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W Q Ming, J H Chen, Y T He, R H Shen, Z K Chen
Exit wavefunction reconstruction is a powerful image processing technique to enhance the resolution and the signal-to-noise ratio for atomic-resolution imaging in both aberration uncorrected and corrected transmission electron microscopes. The present study aims to improve the performance of the iterative wavefunction reconstruction algorithm in comparison not only with its conventional form but also with the popular commercial Trueimage software for exit wavefunction reconstruction. It is shown that by implementing a wave propagation procedure for refining its image alignment, the iterative wavefunction reconstruction algorithm can be greatly improved in accurately retrieving the wavefunctions while keeping its original advantages, which allow the reconstruction be performed with less images and a larger defocus step in the data set of through-focus image series...
September 5, 2018: Ultramicroscopy
William C Lenthe, Jean Charles Stinville, McLean P Echlin, Zhe Chen, Samantha Daly, Tresa M Pollock
The advancement of materials science at the mesoscale requires improvements in both sampling volumes/areas and spatial resolution in order to make statistically significant measurements of microstructures that influence higher-order material properties, such as fatigue and fracture. Therefore, SEM-based techniques have become desirable due to improvements in imaging resolution, large sample handling capability, and flexibility for in-situ instrumentation. By using fast sampling of SEM electron detector signals, intrinsic beam scanning defects have been identified that are related to the response time of the SEM electron beam deflectors and electron detectors...
September 1, 2018: Ultramicroscopy
T J Ruggles, G F Bomarito, R L Qiu, J D Hochhalter
Conventional high angular resolution electron backscatter diffraction (HREBSD) uses cross-correlation to track features between diffraction patterns, which are then related to the relative elastic strain and misorientation between the diffracting volumes of material. This paper adapts inverse compositional Gauss Newton (ICGN) digital image correlation (DIC) to be compatible with HREBSD. ICGN-based works by efficiently tracking not just the shift in features, but also the change in their shape. Modeling a shape change as well as a shift results in greater accuracy...
August 29, 2018: Ultramicroscopy
Xiao Ma, Zibang Zhang, Manhong Yao, Junzheng Peng, Jingang Zhong
Numerous advanced microscopic imaging techniques have been proposed for optical sectioning, but they generally employ a complex and costly optical system. Here we report a microscopy termed spatially-incoherent annular illumination microscopy (SAIM). It allows for simple, effective, non-fluorescence, and bright-field optical sectioning. The proposed technique is implemented by installing an annular array of light emitting diodes (LEDs) on a standard bright-field microscope for illumination. The LED array produces distinctive illumination, that is, each LED provides coherent, large-angle oblique illumination while all LEDs generate spatially-incoherent annular illumination...
August 27, 2018: Ultramicroscopy
Lihua Wang, Jiao Teng, Yu Wu, Xuechao Sha, Sisi Xiang, Shengcheng Mao, Guanghua Yu, Ze Zhang, Jin Zou, Xiaodong Han
Twin boundary can both strengthen and soften nanocrystalline metals and has been an important path for improving the strength and ductility of nano materials. Here, using in-lab developed double-tilt tensile stage in the transmission electron microscope, the atomic scale twin boundary shearing process was in situ observed in a twin-structured nanocrystalline Pt. It was revealed that the twin boundary shear was resulted from partial dislocation emissions on the intersected {111} planes, which accommodate as large as 47% shear strain...
August 27, 2018: Ultramicroscopy
Hongbing Yu, Xiaoou Yi, Felix Hofmann
We propose an automated stereoscopic imaging approach for reconstructing the 3D spatial distribution of small dislocation loops (DLs) from 2D TEM micrographs. This method is demonstrated for small DLs in tungsten, formed by low-dose ion-implantation, that appear as circular spots in diffraction contrast TEM images. To extract the 3D position of specific DLs, their 2D position in multiple weak-beam dark-field TEM micrographs, recorded at different tilt angles, is fitted. From this fit the geometric centre and size of each DL in each micrograph can be extracted...
August 27, 2018: Ultramicroscopy
M Ajmal Khan, H Algarni, N Bouarissa, O A Al-Hagan, T F Alhuwaymel
The alloy composition dependence of penetration range and backscattering coefficient of electrons normally impinging on Six Ge1 - x and GaAsx N1 - x semiconductor alloys targets for beam energies in the range 0.5-3.5 keV has been investigated. The electron penetration range is calculated using the Ashley's model. The electron backscattering coefficient is determined using both the Vicanek and Urbassek theory where the transport cross-sections are obtained more accurately via an improved approximation and Monte Carlo method in which the inelastic scattering processes are treated via Ashley's optical model...
August 27, 2018: Ultramicroscopy
A Garitagoitia Cid, R Rosenkranz, M Löffler, A Clausner, Y Standke, E Zschech
A novel method to quantify and predict the material contrast using Backscattered Electron (BSE) imaging in Scanning Electron Microscopy (SEM) is presented while using low primary electron beam energies (Ep ). In this study, the parameters for BSE imaging in Low Voltage Scanning Electron Microscopy (LVSEM) are optimized for the layer system Al0.22 Ga0. 78 N/GaN, which is typically used in High Electron Mobility Transistors (HEMTs). The layers are imaged at high resolution and the compounds are identified based on the quantitative BSE material contrast between Al0...
August 27, 2018: Ultramicroscopy
David R Diercks, Brian P Gorman
Atom probe tomography reconstructions provide valuable information on nanometer-scale compositional variations within materials. As such, the spatial accuracy of the reconstructions is of primary importance for the resulting conclusions to be valid. Here, the use of transmission electron microscopy images before and after atom probe analysis to provide additional information and constraints is examined for a number of different materials. In particular, the consistency between the input reconstruction parameters and the output reconstruction is explored...
August 27, 2018: Ultramicroscopy
Yongfeng Kang, Momo Wei, Jingyi Zhao
A Differential algebraic method is of an effective technique in computer numerical analysis. It implements conveniently differentiation up to arbitrary high order, based on the nonstandard analysis. In this paper, the differential algebra (DA) method has been employed to compute the high order aberrations up to the fifth order of electron lenses with quadrupole and octupole corrector whose electric/magnetic fields are in the forms of discrete arrays, for example, the files computed by FEM or FDM method. The quadrupole and octupole electro-magnetic fields of arbitrary point are obtained by local analytic expressions, and then field potentials are transformed into new forms which can be operated in the DA calculation...
August 27, 2018: Ultramicroscopy
Sirong Lu, Kristy J Kormondy, Alexander A Demkov, David J Smith
Background removal is an important step in the quantitative analysis of electron energy-loss structure. Existing methods usually require an energy-loss region outside the fine structure in order to estimate the background. This paper describes a method for signal-from-background separation that is based on subspace division. The linear space is divided into two subspaces. The signal is recovered from a linear subspace containing no background information, and the other subspace containing the background is discarded...
August 22, 2018: Ultramicroscopy
Dmytro Dedovets, Cécile Monteux, Sylvain Deville
If confocal microscopy is an ubiquitous tool in life science, its applications in chemistry and materials science are still, in comparison, very limited. Of particular interest in these domains is the use of confocal microscopy to investigate temperature-dependent phenomena such as self-assembly, diffusio- or thermophoresis, or crystal growth. Several hurdles must be solved to develop a temperature-controlled stage for laser scanning confocal microscopy, in particular regarding the influence of an elevated temperature gradient close to the microscope objective, which most people try very hard to avoid...
August 21, 2018: Ultramicroscopy
Qingping Meng, Lijun Wu, Huolin L Xin, Yimei Zhu
With recent rapid advancement in electron microscopy instrumentation, in particular, bright electron sources and monochromators, valence electron energy-loss spectroscopy (VEELS) has become attractive for retrieving band structures, optical properties, dielectric functions and phonon information of materials. However, Cherenkov radiation and surface-loss contribution significantly alter fine structures of VEELS, even in simple semiconductors and insulators. This leads to the problem that dielectric function or bandgap structure of these materials cannot be determined correctly if these effects are not removed...
August 20, 2018: Ultramicroscopy
M Raghu Ramaiah, K Prabakar, S Tripura Sundari
Laser beam (He-Ne - 6328 A0 ) induced deflection in uncoated, Au, and Al coated Si microcantilevers (MCs) of various dimensions was studied, using an AFM head, to examine the induced stress contribution from photothermal and photostriction phenomenon. The laser beam was made to incident sequentially on front and back surfaces of the MC, by flipping it, and results were compared in terms of deflection magnitude, direction of bending and response time. In case of uncoated MCs, it was observed that the induced deflection was always in the direction of the incident laser beam with a fast response...
August 15, 2018: Ultramicroscopy
Ronald Dixson, Ndubuisi Orji, Ichiko Misumi, Gaoliang Dai
Atomic force microscopes (AFMs) are commonly and broadly regarded as being capable of three-dimensional imaging. However, conventional AFMs suffer from both significant functional constraints and imaging artifacts that render them less than fully three dimensional. To date a widely accepted consensus is still lacking with respect to characterizing the spatial dimensions of various AFM measurements. This paper proposes a framework for describing the dimensional characteristics of AFM images, instruments, and measurements...
August 15, 2018: Ultramicroscopy
Takehito Seki, Naoto Takanashi, Eiji Abe
We describe the optical conditions that are essentially necessary for phase-contrast imaging with aberration-corrected scanning transmission electron microscopy (STEM), whose depth of field has reached almost comparable to the specimen thickness. For such state-of-the-art STEM, contrast-transfer-function (CTF) should be defined not solely for the projected potential but multiply for each wavefront during the beam propagation across the specimen thickness; an integration of multiple CTFs (iCTF). We show that the iCTF concept explains fairly well characteristic annular-bright-field (ABF) imaging behaviors of heavy/light atom sites against the defocus changes, and also provide notable concerns on possible artifacts that arise from different imaging-depth dependences between the heavy/light atom sites...
August 15, 2018: Ultramicroscopy
Claudia Fleischmann, Kristof Paredis, Davit Melkonyan, Wilfried Vandervorst
For the very first time, atomic force microscopy is used to determine quantitatively the 3-dimensional shape of an atom probe tip, which is key towards improved accuracy and understanding of artefacts in atom probe tomography. We have successfully measured by atomic force microscopy the apex and shank region of 3 different atom probe tips, of which two show (severe) deviations from a hemisphere due to either non-uniform laser light absorption or the presence of two different materials. Clearly, our method which overcomes the challenge of aligning two very sharp tips on top of each other, offers new pathways to study physical mechanisms in (laser-assisted) atom probe...
August 14, 2018: Ultramicroscopy
Zhichao Zhong, Willem Jan Palenstijn, Nicola Roberto Viganò, K Joost Batenburg
Energy-dispersive X-ray spectroscopic (EDS) tomography is a powerful three-dimensional (3D) imaging technique for characterizing the chemical composition and structure of nanomaterials. However, the accuracy and resolution are typically hampered by the limited number of tilt images that can be measured and the low signal-to-noise ratios (SNRs) of the energy-resolved tilt images. Various sophisticated reconstruction algorithms have been proposed for specific types of samples and imaging conditions, yet deciding on which algorithm to use for each new case remains a complex problem...
August 11, 2018: Ultramicroscopy
F Vogel, S Ngai, C J Smith, R Holler, G B Thompson
The use of pulsed lasers in atom probe tomography has enabled the analysis of lower conductivity materials such as hafnium carbo-nitrides. The variability of experimental parameters can have a profound effect on field evaporation behavior, data quality and compositional accuracy. This is especially challenging for materials such as hafnium carbo-nitride, where a mixture of covalent, ionic and metallic bonding types is present. Here we study the influence of laser pulse energy on how the field evaporation evolves in a hafnium carbo-nitride and how that impacts data quality and compositional accuracy...
August 10, 2018: Ultramicroscopy
Weishi Wan, Fu-Rong Chen, Yimei Zhu
Ultrafast high-energy electron microscopy, taking advantage of strong interaction of electrons with matter while minimizing space charge problems, can be used to address a wide range of grand challenges in basics energy sciences. However, MeV-electron lenses are inherently bulky and expensive, preventing them from acceptance in a broad scientific community. In this article, we report our novel design of a compact, low-cost imaging-lens system for MeV-electrons based on quadrupole multiplets, including triplet, quadruplet and quintuplet, both symmetric and asymmetric...
August 9, 2018: Ultramicroscopy
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