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Hexagonal boron nitride (h-BN) is recognized as a 2D wide bandgap material with unique properties, such as effective photoluminescence and diverse lattice parameters. Nitride alloys containing h-BN have the potential to revolutionize the electronics and optoelectronics industries. The energy band structures of three boron-containing nitride alloys—BxAl1−xN, BxGa1−xN, and BxIn1−xN—were calculated using standard density functional theory (DFT) with the hybrid Heyd–Scuseria–Ernzerhof (HSE) function to correct lattice parameters and energy gaps. The results for both wurtzite and hexagonal structures reveal several notable characteristics, including a wide range of bandgap values, the presence of both direct and indirect bandgaps, and phase mixing between wurtzite and hexagonal structures. The hexagonal phase in these alloys is observed at very low and very high boron concentrations (x), as well as in specific atomic configurations across the entire composition range. However, cohesive energy calculations show that the hexagonal phase is more stable than the wurtzite phase only when x > 0.5, regardless of atomic arrangement. These findings provide practical guidance for optimizing the epitaxial growth of boron-containing nitride thin films, which could drive future advancements in electronics and optoelectronics applications. [ABSTRACT FROM AUTHOR]

Digital alloy and random alloy Al0.85Ga0.15As0.56 Sb0.44 avalanche photodiodes (APDs) exhibit low excess noise, comparable to Si APDs. Consequently, this material is a promising multiplication layer candidate for separate absorption, charge, and multiplication structure APDs with high gain-bandwidth product. Characterization of the impact ionization coefficients of electrons (α) and holes (β) plays an important role in the simulation of avalanche photodiodes. The multiplication gain curves of eight p+-i-n+ and n+-i-p+ APDs covering a wide range of avalanche widths have been used to determine the electric field dependence of the impact ionization coefficients of Al0.85Ga0.15As0.56Sb0.44. A large impact ionization coefficient ratio between that of electrons to holes was seen across a wide electric field range. Simulations of the avalanche multiplication in these structures using a random path length (RPL) model gave good agreement with experimental results over almost three orders of magnitude, and a mixed injection method was employed to verify the extracted impact ionization coefficients. Interestingly, no difference in the impact ionization coefficients was seen between digital alloy and random alloy Al0.85Ga0.15As0.56Sb0.44. This knowledge of impact ionization coefficients is beneficial for the future utilization of the AlxGa1-xAsySb1-y material system. [ABSTRACT FROM AUTHOR]

[Display omitted] • A straightforward first-principles based method is proposed to determine the average electron band structure of disordered solids using supercell approach. • The average band gap and average effective mass of electron/hole in different valleys have been calculated for a number of alloys. • The method has the potential to explain and predict the experimental observations. • The method can be used to investigate the role of order/disorder in electronic properties of imperfect solids in one, two and three dimensions. In this paper, a straightforward first-principles based method is proposed to determine the average effective electron band structure of disordered solids using supercell approach and plane-wave basis. Calculations have been done by determining the expectation values of the supercell Hamiltonian in a primitive-cell-periodic basis. The formulation and implementation details are presented and discussed. Also, it is shown that, in the cases with small differences in bonding characteristics at atomic-scale resolution, the weighted average bands are almost continuous. Therefore, it is possible to calculate the average effective band gap and average effective mass of electron/hole in different valleys. Analysis of the results for a number of disordered compounds shows that the proposed technique has the potential to explain and predict the experimental observations. This method is a promising tool for the study of the role of order/disorder in the electronic properties of random alloys and 2D and 3D imperfect materials. [ABSTRACT FROM AUTHOR]

Thanks to a dedicated modelling of intensities, the depth sensitivity of X-ray photoemission is used to probe the segregation profile of aluminium at the (110), (100) and (111) low index surfaces of the body-centred Fe 0.85 Al 0.15 random alloy. Sputtered surface composition is close to the nominal bulk one, thus excluding preferential sputtering. Surface enrichment in aluminium upon annealing starts at around 700 K before reaching a stationary state above 1000 K. The average surface composition is close to Fe 0.5 Al 0.5 , corresponding to the B 2 CsCl structure of the phase diagram. The impacted depth, that is in the range of 2.5–3.5 nm, is quite significant. Although not evidenced previously in surface science conditions at FeAl single crystal surfaces, it is qualitatively in agreement with the segregation at grain boundaries and shear planes of Al-alloyed steels. This segregation tendency is rationalized through ab initio calculations. Unlabelled Image • Severe aluminium segregation above 700 K at the surfaces of bcc Fe 0.85 Al 0.15 • Photoemission determination of the concentration profile in a random alloy • Nanometer deep impacted layer with a Fe 0.5 Al 0.5 composition • Ab initio modelling of segregation trends [ABSTRACT FROM AUTHOR]

By combining Scanning Tunnelling Microscopy, Low Energy Electron Diffraction and X-ray Photoelectron Spectroscopy, it was found that the surface of A 2 random alloy Fe 0.85 Al 0.15 (1 1 0) is significantly influenced by the segregation of aluminium but also of carbon bulk impurities. Below ∼ 900  K, carbon segregates in the form of self-organized protruding stripes separated by ∼ 5  nm that run along the [ 0 0 1 ] B bulk direction and cover up to 34% of the surface. Their C 1s spectroscopic signature that is dominated by graphitic carbon peaks around 900 K. Above this temperature, the surface carbon concentration decays by redissolution in the bulk, whereas an intense aluminium segregation is observed giving rise to a hexagonal superstructure. The present findings is interpreted by a competitive segregation between the two elements. [ABSTRACT FROM AUTHOR]

III-(As, Sb) alloys are building blocks for various advanced optoelectronic devices, but the growth of their ternary or quaternary materials are commonly limited by spontaneous formation of clusters and phase separations during alloying. Recently, digital alloy growth by molecular beam epitaxy has been widely adopted in preference to conventional random alloy growth because of the extra degree of control offered by the ordered alloying. In this article, we provide a comparative study of the optical characteristics of AlAsSb alloys grown lattice-matched to GaSb using both techniques. The sample grown by digital alloy technique showed stronger photoluminescence intensity, narrower peak linewidth, and larger carrier activation energy than the random alloy technique, indicating an improved optical quality with lower density of non-radiative recombination centers. In addition, a relatively long carrier lifetime was observed from the digital alloy sample, consistent with the results obtained from the photoluminescence study. [ABSTRACT FROM AUTHOR]

The relationships of structural, magnetic, and electronic properties of bimetallic RhPt (n = 0-55) clusters with cuboctahedral structure as varying compositions have been investigated using density functional theory calculations. Our results indicate that the Pt atoms tend to segregate to the surface, especially locating at the vertex site, while the Rh atoms prefer to the core site. In random alloy structures, RhPt cluster has the lowest excess energy of −2.49 eV. However, the ordered core-shell structure, Rh@Pt, has much lower excess energy of −5.16 eV. In addition, our calculations have indicated that the total magnetic moments of bimetallic RhPt clusters are weakened except the RhPt with respect to Rh cluster, while the average local magnetic moments of Rh and Pt atoms are mainly enhanced compared with their pure phases. As for the electronic properties, the d -band center (|ε|) of Rh and Pt as well as the s- , p- , d-partial density of states ( s- , p- , d-PDOS) reveal the relationship between the electronic properties and structural stabilities. Meanwhile, the d-PDOS has interpreted the varying magnetic moments. Graphical Abstract: The stable bimetallic RhPt (n = 0-55) clusters with cuboctahedral structure as varying compositions are investigated by density functional theory calculations. [ABSTRACT FROM AUTHOR]

Bimetallic nanoparticle catalysts of PtRh supported on carbon were synthesized using an electron beam irradiation reduction method. The PtRh nanoparticle catalysts were composed of particles 2–3 nm in size, which were well dispersed on the surface of the carbon support nanoparticles. Analyses of X-ray diffraction and scanning transmission electron microscopy–energy-dispersive X-ray spectroscopy revealed that the PtRh nanoparticles have a randomly alloyed structure. The lattice constant of the PtRh nanoparticles showed good correlation with Vegard's law. These results are explained by the radiochemical formation process of the PtRh nanoparticles. Catalytic activities of PtRh/C nanoparticles for ethanol oxidation reaction were found to be higher than those obtained with Pt/C. [ABSTRACT FROM AUTHOR]

In this work we review basic aspects of multiscale approaches for combining atomistic with continuous media descriptions and quantum mechanical with semiclassical drift-diffusion transport models for LED simulations. We show how hybrid coupling of the Green's function formalism with drift-diffusion simulations can give additional insight into device behaviour without compromising too much computational efficiency, and that the inclusion of atomistic tight-binding calculations in a multiscale framework can help in understanding specific features related to alloy fluctuations. [ABSTRACT FROM AUTHOR]

Abstract: When a mixture of H2PdCl4 and AgNO3 was co-reduced by ascorbic acid in aqueous solution in the presence of CTAB as a surfactant, aside from irregular shapes of Pd–Ag alloy particles, new cubic Pd–Ag alloy nanocrystals were prepared. The transmission electron microscopic (TEM)–energy dispersed X-ray spectroscopic (EDS) data at the atomic level suggest that Pd–Ag cubic alloys surrounded by {100} facets consist of substitutional solid solution and the arrangement of the solute Ag atoms is random. The Ag atomic content in Pd–Ag alloy must be less than ≈22% for preservation of the cubic structure. Optical properties of Pd–Ag alloys were characterized by observing the extinction spectra in the ultraviolet(UV)–visible(vis) range. [Copyright &y& Elsevier]

A method aimed at calculation of the electronic structure of an atomic cluster embedded either in an ideal crystal or in an effective medium representing a random alloy is developed on the basis of the TB-LMTO scheme. We discuss the construction of embedding potentials, the correct treatment of electrostatic interactions of the cluster with the surrounding medium, and the calculation of cluster energies. We derive the corrections to the band energy of a cluster. The method makes it possible to determine the electronic structure (charge distribution, local densities of states) and magnetic properties of the cluster and to extract impurity formation energies, and effective interactions between atoms and between magnetic moments. As an illustration, the method is applied to studies of magnetism of non-magnetic impurities in oxides, to calculations of the formation energies for impurities in a metal host and to the determination of the parameters of the Bruno-Zingales-Wang model of charge transfer and screening in metallic alloys. [ABSTRACT FROM AUTHOR]

Alloy formation is an advanced approach to improve desired properties that the monoelements cannot achieve. Alloys are usually designed to tailor intrinsic natures or induce synergistic effects by combining materials with distinct properties. Indeed, unprecedented properties have emerged in many cases, superior to a simple sum of pure elements. Here, we present Au-Ag alloy nanostructures with prominent catalytic properties in an electrochemical carbon dioxide reduction reaction (eCO 2 RR). The Au-Ag hollow nanocubes are prepared by galvanic replacement of Au on Ag nanocubes. When the Au-to-Ag ratio is 1:1 (Au 1 Ag 1 ), the alloy hollow nanocubes exhibit maximum Faradaic efficiencies of CO production in a wide potential range and high mass activity and CO current density superior to those of the bare metals. In particular, overpotentials are estimated to be similar to or lower than that of the Au catalyst under various standard metrics. Density functional theory calculations, machine learning, and a statistical consideration demonstrate that the optimal configuration of the *COOH intermediate is a bidentate coordination structure where C binds to Au and O binds to Ag. This active Au-Ag neighboring configuration has a maximum population and enhanced intrinsic catalytic activity on the Au 1 Ag 1 surface among other Au-to-Ag compositions, in good agreement with the experimental results. Further application of Au 1 Ag 1 to a membrane electrode assembly cell at neutral conditions shows enhanced CO Faradaic efficiency and current densities compared to Au or Ag nanocubes, indicating the possible extension of Au-Ag alloys to larger electrochemical systems. These results give a new insight into the synergistic roles of Au and Ag in the eCO 2 RR and offer a fresh direction toward a rational design of bimetallic catalysts at a practical scale.

In this work, a random distribution of Indium in a quantum well has been considered to study the effect on the energy gap of a GaN/InGaN/GaN LED device. Monte Carlo sampling technique has been used to generate hundreds of atomistic model structures of the device active region. In order to calculate pseudomorphic strain and internal deformations of the alloy, a multiscale method combining continuous media elasticity and atomistic valence force field models has been used. A multiphysic quantum/classical simulation coupling driftdiffusion with empirical tight-binding in order to compute the electron and hole states of the system has been performed. The reliable sp3d5s* parametrization has been used in the calculations of the eigenstates. We have found an energy gap difference of 50.9 meV for x (In) = 0.1 molar fraction between using virtual crystal approximation and a random distribution of In which increase with increasing Indium concentration. Moreover, electrons wave function seems to be more sensitive than holes due to Indium fluctuations [ABSTRACT FROM AUTHOR]

Abstract: Au–Pd bimetallic nanoparticles supported on carbon particles were synthesized by reduction of precursor ions in an aqueous solution irradiated with a high energy electron beam. The composition of the samples was analyzed by the inductively coupled plasma atomic emission spectrometry (ICP-AES), and the morphology of the samples was observed by the transmission electron microscope (TEM). TEM micrographs indicated that Au–Pd particles of ca. 5-nm were well dispersed on the surface of carbon particles of ca. 30-nm without any serious agglomeration. Addition of citric acid to the initial solution and high pH were found to be effective for formation of random alloy structure in the resultant bimetallic nanoparticles. The change in the bimetallic structure from core–shell to random alloy was identified by techniques of the X-ray diffraction (XRD) and the extended X-ray absorption fine structure (EXAFS). [Copyright &y& Elsevier]

• The (100) surface is the most stable surface for the random Al x Ti 1 - x N alloys. • Ti segregation to the surface is enhanced at high Al concentrations. • This helps explain the formation of a lamella structure in industrial coatings. • N vacancy segregation to the surface is similarly enhanced at high Al concentrations. The (100), (110) and (111) surface energies of random Al x Ti 1 - x N alloys with homogeneous concentration profile are determined in first-principles calculations. The (100) surface has the lowest energy of 1.25 J/m2 in the case of TiN and 1.32 J/m2 for cubic AlN and exhibit very little concentration dependence. The (110) and (111) surfaces have much higher energy for all the compositions. The segregation energies of Ti and Al were obtained for the (100) surface of pure TiN and cubic AlN as well as Al 0.5 Ti 0.5 N and Al 0.9 Ti 0.1 N random alloys. In the latter case, we have used two different methods: direct averaging of the substitution energies with respect to the local environment of the substitution site and the cluster expansion technique (CLE). We find that the segregation of Ti is favorable in the whole concentration range of random Al x Ti 1 - x N alloys. However, it is weak in almost the whole concentration range except in the Al-rich alloys: Al 0.9 Ti 0.1 N and cubic AlN. The strengthening of the surface segregation of Ti in the latter case is related to the sharp increase in phase separation tendency in Al x Ti 1 - x N alloys at compositions close to pure AlN. The increased tendency for Ti segregation close to pure AlN helps explain the formation of a lamella structure in industrially important Al x Ti 1 - x N coatings. As for nitrogen vacancies, their segregation energies are relatively small in the whole concentration range, but for pure AlN where they exhibit strong preference for the surface. The latter is obviously connected with the fact that cubic AlN has a high degree of ionic bonding and a vacancy creation on the nitrogen sublattice is highly energetically unfavorable, especially in the bulk due to a larger number of Al-N ionic bonds. [ABSTRACT FROM AUTHOR]