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Strain-Induced Metastable Phase Stabilization in Ga2O3 Thin Films
摘要： It is well known that metastable and transient structures in bulk can be stabilized in thin films via epitaxial strain (heteroepitaxy) and appropriate growth conditions that are often far from equilibrium. However, the mechanism of heteroepitaxy, particularly how the nominally unstable or metastable phase gets stabilized, remains largely unclear. This is especially intriguing for thin film Ga2O3, where multiple crystal phases may exist under varied growth conditions with spatial and dimensional constraints. Herein, the development and distribution of epitaxial strain at the Ga2O3/Al2O3 film-substrate interfaces is revealed down to the atomic resolution along different orientations, with an aberration-corrected scanning transmission electron microscope (STEM). Just a few layers of metastable α-Ga2O3 structure were found to accommodate the misfit strain in direct contact with the substrate. Following an epitaxial α-Ga2O3 structure of about couple unit cells, several layers (4~5) of transient phase appear as the intermediate structure to release the misfit strain. Subsequent to this transient crystal phase, the nominally unstable κ-Ga2O3 phase is stabilized as the major thin film phase form. We show that the epitaxial strain is gracefully accommodated by rearrangement of the oxygen polyhedra. When the structure is under large compressive strain, Ga3+ ions occupy only the oxygen octahedral sites to form a dense structure. With gradual release of the compressive strain, more and more Ga3+ ions occupy the oxygen tetrahedral sites, leading to volumetric expansion and the phase transformation. The structure of the transition phase is identified by high resolution electron microscopy (HREM) observation, complemented by the density functional theory (DFT) calculations. This study provides insights from the atomic scale and their implications for the design of functional thin film materials using epitaxial engineering.
关键词： κ-Ga2O3,misfit strain,α-Ga2O3,metastable phase,aberration-corrected scanning transmission electron microscopy
更新于2025-09-23 15:23:52
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Quality of extracellular vesicle images by transmission electron microscopy is operator and protocol dependent
摘要： Transmission electron microscopy (TEM) has nanometre resolution and can be used to distinguish single extracellular vesicles (EVs) from non-EV particles. TEM images of EVs are a result of operator image selection. To which extent operator image selection reflects the overall sample quality, and to which extent the images are comparable and reproducible, is unclear. In a first attempt to improve the comparability and reproducibility of TEM to visualise EVs, we compared operator image selection to images taken at predefined locations from the same grids, using four EV TEM preparation protocols, a single EV-containing sample and a single TEM instrument. Operator image selection leads to high-quality images that are more similar between the protocols. In contrast, images taken at predefined locations reveal differences between the protocols, for example in number of EVs per image and background quality. From the evaluated protocols, for only one protocol the operator image selection is comparable to the TEM images taken at predefined locations. Taken together, operator image selection can be used to demonstrate the presence of EVs in a sample, but seem less suitable to demonstrate the quality of a sample. Because images taken at predefined locations reflect the overall quality of the EV-containing sample rather than the presence of EVs alone, this is a first step to improve the comparability and reproducibility of TEM for monitoring the quality of EV-containing samples.
关键词： urine,negative staining,transmission electron microscopy (TEM),Exosomes,extracellular vesicles (EVs),microvesicles
更新于2025-09-23 15:23:52
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Method for Combined Observation of Serial Sections of Stented Arteries Embedded in Resin by Light Microscopy and Transmission Electron Microscopy
摘要： We have developed a new method for obtaining information on whole tissues by light microscopy (LM) and ultrastructural features by transmission electron microscopy (TEM). This method uses serial sections of a stented artery embedded in resin. Stents were implanted in porcine coronary arteries in this study. The heart was perfusion fixed in a 2% paraformaldehyde and 1.25% glutaraldehyde mixed solution. The stented artery was then removed, fixed in 1% osmium, embedded in Quetol 651 resin, and sectioned serially. For LM, the black color of osmium was removed from the section by immersion in periodic acid and hydrogen peroxide after deplasticization. These sections were stained with hematoxylin and eosin and Elastica–Masson trichrome stain. For TEM, thin sections were re-embedded in Quetol 812 resin by the resupinate method and cut into ultrathin sections. A clear, fine structure was obtained, and organelles, microvilli, and cell junctions in the endothelium were easily observed. The combined observation of adjacent specimens by LM and TEM enabled us to relate histopathological changes in the millimeter scale to those in the nanometer scale.
关键词： porcine,stent,resupinate method,coronary artery,epoxy resin,transmission electron microscopy,light microscopy
更新于2025-09-23 15:22:29
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Correlative infrared nanospectroscopy and transmission electron microscopy to investigate nanometric amyloid fibrils: prospects and challenges
摘要： Propagation of structural information through conformational changes in host-encoded amyloid proteins is at the root of many neurodegenerative disorders. Although important breakthroughs have been made in the field, fundamental issues like the 3D-structures of the fibrils involved in some of those disorders are still to be elucidated. To better characterise those nanometric fibrils, a broad range of techniques is currently available. Nevertheless none of them is able to perform direct chemical characterisation of single protein fibrils. In this work, we propose to investigate the structure of the C-terminal region of a bacterial protein called Hfq as a model amyloidogenic protein, using a correlative approach. The complementary techniques used are transmission electron microscopy and a newly developed infrared nanospectroscopy technique called AFM-IR. We introduce and discuss the strategy that we have implemented as well as the protocol, challenges and difficulties encountered during this study to characterise amyloid assemblies at the nearly single-molecule level.
关键词： correlative measurements,transmission electron microscopy,infrared nanospectroscopy,fibrils,Hfq,atomic force microscopy,Amyloid
更新于2025-09-23 15:22:29
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A facile route to diatoms decorated with gold nanoparticles and their optical properties
摘要： This paper presents a facile route for the decoration of biogenic silica from diatoms with gold nanoparticles (AuNPs) with dimensions from 10 to 40 nm. The AuNP decoration on the diatoms is performed through initial attachment of colloidal AuNPs (2 nm) followed by enhancement of the size of the AuNPs by mild reduction of tetrachloroauric (III) acid from solution. The samples were characterised by transmission electron microscopy (TEM), energy-dispersive X-ray analysis, Fourier transform infrared spectroscopy and light spectroscopy in the ultraviolet and visible (UV/Vis) range. The size of the isolated AuNPs on unmodified acid-cleaned diatoms was 10 nm according to TEM micrograph analysis. The measured UV/Vis spectrum showed an absorption peak at 525 nm, which corresponds well to the optical properties of AuNPs of the same size. The extent of decoration with AuNPs of the diatoms was significantly improved after functionalisation with 3-aminopropyltriethoxysilane of the biogenic silica. The absorption peak in the visible range was redshifted to 590 nm due to enlargement of the AuNPs up to 40 nm and clustering of the AuNPs. The AuNP decoration on the hierarchical and complex structured biogenic silica of diatoms might be interesting for biodiagnostic and surface-enhanced Raman spectroscopic applications.
关键词： transmission electron microscopy,optical properties,nanoparticles
更新于2025-09-23 15:22:29
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Structure and properties of layered perovskites Ba1-Ln Fe1-Co O3-δ (Ln = Pr, Sm, Gd)
摘要： A series of samples of overall composition Ba1-xLnxFe1-yCoyO3-δ (Ln = Pr, Sm, Gd) with x = 0.3-0.4; y = 0-0.5 were prepared by glycerin nitrate technique in air. The crystal structure of single-phase Ba1-xLnxFe1-yCoyO3-δ (Ln = Pr, Sm, Gd) determined by XRD was described as cubic (sp. gr. Pm3(cid:1)m). However, transmission electronic microscopy revealed that both Sm- and Gd-doped oxides possess tetragonal structure with 5-fold and 3-fold increased c parameter respectively. Oxygen content in the complex oxides has been determined in air over wide temperature range by means of thermogravimetry and iodometric titration. The change in oxygen content with temperature for the phases with five-layered ordering was significantly smaller than for the disordered phases.
关键词： oxygen nonstoichiometry,X-ray diffraction,oxide materials,transmission electron microscopy,crystal structure
更新于2025-09-23 15:22:29
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Voids in Kesterites and the Influence of Lamellae Preparation by Focused Ion Beam for Transmission Electron Microscopy Analyses
摘要： Kesterite solar cells based on Cu2 ZnSnS4 and Cu2 ZnSnSe4 (CZTSe) are potential future candidates to be used in thin-film solar cells. The technology still has to be developed to a great extent and for this to happen, high levels of confidence in the characterization methods are required, so that improvements can be made on solid interpretations. In this study, we show that the interpretations of one of the most used characterization techniques in kesterites, scanning transmission electron microscopy (STEM), might be affected by its specimen preparation when using focused ion beam (FIB). Using complementary measurements based on scanning electron microscopy and Raman scattering spectroscopy, compelling evidence shows that secondary phases of ZnSe mixed in the bulk of CZTSe are the likely cause of the appearance of voids in STEM lamellae. Sputtering simulations support this interpretation by showing that Zn in a ZnSe matrix is preferentially sputtered compared with any metal atom in a CZTSe matrix.
关键词： Cu2 ZnSn(S, Se)4 (CZTSSe),thin-film solar cells,transmission electron microscopy (TEM),focused ion beam (FIB),kesterite
更新于2025-09-23 15:22:29
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V-Defect and Dislocation Analysis in InGaN Multiple Quantum Wells on Patterned Sapphire Substrate
摘要： InGaN/GaN multiquantum well (MQW) structures have been grown on cone-shaped patterned sapphire substrates (CPSS) by metalorganic chemical vapor deposition (MOCVD). From the transmission electron microscopy (TEM) results, we found that most of the threading dislocations (TDs) in the trench region of the CPSS were bent by lateral growth mode. Also the staircase-like TDs were observed near the slant region of the cone pattern, they converged at the slope of the cone patterned region by staircase-upward propagation, which seems to effectively prevent TDs from vertical propagation in the trench region. The associated dislocation runs up into the overgrown GaN layer and MQW, and some (a+c) dislocations were shown to decompose inside the multi-quantum well, giving rise to a misfit segment in the c-plane and a V-shape defect. From cross-sectional TEM, we found that all V defects are not always connected with TDs at their bottom, some V defects are generated from the stacking mismatch boundaries induced by stacking faults which are formed within the MQW due to the strain relaxation.
关键词： V defects,Transmission electron microscopy (TEM),InGaN multi-quantum well (MQW),Threading dislocations (TDs)
更新于2025-09-23 15:22:29
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Transmission Electron Microscopy of Halide Perovskite Materials and Devices
摘要： Transmission electron microscopy (TEM)-based techniques are uniquely suited for site-specific structural and analytical characterization of halide perovskites (HPs) at atomic, nanometer, and micrometer length scales. TEM-based studies hold the key to understanding the nature and functionality of these fascinating materials that are at the heart of emerging solar cells and (opto)electronic devices. While TEM-based techniques have made several groundbreaking discoveries that have resulted in astonishing advancements in the field of materials science in general over the past decades, their application to HPs has been relatively sparse. Here, we provide a perspective on TEM-based studies of HPs that have been conducted so far and project a vision for how these powerful characterization techniques can be brought to bear on research problems in the field of HPs. An outlook discussing important challenges and opportunities that lay ahead is also presented.
关键词： Halide Perovskites,Optoelectronics,Materials Characterization,Solar Cells,Transmission Electron Microscopy
更新于2025-09-23 15:22:29
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European Microscopy Congress 2016: Proceedings || Fivefold symmetries in silicon thin films induced by multiple twinning
摘要： Fivefold symmetry, like any kind of n-fold rotational symmetry, can be identifiable when rotating a crystalline configuration 5 times (or n times) around a certain axis and realizing that the structure is transformed into a configuration that is equivalent to the initial one. The occurrence of this specific symmetry, forbidden by the conventional periodic crystallography, was attributed in the literature to the presence of a new state of matter 'the quasicrystals' [1] [2] or simply to an effect of multiple twinning. Particularly, the tendency of multiply twinning in a fivefold symmetry has been widely reported in small particles having a special morphology like the decahedral [3] or icosahedral [4] structures, usually called multiply twinned particles. In this study, we will highlight on the fivefold symmetry observed in the electron diffraction patterns of two types of materials elaborated in different growth conditions, originating from multiple twinning and not from the presence of multiply twinned particles. The first case concerns the fivefold symmetry on p-type doped silicon thin films containing a non-negligible amount of carbon and oxygen. These films were deposited in a plasma enhanced chemical vapor deposition reactor (PECVD) at 0.2 W/cm2 using silane, hydrogen, diborane and hexamethydisiloxane (C6H18OSi2, HMDSO) diluted in argon. Since all the diffraction patterns recorded on different regions of these films exhibit a fivefold symmetry along [0-11] zone axis (Figure 1), it is clear that this symmetry is real and characteristic of our films. Further diffraction measurements reveal that there is a relation of epitaxy with the (100) crystalline silicon substrate. This is also confirmed by high resolution TEM images, where {111} planes are continuing from the substrate to the film across the interface. Moreover, energy filtered TEM images were correlated with SIMS measurements to provide elemental mapping of silicon, carbon and oxygen with absolute values. The second case illustrates a quasi-fivefold symmetry recorded on intrinsic silicon thin films deposited by PECVD using silicon tetrafluoride, hydrogen and argon chemistry at a purposely high power density of 0.3 W/cm2. After few hundred nanometers of epitaxial growth, a high density of defects appears, followed by a multiply twinned part (as shown in Figure 2a). Fourier Transforms recorded on the first part reveal a monocrystalline structure (Figure 2c), and on the second part a fivefold symmetry (Figure 2b), which is, in this case also, linked to an epitaxial growth. It has been proved in some references [5] [6] that a high power density is responsible for a high ion energy impinging on the substrate and causing some surface or even bulk damage. Thus, the twin defects present in our films are most probably caused by the application of a high power density. However, to obtain a fivefold symmetry, it is necessary to have at least three orders of twinning that contribute to 10 spots in the diffraction pattern, i.e, if there only exist two orders of twinning, some additional diffraction spots appear without giving rise to a fivefold symmetry as it is the case of Figure 3. Detailed investigation of the multiple twinning in a fivefold symmetry fashion will be presented.
关键词： silicon,Transmission electron microscopy,epitaxy,twin,fivefold symmetry
更新于2025-09-23 15:22:29