Perovskite-based solar cells, typically CH3NH3PbI3, have reached power conversion efficiencies on par with single crystal silicon solar cells. Perovskite cells prepared with the most common perovskite solvent N,N-dimethylformamide (DMF) by different research groups exhibit disparate efficiencies and stability for nominally identical perovskite films. Although the differences can be related to processing conditions, a consistent physical cause for the differences has been lacking. Highly-sensitive time-of-flight secondary ion mass spectrometry (TOF-SIMS) reveals significant dimethylamine (DMA) included in perovskite films. TOF-SIMS and x-ray photoelectron spectroscopy results suggest DMA levels ranging from roughly 10–50%. Only the highest levels register as perovskite peak shifts in x-ray diffraction; lower levels are invisible. We propose that methylamine (MA) can react with DMF solvent by transamidation to produce dimethylamine (DMA), which then displaces some MA in perovskite crystals, see Fig. 1. Transamidation of DMF can be catalyzed by TiO2, Al2O3, water, or acid, but in perovskite films transamidation is inhibited by water.

A CeO2/ZrO2-hydroxyapatite (HA) composite bio-ceramic coating was prepared on ZK60 magnesium (Mg) alloy by using micro-arc oxidation (MAO) and electrophoretic deposition (EPD). MAO coating was done as the basal layer was grown in alkaline electrolyte with the addition of nanoparticles (CeO2 and ZrO2) to improve the mechanical properties of coating. A HA coating as the covering layer was deposited on the surface of MAO coating for improving the biological properties of the coating. The phase compositions and morphology of coatings were monitored with X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Adhesion and wear resistance of coatings were evaluated using a scratch test and a pin-on-disc sliding wear test. The corrosion resistance of coatings was evaluated in a simulated body fluid (SBF) using electrochemical tests at 36.5 ± 0.5 °C. The experimental results showed that the CeO2/ZrO2-HA composite coating on Mg alloy effectively improved its mechanical properties and corrosion resistance. Combining MAO and EPD is a promising modification technology for degradable Mg alloys as biomaterials.

Surface treatments such as shot peening, deep rolling, or nitriding are known to be very effective for the protection of a surface against fatigue crack initiation, due to surface hardening and residual compressive stresses introduced below the surface. Thus, crack initiation of cyclically loaded materials occurs predominantly at internal nonmetallic inclusions (NMIs). Two different plasma-nitriding treatments were performed on a quenched and tempered 42CrMo4 cast steel. Ultrasonic fatigue tests were performed up to 109 cycles. Resonant frequency and the nonlinearity parameter were recorded in situ during the fatigue tests. Fractographic analyses were performed by means of scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy. The results showed that nitriding, as expected, led to improvements in both fatigue life and rates of internal crack initiation at NMIs. However, the analysis of in situ parameters revealed that internal crack initiation occurred at stress amplitude levels well below the failure stress amplitude even for repeated loading until the run-out limit of 109 cycles.

The effects of high magnetic fields on the solidification structures of ternary Al–Fe–Zr alloy were investigated. The results showed that the primary Al3Fe crystals mainly show bar-like form, whereas the unmelted Al3Zr crystals reveal tabular and the newly crystallized primary Al3Zr crystals have fine/coarse needle-like forms. When a 12 T magnetic field is applied, the primary Al3Fe crystals are distributed homogenously and the fine needle-like primary Al3Zr levitated. Moreover, the primary Al3Fe crystals align horizontally in the upper but vertically in the lower part of the specimen. The needle-like primary Al3Zr crystals align vertically, whereas the tabular ones have their two opposite corners on the large surfaces toward the positive and negative magnetic field direction. Crystallographic analysis indicates that 〈100〉 and 〈110〉 are the preferred axes of the primary Al3Fe and the Al3Zr crystals with respect to the magnetic field, respectively. The redistribution and realignments of the crystals are discussed.

The growth behavior of epitaxial transition metal oxides with the perovskite structure often shows discrepancies with models established for semiconductor and metal films. The reason is rooted in the versatility of such octahedral framework structures to accommodate the interfacial dissimilarity and the participation of strongly coupled electron and lattice degrees of freedom in strain relaxation mechanisms. Here, we revisit the behavior of the prototypic La0.7Sr0.3MnO3 manganite under specific growth conditions, enabling the isolation of pure octahedral tilting and misfit dislocation mechanisms in the same material. Analysis of the observed behavior provides insights into the competition between octahedral tilting and classical relaxation mechanisms by misfit dislocations or domain formation, and the effect of additional contributions to dissimilarity such as symmetry mismatch and polar discontinuities. Moreover, given the intimate association between misfit relaxation and self-organization mechanisms, opportunities and limitations of the observed behavior in the generation of novel bottom-up functional nanostructures is also addressed.

Metallic glasses (MGs) are known to have high strength, but poor ductility. Prior studies have shown that plasticity in MG can be enhanced by significantly reducing their dimension to nanoscale. Here we show that, via the introduction of certain types of crystalline/amorphous interfaces, plasticity of MG can be prominently enhanced as manifested by the formation of ductile “dimples” in a 2 μm thick amorphous CuNb film. By tailoring the volume fraction and architecture of crystalline/amorphous multilayers, tensile fracture surface of MG can evolve from brittle featureless morphology to containing ductile dimples. In situ micropillar compression studies performed inside a scanning electron microscope show that shear instability in amorphous layers can be inhibited by interfaces. The mechanisms for improving plasticity and fracture resistance of MG via interface and size effect are discussed.

The amorphous carbon thin films were deposited by the ion beam sputtering deposition technique on Ni–Cu alloy substrates. The effect of sputtering ion beam energy on wettabillity, surface, and structural properties of thin films was examined. The sputtering ion beam energy was varied over a wide range from 2 to 5 keV. Raman spectra showed that the values of ID/IG ratio and the ‘G’ peak position have a reduction trend by increasing the argon ion beam energy while the surface roughness increased due to the resputtering effect. The wettability and surface energy of a-C carbon films were studied by contact angle measurements in relation to structure and topography. The deposited films showed a relatively high water contact angle (CA) that decreases from 87° to 75°. The X-ray photoelectron spectroscopy showed that the value of sp3/sp2 bond content of a-C thin films deposited with the highest argon ion beam energy of 5 keV was about 0.8. Furthermore, the optical band gap followed similar trends of the structural properties.

Three dimensional (3D) porous graphene decorated with MoO2 nanoparticles were successfully synthesized by hydrothermal method and characterized by SEM and TEM, x-ray diffraction, Raman spectra, x-ray photoelectron spectroscopy, nitrogen adsorption–desorption analysis and electrochemical experiments. The results revealed that the in situ formed monoclinic MoO2 nanoparticles were randomly decorated on the surface of graphene sheets and the obtained graphene–MoO2 nanohybrids were 3D porous structures. The mass ratio of molybdenum precursor with GO has effects on the specific surface area and the electrochemical properties of the nanocomposite. The M30G1 (the mass ratio of molybdenum precursor with GO was 30:1) composite electrode exhibited a higher specific capacitance and better cycling stability. The specific capacitances were 356 F/g at the current density of 0.1 A/g in KOH electrolyte, which predicted their potential application in energy storage. The electrochemical performance of M30G1 composite was also investigated in Na2SO4 electrolyte, which was poorer than that in KOH electrolyte. Therefore, the chosen of electrolyte is important to materials performance.

This article presents innovative work undertaken to evaluate the auxetic composite materials developed using weft-knitted fabrics with negative Poisson’s ratio (NPR) produced from high-tenacity filaments of para-aramid (p-AR) and polyamide. The aim of this study is to develop polymeric composite materials reinforced with auxetic knitted fabrics and to evaluate the degree of transference of the auxetic behavior from the fibrous reinforcement to the composite produced. The results show that the NPR values remained in the composites. Regardless of the type of resin used, either epoxy or polyester, the highest values were obtained for samples produced with p-AR auxetic knitted fabrics. The NPR composites developed within this work present great potential for applications in industrial areas, including personal protection products, such as bulletproof vests, helmets, knee, and elbow protectors, and in all other areas where energy absorption is a key factor to be considered.

Copper(I) oxide (Cu2O) is a very favorable p-type semiconductor. It is an appealing candidate for photoelectrochemical water splitting. Here we report the fabrication and performance of gold (Au) underlayer–Cu2O composite photocathode for photoelectrochemical water splitting. The composite photocathode was fabricated by the electrodeposition technique. The different morphologies of the Au underlayer were achieved via variation in the process parameters including applied potential, electrolyte pH, and the presence of L-cysteine in the electrolyte. The Cu2O overlayer was also deposited using electrodeposition. Additionally, the influence of morphology variation, of the Au underlayer, on the performance of the composite photocathode was evaluated. It was observed that the performance of the composite photocathode increased by 81% when compared to a control sample of Cu2O. The composite photocathodes were characterized by scanning electron microscopy, X-ray diffraction, and electrochemical impedance spectroscopy.

The present work describes the shear creep behavior of the superalloy LEK 94 at temperatures between 980 and 1050 °C and shear stresses between 50 and 140 MPa for loading on the macroscopic crystallographic shear system (MCSS) (011) $\left[ {01\bar 1} \right]$ . The strain rate versus strain curves show short primary and extended secondary creep regimes. We find an apparent activation energy for creep of Q app = 466 kJ/mol and a Norton-law stress exponent of n = 6. With scanning transmission electron microscopy, we characterize three material states that differ in temperature, applied stress, and accumulated strain/time. Rafting develops perpendicular to the maximum principal stress direction, γ channels fill with dislocations, superdislocations cut γ′ particles, and dislocation networks form at γ/γ′ interfaces. Our findings are in agreement with previous results for high-temperature and low-stress [001] and [110] tensile creep testing, and for shear creep testing of the superalloys CMSX-4 and CMSX-6 on the MCSSs (111) $\left[ {01\bar 1} \right]$ and (001)[100]. The parameters that characterize the evolving γ/γ′ microstructure and the evolving dislocation substructures depend on creep temperature, stress, strain, and time.

The predictability of modified constitutive model, based on Arrhenius type equation, for illustrating the flow behavior of Fe–36%Ni Invar alloy was investigated via isothermal hot compression tests. The hot deformation tests were carried out in a temperature range of 850–1100 °C and strain rates from 0.01 to 10 s−1. True stress-true strain curves exhibited the dependence of the flow stress on deformation temperatures and strain rates, which then described in Arrhenius-type equation by Zener–Holloman parameter. Moreover, the related material constants and hot deformation activation energy (Q) in the constitutive model were calculated by considering the effect of strain as independent function on them and employing sixth polynomial fitting. Subsequently, the performance of the modified constitutive equation was verified by correlation coefficient and average absolute relative error which were estimated in accordance with experimental and predicted data. The results showed that the modified constitutive equation possess reliable and stable ability to predict the hot flow behavior of studied material under different deformation conditions. Meanwhile, Zener–Holloman parameter map was established according to the modified constitutive equation and used to estimate the extent of dynamic recrystallization.

A comparison of two electron microscopy techniques used to determine the polarity of GaN nanowires is presented. The techniques are convergent beam electron diffraction (CBED) in TEM mode and annular bright field (ABF) imaging in aberration corrected STEM mode. Both measurements were made at nominally the same locations on a variety of GaN nanowires. In all cases the two techniques gave the same polarity result. An important aspect of the study was the calibration of the CBED pattern rotation relative to the TEM image. Three different microscopes were used for CBED measurements. For all three instruments there was a substantial rotation of the diffraction pattern (120 or 180°) relative to the image, which, if unaccounted for, would have resulted in incorrect polarity determination. The study also shows that structural defects such as inversion domains can be readily identified by ABF imaging, but may escape identification by CBED. The relative advantages of the two techniques are discussed.

Sheets made of 316 stainless steel (100 × 100 × 1 mm3) were irradiated by laser at 1, 5, 10, and 15 passes under natural and forced cooling. Results showed that the deflection angle increased with the number of radiation passes. The bending angle after 15 passes of exposure under forced cooling was 5° higher than under natural cooling. The grain size under natural cooling increased from approximately 23–35 μm. By contrast, under forced cooling, the grain size decreased from approximately 37–27 μm. The sample hardness declined under natural cooling from approximately 212–200 HV. By contrast, sample hardness increased from approximately 216–233 HV under forced cooling. Polarization results show that the breakdown potential versus the number of lasing passes increased from −0.14 to −0.08 V under natural cooling and −0.16 to −0.06 V under forced cooling.

SrTiO3 is an important photocatalyst for hydrogen evolution under solar light, a promising way to solve energy shortage. However, a rapid and efficient method to synthesize high-performance SrTiO3 used for this purpose still remains a challenge. In this work, we successfully prepared SrTiO3 catalyst with narrowed band gap through a rapid laser-melting method of a limited reaction time to seconds. The prepared SrTiO3 catalyst, which has a band gap of 3.05 eV, presents enhanced photocatalytic performance for hydrogen evolution under visible light. The evolution rate of laser-melted SrTiO3 is approximately 3.5 times higher than that of pristine SrTiO3. In addition, the magnetism in laser-melted SrTiO3 is also enhanced, which could not be observed in pristine SrTiO3, confirming the defective structure of the obtained laser-melted SrTiO3. The proposed laser-melting method will be a promising way to rapidly and efficiently synthesize homogeneous, solar-driven SrTiO3 photocatalyst for hydrogen evolution with rich defects and thus high-performance.

Gold, palladium, and platinum aerogels were prepared by a rapid, direct solution-based reduction synthesis with densities of 0.54, 0.065, and 0.055 g/cm3, respectively. Salt solutions were reduced at 1:1 (v/v) with dimethylamine borane and sodium borohydride to rapidly form gels within seconds to minutes above a threshold salt concentration and were then rinsed and freeze dried. Au, Pd, and Pt aerogels had no presence of oxide phases confirmed by X-ray diffractometry. Specific surface areas determined with gas physisorption were 3.06, 15.43, and 20.56 m2/g for Au, Pd, and Pt. Electrochemically determined specific capacitances using electrochemical impedance spectroscopy and cyclic voltammetry were 2.18, 4.13, and 4.20 F/g, and 2.67, 7.99, and 5.12 F/g for Au, Pd, and Pt, respectively. The rapid synthesis, high solvent accessible specific surface area, conductivity, and capacitance make these noble metal aerogels candidates for many of catalytic, energy, and sensor applications.

For the first time, valence electron energy-loss spectroscopy (VEELS) was applied to individual single-crystalline SnO2 nanowires to investigate the dielectric function, band gap, and optical absorption coefficient. The results are compared with data from optical techniques such as spectroscopic ellipsometry and UV-Vis, and theoretical calculations from variations of density functional theory. The data obtained agree well with the standard optical and theoretical techniques. The dielectric function and optical absorption coefficient are given up to 20 eV, which otherwise requires a synchrotron source and large single crystals via optical methods. The energy loss function is given up to 40 eV, which gives a useful comparison to previous theoretical studies in an energy range that cannot be achieved via optical measurements. The comparison gives confidence in the accuracy of this method for exploring spatially-resolved measurements in individual nanoparticles or more complex nanostructures that are otherwise difficult to measure accurately using optical techniques.

In this paper, drop-weight impact test was carried out on an integrated composite sandwich panel of aluminum honeycomb and epoxy resin to investigate its failure modes and typical force–displacement curves, and the influences of different parameters on plateau phase duration time, nominal stress, and energy absorption capacity were analyzed. Dynamic impact test results indicated that this integrated composite sandwich panel had good integrality, stability, and energy absorption capacity. The force–displacement curves of flat-bottom impactor and gradual impactor respectively had seven and five phases. Impact velocity, impactor shape, and specimen thickness had significant influences on the plateau phase duration time, nominal stress, and energy absorption capacity of the composite panel. It can be found from our results that the mechanical properties of the integrated composite sandwich panel were superior to those of traditional sandwich panels.

This research was designed for the first time to investigate the photocatalytic activities of MoO3/g-C3N4 composite in converting CO2 to fuels under simulated sunlight irradiation. The composite was synthesized using a simple impregnation-heating method and MoO3 nanoparticles was in situ decorated on the g-C3N4 sheet. Characterization results indicated that the introduction of MoO3 nanoparticles into g-C3N4 fabricated a direct Z-scheme heterojunction structure. The effective interfacial charge-transfer across the heterojunction significantly promoted the separation efficiency of charge carriers. The optimal CO2 conversion rate of the composite reached 25.6 μmol/(h gcat), which was 2.7 times higher than that of g-C3N4. Additionally, the synthesized MoO3/g-C3N4 also presented excellent photoactivity in RhB degradation under visible-light irradiation.

Bragg coherent X-ray diffraction imaging has been used to determine the structure of the initial clusters of α-Fe nano crystals which form upon annealing of an iron-based amorphous alloy or metallic glass. The method is able to identify the shapes and strain of these crystallites without any need for cutting the sample, so can visualize them in three dimensions in their intact state. In this way, the delicate dendritic structures on the exterior of the crystallites can be seen and its density versus radius relationship identifies a fractal dimension of the porous region that is consistent with diffusion-limited aggregation models. The crystal sizes were found to be around 60 nm after annealing at 700 °C growing to about 330 nm after annealing at 750 °C. This article introduces the BCDI method and describes its application to characterize previously recrystallized samples of iron-based amorphous alloys. It paves the way for a possible future in situ nucleation/growth investigation of the relationship between kinetics and nanostructure of metallic glass.