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Boron nitride (BN) is a wide-bandgap material for various applications in modern nanotechnologies. In the technology of material science, computational calculations are prerequisites for experimental works, enabling precise property prediction and guidance. First-principles methods such as density functional theory (DFT) are capable of capturing the accurate physical properties of materials. However, they are limited to very small nanoparticle sizes (<2 nm in diameter) due to their computational costs. In this study, we present, for the first time, an important computational approach to DFT calculations for BN materials deposited on different substrates. In particular, we predict the total energy and cohesive energy of a variety of face-centered cubic (FCC) and hexagonal close-packed (HCP) boron nitrides on different substrates (Ni, MoS2, and Al2O3). Hexagonal boron nitride (h-BN) is the most stable phase according to our DFT calculation of cohesive energy. Moreover, an experimental validation equipped with a molecular beam epitaxy system for the epitaxial growth of h-BN nanodots on Ni and MoS2 substrates is proposed to confirm the results of the DFT calculations in this report. [ABSTRACT FROM AUTHOR]

Presently, thermal neutron detectors fabricated from boron-10 enriched hexagonal boron nitride (h-10BN) ultrawide bandgap semiconductor grown by metal organic chemical vapor deposition (MOCVD) hold the record high detection efficiency among all solid-state detectors at 59%. To overcome the short comings of MOCVD growth, including inherently low growth rate and unavoidable impurities such as carbon in metal organic source, we demonstrate here the growth of natural hexagonal boron nitride (h-BN) semi-bulk wafers using halide vapor phase epitaxy (HVPE), which is an established technique for producing GaN semi-bulk crystals at a high growth rate. Electrical transport characterization results revealed that these HVPE grown materials possess an electrical resistivity of 1 × 1013 Ω cm, and a charge carrier mobility and lifetime product of 2 × 10−4 cm2/V s. Detectors fabricated from a 100 μm thick h-BN wafer have demonstrated a thermal neutron detection efficiency of 20%, corresponding to a charge collection efficiency of ∼60% at an operating voltage of 500 V. This initial demonstration opens the door for mass producing high efficiency h-BN semiconductor neutron detectors at a reduced cost, which could create unprecedented applications in nuclear energy, national security, nuclear waste monitoring and management, the health care industry, and material sciences. [ABSTRACT FROM AUTHOR]

Although silicon carbide (SiC) is widely regarded as the material of choice for power electronics, the development of several new applications on the SiC material platform is currently explored. The integration of two dimensional (2D) materials, such as graphene and molybdenum disulfide (MoS 2) provides silicon carbide (SiC) with additional functionalities, allowing to expand its range of applications. This article reviews the state-of-the art methods for scalable growth of graphene and MoS 2 on SiC, specifically on the hexagonal polytypes. Some open research directions in materials integration have been also discussed, like the use of epitaxial graphene (Epi-Gr) as interlayer for van der Waals (vdW) epitaxy of GaN or Ga 2 O 3 on SiC substrates, and the growth of 2D forms of GaN materials by confined epitaxy at Epi-Gr/SiC interface. Finally, an overview of recently proposed electronics/optoelectronics applications of these material systems, specifically for high frequency electronics, quantum metrology, THz and UV detectors, is provided. This work can be a useful guide for silicon carbide community on these open research directions. [ABSTRACT FROM AUTHOR]

The precision control of monodisperse nanomaterials with spatially distinct functionalities and properties is of particular interest in materials science. Creating biocompatible/biodegradable nanoparticles that can be colloidally stable in aqueous solution further paves the way to a broad range of bio-related applications. In present work, we demonstrate the precise fabrication of aliphatic polycarbonate based one-dimensional (1D) cylinders and 2D platelet micelles using living crystallization-driven self-assembly (CDSA) by seeded growth method. By synthesizing aliphatic polycarbonate core-forming block copolymers with different corona-to-core ratios, excellent control over dimensions of 1D cylinders and 2D platelets with good uniformity is achieved through effectively epitaxial growth in ethanol based on the mass ratios of unimer-to-seed. Meanwhile, segmented nanoparticles with spatially-defined chemistries can further be prepared by sequential seeded growth approach. Moreover, these 1D/2D nanostructures are colloidally stable in water, and further show excellently biocompatible property towards L929 cells. These promising properties of polycarbonate-based micelles enable to a wide application as cargo vehicles in bio-related fields. [Display omitted] • Aliphatic polycarbonate core-forming block copolymers are prepared via sequential polymerizations. • Uniform 2D platelets are created by seeded growth using a BCP with short corona-to-core ratio. • 1D cylinders with low dispersity in length are fabricated by seeded growth using a BCP with long corona-to-core ratio. • The 1D and 2D nanostructures are colloidally stable in water and show excellent biocompatibility towards L929 cells. [ABSTRACT FROM AUTHOR]

Two-dimensional materials have become one of the central research topics of scientists around the world after the production of graphene – a monatomic layer of carbon. Currently, two-dimensional crystals are among the most promising materials for next-generation nanoelectronics and photonics. The exploration of the feasibility of 2D materials devices causes a deeper insight into the physical properties of these new materials and provides a starting point for the development of a number of important practical areas. Over the past few years, researchers have been paying increased attention to graphene-like materials of group IVA elements, such as silicene (Si), germanene (Ge), stanene (Sn), and plumbene (Pb). Experimental production and study of the unique properties of two-dimensional monatomic layers of carbon, silicon, germanium, tin, and lead on various substrates created the prerequisites for the development of new generation devices based on them. The wide possibilities for controlling their exotic electronic, magnetic, and optical properties through the choice of the substrate, the design and geometry of the two-dimensional layer, as well as by controlling the magnitude of elastic stresses, have made them a dominating topic for studying in the field of nanotechnology and materials sciences. This paper reviews the latest advances in growing silicene, germanene, stanene, and plumbene using epitaxial methods. Growth technologies for creation of high-quality two-dimensional structures of large area required for promising instrumentation area are considered in more detail. [ABSTRACT FROM AUTHOR]

Wei I et al. i reported that ferroelectricity could be enhanced in epitaxial Hf SB 0.5 sb Zr SB 0.5 sb O SB 2 sb films when the film thickness was decreased to 5 nm.[11] Cheema I et al. i reported the so-called "inverse size effect" accompanied by an enhancement in piezoelectricity,[51] which is generally related to ferroelectricity, with decreasing thickness of the Hf SB 0.8 sb Zr SB 0.2 sb O SB 2 sb films. Ferroelectricity is a material property that enables a large variety of device applications like nonvolatile memories, variable capacitors, sensors, actuators, and energy storage/harvesting devices.[[1], [3], [5]] In particular for the application in nonvolatile memories, but also for some of the other fields, an integration into a complementary metal-oxide-semiconductor process (CMOS) is of great benefit or even necessary. Kim I et al. i comparatively studied the ferroelectricity in Hf SB 0.5 sb Zr SB 0.5 sb O SB 2 sb films grown on sputtered and atomic-layer-deposited TiN electrodes,[33] and reported that the increased grain size of an ALD deposited (200)-textured TiN electrode was beneficial to improve ferroelectricity. Zacharaki I et al. i investigated ferroelectricity and reliability of TiN/Hf SB 0.5 sb Zr SB 0.5 sb O SB 2 sb /Ge capacitors,[43] and suggested that the suppression of the interfacial GeO SB x sb layer could attribute to the improved reliability of the metal-ferroelectric-Ge capacitors. [Extracted from the article]

The article presents a study on a design route for a direct three-dimensional to two-dimensional structural phase transition and electronic modulation in a chalcogenide semiconductor alloy system. It discusses the switching of the pseudo-isostructures by external stresses, synthesis of lead-tin-selenide alloy films, and electronic structure of these alloy films.

The article discusses increasing demand for faster telecommunication technologies calls for the shift of signal processing from electronic to optical domain. Topics include the strain induced by the lattice mismatch at the interface results in high concentration of defects; and the difference between the intrinsic bilayer sample and the layer-by-layer fabricated heterostructure has observed by microscopy.

In this article the author offers information of the epitaxial antiperovskite and perovskite heterostructures for materials design. Topics discussed include Engineered heterostructures formed by complex oxide materials are a rich source of emergent phenomena and technological applications; and important step for the development of functional antiperovskite/perovskite heterostructures, combining their unique characteristics such as topological properties for ultralow-power applications.

The article presents physics research on p-type transparent superconductivity in a layered oxide. Topics include development of p-type transparent conducting materials has been a challenging issue; the known p-type transparent conductors unsatisfied both of high transparency and high conductivity nor exhibit superconductivity; and transparent conductors (TCs) is one of the most important subjects not only for practical use but also for advances in materials science.

The article offers information about the invar behavior of a continuous film of Iron–platinum (FePt), along with mentions the transient expansion upon laser heating in femtosecond x-ray diffraction experiments. It discusses about the finite-element modeling of the mechanical response of FePt nanosystems confirms the morphology dependence of the dynamics.

The article demonstrates the three-dimensional superlattice engineering with block copolymer epitaxy. It discusses that three-dimensional superlattice formed by block copolymers micelles can be controlled by lithographically defined two-dimensional templates matching a crystallographic plane in the three-dimensional superlattice.

The article presents a research on zeolite nanosheets that have shown unprecedented opportunities for a wide range of applications such as developing facile methods for fabrication of uniform zeolite nanosheets remains a great challenge. Topics discussed include facile approach involving anisotropic etching with an aqueous solution of tetrapropylammonium hydroxide; and dynamic air-liquid interface–assisted self-assembly method and single-mode microwave heating.

The shapes of the recrystallization fronts observed during solid phase epitaxy (SPE) in line-shaped amorphized Si (a-Si) regions in single-crystal (001) and (011) Si are shown to exhibit a complex time evolution inconsistent with simple models in which regrowth behavior is determined exclusively by the competition between fixed-growth-rate lateral and vertical SPE. We find that the main features of our data for <110>-aligned a-Si lines may be explained by the propensity of the lateral and vertical growth fronts to form stable a-Si/{111} interfaces at their edges. These same a-Si/{111} interfaces have been previously implicated as the root cause of the trench-edge defects produced during the recrystallization of patterned a-Si regions bounded laterally by oxide-filled trenches. An extension of a nanofacet model recently developed to explain the trench-edge defects is shown to explain many of the observed recrystallization behaviors. [ABSTRACT FROM AUTHOR]

Thermal-field directed self-assembly (TDSA) of epitaxial self-assembled quantum dots (SAQDs) is the method of using spatially varying temperature patterns to influence SAQD growth kinetics and ultimately the order and positions of SAQDs. The effectiveness of TDSA in enhancing the size and spatial order or precision placement of single dot or dot cluster is investigated via a two dimensional (one dimensional surface) finite element based model of Ge dots grown on Si. Three different cases of heating are studied, namely, spatially constant heating, spatially periodic heating, and a Gaussian shaped hot spot. Statistical measures are used to study the evolution of quantum dot heights and spacings between the quantum dots for different temperatures and heating cases. Spatially periodic heating is investigated for a wavelength of about 185 nm corresponding to the wavelength of an excimer laser. In order to investigate the effectiveness of spatially periodic heating in enhancing the spatial and size order of the SAQD array, the results are compared with those obtained from spatially uniform heating. Simulations using Gaussian shaped hot spot are performed to demonstrate its effectiveness in placing a distinct dot at a desired location. Results from the simulations indicate that spatially periodic heating proves to be an effective means for producing an array of uniformly sized and spaced quantum dots for a broad range of temperatures. Also, the results from the simulations using Gaussian shaped hot spots show that such a form of heating can effectively place a distinct quantum dot near a desired location for a broad range of temperature values. [ABSTRACT FROM AUTHOR]

Crystalline silicon single quantum wells (QWs) with a minimum Si layer thickness of around 1 nm were fabricated by high temperature thermal oxidation of separation by implantation of oxygen (SIMOX) and epitaxial layer transfer (ELTRAN®) silicon-on-insulator (SOI) wafers. Not only Si thickness but also defect-free SOI materials may be important factors for observation of quantum-confined transition in the Si QWs. Si QWs fabricated from SIMOX SOI wafers showed strong interface-mediated luminescence, which is independent of Si thickness, at 1.63 and 1.49 eV in the Si thickness range from 1 to 7 nm. On the other hand, Si QWs fabricated from ELTRAN SOI wafers showed very strong thickness dependent luminescence in the range of 1.36–1.77 eV without interface-mediated luminescence, where the Si thickness range was 3–1 nm. The ability to detect quantum-confined luminescence seems to arise from the use of high-quality defect-free ELTRAN SOI wafers, from suppressed interface state luminescence by high temperature oxidation, and, possibly, from interface matching by crystalline silicon oxide. Hydrogen passivation suggests luminescence from a weak Si==O state at around 1.59 eV, but luminescence due to quantum confinement is more predominant in the ELTRAN Si QWs. [ABSTRACT FROM AUTHOR]

We report on the fabrication and electrical characterization of epitaxial metal-semiconductor junctions between Y1Ba2Cu3O7-δ (YBCO) (optimally doped and Zn doped) and (001) Nb:SrTiO3 with different Nb concentrations (0.05%, 0.1%, and 0.5%). The current-voltage characteristics of such epitaxial junctions are nonlinear and rectifying, and these are dramatically enhanced with decreasing Nb concentration and Zn doping. Indeed, for the case of 0.05% Nb:STO, reverse breakdown voltage as high as -18 V(-28 V) is realized for optimally doped (Zn doped) YBCO. These data are analyzed within the framework of thermionic emission/diffusion models for Schottky and metal-insulator-semiconductor-type junctions. [ABSTRACT FROM AUTHOR]

CdO(110) layers with a self-organized surface structure have been grown on (1010) sapphire (m Plane) substrates by metal-organic vapor phase epitaxy. The epitaxial relationships between layer and substrate have been determined and a crystallographic model that accounts for the CdO in-plane orientation, which results in a reduced lattice mismatch when the CdO[001] direction is perpendicular to the sapphire c axis, has been proposed. Although the measured lattice parameters indicate that the layers are almost fully relaxed, an anisotropic mosaicity is detected with symmetrical rocking curves attaining minimum values when measured along the CdO[110] direction. The layer morphology consists of a regular ridge-and-valley structure which defines, again, a preferential in-plane direction. The grooves run parallel to the CdO[001] axis and exhibit lateral surfaces sloped at 28° with respect to the (110) surface. The influence of growth temperature and VI/II molar ratio on the anisotropic mosaicity and morphology has been analyzed. [ABSTRACT FROM AUTHOR]

This paper presents a compact survey of the various material schemes and device structures that have been explored in the quest toward developing light-emitting diodes (LEDs) based on zinc oxide (ZnO) and related II-oxide semiconductors. Both homojunction and heterojunction devices have been surveyed. Material for fabricating these devices has been grown with a number of different techniques, such as pulsed laser deposition, molecular beam epitaxy, metal-organic chemical vapor deposition, and atomic layer epitaxy. This review also features a self-contained introduction to materials science and device processing technologies that are relevant for fabricating ZnO LEDs. These topics include dry and wet etching, contact formation, and optical doping of ZnO. Due to the overwhelming importance of p-type doping of ZnO for making electronic and optoelectronic devices, a separate short section on electrical doping of ZnO is also included. The rest of this paper describes several different attempts at making blue- and ultraviolet-emitting ZnO LEDs. These include simple pn-junction devices as well as more complicated heterostructure devices incorporating charge carrier barriers and quantum wells. [ABSTRACT FROM AUTHOR]

The planar electrodeposition of the metal anode decreases the contact area between the electrode and electrolyte, thus mitigating interfacial side reactions and benefiting the battery performance. The authors claimed the reversible epitaxial electrodeposition of zinc (Zn), which is a safe, low-cost and energy-dense battery anode material, on graphene with a low lattice mismatch for Zn. S14 to S16 in Ref. [1], one can see that the relative integrated intensities of the (0 0 2), (1 0 0) and (1 0 1) peaks or rings are approximately in accordance with those (37.5:22.8:100) in the power diffraction data of Zinc (PDF#99-0110) for the Zn deposits on both bare stainless steel and graphene-coated steel. The (0 0 2) SB Zn sb peaks or rings in the GIXRD patterns result from the Zn grains whose (0 0 2) planes make an angle of ~17.34° ( - = 18.144°-0.8°) with the sample surface, rather than from any (0 0 1)-oriented Zn grains. [Extracted from the article]

Directed self-assembly (DSA) of block copolymers (BCP) is one of the most promising patterning solutions for sub-10 nm nodes. While significant achievements are demonstrated in pattern fidelity for various applications (contact shrink, line patterning), some challenges are still needed to be overcome especially regarding the defect density reduction, in order to ensure DSA insertion in high-volume manufacturing. In particular, in the case of the graphoepitaxy approach, a remaining challenge is to solve the pattern-densities-related defect issue due to BCP film thickness variation inside the guiding template. In order to address this issue, a new DSA process flow called 'DSA planarization' is employed for contact-hole patterning, and consists in overfilling the guiding pattern cavities with a thick BCP film, followed by a plasma etch-back step. This new approach ensures a uniform control of the final thickness of the BCP inside guiding cavities of different densities, as demonstrated herein by AFM measurement. Thus, defect-free isolated and dense patterns for both contact shrink and multiplication are simultaneously resolved. Furthermore, the simulation results of BCP self-assembly overfilling the templates demonstrate that BCP domains are well-directed in vertical cylinders ordering inside guiding cavities, which confirms the experimental results and the viability of this approach. [ABSTRACT FROM AUTHOR]

Epitaxial chromium ferrite (Fe2CrO4), prepared by state-of-the-art oxygen plasma assisted molecular beam epitaxy, is shown to exhibit unusual electronic transport properties driven by the crystallographic structure and composition of the material. Replacing 1/3 of the Fe cations with Cr converts the host ferrimagnet from a metal into a semiconductor by virtue of its fixed valence (3+); Cr substitutes for Fe at B sites in the spinel lattice. By contrast, replacing 2/3 of the Fe cations with Cr results in an insulator. Three candidate conductive paths, all involving electron hopping between Fe2+ and Fe3+, are identified in Fe2CrO4. Moreover, Fe2CrO4 is shown to be photoconductive across the visible portion of the electromagnetic spectrum. As a result, this material is of potential interest for important photo-electrochemical processes such as water splitting. [ABSTRACT FROM AUTHOR]

Understanding of metal oxidation is critical to corrosion control, catalysis synthesis, and advanced materials engineering. Although, metal oxidation process is rather complicated, different processes, many of them coupled, are involved from the onset of reaction. Since first introduced, there has been great success in applying heteroepitaxial theory to the oxide growth on a metal surface as demonstrated in the Cu oxidation experiments. In this paper, we review the recent progress in experimental findings on Cu oxidation as well as the advances in the theoretical simulations of the Cu oxidation process. We focus on the effects of defects such as step edges, present on realistic metal surfaces, on the oxide growth dynamics. We show that the surface steps can change the mass transport of both Cu and O atoms during oxide growth, and ultimately lead to the formation of different oxide morphology. We also review the oxidation of Cu alloys and explore the effect of a secondary element to the oxide growth on a Cu surface. From the review of the work on Cu oxidation, we demonstrate the correlation of theoretical simulations at multiple scales with various experimental techniques. [ABSTRACT FROM AUTHOR]

The complex index of refraction in the spectral range of 0.74 to 4.5 eV is studied by variable-angle spectroscopic ellipsometry in ferroelectric K0.5Na0.5NbO3 films. The 20-nm-thick cube-on-cube-type epitaxial films are grown on SrTiO3(001) and DyScO3(011) single-crystal substrates. The films are transparent and exhibit a significant difference between refractive indices Δn = 0.5 at photon energies below 3 eV. The energies of optical transitions are in the range of 3.15–4.30 eV and differ by 0.2–0.3 eV in these films. The observed behavior is discussed in terms of lattice strain and strain-induced ferroelectric polarization in epitaxial perovskite oxide films. [ABSTRACT FROM AUTHOR]

We report on an experimental verification that emission properties of photocathodes can be manipulated through the engineering of the surface electronic structure. Ultrathin multilayered MgO/Ag(0 0 1)/MgO films were grown by pulsed laser deposition, tuning the thickness n of the flanking MgO layers to 0, 2, 3, and 4 monolayers. We observed an increase in quantum efficiency and simultaneous decrease in work function with layer thickness. The scale and trend direction of measurements are in good but not excellent agreement with theory. Angle resolved photoemission data for the multilayered sample n = 3 showed that the emission profile has a metallic-like momentum dispersion. Deviations from theoretical predictions [K. Németh et al., PRL 104, 046801 (2010)] are attributed to imperfections of real surfaces in contrast with the ideal surfaces of the calculation. Photoemissive properties of cathodes are critical for electron beam applications such as photoinjectors for Free Electron Lasers (FEL) and Energy Recovery Linacs (ERL). An ideal photoemitter has a high quantum efficiency, low work function, low intrinsic emittance and long lifetime. It has been demonstrated here that emission properties may be systematically tailored by control of layer thickness in ultrathin multilayered structures. The reproducibility of the emission parameters under specific growth conditions is excellent, even though the interfaces themselves have varying degrees of roughness. [ABSTRACT FROM AUTHOR]

The article discusses structure of two dimensional (2D) and three dimensional (3D) colloidal assembly. It talks about application of collidal assembly in various fields such as fundamental physics, materials science and energy migration, and mentions its characteristics features which include order, length scale and porosity. Topics include binary monolayers, non-close-packed monolayers, and colloidal epitaxy.

Constructing nanoparticles into well-defined structures at mesoscale and larger to create novel functional materials remains a challenge. Inspired by atomic epitaxial growth, we propose an "epitaxial assembly" method to form two-dimensional nanoparticle arrays (2D NAs) directly onto desired materials. As an illustration, we employ a series of surfactant-capped nanoparticles as the "artificial atoms" and layered hybrid perovskite (LHP) materials as the substrates and obtain 2D NAs in a large area with few defects. This method is universal for nanoparticles with different shapes, sizes, and compositions and for LHP substrates with different metallic cores. Raman spectroscopic and X-ray diffraction data support our hypothesis of epitaxial assembly. The novel method offers new insights into the controllable assembly of complex functional materials and may push the development of materials science at the mesoscale. [ABSTRACT FROM AUTHOR]

We grew epitaxial layers on 4H-silicon carbide (SiC) Si-face substrates with a 1° off-angle. The suppression of 3C-inclusion formation during growth at a high C/Si ratio was investigated, because a growth technique with a high C/Si ratio is needed to decrease residual nitrogen incorporation. 3C inclusions were generated both at the interface between the substrate and epitaxial layer, and during epitaxial growth. 3C-SiC nucleation is proposed to trigger the formation of 3C inclusions. We suppressed 3C-inclusion formation by performing deep in situ etching and using a high C/Si ratio, which removed substrate surface damage and improved the 4H-SiC stability, respectively. The as-grown epitaxial layers had rough surfaces because of step bunching due to the deep in situ etching, but the rough surface became smooth after chemical mechanical polishing treatment. These techniques allow the growth of epitaxial layers with 1° off-angles for a wide range of doping concentrations. [ABSTRACT FROM AUTHOR]

Materials integration in heterostructureswith novel propertiesdifferent from those of the constituents has become one of the mostpowerful concepts of modern materials science. Two-dimensional (2D)crystals represent a new class of materials from which such engineeredstructures can be envisioned. Calculations have predicted emergentproperties in 2D heterostructures with nanoscale feature sizes, butmethods for their controlled fabrication have been lacking. Here,we use sequential graphene and boron nitride growth on Ru(0001) toshow that lateral heteroepitaxy, the joining of 2D materials by preferentialincorporation of different atomic species into exposed 1D edges duringchemical vapor deposition on a metal substrate, can be used for thebottom-up synthesis of 2D heterostructures with characteristic dimensionson the nanoscale. Our results suggest that on a proper substrate,this method lends itself to building nanoheterostructures from a widerange of 2D materials. [ABSTRACT FROM AUTHOR]

Nanocrystals (NCs) attract tremendousresearch interests becauseof their unique properties to meet the demands of functionalities.To date, hybrid NCs with multiple components are developed to meetthe rising demands that could be very difficult, or even impossibleto be achieved by single-component NCs. Tuning properties by strainvia conjugation could be an alternative solution. Strain engineeringhas been discovered and widely applied to many thin-film materialsfor tuning physical properties. Then, there is a further questionto be addressed in this study: can we take the advantages we havelearned in heteroepitaxy of thin films and transfer that into theNC conjugation? In order to demonstrate this possibility, we investigatedNC conjugation of BiFeO3and LaAlO3. We foundthat change in either LaAlO3-NC or BiFeO3-NCsize would change the stability of rhombohedral-to-tetragonal phasetransition. The present results show that strain engineering is possibleto be realized in not only thin film but also NC conjugation. Thesame concept should be applicable to other complex oxide systems inorder to broaden their practical applications for the rising demandsof multifunctionalities. [ABSTRACT FROM AUTHOR]

The plate-like Bi4Ti3O12particles were prepared by molten salt synthesis method. The influence of sintering temperature and cooling process on the microstructure of Bi4Ti3O12powders was studied. Much larger particles were formed at higher temperatures. The particles could grow larger in slow cooling process. The formation mechanism of plate-like Bi4Ti3O12particles in Na2SO4-K2SO4system could be viewed as four processes: (1) solid reaction and nucleation, (2) plate-like structure formation, (3) diffusion and edge nucleation, (4) diffusion and epitaxial growth. [ABSTRACT FROM AUTHOR]

We quantitatively interpret HAADF-STEM images of SrRuO3/Pr0.7Ca0.3MnO3 (SRO/PCMO) superlattices. The images were taken in a probe-corrected ( cs = 0) FEI microscope at 300 kV. The specimen thickness is estimated by comparing experimental and simulated Z-contrast ratios. The intermixing at the interfaces is different for the growth of SRO on PCMO and that of PCMO on SRO. In addition, the thermal stability of SRO/PCMO superlattices is studied by HAADF-STEM, based on a series of annealing experiments. Colored HAADF-STEM image ( V = 300 kV, cs = 0 mm) of part of a SrRuO3/Pr0.7Ca0.3MnO3 epitaxial superlattice. [ABSTRACT FROM AUTHOR]

Self-assembly SiO2 nanosphere monolayer template is utilized to fabricate nanopatterned sapphire substrates (NPSSs) with 0-nm, 50-nm, and 120-nm spacing, receptively. The GaN growth on top of NPSS with 0-nm spacing has the best crystal quality because of laterally epitaxial overgrowth. However, GaN growth from pattern top is more difficult to get smooth surface than from pattern bottom. The rougher surface may result in a higher work voltage. The stimulation results of finite-difference timedomain (FDTD) display that too large or too small spacing lead to the reduced light extracted efficiency (LEE) of LEDs. Under a driving current 350 mA, the external quantum efficiencies (EQE) of GaN-based LEDs grown on NPSSs with 0-nm, 50-nm, and 120-nm spacing increase by 43.3%, 50.6%, and 39.1%, respectively, compared to that on flat sapphire substrate (FSS). The optimized pattern spacing is 50 nm for the NPSS with 600-nm pattern period. [ABSTRACT FROM AUTHOR]

A vertical ultraviolet (UV) light-emitting diode (LED) that does not require substrate removal is developed. Spontaneous via holes are formed in n-AlN layer epitaxially grown on a high conductive n+Si substrate and the injected current flows directly from the p-electrode to high doped n+ Si substrate through p-AlGaN, multi-quantum wells, n-AlGaN and spontaneous via holes in n-AlN. The spontaneous via holes were formed by controlling feeding-sequence of metal-organic gas sources and NH3 and growth temperature in MOCVD. The via holes make insulating n-AlN to be conductive. We measured the current-voltage, current-light intensity and emission characteristics of this device. It exhibited a built-in voltage of 3.8 V and emission was stated at 350 nm from quantum wells with successive emission centered at 400 nm. This UV LED can be produced, including formation of n and p electrodes, without any resist process. [ABSTRACT FROM AUTHOR]

Abstract: This is a review of the wetting properties of solid helium on various solid substrates. Due to its extreme purity and to its very fast growth dynamics, solid helium 4 is often considered as a model system in materials science. Several wetting phenomena have been studied with helium 4 crystals, namely contact angles on solid substrates with variable roughness, wetting on graphite where epitaxial growth takes place, the roughening transition as a function of film thickness, the wetting of grain boundaries by the liquid phase. [Copyright &y& Elsevier]

The epitaxial growth of PtSe 2 monolayer has brings new opportunities for the application and development of materials science. Using first-principles calculations, the effect of vacancy defects, and strain engineering on the electronic properties of PtSe 2 monolayer are systematically investigated. The results show that the Pt single vacancy induces a large magnetic moment of 4.0 μ B on PtSe 2 monolayer and transforms it from semiconductor to metal. However, the Se single vacancy systems are nonmagnetic and realize the PtSe 2 from an indirect semiconductor to a direct one. Moreover, the band gap of PtSe 2 monolayer can be prominently modulated within a appreciable uniaxial strain range, and the band gap are monotonically increase/decrease as decrease/increase the magnitude of the compressive/tensile strain. In particular, when a specific strain applied, a wide and high absorption peak across near-infrared, visible light and ultraviolet region. These findings not only enrich the fundamental understanding of PtSe 2 monolayer but also provide useful guidance to design PtSe 2 -based spintronic, optoelectronic and gas sensing applications. • Pt single vacancy induces a large magnetic moment and transforms PtSe 2 from semiconductor to metal. • The band gaps of 2D PtSe 2 are monotonically increase/decreas as decrease/increase the magnitude of the compressive/tensile strain. • Applying external strain reduce the band gap of PtSe 2 monolayer. [ABSTRACT FROM AUTHOR]

We have investigated the pulsed laser deposition (PLD) growth processes of spinel lithium titanates based on the preparation of Li4Ti5O12 and LiTi2O4 from a Li4Ti5O12 target. The Li/Ti atomic ratio of the species arriving at substrate during the deposition was only ∼0.5. The LiTi2O4 epitaxial thin films fabricated on MgAl2O4 (111) substrate exhibited high conductivity at room temperature (∼3.0 × 103 Ω-1 cm-1) and a superconducting transition temperature of ∼12 K. These values are the highest reported for epitaxial thin films. Our results demonstrate the importance of the target composition, providing further insights into the Li-containing metal oxide deposition processes using PLD. [ABSTRACT FROM AUTHOR]

Semiconductor nanowires have made a deep impact on materials science related research, and are being explored for applications in several disciplines. Many of these applications require heterostructures, which can be defined as the combination of two or more materials within the same nanowire structure. In this paper we briefly review the current state-of-the-art concerning epitaxial nanowire heterostructures. We discuss growth, understanding, and promising applications of such structures, which we divide into three categories: nanowire–substrate, axial, and radial heterostructures. For each of these categories, we review recent experimental results, and address possible difficulties and how they have been resolved. In addition, we also highlight interesting applications relying on heterostructures in nanowires. To illustrate that nanowires and their heterostructures have been grown in a plethora of materials, we pick examples from a wide range of semiconductor materials. [ABSTRACT FROM AUTHOR]

The large-scale assembly of nanowires with controlled orientation on surfaces remains one challenge preventing their integration into practical devices. We report the vapor-liquid-solid growth of aligned, millimeter-tong, horizontal GaN nanowires with controlled crystallographic orientations on different planes of sapphire. The growth directions, crystallographic orientation, and faceting of the nanowires vary with each surface orientation, as determined by their epitaxial relationship with the substrate, as well as by a graphoepitaxial effect that guides their growth along surface steps and grooves. Despite their interaction with the surface, these horizontally grown nanowires display few structural defects, exhibiting optical and electronic properties comparable to those of vertically grown nanowires. This paves the way to highly controlled nanowire structures with potential applications not available by other means. [ABSTRACT FROM AUTHOR]

Abstract: Features of the two thin-film techniques, atomic layer deposition (ALD) and molecular layer deposition (MLD), are combined to build up a stable novel inorganic–organic hybrid material of the (–Ti–N–C6H4–O–C6H4–N–) n type, deposited from successive pulses of TiCl4 and 4,4′-oxydianiline precursors. Depositions in the temperature range of 160–230°C resulted in unstable films, while the films obtained in the temperature range of 250–490°C were found stable in atmospheric air. The growth rate increased with increasing temperature, from 0.3Å per cycle at 160°C to 1.1Å per cycle at 490°C. [Copyright &y& Elsevier]

Abstract: This paper reviews the most important properties of germanium, gives an insight into the newer techniques and technology for the growth of epitaxial Ge thin layers and focuses on some applications of this material, with a special emphasis on recent achievements in electronics and photovoltaics. We will highlight the recent development of Ge research and will give an account of the most important Ge applications that emerged in the last two decades. Germanium is a key material in modern material science and society: it is used as a dopant in fiber optic glasses and in semiconductor devices, both in activating conduction in layers and also as a substrate for III–V epitaxy. Ge is also widely used in infrared (IR) detection and imaging and as a polymerization catalyst for polyethylene terephthalate (PET). Moreover, high-speed electronics for cell phone communications relies heavily on SiGe alloys. Ge electronics is nowadays gaining new interest because of the enhanced electronic properties of this material compared to standard silicon devices, but the lack of a suitable gate oxide still limits its development. High efficiency solar cells, mainly for space use but also for terrestrial solar concentration have surpassed 40% efficiency and Ge has a lead role in achieving this goal. The main focus of the paper is on Ge epitaxy. Since epitaxy starts from the surface of the substrate, different studies on substrate pre-epitaxy, surface analysis and preparations are reviewed, covering the most common substrates for Ge deposition such as Ge, Si and GaAs. The most used Ge precursors such as GeH4 and GeCl4 are described, but several novel precursors, mostly metal-organic, have recently been developed and are becoming more common in epitaxial Ge deposition. Epitaxial growth of Ge by means of the most common methods, including Chemical Vapour Deposition and Molecular Beam Epitaxy is discussed, along with some recent advances in Ge deposition, such as Atomic Layer Deposition and Low Energy Plasma-Enhanced Chemical Vapour Deposition. Several Ge applications are finally discussed, with the aim of providing insights into the potential of this material for the development of novel devices that are able to surpass the current limits of standard device design. Ge in microelectronics is becoming more and more important, thanks to the possibilities offered by bandgap engineering of strained SiGe/Si. However, lack of a good Ge oxide is posing several problems in device improvement. In the field of photovoltaics Ge is mainly used as a substrate for high efficiency III–V solar cells and for the development of thermophotovoltaic devices instead of the most expensive and scarcer GaSb. In this field, Ge epitaxy is very rare but the development of an epitaxial Ge process may help in developing new solar cells concepts and to improve the efficiency of thermophotovoltaic converters. Ge may play a role even in new spintronics devices, since a GeMn alloy was found to have a higher Curie temperature than GaAsMn. [Copyright &y& Elsevier]

GaP films have been grown by migration-enhanced epitaxy on Si (001) substrates tilted by 6° about the 〈011〉 axis. High-energy electron diffraction, transmission electron microscopy, and X-ray diffraction analysis were used to demonstrate that introduction of atomic hydrogen in the course of epitaxy markedly improves the overall structural quality of GaP films. Up to thicknesses of about 0.1 μm, the full width at half-maximum of the (004) reflection in the X-ray diffraction pattern of these films almost coincides with the theoretical value for defect-free films, which indicates that their state is nearly pseudomorphic. [ABSTRACT FROM AUTHOR]

Abstract: Stress-induced surface instability and evolution of epitaxial thin films leads to formation of a variety of self-assembled surface patterns with feature sizes at micro- and nanoscales. The anisotropy in both the surface and bulk properties of the film and substrate has profound effects on the nonlinear dynamics of surface evolution and pattern formation. Experimentally it has been demonstrated that the effect of anisotropy strongly depends on the crystal orientation of the substrate surface on which the film grows epitaxially. In this paper we develop a nonlinear model for surface evolution of epitaxial thin films on generally anisotropic crystal substrates. Specifically, the effect of bulk elastic anisotropy of the substrate on epitaxial surface pattern evolution is investigated for cubic germanium (Ge) and SiGe films on silicon (Si) substrates with four different surface orientations: Si(001), Si(111), Si(110), and Si(113). Both linear analysis and nonlinear numerical simulations suggest that, with surface anisotropy neglected, ordered surface patterns form under the influence of the elastic anisotropy, and these surface patterns clearly reflect the symmetry of the underlying crystal structures of the substrate. It is concluded that consideration of anisotropic elasticity reveals a much richer dynamics of surface pattern evolution as compared to isotropic models. [Copyright &y& Elsevier]

Abstract: Buried amorphous silicon (a-Si) is produced in Czochralski single crystalline silicon implanted at 340K with Mn+ (Si:Mn, 55Mn+ doses, D =2×1015 or 1.2×1016 cm−2, energy 160keV). Stress-mediated redistribution of Mn and solid phase epitaxial re-growth (SPER) of a-Si at up to 1273K (HT), also under hydrostatic Ar pressure up to 1.1GPa (HP), have been investigated by SIMS, X-ray and related methods. As-implanted Si:Mn indicates magnetic ordering. SPER depends on Mn+ dosage, HT, HP an on processing time. Processing at 870–1000K results in a minimum in the Mn concentration at ∼0.15μm depth. At 1170K and above, the diffusion of Mn to the surface increases with HP. Our results help in understanding the mechanisms of SPER and of origin of magnetic ordering in Mn:Si. [Copyright &y& Elsevier]

Abstract: Samples of epitaxially grown n-type Si have been implanted with low doses (<1×109 cm−2) of He, C, Si, and I ions using energies from 2.75 to 48MeV. Deep level transient spectroscopy (DLTS) analysis of the implanted samples reveals a stronger signal for the signature of the singly negative charge state of the divacancy (V2(–/0)) as compared to that of the doubly negative charge state of the divacancy (V2(=/–)). Isochronal annealing for 20min ranging from 150 to 400°C results in a gradual decrease in the DLTS peak amplitude of the V2(–/0) signature, accompanied by an increase in the peak amplitudes of both the vacancy oxygen pair (VO) and the V2(=/–) levels, as well as an increase in the carrier capture rates for the levels. A model based on local compensation of charge carriers from individual ion tracks is proposed in order to explain the results, involving two fractions of V2: (1) V2 centers localized in regions with high defect density around the ion track and (2) V2 centers located in regions with a low defect density . [Copyright &y& Elsevier]

We present the Monte Carlo simulation of submonolayer film growth during molecular beam epitaxy (MBE) at low temperature. We have made systematic study to see how the parameters diffusion to flux ratio (D/F), diffusional anisotropy (DA) and sticking anisotropy influences on island density exponent (χ), size distribution and scaling behaviour. We have found that, as diffusional anisotropy changes from DA = 1 to DA = ∝, the density exponent changes from χ = 0.34 ± 0.01 to 0.28 ± 0.01 for isotropic sticking case but when sticking is anisotropic the density exponent changes from χ = 0.31 ± 0.01 to 0.24 ± 0.01. The influence produced by DA on island size distribution is observed to depend on D/F ratio and sticking anisotropy. Depending on DA values and D/F ratio, the size distribution is also observed to be insensitive to the change in diffusional anisotropy. We also study the influence of diffusional anisotropy on scaling function for two sticking anisotropy condition. The scaling behaviour of island size distribution is observed to be not affected by all diffusional anisotropy as well as sticking anisotropy condition. [ABSTRACT FROM AUTHOR]

Abstract: We compare four different selective etching solutions commonly used to highlight threading dislocations (TD), in SiGe hetero-epitaxial layers. The aim is to identify, amongst the many reported in the literature, an etching solution effective over the whole Ge concentration range. Etching experiments have been performed on Si1− x Ge x linearly graded relaxed buffer layers with a final germanium concentration x varying from to 0.9. All samples have been deposited on Si(100) by low-energy plasma-enhanced chemical vapour deposition (LEPECVD). The experimental results show that a variant of the so-called Schimmel-etch is successful in revealing TD over the Ge concentration range investigated. [Copyright &y& Elsevier]

Abstract: Dislocations in stair-like composition graded SiGe layer and relaxed SiGe layer with Ge composition of 15%, 20% and 20% have been investigated with chemical etching and cathodeluminescence (CL). Etch pit density in the s-Si region is contained with the order of 104 cm−2 and it is almost constant in the relaxed and graded SiGe layer with the order of 105 cm−2 for every Ge composition samples. From the observation of the cleaved surface, misfit dislocations pile up at the boundary in each layer and Ge composition changing regions. Defect relative luminescence lines (D1 and D2 lines) were observed, but D3 and D4 lines were not present in the present samples. It is found that the luminescence intensity ratio of D1 to D2 depends on acceleration voltage of CL. From these results, it is suggested that the amount ratio of dislocation type causing D1 and D2 changes with the depth from surface. [Copyright &y& Elsevier]

Abstract: Epitaxial fully strained Si films are known to form an effective passivation of the Ge(100) surface. However, we show using low-energy secondary ion mass spectrometry (SIMS) that considerable Ge surface segregation occurs for Si films grown from SiH4 at 500°C. In this study, we develop an alternative deposition process at 350°C using Si3H8 which significantly decreases the Ge peak at the Si surface. We attribute this strong reduction mainly to the fact that growth at 350°C from trisilane proceeds below the Si–H desorption temperature. Charge pumping measurements on n-type Ge devices show a reduction by approximately a factor three in the high-k/substrate interface trap density for the samples with 350°C Si passivation, compared to those using a Si passivation deposited at 500°C. [Copyright &y& Elsevier]