2‐bonded phase in the films characterized by Fourier transform infrared spectroscopy and X‐ray diffraction are increased with decreasing ion energy, while the mass density of the films characterized by X‐ray reflectivity is retained relatively high with a slight dependence upon ion energy.
关键词： surface‐wave plasma,Fourier transform infrared spectroscopy (FTIR),chemical vapor deposition (CVD),hexagonal boron nitride (hBN),X‐ray diffraction (XRD),X‐ray reflectivity (XRR)
更新于2025-09-23 15:21:21