We demonstrate a resonant Bragg structure formed by quasi-two-dimensional excitons in periodic systems of InGaN quantum wells (QWs) separated by GaN barriers. When the Bragg resonance and exciton–polariton resonance are tuned to each other, the medium exhibits an exciton-mediated resonantly enhanced optical Bragg reflection. The enhancement factor appeared to be largest for the system of 60 QWs. Owing to a high binding energy and oscillator strength of the excitons in InGaN QWs, the resonant enhancement was achieved at room temperature. The samples were grown by the metal–organic vapor-phase epitaxy (MOVPE) on GaN-on-sapphire templates. The most important technological problem of the developed structures is inhomogeneous broadening of the excitonic states due to nonuniform chemical composition of the QWs driven by InN–GaN phase separation trend. We addressed this problem by variation of the vapor pressure, growth rate, growth interactions, and admixing of hydrogen during the MOVPE. The lowest width of 74 meV at room temperature and 41 meV at 77 K was achieved for the excitonic emission line from a single InGaN QW.

We introduce a novel approach to the synthesis of high-quality and highly uniform few-layer graphene on silicon wafers, based on solid source growth from epitaxial 3C-SiC films. Using a Ni/Cu catalytic alloy, we obtain a transfer-free bilayer graphene directly on Si(100) wafers, at temperatures potentially compatible with conventional semiconductor processing. The graphene covers uniformly a 2″ silicon wafer, with a Raman I D/I G band ratio as low as 0.5, indicative of a low defectivity material. The sheet resistance of the graphene is as low as 25 Ω/square, and its adhesion energy to the underlying substrate is substantially higher than transferred graphene. This work opens the avenue for the true wafer-level fabrication of microdevices comprising graphene functional layers. Specifically, we suggest that exceptional conduction qualifies this graphene as a metal replacement for MEMS and advanced on-chip interconnects with ultimate scalability.

While planar graphene has revolutionized science and engineering in many different areas, one of its close relatives, vertical graphene (VG), also known as carbon nanowalls, has not been investigated as extensively. Compared to planar graphene that is grown parallel to the substrate, VG can grow almost vertically on a wide variety of substrates. In this study, we report the fabrication and characterization of VG-based nanocomposite thin films, where the graphene sheets are uniformly distributed in the host polymer. A novel fabrication method was developed and the properties of the fabricated nanocomposites were characterized. The results showed that in our method graphene sheets are much more uniformly dispersed and common issues in graphene nanocomposites, such as agglomeration and breaking of the sheets during dispersion, are avoided. The increase in the Young's modulus and tensile strength of the fabricated nanocomposites is much higher than that of the samples fabricated using the traditional methods of randomly dispersing graphene using a sonicator or high-speed stirrer.

Four epitaxial ScN(001) thin films were successfully deposited on MgO(001) substrates by dc reactive magnetron sputtering at 2, 5, 10, and 20 mTorr in an Ar/N2 ambient atmosphere at 650 °C. The microstructure of the resultant films was analyzed by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Electrical resistivity, electron mobility and concentration were measured using the room temperature Hall technique, and temperature dependent in-plain measurements of the thermoelectric properties of the ScN thin films were performed. The surface morphology and film crystallinity significantly degrade with increasing deposition pressure. The ScN thin film deposited at 20 mTorr exhibits the presence of <221> oriented secondary grains resulting in decreased electric properties and a low thermoelectric power factor of 0.5 W/mK2 at 800 K. The ScN thin films grown at 5 and 10 mTorr are single crystalline, yielding the power factor of approximately 2.5 W/mK2 at 800 K. The deposition performed at 2 mTorr produces the highest quality ScN thin film with the electron mobility of 98 cm2 V−1 s−1 and the power factor of 3.3 W/mK2 at 800 K.

The production of aluminum nitride (AlN) from aluminum metal was investigated in this study. The nitridation of Al (in rod, powder, and thin-plate forms) was facilitated by dissolving the Al2O3 thin films formed on the Al samples with a molten fluoride mixture (KF–45 mol% AlF3, KF, or LiF–50 mol% KF). AlN was formed when NH3 gas was supplied to the Al sample (in both solid and liquid forms) wetted by molten fluoride mixture. The lowest temperature at which AlN was successfully produced was 773 K. No AlN was formed when N2 or H2–25% N2 gas was supplied to the Al sample, even when a molten fluoride mixture was used. The reaction rate for the nitridation of Al powder increased with the temperature and reached 99% after 3 h at 1173 K. AlN thin films of 2–5 μm thickness were formed on Al thin plates (0.075–1.0 mm thick) at 873 K.

Two novel series of cathode materials LiFe1−x M x PO4/C (x ≈ 0.0040; M = Mn, Fe, Co, Ni, Cu, and Zn) composites based on metal phthalocyanines (MPc) and metal tetrasulfophthalocyanines (MPcTs) to modify lithium iron phosphate (LiFePO4) for lithium-ion batteries (LIBs) are in situ prepared by solvothermal and calcination techniques. Structures and morphologies of all the composites are characterized by normal methods. To evaluate the electrochemical performance of the composites, the charge/discharge capabilities, rate performance, cycling stabilities, cyclic voltammetry profiles, and electrochemical impedance spectroscopy plots of the LIBs using them as cathode materials are measured carefully. The results indicate that most of the composites deliver highly improved initial discharge capacity and show remarkable reversibility and cycling stabilities. Especially, composites using MPcTs as additives are more efficient for the improvement of specific capacity, rate capability, reversibility, and cycling stability.

The present study focuses on a quantitative analysis of electrical resistivity in monovalent-doped manganites La1−x Ag x MnO3 (x = 0.05 and 0.1). The electrical resistivity data in the ferromagnetic (FM) metallic phase are analyzed by considering a temperature-independent inelastic scattering of the electrons (due to domain and grain boundaries, defects, etc.) and other temperature-dependent elastic scattering mechanisms (electron–electron, electron–phonon, and electron–magnon). The Debye and Einstein temperatures are deduced from the model Hamiltonian containing potential energy contribution from the long-range Coulomb, van der Waals (vdW) interaction, and short-range repulsive interaction up to the second-neighbor ions. The electron–phonon scattering partially describes the reported FM metallic resistivity behavior with temperature for La1−x Ag x MnO3 (x = 0.05 and 0.1). The T 2 and T 4.5 terms accounting for electron–electron and electron–magnon interactions are essential for the correct description of resistivity. The Mott–Ioffe–Regel criterion for metallic conductivity is valid, and k F l ∼ 1, εFτ ∼ 1.

The effect of adding nucleic acids to gold seeds during the growth stage of either nanospheres or nanorods was investigated using UV–Vis spectroscopy to reveal any oligonucleotide base or structure-specific effects on nanoparticle growth kinetics or plasmonic signatures. Spectral data indicate that the presence of DNA duplexes during seed aging drastically accelerated nanosphere growth while the addition of single-stranded polyadenine at any point during seed aging induces nanosphere aggregation. For seeds added to a gold nanorod growth solution, single-stranded polythymine induces a modest blue shift in the longitudinal peak wave length. Moreover, a particular sequence comprised of 50% thymine bases was found to induce a faster, more dramatic blue shift in the longitudinal peak wave length compared to any of the homopolymer incubation cases. Monomeric forms of the nucleic acids, however, do not yield discernable spectral differences in any of the gold suspensions studied.

The uniform Ag@AgBr core–shell microspheres were synthesized by a very facile wet-chemical route in aqueous solution, including a reduction process to prepare sphere-like Ag core and a deposition process to synthesize AgBr shell. X-ray diffraction, x-ray photoelectron spectroscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy results confirmed the formation of Ag@AgBr core–shell heterostructures which had been achieved by this simple method. Field emission scanning and high-resolution transmission electron microscopy results of the as-synthesized Ag@AgBr composite revealed that AgBr particles were deposited on the surface of sphere-like Ag core. Under visible-light (λ > 420 nm) and real sunlight irradiation, the as-synthesized Ag@AgBr samples exhibit high activity and good stability for the photodegradation of Rhodamine 6G (R6G) in water. The present work suggests that the as-synthesized Ag@AgBr core–shell microsphere can be applied as a visible light-activated photocatalyst in efficient utilization of solar energy for treating water polluted by some chemically stable azo dyes in environment. The enhanced photocatalytic performance of the as-synthesized Ag@AgBr composite might be attributed to accelerated separation efficiency of electron–hole pairs on the interface of the Ag@AgBr hybrids and improved visible-light absorption abilities when AgBr is coupled with Ag.

Fracture toughness testing of materials at the micrometer scale has become essential due to the continuing miniaturization of devices accompanied by findings of size effects in fracture behavior. Many techniques have emerged in the recent past to carry out fracture toughness measurements at the relevant micro and nanolength scales, but they lack ASTM standards that are prescribed for bulk scale tests. Also, differences in reported values arise at the microscale due to the sample preparation technique, test method, geometry, and investigator. To correct for such discrepancies, we chose four different fracture toughness test geometries in practice, all of them micromachined in the focused ion beam (FIB), to investigate the fracture toughness of Si(100) at the micrometer scale. The average K IC that emerges from all four cases is a constant (0.8 MPa m1/2). The advantages and limitations of each of these geometries in terms of test parameters and the range of materials that can be tested are discussed.

The finite element method is used to simulate indentation with a 100 nm spherical indenter on Al/Pd multilayer thin films and Al and Pd monolayer thin films. The elastic/plastic properties of bulk Al and Pd and the material formulation are obtained by molecular dynamics simulations of tensile and indentation loadings. Hill's plasticity with isotropic hardening is found to best represent the stress–strain response of both bulk Al and Pd. The Pd monolayers appear the hardest and the Al monolayers the softest. The indentation hardness of both monolayered and multilayered films is found to increase with the indentation depth and appears independent of the layer order and thickness in the multilayer films. The hardness values determined by the finite element method simulations are close to those obtained using the well-known formula of Field and Swain. No hardness enhancement in very thin multilayered films (3–5 nm per layer) is evident, in contrast to experimental reports.

The fracture behavior of precracked nanocrystals with grain size gradients is simulated using the molecular dynamics method. A large grain size gradient is found to elevate resistance to crack propagation and transform the fracture mode from intergranular to intragranular when the crack is obstructed by a coarse grain. But the intragranular crack is nipped in its bud due to the difficulty of intragranular fracture. However, intergranular fractures can be always kept in nanocrystals with a small grain size gradient. Both the Schmid factors for the slip systems of grains near the crack tip and the critical stress intensity factors are calculated, and energy partitioning is conducted to analyze the mechanisms behind this phenomenon. The research exhibits the key role of grain size gradient in improving the antifracture ability of nanocrystals.

The laser cladding Co–Cr–W coating has coarse dendritic and network carbides, which can lead to crack and exfoliation easily, limiting the application of Co–Cr–W coating. In this work, friction stir processing (FSP) was carried out on a laser cladding Co–Cr–W alloy coating to modify its microstructure. FSP transforms the laser clad coarse dendritic grains (grain size: 2–4 μm) into nanograins (grain size: 50–200 nm) and crushes the network carbides into nanoparticles dispersed in Co-base solution. The microstructure and thickness of plastic surface layer are controllable by the condition of FSP. Moreover, a WC x reinforced Co–Cr–W thin layer was formed because the WC particles of stir tool were squeezed into the Co–Cr–W coating surface layer. More interestingly, when the FSP rotary speed was 1500 rpm, an interlocking bonding between Co–Cr–W coating and steel substrate was formed, which was favorable for the connection with substrate. The surface nanocrystallization significantly strengthened the laser clad Co–Cr–W alloy after FSP.

The erosion–corrosion properties and interface microstructure of a Fe–B alloy that contains 3.5 wt% B in flowing liquid zinc have been investigated by electron backscattered diffraction, x-ray diffraction, and scanning electron microscopy to clarify the flowing effect of liquid zinc on erosion performance using a rotating-disk technique. The Fe–B alloy erodes at a low and steady rate in flowing liquid zinc. Flowing liquid zinc can accelerate the iron and zinc mass transfer to form Fe–Zn compounds and promote the removal of loose FeZn13. Much residual corrosion-resistant Fe2B and some erosion products coexist at the erosion interface because of the chemical and micromechanical effects that are created by flowing liquid zinc. The failure of the Fe2B corrosion-resistant skeleton in flowing liquid zinc occurs because of the loss of supporting matrix and also the formation and spread of microcracks during erosion.

The variation of properties and evolution of microstructure of Cu–10Ni–3Al–0.8Si alloy during isothermal and aging treatment was studied. The time–temperature–property curves of the alloy were established. The nose temperature of the alloy was about 662 °C, and the alloy presented high quench sensitivity when quenched in the nose temperature zone. Discontinuous precipitation occurred when Cu–10Ni–3Al–0.8Si alloy was isothermally treated at 550 °C, and the discontinuous precipitates at the grain boundary became coarse when the isothermal temperature increased to 650 °C. Further increasing the isothermal temperature to 750 °C, cellular precipitation occurred in the alloy. Both Ni3Al precipitates with L12 ordered structure and δ-Ni2Si precipitates with DO22 ordered structure precipitated in the isothermally treated Cu–10Ni–3Al–0.8Si alloy. The orientation relationships between the precipitates and matrix were determined as ${[001]_{{\rm{Cu}}}}{\left\| {{{[001]}_{{\rm{N}}{{\rm{i}}_3}{\rm{Al}}}}\left\| {[001]} \right.} \right._\delta }$ , ${(110)_{{\rm{Cu}}}}{\left\| {{{(110)}_{{\rm{N}}{{\rm{i}}_3}{\rm{Al}}}}\left\| {(010)} \right.} \right._\delta }$ , and ${(1\bar 10)_{{\rm{Cu}}}}\left\| {{{(1\bar 10)}_{{\rm{N}}{{\rm{i}}_3}{\rm{Al}}}}} \right\|{(100)_\delta }$ .

Effect of combined electromagnetic fields (EMFs) on the structures of a 3004 aluminum alloy ingot produced by horizontal direct chill casting was crystallographically investigated. The results showed that the structure was transformed from a mixture of equiaxed and fine columnar grains to coarse columnar grains with switching off the EMFs. With the EMFs the grain size is small and shows a uniform distribution, whereas without the EMFs it is increased and reveals inhomogeneous distribution on the cross section. Besides, a transition region composed of fine equiaxed grains appeared at the moment the EMFs were switched off (between the mixture and coarse columnar grains). Furthermore, the microstructure transformation is accompanied by a crystallographic orientation change from a preferred <100> orientation to a random orientation, and then to an intense <100> fiber texture. The structural and crystallographic transformations are mainly related to the forced convection in the melt due to the induced Lorentz force by the EMFs.