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Formation and Evolution of Ultrathin Silica Polymorphs on Ru(0001) Studied with Combined in Situ, Real-Time Methods
摘要： Silica mono- and bilayer films on Ru(0001) can be physisorbed or chemisorbed, with ordered or vitreous structures, depending on the particular preparation procedures applied. Using the SMART spectro-microscope at BESSY-II with its capabilities for μ-spectroscopy, μ-diffraction, and LEEM imaging with lateral resolution below 5 nm, in situ and in real time and applied to identical areas, we have investigated the formation of these layers, defined and characterized their properties and their connected morphology, and followed their evolution. Two distinct chemisorbed monolayers and three bilayers (physisorbed crystalline and vitreous, and chemisorbed zigzag phases), and some transitions between them, have been studied. We found that, apart from the deposited silicon amount, the most important parameter for steering the evolution to a particular well-defined layer is the oxygen content at the Ru interface. Nucleation and growth of all layers are homogeneous on the scale of our resolution, leading to rather small domains (20 – 40 nm), mostly of the same phase, separated by defect lines. We discuss these and other basic findings in context and point out open questions. We also offer alternative recipes for the preparation of some phases, to obtain more homogeneous layers on a mesoscopic scale.
关键词： Silica films,SMART spectro-microscope,real-time methods,in situ,LEEM,chemisorbed,physisorbed,polymorphs,Ru(0001),μ-spectroscopy,μ-diffraction
更新于2025-09-04 15:30:14
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Towards simulation at picometer-scale resolution: Revisiting inversion domain boundaries in GaN
摘要： Motivated by recent high resolution results on the inversion domain boundaries (IDB) in gallium nitride, we re?ne by ab initio DFT calculations the well established atomic model IDB? derived by Northrup et al. This allows us to recover these experimental results obtained by coherent x-ray diffraction and showing small additional shifts of the polarity domains, in particular 8 pm shift along the hexagonal direction. The in?uence of boundary conditions and electrostatic ?elds (IDB-IDB and IDB-surface interactions) on the results and the existence of metastable solutions is carefully discussed to stress the accuracy of the method. These results demonstrate a cross-talk between advanced characterization tools and state-of-the-art ab initio calculations that opens perspectives for the structural analysis of defects in the picometer range.
关键词： picometer resolution,ab initio DFT calculations,coherent x-ray diffraction,gallium nitride,inversion domain boundaries
更新于2025-09-04 15:30:14
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Structural characteristics of m-plane AlN substrates and homoepitaxial films
摘要： Homoepitaxial non-polar AlN films were realized on m-plane (1010)-oriented AlN single crystals by metalorganic chemical vapor deposition (MOCVD). The microstructural properties of m-plane AlN substrates and homoepitaxial films were assessed by means of atomic force microscopy and high resolution x-ray diffraction characterization. Results indicated that both m-plane AlN substrates and films possessed exceptional structural quality, with some anisotropic mosaic distributions due to the quasi-bulk nature of the non-polar single crystals. An increase in the MOCVD growth temperature was noted to minimize the degree of inherited mosaic anisotropy without altering the m-plane AlN film growth rate, indicating that high temperature growth is critical to produce optimal film crystallinity. A dramatic change in the film surface morphology from heavily faceted “slate-like” features to monolayer steps was observed as the growth temperature was increased. The “slate-like” surface morphology produced low intensity cross-streaks in symmetric (1010) reciprocal space maps, tilted about 18° away from the (1010) crystal truncation rod. The orientation of these diffuse streaks corresponds to the physical alignment of the slates with respect to the substrate surface normal. X-ray line scans and defect-selective reciprocal space mapping confirmed that these low intensity streaks are solely dependent on this peculiar surface structure produced at low MOCVD growth temperatures and unrelated to basal plane stacking faults or other extended defects. All observations confirm that high quality III-nitride epitaxial structures on m-plane AlN substrates are attainable with controllable MOCVD growth processes, as demanded for future high performing AlN-based non-polar devices.
关键词： Characterization,Metalorganic chemical vapor deposition,High resolution x-ray diffraction,Surface structure,Nitrides,Crystal structure
更新于2025-09-04 15:30:14
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Archaeological applications of spectroscopic measurements. Compatibility of analytical methods in comparative measurements of historical Polish coins
摘要： The ED-XRF (energy-dispersive X-ray fluorescence) compact system was used to analyze selected Polish historical coins. The compact X-ray tube developed in the National Centre for Nuclear Research (NCBJ) was used as an X-ray source in the system designed for the ED-XRF studies. The XRF spectra were recorded with the Amptek SDD spectrometer. The elemental compositions of the coins have been determined using above mentioned system and the results were compared to those obtained with WD-XRF method. Other techniques such as SEM-EDX and XRD were also included into this work for comparison. The experimental data show that the X-ray system with transmission type X-ray tube with silver anode operating at 50 kV/30 mA which was developed in NCBJ together with the Amptek SDD spectrometer is an effective tool for chemical composition analyze of historical coins and can be successfully used in archaeometry.
关键词： Elemental composition,Energy-dispersive X-ray fluorescence,X-ray powder diffraction,Scanning electron microscope with Energy Dispersive X-Ray Spectroscopy,Wavelength-dispersive X-ray fluorescence
更新于2025-09-04 15:30:14
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Investigation of Material Nonlinearity Measurements Using the Third-Harmonic Generation
摘要： With respect to harmonic generation measurements in isotropic materials, the amplitude of the third-harmonic wave generally depends on both β2 (the square of the second-order nonlinear parameter β) and γ (the third-order nonlinear parameter). Therefore, some care should be taken when measuring these parameters using the third-harmonic amplitude. The purpose of this paper is to investigate detailed theoretical and measurement techniques for the accurate determination of β2 which dominates the third-harmonic amplitude in most biological ?uids and crystalline solids. The theory deals with harmonic generation in materials with cubic nonlinearity and de?nes the formula for measuring β2 with corrections for diffraction and attenuation. These corrections are derived from the Westervelt equation and play an important role in the measurement of nonlinear parameters. The third-harmonic amplitude that varies with the distance in water is obtained for the measurement of β2. β is also measured from the second-harmonic amplitude for comparison. We also con?rm the required input voltage to stably generate the third harmonic and discuss the effects of diffraction and attenuation correction on the β2 determination. The measured β2 in the propagation range of 0.05–0.2 m agrees well with the square of the measured β, revealing that the third-harmonic amplitude is closely related to β2, not γ . This paper covers comprehensive theories, experimentation, and analysis related to the measurement of third-harmonic generation in isotropic media and can be immediately applied to crystalline solids.
关键词： second harmonic,?nite amplitude method,nonlinear parameter,diffraction,quasi-linear solution,Attenuation,third harmonic
更新于2025-09-04 15:30:14
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Photoluminescence Imaging for Buried Defects Detection in Silicon: Assessment and Use-cases
摘要： In this work, the innovative photoluminescence imaging technique is described for applications to buried defect detection in silicon devices. The validity of this emerging technique is first assessed in comparison with well-established characterization techniques (defect selective etching of silicon, X-Ray diffraction topography, cross-sectional transmission electron microscopy imaging and photoluminescence spectroscopy). The paper then describes specific applications illustrating the use of the photoluminescence imaging technique for common processes of the CMOS semiconductor industry. The benefit of this fast, high resolution and non-destructive technique is demonstrated: this includes industrial use of the technique for in-line production control on product wafers.
关键词： photoluminescence imaging,dislocations,non-visual defects,X-Ray diffraction topography,photoluminescence spectroscopy,buried defects
更新于2025-09-04 15:30:14
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Impact of Magnesium substitution in Nickel ferrite: Optical and Electrochemical studies
摘要： Magnesium doped Ni ferrite nanoparticle (Ni1-xMgxFe2O4) has been synthesized by sol-gel combustion method and it has been analyzed using XRD, UV, FTIR and electrochemical charge-discharge studies. The observed XRD result confirms the nanostructure and it ranges from 23 to 28 nm. Furthermore, band gap energy values and functional group elements have been observed by UV and FTIR, respectively. The lattice constant values varies slightly with respect to magnesium concentration. The band gap energy values increase at the calcination temperature of 500oC as 0.85, 1.15, 1.2, and 1.45 eV and it decreases when it was calcined at 900oC as 1.3, 1.25, 1.15, 1.1 eV for x =0.25, 0.5, 0.75, 1, respectively. The voltage profiles of Ni1-xMgxFe2O4 nanoparticle electrodes show the discharge and charge capacities of 1021 and 718 mAh/g at 500oC and 1099 and 747 mAh/g at 900oC, respectively. The high reversible capacities for the Mg doped Ni ferrite nanoparticle electrodes are confirmed as anode materials for Li ion batteries.
关键词： X-ray diffraction,electrochemical study,Nanoferrite,bandgap energy
更新于2025-09-04 15:30:14
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Label-Free Identification of Lymphocyte Subtypes Using Three-Dimensional Quantitative Phase Imaging and Machine Learning
摘要： We describe here a protocol for the label-free identification of lymphocyte subtypes using quantitative phase imaging and machine learning. Identification of lymphocyte subtypes is important for the study of immunology as well as diagnosis and treatment of various diseases. Currently, standard methods for classifying lymphocyte types rely on labeling specific membrane proteins via antigen-antibody reactions. However, these labeling techniques carry the potential risks of altering cellular functions. The protocol described here overcomes these challenges by exploiting intrinsic optical contrasts measured by 3D quantitative phase imaging and a machine learning algorithm. Measurement of 3D refractive index (RI) tomograms of lymphocytes provides quantitative information about 3D morphology and phenotypes of individual cells. The biophysical parameters extracted from the measured 3D RI tomograms are then quantitatively analyzed with a machine learning algorithm, enabling label-free identification of lymphocyte types at a single-cell level. We measure the 3D RI tomograms of B, CD4+ T, and CD8+ T lymphocytes and identified their cell types with over 80% accuracy. In this protocol, we describe the detailed steps for lymphocyte isolation, 3D quantitative phase imaging, and machine learning for identifying lymphocyte types.
关键词： lymphocyte identification,machine learning,holotomography,immune cell,immunology,Immunology and Infection,Quantitative phase imaging,optical diffraction tomography,holographic microscopy,label-free imaging
更新于2025-09-04 15:30:14
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Comparison between Grating Imaging and Transient Grating Techniques on Measuring Carrier Diffusion in Semiconductor
摘要： Optical grating technique, where optical gratings are generated via light inference, has been widely used to measure charge carrier and phonon transport in semiconductors. In this paper, compared are three types of transient optical grating techniques: transient grating diffraction, transient grating heterodyne, and grating imaging, by utilizing them to measure carrier diffusion coefficient in a GaAs/AlAs superlattice. Theoretical models are constructed for each technique to extract the carrier diffusion coefficient, and the results from all three techniques are consistent. Our main findings are: (1) the transient transmission change ΔT/T0 obtained from transient grating heterodyne and grating imaging techniques are identical, even these two techniques originate from different detection principles; and (2) by adopting detection of transmission change (heterodyne amplification) instead of pure diffraction, the grating imaging technique (transient grating heterodyne) has overwhelming advantage in signal intensity than the transient grating diffraction, with a signal intensity ratio of 315:1 (157:1).
关键词： diffraction,Transient grating heterodyne,grating imaging,carrier diffusion
更新于2025-09-04 15:30:14
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Reduced Graphene Oxide Nanostructures by Light: Going Beyond the Diffraction Limit
摘要： Graphene oxide (GO) offers excellent possibilities that are recently demonstrated in many applications ranging from biological sensors to optoelectronic devices. The process of thermal annealing aids in removing the oxygen-containing groups in GO, making GO more graphene-like, or the so-called reduced graphene oxide (rGO). Thermal reduction can also be achieved by intense light. Here, we demonstrate a scalable, inexpensive, and environmentally friendly method to pattern graphene oxide films beyond the diffraction limit of light using a conventional laser. We show that contrary to previous reports, non-linear effects that occur under high intensity conditions of laser irradiation allow the fabrication of highly conductive carbon nanowires with dimensions much smaller than the laser spot size. The potential of this method is illustrated by the fabrication of several devices on flexible and transparent substrates, including hybrid plasmonic/rGO sensors.
关键词： reduced graphene oxide,optoelectronic devices,laser reduction,Graphene oxide,diffraction limit
更新于2025-09-04 15:30:14