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The strengths of glasses are intricately linked to their atomic-level heterogeneity. Atomistic simulations are frequently used to investigate the statistical physics of this relationship, compensating for the limited spatiotemporal resolution in experimental studies. However, theoretical insights are limited by the complexity of glass structures and the accuracy of the interatomic potentials used in simulations. Here, we investigate the strengths and fracture mechanisms of 2D silica, with all structural units accessible to direct experimental observation. We develop a neural network force field for fracture based on the deep potential-smooth edition framework. Representative atomic structures across crystals, nanocrystalline, paracrystalline, and continuous random network glasses are studied. We find that the virials or bond lengths control the initialization of bond-breaking events, creating nanoscale voids in the vitreous network. However, the voids do not necessarily lead to crack propagation due to a disorder-trapping effect, which is stronger than the lattice-trapping effect in a crystalline lattice, and occurs over larger length and time scales. Fracture initiation proceeds with void growth and coalescence and advances through a bridging mechanism. The fracture patterns are shaped by subsequent trapping and cleavage steps, often guided by voids forming ahead of the crack tip. These heterogeneous processes result in atomically smooth facets in crystalline regions and rough, amorphous edges in the glassy phase. These insights into 2D crystals and glasses, both sharing SiO 2 chemistry, highlight the pivotal role of atomic-level structures in determining fracture kinetics and crack path selection in materials. [ABSTRACT FROM AUTHOR]

Controlling the placement of dopants can significantly tailor graphene's properties, but this process is influenced by copper substrates during vapor deposition. Understanding the influence of interfacial atomic structures on the preference for dopant locations is crucial. In this work, we conducted a systematic first-principles study of boron- and nitrogen-doped graphene on copper {111}, considering both sublattice and superlattice configurations. Our calculations revealed that the formation energy is minimized at the top-fccb site (−0.60 eV) for boron and the hcp-fcca site (1.94 eV) for nitrogen, suggesting a possible selective distribution of dopants in both sublattice and superlattice arrangements at the graphene/copper interface. Furthermore, a lower formation energy indicates a higher release of energy during doping, resulting in a stronger interfacial binding. Since formation energy is closely associated with out-of-plane interactions, while in-plane interactions remain relatively stable, these differences offer potential avenues for modifying dopant distribution at graphene/copper interfaces. [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]

The spontaneous formation of a Ga-oxide (GaO x ) intermediate layer at the GaN/SiO 2 interface has been reported during the SiO 2 deposition on the GaN substrate. In this study, we have performed first-principles calculations and unveiled atomic and electronic structures of the GaN/SiO 2 interface with 1-nm thick GaO x intermediate layer. Our calculations show that the top-layer Ga atoms on the GaN side are terminated with the O atoms on the GaO x side, leading to the clean GaN/GaO x interface and the absence of the electronic state in the midgap region. However, strongly localized states, which are originated from O atoms lone-pair orbitals in the –GaOSi– local structures, emerge in the gap near the valence-band maximum of GaN. These in-gap states become hole traps in GaN MOS devices, leading to a degradation in device controllability and operational speed. [ABSTRACT FROM AUTHOR]

C-incorporated amorphous silica (a-SiOC) is expected to be a significant dielectric film for miniaturized semiconductor devices. However, information on the relationship among its composition, atomic structures, and material properties remains insufficient. This study investigated the dependence of the elastic modulus on the C content in a-SiOC, employing a universal neural network interatomic potential to realize a high-accuracy and high-speed simulation of multicomponent systems. The relationship between elastic modulus and atomic network structures was explored by fabricating 480 amorphous structures through the melt-quenching method without predetermined structure assumptions. The bulk modulus increased from 45 to 60 GPa by incorporating 10% C atoms under O-poor conditions and 20% C atoms under O-rich conditions, respectively. This result is attributed to the formation of denser crosslinking atomic network structures. In particular, the C atoms bonded with the Si atoms with higher coordination under O-poor conditions, whereas they tend to bond with O atoms under O-rich conditions, breaking the SiO2 network. Large C clusters precipitated as the C fraction was increased under O-rich conditions. Gas molecules, such as CO and CO2, were also generated. These results are consistent with reported ab initio calculation results of the formation energies of C defects and gas molecules in SiO2. The findings suggest that realizing O-poor conditions during deposition is crucial for fabricating stronger dielectric films. Therefore, this work contributes to understanding the fabrication of stronger dielectric films and elucidating the underlying mechanism of C cluster formation. [ABSTRACT FROM AUTHOR]

The investigation of charge carrier transport in state-of-the-art nanoelectronic devices based on III/V semiconductors proves to be challenging, even more so when the highly non-parabolic energy dispersion exhibited by these materials is taken into account. Unlike the common approach of neglecting this behavior by the use of the parabolic band approximation, a novel combination of a tight-binding approach with a quantum Liouville-type equation is introduced here, where any arbitrary energy dispersion can effectively be included. This leads to a discretization based on the atomic structure without the need for finite difference approximations of the Hamiltonian. Because this allows for the stationary as well as the transient simulation of quantum charge carrier transport, it is well suited for the analysis of ultrathin FETs such as dual-gate FETs when it is combined with a mode-space approach. We demonstrate that the parabolic approximation not only vastly underestimates the current densities when compared to the non-parabolic case but also fails to capture transient effects such as gain compression when amplifier operation is considered. [ABSTRACT FROM AUTHOR]

Lattice dynamics (LD) enables the calculation of mode-resolved transmittance of phonons passing through an interface, which is essential for understanding and controlling the thermal boundary conductance (TBC). However, the original LD method may yield unphysical transmittance over 100% due to the absence of the constraint of energy conservation. Here, we present a robust LD algorithm that utilizes linear algebra transformations and projection gradient descent iterations to ensure energy conservation. Our approach demonstrates consistency with the original LD method on the atomically smooth Si/Ge interface and exhibits robustness on rough Si/Ge interfaces. The evanescent modes and localized effects at the interface are revealed. In addition, bottom-up analysis of the phonon transmittance shows that the anisotropy in the azimuth angle can be ignored, while the dependency on the frequency and polar angle can be decoupled. The decoupled expression reproduces the TBC precisely. This work provides comprehensive insights into the mode-resolved phonon transmittance across interfaces and paves the way for further research into the mechanism of TBC and its relation to atomic structures. [ABSTRACT FROM AUTHOR]

The nitrogen-vacancy (NV) centers (NCVSi)− in 4H silicon carbide (SiC) constitute an ensemble of spin S = 1 solid state qubits interacting with the surrounding 14N and 29Si nuclei. As quantum applications based on a polarization transfer from the electron spin to the nuclei require the knowledge of the electron–nuclear interaction parameters, we have used high-frequency (94 GHz) electron–nuclear double resonance spectroscopy combined with first-principles density functional theory to investigate the hyperfine and nuclear quadrupole interactions of the basal and axial NV centers. We observed that the four inequivalent NV configurations (hk, kh, hh, and kk) exhibit different electron–nuclear interaction parameters, suggesting that each NV center may act as a separate optically addressable qubit. Finally, we rationalized the observed differences in terms of distinctions in the local atomic structures of the NV configurations. Thus, our results provide the basic knowledge for an extension of quantum protocols involving the 14N nuclear spin. [ABSTRACT FROM AUTHOR]

The honeycomb's eponymous structure is omnipresent in our every day lives. We want to provide some inspiration to perform structural analyses of these structures and to draw comparisons between them. In the present study, we detect honeycomb patterns and related complex network structures on different length scales ranging from macroscopic objects down to the atomic scale of 2D materials. In 2D materials, a subset of the honeycomb structure—the kagome lattice—is very interesting due to unique material properties. For structure detection, we developed a program written in Python. The program is very adaptable and provides a graphical user interface to modify the detected network interactively. With the help of this program, we directly compare honeycomb structures with atomic network structures. Both honeycombs and 2D atom networks can show local deviations from their characteristic hexagonal pattern. The structural deviations at the macroscopic scale and at the atomic scale are very similar. We provide additional structural analyses of every day objects and encourage everyone to use our software that is freely accessible. [ABSTRACT FROM AUTHOR]

Microscopic mechanics of thermal dissipation induced by fast-moving edge dislocations are crucial for a deeper understanding of the nature of plastic deformation. Herein, we study the thermal dissipation induced by a fast-moving edge dislocation and discuss the effect of non-Schmid stress on the thermal dissipation using molecular dynamics simulations that can quantitatively distinguish the thermal dissipation and stored energy part of the energy emitted from a moving dislocation. We show that, of the energy emitted by the fast-moving edge dislocation, no more than 5% is used to generate elastic distortion of the local atomic structure, especially at low-stress levels, and almost all the energy emitted by the moving dislocation is converted into thermal energy and dissipated. The thermal dissipation of the moving edge dislocation depends significantly on the non-Schmid stress, specifically, temperature rise decreases almost linearly as the non-Schmid stress normal to the slip plane increases, and the possible mechanism is disclosed. [ABSTRACT FROM AUTHOR]

The stacking orders that may be generated by mirroring a layer of Cr X 3 (X = I, Br, Cl) through its Cr atomic layer in heterostructures are easy to be ignored so that the influence of these stacking orders has not yet been well explored. In this paper, we have constructed all eight stable highly symmetric stacking orders that maintain translational symmetry in a Cr I 3 / α - In 2 S e 3 heterostructure and systematically studied the dependence of the structure, magnetism, electronic structure on stacking orders, and ferroelectric polarization directions by using the first principles method, especially that the system energy and magnetism have certain differences between normal and mirror stacking orders. The regulation of system energy and interlayer distance, magnetism, and band structure can be, respectively, explained by the different stacking relationships of atomic layers in different stacking orders, the different influences of different deformations of a Cr I 3 atomic structure on a magnetic exchange interaction in different stacking orders, and the different band alignments corresponding to different vacuum energy levels at different interfaces of α - In 2 S e 3. Our work will have a certain reference value for understanding the material properties and practical applications of such ferromagnetic/ferroelectric heterostructures. [ABSTRACT FROM AUTHOR]

We report first-principles molecular-dynamics calculations with the simulated annealing technique that clarify the atomic and electronic structures of the semiconductor–insulator interfaces consisting of GaN (0001) and (000 1 ¯ ) faces and the amorphous (Al 2 O 3) 1 − x (SiO 2) x. We confirm that the obtained interfaces are free from dangling bonds, as predicted by our previous calculations, irrespective of the thickness of the amorphous (Al 2 O 3) 1 − x (SiO 2) x layer. This is due to the high atomic density and large mean coordination number near the interfaces caused by atomic diffusion from inside of the insulator to the interfaces. The calculated local density of states of the (Al 2 O 3) 1 − x (SiO 2) x /GaN system quantitatively shows clear band offsets and, more importantly, the absence of deep states in the GaN energy gap. Interestingly, we find that the band alignment causing the offset is not abrupt at the interface but varies gradually near the interface, predicting the existence of transition layers. We determine the thicknesses of the transition layers in the (Al 2 O 3) 1 − x (SiO 2) x /GaN system to be about 10 Å. We argue that those structural characteristics prevent the formation of the dangling-bond origin carrier traps at the interface, and this is a superior feature of the (Al 2 O 3) 1 − x (SiO 2) x as a gate oxide for the GaN-based metal–oxide–semiconductor devices. [ABSTRACT FROM AUTHOR]

Transition metal nitrides (TMNs) exhibit fascinating physical properties that show great potential in future device applications. Stacking two-dimensional TMNs with other functional materials with different orientations and symmetries requires separating epitaxial TMNs from the growth substrates. However, the lattice constants of TMNs are incompatible with those of most sacrificial layers, resulting to a great challenge in fabricating high-quality single-crystalline TMN membranes. In this study, we report the application of a water-soluble BaO sacrificial layer as a general method for creating freestanding TMN membranes. Using CrN as an example, the relatively small lattice mismatch and identical cubic structure between BaO and CrN ensure the formation of heterostructures. We directly observe the planar atomic structure and correlate its electronic state with its intrinsic transport properties using millimeter-size CrN membrane. Our research enables the fabrication of freestanding TMN membranes and transfers them to arbitrary substrates. By integrating TMN membranes with other materials will stimulate further studies in the emergent phenomena at heterointerfaces. [ABSTRACT FROM AUTHOR]

Hybrid organic–inorganic perovskites (HOIPs) have emerged as outstanding candidates for high-performance photovoltaic devices, and a large variety of HOIPs has been synthesized with different compositions and structural motifs. However, issues remain about their stability and optimization for applications, motivating studies to provide better insight into understanding the structure-property relationship. The application of pressure has proven to be a valuable tool to reach this goal without altering the chemical composition. Indeed, through compression, the atomic and electronic structures of HOIPs can be both finely tuned and dramatically changed, leading to bandgap reduction, phase transitions, and even semiconductor-to-metal transition. In this Perspective, we first provide a general overview of HOIPs, introducing their structure and properties at ambient conditions, focusing only on fully hybrid metal halide perovskites, and thus neglecting the inorganic counterparts. Second, we review and summarize the findings of previous high-pressure research works on these materials, highlighting the common patterns in their high-pressure behavior. We then give an outlook of the main gaps in present work that needs to be filled in our opinion and suggest possible future directions for high-pressure research program on HOIPs. Finally, we provide a first example of such future investigations presenting a preliminary high-pressure low-temperature phase diagram of MAPbBr3 established through synchrotron x-ray diffraction and infrared spectroscopy. [ABSTRACT FROM AUTHOR]

Bournonite (CuPbSbS3) and enargite (Cu3AsS4) have recently been used as absorber layers in thin-film photovoltaic devices due to their ideal bandgap and ferroelectric properties. An understanding of the ferroelectric domain structure in these materials is required so that the benefits of the internal depolarizing electric fields can be fully exploited. Here, the atomic structure and electronic properties of domain walls (DWs) are elucidated through a combined aberration-corrected scanning transmission electron microscopy and density functional theory study. ∼90° and 180° DWs are observed in bournonite. As the 180° DW is charge neutral, it cannot contribute to the anomalous photovoltaic effect that leads to high open circuit voltages. The ∼90° DW shows a slight offset across the boundary, but the contributions of this to the anomalous photovoltaic effect are negligible. The DWs are also electrically passive, i.e., they do not result in significant recombination and do not block charge carrier transport. A high density of stacking faults (SF) was, however, observed in enargite. The SFs have a large number of defect states within the bandgap, which would lower the device efficiency through Shockley–Read–Hall recombination. [ABSTRACT FROM AUTHOR]

We propose the atomic structures of the 4H-SiC/ SiO 2 interface for a face (1 1 ¯ 00), m face (11 2 ¯ 0), the C face (000 1 ¯ ), and Si face (0001) after NO annealing using the OH-terminated SiC surface models. Our proposed structures preferentially form at the topmost layers of the SiC side of the interface, which agrees with the experimental finding of secondary-ion mass spectrometry; that is, the N atoms accumulate at the interface. In addition, the areal N-atom density is of the order of 10 15 atom / cm 2 for each plane, which is also consistent with the experimental result. Moreover, the electronic structure on the interface after NO annealing in which the CO bonds are removed and the nitride layer only at the interface is inserted, is free from gap states, although some interface models before NO annealing include the gap states arising from the CO bonds near the valence band edge of the bandgap. Our results imply that NO annealing can contribute to the reduction in the density of interface defects by forming the nitride layer. [ABSTRACT FROM AUTHOR]

The gate defect of the ferroelectric HfO2-based Si field-effect transistor (Si FeFET) plays a dominant role in its reliability issue. The first-principles calculations are an effective method for the atomic-scale understanding of gate defects. However, the first-principles study on the defects of FeFET gate stacks, i.e., the metal/orthorhombic-Hf0.5Zr0.5O2/SiOx/Si structure, has not been reported so far. The key challenge is the construction of metal/orthorhombic-Hf0.5Zr0.5O2/SiOx/Si gate stack models. Here, the atomic structure and defect property of orthorhombic-Hf0.5Zr0.5O2/SiO2/Si gate stack are systematically studied by first-principles calculations. We use the Hf0.5Zr0.5O2(130) high-index crystal face as the orthorhombic ferroelectric layer and construct a robust atomic structure of the orthorhombic-Hf0.5Zr0.5O2/SiO2/Si gate stack without any gap states based on the electron counting rule. The calculated band offsets show that this gate structure is of type-I band alignment. Furthermore, the formation energies and charge transition levels (CTLs) of defects reveal that the oxygen vacancy defects are more favorable to form compared with other defects such as oxygen interstitial and Hf/Zr vacancy, and their CTLs are mainly localized near the Si conduction band minimum and valence band maximum, in agreement with the reported experimental results. The oxygen vacancy defects are responsible for charge trapping/de-trapping behavior in Si FeFET. This work provides an insight into gate defects and paves the way to carry out the first-principles study of ferroelectric HfO2-based Si FeFET. [ABSTRACT FROM AUTHOR]

Graphene on L 1 0 -FePd(001), which has been experimentally studied in recent years, is a heterogeneous interface with a significant lattice symmetry mismatch between the honeycomb structure of graphene and tetragonal alloy surface. In this work, we report on the density functional study of its atomic-scale configurations, electronic and magnetic properties, and adsorption mechanism, which have not been well understood in previous experimental studies. We propose various atomic-scale models, including simple nontwisted and low-strain twisted interfaces, and analyze their energetical stability by performing structural optimizations using the van der Waals interactions of both DFT-D2 and optB86b-vdW functionals. The binding energy of the most stable structure reached E B = − 0.22 eV/atom for DFT-D2 (E B = − 0.19 eV/atom for optB86b-vdW). The calculated FePd-graphene spacing distance was approximately 2 Å, which successfully reproduced the experimental value. We also find out characteristic behaviors: the modulation of π -bands, the suppression of the site-dependence of adsorption energy, and the rise of moiré-like corrugated buckling. In addition, our atomic structure is expected to help build low-cost computational models for investigating the physical properties of L 1 0 alloys/two-dimensional interfaces. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) ferroelectrics have attracted extensive attention due to their rich variety of exquisite functionalities in novel nanoscale electronic devices. As domain walls (DWs) in ferroelectrics are topological defects separating domains with different orientations of the electric polarization, a detailed understanding of the energetic and atomistic characteristics of 2D ferroelectric DWs is a crucial issue due to its theoretical and technological importance. In the current study, using first-principles calculations, we provided a detailed investigation on the energy, variation of the atomic structure with applied strain, and the electronic properties of 180° and 90° DWs in 2D GeS including the uncharged and charged DWs. All types of DWs in 2D GeS were found to be atomically sharp. In addition, the 90° uncharged DW was more energetically favorable than the 180° DW, which is similar to DWs of perovskites. However, due to the effect of adverse electrostatic energy, the charged DW possessed higher energy than that of the uncharged DW. On the other hand, the polarization distortion of the domain region in all DWs is significantly strengthened by the biaxial strain. In addition, the density of states showed that the charged DW is conductive relative to the uncharged domain wall, because the uncompensated positive or negative charges exist at the charged domain wall. Our results provide necessary theoretical guidance to the future exploration and application of 2D ferroelectric materials. [ABSTRACT FROM AUTHOR]

The microstructural evolutions and dynamic properties of the Zr77Rh23 alloy during the rapid cooling process have been studied by molecular dynamics (MD) simulations using tight-binding (TB) potential. The total pair distribution functions [or structure factors, S(q)], g(r), calculated at different temperatures are in good agreement with the ab initio MD (AIMD) simulation (or experimental) results. The splitting in the second peak of all g(r) is notable for the formation and development of a medium-range order (MRO) in the Zr77Rh23 system. Moreover, the total number of atoms determined from TB-MD simulations at 300 K is also consistent with the number of atoms of the three shells for the Bergman-type MRO cluster and AIMD simulation results. By analyzing the structure of the system with methods such as the Honeycutt–Andersen index, Voronoi tessellation, and bond-angle distribution, it has been shown that the icosahedron short-range order (SRO) increases upon cooling. The dominant short-range structure in Zr77Rh23 metallic glass is found to consist mostly of perfect and distorted icosahedral clusters. The findings show that, for all temperatures, Zr atoms have greater mobility than Rh atoms. The critical temperature Tc estimated from fitting the mode-coupling theory equation is ∼993 K. A dynamic crossover is observed at temperatures around Tc. The present findings contribute to understanding the nature of the atomic local structures of the Zr77Rh23 alloy during the cooling process and the formation of SRO/MROs in metallic glasses. [ABSTRACT FROM AUTHOR]

The development of inkjet-printed 2D crystal inks offers the ability to print different 2D materials on various substrates to form vertical heterostructures. However, the detailed characterization of the atomic structures of the inkjet-printed MoTe2 nanosheets has been rarely reported. In this work, water-based 2D crystal inks of MoTe2, WS2, and graphene have been prepared and printed to obtain the flexible photodetectors. The absorption coefficient of MoTe2 has been estimated as α (500 nm) = 925 ± 47 lg−1 m−1 using the gravimetric method. Intriguingly, the inkjet-printed MoTe2 nanosheets down to 4 nm show both the semiconducting 2H and metallic 1T′ phases. The responsivities of the photodetectors based on MoTe2/graphene and WS2/graphene heterostructures can reach 120 mA/W and 2.5 A/W at 532 nm, respectively. Moreover, the inkjet-printed MoTe2/graphene shows a responsivity of 7.7 mA/W at 940 nm. The fabrication technique of inkjet printing will help design flexible optoelectronic devices based transition metal dichalcogenide–graphene heterostructures for the near-infrared photo detection. [ABSTRACT FROM AUTHOR]

In previous studies, the influence of flaws on macro-scale and nano-scale metallic glasses (MGs) has always been a topic of great interest, with important applications in engineering. Moreover, through experiments and simulations, many researchers draw contradictory conclusions of the notch sensitivity, including the notch strengthening, weakening, and insensitivity in different MGs. In order to better understand its atomic mechanism, classical molecular dynamics simulations have been performed on the nano-scale notched MGs in the present work to investigate the deformation modes under the uniaxial tension. According to the results, after setting notches, the MG samples exhibit a significant change from the shear to necking failure, which indicates a notch strengthening phenomenon. At the same time, the evolution of atomic structures suggests that the introduction of notches will increase the degree of shear localization and further disturb the structural order of MGs. The atomic displacement, which is different from shear strain, can also be used as an index to visually describe the deformation behavior of MGs and shows the high notch sensitivity. [ABSTRACT FROM AUTHOR]

The β phase of tungsten has attracted great interest for spintronic applications due to its higher spin Hall angle compared to other elemental solids and large spin–orbit torque, but the stability of this phase is yet to be well understood as many different results are there in the literature mainly based on the film thickness, temperature, and overall growth conditions. The growth of films by sputter deposition has emerged as a promising technique to achieve β-W owing to its compatibility with current spintronic technology. We demonstrate here the efficient ability of dc magnetron sputtering to grow stable β-W films up to a thickness of ∼180 nm at room temperature by varying a set of deposition parameters like pressure, power, and deposition time and discuss the various underlying mechanisms. From these results, the optimized set of deposition parameters for growing β-W films is given. A clear understanding of the influence of oxygen in the atomic structure of β-W is obtained by varying the thickness of the films. This is confirmed from the ab initio molecular dynamics (MD) simulations, where the atomic structure is influenced by the oxygen doping concentration. A stable polycrystalline β phase can be achieved by controlled doping of oxygen. Additionally, a phase transformation from α to β with the doping of oxygen is also evident by MD simulations. [ABSTRACT FROM AUTHOR]

While microalloying of metallic glasses (MGs) using hydrogen emerged a few years ago, the underlying mechanism of how hydrogen microalloying influences mechanical behaviors is currently still under debate. Herein, we perform atomistic simulations to investigate the effect of hydrogen microalloying on the mechanical profiles of MGs. The mitigation of strain localization accompanied with plenty of shear transformation zones (STZs) is exhibited in H-alloyed MGs and becomes more significant with the increase of H content. The addition of hydrogen induces a loose atomic structure with fertile liquid-like regions and abundant free volume, which triggers more STZ events and the softening behavior. Furthermore, hydrogen doping lowers the STZ activation energy barrier, which is verified by a theoretical model based on the concept of energetic criterion. Our work provides some new insight on how to tune the local packing of MGs and further alter the deformation behavior. [ABSTRACT FROM AUTHOR]

Over the past decade, a combination of crystal structure prediction techniques and experimental synthetic work has thoroughly explored the phase diagrams of binary hydrides under pressure. The fruitfulness of this dual approach is demonstrated in the recent identification of several superconducting hydrides with T c s approaching room temperature. We start with an overview of the computational procedures for predicting stable structures and estimating their propensity for superconductivity. A survey of phases with high T c reveals some common structural features that appear conducive to the strong coupling of the electronic structure with atomic vibrations that leads to superconductivity. We discuss the stability and superconducting properties of phases containing two of these—molecular H 2 units mixed with atomic H and hydrogenic clathrate-like cages—as well as more unique motifs. Finally, we argue that ternary hydride phases, whose exploration is still in its infancy, are a promising route to achieve simultaneous superconductivity at high temperatures and stability at low pressures. Several ternary hydrides arise from the addition of a third element to a known binary hydride structure through site mixing or onto a new site, and several more are based on altogether new structural motifs. [ABSTRACT FROM AUTHOR]

Multi-layered stacking structures and atomic mixing interfaces were constructed. The effects of various factors on the thermal conductivity of different lattice structures were studied by non-equilibrium molecular dynamics simulations, including the number of atomic mixing layers, temperature, total length of the system, and period length. The results showed that the mixing of two and four layers of atoms can improve the thermal conductivities of the multi-layer structure with a small total length due to a phonon "bridge" mechanism. When the total length of the system is large, the thermal conductivity of the multi-layer structure with atomic mixing interfaces decreases significantly compared with that of the perfect interfaces. The interfacial atom mixing destroys the phonon coherent transport in the multi-layer structure and decreases the thermal conductivity to some extent. The thermal conductivity of the multi-layer structure with perfect interfaces is significantly affected by temperature, whereas the thermal conductivity of the multi-layer structures with atomic mixing is less sensitive to temperature. [ABSTRACT FROM AUTHOR]

In this article, we describe the characterization of a newly fabricated amorphous alloy system (TiZrNbCu)1−xCox covering a broad composition range from high-entropy (HEA) to Co-rich alloys (x ≤ 0.43). We investigated thermal stability, atomic and electronic structure, and magnetic and mechanical properties as a function of chemical composition x. One of the important findings is that all studied properties change their dependence on concentration x within the HEA range. In particular, it has been found that the average atomic volume deviates from Vegard's law for x > 0.2, the concentration for which the average atomic packing fraction suddenly changes. The valence band structure, studied with ultraviolet photoemission spectroscopy, shows a split-band shape with 3d-states of Co approaching the Fermi level on increasing x. Due to the onset of magnetic correlations, magnetic susceptibility rapidly increases for x > 0.25. Very high microhardness increases rapidly with x. The results are compared with those for similar binary and quinary metallic glasses and with those for Cantor type of crystalline alloys. [ABSTRACT FROM AUTHOR]

Nanomaterials with enzyme-like activity have been the spotlight of scientific and technological efforts to substitute natural enzymes, not only in biological research but also for industrial manufacturing, medicine, and environment healing. Notable advancements in this field along the last years relied on to the rational design of single-atom active sites, knowledge of the underlying atomic structure, and realistic ab initio theoretical models of the electronic configuration at the active site. Thus, it is plausible that a next generation of nanozymes still to come will show even improved catalytic efficiency and substrate specificity. However, the dynamic nature of the protein cage surrounding most active sites in biological enzymes adds a flexible functionality that possess a challenge for nanozyme's mimicking of their natural counterparts. We offer a perspective about where the main strategies to improve nanozymes are headed and identify some of the big challenges faced along the road to better performance. We also outline some of the most exciting bio-inspired ideas that could potentially change this field. [ABSTRACT FROM AUTHOR]

The knowledge of atomic structure for liquids, especially for liquid alloys with complex crystal structure and high liquidus temperatures, remains poorly understood. In this work, we have extended the development of deep neural network (DNN) potential for liquid Nb5Si3. The DNN potential captures the structural features of liquid alloys compared with ab initio results. The chemical short-range order parameter suggests that there exists strong affinity between Nb and Si atoms. The dynamic property was investigated, and the diffusion coefficient obeys the Arrhenius relationship. The atomic structure has been subsequently explored for normal and undercooled liquid Nb5Si3. Large amounts of fivefold symmetry Honeycutt–Andersen pairs have been identified in liquid Nb5Si3. However, due to the violent thermal motion in a high-temperature Nb5Si3 melt, icosahedral symmetry and distorted icosahedrons (ICOs) account for little proportion according to Voronoi polyhedron (VP) analysis. The effect of thermal motion on VPs has been discussed. Except from the well documented ⟨0,2,8,2⟩ and ⟨0,1,10,2⟩ distorted ICOs, six more quasi-ICOs (⟨0,1,9,3⟩, ⟨0,2,8,1⟩, ⟨0,2,8,4⟩, ⟨0,2,8,5⟩, ⟨0,1,10,3⟩, and ⟨0,1,10,4⟩) have been proven to deform from ICOs at high temperatures. The local environment motif obtained by the atomic cluster alignment method demonstrates the existence of dominant distorted ICOs. At last, the atomic structure during melting process is discussed by VP analysis. It is found that ⟨0,2,8,1⟩, ⟨0,2,8,2⟩, ⟨0,2,8,5⟩, and ⟨0,1,10,4⟩ prefer to form at the beginning of the melting but rapidly reduce when it is fully melted. [ABSTRACT FROM AUTHOR]

Molecular dynamic simulation was performed to study the correlation between atomic packing and shear transformation under compressive deformation in apparent elastic regime in CuZr metallic glass. The packing feature of atomic structures was characterized in terms of cavities in metallic glass. It is found that while atoms surrounded by larger cavity volumes, i.e., loosely packed regions, show very small nonaffine displacements, some atoms surrounded by very small cavities, i.e., densely packed regions, undergo very large nonaffine displacement and form cooperative shear transformations with large scale in space. The size of shear transformation zones monotonically increases with decreasing cavity volume. However, shear transformations rarely occur in either densely packed or loosely packed regions with very small probability. In addition, metallic glasses are revealed to possess characteristic cavity volumes around which atoms have more probability to undergo relatively larger nonaffine displacements. It is found that more neighboring atoms together with these central atoms experience cooperative shear transformations. These findings are general in different metallic glasses and provide a general underlying structural basis for different sizes of shear transformation zones observed in previous studies. [ABSTRACT FROM AUTHOR]

Ge2Sb2Te5 (GST) alloy has the ability to quickly transform between the amorphous phase and the crystalline phase; therefore, it can be used in non-volatile phase change storage. First-principles molecular dynamics was used to simulate the reversible phase change process of GST alloy, namely, amorphization and crystallization. The amorphous state was obtained by melting (∼3000 K) and cooling, and the amorphization process was characterized by the pair correlation function and bond angle distribution. The bond angles of amorphous GST were mainly distributed around 60°, 90°, and 110°, indicating the existence of octahedral and tetrahedral bonding configurations. The crystalline state was obtained by annealing at a temperature of 600 K, and the crystallization process was characterized by the pair correlation function, component disordered number, bond angle distribution, and dynamic atomic structure change. The results show that the bond angle of GST in crystallization is mainly distributed around 90°, and the structure mainly contains four-membered rings formed by Ge–Te and Sb–Te. By analyzing the optical properties, with the growth of crystallization time, the absorption coefficient, reflectivity, and conductivity of GST were significantly improved. [ABSTRACT FROM AUTHOR]

The pressure effect on structures and properties of a Fe78Si9B13 metallic glass was investigated by in situ high-pressure synchrotron Fe Kβ x-ray emission spectroscopy and x-ray diffraction, and electrical resistivity measurements up to ∼51 GPa. The study reveals a reversible and continuous pressure-induced high- to low-spin crossover of Fe atoms in an amorphous structure. The changes of the local spin moment can be scaled to match its average atomic distance shrinkage very well during compression. The crossover of electronic spin states in the Fe78Si9B13 metallic glass resembles that of typical crystalline Fe-bearing materials but without a sharp atomic volume collapse and an abrupt electrical resistivity jump. These findings could help guide applications of Fe-based metallic glasses as a soft ferromagnetic material at extreme conditions and also improve our understanding of magnetism and coupling of its changes with disordered atomic structures and other properties in metallic glasses. [ABSTRACT FROM AUTHOR]

Oxygen vacancies are found to play a crucial role in inducing many functional properties at the heterointerfaces in complex oxides. Gaining better control over the properties requires an understanding of the atomic structure of oxygen vacancies at the heterointerfaces. In this paper, we elucidate the effects of the interfacial strain on the oxygen-vacancy ordering in fluorite δ-Bi2O3 and perovskite LaNiO2.5 using first-principles calculations. By applying biaxial strains, we find that the 〈110〉−〈111〉 oxygen vacancy order in δ-Bi2O3 is broken, resulting in a faster diffusion of oxygen ions. Similarly, the biaxial strain is used to leverage both ordered and disordered arrangements of vacancies in LaNiO2.5. Besides the vacancy order, we find that the biaxial strain can also be used to break the cation order in Gd2Ti2O7, where Gd and Ti antisites can be created on the cation sublattice, which leads to enhanced radiation tolerance and higher oxygen diffusivity. These results indicate that the biaxial strain that is commonly present at heterointerfaces can be used to gain control over both ordered and disordered arrangements of defects, potentially opening new opportunities to functionalize complex oxides. [ABSTRACT FROM AUTHOR]

Using density functional theory calculations, we investigate and report the electronic structure basis of symmetry-breaking in atomic structures and variations in extreme mechanical properties of a number of widely used polymers, namely, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyethylene, and three structural variants of PVDF. All of these polymers consist of C–C bonds in the backbone and a combination of C–H and C–F bonds attached to the backbone. Our results show that the relative proportion and arrangement of the C–H and C–F bonds, hereafter called the chemical heterogeneity, lead to two distinct sets of structural symmetries and mechanical properties. The set with the lower chemical heterogeneity possesses higher structural symmetry and exhibits higher strength and toughness. Electronic population analysis shows that chemical heterogeneity breaks the structural symmetry and alters deformation induced "electron redistribution patterns" in the C–C backbone. Strong variations in electron redistribution serve as the basis for distinctive mechanical behavior among the polymers: the higher the structural variation and electron redistribution, the lower the bond rupture force and toughness of the polymer. The bond rupture process is initiated by a decrease in the electronic population in the backbone, while the electronic interactions at the C–H and C–F bonds dictate where, how, and which bonds rupture. Furthermore, in the linear regime of mechanical deformation, the force–strain behavior is insensitive to the chemical heterogeneity and controlled by the strong covalent interactions of the C–C bonds. In the nonlinear regime, the chemical heterogeneity dramatically reduces the strength and toughness of the polymer chain. [ABSTRACT FROM AUTHOR]

Nanoparticles possess many distinguished properties due to their small size and unique internal and surface structures. For metallic glass nanoparticles, the small size combined with disordered atomic structure results in many unexpected results, some of which are superior to crystalline particles. This field, however, remains largely unexplored. Here, we report the mechanical and thermomechanical responses caused by the increasing strain rate in metallic glass nanoparticles under compression. The mechanical properties of nanoparticles resemble those of the bulk when the strain rate is below 1010 s−1; above this threshold, the nanoparticle exhibits localized deformation and then melting and even chemical segregation at the contact surface area. We reveal that these unique behaviors are the direct results of the lack of effective energy dissipation mechanisms in the disordered materials that are different from crystalline nanoparticles. [ABSTRACT FROM AUTHOR]

Monolayer group-IV monochalcogenides (MX, M = Ge , Sn, Pb; X = S , Se, Te) are a family of novel two-dimensional (2D) materials that have atomic structures closely related to that of the staggered black phosphorus lattice. The structure of most monolayer MX materials exhibits a broken inversion symmetry and many of them exhibit ferroelectricity with a reversible in-plane electric polarization. A further consequence of the noncentrosymmetric structure is that when coupled with strong spin–orbit coupling, many MX materials are promising for the future applications in non-linear optics, photovoltaics, spintronics, and valleytronics. Nevertheless, because of the relatively large exfoliation energy, the creation of monolayer MX materials is not easy, which hinders the integration of these materials into the fast-developing field of 2D material heterostructures. In this Perspective, we review recent developments in experimental routes to the creation of the monolayer MX, including molecular beam epitaxy and two-step etching methods. Other approaches that could be used to prepare the monolayer MX are also discussed, such as liquid phase exfoliation and solution-phase synthesis. A quantitative comparison between these different methods is also presented. [ABSTRACT FROM AUTHOR]

The interfacial structure of coincidence site lattice grain boundaries in multi-crystalline silicon plays a decisive role in their electrical behavior as revealed by high-resolution (scanning) transmission electron microscopy investigations. Considering only the global misorientation of the adjacent grains can lead to a false correlation between the structural and electrical properties of a grain boundary. The grain boundary habit plane as well as local deviations in the orientation and misorientation that induce additional structural defects need to be analyzed. Indeed, a Σ9 {221} grain boundary, presenting a perfect coincidence and periodicity at the atomic scale, appears electrically non-active. However, a grain boundary also identified as Σ9 {221} at the mesoscale is found to be composed of nano-sized triangular structures involving Σ3 {111} and Σ3 {112} facets at the nano-scale. This leads to the formation of grain boundary kinks and triple junctions that induce additional structural defects and turn the overall grain boundary interface electrically active. The possible origin of such a grain boundary dissociation, as well as its impact on the electrical activity, is discussed. [ABSTRACT FROM AUTHOR]

Ni/Al nanolaminates are reactive materials with customizable combustion characteristics. A common approach to synthesize the repeating Ni and Al nanolayers is physical vapor deposition, which often results in columnar grains with ⟨ 111 ⟩ texture and grain diameters on the order of a single layer thickness. Changes in grain size have been reported to affect combustion rates, yet the role of individual grain boundaries (GBs) on this process is unclear. Thus, this work investigates the role of the GB structure on atomic diffusion/dissolution and the resulting combustion reaction via molecular dynamics simulations. Nanolaminate combustion is simulated in bicrystal models containing columnar symmetric tilt GBs with ⟨ 111 ⟩ misorientation axis perpendicular to the Ni/Al interface. A range of GB misorientation angles is studied, and combustion in a Ni/Al nanolaminate without GBs is simulated for comparison. Combustion in bicrystal models reveals a rise in temperature with an exponential form prior to complete Al melting, while the model without GBs shows a linear temperature increase. Diffusion coefficients are measured for each bicrystal model, and separate Arrhenius fits are used to identify the first three combustion stages. Models containing higher energy GBs generally have higher diffusion coefficients and lower activation energies prior to complete melting of Al, while the GB structure shows little effect on dissolution after the Al layer melts. Thus, the GB structure plays a key role in Ni/Al nanolaminate ignition sensitivity but does not impact runaway combustion. [ABSTRACT FROM AUTHOR]

High-angle annular dark-field (HAADF) imaging and electron energy loss spectroscopy (EELS) in a Cs-corrected scanning transmission electron microscope were utilized to analyze the interfacial atomic structure of InAs/GaSb superlattices (SLs) grown by metalorganic chemical vapor deposition (MOCVD) on InAs substrates. Despite high growth temperature, narrow interface (IF) widths of less than 2.5 monolayers (MLs) and 3.8 MLs were extracted from HAADF and EELS, respectively, indicating that the IF quality of MOCVD-grown InAs/GaSb SLs is comparable to those grown by molecular beam epitaxy. GaAs-type IFs are considered to account for the narrow IF width. In addition, GaSb-on-InAs IFs were found to be sharper and more strained than InAs-on-GaSb IFs, which is correlated with the special gas supply and switching sequence during MOCVD growth. The strain profile deduced from the HAADF image suggests that little Sb is incorporated into InAs sublayers and 7% In is incorporated into GaSb sublayers. [ABSTRACT FROM AUTHOR]

Classical molecular dynamics simulations have been performed to study the atomic structures and thermal expansion of coordination shells in solid and liquid Invar alloys. Analysis of atomic structures reveals that there is an attraction between Fe-Ni nearest pairs, and that structural order still exists in the liquid Invar alloy. Fe—Ni bonds are found to have the smallest thermal expansion in the solid Invar alloy among three types of bonds, which plays an important role in the Invar effect. We also discover that the thermal expansion coefficient will gradually get close to the macroscopic level as the coordination shell number increases in Invar alloys. It is until the 5th coordination shell in the solid state and the 4th coordination shell in the liquid state that the thermal expansions of the coordination shells can reach the macroscale value. This study further promotes the understanding of the thermal expansions from the atomic scale. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs), which have been intensely studied due to their excellent mechanical properties, generally refer to alloys with multiple equimolar or nearly equimolar elements. According to this definition, Si-Ge-Sn alloys with equal or comparable concentrations of the three group IV elements belong to the category of HEAs. As a result, the equimolar elements of Si-Ge-Sn alloys likely cause their atomic structures to exhibit the same core effects of metallic HEAs such as lattice distortion. Here, we apply density functional theory (DFT) calculations to show that the SiGeSn HEA indeed exhibits a large local distortion effect. Unlike metallic HEAs, our Monte Carlo and DFT calculations show that the SiGeSn HEA exhibits no chemical short-range order due to the similar electronegativity of the constituent elements, thereby increasing the configurational entropy of the SiGeSn HEA. Hybrid density functional calculations show that the SiGeSn HEA remains semiconducting with a bandgap of 0.38 eV, promising for economical and compatible midinfrared optoelectronic applications. We then study the energetics of neutral single Si, Ge, and Sn vacancies and (expectedly) find wide distributions of vacancy formation energies, similar to those found in metallic HEAs. However, we also find anomalously small lower bounds (e.g., 0.04 eV for a Si vacancy) in the energy distributions, which arise from the bond reformation near the vacancy. Such small vacancy formation energies and their associated bond reformations retain the semiconducting behavior of the SiGeSn HEA, which may be a signature feature of a semiconducting HEA that differentiates from metallic HEAs. [ABSTRACT FROM AUTHOR]

Dislocations in perovskite oxides have important impacts on their physical and chemical properties, which are determined by their unique atomic environments. In the present study, the structure of dislocations in a 10° low-angle grain boundary of SrTiO3 that was fabricated in an N2 annealing atmosphere is characterized by spherical aberration-corrected scanning transmission electron microscopy and spectroscopy. We find that the dislocation cores are deficient in titanium (Ti) due to Sr substitution and under Ti occupancy. This differs from previously reported dislocation cores fabricated in an air annealing atmosphere, which show Ti enrichment. The presence of oxygen vacancies and partially reduced Ti are also detected in these Ti-deficient dislocation cores. These findings indicate that atomic structures of dislocations can be very different even when they have the same Burgers vectors. Controllable element segregation in the dislocations and grain boundaries via bicrystal engineering should be very useful for designing devices with novel functions. [ABSTRACT FROM AUTHOR]

We present variation of the magnetic properties of Fe77.8Nb0.2B14P6C2 amorphous alloys vitrified at different temperatures by changing the atomic structures dependent on the critical cooling rate. The thermophysical properties of the amorphous state achieved after quenching the melt with cold nitrogen atomization gas are compared with those obtained using hot nitrogen gas with a temperature corresponding to the supercooled liquid of the alloy above the glass transition (Tg) but below crystallization temperature (Tx). The differently vitrified Fe77.8Nb0.2B14P6C2 glasses represent different states of high pressure gas atomized amorphous powder at different temperatures obtained by adjusting the gas temperature during the atomization process. The magnetic properties of these different amorphous powders are also investigated. The saturation magnetic flux density of slowly cooled Glass2 is 1.38 T with 450 A/m coercivity corresponding to "semi-soft" magnetic materials. The fast cooled Glass1 powder shows typical soft magnetic properties with lower coercivity (174 A/m), even though the saturation magnetization flux densities are similar in both identical compositions of amorphous powder due to its entropy difference related to the formation of clusters. We can control the magnetic property of amorphous materials from soft to half-soft by adjusting freezing temperature and ordering of atoms. [ABSTRACT FROM AUTHOR]

A study of a transition from conventional multicomponent alloys to high-entropy alloys (HEAs) is important both for understanding the formation of HEAs and for proper evaluation of their potential with respect to that of conventional alloys. We report the main result of such a study performed on (TiZrNbNi)1−xCux metallic glasses (MG) over a broad concentration range x ≤ 0.52 encompassing both high-entropy-MGs and Cu-based MGs. A comprehensive study of the composition, homogeneity, thermal stability, atomic structure, electronic structure, and magnetic susceptibility of 11 alloys has been performed. Thermal analysis revealed a rather weak variation of thermal parameters and glass forming ability with x. The study of the atomic structure showed a linear variation of average interatomic distances and atomic volumes close to those predicted by Vegard's law. The coordination numbers and atomic packing fractions were constant throughout the explored concentration range. The electronic density of states (DOS) showed a split-band structure with DOS close to the Fermi level dominated with d-states of Ti, Zr, and Nb. Accordingly, magnetic susceptibility decreased linearly with x and extrapolated to that of Cu. Thus, the studied alloys show ideal solution behavior similar to that of binary Cu-Ti, Zr, and Hf MGs. The results are compared with those for (TiZrNbCu)1−xNix MGs and (CrMnFeCo)1−xNix alloys and their impact on understanding the transition from high-entropy-MGs to conventional MGs with the same composition is briefly discussed. [ABSTRACT FROM AUTHOR]

Induced Pt ferromagnetism in Fe 3 O 4 / Pt / Fe 3 O 4 epitaxial trilayer films has been investigated by means of X-ray magnetic circular dichroism (XMCD) at the Pt L 3 , 2 -edges at various temperatures from 300 K to 12 K , including the metal-insulator transition temperature of Fe 3 O 4 (T V ∼ 114 K). At all the temperatures, we observed clear XMCD signals due to Pt ferromagnetism, the amplitude of which was determined to be 0.39 μ B at 300 K and 0.52 μ B at 12 K for the sample with the Pt thickness of ∼ 2 nm. Interestingly, these values are comparable to or even greater than those in Pt/3 d -ferromagnetic-metal (Fe, Ni, Co, and Ni 81 Fe 19) junction systems. The results can be interpreted in terms of a possible Fe interdiffusion into the Pt layer and also possible Fe-Pt alloying due to its high-temperature deposition. [ABSTRACT FROM AUTHOR]

High entropy alloys (HEAs), or concentrated solid solution alloys, are chemically complex metallic solid solutions in which five or more elements occupy the same crystallographic lattice sites with nearly equal compositions. The high degree of chemical disorder gives rise to considerable local lattice distortions, atomic-level stresses, and complex electronic structure, resulting in interesting properties. We calculated the electronic structure and the atomic-level stresses of AlxTiyZryPdyCuyNiy, x = 0.5, y = 1 (Al0.5TiZrPdCuNi) HEA in the glassy phase using the density functional theory (DFT) approach. We also briefly discuss the electronic structure in its crystalline phase. Whereas it has been reported recently that the crystalline phase of this HEA is obtained as a metastable phase during the crystallization of a glassy phase, the crystalline phase was found to be unstable at T = 0 in the DFT calculation. For this reason, we focus mainly on the glassy phase in this work. The importance of charge transfer among elements on the atomic-level pressure and the role for atomic-level stresses to characterize the electronic and structural heterogeneity are discussed. [ABSTRACT FROM AUTHOR]

The electronic structure, magnetic properties, and atomic structure of SrVO 3 / PbTiO 3 superlattices along different crystallographic orientations are investigated using density functional theory. It is revealed that Ti ions in the PbTiO 3 layers exhibit a weak ferromagnetic order. Such ferromagnetism in the PbTiO 3 layers near the interface is related to charge transfer from V to Ti and the ferroelectric polarization of PbTiO 3. The electronic structure of the superlattices indicates that spin-polarized two-dimensional polar metals are obtained for all orientations. In addition, different superlattice orientations correspond to different bandwidths of 3 d orbitals of SrVO 3 due to the dimensional confinement effect. The present work suggests a possible scenario by which two-dimensional polar metals and the coupling between the structural, electronic, and magnetic degrees of freedom in oxide superlattices can be extensively explored. [ABSTRACT FROM AUTHOR]

The success in the synthesis of wafer-size single-crystal graphene enables a tremendous breakthrough in the development of graphene-based devices. Understanding the growth mechanism is essential for the design of suitable substrates to meet the demand of various applications. Here, we investigate the detailed growth process of the monolayer single-crystal graphene on Cu/Ni(111) and Ge(110) surfaces using scanning tunneling microscopy. The (3 × 3) R 30 ° surface structure on Cu/Ni(111) and 1 × 1 atomic structure on Ge(110) are found to match the graphene lattice along the armchair direction. These specific atomic arrangements dictate the quasiepitaxial nature of graphene growth on both substrates despite their apparent differences in native lattice geometry. [ABSTRACT FROM AUTHOR]

The atomic structure of (1 − x) PbTiO 3 - x Bi (Zn 0.5 Ti 0.5) O 3 (x = 0.1 , 0.2, 0.25) is investigated across the tetragonal to cubic phase transition by neutron powder diffraction measurements up to temperature T = 750 ° C. Both the long-range average structure and the local atomic distributions are studied from Rietveld refinements and atomic pair distribution function (PDF) analysis combined with reverse Monte-Carlo (RMC) modeling, respectively. In the tetragonal phase, the average structure is featured with a large shift of oxygen, which is responsible for an off-centering of cations. With increasing concentration x , the shift of the planar oxygen along the c -axis increases further. The increment of the oxygen displacement is larger than that of the Ti/Zn displacement. This makes the off-centering of cations larger at higher x , which enhances the stability of the tetragonal phase with higher transition temperature. On thermal displacements, the heaviest ion Pb/Bi in the structure exhibits the largest value and is also increased by the concentration x in both the tetragonal and cubic phases. The local structure from PDF and RMC modeling shows that the abnormal thermal displacements are due to a large distribution of Pb off-centering and a bond-length mismatch between Ti–O and Zn–O bonds. Based on these complementary local and average structures, a splitting between Ti and Zn displacements is discussed. [ABSTRACT FROM AUTHOR]

We investigate the atomic scale structure of m-plane InGaN quantum wells grown on bulk m-plane GaN templates and reveal that as the indium content increases there is an increased tendency for nonrandom clustering of indium atoms to occur. Based on the atom probe tomography data used to reveal this clustering, we develop a k · p model that takes these features into account and links the observed nanostructure to the optical properties of the quantum wells. The calculations show that electrons and holes tend to colocalize at indium clusters. The transition energies between the electron and hole states are strongly affected by the shape and size of the clusters. Hence, clustering contributes to the very large line widths observed in the experimental low temperature photoluminescence spectra. Also, the emission from m-plane InGaN quantum wells is strongly linearly polarized. Clustering does not alter the theoretically predicted polarization properties, even when the shape of the cluster is strongly asymmetric. Overall, however, we show that the presence of clustering does impact the optical properties, illustrating the importance of careful characterization of the nanoscale structure of m-plane InGaN quantum wells and that atom probe tomography is a useful and important tool to address this problem. [ABSTRACT FROM AUTHOR]