To detect low concentrations of formaldehyde selectively, the sensing properties of SnO2 nanostructured are enhanced by modifying with p-type semiconductor NiO. In this study, a nanostructured SnO2/NiO composite was prepared by a simple hydrothermal method. The X-ray photoelectron spectroscopy (XPS) peak in 532.4 eV proved that the existence of the SnO2/NiO composite structure increased the amount of adsorbed oxygen O− and O2− significantly. Gas-sensing tests showed that these mixed phases SnO2/NiO are highly promising for gas sensor applications, as the gas response for formaldehyde was significantly enhanced in gas response, selectivity at an operating temperature of 230 °C. The sensor fabricated by SnO2/NiO composite can detect as low as 1 ppm of formaldehyde at 230 °C, and the corresponding response is 1.57. The results of physicochemical properties tests of the samples show that the enhancement in sensitivity and selectivity is attributed to the oxygen vacancies and heterojunction between SnO2 and NiO. The SnO2/NiO composites can be applied to sensitive materials of formaldehyde sensors.

In this study, we report a simple one-pot synthesis of iron oxide nanoparticles (IONPs) modified with thermoresponsive polymers potentially applicable for nucleic acid capture. Ferrous (Fe2+) and ferric (Fe3+) ions were coprecipitated to a dispersion of previously prepared poly(N-isopropylacrylamide-co-2-aminoethyl methacrylate) P(NIPAAm-co-AEM) for in situ synthesis of magnetite (Fe3O4) and concurrent surface modification of Fe3O4 with the polymer to obtain magnetic nanocomposites. Fourier-transform infrared (FTIR) spectroscopy analysis reveals the surface modification of Fe3O4 with P(NIPAAm-co-AEM) and P(NIPAAm) as functional and control polymers, respectively. Fe3O4@P(NIPAAm-co-AEM) and Fe3O4@P(NIPAAm) nanocomposites’ surfaces contain 7.5 and 2.3 wt% of immobilized polymers, respectively. Vibrating sample magnetometry (VSM) result indicates a high saturation of magnetization value, 75 emu/g, for Fe3O4@P(NIPAAm-co-AEM) nanocomposites. The hydrodynamic diameter of Fe3O4@P(NIPAAm-co-AEM) in water changes depending on pH and temperature. A study for deoxyribonucleic acid (DNA) capture ability of Fe3O4@P(NIPAAm-co-AEM) nanocomposites shows a maximum 18.5 mg/g of DNA can be adsorbed on Fe3O4@P(NIPAAm-co-AEM).

In this research, the mechanical alloying (MA) technique was used to study solid solubility in the immiscible Zr–Cr alloy system. At first, Zr and Cr powders were milled, and then, the phase evolution, alloying mechanism, microstructural change, and mechanical properties of the milled powders were investigated by X-ray diffraction technique, scanning electron microscopy along with energy dispersive spectroscopy, transition electron microscopy, and microhardness measurements. Moreover, the solubility limit of Zr in Cr lattice was obtained by Vegard's law. The results showed that the MA was significantly enhanced the solubility of Zr in Cr up to about 21.6 wt% after an optimum milling time of 32 h and led to form an amorphous/nanocrystalline composite of Zr-reach and Cr-reach supersaturated solid solutions with the microhardness value of 503 Hv approximately. Also, the thermodynamic analysis indicated that the Gibbs free energy changes for the amorphous and solid solution were positive, which were provided by the MA process.

A systematic analysis was carried out to study the effect of shock waves on copper sulfate crystal in such a way that its optical properties and surface morphological properties were examined for different number of shock pulses (0, 1, 3, 5, and 7) with the constant Mach number 1.7. The test crystal of copper sulfate was grown by slow evaporation technique. The surface morphological and optical properties were scrutinized by optical microscope and ultraviolet–visible spectrometer, respectively. On exposing to shock waves, the optical transmission of the test crystal started increasing from the range of 35–45% with the increase of shock pulses and thereafter started decreasing to 25% for higher number of applied shocks. The optical band transition modes and optical band gap energies were calculated for pre- and post-shock wave loaded conditions. The experimentally obtained data prove that the optical constants such as absorption coefficient, extinction coefficient, skin depth, optical density, and optical conductivity are strongly altered, so also the optical transmission due to the impact of shock waves. Hence, shock wave induced high transmission test crystal can be used as an appropriate candidate for ultraviolet light filter applications.

Co–Cr–B amorphous catalysts have been synthesized by the chemical reduction method. Catalyst powders were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Brunner-Emmet-Teller measurements (BET). Catalytic performance of the catalyst was measured by the hydrolysis rate of the sodium borohydride solution. Results showed that the particle size of the catalyst was reduced with the addition of a small amount of Cr. The specific surface area increased significantly, and the performance of the catalyst was improved. However, excess addition of Cr caused excess oxides and Cr3+, covering the surface active sites of the catalyst, which degraded the performance of the catalyst. When the ratio of Cr/Co is 0.005, the catalyst performance was optimal and showed nearly 2 times higher H2 generation rate than that of pure Co–B catalyst. In addition, the effect of catalyst content, NaBH4 concentration, reaction temperature, and NaOH concentration on the hydrogen generation of NaBH4 solution was also studied.

The design of high energy Li-ion batteries (LIBs) by coupling high voltage LiNi0.5Mn1.5O4 (LNMO) cathode and Li4Ti5O12 (LTO) anode ensures effective and safe energy-storage. LTO–LNMO full-cells (FCs) with difference in electrode grain sizes and presence of excess Mn3+ in cathode were studied using micron-sized commercial LTO, nanostructured LTO donuts (LTOd), P4332 LNMO nanopowders, and nanostructured Fd3m LNMO caterpillars (LNMOcplr). Among the studied FCs, LTOd–LNMOcplr was detected with a stable capacity of 69 mA h/g (1C rate), 99% coulombic efficiency, and 87% capacity retention under 200 cycles of continuous charge–discharge studies. The superior electrochemical performance observed in LTOd–LNMOcplr FC was due to the low charge transfer resistance, which is corroborated to the effect of grain sizes and the longer retention of Mn3+ in the electrodes. An effective and simple FC design incorporating both nanostructuring and in situ conductivity in electrode materials would aid in developing future high-performance LIBs.

Iron oxide nanoparticles presenting colloidal stability in water were prepared through precipitation and then surface-functionalized with varying citric acid (CA) concentrations (0.10, 0.25, 0.50, and 0.70 g/mL). CA introduced functionality and minimized agglomeration. Iron oxide nanoparticles with colloidal stability in water at physiological pH were obtained after functionalization with 0.25–0.70 g/mL CA, whereas iron oxide nanoparticles without stability in water were obtained after functionalization with 0.10 g/mL CA. An electrode for glucose detection was fabricated by self-assembling colloidal-stable γ-Fe2O3 NP–CA in water on indium tin oxide (ITO) glass, followed by a glucose oxidase (GOx) and Nafion layer. The optimal functionalization of the γ-Fe2O3 NPs was obtained at a CA concentration of 0.25 g/mL. The electrochemical properties and electrocatalytic behavior of the modified electrode designated as Nafion/GOx/γ-Fe2O3 NP–0.25 CA/ITO were then evaluated. The electrode showed high sensitivity for glucose detection of 995.57 and 5.81 µA/(mM cm2) within the linear ranges of 0.1–5.0 µM and 5.0 µM–20.0 mM, respectively. The modified electrode also demonstrated a low limit of detection, good repeatability of 2.5% (n = 10), and sufficient reproducibility of 3.2% (n = 5).

Microwave plasma chemical vapor deposition (MPCVD) was used to diffuse boron into tantalum using plasma initiated from a feedgas mixture containing hydrogen and diborane. The role of substrate temperature and substrate bias in influencing surface chemical structure and hardness was investigated. X-ray diffraction shows that increased temperature results in increased TaB2 formation (relative to TaB) along with increased strain in the tantalum body-centered cubic lattice. Once the strained tantalum becomes locally supersaturated with boron, TaB and TaB2 precipitate. Additional boron remains in a solid solution within the tantalum. The combination of precipitation and solid solution hardening along with boron-induced lattice strain may help explain the 40 GPa average hardness measured by nanoindentation. Application of negative substrate bias did not further increase the hardness, possibly due to etching from increased ion bombardment. These results show that MPCVD is a viable method for synthesis of superhard borides based on plasma-assisted diffusion.

In this investigation, the superalloy IN718 has been prepared by additive manufacturing (AM) following a selective laser melting technique, and the post-AM heat treatments have been optimized. The microstructure of additively manufactured (AM) IN718 is characterized by the presence of dendritic and cellular features with large spatial heterogeneity along and across the build plane. Along the build direction, the 〈100〉 fiber texture dominates. Heat treatment involving two-step solution treatment, and subsequently, two-step aging treatment was specifically designed to facilitate the precipitation of δ phase at the grain boundaries to make the material resistant to grain boundary sliding (GBS). The AM IN718 showed dynamic strain aging (DSA) at three different temperatures, while the critical strain for the onset of serration was extended to a higher value after the heat treatment.

We show interlayer stacking shifts occur in transition metal dichalcogenides (TMD) bilayers due to the strain introduced during sample heating, and attributed to rippling of one layer relative to the other. The atomic structure of the interlayer stacking is studied using annular dark field scanning transmission electron microscopy with an in situ heating holder. Before heating, bilayers show uniform interlayer stacking of AA′ and AB. When heated, contrast change is seen and associated with interlayer stacking changes at the atomic scale due to ripples. When cooled down to room temperature, these contrast features disappear, confirming it is a reversible process that is not related to defects or vacancies. Because the bottom layer is attached to the in situ heating chip made from Si3N4 and the top layer is in contact with the underlying TMD layer with weak van der Waals interaction, the two layers experience different forces during thermal expansion.

The role of negative substrate bias voltage in influencing the microstructural evolution, along with the mechanical and scratch behavior of magnetron sputtered Ni–Zr alloyed thin films, has been investigated. The films have been deposited on a Si(100) substrate by direct current (DC) magnetron co-sputtering of high-purity elemental Ni and Zr targets, using an optimized target power in an argon atmosphere at room temperature by altering the negative substrate bias voltage (0 to −80 V). The increase in negative substrate bias voltages leads to an increase in Zr content of the investigated films. The characterization techniques such as grazing incidence X-ray diffraction and high-resolution transmission electron microscopy studies confirm that an increase in the negative substrate bias voltage leads to an increase in the volume fractions of amorphous phase and Ni3Zr, but a decrease in the deposition rate, surface roughness, and average grain sizes. Hardness and Young's modulus obtained by nanoindentation, along with the coefficient of friction obtained from nano-scratch experiments, appear to be related to the relative volume fractions of both nanocrystalline and the amorphous phase. Furthermore, increase in Ni3Zr volume fraction with decrease in grain size within the crystalline part of the film, with increase in substrate bias used during deposition may have contributed to both increase in both hardness and scratch resistance.

The thermal expansion coefficient (CTE) is a vital design parameter for reducing the thermal-stress-induced structural failure of electronic chips/devices. At the micro- and nano-scale, the typical size range of the components in chips/devices, the CTEs are probably different from that of the bulk materials, but an easy and accurate measurement method is still lacking. In this paper, we present a simple but effective method for determining linear CTEs of micro-scale materials only using the prevalent nanoindentation system equipped with a heating stage for precise temperature control. By holding a constant force on the sample surface, while heating the sample at a constant rate, we measure two height–temperature curves at two positions, respectively, which are close to each other but at different heights. The linear CTE is obtained by analyzing the difference of height change during heating. This method can be applied to study the size effect or surface effect of CTE of embedded micro-scale structures, aiding the failure analysis and structural design in the semiconductor industry.

Lead-free perovskite layers may provide a good alternative to the commonly used lead-halide-based perovskite absorber layers in photovoltaics. Energy level alignment of the active semiconductor with contact layers is a key factor in device performance. Kelvin probe force microscopy was used during vapor deposition of C60 onto formamidinium tin iodide to investigate contact formation with detailed local resolution of these materials that are significant for photovoltaic cells. Significant differences dependent on the growth rate of C60 were detected. Sufficiently high deposition rates were essential to reach compact C60 films needed for good contact. A space charge layer larger than 90 nm within the C60 layer was established without indication of interfacial dipoles. The present analysis gives a clear indication of a well-functioning contact of fullerenes to formamidinium tin iodide that is suitable for the use in photovoltaic devices provided that thin compact fullerene films are formed.

In this study, the quasi-static and dynamic mechanical behaviors and the energy absorption capacity of closed-cell aluminum foams with uniform and graded densities were experimentally studied. The effects of density, strain rate, and graded density on the mechanical performances of aluminum foams were quantitatively evaluated. It was shown that the density had a significant effect on the quasi-static and dynamic compressive stress of aluminum foams. Moreover, impact compression experiment results revealed that aluminum foam was sensitive to the strain rate. As the strain rate increased, the plateau stress and energy absorption capacity increased distinctly and the rate of deformation increased correspondingly. Finally, the investigation of aluminum foams with uniform and graded densities to study their deformation and failure mechanisms, mechanical characteristics, and energy absorption capacities showed that the GD 0.48-IV specimen exhibited superior impact resistance. The present work can provide a valuable reference for the optimum design of aluminum foam against impact loading.

Chiral magnets in the B20 crystal structure host a peculiar spin texture in the form of a topologically stable skyrmion lattice. However, the helical transition temperature (TC) of these compounds is below room temperature, which limits their potential in spintronics applications. Here, a data-driven approach is demonstrated, which integrates density functional theory (DFT) calculations with machine learning (ML) in search of alloying elements that will enhance the TC of known B20 compounds. Initial DFT screening led to the identification of chromium (Cr) and tin (Sn) as potential substituents for alloy design. Then, trained ML models predict Sn substitution to be more promising than Cr-substitution for tuning the TC of FeGe. The magnetic exchange energy calculated from DFT validates the promise of Sn as an effective alloying element for enhancing the TC in Fe(Ge,Sn) compounds. New B20 chiral magnets are recommended for experimental investigation.

Calcium–magnesium–alumino-silicate (CMAS) particulates enter the aero-engine in a sandy environment, melt and infiltrate into 7 wt% yttria-stabilized zirconia (7YSZ) thermal barrier coatings (TBCs), reducing their lifetime. This leads to chemical degradation in 7YSZ accompanied by tetragonal to monoclinic phase transformation upon cooling. In this work, electron-beam physical vapor deposition coatings were infiltrated with a synthetic CMAS. Synchrotron X-ray diffraction measurements show that CMAS infiltration at 1250 °C has about 43% higher monoclinic phase volume fraction (PVF) at the coating surface compared to 1225 °C and remains consistently higher throughout the coating depth. Additionally, the increase in annealing time from 1 to 10 h results in a 31% higher monoclinic phase at the surface. Scanning electron microscopy revealed the presence of globular monoclinic phases corresponding spatially with the above findings. These results resolve the impact of time and temperature on CMAS infiltration kinetics which is important for mitigation.

For the first time in the literature, experimental determination of entire sets of exact interdiffusion coefficients in quaternary and quinary alloy systems is reported. Using the method of body-diagonal diffusion couple, a set of nine quaternary interdiffusion coefficients were evaluated in Fe–Ni–Co–Cr and a set of sixteen quinary interdiffusion coefficients were determined in a Fe–Ni–Co–Cr–Mn system, both at approximately equimolar compositions. Regions of uphill interdiffusion and zero flux planes were observed for nickel and cobalt in quinary couples, indicating the existence of strong diffusional interactions in Fe–Ni–Co–Cr–Mn alloys. The strong diffusional interactions were also manifested in the large magnitudes of cross coefficients in both the systems. The existence of strong diffusional interactions in high-entropy alloys (HEAs) as observed through experimentally determined interdiffusion coefficients in this study establishes beyond doubt the fact that cross interdiffusion coefficients cannot be ignored in HEAs.

A multilevel nonvolatile memory based on an amorphous indium–gallium–zinc oxide thin-film transistor is successfully demonstrated by using an atomic layer–deposited ZnO film as a charge trapping layer. The memory device shows a much higher erasing efficiency at a negative bias, i.e., after erasing at −13 V for 1 μs, the threshold voltage shift is as large as −7.4 V. In the case of 13 V/1 μs programming (P) and −12 V/1 μs erasing (E), the device demonstrates an ON/OFF readout drain current (IDS) ratio of ∼103 after 105 s, and a large and stable ON/OFF IDS ratio of ∼106 till 104 of P/E cycles. Furthermore, multilevel memory characteristics are also demonstrated on the device, showing an IDS ratio of >102 for 4 different states. Additionally, the device also successfully demonstrates typical synaptic behaviors, such as excitatory and inhibitory postsynaptic current with different memory times at different memory states.

The mitigation of CMAS (calcium–magnesium–aluminum–silicon oxide) infiltration is a major requirement for the stability of thermal barrier coatings. In this study, yttria-stabilized zirconia (YSZ)–Al2O3–SiC, YSZ–Al2O3–Ta2O5, and YSZ–Al2O3–Nb2O5 self-healing composites produced by uniaxially pressing powders were investigated as an alternative to YSZ. CMAS infiltration in these materials was tested at 1250 °C for 10 h. Comparing the depth of CMAS infiltration using scanning electron microscope (SEM) in tandem with electron-dispersive X-ray spectroscopy (EDS), all self-healing materials were found to perform better than the reference materials. While standard YSZ shows massive CMAS infiltration, SEM micrographs and EDS maps revealed a 33-fold improvement in CMAS resistance for the YSZ–Al2O3–Nb2O5 system, which exhibited the best performance among the selected self-repairing materials. X-ray diffraction and high-resolution SEM micrographs taken 10 μm below the surface revealed that CMAS only infiltrated pores in the topmost region of the samples. Both YSZ–Al2O3–Ta2O5 and YSZ–Al2O3–Nb2O5 systems showed no signs of chemical reaction with CMAS.

The disruptive potential of additive manufacturing (AM) relies on its ability to make customized products with considerable weight savings through geometries that are difficult or impossible to produce by conventional methods. Despite its versatility, applications of AM have been restricted due to the formation of columnar grains, resulting in solidification defects and anisotropy in properties. To achieve fine equiaxed grains in AM, alloy design and solidification conditions have been optimized in various alloy systems. In this review paper, the microstructure of high-entropy alloy (HEA) parts produced by selective laser melting and powder-based directed energy deposition is investigated. Solidification maps based on laser process parameters (as opposed to most commonly used solidification velocity and temperature gradient) are constructed by compiling available literature for single-phase face-centered cubic, body-centered cubic, and multiphase HEAs. These maps could guide printing of HEAs and provide an insight into the design of novel HEAs for AM.