Resolution Micrographs Research Articles

Can Conventional Classifiers Outperform Neural Networks in Identifying Structural Defects from Atomic Resolution Micrographs?

Can Conventional Classifiers Outperform Neural Networks in Identifying Structural Defects from Atomic Resolution Micrographs?

Compositional analysis of oxide-embedded III–V nanostructures

Nanowire growth enables creation of embedded heterostructures, where one material is completely surrounded by another. Through materials-selective post-growth oxidation it is also possible to combine amorphous oxides and crystalline, e.g. III–V materials. Such oxide-embedded structures pose a challenge for compositional characterization through transmission electron microscopy since the materials will overlap in projection. Furthermore, materials electrically isolated by an embedding oxide are more sensitive to electron beam-induced alterations. Methods that can directly isolate the embedded material, preferably at reduced electron doses, will be required in this situation. Here, we analyse the performance of two such techniques—local lattice parameter measurements from high resolution micrographs and bulk plasmon energy measurements from electron energy loss spectra—by applying them to analyse InP-AlInP segments embedded in amorphous aluminium oxide. We demonstrate the complementarity of the two methods, which show an overall excellent agreement. However, in regions with residual strain, which we analyse through molecular dynamics simulations, the two techniques diverge from the true value in opposite directions.

From colony to rodlet: “A six meter long portrait of the xerophilic fungus Aspergillus restrictus decorates the hall of the Westerdijk institute.”

The extreme xerophilic fungus Aspergillus restrictus is used as a model for a large artwork created out of five microscopic pictures in total measuring 80 cm by 624 cm. The artwork is printed on aluminium and located at the entrance of the Westerdijk Institute, Utrecht, The Netherlands. The first picture is made from a colony of the fungus, which has a dimension of 1 cm and the last picture shows details of ornamentation on conidia and phialides of the fungus. The first two pictures of the artwork are made using a unique method of light microscopy in which many hundreds of pictures are made at different focal depths resulting in high detail and resolution of the pictures. For three other pictures, cryo-electron scanning microscopy was used including both a conventional system for lower magnification and a field emission scanning electron microscope for high resolution micrographs. The range of magnification is, at real size, between 78 and 63,000 times. When the observer passes the artwork it acts like a virtual microscope, just by walking past it you zoom-in to the smallest possible details. This coherent increase of magnification of one fungus, with very high quality light- and electron microscopy micrographs, shows different layers of fungal organization and emergent properties. These include the occurrence of secondary outcrops of hyphae and conidiophores in a colony; the formation of a stipe on a thin aerial hyphae; the presence and formation of characteristic structures on stipes, vesicles and phialides and a continuous zone between the forming conidia and phialides.

The evolution of subsurface micro-structure and tribo-chemical processes in cocrmo-ti6al4v fretting-corrosion contacts: What lies at and below the surface?

Titanium and its alloys are attractive biomaterials because of their desirable corrosion, mechanical, biocompatibility and osseointegration properties. Ti6Al4V alloy in particular remains a prominent biomaterial used in Total Hip Arthroplasty (THA). Recently, researchers have shown interest in understanding the degradation mechanisms and the subsurface implications of fretting-corrosion at the modular taper interface in THA. The purpose of this study was to utilise advanced microscopy and spectroscopy to characterise in-vitro fretting-corrosion induced subsurface refinement and microstructural changes in Ti6Al4V alloy. In-vitro fretting-corrosion tests were carried at four displacement: ±10, ±25, ±50 and ± 150 μm for a CoCrMo – Ti6Al4V ball-on-flat material couple. Subsequently, high resolution micrographs of the alloy microstructure were obtained using the Transmission Electron Microscope (TEM) together with Energy Dispersed X-Ray spectroscopy (EDX). The degree of subsurface microstructural changes was observed to be linked to the slip regime and magnitude of energy dissipated at the interface. Strain-induced orientation were observed at the stick regime. The mixed and gross-slip regimes were both characterised with mechanical mixing and formation of nano-crystalline structures. Specific to the mixed fretting regime, fluid ingression and material entrapment at the interface led to further refinement of nano-crystalline structures which resulted in the formation of an amorphous Ti6Al4V structure. The interwoven relationship between energy dissipation, contact condition and mechanisms of clinical failure in Ti6Al4V alloy are discussed.

Soft X-ray microscopy for probing of topical tacrolimus delivery via micelles

The penetration of topically applied tacrolimus formulated in micelles into murine skin is reported, measured by X-ray microscopy. Tacrolimus and micelles are probed for the first time by this high spatial resolution technique by element-selective excitation in the C 1s- and O 1s-regimes. This method allows selective detection of the distribution and penetration depth of drugs and carrier molecules into biologic tissues. It is observed that small, but distinct quantities of the drug and micelles, acting as a drug carrier, penetrate the stratum corneum. A comparison is made with the paraffin-based commercial tacrolimus ointment Protopic®, where local drug concentrations show to be low. A slight increase in local drug concentration in the stratum corneum is observed, if tacrolimus is formulated in micelles, as compared to Protopic®. This underscores the importance of the drug formulations for effective drug delivery. Time-resolved penetration shows presence of drug in the stratum corneum 100 min after formulation application, with penetration to deeper skin layers at 1000 min. High resolution micrographs give indications for a penetration pathway along the lipid membranes between corneocytes, but also suggest that the compound may penetrate corneocytes.

Analysis of Point Defects in Graphene Using Low Dose Scanning Transmission Electron Microscopy Imaging and Maximum Likelihood Reconstruction (Phys. Status Solidi B 11/2017)

Freestanding graphene displays an outstanding resilience to electron irradiation at low electron energies. Point defects in graphene are, however, subject to beam driven dynamics. This means that high resolution micrographs of point defects, which usually require a high electron irradiation dose might not represent the intrinsic defect population. Here, we capture the inital defects formed by ejecting carbon atoms under electron irradiation, by imaging with very low doses and subsequent reconstruction of the frequently occuring defects via a maximum likelihood algorithm.

Analysis of Point Defects in Graphene Using Low Dose Scanning Transmission Electron Microscopy Imaging and Maximum Likelihood Reconstruction

Freestanding graphene displays an outstanding resilience to electron irradiation at low electron energies. Point defects in graphene are, however, subject to beam driven dynamics. This means that high resolution micrographs of point defects, which usually require a high electron irradiation dose might not represent the intrinsic defect population. Here, we capture the initial defects formed by ejecting carbon atoms under electron irradiation, by imaging with very low doses and subsequent reconstruction of the frequently occuring defects via a maximum likelihood algorithm.

CuBi2S3 precursor based polymer composites for low frequency capacitor applications

In the present research work we successfully demonstrated the preparation of polyvinyl alcohol (PVA) composed with copper bismuth sulphide (CuBi2S3) precursor (0, 10, 20, 30 wt%) by solution blending. The structure, morphology, thermal and dielectric properties of PVA/CuBi2S3 composites were tested. The decrease in interplanar distance was confirmed by X-ray diffraction method. The electronic structure co-related to the band gap (Eg) decreased as a function of precursor loading. The rate of thermal degradation controlled due to the precursor occupied in composite measured by the thermo gravimetric analysis. Presence of filler traces based on micro arrays were captured by scanning electron microscope was confirmed, observed and evaluated respectively. The subatomic lateral resolution micrographs observed by atomic force microscopy technique. Low dielectric loss of flexible composites increased by 94.4 % compared to virgin PVA system. Hence this investigation is useful for low frequency (50–500 Hz) capacitor applications in electronics domain.

Atomic Observations of Microporous Materials Highly Unstable under the Electron Beam: The Cases of Ti‐Doped AlPO4‐5 and Zn–MOF‐74

AbstractThis work presents the highest resolution micrographs reported so far of two beam‐sensitive microporous materials: Ti‐doped AlPO4‐5 (TAPO‐5) and the metal–organic framework Zn–MOF‐74. They were registered by means of Cs‐corrected STEM. The high‐resolution images of the TAPO‐5 along the [0 0 1] orientation allows a clear observation of the aluminophosphate‐five (AFI) type framework, and illustrates the atomic distribution of the “T” atoms of the structure. However, no definitive conclusions about Ti substitution mechanism could be afforded because of the high symmetry of the AFI framework. In the case of Zn–MOF‐74, the images were also obtained at 300 kV proving that under certain conditions of beam current this technique can provide invaluable information of an ever‐increasing variety of molecular sieves.

Structural study of growth, orientation and defects characteristics in the functional microelectromechanical system material aluminium nitride

The real structure and morphology of piezoelectric aluminum nitride (AlN) thin films as essential components of magnetoelectric sensors are investigated via advanced transmission electron microscopy methods. State of the art electron diffraction techniques, including precession electron diffraction and automated crystal orientation mapping (ACOM), indicate a columnar growth of the AlN grains optimized for piezoelectric application with a {0 0 0 1} texture. Comparing ACOM with piezoresponse force microscopy measurements, a visual correlation of the structure and the piezoelectric properties is enabled. With a quantitative analysis of the ACOM measurements, a statistical evaluation of grain rotations is performed, indicating the presence of coincidence site lattices with Σ7, Σ13a, Σ13b, Σ25. Using a geometric phase analysis on high resolution micrographs, the occurrence of strain is detected almost exclusively at the grain boundaries. Moreover, high resolution imaging was applied for solving the atomic structure at stacking mismatch boundaries with a displacement vector of 1/2 ⟨1 0 -1 1⟩. All real structural features can be interpreted via simulations based on crystallographic computing in terms of a supercell approach.

From Chalcogenides to Polychalcogenidehalides – First Identification in Mineral Samples

AbstractMineral samples from the Prasolovskoe epithermal Au‐Ag deposit, Russia, were investigated via transmission electron microscopy (TEM). One component was identified as the mineral kurilite Ag8Te3Se according to the data obtained from electron diffraction (ED) and Fourier transform analyses of high resolution micrographs. Micrometer‐sized grains of kurilite were found next to other noble metal chalcogenide domains like the hessite‐type. The EDX microprobe analyses of the kurilite domains were determined with the chemical composition Ag7.9Au0.1Te2.9Se1.0 which is consistent with kurilite doped by gold. Additionally noble metal polychalcogenidehalides (NMPH) were identified via ED. Monoclinic and tetragonal polymorphs of Ag5Te2Cl were observed for the first time in a mineral sample. One additional component, whose composition equates the kurilite‐type component with regard to Ag, Au, Te, and Se but with a marginal chlorine component, crystallizes in a structure type known from synthetic NMPH, namely Ag23Te12X (X = Cl, Br). This phase as well as the phases Ag10Te4Br3 and Ag20Te10Br2 was found next to each other in an also investigated synthetic sample.

CuS2-Passivated Au-Core, Au3Cu-Shell Nanoparticles Analyzed by Atomistic-Resolution Cs-Corrected STEM

Au-core, Au3Cu-alloyed shell nanoparticles passivated with CuS2 were fabricated by the polyol method, and characterized by Cs-corrected scanning transmission electron microscopy. The analysis of the high-resolution micrographs reveals that these nanoparticles have decahedral structure with shell periodicity, and that each of the particles is composed by Au core and Au3Cu alloyed shell surrounded by CuS2 surface layer. X-ray diffraction measurements and results from numerical simulations confirm these findings. From the atomic resolution micrographs, we identified edge dislocations at the twin boundaries of the particles, as well as evidence of the diffusion of Cu atoms into the Au region, and the reordering of the lattice on the surface, close to the vertices of the particle. These defects will impact the atomic and electronic structures, thereby changing the physical and chemical properties of the nanoparticles. On the other hand, we show for the first time the formation of an ordered superlattice of Au3Cu and a self-capping layer made using one of the alloy metals. This has significant consequences on the physical mechanism that form multicomponent nanoparticles.

High resolution micrograph synthesis using a parametric texture model and a particle filter

AbstractWe present a methodology for synthesizing high resolution micrographs from low resolution ones using a parametric texture model and a particle filter. Information contained in high resolution micrographs is relevant to the accurate prediction of microstructural behavior and the nucleation of instabilities. As these micrographs may be tedious and uneconomical to obtain over an extended spatial domain, we propose a statistical approach for interpolating fine details over a whole computational domain starting with a low resolution prior and high resolution micrographs available only at a few spatial locations. As a first step, a small set of high resolution micrographs are decomposed into a set of multi-scale and multi-orientation subbands using a complex wavelet transform. Parameters of a texture model are computed as the joint statistics of the decomposed subbands. The synthesis algorithm then generates random micrographs satisfying the parameters of the texture model by recursively updating the gray level values of the pixels in the input micrograph. A density-based Monte Carlo filter is used at each step of the recursion to update the generated micrograph, using a low resolution micrograph at that location as a measurement. The process is continued until the synthesized micrograph has the same statistics as those from the high resolution micrographs. The proposed method combines a texture synthesis procedure with a particle filter and produces good quality high resolution micrographs.

Structure and Composition of Magnetocaloric Ni–Mn–In–Co Thin Films on the Nanoscale—A TEM Study

AbstractA complementary set of electron microscopy techniques is applied for the determination of structural and chemical segregation phenomena within a 300 nm thick metamagnetic Ni–Mn–In–Co thin film. The structure is predominantly composed of distinct modulated martensites of the 5M‐, 6M‐, 7M‐, and 8M‐type. Additionally these modulated structures exhibit twinning and stacking disordering. The nature of the disordering and the structural misfit at the twin interface were analyzed via high resolution micrographs. Next to an adhesion layer of Cr interdiffusion on the nanoscale was observed producing a penternary chemically and structurally homogeneous precipitate. The structure can be assigned to a twinned non‐modulated pseudocubic model.

SimulaTEM: Multislice simulations for general objects

In this work we present the program SimulaTEM for the simulation of high resolution micrographs and diffraction patterns. This is a program based on the multislice approach that does not assume a periodic object. It can calculate images from finite objects, from amorphous samples, from crystals, quasicrystals, grain boundaries, nanoparticles or arbitrary objects provided the coordinates of all the atoms can be supplied.

High Resolution Imaging by Means of Backscattered Electrons in the Scanning Electron Microscope

This paper deals with imaging by means of backscattered electrons in the high resolution scanning electron microscopy. Possible backscattered electrons detection systems are outlined and one of the most efficient, the high take of angle single crystal scintillation detector, is described in detail. Its advantages and disadvantages are discussed and the comparison with the secondary electron detection modes is shown. The high resolution micrographs taken by the backscattered electron detector as well as by the secondary electron detectors are displayed.

Residual Stress Measurement on a MEMS Structure With High-Spatial Resolution

A new approach to the local measurement of residual stress in microstructures is described in this paper. The presented technique takes advantage of the combined milling-imaging features of a focused ion beam (FIB) equipment to scale down the widely known hole drilling method. This method consists of drilling a small hole in a solid with inherent residual stresses and measuring the strains/displacements caused by the local stress release, that takes place around the hole. In the presented case, the displacements caused by the milling are determined by applying digital image correlation (DIC) techniques to high resolution micrographs taken before and after the milling process. The residual stress value is then obtained by fitting the measured displacements to the analytical solution of the displacement fields. The feasibility of this approach has been demonstrated on a micromachined silicon nitride membrane showing that this method has high potential for applications in the field of mechanical characterization of micro/nanoelectromechanical systems

A domain partitioning based pre-processor for multi-scale modelling of cast aluminium alloys

In this paper, a microstructural morphology based domain partitioning MDP methodology is developed for materials with non-uniform heterogeneous microstructure. The comprehensive set of methods is intended to provide a concurrent multi-scale analysis model with an initial computational domain that delineates regions of statistical homogeneity and inhomogeneity. The MDP methodology is intended to be a pre-processor to multi-scale analysis of mechanical behaviour and damage of heterogeneous materials, e.g. cast aluminium alloys. It introduces a systematic three-step process that is based on geometric features of morphology. The first step simulates high resolution microstructural information from low resolution micrographs of the material and a limited number of high resolution optical or scanning electron microscopy micrographs. The second step is quantitative characterization of the high resolution images to create effective metrics that can relate microstructural descriptors to material behaviour. The third step invokes a partitioning method to demarcate regions belonging to different length scales in a concurrent multi-scale model. Partitioning criteria for domain partitioning are defined in terms of microstructural descriptors and their functions. The effectiveness of these metrics in differentiating microstructures of a 319-type cast aluminium alloy with different secondary dendrite arm spacings SDAS is demonstrated. The MDP method establishes intrinsic material length scales for the different SDAS, namely, 23, 70 and 100 µm, and consequently subdivides the computational domain for concurrently coupling macro- and micromechanical analyses in the multi-scale model.

Morphology based domain partitioning of multi‐phase materials: a preprocessor for multi‐scale modelling

AbstractThis paper develops a microstructural morphology‐based domain partitioning method (MDP) as a comprehensive pre‐processor for multi‐scale simulation of heterogeneous multi‐phase materials. The MDP method systematically creates a multi‐scale image simulation–characterization methodology to enable domain partitioning that can delineate homogenizable regions from those where explicit representation of phases is necessary for analysis. The methods are strictly based on geometric features of the material morphology and do not use any mechanical response functions. The first step in this development simulates high‐resolution microstructural information from low resolution images of the domain and only a limited high resolution micrographs from optical or scanning electron microscopy. The second step uses quantitative characterization of these high resolution images with, e.g. phase distribution functions, to create effective metrics that can relate microstructural features to the material's physical behaviour. The third step invokes domain partitioning to demarcate regions corresponding to different length scales in a concurrent multi‐scale model. Partitioning criteria are defined in terms of descriptors of microstructural characteristics and these are used to adaptively create multi‐level domain partitions. The method developed is tested on a micrograph of a cast aluminium alloy A356. Copyright © 2006 John Wiley & Sons, Ltd.

The equilibrium structures of the90° partial dislocation in silicon

We consider the free energies of the single-period (SP) and double-period (DP) core reconstructions of thestraight 90° partial dislocation in silicon. The vibrational contributions are calculated with aharmonic model. It is found that it leads to a diminishing difference between thefree energies of the two core reconstructions with increasing temperature. Thequestion of the relative populations of SP and DP reconstructions in a single straight90° partial dislocation is solved by mapping the problem onto a one-dimensional Ising model ina magnetic field. The model contains only two parameters and is solved analytically. Itleads to the conclusion that for the majority of the published energy differences betweenthe SP and DP reconstructions the equilibrium core structure is dominated by the DPreconstruction at all temperatures up to the melting point. We review whether it is possibleto distinguish between the SP and DP reconstructions experimentally, both in principleand in practice. We conclude that aberration corrected transmission electronmicroscopy should be able to distinguish between these two core reconstructions, butpublished high resolution micrographs do not allow the distinction to be made.