Buffer leakage in aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure transistors is recognized as an issue that has deleterious consequences on device performance for high-power, high-frequency transistors and has been related to the presence of uncharged threading screw dislocations. In this study, we demonstrate that measurements of buffer leakage in AlGaN/GaN heterostructures grown on bulk gallium nitride (GaN) substrates are consistent with a mechanism based on the concept of dislocations acting as quantum wires in series with unintentional silicon (Si) impurity incorporation at the bulk GaN substrate/GaN buffer interface. The number of electronic channels N deduced from the leakage data using Landauer’s formula for the quantum resistance of N electronic channels is consistent with the number of dislocations along the ohmic contact pads determined from panchromatic cathodoluminescence and x-ray diffraction measurements of the dislocation density. This mechanism is consistent with Shockley’s suggestion that dislocations can act as one-dimensional conductors due to the presence of edge states along the dislocation core.

Semicoherent interfaces containing discrete dislocations are more energetically favorable than those containing continuous distributions because of lower chemical energy. The classical Frank-Bilby theory provided a way to determine the interface Burgers vectors content but could not effectively predict the characteristics of discrete dislocations. Atomistic simulations provide insights into analyzing the characteristics of discrete dislocations but the analysis is often disturbed by the reaction of interface dislocations. By combining the classical Frank-Bilby theory and atomistic simulations, an atomically informed Frank-Bilby theory proposed in this work can overcome shortcomings in both the classic Frank-Bilby theory and atomistic simulations, and enable quantitative analysis of interface dislocations. The proposed method has been demonstrated via studying two typical dissimilar metallic interfaces. The results showed that Burgers vectors of interface dislocations can be well defined in a Commensurate/Coherent Dichromatic Pattern (CDP) and the Rotation CDP (RCDP) lattices. Most importantly, the CDP and RCDP lattices are not simply a geometric average of the two natural lattices, that is the lattice misfit and the relative twist take the nonequal partition of the misfit strain and the twist angle.

Bismuth silicate with two morphologies (nanoflowers/nanoplates) was successfully fabricated with silica aerogels via a hydrothermal method in polyvinylpyrrolidone (PVP)-mediated processes for the first time. The obtained nanomaterials were characterized using x-ray powder diffraction, scanning electron microscopy, the Brunauer–Emmett–Teller (BET) surface area analysis, and UV-vis diffuse reflectance spectroscopy. It was found that the concentration of PVP plays an important role in the formation of the hierarchical nanoflowers. The formation mechanism for this novel morphology was proposed on the basis of experimental results. Moreover, the photocatalytic performances of Bi2SiO5 nanoflowers/nanoplates were also investigated. The results revealed that Bi2SiO5 nanoflowers exhibited higher activity than Bi2SiO5 nanoplates due to its suitable morphology, higher BET surface area.

We have investigated the formation of the rutile and the anatase polymorphs of TiO2, with emphasis on epitaxial growth characteristics, and defect content as a function of laser and substrate variables. X-ray diffraction (XRD) studies revealed that the rutile phase is more stable at higher substrate temperatures and lower oxygen pressures; in contrast, decreasing the temperature and increasing the oxygen pressure gave rise to formation of anatase. Epitaxial rutile films with a <100] orientation were obtained at 450 °C using the pressure of 5 × 10−4 Torr, and laser energy of 3.5–4.0 J/cm2. The epitaxial relationship, determined by 2θ−θ and φ scan of XRD and confirmed by transmission electron microscopy (TEM) diffraction patterns, was shown to be rutile(100)||sapphire(0001), rutile[001]||sapphire[10$\bar 1$0] and rutile[010]||sapphire[1$\bar 2$10]. An atomically sharp interface between the rutile epitaxial film and the sapphire substrate was observed in the scanning transmission electron microscopy (STEM) images. The films exhibited a transmittance of 75–90% over the visible region. The absorption edge was observed to shift toward longer wave lengths at higher deposition temperatures or lower pressures. X-ray photoelectron spectroscopy and photoluminescence results showed that concentration of lattice point defects, namely oxygen vacancies and titanium interstitials, increased at lower oxygen pressures. Formation of nanostructured films with a surface roughness of -1.5–13.1 nm was confirmed by atomic force microscopy investigations.

High-quality epitaxial silicon thin films have been deposited by plasma-enhanced chemical vapor deposition (PECVD) at 200 °C in a standard radiofrequency (RF) PECVD reactor. We optimized a silicon tetrafluoride (SiF4) plasma to clean the surface of <100> crystalline silicon wafers and without breaking vacuum, an epitaxial silicon film was grown from SiF4, hydrogen (H2), and argon (Ar) gas mixtures. We demonstrate that the H2/SiF4 flow rate ratio is a key parameter to grow high-quality epitaxial silicon films. Moreover, by changing this ratio, we can fine-tune the composition of the interface between the crystalline silicon (c-Si) wafer and the epitaxial film. In this way, at low values of the H2/SiF4 flow rate ratio, an abrupt interface is achieved. On the contrary, by increasing this ratio we can obtain a porous and fragile interface layer, composed of hydrogen-rich microcavities, which allows the transfer of the epitaxial film to foreign substrates.

During directional solidification of Cu–Ge peritectic alloys, a two-phase separated structure has been observed. With proper growth conditions, the peritectic ζ-Cu5Ge and primary α-Cu phases completely separate and form cylindrical layered structures. It is found that the formation of the separated structure is closely related to double diffusive convection and growth conditions. In the two-phase separated structure, a large trijunction region of peritectic reaction forms around the cylindrical α-Cu phase. During peritectic reaction, the morphological instabilities of ζ-Cu5Ge occur under high pulling velocities and are explained by the constitutional undercooling criterion. A new coupling growth between the ζ-Cu5Ge-phase and the groove of α-Cu phase near the trijunction is observed. Different from peritectic coupling growth, the diffusion coupling is established below the peritectic temperature. This two-phase separated growth process creates new opportunities for the fabrication of functionally layered materials.

A special type of epitaxial growth appears during solid-phase thin film reactions, where the reaction product grows epitaxially on the substrate. Some metal silicide layers and nanostructures are known to develop such epitaxial structures. In this study, iron silicide was used to study the effect of the growth mode on the epitaxial growth. Strain-induced, self-assembled iron silicide nanostructures were grown on Si(001) substrates by electron gun evaporation of 1.0 nm iron and subsequent annealing at 500–850 °C for 60 min. The growth processes were checked by reflection high-energy electron diffraction, and the formed structures were characterized by scanning electron microscopy and optical microscopy. The iron silicide nanostructures were oriented in square directions epitaxially fitting to the surface of Si(001). The shape and size of the nanostructures depended on the annealing temperature. In some cases, the nanoparticles were arranged in circles. This might be the direct consequence of a nucleation-controlled type transition of iron monosilicide to iron disilicide phase at nanoscale.

In this work, we succeeded in synthesis of spinel LiMn2O4 via a facile self-template method. The product displays a micro-/nanohybrid structure. Nanoparticles/plates act as the primary nanoblocks to build the secondary microarchitecture. There is the open space between the nanoblocks and the void space between the secondary structures. Electrochemical tests demonstrate that the as-synthesized sample exhibits superior rate capability and high-rate cycleability when contrasted with its solid counterpart. The initial discharge capacity is 126 mAh/g at 0.1 C, 110 mAh/g at 10 C, and 84 mAh/g at 20 C. The discharge capacity retention of about 80% is obtained after 800 cycles at 10 C. The high capacity and excellent cycling life of the material shows its potential for application as high-power batteries. The improved rate capability and cycleability can be attributed to its secondary structure that can facilitate fast Li-insertion/extraction and buffer the volume expansion/contraction upon cycling.

Deformation mechanism maps are well established in the field of high temperature creep for materials having conventional coarse grain sizes but they are almost unknown within the field of nanostructured materials. This paper summarizes the background to deformation mechanism mapping, presents simplified examples that may be used to easily construct appropriate maps for any selected condition, demonstrates the potential extension of this approach to other areas such as creep fracture, and then considers the potential limitations associated with using the same approach to predict the deformation mechanisms in true nanostructured materials. Two representative deformation mechanism maps are shown for an ultrafine-grained alloy processed either by equal-channel angular pressing or by high-pressure torsion.

The monomer dimethylaminoethyl methacrylate (DMAEMA) was cross-linked by clay Laponite XLG and Laponite XLS, respectively, in situ free-radical polymerization to prepare nanocomposite gels (named as G-NC gels and S-NC gels). From the analysis of yield, transparency, Fourier transform infrared spectroscopy, x-ray, and scanning electron microscopy, it was proved that the clay Laponite XLS is an appropriate cross-linker for preparing PDMAEMA NC gels with better homogeneous and higher yield due to the uniform dispersion of clay in gels. The resulting S-NC gels show obvious temperature and pH double sensitiveness, and the lowest critical solution temperatures of gels with a low clay content are close to the temperature of the human body, which makes this gel a potential candidate for application in drug release. Comparing with the gels cross-linked by a chemical cross-link agent, the S-NC gels exhibit a considerable improvement in the mechanical properties, swelling ratio, and deswelling rate. The properties of S-NC gels could be adjusted by controlling the content of clay.