We apply n- and p-type polycrystalline silicon (poly-Si) films on tunneling SiOx to form passivated contacts to n-type Si wafers. The resulting induced emitter and n+/n back surface field junctions of high carrier selectivity and low contact resistivity enable high efficiency Si solar cells. This work addresses the materials science of their performance governed by the properties of the individual layers (poly-Si, tunneling oxide) and more importantly, by the process history of the cell as a whole. Tunneling SiOx layers (<2 nm) are grown thermally or chemically, followed by a plasma enhanced chemical vapor deposition growth of p+ or n+ doped a-Si:H. The latter is thermally crystallized into poly-Si, resulting in grain nucleation and growth as well as dopant diffusion within the poly-Si and penetration through the tunneling oxide into the Si base wafer. The cell process is designed to improve the passivation of both oxide interfaces and tunneling transport through the oxide. A novel passivation technique involves coating of the passivated contact and whole cell with atomic layer deposited Al2O3 and activating them at 400 °C. The resulting excellent passivation persists after subsequent chemical removal of the Al2O3. The preceding cell process steps must be carefully tailored to avoid structural and morphological defects, as well as to maintain or improve passivation, and carrier selective transport. Furthermore, passivated contact metallization presents significant challenges, often resulting in passivation loss. Suggested remedies include improved Si cell wafer surface morphology (without micropyramids) and postdeposited a-Si:H capping layers over the poly-Si.

Tantalum carbide (TaC) is an ultrahigh temperature ceramic, where low damage tolerance limits its potential application in propulsion sector. In this respect, current work focuses on enhancing the toughness of TaC based composites via synergistic reinforcement of SiC and carbon nanotubes (CNTs). Spark plasma sintering of TaC, reinforced with 15 vol% SiC and 15 vol% CNT (processed at 1850 °C, 40 MPa, 5 min), has shown enhanced densification from ∼93% (for TaC) to ∼98%. Potential damage of the tubular CNTs to flaky graphite was revealed using transmission electron microscopy, and was supplemented via Raman spectroscopy. SiC addition has enhanced the hardness to ∼19.5 GPa while a decreases to 12.6 GPa was observed with CNT addition when compared to the hardness of TaC (∼15.5 GPa). The increase in the indentation fracture toughness (from 3.1 MPa m1/2 for TaC to 11.4 MPa m1/2) and fracture strength (from ∼23 MPa for TaC to ∼183 MPa) via synergetic reinforcement of SiC and CNT is mainly attributed to energy dissipating mechanisms such as crack branching, CNT bridging, and crack-deflection. In addition, the reduction of interfacial residual tensile-stresses with SiC- and CNT-reinforcement, resulting an overall increase in the fracture energy and toughening, is also established.

(KxNa1−x)NbO3 films were deposited on Nb-doped (100)SrTiO3 substrates at 240 °C for times between 1 and 6 h by a hydrothermal method. Over this time series, the measured (K + Na)/Nb ratio of the films was found to remain constant, but the bulk K/(K + Na) ratio, x, decreased from an initial value of 0.75–0.56. It was determined that film growth initially proceeded through crystallization of the K-rich phase (K0.75Na0.25)NbO3. For film growth times greater than 3 h, a second perovskite phase with a smaller unit cell volume was detected, with an estimated composition of (K0.36Na0.64)NbO3. As such, the measured bulk composition value x = 0.56 was determined to be the result of a combination of these two phases, as opposed to originating from a single phase. Cross-sectional transmission electron microscopy analyses of films prepared for 6 h revealed that they consist of two layers in the direction normal to the substrate; this bilayer-type structure, only observed for hydrothermal growth of this material, is considered to arise from the large solubility mismatch between the Nb precursor and KOH and NaOH in the growth solution.

In this study, the MnOx–FeOy hollow nanospheres with solid solution structure were prepared by supercritical antisolvent (SAS) process. The average particle size was about 50 nm, and average pore diameter was 7 nm. By applying the SAS method, novel nonsupported MnOx–FeOy catalysts with a Mn/Fe mass ratio of 1:1 showed rather high selective catalytic reduction activity and broad active temperature window. The NOx conversion rate reached 97% at 220 °C, and maintained above 92% from 180 to 260 °C. The experiment results showed that iron doping could cause the apparent change of MnOx morphology and structure, which enhanced the oxidative ability of manganese species and increased surface active oxygen species. Meanwhile, compared with traditional methods, the SAS process could efficiently enhance the interaction between manganese and iron, and produce smaller size and larger pore volume nanoparticles with more active sites on the surface.

C3N4/Bi2WO6 heterojunction photocatalysts were successfully synthesized using consecutive hydrothermal and calcination processes. These photocatalysts were characterized using x-ray diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet-visible diffuse reflectance spectroscopy, x-ray photoelectron spectroscopy, and photoluminescence measurements. The results of these measurements indicated that the Bi2WO6 nanoparticles were approximately 30–50 nm and uniformly distributed on the surface of C3N4 lamellar structures. The 20% C3N4/Bi2WO6 displayed enhanced visible-light absorption from 432 nm to 468 nm. Photocatalytic tests also revealed that the 20% C3N4/Bi2WO6 photocatalyst exhibited significantly enhanced photocatalytic activity compared to that of pure C3N4 and Bi2WO6 under irradiation by visible light (λ > 420 nm). Furthermore, the excellent photocatalytic efficiency of the 20% C3N4/Bi2WO6 photocatalyst was determined to be related to the formation of C3N4/Bi2WO6 heterojunctions, and their presence was found to be generally beneficial for the separation of photogenerated electron–hole pairs.

Segmented nanoporous WO3 is prepared via anodization with an electrolyte containing 1 M Na2SO4 and 0.07–0.7 g of NH4F. Annealing (500 °C for 1 h) was also performed to induce crystallinity in WO3. More pores (50–80 nm in diameter) and thicker porous layer were formed by increasing the amount of NH4F (400 nm for 0.3 g of NH4F). However, further increase of the NH4F amount to 0.5 and 0.7 g did not increase the porous layer thickness. Segmented nanoporous structure formation was attributed to the dissolution of anodic oxide by H+ and F− ions in the electrolyte, as well as the healing process induced by the electric field. The photocatalytic activity of the WO3 samples was evaluated through degradation of methyl orange solution. The as-anodized sample showed lower photocatalytic ability in comparison with the annealed sample because of the amorphous behavior of as-anodized WO3.

Three classical methods (Pseudo-Avrami, Ozawa, and Mo models) were used to correlate nonisothermal melt and cold crystallization kinetics data of neat poly(3-hydroxybutyrate) (PHB) and PHB/carbon black compounds, measured by differential scanning calorimetry. The applicability of the three models was tested comparing model predictions with experimental data. Results suggest that Pseudo-Avrami model fits the experimental data well. Ozawa model does not fit data well, as verified by the large uncertainties and unphysical values of the fitting parameters. Mo model may be considered adequate if moderately deviations could be tolerated. Datasets of all compositions are included as the Supplementary Information.

Recent studies have shown the potential for nanocrystalline metals to possess excellent fatigue resistance compared to their coarse-grained counterparts. Although the mechanical properties of nanocrystalline metals are believed to be particularly susceptible to material defects, a systematic study of the effects of geometric discontinuities on their fatigue performance has not yet been performed. In the present work, nanocrystalline Ni–40 wt%Fe containing both intrinsic and extrinsic defects were tested in tension–tension fatigue. The defects were found to dramatically reduce the fatigue resistance, which was attributed to the relatively high notch sensitivity in the nanocrystalline material. Microstructural analysis within the crack-initiation zones underneath the defects revealed cyclically-induced abnormal grain growth (AGG) as a predominant deformation and crack initiation mechanism during high-cycle fatigue. The onset of AGG and the ensuing fracture is likely accelerated by the stress concentrations, resulting in the reduced fatigue resistance compared to the relatively defect-free counterparts.

Tungsten foams with directional, controlled porosity were created by directional freeze-casting of aqueous WO3 powder slurries, subsequent freeze-drying by ice sublimation, followed by reduction and sintering under flowing hydrogen gas to form metallic tungsten. Addition of 0.51 wt% NiO to the WO3 slurry improved the densification of tungsten cell walls significantly at sintering temperatures above 1250 °C, yielding densely sintered W–0.5 wt% Ni walls with a small fraction of closed porosity (<5%). Slurries with powder volume fractions of 15–35 vol% were solidified and upon reduction and sintering the open porosity ranges from 27–66% following a linear relation with slurry solid volume fraction. By varying casting temperature and powder volume fraction, the wall thickness of the tungsten foams was controlled in the range of 10–50 µm. Uniaxial compressive testing at 25 and 400 °C, below and above the brittle-to-ductile-transition temperature of W, yields compressive strength values of 70–96 MPa (25 °C) and 92–130 MPa (400 °C).

In this paper, numerical study was systematically conducted to analyze the shear banding evolution in bulk metallic glasses (BMGs) with various notches subjected to the uniaxial compression, and the relation between the notched configurations and compressive malleability was therefore elucidated. Free volume was used to be an internal state variable to depict the shear banding nucleation, growth and coalescence in the BMGs with the aid of free volume theory, which was incorporated into ABAQUS finite element method code as a user material subroutine. The present numerical procedure was firstly verified by comparing with the existing experimental data, and then parameter analysis was performed to discuss the impacts of notch shape, notch size, notch orientation, and notch configuration on the plastic deformability of notched samples. The present modeling will shed some light on the failure mechanisms and the toughening design of notched BMG structures in the engineering applications.

Al–Sn binary alloys are fabricated by powder consolidation using high-pressure torsion (HPT). The HPT-processed samples are immersed in pure water and hydrogen generation behavior is investigated with respect to the imposed strain through the HPT processing at a selected temperature in the range of 297–333 K. Microstructures of HPT-processed alloys are analyzed by x-ray diffraction, transmission electron microscopy (TEM), electron probe microanalysis (EPMA) and electron back scattered diffraction (EBSD) analysis. Results show that it is important to add more than 60 wt% of Sn to activate hydrogen generation from the Al–Sn alloys in pure water. TEM and EBSD images reveal significant grain refinement while EPMA results exhibit homogenous distribution of elements achieved by HPT. The grain refinement and distribution of elements attained by HPT processing influence greatly the hydrogen generation rate and yield of the alloys. An Al–80 wt% Sn alloy with an average grain size of ∼270 nm exhibits the highest hydrogen yield and generation rate in pure water at 333 K.

The thixoforging technology has been proved as an effective method to fabricate the in situ Mg2Sip/AM60B composite with excellent performances. The effects of reheating temperature on microstructure and tensile properties have been investigated. The results indicate that the liquid amount, the solubility of Al in α-Mg particles, and the coarsening of the α-Mg particles are changed as the reheating temperature changes, and thus the subsequent solidification behavior and plastic deformation are thereby changed. The morphology of the Mg2Si particle also varies as the reheating temperature rises owing to partial remelting operating in the edges and corners of the particles. The best ultimate tensile strength and elongation of 209 MPa and 11.9% of the thixoforged composite, which are 93 and 138% higher than the traditional permanent mold casting respectively, are obtained under the reheating temperature of 600 °C.

The microstructure evolution and mechanical properties of ultrafine-grained (UFG) Al sheets subjected to accumulative roll bonding (ARB) and subsequent cryorolling was studied. Cryorolling can suppress the dynamic softening of UFG Al sheets subjected to ARB at room temperature. After the third ARB pass, the grains are slightly refined as the number of ARB passes increases. However, the grains are significantly refined further during cryorolling. The grain size of 460 nm achieved after the third ARB pass is reduced to 290 nm after two cryorolling passes with total reduction ratio 80%. Sheets subjected to ARB + cryorolling show improved mechanical properties compared to only ARB-processed sheets due to a change in the fraction of high-angle boundaries and elongated grains. The deformation mechanism for ultrafine grains at room temperature is determined by grain boundary sliding or dislocation-based recovery, while it is governed by dislocation glide at cryogenic temperature.

An Fe–0.26C–1.96Si–2Mn with 0.31Mo (wt%) steel was subjected to a novel thermomechanical processing route to produce fine ferrite with different volume fractions, bainite, and retained austenite. Two types of fine ferrites were found to be: (i) formed along prior austenite grain boundaries, and (ii) formed intragranularly in the interior of austenite grains. An increase in the volume fraction of fine ferrite led to the preferential formation of blocky retained austenite with low stability, and to a decrease in the volume fraction of bainite with stable layers of retained austenite. The difference in the morphology of the bainitic ferrite and the retained austenite after different isothermal ferrite times was found to be responsible for the deterioration of the mechanical properties. The segregation of Mn, Mo, and C at distances of 2–2.5 nm from the ferrite and retained austenite/martensite interface on the retained austenite/martensite site was observed after 2700 s of isothermal hold. It was suggested that the segregation occurred during the austenite-to-ferrite transformation, and that this would decrease the interface mobility, which affects the austenite-to-ferrite transformation and ferrite grain size.