We present a route for direct growth of boron nitride via a polyborazylene to h-BN conversion process. This two-step growth process ultimately leads to a >25x reduction in the root-mean-square surface roughness of h-BN films when compared to a high temperature growth on Al2O3(0001) and Si(111) substrates. Additionally, the stoichiometry is shown to be highly dependent on the initial polyborazylene deposition temperature. Importantly, chemical vapor deposition (CVD) graphene transferred to direct-grown boron nitride films on Al2O3 at 400 °C results in a >1.5x and >2.5x improvement in mobility compared to CVD graphene transferred to Al2O3 and SiO2 substrates, respectively, which is attributed to the combined reduction of remote charged impurity scattering and surface roughness scattering. Simulation of mobility versus carrier concentration confirms the importance of limiting the introduction of charged impurities in the h-BN film and highlights the importance of these results in producing optimized h-BN substrates for high performance graphene and TMD devices.

A series of Ni/C catalysts with different Ni content (15, 20, and 30 wt% Ni) were prepared by the wet incipient impregnation method. Their textural properties were studied by surface fractal dimension (D s) and nonlocal density functional theory using nitrogen sorption data. Their structural properties were studied by x-ray diffraction, Rietveld refinement, radial distribution functions (RDFs), and electron density maps of Fourier. Surface areas of Ni/C catalysts decreases slightly from 614 to 533 m2/g as Ni content increases from 15 to 30 wt%; however, the Ni crystallite size (5.1–31.4 nm) increases as the nickel content increases. Many point defects were found by Rietveld refinement in nickel nanostructures of Ni/C catalysts with 20 and 30 wt% Ni. This was confirmed by RDFs and electronic density maps. On the other hand, the hydrogen production via the photodehydrogenation of ethanol is very sensitive to the nickel crystallite size and the number Ni atoms in nickel nanostructures. The maximum reaction rate (363.64 μmol/h) is achieved on Ni/C catalyst with 15 Wt% Ni content which has the smallest crystallite size (5.1 nm) and less point defects in its nickel nanostructures. Ab initio calculations were performed to propose a reaction mechanism in the photodehydrogenation of ethanol.

In this study, stimuli-responsive ionic poly(acrylamide–itaconic acid) (P(AAm–IA)) and poly(N,N-dimethylacrylamide–itaconic acid) (P(DMA–IA)) hydrogels have been prepared by free radical crosslinking copolymerization in aqueous solution using N,N-methylenebisacrylamide as the crosslinking agent. In particular, the swelling ratio and elasticity of both hydrogel systems including the effect of ionic comonomer itaconic acid (IA) content were investigated. In spite of the similarity in monomer/crosslinker ratio and the content of ionic comonomer in the hydrogel structures, comparable differences were observed in their swelling capacity and elasticity. Compared to P(DMA–IA) hydrogels, P(AAm–IA) hydrogels exhibit higher swelling capacity in water and a more pronounced dependency of the swelling ratio on the ionic comonomer content. The incorporation of a small amount of IA into the network structure causes the hydrogel system to exhibit polyelectrolyte type swelling behavior. P(AAm–IA) and P(DMA–IA) hydrogels showed good response to the valency of counterions and pH of the external solution.

Absorption losses in tellurite glasses due to OH− ions were reduced by melting the glasses under a reactive atmosphere of Cl2 + O2 gas. Incorporation of dry Cl2 + O2 gas has a major influence on the reduction of OH− species, which is found to be consistent with thermochemical data. Absorption loss due to OH− ions in bulk glasses prepared from the as-received raw materials and processed under a reactive atmosphere was 1000 and 60 dB/m, respectively. Gaussian fits have been used to identify the different species of OH− attached to the structural units present in the glass. All of the OH− species (free and bonded to Te), units can be reduced by melting the starting raw materials in a reactive atmosphere of Cl2 + O2. The net reduction in OH− absorbance at 3.2 µm was 1.1 cm−1, which is equivalent to 500 ppm. OH− reduction in tellurite glasses using O2 gas bubbling shows a reduction in the fundamental absorption band from 1.8 to 0.57 cm−1 after 75 min.

We show that, by changing and tuning the direction of the As flux on a rippled substrate, at temperatures higher than 530 °C and high As/In flux ratio, a selective growth of InAs dots can be obtained on GaAs. This is an undisclosed effect related to the Arsenic flux in the molecular beam epitaxial growth of InAs quantum dots (QDs) on GaAs(001). This effect cannot be explained by a shadowing effect, due to the gentle slopes of the mounds (1–3°), and reveals instead that As plays a fundamental role at these growth conditions. We have developed a kinetic model, which takes into account the coupling between cations and anions, and found that the very small surface gradient in the anion flux, due to the oblique evaporation on the mounded surface, is responsible for a massive drain of cations toward the surface anion-rich areas, thus generating the selective growth of QDs.

A Cu–Ni sectioned cathode made up of two hemicycles of each of the metals was used for reactive co-sputtering of a thin film combinatorial library of Cu–Ni oxides covering a total compositional spread of 63 at.%. The thickness profiling of the library showed a nonuniform film thickness with a maximum region shifted toward the Cu side of the cathode. The presence of CuO, Cu2O, NiO, and metallic Cu–Ni alloys was identified during the scanning x-ray diffraction investigations along the compositional spread. A distinct structural zone was defined between Cu–14 at.% Ni and Cu–19 at.% Ni, where the scanning electron microscopy investigations showed a higher surface porosity combined with smaller grain sizes. This zone corresponds to the maximum film thickness region and correlates well with the position of the maximum work function of the Cu–Ni oxide films as mapped using a scanning Kelvin probe. During local corrosion studies focused on Cu dissolution, an improved corrosion resistance was identified in the Ni rich side of the compositional spread.

Field emission (FE) measurements are reported from carbon nanotube (CNT) fibers and laser-patterned free standing films fabricated by direct online condensation from a floating catalyst chemical vapor deposition reactor. Fiber and film cathodes showed stable emission in the 1–2 mA current (I) range at maximum cathode temperatures less than 1000 °C; film cathodes show localized heating at the triangular tips and higher maximum temperatures than the fibers. Fowler–Nordheim (FN) analysis indicated a change in the morphology of the emitters with increasing external electrical field (E ext). Fiber cathode I–E ext data are interpreted as FN emission from the fiber tip which is eventually limited by space-charge effects. At higher E ext, FN emission from the fiber sidewall occurs. The single fiber cathode stopped emitting abruptly when field induced self-heating effects became significant. For CNT films, self-heating effects can destroy a portion of the film, but FE can still occur from other areas.

Antiperovskite manganese nitrides Mn3MN (M = Zn, Ni, Cu…) have been extensively studied in the past decade due to their many interesting properties, such as negative thermal expansion. To get a better understanding of the origin of these phenomena, the information from the microscopic scale is necessary, so we performed systematic transmission electron microscopic study of Mn3Zn0.8Ni0.2N and found that the sample particle is wrapped in a thin MnO layer. The same result was also found in Mn3Zn0.5Ni0.5N and Mn3ZnN, indicating that it is a common phenomenon in this kind of compound. The presence of the MnO surface layer was also confirmed by the macroscopic XPS measurements. Our study suggests that M is easier to be lost than Mn in manganese nitrides Mn3MN (M = Zn, Ni, Cu…), and this character is much more obvious on the surface, i.e., this kind of compound has a strong surface activity. Figure 6 could best represent this manuscript.

Dielectric aging of Dy and Mn-codoped BaTiO3 multilayer ceramic capacitors was investigated. The increase of Dy concentration significantly decreased the aging rate and caused a disappearance of the thermally stimulated depolarization current peak associated with the defect dipole of Mn such as ${\rm{Mn}}_{{\rm{Ti}}}^{\prime \prime } {\rm{ - V}}_{\rm{O}}^{\cdot\cdot}$ or ${\rm{Mn}}_{{\rm{Ti}}}^\prime {\rm{ - V}}_{\rm{O}}^{\cdot\cdot}$ , which was observed in low Dy-concentration specimens. These results experimentally demonstrate that the rare earth element, Dy, decreases the concentration of the defect dipoles and thereby controls dielectric aging.

This article explores the growth of graphene under low-pressure Ar conditions. Carbon- and silicon-face 4H–SiC samples are subjected to epitaxial graphene growth at 1600 °C in vacuum, in 1 mbar argon, or in 10 mbar of argon. High-resolution x-ray scattering is used to characterize all graphene films. On the C-face, specular scans reveal a bimodal distribution of thicknesses that decrease with increasing Ar pressure. Thin and thick regions are approximately 15 and 46 monolayers in C-face graphene grown at high vacuum, 14 and 42 monolayers thick in graphene grown at 1 mbar, and 12 and 32 monolayers thick in graphene grown at 10 mbar. Azimuthal scans confirm in all cases that graphene layers are epitaxial and display expected crystallographic relationships with the underlying SiC substrate. In-plane azimuthal scans show the rotational disorder increases as pressure increases. Peaks in radial scans are asymmetric, suggesting the grain structure has a bimodal distribution of large and small domains. The sample displaying the lowest average Hall mobility (grown at 1 mbar) has the largest population of small crystallites (coherence length on the order of ∼30 nm). Variations in structure and mobility of C-face graphene are attributed to inadequate control of Si sublimation during growth.

Zr-based bulk metallic glasses (BMGs) exhibit superior physical and chemical properties in comparison to their crystalline counterparts. In the present work, drilling behavior of Zr57.5Cu11.2Ni13.8Al17.5 BMG was investigated at various operating conditions. Drilling was performed using high-speed steel (HSS) and carbide bits. Chip morphology, chip light emission, and burr formation at various drilling parameters were studied to achieve a feasible operating condition for drilling hole without light emission, chip clogging, and debris accumulation. Short spiral chip morphology which is considered ideal in the drilling process was observed at relatively low feed rate (1.5 mm/min) and medium spindle speed (1500 rpm). This also resulted in a small amount of molten debris around the entry hole. It was observed that at the same feed rate, the gradual increase in the speed of the HSS drill bit results in more light emission from the machining surface, whereas no light emission was observed in the case of the carbide drill bit at all drilling parameters.

During peritectic solidification, besides the longitudinal remelting of the primary phase at the temperature of peritectic reaction $\left( {T_{\rm{p}}^K} \right)$ , a lateral remelting phenomenon of the primary phase below $T_{\rm{p}}^K$ is observed under high velocity in directionally solidified Cu–Ge alloys. The lateral remelting occurs continuously along a liquid channel as temperature decreases, and the lateral remelting velocity is larger than that of peritectic transformation. The lateral remelting leads to the morphological change of the primary dendrites, even the fragmentation of dendrite arms. The phenomenon also means that the classical theory calculating the volume fraction of the primary phase during peritectic transformation can need to be modified under some conditions. However, under low velocity, the phenomenon is not so significant. The phenomenon is explained by means of solidification and remelting theory.

In this work, the effects of annealing treatment on the crystalline structure and mechanical property changes of polypropylene random copolymer (PPR) were comparatively investigated. Wide angle x-ray diffraction and differential scanning calorimetry were used to study the crystalline structure evolution of the annealed PPR sample. The relaxation behavior of the annealed PPR sample was analyzed using dynamic mechanical analysis. The mechanical properties and the toughening mechanism were also investigated. The results showed that the crystalline structure evolution of the annealed PPR sample depended on the annealing temperature. Due to the largely increased molecular chain mobility in the amorphous region, which promoted the plastic deformation of the annealed PPR sample under the impact condition, largely enhanced impact strength was achieved at a moderate annealing temperature. Further results showed that relatively shorter annealing duration could induce the apparent changes of crystalline structure and mechanical properties of the PPR sample.

In the present work, it has been suggested that the gene expression programing is a good tool for determination of hardness of metal matrix nanocomposite produced by mechanical alloying (MA). For example, we studied the Al matrix nanocomposite, and to build the models, 35 input-target data were gathered from the literature, randomly divided into 28 and 7 data sets and then were respectively trained and tested by the proposed models. The differences between the models were in their gene number, chromosomes, and head size. The amount of reinforcement, ball to powder ratio, compaction pressure, milling time, reinforcement hardness, sintering temperature, sintering time, and vial speed were 8 independent input parameters. The output parameter was mean hardness of nanocomposites. The results indicate that gene expression programing is a powerful tool for predicting the hardness of the nanocomposite produced by MA.

Three-dimensional (3D) nanostructures and nanodevices have attracted tremendous interest in the past few years due to their special mechanical and physical properties. Nanodevices using 3D nanostructures as the building blocks have been demonstrated to exhibit multifunctionality and functions that conventional planar devices cannot achieve. In this article, we report and review focused ion beam techniques for direct site-specific growth of 3D nanostructures and postgrowth shape modification of freestanding nanostructures by ion beam-induced chemical vapor deposition and ion-beam-irradiation-induced plastic bending, respectively. Such techniques have shown nanometer-scale resolution and accuracy in the fabrication of metallic nanoelectrodes, 3D pickup coils, nanogaps, and multibranched structures. Characterization of the resulting nanostructures shows that focused ion beam techniques allow conducting and superconducting freestanding 3D structures to be tailored in size, geometry, and integrated with planar electronic, mechanical, and superconducting nanodevices, potentially enabling lab-on-a-chip experiments.

Solutions to the technical challenge of bonding and joining bulk metallic glasses have long been sought after due to the exceptional property sets displayed by this class of engineering materials. Here, we demonstrate the ability to deposit a compositionally and functionally graded hybrid coupling layer using sol–gel processing methods to promote adhesion at the metallic glass–epoxy interface. In this study, we fine-tune the molecular composition by varying the sol Zr:Si ratio, altering film properties that consequently influence crack path selection at the interface. When optimized, up to 3-fold improvements in the adhesive/cohesive properties of these structural bond lines can be attained, with the highest GC values correlating with cohesive cracking through the hybrid. We also demonstrate the ability of these hybrid structures to significantly reduce the influence of moisture-assisted degradation as evidenced by reductions in crack growth rates of over two orders of magnitude and increased threshold limits.

The graded composition buffer layers are very commonly used in the semiconductor triple-junction solar cell device. To grow a strain-free 1.0-eV In0.3Ga0.7As thin film on a GaAs substrate, a total of 2.2% misfit strain must be relaxed through well-designed buffer layer structures. In this work, a phase-field model of a multilayered system is developed to probe the roughness of top surface morphology and predict optimal buffer layer thickness. Our simulation shows time evolution of the thin film morphology and the root-mean-square roughness of the surface with different buffer layer thickness designs. The strain distribution is investigated to explain the surface morphology evolution with the effect of the buffer layer. The simulation results show that the buffer layer thickness is a key parameter that affects the quality of the In0.3Ga0.7As epilayers. The simulation results can be effective in improving the design of graded buffer layers.

A systematic study was done to understand the influence of volume fractions and bilayer spacings for metal/nitride multilayer coating using finite element method (FEM). An axisymmetric model was chosen to model the real situation by incorporating metal and substrate plasticity. Combinations of volume fractions and bilayer spacings were chosen for FEM analysis consistent with experimental results. The model was able to predict trends in cracking with respect to layer spacing and volume fraction. Metal layer plasticity is seen to greatly influence the stress field inside nitride. It is seen that the thicker metal induces higher tensile stresses inside nitride and hence leads to lower cracking loads. Thin metal layers <10 nm were seen to have curved interfaces, and hence, the deformation mode was interfacial delamination in combination with edge cracking. There is an optimum seen with respect to volume fraction ∼13% and metal layer thickness ∼30 nm, which give maximum crack resistance.