Transmission electron microscopy characterization of two major long-period stacking ordered (LPSO) phases in Mg–Zn–Y alloy, i.e., 18R- and 14H-LPSO are reported. The space group and atomic-scale microstructures of both compounds were determined using a combination of electron diffraction, convergent beam electron diffraction, high-resolution transmission electron microscopy, and Z-contrast scanning transmission electron microscopy. The 18R-LPSO phase is demonstrated to have a point group and space group 3m and R3m (or 3m and R3m), with the lattice parameter a = 1.112 nm and c = 4.689 nm in a hexagonal coordinate system. The 14H-LPSO phase has a point group 6/mmm and a space group P63 /mmc, and the lattice parameter is a = 1.112 nm and c = 3.647 nm. In addition, insertion of extra thin Mg platelets of several atomic layers, results in stacking faults in the LPSO phase. These results may shed some new light on a better understanding of the microstructure and deformation mechanisms of LPSO phases in Mg alloys.

A system for illuminating a sample in situ with visible and ultraviolet light inside a transmission electron microscope was devised to study photocatalysts. There are many mechanical and optical factors that must be considered when designing and building such a system. Some of the restrictions posed by the electron microscope column are significant, and care must be taken not to degrade the microscope's electron-optical performance or to unduly restrict the other capabilities of the microscope. We discuss the nature of the design considerations, as well as the practical implementation and characterization of a solution. The system that has been added to an environmental transmission electron microscope includes a high brightness broadband light source with optical filters, a fiber to guide the light to the sample, and a mechanism for precisely aligning the fiber tip.

In this paper, we have observed an atomic-scale structure and compositional variation at the interface of the InGaN/GaN multi-quantum wells (MQW) by both scanning transmission electron microscopy (STEM) using high-angle annular dark-field mode and atom probe tomography (APT). The iso-concentration analysis of APT results revealed that the roughness of InGaN/GaN interface increased as the MQW layers were filled up, and that the upper interface of MQW (GaN/InGaN to the p-GaN side) was much rougher than that of the lower interface (InGaN/GaN tot he n-GaN side). On the basis of experimental results, it is suggested that the formation of interface roughness can affect the quantum efficiency of InGaN-based light-emitting diodes.

Structures comprising single-crystal, iron-carbon-based nanowires encapsulated by multiwall carbon nanotubes self-organize on inert substrates exposed to the products of ferrocene pyrolysis at high temperature. The most commonly observed encapsulated phases are Fe3C, α-Fe, and γ-Fe. The observation of anomalously long-period lattice spacings in these nanowires has caused confusion since reflections from lattice spacings of ≥0.4 nm are kinematically forbidden for Fe3C, most of the rarely observed, less stable carbides, α-Fe, and γ-Fe. Through high-resolution electron microscopy, selective area electron diffraction, and electron energy loss spectroscopy we demonstrate that the observed long-period lattice spacings of 0.49, 0.66, and 0.44 nm correspond to reflections from the (100), (010), and (001) planes of orthorhombic Fe3C (space group Pnma). Observation of these forbidden reflections results from dynamic scattering of the incident beam as first observed in bulk Fe3C crystals. With small amounts of beam tilt these reflections can have significant intensities for crystals containing glide planes such as Fe3C with space groups Pnma or Pbmn.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Heterostructures and interfacial defects in a 40-nm-thick SrTiO3 (STO) film grown epitaxially on a single-crystal MgO (001) were investigated using aberration-corrected scanning transmission electron microscopy and geometric phase analysis. The interface of STO/MgO was found to be of the typical domain-matching epitaxy with a misfit dislocation network having a Burgers vector of ½ aSTO ⟨100⟩. Our studies also revealed that the misfit dislocation cores at the heterogeneous interface display various local cation arrangements in terms of the combination of the extra-half inserting plane and the initial film plane. The type of the inserting plane, either the SrO or the TiO2 plane, alters with actual interfacial conditions. Contrary to previous theoretical calculations, the starting film planes were found to be dominated by the SrO layer, i.e., a SrO/MgO interface. In certain regions, the starting film planes change to the TiO2/MgO interface because of atomic steps at the MgO substrate surface. In particular, four basic misfit dislocation core configurations of the STO/MgO system have been identified and discussed in relation to the substrate surface terraces and possible interdiffusion. The interface structure of the system in reverse—MgO/STO—is also studied and presented for comparison.

A multi-scale investigation of twin bundles in Fe–22Mn–0.6C (wt%) twinning-induced plasticity steel after tensile deformation has been carried out by truly correlative means; using electron channelling contrast imaging combined with electron backscatter diffraction, high-resolution secondary ion mass spectrometry, scanning transmission electron microscopy, and atom probe tomography on the exact same region of interest in the sample. It was revealed that there was no significant segregation of Mn or C to the twin boundary interfaces.

New methods for defect analysis can lead to improved interpretation of experimental data and thus better understanding of material properties. Although transmission electron microscopy (TEM) has been used to study defects for many decades, interpretive ambiguities can arise for cases that seem simple or even trivial. Using geometric phase analysis (GPA), an image processing procedure, we show that an apparent simple line defect in pyrite has an entirely different character. It appears to be a b = ½[100] edge dislocation as viewed in a [001] high-resolution TEM (HRTEM) image, but the measured ux and uy displacements are asymmetric, which is inconsistent with a simple line dislocation. Instead, the defect is best understood as a terminating {101} marcasite slab in pyrite. The simulated HRTEM image based on this model reproduces the defect contrast and illustrates the power of GPA analysis for (1) avoiding potential pitfalls of misinterpreting apparently simple defects in HRTEM images, (2) detecting differences in elastic properties at the atomic scale, and (3) providing data for the positions of atom columns, thereby facilitating the construction of structure models for complex defects.

The microstructural evolution of a cold drawn copper wire (reduction area of 38%) during primary recrystallization and grain growth was observed in situ by electron backscatter diffraction. Two thermal treatments were performed, and successive scans were acquired on samples undergoing heating from ambient temperature to a steady state of 200°C or 215°C. During a third in situ annealing, the temperature was continuously increased up to 600°C. Nuclei were observed to grow at the expense of the deformed microstructure. This growth was enhanced by the high stored energy difference between the nuclei and their neighbors (driving energy in recrystallization) and by the presence of high-angle grain boundaries of high mobility. In the early stages of growth, the nuclei twin and the newly created orientations continue to grow to the detriment of the strained copper. At high temperatures, the disappearance of some twins was evidenced by the migration of the incoherent twin boundaries. Thermal grooving of grain boundaries is observed at these high temperatures and affects the high mobile boundaries but tends to preserve the twin boundaries of lower energy. Thus, grooving may contribute to the twin vanishing.

Doping of silicon with chalcogens (S, Se, Te) by femtosecond laser irradiation to concentrations well above the solubility limit leads to near-unity optical absorptance in the visible and infrared (IR) range and is a promising route toward silicon-based IR optoelectronics. However, open questions remain about the nature of the IR absorptance and in particular about the impact of the dopant distribution and possible role of dopant diffusion. Here we use electron tomography using a high-angle annular dark-field (HAADF) detector in a scanning transmission electron microscope (STEM) to extract information about the three-dimensional distribution of selenium dopants in silicon and correlate these findings with the optical properties of selenium-doped silicon. We quantify the tomography results to extract information about the size distribution and density of selenium precipitates. Our results show correlation between nanoscale distribution of dopants and the observed sub-band gap optical absorptance and demonstrate the feasibility of HAADF-STEM tomography for the investigation of dopant distribution in highly-doped semiconductors.

The advent of aberration correction for transmission electron microscopy has transformed atomic resolution imaging into a nearly routine technique for structural analysis. Now an emerging frontier in electron microscopy is the development of in situ capabilities to observe reactions at atomic resolution in real time and within realistic environments. Here we present a new in situ gas cell holder that is designed for compatibility with a wide variety of sample type (i.e., dimpled 3-mm discs, standard mesh grids, various types of focused ion beam lamellae attached to half grids). Its capabilities include localized heating and precise control of the gas pressure and composition while simultaneously allowing atomic resolution imaging at ambient pressure. The results show that 0.25-nm lattice fringes are directly visible for nanoparticles imaged at ambient pressure with gas path lengths up to 20 μm. Additionally, we quantitatively demonstrate that while the attainable contrast and resolution decrease with increasing pressure and gas path length, resolutions better than 0.2 nm should be accessible at ambient pressure with gas path lengths less than the 15 μm utilized for these experiments.

Hypericum L, the largest genus of Hypericaceae comprising ca. 484 species of shrubs and perennial and annual herbs, is worldwide in a large variety of habitats in subtropical and temperate areas. Hypericum species, namely H. perforatum (St. John’s wort) the most representative species of the genus, have been used in folk medicine thought the centuries for a large number of ailments. Nowadays, it is well known the therapeutic potentialities of their main compounds, hypericin, pseudohypericin and hyperforin, which justify its clinical use. Despite the intense phytochemical and pharmacological research conducted in Hypericum species during the last decades, morpho-anatomical studies on the glands that produce the bioactive compounds are scarce and fragmented, only H. perforatum was studied in detail. As part as an ongoing project on Hypericum glands, the present research aims to provide information about the morphology, anatomy and histochemistry of the secretory structures present on the aerial organs of H. perfoliatum, one of the seventeen species of Hypericum that occur wild in Portugal.

The types of glandular structures and their pattern of distribution on the leaves and flowers were studied by light (MO) and scanning electron microscopy (SEM). Samples for SEM were fixed with glutaraldehyde, dehydrated in a graded acetone series, critical-point dried and coated with gold. For general anatomy samples were fixed in the same fixative and embedded in Leica historesin®. Histochemical tests and standard control procedures were carried out in fresh material to localize in situ the main chemical classes of compounds present in the secretion. Observations were carried out Observations were carried out on a JEOL T220 scanning electron microscope and with a Leica DM-2500 microscope.

The aerial organs of H. perfoliatum present four different types of secretory structures (idioblasts, translucent glands, ducts and black nodules), that can occur exclusively in a specific organ or in more than one organ. Tanniniferous secretory cells are frequent in the epidermis, as well as in the ground parenchyma of all organs, where they are scattered together with crystal idioblasts containing druses of calcium oxalate. Translucent glands are spheroidal subepidermical glandular pockets delimited by two or three cell layers of fattened and densely-stained cells (Fig. 1A). They are typically found in the leaves, giving them a perforated appearance. Two types of secretory ducts, cavities that differ from translucent glands in the length, are present in the vegetative and floral organs. Type A ducts have a narrow lumen delimited by four secretory epithelial cells and occur associated to the phloem in all aerial organs with exception of stamens (Fig. 1B, arrow). Type B ducts have a wider lumen, are generally limited by ten thin-walled secretory cells surrounding by a sheath of thick-walled cells and are located in the parenchyma of sepals, petals and ovary. Black nodules are clusters of cells lacking a central intercellular space (lumen), surrounded by one or two-layers of flat cells of a delimiting sheath (Fig. 1C). The inner cells are large, irregular, tightly packed and filled with a dark red stained content. Spheroidal black nodules are found punctuating the leaf margins and in the connective tissue of the stamen (Fig. 1D), whereas long-shaped black nodules are distributed across the lamina of bracts, sepals and petals. Peculiar glandular emergences, which look like peduncular black nodules, are present along the margin of the bracts and sepals. They consist of a multicellular peduncle and a dark-red multicellular secretory head-a black nodule (Fig. 1E). Histochemical tests showed that translucent glands secreted essential oils rich in phenolic compounds (flavonolic aglycones), ducts produce oleoresins and nodules contain essentially hypericin. In mature organs, the disorganization of the inner cells of the nodules seems to form a large intercellular space, a lumen.

All these secretory structures were also found in H. perforatum with exception of peduncular black nodules, that was only reported in H. elodes, but not studied in detail. The obtained results allow as speculating that nodules may be primitive multicellular structures, relics of an evolutionary process, that give rise to cavities, internal secretory structures that stores secretion material in intercellular spaces.

The authors acknowledge the funding by Fundação para a Ciência e Tecnologia through the project FCT PEst-OE/EQB/LA0023/2011.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Dermal bone is an important component of the teleost fins, and its ability to regenerate after fin amputation appears to be unlimited. The organic bone matrix contain type I collagen fibers, proteoglycans enriched in chondroitin sulfate, and noncollagenous matrix protein such as osteocalcin, osteopontin, and osteonectin. These molecules are synthesized by fin osteoblasts. Inorganic components chiefly consist of calcium and phosphate that form crystals of hydroxyapatite. Fin rays are described as models to study ossification. Due to this, the identification of the components involved in the synthesis of the organic and inorganic components of lepidotrichial bone are of great interest for the analysis of skeletal disorders in fish ossification. The present study investigates expression of alkaline phosphatase, osteopontin, osteocalcin, and chondroitin sulfate during pectoral fin regeneration in Carassius auratus gibelio. Alkaline phosphatase reaction has been found in the epidermis covering the wound, proximal blastema, near the cells that surround newly-formed lepidotrichia matrix and the tips of regenerating fin rays. Osteopontin has been observed throughout the regeneration blastema but excluded from the scleroblasts lining the inner side of the lepidotrichia. Osteocalcin and chondroitin sulfate expression coincides with the onset of mineralization of lepidotrichial matrix, suggesting its involvement in bone mineralization.

Kirkendall void formation at the solder/metallization interface is an important reliability concern for Cu conductors and under-bump metallization in microelectronic packaging industry, whose mechanism is still hard to be understood for different individual cases. In the present work, two typical solder/Cu-diffusing couples, eutectic SnIn/Cu and SnBi/Cu, were studied by scanning/transmission electron microscopy to investigate the microstructural evolution and voiding process after soldering and then solid-state aging. It was concluded that Kirkendall voids formed between two sublayers within Cu2(In,Sn) phase in eutectic SnIn/Cu solder joint, whereas they appeared at the Cu3Sn/Cu interface or within Cu3Sn for eutectic SnBi/Cu solder joint. Besides the effect of impurity elements, the morphological difference within one intermetallic compound layer could change the diffusing rates of reactive species, hence resulting in void formation in the reaction zone.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

The role of grain orientation and grain boundary misorientation on the formation of subcritical grain boundary cracks in creep of a conventionally cast nickel-based superalloy has been studied. The crystallographic orientations of the grains adjacent to grain boundaries normal to the tensile axis were measured using electron backscattered diffraction. The difference in the Schmid factor for the {111} ⟨112⟩ slip system between the grains was compared to the occurrence of grain boundary cracking. In addition, the difference in the amount of potential primary creep was calculated. The cracked grain boundaries were found to have a larger difference in Schmid factor, as well as a larger difference in potential primary creep, compared with uncracked grain boundaries.

Tomography is a standard and invaluable technique that covers a large range of length scales. It gives access to the inner morphology of specimens and to the three-dimensional (3D) distribution of physical quantities such as elemental composition, crystalline phases, oxidation state, or strain. These data are necessary to determine the effective properties of investigated heterogeneous media. However, each tomographic technique relies on severe sampling conditions and physical principles that require the sample to be adequately shaped. For that purpose, a wide range of sample preparation techniques is used, including mechanical machining, polishing, sawing, ion milling, or chemical techniques. Here, we focus on the basics of tomography that justify such advanced sample preparation, before reviewing and illustrating the main techniques. Performances and limits are highlighted, and we identify the best preparation technique for a particular tomographic scale and application. The targeted tomography techniques include hard X-ray micro- and nanotomography, electron nanotomography, and atom probe tomography. The article mainly focuses on hard condensed matter, including porous materials, alloys, and microelectronics applications, but also includes, to a lesser extent, biological considerations.

This work studied the phases in the Al corner of the Al–Mn–Be phase diagram in the as-cast state and heat-treated conditions. Metallographic investigations, X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy were used for identifying the phases. The Be contents in the identified phases were precisely determined using Auger electron spectroscopy. The results indicated that Al6Mn does not dissolve Be, whilst λ-Al4Mn dissolves up to 7 at.% Be. The average composition of the T phase, which is normally designated as Al15Mn3Be2, was 72 at.% Al, 19 at.% Mn, and 9 at.% Be. The phase with the nominal composition Be4AlMn contained more Al than Mn. The atomic ratio Al:Mn was between 1.3:1 and 2:1. The hexagonal Be-rich phase did not dissolve any Al and Mn. The icosahedral quasicrystalline (IQC) phase contained up to 45 at.% Be. The compositions of T phase, λ–Al4Mn, IQC, and Be4AlMn may vary, however, the ratio (Al + Be):Mn remained constant, and was close either to four or six indicating substitution of Al atoms with Be atoms in these phases.

Equations governing the elastic scattering of electrons are applied to the knock-on displacement of atoms along a substrate, yielding analytical expressions for the surface-translation energy, threshold incident energy, and displacement rate. For a surface perpendicular to the incident beam, scattering angles around 90° contribute most to the kinetic energy of surface atoms. Tilting the specimen lowers the threshold incident energy for displacement and leads to anisotropy in the atomic motion but has little effect on the directionally-averaged displacement rate. The rate of beam-induced adatom motion is predicted to exceed that of room-temperature thermal motion when the surface-diffusion energy is greater than about 0.5 eV.