In this work, we present a detailed investigation of the growth of palladium-seeded GaAs nanowires. Nanowires grown on GaAs (111)B substrates consist of three different morphologies, denoted as curly (containing multiple kinks), inclined (relative to the substrate, such as 〈001〉), and vertical. We show that the relative yield of the different types is controllable by a combination of V/III ratio and temperature, where vertical and inclined nanowires are promoted by a high temperature and low V/III ratio. These growth conditions are expected to promote a higher Ga incorporation into the Pd particle, which is confirmed by energy dispersive x-ray analysis. We propose that the observed relationship between particle composition and nanowire morphology may be related to the particle phase, with liquid particles promoting straight nanowire growth. In addition, particles at the tips of nanowires are sometimes observed to be smaller than the initial particle size, suggesting that Pd has been lost during the growth process. Finally, we demonstrate the importance of initial particle size-control to interpret diameter changes after growth.

In this study, the temperature gradient on lunar surface was simulated by deep cryogenic treatment and cryogenic thermocycling. The influence of these treatments on room and low temperature tensile properties and fracture behavior of the as-cast Mg–10Gd–3Y–0.5Zr alloy was then investigated. The results have shown that the cryogenic treatments caused the precipitation of Mg24(Gd, Y)5 phase and improved the ductility of the alloy. The deep cryogenic treatment almost has no influence on the tensile properties of the alloy, while the cryogenic thermocycling slightly improve its tensile properties at room temperature and slightly deteriorate the ultimate tensile strength of the alloy at low temperature. The cleavage fracture is the main fracture mechanism at both room and low temperatures. To conclude, this alloy can withstand the huge temperature gradient on the lunar surface and shows application perspective.

Magnetotactic bacteria mineralize nanometer-size crystals of magnetite (Fe3O4) through a series of protein-mediated reactions that occur inside of organelles called magnetosomes. Mms6 is a transmembrane protein thought to play a key role in magnetite mineralization. We used both electron and fluorescent microscopy to examine the subcellular location of Mms6 protein within single cells of Magnetospirillum magneticum AMB-1 using Mms6-specific antibodies. We also purified magnetosomes from M. magneticum to determine if Mms6 was physically attached to magnetite crystals. Our results show that Mms6 proteins are present during crystal growth, and Mms6 is found in direct contact with the magnetite crystals or within the lipid/protein membrane surrounding the magnetite crystals. Mms6 was not detected at other subcellular locations within the bacteria or isolated fractions. Because Mms6 was found to completely surround the magnetosomes rather than being localized to one specific area of the magnetosome, it appears that this protein could act on the entire magnetite crystal during the biomineralization process. This supports a model in which Mms6 functions to regulate Fe3O4 crystal morphology. This knowledge is important for future in vitro experiments utilizing Mms6 to synthesize tailored nanomagnets with specific physical or magnetic properties.

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.

The 1 nm tin oxides–tin (SnO x –Sn) compound films were thermally evaporated onto the chemical vapor deposition (CVD)-grown graphene films for the improved nitrogen dioxide (NO2) gas sensitivity, and the effects of the fabrication temperature and oxygen (O2) flux on the properties of the SnO x –Sn/graphene hybrid sensors including their composition, morphology, and microstructure as well as NO2 sensitivity were investigated. The composition of the SnO x –Sn compound films exhibited strong dependence on the fabrication temperature and O2 flux which could be ascribed to the hybrid effect of the desorption of the oxygen functional groups on the graphene and oxidation of the graphene and Sn. Such combining effects also demonstrated tremendous influence on the SnO x –Sn film morphology, in which the enhanced desorption of the oxygen functional groups on the graphene together with the oxidation of Sn with increasing fabrication temperature would facilitate the formation of large grain-sized and discontinuous films while the increasing O2 flux showed the opposite effects. Meanwhile, the crystallization of the SnO x –Sn compound films was promoted and deteriorated with the increasing temperature and O2 flux, respectively. The SnO x –Sn film morphology played vital role in NO2 gas sensitivity at room temperature, and the mechanism responsible for that was also discussed.

Among the different energy storage technologies under study, lithium–oxygen batteries are one of the most promising due to their great gravimetric energies and capacities 6–10 times greater than other technologies such as conventional lithium-ion cells. The current study provides a comprehensive understanding of how the anodic (e.g., dendrites) and cathodic designs (e.g., porosity of the carbon cathode and mass fraction of oxygen) affect the discharge characteristics of lithium–oxygen cells. When comparing all changes in dendrite surface, porosity and oxygen restriction, it is concluded that although the changes in porosity and oxygen decrease the performance of the cells, the dendrites led to the greatest decrease in performance of the battery when examining the capacity of the cell. This comprehensive understanding will aid in the design of a cyclable and commercially viable lithium–oxygen battery that could be used for a wide range of energy storage applications.

The solid–liquid interfacial free energy of silicon was calculated by the method based on classical nucleation theory (CNT), where the molecular dynamic (MD) simulations were carried out, and a series of cylindrical solid nuclei were equilibrated with undercooled liquid phase to create an ideal model of a homogeneous nucleation. The interfacial free energy was extracted from the relationship between the critical nuclei radii and their corresponding equilibrium temperatures. The influence of the interfacial curvature on its free energy was for the first time considered in our work, the influence can be measured by a Tolman length which was introduced to modify the traditional CNT; therefore, more accurate results were obtained. The averaged melting point and Tolman length extracted from simulations were 1678.27 K and 2.82 Å, respectively, which are consistent with the expected results. The averaged interfacial free energy is 401.92 mJ/m2, which is in good agreement with the results from experiments.

In this study, hematite nanoparticles (α-Fe2O3 NPs) were synthesized by hydrothermal method, with morphologies (e.g., nanorhombohedra, nanobars, and nanospheres) facilely tuned by changing the concentrations of glycol in the hydrothermal solution. Then a low-cost and scalable electrophoretic deposition method was used to fabricate nanostructured α-Fe2O3 films as photoanodes for solar hydrogen generation. It was found that the film of α-Fe2O3 nanobars showed the highest photoelectrochemical (PEC) performance compared to those films of α-Fe2O3 nanorhombohedra and nanospheres, with photocurrent density reaching 0.7 mA/cm2 at 0.6 V versus Ag/AgCl. This PEC improvement may be related to the smaller diameters of nanobars shortening the carrier migration distance, reducing the recombination rate of photo-generated carriers. Moreover, all the α-Fe2O3 films showed much higher PEC performances with surface modified by Sn4+, mainly due to the reduced surface charge recombination, as the Sn4+ doped overlayer passivated surface defects. For the film of α-Fe2O3 nanobars, the photocurrent density was increased by 100%, reaching 1.4 mA/cm2 at 0.6 V versus Ag/AgCl.

Sn doped TiO2 (SDT) hierarchical nanorods have been synthesized by using nanocystalline cellulose nanorod as biotemplate. Experimental results show that the phase transition from anatase to rutile can be realized by increasing the calcination temperature. In contrast to enhancing the calcination temperature, the Sn doping can more effectively improve the phase transition with remaining morphology due to the similar ionic radius and charge between Sn and Ti. The crystallinity, electronic structure, interface charge transfer process, and the specific surface area have a strong effect on the photocatalytic activity of the hierarchical TiO2 and SDT nanorods. Furthermore, the photocatalytic activity of SDT hierarchical nanorods can be obviously improved by loaded Au nanoparticles on the surface due to the local surface plasmon resonance effect of Au and formation of a Schottky barrier at the Au/TiO2 interface, which is in favor of the effective separation of photoinduced carriers and the formation of superoxide anion radicals.

In the past decade, the research in designing fast oxygen conducting materials for electrochemical applications has largely shifted to microstructural features, in contrast to material-bulk. In particular, understanding oxygen energetics in heterointerface materials is currently at the forefront, where interfacial tensile strain is being considered as the key parameter in lowering oxygen migration barriers. Nanocrystalline materials with high densities of grain boundaries have also gathered interest that could possibly allow leverage over excess volume at grain boundaries, providing fast oxygen diffusion channels similar to those previously observed in metals. In addition, near-interface phase transformations and misfit dislocations are other microstructural phenomenon/features that are being explored to provide faster diffusion. In this review, the current understanding on oxygen energetics, i.e., thermodynamics and kinetics, originating from these microstructural features is discussed. Experimental observations, theoretical predictions and novel atomistic mechanisms relevant to oxygen transport are highlighted. In addition, the interaction of dopants with oxygen vacancies in the presence of these new microstructural features, and their future role in the design of future fast-ion conductors, is outlined.

The aim of this study was the synthesis of hard and low-abrasive novel implant materials with built-in time-dependent antibacterial properties, which can be tailored by a well-defined time-dependent and finite release of metal ions. We were able to synthesize such smart implant surfaces employing ECR (electron cyclotron resonance)-plasma on typical titanium implant material by transforming a polymer film into diamond-like carbon (DLC) which contains metal nanoparticles as reservoirs for controlled metal ion release. We found that the amount of released antibacterial metal ions is a biexponential function of time with a high release rate during the first few hours followed by a decreased ion release rate within the following days. To describe our experimental findings, we developed a kinetic model assuming that both nanoparticles near the surface and nanoparticles in the DLC bulk contribute to the total amount of ions released with different time constants.

This paper, for the first time, reports the results of microwave sintering of two emerging biomaterials, magnesium phosphate and amorphous magnesium calcium phosphate. Beneficial aspects of successful microwave sintering of calcium phosphate are well documented in the literature. The motivation for this work derives from the absence of any publication of similar nature on magnesium phosphates, which are becoming important with the rapid rise in interest in biodegradable Mg-alloys. Starting off with amorphous calcium magnesium phosphate and magnesium phosphate, the resulting microwave sintered product is a biphasic mixture of whitlockite substituted with magnesium and magnesium phosphate. The influence of the extent of Mg substitution on the mechanical properties, microstructure, and sintering behavior of tricalcium phosphate was evaluated. The results showed that the addition of Mg (up to the 50% wt/wt in relation to Ca mass) in the precursor compound of magnesium calcium phosphate improved the kinetics of the densification process and enhanced hardness values.

Tribological performance of industrial applications involving boundary lubrication regime can be improved by depositing surface coatings such as diamond-like carbon (DLC) on the interacting surfaces. DLCs are considered as hard coatings with unique combination of properties which results in minimizing the friction induced energy and material losses especially under starved lubrication conditions. In spite of high wear-resistance and ultralow friction coefficients, there are a lot of factors that can directly influence the tribological characteristics of DLC coatings. Although, many studies were conducted to comprehend the effects of intrinsic/extrinsic conditions on tribological behavior of these coatings, still there is a lack of understanding due to contradictory remarks. Therefore, there is a need to rearrange the published data in an organized manner for logical continuation of research. In this paper, a brief introduction of DLC coatings is presented followed by detailed discussion on conditions that can directly influence their tribological properties.

The evolution behavior of Ni2(Cr, Mo) phase with Pt2Mo-type structure in the Ni–Cr–Mo alloy with a low atomic Mo/Cr ratio subjected to a long-term thermal exposure of 100–340 h at 600 °C was investigated using transmission electron microscopy and microhardness. Results demonstrate that there is a linear relationship between major axis cube (L 3) of ordered domain and thermal exposure time (t) followed by a coarsening regime described by the Lifshitz–Slyozov–Wagner model, as well as between the aspect ratio (D) of ordered domain and thermal exposure time. The volume fraction of ordered domain increases with increasing thermal exposure time, whereas the hardening of samples decreases due to growth-coarsening of ordered domain. Prolonged thermal exposure time led to the coarsening of ordered domain by rate of (3.39 ± 0.02) × 10−30 m3/s without changing their crystallography and ordering characteristics during thermal exposure. Plastic deformation before thermal exposure do not lead to decomposition of initial Ni2(Cr, Mo) phase, but both plastic deformation and thermal exposure affect their morphology and distribution.

The structural organization of the palliostracum—the dominant part of the shell which is formed by the mantle cells—of Glycymeris glycymeris (Linné 1758) is comprised of five hierarchical levels with pronounced structural commonalities and deviations from other crossed-lamellar shells. The hierarchical level known as second order lamellae, present within other crossed-lamellar shells, is absent highlighting a short-coming of the currently used nomenclature. On the mesoscale, secondary microtubules penetrate the palliostracum and serve as crack arrestors. Moreover, the growth lamellae follow bent trajectories possibly impacting crack propagation, crack deflection, and energy dissipation mechanisms whilst circumventing delamination. Finally, at least two structural elements are related to external circatidal and circaanular stimuli. This emphasizes that endogeneous rhythms may contribute and (co-)control the self-organization of a complex mineralized tissue and that it is insufficient to rely fully on a reductionistic approach when studying biomineralization.

Dentinogenesis imperfecta type II (DGI-II) lacks intrafibrillar mineral with severe compromise of dentin mechanical properties. A Dspp knockout (Dspp–/–) mouse, with a phenotype similar to that of human DGI-II, was used to determine if poly-L-aspartic acid [poly(ASP)] in the “polymer-induced liquid-precursor” (PILP) system can restore its mechanical properties. Dentin from six-week old Dspp–/– and wild-type mice was treated with CaP solution containing poly(ASP) for up to 14 days. Elastic modulus and hardness before and after treatment were correlated with mineralization from Micro x-ray computed tomography (Micro-XCT). Transmission electron microscopy (TEM)/Selected area electron diffraction (SAED) were used to compare matrix mineralization and crystallography. Mechanical properties of the Dspp–/– dentin were significantly less than wild-type dentin and recovered significantly (P < 0.05) after PILP-treatment, reaching values comparable to wild-type dentin. Micro-XCT showed mineral recovery similar to wild-type dentin after PILP-treatment. TEM/SAED showed repair of patchy mineralization and complete mineralization of defective dentin. This approach may lead to new strategies for hard tissue repair.

The NaLa(MoO4)2:Yb3+/Er3+ phosphor is synthesized through hydrothermal method with the further calcinations. The intense green upconversion (UC) emission is observed when it is excited by 980 nm pump power. Then we investigate the mechanism of UC emission based on the power dependent upconversion luminescence (UCL) spectra. Temperature sensing performance based on the Stark levels (2H11/2/4S3/2) of Er3+ is estimated through investigating temperature-dependent UCL spectra from 298 K to 573 K. And the maximum value of sensor sensitivity based on FIR is approximately 0.00474 K−1. Moreover, the variations of UCL intensities from 2H11/2/4S3/2 → 4I15/2 transitions have been monitored with increasing pump power, which suggests that the pump energy can be absorbed by sample and heat it. In addition, the internal temperature of materials can be estimated by FIR technique. All the experimental results indicate that the phosphor has good potential in optical temperature sensing and optical heating.

Device quality CdS/CdTe heterostructures and completed solar cells (∼12% efficient) have been studied using photoluminescence (PL) as a function of temperature and laser excitation power. The CdS/CdTe junctions were grown on transparent conducting oxide covered soda lime glass using radio frequency sputter deposition. In the current work we found that the PL spectra of sputtered and thermally evaporated CdTe absorber films share common features. It was found that the luminescence shifts from being dominated by sub-gap defect-mediated emission at lower excitation powers to near band edge excitonic emission at higher excitation powers. It was found that the presence of Cu suppresses the sub-band gap PL emissions. This effect was concluded to be due either to Cu occupying cadmium vacancies (VCd) or forming acceptor complexes with them. This points to a potential role of Cu in eliminating sub-band gap recombination routes and hence increasing the charge separation ability of the device.

In the present investigation, AA6351 aluminum alloy matrix composites reinforced with various percentages of AlN particles were fabricated by stir casting technique. The percentage of AlN was varied from 0 to 20% in a step of 4%. The prepared AA6351-AlN composites were characterized using scanning electron microscope (SEM) and x-ray diffraction (XRD). The mechanical properties such as micro-hardness, compression strength, flexural strength, and tensile strength of the proposed composite have been studied. X-ray diffraction patterns confirm the presence of AlN particles in the composites. SEM analysis reveals the homogeneous distribution of AlN particles in the AA6351 matrix. The mechanical properties of the composite were found to be noticeably higher than that of the plain matrix alloy due to augmented particle content. The produced composites exhibit superior mechanical properties when compared with unreinforced matrix alloy. Fracture surface analysis of tensile specimens show the ductile–brittle nature of failure in the composites.