- 标题
- 摘要
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Improved molecular structure retrieval method for photoelectron holography
摘要： Photoelectron holography is a method that retrieves molecular structure information from photoelectron diffraction patterns generated by x-ray free-electron lasers, which have the promise of following dynamic molecular structure evolutions with angstrom spatial and femtosecond temporal resolutions (the so-called molecular movie). However, an additional phase is introduced when the photoelectron is scattered by an atom, and this scattering phase turns into a spatial error when the position of the atom is retrieved using a Fourier-type transform. We propose a method to remove, or greatly suppress, this error, with demonstrations using numerical examples.
关键词： x-ray free-electron lasers,Fourier-type transform,molecular structure retrieval,scattering phase,photoelectron holography
更新于2025-09-12 10:27:22
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Micro‐ and Nanolasers
摘要： A laser is a device that emits strong coherent light through a process of light amplification by stimulated emission of radiation. The theoretical foundation for the laser was established by Albert Einstein theorizing on the existence of stimulated emission in 1916. The first laser was built by Theodore Maiman in 1960 based on the theoretical work of Charles Townes and Arthur Schawlow. The invention and continuous development of the laser has revolutionized science, technology, and industry. Miniaturization of lasers has been promoting the development and application of laser technology. For example, compact semiconductor lasers have become an integral part of our everyday life. With the development of micro- and nanofabrication technology, including both top-down and bottom-up techniques, the dimensions of lasers have been shrunk down to micro- and nanoscale. With an unprecedented ability to deliver intense coherent light at (sub)wavelength scale, such micro- and nanolasers are promising to trigger the next revolution in the laser and related fields. Indeed, the micro- and nanolasers are or will be unlocking their potential in photonic and optoelectronic applications, such as chemical and biological sensing, laser display and holography, on-chip optical communication and processing, and so on.
关键词： micro- and nanolasers,on-chip optical communication and processing,chemical and biological sensing,photonic and optoelectronic applications,laser display and holography
更新于2025-09-11 14:15:04
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Dual-beam interferometric particle imaging for size and shape characterization of irregular coal micro-particle: validation with digital inline holography
摘要： The size and shape characterization of irregular particles is of great significance in the comprehensive understanding of many natural and industrial processes. The dual-beam interferometric particle imaging (DIPI) technique is adapted from a dual-beam backward illumination configuration of interferometric particle imaging to access the size and 2D shape of an irregular particle from its interferogram. An experimental setup combining the digital inline holography (DIH) and DIPI techniques characterizes the same projection of the same particle with a color camera, permitting the accuracy evaluation and validation between these two techniques. The comparison results show a good agreement between the 2D-Fourier transform of DIPI interferogram and the 2D-autocorrelation of DIH reconstructed in-focus image. The DIH gives the reference result for the size measurement of the particles, and we observe a maximum difference as low as 9% with the DIPI measurement. The backward arrangement of the dual-beam interferometric particle imaging technique facilitates its further instrumental development and application to a variety of real circumstances, e.g., solid fuel particles and ice crystals.
关键词： Irregular particle,Size,Holography,Shape measurement,Interferometric particle imaging
更新于2025-09-11 14:15:04
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Multi-height phase recovery combined with Fast Iterative Shrinkage-Thresholding Algorithm to handle phase microspheres from complex diffracted field in inline holography
摘要： We describe in this work an approach that individually combines constant initialization, free-space backpropagation, transport of intensity equation (TIE) and multi-height phase recovery with Fast Iterative Shrinkage-Thresholding Algorithm (FISTA) to predict reconstruction of the phase microspheres from diffracted field measurements. We incorporate appropriate initialization and regularization to reconstruct unknown phase microspheres (transparent objects).
关键词： phase recovery,diffraction,object bounds,phase microsphere,computational imaging,Inline holography
更新于2025-09-11 14:15:04
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Super-Bandwidth Two-Step Phase-Shifting Off-Axis Digital Holography by Optimizing Two-Dimensional Spatial Frequency Sampling Scheme
摘要： The presence of the auto correlation and twin cross correlation noises restrict the available spatial bandwidth of the holographic microscopy to much less than the available bandwidth of the digital sensor. Therefore, in order to record the same image area as conventional 2D intensity imaging techniques, several images should be taken. We present two-step phase-shifting off-axis digital holography with maximum space-bandwidth product for three-dimensional (3D) digital holography. Removing the autocorrelation term using a two-step phase-shifting technique significantly increases the available bandwidth for off-axis interferometry. An optimizing super-diagonal two-dimensional (2D) spatial frequency sampling scheme at the sub-Nyquist frequency is employed for performing off-axis interferometry in the absence of the autocorrelation term. The spatial bandwidth of the proposed two-step phase-shifting technique is 400% of that in square scheme off-axis digital holography. Experimental results demonstrate the feasibility of this technique in extracting the 3D morphology of transparent microscopic objects with a larger bandwidth.
关键词： Holography,sampling methods,interferometry,microscopy
更新于2025-09-11 14:15:04
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Enhances surface sensitivity of X-ray photoelectron holography through the example of Bi2Te3(111) surface
摘要： X-ray photoelectron holography (XPH) is new tool in surface science capable to visualize in real space coordination of the atom of interest (emitter). To study surface phenomena the ultimate and variable (in the range of 1-5 ML) surface sensitivity is needed. Here we discuss possibilities to improve surface sensitivity of XPH by the example of Bi2Se3 (111) surface where different coordinations of the same kind of atoms are present in different layers. To reach ultimate surface sensitivity we used both lower electron kinetic energy and partial analysis of hologram related to grazing angle photoemission. Using calculations of diffraction patterns based on EDAC code and reverse reconstruction of the real space within SPEA-MEM formalism we evaluate the contribution of each atomic layer into diffraction pattern and found that the surface relaxation could be directly visualised at the kinetic energy less than 100 eV, whereas the contribution of the second quintuple layer can be vanished at 200 eV or below. The same effect can be achieved by partial analysis of hologram at grazing detection angles more than 55° to the surface normal. This approach enables broader practical applications of the XPH to various materials in applied surface science.
关键词： surface structure,photoelectron holography
更新于2025-09-11 14:15:04
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European Microscopy Congress 2016: Proceedings || Measuring Charge Distribution in Nanoscale Magnesium Aluminate Spinel by Electron Energy-Loss Spectroscopy and Electron Holography
摘要： Charge distribution resulting in the formation of a space charge zone (SCZ) in ionic materials has a critical role on functional properties [1]. Even though significant advances in theoretical models have been accomplished, experimental evidence in nanoscale granular materials is indirect. Here, we investigated the distribution of cations and defects on the formation of a SCZ in a nanoscale granular model system of non-stoichiometric MgO?nAl2O3 (MAS, n= 0.95 and 1.07). The SCZ was investigated experimentally by electron energy-loss spectroscopy (EELS) and off-axis electron holography (OAEH). EEL spectra were collected along directions perpendicular to grain boundaries (GB’s), from which the magnesium-to-aluminum relative cation concentrations were calculated, as presented in Fig.1. We found that regardless of annealing processes, the vicinity of GB’s of the Mg rich spinel has excess Mg+2 cations while the vicinity of GB’s of the Al rich spinel has excess of Al+3 cations. Additionally, the cation distribution shows strong dependency on the grain size. For non-stoichiometric MAS, cation concentration is proportional to the defect concentration, because deviation from stoichiometry results in adjacent defects that compensate for the electric charge [2, 3, 4]. In both materials, the cation distribution is inhomogeneous for grains smaller than 40 nm. For larger grains, the defect concentration approaches the bulk value at the center of the grain. Furthermore, excess of Mg (Al) cations at the vicinity of the GB decreased with increase of grain size. Maier et al. [1] calculated that for grain size at the scale of the Debye length (estimated at 9nm for non-stoichiometric MAS studied here [7]), the GC is no longer electrically neutral, instead influenced by accumulation or depletion of charge at the boundaries. Due to the lack of accurate values for defect formation energy [5, 6], we applied OAEH to measure directly the electrostatic charge distribution in nano-sized MAS. We show that charge distribution and the buildup of electrostatic potential between GB and core are linked to the spatial distribution of defects rather than the overall composition of MAS (Fig. 2). At the vicinity of GB’s, excess Mg+2 or Al+3 cations accumulate depending on the composition, the magnitude of which increases with decreasing grain size. Indeed, the potential distributions show the relation between the excess cation species, grain size and the Debye length, in agreement with theoretical models [1].
关键词： Lattice ordering,Electron holography,Ionic nano-materials,Electron energy loss spectroscopy,Space charge potential
更新于2025-09-11 14:15:04
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European Microscopy Congress 2016: Proceedings || Using a simplified in line holography method as a qualitative tool to detect local heterogeneities in HfO2 layers
摘要： Oxygen vacancies in high-k oxides are foreseen to have detrimental effects in devices like high-k metal gate MOS transistors [1] and beneficial ones in RRAM [2]. In this context techniques capable to characterize defects in ultra-thin (2 thin films and revealed the impact of the grain nanostructure on the electronic structures [4]. When traversing the sample electron waves experience a phase shift related to the local inner potential created by atoms. The reference technique to retrieve this phase shift is off axis electron holography. However as it is a delicate technique, the alternative in line holography based on the acquisition of a focal series can be of interest. The advantage of in line holography is to be easy to carry out in the course of a classical TEM study and to provide phase image on a large scale (up to several microns). The present work aims at examining the capabilities of a simplified approach of in line electron holography to evidence heterogeneities in a polycrystalline HfO2 layer.
关键词： oxide,defect,in line holography,phase retrieval
更新于2025-09-11 14:15:04
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European Microscopy Congress 2016: Proceedings || Visualization of 2-dimensional potential map in multilayer organic electroluminescence materials by phase-shifting electron holography
摘要： Electron holography (EH) is a TEM method which can quantitatively measure electromagnetic fields of various samples [1-3]. In this study, we tried observing a local two-dimensional electric distribution, formed in multilayer organic electroluminescence (OEL) quantitatively with phase-shifting EH [4-5] by HF-3300EH Cold-FE TEM operated at 300 kV equipped with multiple biprism system. An OEL multilayer sample (CuPc/α-NPD/Rubrene/Alq3/LiF/Ag) was fabricated on a Si substrate using a vacuum evaporation method. Each layer’s thickness and the surface morphology of the OEL multilayer sample were evaluated by X-Ray Reflectometry (XRR) and Atomic Force Microscopy (AFM), respectively. The sample for phase-shifting EH observation was fabricated by focused ion beam (FIB) technique. A part of the multilayer sample, which formed a multilayer structure on a Si substrate, was picked up by the microsampling technique and was fixed onto a W deposition on the mesh for TEM observation. Then, a thin film sample of thickness 450 nm was fabricated by FIB processing. Generally, the OEL sample is vulnerable to water, and the structure may change in quality in reaction to atmospheric water vapor, depending on the formed materials. Therefore, in this study, after thin film processing, contact with the atmosphere was prevented by using an air protection mesh holder. Figure 1 shows a TEM image, and a hologram by double-biprism EH technique [6]. The model structure of an OEL multilayer is inserted in the TEM image. Sample thickness was about 450 nm. From the TEM image, some contrast is observed in the position of the CuPc layer, but we cannot confirm the image contrast corresponding to the other layers. Figure 2 shows the result of the visualization of the 2-dimensional potential map of an OEL multilayer. We can clearly observe the contrast of the OEL multilayer, as shown in the reconstruction image (Figure 2b). Because the inner potential of the materials in each layer is constant, we can consider phase shifts to be an electric potential change in the sample. In the future, we will investigate the accuracy of this experimental data by comparing our data with a simulation.
关键词： 2-dimensional potential distribution,organic electroluminescence material,phase-shifting electron holography
更新于2025-09-11 14:15:04
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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