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From simple averaging to more sophisticated registration and restoration strategies, such as super-resolution (SR), there exist different computational techniques that use a series of images of the same object to generate enhanced images where noise and other distortions have been reduced. In this work, we provide qualitative and quantitative measurements of this enhancement for high-angle annular dark-field scanning transmission electron microscopy imaging. These images are compared in two ways, qualitatively through visual inspection in real and reciprocal space, and quantitatively, through the calculation of objective measurements, such as signal-to-noise ratio and atom column roundness. Results show that these techniques improve the quality of the images. In this paper, we use an SR methodology that allows us to take advantage of the information present in the image frames and to reliably facilitate the analysis of more difficult regions of interest in experimental images, such as surfaces and interfaces. By acquiring a series of cross-sectional experimental images of magnetite (Fe3O4) thin films (111), we have generated interpolated images using averaging and SR, and reconstructed the atomic structure of the very top surface layer that consists of a full monolayer of Fe, with topmost Fe atoms in tetrahedrally coordinated sites.

The influence of the neighbouring atomic-columns in determining the composition at atomic column scale of quaternary semiconductor compounds, using simulated HAADF-STEM images is evaluated. The InAlAsSb alloy, a promising material in the photovoltaic field, is considered. We find that the so called 'crosstalk' effect plays an important role for the aimed compositional determination. The intensity transfer is larger from neighbouring atomic columns with higher average Z, and towards atomic columns with smaller Z. Our results show that in order to obtain precise information on the column composition, the HAADF-STEM intensities of both columns need to be taken into account simultaneously.

In this paper, the concept of homogeneity is defined, from a topological perspective, in order to analyze how uniform is the material composition in 2D electron microscopy images. Topological multiresolution parameters are taken into account to obtain better results than classical techniques. Ministerio de Economía y Competitividad MTM2016-81030-P Ministerio de Economía y Competitividad TEC2012-37868-C04-02

In this article a method for determining errors of the strain values when applying strain mapping techniques has been devised. This methodology starts with the generation of a thickness/defocus series of simulated high-resolution transmission electron microscopy images of InAsxP1−x/InP heterostructures and the application of geometric phase. To obtain optimal defocusing conditions, a comparison of different defocus values is carried out by the calculation of the strain profile standard deviations among different specimen thicknesses. Finally, based on the analogy of real state strain to a step response, a characterization of strain mapping error near an interface is proposed.

In this paper, stress fields at the surface of the capping layer of self-assembled InAsP quantum wires grown on an InP (001) substrate have been determined from atomistic models using molecular dynamics and Stillinger-Weber potentials. To carry out these calculations, the quantum wire compositional distribution was extracted from previous works, where the As and P distributions were determined by electron energy loss spectroscopy and high-resolution aberration-corrected Z-contrast imaging. Preferential sites for the nucleation of wires on the surface of the capping layer were studied and compared with (i) previous simulations using finite element analysis to solve anisotropic elastic theory equations and (ii) experimentally measured locations of stacked wires. Preferential nucleation sites of stacked wires were determined by the maximum stress location at the MD model surface in good agreement with experimental results and those derived from finite element analysis. This indicates that MD simulations based on empirical potentials provide a suitable and flexible tool to study strain dependent atom processes.

This paper compares the pozzolanic activity of metakaolin (MK) obtained by thermal treatment at 700°C for 1. h and amorphous kaolin obtained by mechanochemical treatment in a Herzog oscillating mill for 15-120. min. The starting materials used included two raw kaolins and an industrial (washed) kaolin. The production of the amorphous materials was followed by their thermal analysis (DTA, TGA), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), particle size distribution (PSD) and transmission electron microscopy (TEM). The pozzolanic activity of the amorphous kaolins was assessed in accordance with ASTM C 311. Based on the results, both types of treatment allow reactive pozzolans to be obtained from kaolinite clays. The pozzolan obtained by mechanochemical treatment of raw kaolin with high quartz content was found to perform especially well. In sample KV2, with a minor amount of kaolinite, it was possible to obtain an active pozzolan by mechanical treatment but not by thermal treatment. The pozzolanic index and the mechanical resistances obtained by grinding were similar to the thermal treatment. The outcome of the mechanochemical process depends on the type of kaolin used and its and mineralogical composition, and also on its grinding time., The authors wish to thank the University of Valle (Colombia), the “Francisco José de Caldas” Colombian Institute for the Development of Science and Technology (COLCIENCIAS), Spain's Center of Environmental Sciences (CCMA-CSIC), and the Colombian Excellence Center for Novel Materials (CENM) for their support in the conduct of this study.

The combination of strain measurements1 and the analysis of High Angle Annular Dark Field (HAADF) Scanning Transmission Electron Microscopy (STEM) images constitutes a powerful approach to investigate strained heterostructures on the nanometer scale and has proved to be extremely powerful for characterizing nanomaterials2,3.

In this work, we analyze the influence of atomic displacements due to elastic strain in HAADF-STEM simulated images. This methodology is demonstrated on an InP/InAsxP(1−x) nanowire heterostructure theoretical model under strained/unstrained conditions. Since the HRTEM image simulation requires an enormous amount of computing power, all simulations have been obtained using a parallel version of HAADFSTEM simulation software[1] running in the University of Cadiz supercomputer (3.8 Tflops). This program is able to simulate HAADF-STEM images from nanostructures containing more than one million of atoms in a few days.

The distribution of bismuth in InAs1-xBix/GaAs quantum dots is analyzed by atomic-column resolution electron microscopy and imaging simulation techniques. A random Bi distribution is measured in the case of

The distribution of Bi atoms in epitaxial GaAs(1−x)Bix is analyzed through aberration-corrected Z-contrast images. The relation between the atomic number and the intensity of the images allows quantifying the distribution of Bi atoms in this material. A bidimensional map of Bi atoms is extracted showing areas where nanoclustering is possible and evidencing the location of Bi at As-substitutional positions in the lattice. The distribution of Bi atoms differs from a random spatial pattern of Bi atoms in the material.

High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) in combination with strain mapping techniques provides a powerful tool for quantitative analysis of crystalline semiconductor materials. Due to the complex interaction of a focused probe and a sample in HAADF, the calculation of each pixel in a simulation process requires a complete multislice iteration, making the overall computing process a rather demanding task in time and memory. SICSTEM is a parallel software code recently developed for running on the University of Cadiz Supercomputer (3.75 Tflops) that allows the simulation of images from large nanostructures containing more than one million atoms. The software has been designed to be able to generate not only one dimensional line scans or two dimensional images, but also to perform optical sectioning in the STEM simulation process, providing an easy way to simulate 3D HAADF-STEM images. In this work we consider GaAs capped GaSb nanostructures epitaxially oriented on a GaAs substrate. A methodology has been developed by combining the through-focal series STEM imaging and image analysis to estimate shape and position of buried GaSb nanostructures.

Geometric phase and peak pairs strain mapping techniques have been applied to high angular annular dark field scanning transmission electron microscopy (HAADF-STEM) simulated images of an InAs/InP strained nanowire at different sample thicknesses. Strain values determined from HAADF-STEM images have been compared to theoretical values obtained by solving the elastic theory equation by finite element analysis, in order to analyze and assess both techniques in terms of accuracy of the predictions.

We show in this work that GaAs capping of 2 ML of GaSb grown by molecular beam epitaxy results in the formation of very small (with heights of about 1 nm) GaAsxSb1−x nanostructures surrounded by a GaAs rich layer. This conclusion is obtained by analyzing the morphology of the GaAsxSb1−x nanostructures by high resolution scanning transmission electron microscopy in Z-contrast mode. This result shows that a significant fraction of the Sb atoms must segregate along the growth direction during the GaAs capping process., This work was supported by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, U.S. DOE MFC, the SANDiE European Network of Excellence Contract No. NMP4-CT-2004-500101, the Spanish MEC Grant No. TEC2005-05781-C03-01 y 02, TEC2008-06756-C03-02/TEC, NAN2004-09109-C04-01, Consolider-Ingenio 2010 CSD2006-00019, the CAM Grant No. S 0505ESP 0200, and the Junta de Andalucía PAI research groups TEP-120 and TIC-145; projects PAI05-TEP-00383 and TEP-03516.

High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) is a powerful tool to quantify size, shape, position, and composition of nano-objects with the assessment of image simulation. Due to the high computational requirements needed, nowadays it can only be applied to a few unit cells in standard computers. To overpass this limitation, a parallel software (SICSTEM) has been developed. This software can afford HAADF-STEM image simulations of nanostructures composed of several hundred thousand atoms in manageable time. The usefulness of this tool is exemplified by simulating a HAADF-STEM image of an InAs nanowire.