查看更多>>摘要：A full-space analysis based on the multislice method is presented and has been applied to the simulation of mechanical interaction of electron vortex beam with a nanoparticle. The moment acting on the particle is calculated and presented as a moment map. We have calculated the total torque and compared it with the result from orbital angular momentum analysis. The thickness dependent torque and angular momentum are derived and discussed for different incident energies, convergence angles and angular momenta of the incident electron vortex beam. For different incident beams, the enhanced torque caused by diffraction enhancement is discussed. The oscillation behavior of the torque and angular momentum on depth is explained by a channeling theory. A comparison of thickness dependent angular momentum between the proposed analysis and conventional orbital angular momentum analysis in both the multislice method and the Bloch wave method is presented and discussed.
查看更多>>摘要：The properties of polycrystalline materials are related to their microstructures and hence a complete description, including size, shape, and orientation of the grains, is necessary to understand the behavior of materials. Here, we use Scanning Precession Electron Diffraction (SPED) in the Transmission Electron Microscope (TEM) combined with a tilt series to reconstruct individual grains in 3D within a polycrystalline dual-phase cold wire-drawn pearlitic steel sample. Nanoscale ferrite grains and intragranular cementite particles were indexed using an Automated Crystallographic Orientation Mapping (ACOM) tool for each tilt dataset. The grain orientations were tracked through the tilt datasets and projections of the individual grains were reconstructed from the diffraction data using an orientation-specific Virtual Dark Field (VDF) approach for tomographic reconstruction. The algorithms used to process and reconstruct such datasets are presented. These algorithms represent an extension to the ACOM approach that may be straightforwardly applied to other multi-phase polycrystalline materials to enable 3D spatial and orientation reconstructions.
查看更多>>摘要：Photogrammetric methods enable the construction of 3D SEM models from 2D images. Most software for this purpose is designed for photographic images. The software tries to minimize modelling error but some uncertainty usually remains in the model. In such approaches no ground truth measurement for microscopic objects exists for comparison with the finished model. In the proposed method, a textured model surface is compared to the SEM images to map the error locations on the model. The method is illustrated using two datasets.
查看更多>>摘要：Generating quantitative phase maps is unvaluable to access the phase distribution in a material. X-ray hyperspectral mapping using an energy dispersive spectrometer (EDS) attached to a scanning electron microscope (SEM) is the most practical way to collect these data, mainly due to its relatively ease of operation and availability around the world. In this work, we demonstrate an innovative technique to produce high-quality phase maps based on the correlation between each hyperspectral image pixel spectrum and a set of standards spectra. The standards spectra can be obtained experimentally from bulk specimens of known materials but also via analytical computations. The method is not only robust against electron beam current and spectrometer instabilities but also to statistical noise in the standards as well as in the hyperspectral image spectra. Equally, the method is reliable to produce phase distribution maps at low operating voltage where SEM-EDS quantitative xray microscopy is limited by many factors like peak overlapping, continuous background approximations and produces inaccurate phase maps. The results presented in this study will certainly open a new path to produce useful x-ray quantitative data and potentially break the locks of conventional x-ray microanalysis using EDS.
查看更多>>摘要：Electron spectroscopy proves to be a handy tool in material science. Combination of electron spectroscopy and scanning probe microscopy is possible through Scanning Field Emission Microscopy (SFEM), where a metallic probe positioned close to the surface is used as an electron source. However, using this not too much technologically demanding technique, it looks like the compromise between the lateral resolution and spectroscopic clarity must be considered. Here, we demonstrate, using experimental and simulation data, that the spectroscopic information can be understood without the need to grossly deteriorate the potential spatial resolution of the microscope. We prepared a three-section sample with clean W(110), sub-monolayer Cs on W(110) and monolayer of Cs on W(110) on which electron energy loss spectra are obtained via Scanning Probe Energy Loss Spectroscopy (SPELS) measurements. To explain the detected spectra a new model describing SPELS measurements in a SFEM is developed which aids to uncover the origin of spectral features typically detected during experiments. Experimental and simulation data are in a mutual agreement and observed spectral features on different surfaces could be explained. This novel understanding of SPELS can solve the main issue previously related to this technique, and good spatial resolution can be accompanied by the understanding of the measured spectra.
查看更多>>摘要：In this paper we perform angular resolved annular-dark field (ADF) scanning-transmission electron microscopy (STEM) to study the scattered intensity in an InGaN layer buried in GaN as a function of the scattering angle. We achieved angular resolution with a motorized iris aperture in front of the ADF detector. Using this setup, we investigated how the intensities measured in various angular ranges agree with multislice simulations in the frozen-lattice approximation. We observed a strong influence of relaxation induced surface-strain fields on the ADF intensity, measured its angular characteristics and compared the result with simulations. To assess the agreement of the measured intensity with simulations, we evaluated the specimen thickness in GaN and the indium concentration in InGaN for each angular interval by comparing the measured intensities with simulations. The thickness was strongly overestimated for scattering angles below 40 mrad and also the evaluated indium concentration varies with the considered angular range. Using simulations, we investigated which angular ranges show a high sensitivity to variations of the thickness and which intervals strongly depend on the indium concentration. By combining two angular intervals, the indium concentration and the specimen thickness were determined simultaneously, which has potential advantages over the usual quantification method. It is shown that inelastic scattering, surface contamination and mistilt can have an influence on the measured intensity, especially at lower scattering angles below 30-50 mrad, which might explain the observed difference between the frozen lattice simulation and the experiment.
Zhang, FanPen, MerijnSpruit, Ronald G.Garza, Hugo Perez...
11页
查看更多>>摘要：Time-resolved correlations of the environment, the reaction products, the energy transfer and the material structures during the reaction processes make operando gas and heating TEM more and more attractive in recent years. The time delays existing among parameter measurement locations need to be calibrated for valid correlations. Otherwise, erroneous conclusions would be drawn, such as over/under-estimating the critical temperatures, mismatching the structure and composition relationships to activities, and so on. Herein, we report on a method synchronizing the data from pre-, in- and post-TEM by measuring and calibrating the time delays involved. This method relies on the unique capability of on-chip calorimetry of the gas Nano-Reactor, which is intrinsically synchronized with the TEM imaging and spectroscopy data. The time delay is found to be dependent on the gas flow rate and pressure, and have little dependence on the gas type. A functional relationship fitted between the time delay and the gas flow rate and pressure can automate the time delay calibration and thus synchronize the data from different locations. Based on the investigations, we developed algorithms and scripts to enable the automatic data synchronization in operando gas and heating TEM in both real time experiments and post experiments.
查看更多>>摘要：Differential phase contrast (DPC) in scanning transmission electron microscopy can be used to visualize electric field distributions within specimens in real space. However, for electric field mapping in crystalline specimens, the concomitant diffraction contrast is seriously problematic. In particular, for heterostructures with large lattice distortions, such as GaN-based semiconductor devices, the diffraction contrast cannot be reduced using conventional methods such as DPC image acquisition under off-axis conditions. In the present study, the electric field imaging of heterostructures is shown to suppress the diffraction contrast by averaging multiple DPC signals, obtained under various beam-tilt conditions near the zone axis. The remaining diffraction contrast was quantitatively estimated through simulations. This technique was demonstrated to enable the quantitative evaluation of electric field distributions across GaN/AlGaN multi-heterostructures, with errors possibly attributed to the residual diffraction contrast.
查看更多>>摘要：Variation in the (220) lattice spacing of Si due to specimen processing for transmission electron microscopy (TEM) was experimentally evaluated by comparing the measured lattice spacings of crystalline specimens processed by crushing, mechanical polishing only, and combined mechanical and Ar ion polishing. Although distinct variation in the (220) lattice spacing between the Si specimens processed by crushing and by mechanical polishing only is not observed, the (220) lattice spacing of specimens prepared by combined mechanical and Ar ion polishing imply increasing tendency with increasing Ar ion beam irradiation time. Moreover, the (220) lattice spacing measured from the outermost region of the specimen edge tends to be approximately 3% to 5% larger than that measured from the inner region, irrespective of the processing method. These results demonstrate that differences in the processing conditions of Si specimens and in the measurement location of the Si lattice spacing can be major component of the measurement uncertainty in sub-nanometer metrology using TEM with magnification calibration by the Si lattice spacing. When attempting to apply the lattice spacing of Si as a reference with traceability to the International System of Units for TEM magnification calibration in sub-nanometer metrology, the results suggest that the effect of specimen processing on variation in the lattice spacing is not negligible.
NSTL
Elsevier