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We attain N-polar and Al-polar AlN thin films on Si(111) substrates by plasma-assisted molecular beam epitaxy. The polarity of AlN epilayers has been validated by wet chemical etching using tetramethylammonium hydroxide and by the direct cross-sectional observation of atomic stacking under high-angle annular dark-field scanning transmission electron microscopy. For the 290 nm-thick as-grown N-polar AlN epilayer, x-ray diffraction (XRD) (002) and (102) ω rocking curve peak full width half maximums (FWHMs) are 475 and 1177 arcsec, and the surface mean square roughness (RMS) is 0.30 nm. We flipped the polarity using the metal-flux-modulation-epitaxy (MME) strategy. The MME strategy promotes anti-phase boundaries (APBs) on the { 2 2 ¯ 01 } crystalline planes instead of commonly observed lateral planar APBs in AlN epilayers. Merging of the tilted APBs at ∼50 nm leads to a complete Al-polar surface. For the 180 nm-thick Al-polar AlN epilayer, XRD (002) and (102) peak FWHMs are 1505 and 2380 arcsec, and the surface RMS is 1.41 nm. Strain analysis by XRD and Raman spectroscopy indicates a uniform tensile strain of 0.160% across the N-polar AlN epilayer surface and a strain distribution of 0.113%–1.16% through the epilayer. In contrast, the Al-polar AlN epilayer exhibits a much broader tensile strain distribution of 0.482%–2.406% along the growth direction, potentially due to the interaction of polarity inversion and strain relaxation. [ABSTRACT FROM AUTHOR]

Hafnium diboride (HfB2) is a promising candidate as a seed layer for GaN growth on Si substrates due to its excellent lattice and thermal coefficients matching with both materials. This work investigates the epitaxial growth of AlB2-type non-stoichiometric HfB2 (HfB2+δ with −0.1 < δ < 0.6) thin films on Si(111) using magnetron co-sputtering. We demonstrated that the process temperature significantly affected the surface roughness (RRMS ∼ 0.5–4 nm), film composition, and the nucleation of secondary impurity phases. Films deposited between 700 and 900 °C exhibit epitaxial growth on the Si substrate with a well-defined relationship of (0001) HfB 2 ‖ (111) Si and [ 11 2 ¯ 0 ] HfB 2 ‖ [ 1 1 ¯ 0 ] Si . Detailed x-ray diffraction and scanning transmission electron microscopy analyses reveal that impurity phases detected at high temperatures are primarily carbon-rich phases, identified as HfCx or HfCxBy. Interestingly, this secondary phase's crystal orientation follows the orientation of its surroundings. The different findings in terms of contamination (C and O) and deposition temperature offer valuable insights for further growth optimizing of high-quality epitaxial HfB2 thin films on Si(111) for future GaN-on-Si integration. [ABSTRACT FROM AUTHOR]

Ag-induced crystallization and layer exchange (AgILE) in a stack of amorphous Si/Ag/quartz substrate has been investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy (TEM), scanning TEM-high angle annular dark field (STEM-HAADF) imaging, and electron tomography, covering length scales from a few tens of micrometers to a few tens of nanometers. The size of Ag grains in the underlying as-deposited Ag film varied from ∼10 to 500 nm. The following processes could be discerned using in situ heating of plan-view samples at 500 °C in STEM: (i) AgILE propagation preferentially along regions of small Ag grains, (ii) formation of pushed-up Ag in the vicinity of AgILE reaction cells, (iii) migration and agglomeration of pushed-up Ag on small and large Ag grains, which tend to inhibit AgILE and promote dendricity, and (iv) dispersion of pushed-up Ag, which tend to reduce dendricity. The resulting dendricity was largely confined to the peripheral regions of the impinging reaction cells and decreased with annealing time. In contrast, dendricity due to AgILE and crystallization at 550 °C is stable and extends right from the center to the periphery of the reaction cells. The microscopic mechanism of AgILE and, in particular, the effect of annealing temperature is investigated. The results are discussed in the light of existing literature and compared with Al-induced layer exchange. Annealing at temperature equal to or slightly less than 500 °C is found to be necessary in the case of AgILE to avoid dendricity and to obtain a continuous Si layer with large Si grains. [ABSTRACT FROM AUTHOR]

Achieving high material perfection in aluminum (Al) films and their associated Al/AlOx heterostructures is essential for enhancing the coherence time in superconducting quantum circuits. We grew Al films with thicknesses ranging from 3 to 30 nanometers (nm) epitaxially on sapphire substrates using molecular beam epitaxy (MBE). An integral aspect of our work involved electron-beam (e-beam) evaporation to directly deposit aluminum oxide (Al2O3) films on the freshly grown ultrathin epitaxial Al films in an ultra-high-vacuum (UHV) environment. This in situ oxide deposition is critical for preventing the oxidation of parts of the Al films, avoiding the formation of undesired native oxides, and thereby preserving the nm-thick Al films in their pristine conditions. The thicknesses of our Al films in the study were accurately determined; for example, coherence lengths of 3.0 and 20.2 nm were measured in the nominal 3.0 and 20 nm thick Al films, respectively. These Al films were epitaxially grown on sapphire substrates, showing an orientational relationship, denoted as Al (111) ⟨ 2 1 ¯ 1 ¯ ⟩ ∥ sapphire (0001) [ 2 1 ¯ 1 ¯ 0 ]. The Al/sapphire interface was atomically ordered without any interfacial layers, as confirmed by in situ reflection high-energy electron diffraction (RHEED) and cross-sectional scanning transmission electron microscopy (STEM). All sample surfaces exhibited smoothness with a roughness in the range of 0.1–0.2 nm. The Al films are superconducting with critical temperatures ranging from 1.23 to around 2 K, depending on the film thickness. [ABSTRACT FROM AUTHOR]

Bragg interferometry (BI) is an imaging technique based on four-dimensional scanning transmission electron microscopy (4D-STEM) wherein the intensities of select overlapping Bragg disks are fit or more qualitatively analyzed in the context of simple trigonometric equations to determine local stacking order. In 4D-STEM based approaches, the collection of full diffraction patterns at each real-space position of the scanning probe allows the use of precise virtual apertures much smaller and more variable in shape than those used in conventional dark field imaging such that even buried interfaces marginally twisted from other layers can be targeted. With a coarse-grained form of dark field ptychography, BI uses simple physically derived fitting functions to extract the average structure within the illumination region and is, therefore, viable over large fields of view. BI has shown a particular advantage for selectively investigating the interlayer stacking and associated moiré reconstruction of bilayer interfaces within complex multi-layered structures. This has enabled investigation of reconstruction and substrate effects in bilayers through encapsulating hexagonal boron nitride and of select bilayer interfaces within trilayer stacks. However, the technique can be improved to provide a greater spatial resolution and probe a wider range of twisted structures, for which current limitations on acquisition parameters can lead to large illumination regions and the computationally involved post-processing can fail. Here, we analyze these limitations and the computational processing in greater depth, presenting a few methods for improvement over previous works, discussing potential areas for further expansion, and illustrating the current capabilities of this approach for extracting moiré-scale strain. [ABSTRACT FROM AUTHOR]

An area-selectable Mg doping via ion implantation (I/I) is essential to realize gallium nitride (GaN) based power switching devices. Conventional post-implantation annealing forms considerable defects in the GaN, resulting in extremely low activation efficiency. The recent invention of ultrahigh-pressure annealing (UHPA) has substantially improved the p-type activation efficiency; however, the UHPA causes an unexpected Mg diffusion. Thus, both annealing processes resulted in a much lower Mg concentration in the GaN matrix than the Mg dose. In this study, the effect of a sequential N I/I for p-type Mg-implanted GaN was investigated by the correlative cathodoluminescence, transfer length method, scanning transmission electron microscopy, and atom probe tomography (APT) analyses. APT results have revealed that the sequential N I/I can successfully maintain the Mg concentration in the GaN matrix in the higher range of 1018 cm−3 or more. Our investigation suggests that sequential N I/I is a promising technique to maintain the Mg concentration higher and improve the p-type activation efficiency. [ABSTRACT FROM AUTHOR]

Dislocations have been proposed to affect the performance and reliability of GaN power semiconductors by being conductive pathways for leakage current. However, no direct evidence of a link between their electrical behavior and physical nature in carbon-doped semi-insulating GaN buffer layers has been obtained. Therefore, we investigate the electrical activity of dislocations by conductive atomic force microscopy and electron beam induced current to distinguish electrically active dislocations from non-active ones. We investigated six electrically active dislocations and discovered distinct carbon enrichment in the vicinity of all six dislocations, based on cross-sectional scanning transmission electron microscopy using electron energy loss spectrometry. Electrically non-active dislocations, which are the vast majority, sometimes also showed carbon enrichment, however, in only two out of seven cases. Consequently, carbon segregation seems to be a requirement for electrical activity, but a carbon surplus is not sufficient for electrical activity. We also performed first-principles total-energy calculations for mixed type threading dislocations, which validates carbon accumulation in the dislocation vicinity. The electrical and physical characterization results, complemented by density functional theory simulations, support the previously hypothesized existence of a carbon defect band and add new details. [ABSTRACT FROM AUTHOR]

Conductive-bridge random access memory can be used as a physical reservoir for temporal learning in reservoir computing owing to its volatile nature. Herein, a scaled Cu/HfOx/n+-Si memristor was fabricated and characterized for reservoir computing. The scaled, silicon nanofin bottom electrode formation is verified by scanning electron and transmission electron microscopy. The scaled device shows better cycle-to-cycle switching variability characteristics compared with those of large-sized cells. In addition, synaptic characteristics such as conductance changes due to pulses, paired-pulse facilitation, and excitatory postsynaptic currents are confirmed in the scaled memristor. High-pattern accuracy is demonstrated by deep neural networks applied in neuromorphic systems in conjunction with the use of the Modified National Institute of Standards and Technology database. Furthermore, a reservoir computing system is introduced with six different states attained by adjusting the amplitude of the input pulse. Finally, high-performance and efficient volatile reservoir computing in the scaled device is demonstrated by conductance control and system-level reservoir computing simulations. [ABSTRACT FROM AUTHOR]

This study explores the effect of molecular permanent dipole moment (PDM) on aggregation of guest molecules in phosphorescent host–guest organic light-emitting diodes (OLEDs). Through a combination of photoluminescence measurements, high-angle annular dark-field scanning transmission electron microscopy analysis, and an Ising model based physical vapor-deposition simulation, we show that higher PDM of tris[2-phenylpyridinato-C2,N]iridium(III) guest can actually lead to a reduced aggregation relative to tris[bis[2-(2-pyridinyl-N)phenyl-C] (acetylacetonato)iridium(III) when doped into a non-polar host 1,3,5-tris(carbazol-9-yl)benzene. This study further explores the effect of host polarity by using a polar host 3′,5′-di(carbazol-9-yl)-[1,1′-biphenyl]-3,5-dicarbonitrile, and it is shown that the polar host leads to reduced guest aggregation. This study provides a comprehensive understanding of the impact of molecular PDM on OLED material efficiency and stability, providing insights for optimizing phosphorescent OLED materials. [ABSTRACT FROM AUTHOR]

Energy-dispersive x-ray spectroscopy and high-angle annular dark-field in a Cs-corrected scanning transmission electron microscope are employed to characterize the atomic-scale strain distribution in the active region of the InAs-based interband cascade laser. For the first time, energy-dispersive x-ray spectroscopy is utilized for the quantitative calculation of the zero-strain region, by which the geometric phase analysis of high-angle annular dark-field imaging has been carried out. The strain distribution of the active region with high accuracy has been obtained. The analysis of the out-of-plane strain shows that the active region in the InAs-based interband cascade laser is strain-compensated, while a certain degree of elemental intermixing still exists in the active region. This detailed strain distribution can provide valuable insights into the optimization of the growth conditions for the active region such as growth temperature, V/III flux ratio, and growth process to minimize the elemental intermixing and obtain a better performance interface while maintaining the strain-compensated state. [ABSTRACT FROM AUTHOR]

Domain boundaries in perovskite oxides often exhibit abundant physical properties and phenomena. Here, epitaxial LaTiO3 thin films on (100) SrTiO3 substrates are prepared by pulsed-laser deposition. X-ray diffraction and transmission electron microscopy investigations reveal that the epitaxial LaTiO3 thin films have good crystallinity but a high density of domain boundaries. Atomic-scale scanning transmission electron microscopy observations reveal that two types of domain boundaries are formed in the LaTiO3 thin films. The type I domain boundaries are formed on the {100} crystal planes, while the type II domain boundaries on the {110} crystal planes. Electron energy-loss spectroscopy analyses suggest that the valence states of Ti ions at the type I domain boundaries are +3, while those at the type II domain boundaries are +4. First-principles calculations reveal that the bandgap decreases at both domain boundaries compared to the bulk. The carrier concentration at the type I domain boundaries is significantly higher than that of the bulk, while the carrier concentration at the type II domain boundaries is lower. These findings suggest that domain boundaries play an important role in tailoring the electrical properties of the LaTiO3 thin films, thereby promoting the potential applications and property modulation of related materials and devices. [ABSTRACT FROM AUTHOR]

We report on the magnetic coupling behavior in all-ferromagnetic La0.7Sr0.3MnO3/SrRuO3 (LSMO/SRO) heterostructures deposited on the SrTiO3 (111) substrate, where the interface leads to an enhanced exchange field as compared to the one deposited on SrTiO3 (001). Importantly, high-resolution scanning transmission electron microscopy reveals distinct interface structures of the (111) heterostructures depending on the growth sequence. The heterostructure with an SRO bottom layer shows an atomically flat and abrupt interface, while the one with an LSMO bottom layer shows a deformed interface due to the surface roughening of LSMO deposited directly on SrTiO3 (111). As a result, the heterostructure with an abrupt interface exhibits a robust antiferromagnetic coupling between LSMO and SRO, while the one with a rough interface shows negligible magnetic coupling. Our results demonstrate the key role of an abrupt interface in determining the magnetic properties of oxide heterostructures. [ABSTRACT FROM AUTHOR]

We describe the development, operation, and application of the 4D Camera-a 576 by 576 pixel active pixel sensor for scanning/transmission electron microscopy which operates at 87,000 Hz. The detector generates data at ∼480 Gbit/s which is captured by dedicated receiver computers with a parallelized software infrastructure that has been implemented to process the resulting 10-700 Gigabyte-sized raw datasets. The back illuminated detector provides the ability to detect single electron events at accelerating voltages from 30 to 300 kV. Through electron counting, the resulting sparse data sets are reduced in size by 10--300× compared to the raw data, and open-source sparsity-based processing algorithms offer rapid data analysis. The high frame rate allows for large and complex scanning diffraction experiments to be accomplished with typical scanning transmission electron microscopy scanning parameters.

Ferroelectric domain walls are a rich source of emergent electronic properties and unusual polar order. Recent studies show that the configuration of ferroelectric walls can go well beyond the conventional Ising-type structure. Néel-, Bloch-, and vortex-like polar patterns have been observed, displaying strong similarities with the spin textures at magnetic domain walls. Here, the discovery of antiferroelectric domain walls in the uniaxial ferroelectric Pb5Ge3O11 is reported. Highly mobile domain walls with an alternating displacement of Pb atoms are resolved, resulting in a cyclic 180° flip of dipole direction within the wall. Density functional theory calculations show that Pb5Ge3O11 is hyperferroelectric, allowing the system to overcome the depolarization fields that usually suppress the antiparallel ordering of dipoles along the longitudinal direction. Interestingly, the antiferroelectric walls observed under the electron beam are energetically more costly than basic head-to-head or tail-to-tail walls. The results suggest a new type of excited domain-wall state, expanding previous studies on ferroelectric domain walls into the realm of antiferroic phenomena.

The exploration of 1D magnetism, frequently portrayed as spin chains, constitutes an actively pursued research field that illuminates fundamental principles in many-body problems and applications in magnonics and spintronics. The inherent reduction in dimensionality often leads to robust spin fluctuations, impacting magnetic ordering and resulting in novel magnetic phenomena. Here, structural, magnetic, and optical properties of highly anisotropic 2D van der Waals antiferromagnets that uniquely host spin chains are explored. First-principle calculations reveal that the weakest interaction is interchain, leading to essentially 1D magnetic behavior in each layer. With the additional degree of freedom arising from its anisotropic structure, the structure is engineered by alloying, varying the 1D spin chain lengths using electron beam irradiation, or twisting for localized patterning, and spin textures are calculated, predicting robust stability of the antiferromagnetic ordering. Comparing with other spin chain magnets, these materials are anticipated to bring fresh perspectives on harvesting low-dimensional magnetism.

MnO(001) thin films were grown on commercial MgO(001) substrates at 520 °C by reactive molecular beam epitaxy (MBE) using Mn vapor and O2-seeded supersonic molecular beams (SMBs) both with and without radio frequency (RF) plasma excitation. For comparison, MnO(001) films were grown by reactive MBE using O2 from a leak valve. X-ray photoelectron spectroscopy confirmed the Mn2+ oxidation state and 10%–15% excess oxygen near the growth surface. Reflection high-energy electron diffraction and x-ray diffraction evidenced that the films were rock salt cubic MnO with very strong (001) orientation. High-angle annular dark field scanning transmission electron microscopy with energy-dispersive x-ray spectroscopy demonstrated abrupt MnO/MgO interfaces and indicated [(001)MnO||(001)MgO] epitaxial growth. Ex situ atomic force microscopy of films deposited without RF excitation revealed smooth growth surfaces. An SMB-grown MnO(001) film was converted to Mn3O4 with strong (110) orientation by post-growth exposure to an RF-discharge (RFD) SMB source providing O atoms; the surface of the resultant film contained elongated pits aligned with the MgO 110 directions. In contrast, using the RFD-SMB source for growth resulted in MnO(001) films with elongated growth pits and square pyramidal hillocks aligned along the MgO 110 and 100 directions, respectively. [ABSTRACT FROM AUTHOR]

A unique on-chip method for the direct correlation of optical properties, with atomic-scale chemical–structural characteristics for a single quantum dot (QD), is developed and utilized in various examples. This is based on performing single QD optical characterization on a modified glass substrate, followed by the extraction of the relevant region of interest by focused-ion-beam–scanning electron microscope processing into a lamella for high resolution scanning transmission electron microscopy (STEM) characterization with atomic scale resolution. The direct correlation of the optical response under an electric field with STEM analysis of the same particle allows addressing several single particle phenomena: first, the direct correlation of single QD photoluminescence (PL) polarization and its response to the external field with the QD crystal lattice alignment, so far inferred indirectly; second, the identification of unique yet rare few-QD assemblies, correlated directly with their special spectroscopic optical characteristics, serving as a guide for future designed assemblies; and third, the study on the effect of metal island growth on the PL behavior of hybrid semiconductor–metal nanoparticles, with relevance for their possible functionality in photocatalysis. This work, therefore, establishes the use of the direct on-chip optical–structural correlation method for numerous scenarios and timely questions in the field of QD research. [ABSTRACT FROM AUTHOR]

This paper explores the fundamental structural origins of the 0.7 eV band emission peak, known as D07. The increased attention on these d-band emission lines originates mainly from the correlation between crystal defect and the intensified recombination of less dominant charge carriers. This association holds substantial importance, impacting not just the electronics sector but also raising concerns about reduced efficiency in silicon solar cells. By employing hyperspectral photoluminescence imaging, we pinpointed regions manifesting high D07 peak emissions on a microscopic scale. Subsequently, we conducted a structural investigation utilizing scanning electron microscopy and electron backscatter diffraction. Following this, we used a focused ion beam to extract areas of interest, allowing for a detailed characterization of the sample using high-resolution scanning transmission electron microscopy at the atomic scale. This approach aids in identifying defects and determining grain boundary orientation. In areas of high D07 band emission, we found Σ 3 { 114 } { 101 } grain boundaries decorated with two-layer fault twin and/or an extrinsic two-layer stacking faults. In addition, density functional theory calculations suggest oxygen impurities as a possibility for substitutional segregation to these types of defects. It is therefore plausible that the D07 line might be attributed to stacking faults featuring oxygen agglomerates. [ABSTRACT FROM AUTHOR]

For two-dimensional (2D) materials, the exact thickness of the material often dictates its physical and chemical properties. The 2D quantum material WTe2 possesses properties that vary significantly from a single layer to multiple layers, yet it has a complicated crystal structure that makes it difficult to differentiate thicknesses in atomic-resolution images. Furthermore, its air sensitivity and susceptibility to electron beam-induced damage heighten the need for direct ways to determine the thickness and atomic structure without acquiring multiple measurements or transferring samples in ambient atmosphere. Here, we demonstrate a new method to identify the thickness up to ten van der Waals layers in Td-WTe2 using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy image simulation. Our approach is based on analyzing the intensity line profiles of overlapping atomic columns and building a standard neural network model from the line profile features. We observe that it is possible to clearly distinguish between even and odd thicknesses (up to seven layers), without using machine learning, by comparing the deconvoluted peak intensity ratios or the area ratios. The standard neural network model trained on the line profile features allows thicknesses to be distinguished up to ten layers and exhibits an accuracy of up to 94% in the presence of Gaussian and Poisson noise. This method efficiently quantifies thicknesses in Td-WTe2, can be extended to related 2D materials, and provides a pathway to characterize precise atomic structures, including local thickness variations and atomic defects, for few-layer 2D materials with overlapping atomic column positions. [ABSTRACT FROM AUTHOR]

Optimizing thermal anneals of Si-implanted β-Ga2O3 is critical for low resistance contacts and selective area doping. We report the impact of annealing ambient, temperature, and time on the activation of room temperature ion-implanted Si in β-Ga2O3 at concentrations from 5 × 1018 to 1 × 1020 cm−3, demonstrating full activation (>80% activation, mobilities >70 cm2/V s) with contact resistances below 0.29 Ω mm. Homoepitaxial β-Ga2O3 films, grown by plasma-assisted molecular beam epitaxy on Fe-doped (010) substrates, were implanted at multiple energies to yield 100 nm box profiles of 5 × 1018, 5 × 1019, and 1 × 1020 cm−3. Anneals were performed in an ultra-high vacuum-compatible quartz furnace at 1 bar with well-controlled gas compositions. To maintain β-Ga2O3 stability, pO2 must be greater than 10−9 bar. Anneals up to pO2 = 1 bar achieve full activation at 5 × 1018 cm−3, while 5 × 1019 cm−3 must be annealed with pO2 ≤ 10−4 bar, and 1 × 1020 cm−3 requires pO2 < 10−6 bar. Water vapor prevents activation and must be maintained below 10−8 bar. Activation is achieved for anneal temperatures as low as 850 °C with mobility increasing with anneal temperatures up to 1050 °C, though Si diffusion has been reported above 950 °C. At 950 °C, activation is maximized between 5 and 20 min with longer times resulting in decreased carrier activation (over-annealing). This over-annealing is significant for concentrations above 5 × 1019 cm−3 and occurs rapidly at 1 × 1020 cm−3. Rutherford backscattering spectrometry (channeling) suggests that damage recovery is seeded from remnant aligned β-Ga2O3 that remains after implantation; this conclusion is also supported by scanning transmission electron microscopy showing retention of the β-phase with inclusions that resemble the γ-phase. [ABSTRACT FROM AUTHOR]

We study epitaxial growth, crystal structures, and magnetic properties of Fe–As compound thin films grown on GaAs (111)B substrates at various values of the As4:Fe flux ratio γ, using molecular beam epitaxy. The samples grown at low As4 flux (γ = 0.3, sample A) show mainly a body-centered-cubic (bcc) crystal structure, exhibiting ferromagnetic properties similar to bcc Fe. Meanwhile, the Fe–As samples grown at medium γ (2.7–4.5, sample group B) comprise regions of Ni2In-type FeAs (a hexagonal crystal with lattice constants of a = 0.399 nm and c = 0.536 nm), which are grown at the bottom and interface with the GaAs buffer layer, and a layer of non-stoichiometric FeAs with a DO3 structure (a = 0.522 nm) formed on the top. The DO3-structure FeAs phase contains partially transformed regions, which are characterized by thin stripes in a scanning transmission electron microscopy image. Furthermore, in the sample grown with high γ = 8.5 (sample C), a hexagonal Fe–As crystal with a large in-plane lattice constant (a = 0.691 nm and c = 0.542 nm) and threefold screw axes are observed. None of these crystal structures of Fe–As compounds has ever been reported. While sample C shows no ferromagnetism, the samples in group B exhibit strong ferromagnetism with high Curie temperature TC above 400 K. These new ferromagnetic Fe–As compounds are promising for spintronic device applications. [ABSTRACT FROM AUTHOR]

Load-dependent and angle-dependent nanoindentation tests were performed on a ( 2 ¯ 01) -oriented single-crystal β-Ga2O3 substrate to study the mechanical properties of the material. The anisotropy of the mechanical properties was examined, especially with regard to the dependence of the elastic modulus (E), hardness (H), and form of plastic deformation on the rotation angle of a Berkovich indenter with respect to the monoclinic structure. E reached a maximum value and H a minimum value when the sample was rotated to such an angle that one of the three facets of the Berkovich indenter was parallel to the [010] direction. To compare our experimental results with the theoretical calculation based on the monoclinic structure, the elastic surface of β-Ga2O3 was calculated using fourth-rank stiffness and compliance tensors and visualized in three-dimensional space. Two-dimensional sectional maps of the elastic surface were obtained for a range of crystal planes, and good agreement was obtained between the experimental observations and calculations. Plastic deformation at the indenter impressions was evaluated using scanning and transmission electron microscopy, and dislocations, cleavage, and cracks were observed. Their structure and density depended on the rotation angle. Our results clearly show a strong anisotropy of the mechanical properties of β-Ga2O3, which is very different from what is found in other compound semiconductors for power-device applications, such as GaN and 4H-SiC. This emphasizes the importance of customizing the machining process for β-Ga2O3, rather than simply using "machining recipes" for other materials. [ABSTRACT FROM AUTHOR]

GeSnC alloys offer a route to direct bandgap semiconductors for CMOS-compatible lasers, but the use of CBr4 as a carbon source was shown to reduce Sn incorporation by 83%–92%. We report on the role of thermally cracked H in increasing Sn incorporation by 6x–9.5x, restoring up to 71% of the lost Sn, and attribute this increase to removal of Br from the growth surface as HBr prior to formation of volatile groups such as SnBr4. Furthermore, as the H flux is increased, Rutherford backscattering spectroscopy reveals a monotonic increase in both Sn and carbon incorporation. X-ray diffraction reveals tensile-strained films that are pseudomorphic with the substrate. Raman spectroscopy suggests substitutional C incorporation; both x-ray photoelectron spectroscopy and Raman suggest a lack of graphitic carbon or its other phases. For the lowest growth temperatures, scanning transmission electron microscopy reveals nanovoids that may account for the low Sn substitutional fraction in those layers. Conversely, the sample grown at high temperatures displayed abrupt interfaces, notably devoid of any voids, tin, or carbon-rich clusters. Finally, the surface roughness decreases with increasing growth temperature. These results show that atomic hydrogen provides a highly promising route to increase both Sn and C to achieve a strongly direct bandgap for optical gain and active silicon photonics. [ABSTRACT FROM AUTHOR]

High quality, uni-polar, epitaxial AlN with minimum oxygen content promises excellent surface acoustic wave and bulk acoustic wave resonator characteristics such as high electromechanical coupling coefficient and power handling capabilities, which is particularly useful for RF filter applications. By systematically varying the growth temperature, the study investigates its impact on the oxygen levels, defect states, and crystallographic texture of the AlN thin films using a combination of atomic force microscopy, X-ray diffraction, time-of-flight secondary ion mass spectrometry, spectroscopic ellipsometry, scanning transmission electron microscopy, as well as room temperature and temperature dependent I–V measurements. The research demonstrates that the films grown at a temperature of 700 ° C exhibit the most favorable results. These films exhibit the lowest oxygen levels, possess epitaxial growth, and display the highest crystalline quality (XRD AlN 0002 ω − FWHM = 1.3 °). Additionally, these films demonstrate a significant reduction in sub-bandgap absorption. By comparing the cathode current measured during deposition, we suggest that the presence of an impurity layer formed during idle time between depositions as a possible source of oxygen in the sputter chamber. In addition, the study presents a possible model to explain the mixed polarity observed in AlN and proposes various ways to achieve uni-polar AlN on silicon substrates. [ABSTRACT FROM AUTHOR]

Crystallographic defects play a crucial role in cement hydration, with initial dissolution being dominated by the formation of etch pits that rely on the intersection of defects on surfaces. However, the defects present in cement particles have remained a mystery due to the lack of detailed direct observation at the atomic scale. In this study, we used scanning transmission electron microscopy to unravel the defects in alite particles at the single-atom level. Our observations identified different types of defects, including vacancies, doping, dislocations, rough surfaces, and grain boundaries. Atomic ordering in the alite crystal was further examined based on our single-atom recognition method. Our findings indicate that defects in cement particles may serve as reactive sites during the early hydration stage, facilitating the initial dissolution and providing nucleation sites for hydration products. This work provides insights into cement defect formation at the single-atom level and offers new opportunities in tuning the hydration process through defect engineering of cement particles.

Here, we describe a fully in situ method of fabricating light-scattering structures on III-V materials that generates a rough morphology via vapor phase etching and redeposition. Fully in situ methods support higher industrial throughput by utilizing the growth reactor to generate the light-trapping structures after device growth without removal from the reactor. We use HCl and PH3 to etch and redeposit scattering morphologies on Ga0.5In0.5P in a dynamic hydride vapor phase epitaxy (D-HVPE) reactor. We show that the addition of PH3 leads to redeposition during the vapor phase HCl etching of Ga0.5In0.5P and that HCl flow rate and time exposed to HCl-PH3 each independently cause a linear increase in the redeposited feature size, indicating that redeposition proceeds by island growth in a III-Cl-limited, hydride-enhanced HVPE regime. Auger electron spectroscopy and scanning transmission electron microscopy with energy dispersive spectroscopy (STEM-EDS) reveal redeposition to be highly Ga-rich GaInP, i.e., Ga(In)P. The Ga-rich nature of the redeposition results from the higher thermodynamic driving force for Ga incorporation than for In during HVPE growth and the difference in the volatility of the III-Cl etch products. The resulting morphologies have high broadband scattering, as determined by normal specular reflectance and integrating sphere measurements, indicating effectiveness as light-scattering structures. In a 270-nm-thick GaAs photovoltaic device with a textured back surface, we achieve a 4.9% increase in short circuit current density (JSC) without any loss in open-circuit voltage (VOC) relative to a planar control using only a 60 s in situ texturing treatment. [ABSTRACT FROM AUTHOR]

In this work, we report quantitative morphometry of freeze-dried graphene-based aerogels (i.e., graphene aerogel-GA, nitrogenated GA-NGA, graphene-carbon nanotube hybrid-Gr-MWCNTs, carbon foam-CF, and CF-GA hybrid-CF-GA) and monoliths, prepared by hydrothermal and organic sol-gel methods, respectively. X-ray micro-computed tomography (XMCT) in combination with scanning and transmission electron microscopy allowed visualization of internal microstructures in three-dimensional space. Quantitative morphometry analysis through the reconstructed volume renderings from two-dimensional sliced images revealed hierarchical structures possessing interlaced thin sheets, honeycomb organization, and topological interconnected pore background domains. The influence of small-diameter functionalized multi-walled carbon nanotubes (MWCNTs) inclusions to graphene-like sheets and integration with CF is assessed through quantitative morphometry analysis in terms of volume-weighted pore size, wall thickness, and porosity levels. Hybrid composite porous solids elucidated cross-linking reinforced by a homogeneous distribution of CNTs into complex sheets of GA and CF matrices. A consistent trend impacting porosity and interconnectedness was found following NGA ≥ GA > CF > Gr-MWCNT2:1 > CF-GA > Gr-MWCNT3:1 > Gr-MWCNT5:1, from XMCT image processing and analyses in corroboration with physical properties and reliability. The experimental results provide insights and guide the design of characteristic porous carbonaceous and graphene-based functional nanomaterials for energy sciences, environmental engineering, and fundamental reactive transport of fluids. [ABSTRACT FROM AUTHOR]

Hollow vaterite microspheres are important materials for biomedical applications such as drug delivery and regenerative medicine owing to their biocompatibility, high specific surface area, and ability to encapsulate a large number of bioactive molecules and compounds. We demonstrated that hollow vaterite microspheres are produced by an Escherichia coli strain engineered with a urease gene cluster from the ureolytic bacteria Sporosarcina pasteurii in the presence of bovine serum albumin. We characterized the 3D nanoscale morphology of five biogenic hollow vaterite microspheres using 3D high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) tomography. Using automated high-throughput HAADF-STEM imaging across several sample tilt orientations, we show that the microspheres evolved from a smaller more ellipsoidal shape to a larger more spherical shape while the internal hollow core increased in size and remained relatively spherical, indicating that the microspheres produced by this engineered strain likely do not contain the bacteria. The statistical 3D morphology information demonstrates the potential for using biogenic calcium carbonate mineralization to produce hollow vaterite microspheres with controlled morphologies. STATEMENT OF SIGNIFICANCE: The nanoscale 3D structures of biomaterials determine their physical, chemical, and biological properties, however significant efforts are required to obtain a statistical understanding of the internal 3D morphology of materials without damaging the structures. In this study, we developed a non-destructive, automated technique that allows us to understand the nanoscale 3D morphology of many unique hollow vaterite microspheres beyond the spectroscopy methods that lack local information and microscopy methods that cannot interrogate the full 3D structure. The method allowed us to quantitatively correlate the external diameters and aspect ratios of vaterite microspheres with their hollow internal structures at the nanoscale. This work demonstrates the opportunity to use automated transmission electron microscopy to characterize nanoscale 3D morphologies of many biomaterials and validate the chemical and biological functionality of these materials.

Scanning transmission electron microscopy is a common tool used to study the atomic structure of materials. It is an inherently multimodal tool allowing for the simultaneous acquisition of multiple information channels. Despite its versatility, however, experimental workflows currently rely heavily on experienced human operators and can only acquire data from small regions of a sample at a time. Here, we demonstrate a flexible pipeline-based system for high-throughput acquisition of atomic-resolution structural data using an all-piezo sample stage applied to large-scale imaging of nanoparticles and multimodal data acquisition. The system is available as part of the user program of the Molecular Foundry at Lawrence Berkeley National Laboratory.

The development of low-cost, highly effective, environmentally friendly, multi-functional bio-cidal substances has become a top priority in the current scenario. This study aimed to create low-cost materials, such as green-engineered magnesium oxide (GEMgO) and chitosan-coated magnesium oxide (GECsMgO) nanoparticles (NPs), using Chara zeylanica Klein ex Willd extract as a reducing agent. The X-ray diffraction results confirmed the cubic face-centered structure of the GEMgO and GECsMgO NPs. The field emission scanning electron microscopy and transmission electron microscopy results showed that GEMgO and GECsMgO NPs exhibit a spherical structure and nanoflakes with spherical structures, respectively. The Mg–O stretching frequencies were measured at 779 and 456 cm−1 for GEMgO and 543 cm−1 for GECsMgO NPs in the Fourier-transform infrared spectra. The oxygen vacancies responsible for the biocidal activities of GEMgO and GEC-MgO NPs were observed in their photoluminescence spectra at 501 and 520 nm and at 506 and 524 nm, respectively. The antioxidant activity of GEMgO and GECsMgO NPs was investigated using a DPPH assay. The GECsMgO NPs exhibited higher scavenging activity than the GEMgO NPs. Antibacterial studies on gram-negative bacteria treated with GEMgO and GECsMgO NPs showed that GECsMgO NPs exhibited the highest antibacterial activity. The ultrastructural morphological results of E. coli showed that GECsMgO NPs can damage it better than GEMgO NPs. An MTT assay determined that GEC-MgO NPs had better anticancer properties than GEMgO NPs when tested against a blood cancer cell line (MOLT-7). Fibroblast L929 cell toxicity tests showed that GEC-MgO NPs were less toxic than GEMgO NPs. In the future, GECsMgO NPs can be used as biocidal agents in clinical and industrial applications. • GEMgO and GECsMgO nanoparticles were synthesized using the Green Engineering method. • GECsMgO NPs exhibit higher antibacterial activity against gram-negative bacteria than GEMgO NPs. • GECsMgO NPs exhibit potential anticancer activity against blood cancer cell lines. • GECsMgO NPs were less harmful to fibroblast cells than GEMgO NPs. [ABSTRACT FROM AUTHOR]

Single‐atom catalysts (SACs) are an emerging class of materials, leveraging maximum atom utilization and distinctive structural and electronic properties to bridge heterogeneous and homogeneous catalysis. Direct imaging methods, such as aberration‐corrected high‐angle annular dark‐field scanning transmission electron microscopy, are commonly applied to confirm the atomic dispersion of active sites. However, interpretations of data from these techniques can be challenging due to simultaneous contributions to intensity from impurities introduced during synthesis processes, as well as any variation in position relative to the focal plane of the electron beam. To address this matter, this paper presents a comprehensive study on two representative SACs containing isolated nickel or copper atoms. Spectroscopic techniques, including X‐ray absorption spectroscopy, were employed to prove the high metal dispersion of the catalytic atoms. Employing scanning transmission electron microscopy imaging combined with single‐atom‐sensitive electron energy loss spectroscopy, we scrutinized thin specimens of the catalysts to provide an unambiguous chemical identification of the observed single‐atom species and thereby distinguish impurities from active sites at the single‐atom level. Overall, the study underscores the complexity of SACs characterization and establishes the importance of the use of spectroscopy in tandem with imaging at atomic resolution to fully and reliably characterize single‐atom catalysts. [ABSTRACT FROM AUTHOR]

Flash healing is a technique that uses power spikes to rapidly repair microcracks on ceramic surfaces. In this study, the microstructures of flash-healed Vickers-indented microcracks near the positive/negative electrodes under a DC electric field were examined by scanning transmission electron microscopy. The microstructural morphology near the positive electrode was almost identical to that of the microcracks located between both electrodes, as previously reported. However, a decrease in the degree of healing was observed near the negative electrode. This was attributed to the insufficient recovery of dislocations generated at the indentation state, which should have occurred in the initial stage of healing. The delay in dislocation recovery prevented contact between the inner surfaces of the microcracks and is possibly related to the increase in oxygen vacancies near the negative electrode. [ABSTRACT FROM AUTHOR]

Magnetised zeolite A, zeolite X and Na,K-CHA composites with superparamagnetic nanoparticles of SiO2-coated Fe3O4 or CoFe2O4 ferrite spinels were prepared, characterised and tested for ion exchange efficacy. They were synthesised by following three steps, synthesising Fe3O4 and CoFe2O4 nanoparticles by a solvothermal method, coating the metal oxide particles with SiO2 by a sol-gel process, and attaching the MxOy/SiO2 onto the zeolites during synthesis. The magnetic zeolites were characterised by X-ray diffraction, X-ray fluorescence spectroscopy, Raman spectroscopy, vibrating sample magnetometry and both scanning and transmission electron microscopy. It was confirmed they had superparamagnetic properties due to successful attachment of the MxOy/SiO2 particles onto the zeolites. Adsorption capacities of Sr2+ onto the magnetic zeolite A and zeolite X and Cs+ onto the magnetic Na,K-CHA were also evaluated. The results show the MxOy/SiO2 did not block the adsorption sites of the zeolites and the MxOy/SiO2 particles were not detached from the zeolites during the adsorption experiments. [ABSTRACT FROM AUTHOR]

By simultaneously achieving high spatial and angular sampling resolution, four dimensional scanning transmission electron microscopy (4D STEM) is enabling analysis techniques that provide great insight into the atomic structure of materials. Applying these techniques to scientifically and technologically significant beam-sensitive materials remains challenging because the low doses needed to minimise beam damage lead to noisy data. We demonstrate an unsupervised deep learning model that leverages the continuity and coupling between the probe position and the electron scattering distribution to denoise 4D STEM data. By restricting the network complexity it can learn the geometric flow present but not the noise. Through experimental and simulated case studies, we demonstrate that denoising as a preprocessing step enables 4D STEM analysis techniques to succeed at lower doses, broadening the range of materials that can be studied using these powerful structure characterization techniques. [ABSTRACT FROM AUTHOR]

In this study, we explore the synthesis of silver nanoparticles (AgNPs) using calyx wastes from Abelmoschus esculentus (okra) and evaluate their anthelmintic potential against poultry pathogen Raillietina spp. The ultraviolet‐visible (UV‐vis) spectrum of nanoparticles showed an absorbance peak at 425 nm, confirming AgNP formation. Fourier transform infrared spectrophotometry (FTIR) analysis indicated the presence of functional groups responsible for reducing silver ions, and X‐ray diffraction (XRD) patterns confirmed the crystallinity of the nanoparticles. Dynamic light scattering (DLS), scanning and transmission electron microscopy (SEM and TEM) analyses were used to measure the size (20–50 nm) and morphology (spherical) of the synthesized AgNPs. The dose‐dependent in vitro anthelmintic efficacy was highest at 125 μg/ml of AgNPs, resulting in paralysis and death within 0.54 and 1.29 hours, respectively, while untreated control parasites survived for ~72 hours. The SEM micrographs of the treated parasites showed swelling and blebbing of the tegument. Histochemical localization studies showed a remarkable decline of tegumental and neurotransmitter enzymes involved with the parasite's metabolism and regulation of the endogenous physiological processes. This study underscores the potential of okra calyces in the green synthesis of AgNPs and provides a novel approach to developing alternative anthelmintics that interfere with the host‐parasite interface. [ABSTRACT FROM AUTHOR]

We report the observation of an electric field in twisted-bilayer molybdenum disulfide (MoS2) and elucidate its correlation with local polar domains using four-dimensional scanning transmission electron microscopy (4D-STEM) and first-principles calculations. We reveal the emergence of in-plane topological vortices within the periodic moiré patterns for both commensurate structures at small twist angles and the incommensurate quasicrystal structure that occurs at a 30° twist. The large-angle twist leads to mosaic chiral vortex patterns with tunable characteristics. A twisted quasicrystal bilayer, characterized by its 12-fold rotational symmetry, hosts complex vortex patterns and can be manipulated by picometer-scale interlayer displacement. Our findings highlight that twisting 2D bilayers is a versatile strategy for tailoring local electric polar vortices. [ABSTRACT FROM AUTHOR]

The results of a combined grazing incidence wide‐angle X‐ray scattering (GIWAXS) and 4D scanning transmission microscopy (4D‐STEM) analysis of the effects of thermal processing on poly(3[2‐(2‐methoxyethoxy)ethoxy]‐methylthiophene‐2,5‐diyl) are reported, a conjugated semiconducting polymer used as the active layer in organic electrochemical transistor devices. GIWAXS provides a measure of overall crystallinity in the film, while 4D‐STEM produces real‐space maps of the morphology and orientation of individual crystallites along with their spatial extent and distribution. The sensitivity of the 4D‐STEM detector allows for collection of electron diffraction patterns at each position in an image scan while limiting the imparted electron dose to below the damage threshold. The effects of heat treatment on the distribution and type of crystallites present in the films is determined. [ABSTRACT FROM AUTHOR]

Background: The deep-sea acorn worm Quatuoralisia malakhovi belongs to the phylum Hemichordata, class Enteropneusta, family Torquaratoridae, which was described in 2005. Owing to their epibenthic lifestyle and deep-sea habitat features, torquaratorids differ anatomically from shallow-water acorn worms; however, their morphology and fine structure are poorly studied. We have the opportunity to make three complete detailed series of histological sections of Q. malakhovi and to study the microscopic anatomy, histology and fine structure of the reproductive system of this acorn worm using scanning and transmission electron microscopy. Results: The sexes of Q. malakhovi are separate and indistinguishable externally. The lobed testes occupy the dorsal side of the genital wings and distinctly bulge into the peribranchial cavity by their mature lobes. The central part of the testis is always submerged into the genital wing and opens via a single gonad pore. The monociliary muscle cells stretch along the external wall of the testis and surround the gonad pore, probably taking part in the contraction of the testis lobes for spawning. The germinative epithelium of the testis contains spermatogenic cells at different stages of development and interstitial cells. Yolk cells are not found. Interstitial cells embrace the spermatogonia and spermatogenic columns, providing horizontal compartmentalization of the germinative epithelium, and contain numerous phagosomes with remnants of degenerating spermatogenic cells. The testis wall contains haemal lacunae, which are usually located on the side opposite the gonad pore. We describe the fine structure of spermatogonia, spermatocytes clustered in spermatogenic columns, spermatids, and spermatozoa. Spermatozoa are of the ectaquasperm type and consist of an acorn-shaped head and a flagellum 18–25 µm long. The sperm head includes a beak-shaped acrosomal part, a spherical nucleus and a midpiece containing a ring of 5 or rarely 6 mitochondria. Conclusions: The male reproductive system and sperm structure of Q. malakhovi, a representative of the family Torquaratoridae, have a number of differences from shallow-water acorn worms; however, the spermatogenesis and sperm structure of Q. malakhovi generally follow the pattern of the other three enteropneust families, and the phylogenetic significance of these deviations should be the subject of further research. [ABSTRACT FROM AUTHOR]

Domains and domain wall engineering have been extensively explored in ferroic materials for a wide range of applications in nanoelectronics and spintronics. Complex oxides exhibiting strongly correlated properties are model platforms for such studies where response to strain or external stimuli such as electric field, temperature and light can be probed. Here, domains in strained SrMnO3 films, grown on a degenerate semiconductor, allowing for conduction in an out‐of‐plane geometry, are studied using a combination of microscopy probes. Using conductive atomic force microscopy, electrically isolated domains with varying conductance are found and their temporal evolution is investigated. Further, their formation and microstructure are studied using scanning transmission electron microscopy and secondary electron contrast in scanning electron microscopy. An important contribution is establishing that the observed domains are formed by cracks, driven by inhomogeneous strain relaxation throughout the film, resulting in significantly high strain planes. The potential of secondary electrons to detect domain dependent contrast over a large area, ensuing due to the use of a degenerate semiconductor correlates with the conductive properties of the domains and serves as a new direction to probe domains and domain walls in ferroic materials. [ABSTRACT FROM AUTHOR]

This study compares the surface patina of ancient tin rich bronze with pure hydrothermally synthesized SnO2 nanoparticles using various analytical techniques, including metallographic microscopy, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and high-angle annular dark-field scanning transmission electron microscopy. The primary crystalline component of the patina consists of approximately 5 nm SnO2 nanoparticles, which closely resemble pure SnO2, indicating their comparability. Cu was also detected in the patina; however, it did not form crystalline structures. The X-ray diffraction results showed a shift in the patina's peak, suggesting the infiltration of Cu into the SnO2 lattice, which compromises its crystallinity. In comparison to synthetic SnO2, the X-ray photoelectron spectroscopy spectra of the patina revealed novel peaks corresponding to both Cu and O, indicating the presence of Cu−O−Sn bonding—a characteristic feature of type-I patina. This suggests that the primary structure of type-I patina consists of crystalline SnO2 nanoparticles, with a limited amount of Cu integrated into its lattice configuration. The concentration of Cu within the SnO2 crystal units is restricted, leading primarily to the formation of amorphous Cu2O in conjunction with Sn. The presence of Sn enhances the structural stability of Cu2O, facilitating its incorporation while inhibiting the crystallization of Cu2O. However, when the Sn concentration is insufficient, an inadequate Cu–O−Sn amorphous phase may form, allowing for the potential crystallization of Cu2O. [ABSTRACT FROM AUTHOR]

How the body interacts with the brain to perform vital life functions, such as feeding, is a fundamental issue in physiology and neuroscience. Here, we use a whole-animal scanning transmission electron microscopy volume of Drosophila to map the neuronal circuits that connect the entire enteric nervous system to the brain via the insect vagus nerve at synaptic resolution. We identify a gut-brain feedback loop in which Piezo-expressing mechanosensory neurons in the esophagus convey food passage information to a cluster of six serotonergic neurons in the brain. Together with information on food value, these central serotonergic neurons enhance the activity of serotonin receptor 7-expressing motor neurons that drive swallowing. This elemental circuit architecture includes an axo-axonic synaptic connection from the glutamatergic motor neurons innervating the esophageal muscles onto the mechanosensory neurons that signal to the serotonergic neurons. Our analysis elucidates a neuromodulatory sensory-motor system in which ongoing motor activity is strengthened through serotonin upon completion of a biologically meaningful action, and it may represent an ancient form of motor learning. [Display omitted] • STEM reconstruction of the entire enteric nervous system at the synaptic level • Piezo-mechanoreceptive neurons convey completed swallowing action to the brain • Central serotonergic neurons evaluate the biological valence of swallowed food • Serotonin modulates swallowing through motor neurons driving esophageal peristalsis Using a whole-animal serial transmission electron microscopy dataset, Schoofs et al. provide a complete reconstruction of a sensorimotor circuit underlying the Drosophila swallowing system. Through the vagus nerve, serotonergic neurons rate food based on mechanosensory and chemosensory information and modulate esophageal peristalsis. [ABSTRACT FROM AUTHOR]

Amorphous phases commonly accompany materials obtained through a number of methods, which often significantly change the functional properties of the materials. Thus, when present in photocatalysts, they decrease the photocatalytic performance of the materials significantly. To minimize the amorphous content in photocatalysts and increase their photocatalytic properties, hydrothermal post-treatment of amorphous photocatalysts is suggested. In this work, a series of brookite-based titania materials were obtained via the post-treatment of amorphous titania under hydrothermal conditions to determine how synthesis parameters affect the properties of the obtained TiO2 materials. The samples were characterized via X-ray diffraction analysis, scanning and transmission electron microscopy, and low-temperature nitrogen adsorption analysis. Special attention was given to the amount of residual amorphous phases in the samples. Results indicated the possibility of selectively crystallizing titania materials with high brookite contents and enhanced photocatalytic properties from amorphous titania without significantly altering the form of the particles. This study presents the amorphous phase as a valuable precursor to obtain highly crystalline materials with vast control of phase composition. [ABSTRACT FROM AUTHOR]

Due to its capacity to achieve nanometre-scale machining and lithography, a focused ion beam (FIB) is an extended tool for semiconductor device fabrication and development, in particular, for diamond-based devices. However, some technological steps are still not fully optimized for its use. Indeed, ion implantation seems to affect the crystalline structure and electrical properties of diamond. For this study, a boron-doped ([B] ∼ 1017 atoms·cm−3) diamond layer grown by chemical vapour deposition was irradiated using Ga+ by FIB, with 1 nA current and 5, 20, and 30 keV of acceleration voltage. The Ga+ implanted diamond layer has been analysed through cathodoluminescence (CL) and scanning transmission electron microscopy (STEM)-related techniques. The beam penetration depth has been simulated by Monte Carlo calculations of both Ga+ (FIB) and e− (CL) beams at different energies. The comparative CL analysis of the layer as-grown and after implantation revealed peaks related to defects, such as A band, H3 centre, and defects present in the green band region. The STEM studies for the 30 keV implanted sample showed that the diamond lattice is affected by the damage, evidencing amorphisation in the layer with a sp2/sp3 ratio of 1.37, estimated by electron energy loss spectroscopy. Therefore, this study highlights the effects of the Ga+ implantation on the optical and structural characteristics of diamond, using different methods. [ABSTRACT FROM AUTHOR]

Near-rigid-body grain rotation is commonly observed during grain growth, recrystallization, and plastic deformation in nanocrystalline materials. Despite decades of research, the dominant mechanisms underlying grain rotation remain enigmatic. We present direct evidence that grain rotation occurs through the motion of disconnections (line defects with step and dislocation character) along grain boundaries in platinum thin films. State-of-the-art in situ four-dimensional scanning transmission electron microscopy (4D-STEM) observations reveal the statistical correlation between grain rotation and grain growth or shrinkage. This correlation arises from shear-coupled grain boundary migration, which occurs through the motion of disconnections, as demonstrated by in situ high-angle annular dark-field STEM observations and the atomistic simulation-aided analysis. These findings provide quantitative insights into the structural dynamics of nanocrystalline materials. [ABSTRACT FROM AUTHOR]

One of the physical methods for obtaining magnetite nanoparticles (NPs) is electron beam physical vapor deposition (EB PVD), which requires complex equipment, but allows obtaining a significant amount of pure (ligand-free) NPs. The biomedical application of such NPs is less studied than materials from other synthesis methods. The objective is to study the effect of pure magnetite NPs in the NaCl matrix obtained by EB PVD on hematological indicators, gases, electrolytes and parameters of iron metabolism in the blood of intact animals. The physical characteristics of NPs were studied using high-resolution transmission electron microscopy, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy mapping, electron energy-loss spectroscopy, selected area electron diffraction and fast Fourier transform. In vivo experiments were conducted on albino male rats, which were injected with solution of magnetite-sodium chloride NPs (1.35 mg Fe/kg). After 3 and 72 h, hematological parameters, blood gases, electrolytes, and serum iron were determined. The synthesized NPs had an average size of 11 nm. They were identified as magnetite, where polycrystals and single crystals were present. The absence of contamination in crystal boundaries, clear orientation and orderliness of atoms in crystals were established. The administration of NPs in the sodium chloride matrix to animals was characterized by a transient increase in the main indicators of red blood accompanied by an increase in the saturation of erythrocytes with hemoglobin and their mean volume after 3 h. It did not worsen blood gases and pH, but decreased blood Na+ content after 72 h. The investigated NPs caused changes in the parameters of serum iron characteristic to iron preparations, which after 3 h were smaller compared to the reference iron drug, and after 72 h—similar to it. More intense rapid effects on hematological parameters at lower serum iron indicate greater activity of the studied pure magnetite NPs obtained by EB PVD syntesis compared to the reference iron preparation. Highlights: Pure magnetite nanoparticles in the NaCl matrix were obtained by EB PVD. They were studied using high-resolution transmission electron microscopy. These nanoparticles had a size of 11 nm, clear orientation and orderliness of atoms in crystals. In healthy animals, they caused a transient increase in red blood indicators. They did not worsen blood gases and pH, but decreased Na+ content in the blood. The nanoparticles caused changes in the serum iron typical to iron preparations. These changes were not toxic and lasting due to compensatory reactions. [ABSTRACT FROM AUTHOR]

Microscopy has been pivotal in improving the understanding of structure‐function relationships at the nanoscale and is by now ubiquitous in most characterization labs. However, traditional microscopy operations are still limited largely by a human‐centric click‐and‐go paradigm utilizing vendor‐provided software, which limits the scope, utility, efficiency, effectiveness, and at times reproducibility of microscopy experiments. Here, a coupled software–hardware platform is developed that consists of a software package termed AEcroscopy (short for Automated Experiments in Microscopy), along with a field‐programmable‐gate‐array device with LabView‐built customized acquisition scripts, which overcome these limitations and provide the necessary abstractions toward full automation of microscopy platforms. The platform works across multiple vendor devices on scanning probe microscopes and electron microscopes. It enables customized scan trajectories, processing functions that can be triggered locally or remotely on processing servers, user‐defined excitation waveforms, standardization of data models, and completely seamless operation through simple Python commands to enable a plethora of microscopy experiments to be performed in a reproducible, automated manner. This platform can be readily coupled with existing machine‐learning libraries and simulations, to provide automated decision‐making and active theory‐experiment optimization to turn microscopes from characterization tools to instruments capable of autonomous model refinement and physics discovery. [ABSTRACT FROM AUTHOR]

The lead iodide (PbI2) in lead‐halide perovskite (LHP) is both a positive additive for material properties and a site for the formation of device defects. Therefore, atomic‐level detection of PbI2 and its derived Pb structures are crucial for understanding the performance and stability of the LHP material. In this work, the atomic imaging of the LHP, PbI2, and Pb lattices is achieved using low‐dose integrated differential phase contrast (iDPC) scanning transmission electron microscopy (STEM). Combining it with the traditional high‐angle annular dark field (HAADF)‐STEM, the Pb precipitation in different LHPs (CsPbI3, CsPbBr3, and FAPbI3) and under different conditions (light, air, and heat) can be investigated in real space. Then, the features of Pb precipitation (positions and sizes) are visually revealed under different conditions and the stabilities of different LHPs. Meanwhile, the pathway of Pb precipitation is directly imaged and confirmed by the iDPC‐STEM during an in situ heating process, supporting the detailed mechanism of Pb precipitation. These results provide the visual evidence for analyzing atomic Pb precipitation in LHPs, which helps better understand the structure‐property relation induced by Pb impurity. [ABSTRACT FROM AUTHOR]

In this work, two different composite nanostructures, YAG:Ce and Ga0.9In0.1N, were prepared by the Urea Glass Route method and tested for the production of white light. The first composite was prepared by synthetizing the Ga0.9In0.1N nanoparticles in the presence of YAG:Ce nanoparticles. The second one was prepared by synthetizing YAG:Ce nanoparticles in the presence of Ga0.9In0.1N nanoparticles. These systems can be useful for the production of white light. X-ray Diffraction and Transmission and Scanning Electron Microscopies (TEM and SEM) were used to evaluate their structural and morphological properties. Excitation and emission spectra, the quantum yield and colour of the emitted light were acquired to evaluate the optical properties of the systems. [ABSTRACT FROM AUTHOR]

REBCO (rare-earth barium copper oxide) coated conductor tapes are a highly attractive option for magnet materials in future tokamak fusion power plants. However, the threat of intense neutron and gamma radiation, together with AC losses during magnet coil ramping, has raised concerns around magnet coil lifetimes. Irradiation-induced changes to flux creep rate has been identified as a key performance-limiting factor in REBCO tapes at low temperatures and high fields post-irradiation with gamma rays; spontaneous flux creep contributes to hysteretic AC loss in REBCO cables under applied AC fields. Knowing that multi-filamentary tapes are under consideration for tokamaks as an AC loss mitigation, magnetic measurements and gamma irradiation experiments are presented here on striated and mono-filamentary YBCO tapes to investigate the differences in post-irradiation screening currents and AC losses. Reduction in AC losses improved magnetisation critical current density (Jc) retention after 1 MGy in the multi- relative to the mono-filamentary samples. After the 5 MGy dose, striations then made the multi-filamentary tape more susceptible to Jc degradation because of the thinner individual filament width. Scanning transmission electron microscopy analysis on an analogous GdYBCO mono-filamentary tape did not indicate the introduction of nm-scale amorphisation to the active GdYBCO layer after gamma irradiation. A potential theoretical explanation for the underlying mechanism altering the flux-pinning landscape across the REBCO layer surface in gamma-irradiated tapes is discussed. This work concluded that gamma effects on screening current capability should be considered in future tokamak REBCO tape qualification studies. [ABSTRACT FROM AUTHOR]

Nanostructured ferritic alloys (NFAs), such as oxide-dispersion strengthened (ODS) alloys, play a vital role in advanced fission and fusion reactors, offering superior properties when incorporating nanoparticles under irradiation. Despite their importance, the high cost of mass-producing NFAs through mechanical milling presents a challenge. This study delves into the microstructure-mechanical property correlations of three NFAs produced using a novel, cost-effective approach combining severe plastic deformation (SPD) with the continuous thermomechanical processing (CTMP) method. Analysis using scanning electron microscopy (SEM)-electron backscatter diffraction (EBSD) revealed nano-grain structures and phases, while scanning transmission electron microscopy (STEM)-energy dispersive X-ray spectroscopy (EDS) quantified the size and density of Ti-N, Y-O, and Cr-O fine particles. Atom probe tomography (APT) further confirmed the absence of finer Y-O particles and characterized the chemical composition of the particles, suggesting possible nitride dispersion strengthening. Correlation of microstructure and mechanical testing results revealed that CTMP alloys, despite having lower nanoparticle densities, exhibit strength and ductility comparable to mechanically milled ODS alloys, likely due to their fine grain structure. However, higher nanoparticle densities may be necessary to prevent cavity swelling under high-temperature irradiation and helium gas production. Further enhancements in uniform nanoparticle distribution and increased sink strength are recommended to mitigate cavity swelling, advancing their suitability for nuclear applications. [ABSTRACT FROM AUTHOR]