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Considering the elastoplastic deformation of a single-crystal copper substrate, based on the atomic scale, a mixed potential function (EAM and Morse) and the Verlet algorithm were used to simulate ...

This paper concerns the heuristic-based material stiffness optimization of frictional linear elastic contact problems for having control over the contact stress distribution, aiming to extend the material stiffness optimization to multiple loading conditions, in which each of the loadings acts solely on the structures. A decrease level of the variance of the contact stress is introduced and a weighted sum of the decrease levels under all load cases is constructed as the objective function. The individual criterion for contact problems with multiple contact regions is addressed. The worst case design is adopted for multiple load cases, and an extreme reference stress, which is the highest stress level of the subdomain under all load cases, is defined to control the Young’s modulus modification process in a finite element framework. Through three numerical examples, it is demonstrated how an even distribution of the contact stress can be obtained for contact problems subjected to multiple load cases with single or multiple contact regions. Some new features of the material stiffness optimization with multiple loading conditions are also illustrated.

Young’s modulus distribution, a significant parameter of a functionally graded material, is investigated to reduce the stress concentration. An evolutionary optimization algorithm of Young’s modulus is developed. A power law function is adopted to control the Young’s modulus evolution process, and the selection criterion of the power law index is presented and evaluated with an evaluation model. The degree of the stress concentration is represented by the stress concentration factor and is defined as the objective function. A finite element analysis is performed to obtain the stress distribution. The effectiveness of the Young’s modulus design for reducing the stress concentration is verified based on two cases. The results indicate that the stress concentration factor together with the maximum stress could be reduced simultaneously. The evolutionary optimization algorithm of Young’s modulus developed in this paper provides an effective approach for the optimal design of functionally graded material for stress concentration reduction.

Purpose: This report aims to characterize ocular changes in a case of ocular siderosis with iron toxicity using multimodal imaging and electroretinography. Methods: A 34-year-old woman presented with ocular siderosis of the left eye following penetrating injury with an iron-containing foreign body. The patient’s uncorrected visual acuities were 20/60 and 20/150 in the right and left eye, respectively, with abnormal pupillary function and presence of a cataract in the left eye. She underwent successful intraocular foreign body removal and cataract surgery with no postoperative complications. Cone contrast threshold (CCT), full-field electroretinogram, spectral-domain optical coherence tomography (OCT), and OCT angiography (OCTA) were used to characterize ocular alterations preoperatively and postoperatively. Results: CCT color vision testing showed abnormal color vision, and OCTA revealed increased vascular flow density associated with the foreign body. Conclusions: CCT color vision testing, OCTA, OCT, and full-field electroretinogram can characterize retinal changes in cases of ocular siderosis.

Contact stress distribution is sensitive to the interface shape and the material stiffness. A combination of the interface shape and the material stiffness is investigated to obtain a uniform conta...

The characteristics of contact interfaces such as the distribution uniformity of the contact pressure and the effective contact area play a crucial role in engineering equipment. To investigate the influences of the variable material stiffness optimization (VMSO) design on the contact characteristics of the contact interfaces in an assembly, an heuristic-based VMSO algorithm is developed in this paper. A bi-objective function is defined by including both the distribution uniformity of the contact pressure and the effective contact area. A single bolted joint model is adopted as a design example. The results indicate that optimizing the stiffness of the materials around the contact interface is an effective approach to enhance the distribution uniformity of the contact pressure, increase the effective contact area and decrease the maximum contact pressure. Furthermore, the improvement effectiveness provided by the proposed variable stiffness design is better than that provided by the traditional variable thickness design.

Significance The investigation of protein-based materials has provided a better understanding of living systems and has led to the development of ubiquitous modern technologies. Within this context, unique cephalopod proteins called reflectins have exhibited promise for biophotonics and bioelectronics applications, but the exploration of reflectins as materials has been hindered by an incomplete understanding of their structures and properties. Here, we resolve the molecular-level structure of a model reflectin variant, establish a straightforward approach to controlling the assembly of this protein, and describe a correlation between its structural characteristics and light-manipulating properties. Taken together, our findings advance current understanding of reflectin-based materials, provide insight into the color-changing capabilities of cephalopods, and afford new opportunities in biochemistry, cellular biology, bioengineering, and optics., Naturally occurring and recombinant protein-based materials are frequently employed for the study of fundamental biological processes and are often leveraged for applications in areas as diverse as electronics, optics, bioengineering, medicine, and even fashion. Within this context, unique structural proteins known as reflectins have recently attracted substantial attention due to their key roles in the fascinating color-changing capabilities of cephalopods and their technological potential as biophotonic and bioelectronic materials. However, progress toward understanding reflectins has been hindered by their atypical aromatic and charged residue-enriched sequences, extreme sensitivities to subtle changes in environmental conditions, and well-known propensities for aggregation. Herein, we elucidate the structure of a reflectin variant at the molecular level, demonstrate a straightforward mechanical agitation-based methodology for controlling this variant’s hierarchical assembly, and establish a direct correlation between the protein’s structural characteristics and intrinsic optical properties. Altogether, our findings address multiple challenges associated with the development of reflectins as materials, furnish molecular-level insight into the mechanistic underpinnings of cephalopod skin cells’ color-changing functionalities, and may inform new research directions across biochemistry, cellular biology, bioengineering, and optics.

A bionic hierarchy generative design algorithm inspired by the leaf vein growth process is presented for the layout design of heat conduction channels. The design domain is discretized based on the element-free Galerkin (EFG) method. The generations of main channels and lateral channels are separated. The effectiveness of the developed bionic hierarchy generative design approach is investigated based on the general “volume-to-point” heat conduction problem.

A generative method inspired by leaf venation is presented for the layout design of heat conduction channels. This method, which is based on the simulation of the growth process of leaf venation, also employs the element-free Galerkin (EFG) method to discretize the design domain for the heat conduction structures. Using the EFG method, the growth of each cooling branch follows any arbitrary direction. In addition, a divergence criterion for the cooling branches is presented. The potential effectiveness and efficiency of this generative optimization design approach is investigated through a numerical examination of the “volume-to-point” heat conduction problem.

Material stiffness, a significant parameter of a contact interface, is investigated to improve the uniformity of the contact pressure. A contact interface material stiffness optimization design algorithm is developed based on the modified solid isotropic material with the penalization (SIMP) method. The uniformity of the contact pressure field is represented by its variance and is defined as the optimization objective. A node-to-node frictionless elastic contact theory is adopted to perform the contact analysis. The effectiveness of the interface material stiffness design for improving the uniformity of the contact surface is verified based on two contact cases. Because the relationship between the material stiffness and the hard-and-soft degree of a contact interface is always a positive correlation, the results in this paper could be extended so that the design of the contact interfaces’ hard-and-soft degree will improve the distributing uniformity of the contact surface.

Air source heat pumps (ASHPs) have been increasingly used to promote energy savings and reduce environmental pollution. However, the evaporator frosting is one of the largest problems in ASHP systems during the heating operation. To examine this issue, a novel frost-free ASHP system has been developed. Nonetheless, the system performance and energy consumption are significantly dependent on the climate conditions. This research aims to identify the characteristics of the novel frost-free ASHP system with radiant floor heating in three different climate zones, China. TRNSYS 17.0 software was employed to investigate the seasonal performance of the new system based on the typical envelope thermal characteristic parameters in the entire heating period in three cities, i.e. Beijing (cold A zone), Xi'an (cold B zone), and Chengdu (hot summer and cold winter zone), located in different climate zones, China. The results showed that the heating seasonal performance factors (HSPFs) of the studied system were 3.9%, 1.9% and 9% higher than the conventional system in Xi'an, Beijing and Chengdu, respectively. It was concluded that the system could operate effectively and reduce substantial energy consumption in comparison with the conventional ASHP system for space heating in cold climate zones.

A deep learning approach combining with the traditional solid isotropic material with penalization (SIMP) method is presented in this paper to accelerate the topology optimization of the conductive heat transfer. This deep learning predictor is structured based on the deep fully convolutional neural network. The validity and accuracy of this deep learning approach is investigated based on the typical ‘Volume-Point’ heat conduction problems. The time consumption of the optimization process will be reduced significantly by introducing the deep learning approach.

Emergent physical properties often arise at interfaces of complex oxide heterostructures due to the interplay between various degrees of freedom, especially those with polar discontinuities. It is desirable to explore if these structures may generate pure and controllable spin currents, which are needed to attain unmatched performance and energy efficiency in the next-generation spintronic devices. Here we report the emergence of a spin-polarized two-dimensional electron gas (SP-2DEG) at the interface of two insulators, SrTiO3 and PbZr0.2Ti0.8O3. This SP-2DEG is strongly localized at the interfacial Ti atoms, due to the interplay between Coulomb interaction and band bending, and can be tuned by the ferroelectric polarization. Our findings open a door for engineering ferroelectric/insulator interfaces to create tunable ferroic orders for magnetoelectric device applications and provide opportunities for designing multiferroic materials in heterostructures.

Taking the influence of alloying elements into consideration, a hardness prediction model based on a newly proposed parameter named actual carbon diffusion time (ACDT), which was calculated by combining temperature history with carbon diffusivity, is developed in this paper. The hardness distribution was directly derived from a 3D thermal model, which was constructed to simulate the laser surface hardening of AISI 1045, and from which the temperature history was also obtained. Using this 3D thermal model, the geometric characteristics after laser hardening (e.g., the width of the hardened layer, the depth of the phase change layer) were determined according to the martensitic transformation. The influences of the scanning speed and the laser power on the geometric characteristics were investigated, and the relations among the geometric characteristics after laser hardening were further determined. The laser hardening experiments with various parameters were conducted, and it was found that the hardness can be accurately predicted using the developed hardness prediction model (R-squared, 97.0%). The proposed parameter ACDT, as the core of the hardness prediction model in this paper, broadens the way for hardness prediction in laser hardening with the alloying effect involved.

An investigation into the material stiffness design for enhancing the uniformity of the contact stress is conducted in this paper. A bidirectional evolutionary optimization design approach for interface material stiffness is developed, in which the standard deviation of the contact stress is defined as the objective function and the Young's modulus is treated as the design variable. A design case of a single bolted joint verifies that the proposed bidirectional material stiffness optimization approach can effectively improve the uniformity of the contact stress. A region-averaging treatment is proposed as the post-processing of the optimized Young's modulus distribution to make the optimized structure more manufacturable. The capabilities for homogenizing the contact stress distribution with various geometry sizes are addressed. A comparison study with the interface shape optimization indicates that with nearly the same improvement of the standard deviation of the contact stress, the material stiffness design around the contact region is more effective on enlarging the effective contact area and is much more computationally efficient than the interface shape optimization.

Although monitoring and diagnosis of fetal diseases in utero remains a challenge, metabolomics may provide an additional tool to study the etiology and pathophysiology of fetal diseases at a functional level. In order to explore specific markers of fetal disease, metabolites were analyzed in two separate sets of experiments using amniotic fluid from fetuses with Down syndrome (DS) as a model. Both sets included 10‑15 pairs of controls and cases, and amniotic fluid samples were processed separately; metabolomic fingerprinting was then conducted using UPLC‑MS. Significantly altered metabolites involved in respective metabolic pathways were compared in the two experimental sets. In addition, significantly altered metabolic pathways were further compared with the genomic characters of the DS fetuses. The data suggested that metabolic profiles varied across different experiments, however alterations in the 4 metabolic pathways of the porphyrin metabolism, bile acid metabolism, hormone metabolism and amino acid metabolism, were validated for the two experimental sets. Significant changes in metabolites of coproporphyrin III, glycocholic acid, taurochenodeoxycholate, taurocholate, hydrocortisone, pregnenolone sulfate, L‑histidine, L‑arginine, L‑glutamate and L‑glutamine were further confirmed. Analysis of these metabolic alterations was linked to aberrant gene expression at chromosome 21 of the DS fetus. The decrease in coproporphyrin III in the DS fetus may portend abnormal erythropoiesis, and unbalanced glutamine‑glutamate concentration was observed to be closely associated with abnormal brain development in the DS fetus. Therefore, alterations in amniotic fluid metabolites may provide important clues to understanding the etiology of fetal disease and help to develop diagnostic testing for clinical applications.

The slip surface has a significant effect on the tribological performances of a slider bearing and a hydrodynamic journal bearing. Less attention has been paid to the influence of a boundary slip on a hybrid journal bearing. However, hybrid journal bearings are increasingly used due to their intrinsic advantages. The effects of slip surface on the performances of a hybrid journal bearing are studied in this work. The affecting rule of both the slip-region location and the size on the load-carrying capacity is obtained. Only a well-designed slip surface could improve the tribological performances of hybrid journal bearings. This work could provide a valuable guide for the design of a slip surface in high-speed hybrid journal bearings.

Films from the cephalopod protein reflectin demonstrate multifaceted functionality as infrared camouflage coatings, proton transport media, and substrates for growth of neural stem cells. A detailed study of the in vitro formation, structural characteristics, and stimulus response of such films is presented. The reported observations hold implications for the design and development of advanced cephalopod-inspired functional materials.

This study proposes a new topology optimization solution providing designers with choices for feasible stiffener layouts inside large-scale containers of garbage trucks. Firstly, the mathematical expressions of loading conditions inside garbage containers are derived. Then, a growth-based layout optimization framework is built, taking inspiration from the morphology of plant ramifications. The principles of the highly effective but individual design rules of existent leaf venation layout problems are explored and transferred into analytical laws. Based on this, an evolutionary algorithm is developed to simulate the load-adapted growth of stiffener layouts, which provides an approximately homogeneous stress distribution along the surface of self-optimizing structures. Unlike the conventional methods, the new approach needs neither the densest ground structure nor the modification of the existing finite element programs, it is fast, easy to apply and nearly constraint free. Finally, a case study is provided showing how a large-scale container structure can be designed by this extremely intelligent CAD approach.

Purpose The purpose of this paper is to study the influences of recess configurations on the performances of high-speed hybrid journal bearing. Hybrid journal bearing earns increasing attention in high-speed machine tool spindle owing to its intrinsic outstanding performances of low temperature rise and high stability. Design/methodology/approach To investigate the coupled effects of temperature, turbulence and the interaction between lubricant and journal/bearing bush, a thermal fluid-structure interaction approach is presented and validated by the experimental results. Findings Ladder-type recess has excellent tribological characteristics in decreasing temperature rise, improving stability and inhibiting cavitation, which are all beneficial to improve the performances of high-speed spindle system. Originality/value This work can be a valuable guide for the future high-speed hybrid journal bearing design.

Domain walls (DWs) have become an essential component in nanodevices based on ferroic thin films. The domain configuration and DW stability, however, are strongly dependent on the boundary conditions of thin films, which make it difficult to create complex ordered patterns of DWs. Here, it is shown that novel domain structures, that are otherwise unfavorable under the natural boundary conditions, can be realized by utilizing engineered nanosized structural defects as building blocks for reconfiguring DW patterns. It is directly observed that an array of charged defects, which are located within a monolayer thickness, can be intentionally introduced by slightly changing substrate temperature during the growth of multiferroic BiFeO3 thin films. These defects are strongly coupled to the domain structures in the pretemperature-change portion of the BiFeO3 film and can effectively change the configuration of newly grown domains due to the interaction between the polarization and the defects. Thus, two types of domain patterns are integrated into a single film without breaking the DW periodicity. The potential use of these defects for building complex patterns of conductive DWs is also demonstrated.

We have developed a simple spin coating method to make high-quality nanoporous photoelectrodes of monoclinic BiVO4 and studied the ability of these electrodes to transport photogenerated carriers to oxidize sulfite and water. Samples containing molybdenum and featuring [001] out-of-plane crystallographic texture show a photocurrent and external quantum efficiency (EQE) for sulfite oxidation as high as 3.1 mA cm−2 and 60%, respectively, at 1.23 V versus reversible hydrogen electrode. By using an optical model of the electrode stack to accurately determine the fraction of electrode absorptance due to the BiVO4 active layer, we estimate that on average 70 ± 5% of all photogenerated carriers escape recombination. A comparison of internal quantum efficiency as a function of film processing, illumination direction, and film thickness shows that electron transport is efficient and hole transport limits the photocurrent (hole diffusion length 64% at 1.23 V. The electrodes quickly photocorrode during water oxidation but show good stability during sulfite oxidation and indefinite stability in the dark. By improving the hole transport efficiency and coating these nanoporous BiVO4 films with an appropriate protective layer and oxygen evolution catalyst, it should be possible to achieve highly efficient and stable water oxidation at a practical pH.

A novel heteroepitaxial growth technique, quasi-van der Waals epitaxy, promises the ability to deposit three-dimensional GaAs materials on silicon using two-dimensional graphene as a buffer layer by overcoming the lattice and thermal expansion mismatch. In this study, density functional theory (DFT) simulations were performed to understand the interactions at the GaAs/graphene hetero-interface as well as the growth orientations of GaAs on graphene. To develop a better understanding of the molecular beam epitaxy-grown GaAs films on graphene, samples were characterized by x-ray diffraction (θ–2θ scan, ω-scan, grazing incidence XRD and pole figure measurement) and transmission electron microscopy. The realizations of smooth GaAs films with a strong (111) oriented fiber-texture on graphene/silicon using this deposition technique are a milestone towards an eventual demonstration of the epitaxial growth of GaAs on silicon, which is necessary for integrated photonics application.

Purpose – The purpose of this paper is to study the influence of large-area texture/slip surface, especially the area and position of large-area texture surface on journal bearing, and improve the tribological performances of journal bearing. Design/methodology/approach – A modified texture/slip numerical boundary condition with double parameters is presented and is applied onto the region where surface textures locate to represent the impact of actual texture/slip surface. A phase change condition is used to analyze cavitation phenomena. Findings – The global/cumulative texture effect can be represented by applying texture/slip condition onto the region where it locates. The area and position of texture/slip surface would significantly affect the cavitation and load-carrying capacity. Texture/slip surface would not affect the pressure and load-carrying capacity when it locates at cavitation zone. The effect of texture/slip surface on load-carrying capacity would be beneficial if it locates at the pressure rise region, but its effect would be adverse if it locates at the pressure drop region. Well-designed texture/slip surface can improve tribological performances. Originality/value – The developed texture/slip boundary condition can be a suitable and useful tool to analyze the effect of large-area texture/slip surface and especially to optimize the area and position of large-area texture surface. This approach can be complementary to conventional approach which is used to analyze the influence of textures’ real configurations and parameters.

Emergent physical properties often arise at interfaces of complex oxide heterostructures due to the interplay between various degrees of freedom, especially those with polar discontinuities. It is desirable to explore if these structures may generate pure and controllable spin currents, which are needed to attain unmatched performance and energy efficiency in the next-generation spintronic devices. Here we report the emergence of a spin-polarized two-dimensional electron gas (SP-2DEG) at the interface of two insulators, SrTiO3 and PbZr0.2Ti0.8O3. This SP-2DEG is strongly localized at the interfacial Ti atoms, due to the interplay between Coulomb interaction and band bending, and can be tuned by the ferroelectric polarization. Our findings open a door for engineering ferroelectric/insulator interfaces to create tunable ferroic orders for magnetoelectric device applications and provide opportunities for designing multiferroic materials in heterostructures., Two-dimensional electron gases that form in some complex oxide heterostructures may have useful functional behavior due to the interaction of the parent materials. Here the authors show that PZT/STO interfaces can host a spin-polarized electron gas, even though the bulk materials are nonmagnetic.

Van der Waals growth of GaAs on silicon using a two-dimensional layered material, graphene, as a lattice mismatch/thermal expansion coefficient mismatch relieving buffer layer is presented. Two-dimensional growth of GaAs thin films on graphene is a potential route towards heteroepitaxial integration of GaAs on silicon in the developing field of silicon photonics. Hetero-layered GaAs is deposited by molecular beam epitaxy on graphene/silicon at growth temperatures ranging from 350 °C to 600 °C under a constant arsenic flux. Samples are characterized by plan-view scanning electron microscopy, atomic force microscopy, Raman microscopy, and X-ray diffraction. The low energy of the graphene surface and the GaAs/graphene interface is overcome through an optimized growth technique to obtain an atomically smooth low­ temperature GaAs nucleation layer. However, the low adsorption and migration energies of gallium and arsenic atoms on graphene result in cluster-growth mode during crystallization of GaAs films at an elevated temperature. In this paper, we present the first example of an ultrasmooth morphology for GaAs films with a strong (111) oriented fiber-texture on graphene/silicon using quasi van der Waals epitaxy, making it a remarkable step towards an eventual demonstration of the epitaxial growth of GaAs by this approach for heterogeneous integration.

Temperature-dependent photoluminescence of nitrogen-doped p-type Mg x Zn1−x O nanocrystalline thin film grown on c-plane sapphire substrate by rf plasma-assisted molecular beam epitaxy is investigated. P-type behavior is confirmed by both Hall effect and Seebeck measurements. Structural defect-related bound excitonic emission peak is distinguished at around ~50 meV lower than peak energy of the near band edge neutral acceptor bound excitonic emission. Typical ‘S shape’ behavior of energy position versus temperature is observed due to polarization-induced internal field. Nitrogen-related acceptor ionization energy is calculated to be ~180–200 meV.

Knowing the movement forms of lubricant during lubricating process should be useful and helpful to understand lubrication mechanism, so a visualisation apparatus improved from classical particle image velocimetry was presented to achieve it in this study. The effects of rotational speed and supply pressure on lubricant's velocity field were discussed and tested. Velocity size of lubricant increased with rotational speed and supply pressure. Velocity angle increased with rotational speed but decreased with supply pressure. Experimental results agreed well with theoretical predictions. This test apparatus can be useful and suitable for the visualisation of flow field during lubricating process. Copyright © 2014 John Wiley & Sons, Ltd.

A supervised deep learning predictor was developed to directly, intelligently, and instantaneously infer conductive heat transfer topologies. The architecture of the proposed supervised predictor consists of an encoder to decrease the dimensionality of the input data and a decoder. The high accuracy of the predictor is enabled by three parallel linked supervised deep learning predictors. Once the predictor has been trained and the physical parameters of the heat conduction problem, such as the boundary and constraint conditions, have been provided as input, the predictor directly and instantly outputs the optimized topology.

Since it's difficult to study the fluid/structure interactions in a rotor-bearing system using the conventional method, a new transient analysis method combining computational fluid dynamics and fluid–structure interaction was applied based on actual physical model. Both thermal influence and cavitation were studied. A comparison with the published experimental results was presented and discussed, and theoretical predictions agreed well with the experimental results. Four rotor-bearing systems with different grooves were studied. This developed method can be a very useful tool for the study on the bearing lubrication problem, and can effectively and accurately predict the transient lubrication process.

Nanoscale materials have been intensely studied since the discovery that the optical properties of semiconductor nanoparticles are size dependent. This and subsequent research has demonstrated that a given physical property of a particle exhibits a size dependence when the size becomes comparable to its characteristic length scale. Examples of relevant length scales include the de Broglie wavelength and/or the mean free path of electrons, phonons, and elementary excitations, all of which typically range from one to a few hundred nanometers. The ability to tune a wide variety of properties by controlling the particle size has spurred the development of novel chemistries for preparing nanostructured elements and compounds with goals of precisely controlling size, shape, and ligand shell. As the size of a nanocrystal decreases, the ratio of bulk to surface atoms decreases. This progression increases the relative contribution of the surface free-energy relative to the volume free-energy of the bulk structure, such that distortions from bulk equilibrium structures might be expected as the nanoparticle size decreases. Unfortunately, while researchers have demonstrated the ability to prepare ordered lattices of nanoparticles, the isolation of lattices of nanoparticles with long-range atomic periodicity is rare. Hence detailed atomic structures and, in turn, the size-structure-property relationships of most nanoparticle systems cannot readily be determined. Recently we reported that the intergrown compounds [(MSe)1+y]m(TSe2)n, with M= {Pb, Bi, Ce} and T= {W, Nb, Ta} self-assemble from designed precursors. The values of m and n represent, respectively, the number of MSe and TSe2 structural units of the unit cell of the superstructure and y describes the misfit between these structural units. As reported herein, the long-range structural order along the modulation direction permits us to determine the atomic structure of these precisely defined one-dimensional (1D) nanolaminate structures as a function of m and n using a combination of scanning transmission electron microscopy (STEM) high-angle annular dark-field (HAADF) imaging and X-ray diffraction (XRD) with Rietveld refinement. STEM-HAADF images of the first five [(PbSe)1.00]m(MoSe2)n compounds in the family where m= n are shown in Figure 1 along with aggregate intensity plots used to quantify the PbSe intraand inter-pair distances. All have a regular periodic structure along the modulated axis with well-defined layers of PbSe and MoSe2. The STEM images show ordered domains of PbSe with characteristic dimensions of a single structural unit along the layering direction and tens of nanometers perpendicular to the layering direction, with random in-plane rotational variants both within a layer and between layers. The orientations of the MoSe2 domains are more difficult to discern from the STEM images, but rotational variants have been observed between individual MoSe2 structural units. The STEM-HAADF images reveal a distortion of the PbSe layers, with the atomic planes grouped into pairs rather than being evenly spaced as expected for the equilibrium (bulk) rock salt structure. The distortion is most evident in the structural variant (m, n)= (2, 2) and decreases in magnitude until it can no longer be observed for (5, 5).

The structures of three new misfit layer compounds, [(PbSe)0.99]1[WSe2]1, [(PbSe)1.00]1[MoSe2]1, and [(SnSe)1.03]1[MoSe2]1, prepared as thin films from designed elementally modulated reactant precursors, have been investigated by synchrotron X-ray diffraction and scanning transmission electron microscopy. This is the second report of a misfit layer compound based on tin selenide and the first structure determinations of tungsten- and molybdenum-containing misfit layer compounds. The compounds have mismatches in both the a- and b-axis (in-plane) lattice parameters of the component structural units, which result in misfit parameters, δ, both greater and smaller than zero. Pole figures of hk0-type reflections indicate that c-axis-oriented (basal plane) dichalcogenide-structured units are randomly oriented within the a-b plane. The widths of diffraction peaks of type hk0, 00l, and hkl (h, k ≠ 0; l ≠ 0) indicate coherence lengths of approximately (6 to 7) nm within the a-b plane, the full thickness of the film along the c-axis, and (1 to 2) nm in mixed-index directions, respectively, consistent with random rotational disorder between the constituents, commonly termed turbostratic disorder in the clay literature. The intensities of 00l- and hk0-type diffraction peaks were modeled to determine the structure of atomic planes along the c axis and the projection of the constituent structures onto the a-b plane, respectively.

Single crystals of LiCoO2 have been grown by a vapor transport method at high temperature and normal atmospheric pressure. The plate-like single crystals have large (00l) facets (up to 1 mm2) and thicknesses ranging from 5 to 50 μm. A single-crystal X-ray diffraction study confirmed the trigonal R3m space group with lattice parameters a = 2.8150(3) A and c = 14.0516(6) A at room temperature. Electrical transport measurements indicated that as-grown crystals are highly insulating, with electrical resistivity in the order of TΩ cm at room temperature. This contrasts with the value of 5 Ω cm previously reported for a flux-grown crystal and suggests that vapor growth crystals may have fewer defects. Li-ion deintercalation of LiCoO2 crystals was carried out by a chemical extraction process. A quasi-in situ XRD approach was utilized to monitor the structural evolution during the Li-ion extraction process, which exhibited the progression of phases widely established for this system, but also shows evidence of i...

Alloying has shown enormous potential for tailoring the atomic and electronic structures, and improving the performance of catalytic materials. Systematic studies of alloy catalysts are, however, often compromised by inhomogeneous distribution of alloying components. Here we introduce a general approach for the synthesis of monodispersed and highly homogeneous Pt-bimetallic alloy nanocatalysts. Pt{sub 3}M (where M = Fe, Ni, or Co) nanoparticles were prepared by an organic solvothermal method and then supported on high surface area carbon. These catalysts attained a homogeneous distribution of elements, as demonstrated by atomic-scale elemental analysis using scanning transmission electron microscopy. They also exhibited high catalytic activities for the oxygen reduction reaction (ORR), with improvement factors of 2-3 versus conventional Pt/carbon catalysts. The measured ORR catalytic activities for Pt{sub 3}M nanocatalysts validated the volcano curve established on extended surfaces, with Pt{sub 3}Co being the most active alloy.

The influence of annealing time and annealing temperature under controlled partial pressure of selenium on the in-plane electrical transport properties of specimens of [(PbSe)0.99]1[WSe2]1 turbostratic nanolaminates was studied. The annealing treatments were found to be very effective in reducing carrier concentrations and improving carrier mobility in the annealed films, which is attributed to the reduction of compositional and structural defects. As a result, room temperature Hall mobilities greater than 60 cm2 V−1·s−1 are observed in spite of the small in-plane domain sizes (on the order of 10 nm) that are related to the turbostratic disorder. The technique appears promising for decreasing the concentration of kinetically trapped defects in these and related self-assembled nanostructures, a key challenge to evaluating the expected potential for controlling electrical and thermal transport properties via designed nanostructure in these and related materials.

Turbostratically disordered tungsten diselenide (WSe2) thin films with as few as two c-axis-oriented (basal plane) structural units were synthesized from modulated elemental reactants. By varying t...

We describe here a general synthesis approach for the preparation of new families of misfit layer compounds and demonstrate its effectiveness through the preparation of the first 64 members of the [(PbSe)0.99]m(WSe2)n family of compounds, where m and n are integers that were systematically varied from 1 to 8. The new compounds [(PbSe)1+y]m(WSe2)n were synthesized by annealing reactant precursors containing m layers of alternating elemental Pb and Se followed by n layers of alternating elemental W and Se, in which the thickness of each pair of elemental layers was calibrated to yield a structural bilayer of rock salt structured PbSe and a trilayer of hexagonal WSe2. The compounds are kinetically trapped by the similarity of the composition profiles and modulation lengths in the precursor and the targeted compounds. The structural evolution from initial reactant of layer elements to crystalline misfit layer compounds was tracked using X-ray diffraction. The crystal structures of new compounds were probed us...