By using a two-dimensional axisymmetric finite element model, the indentation hardness has been studied with different combinations of material properties at different indentation depths. As the forward problem, the testing hardness is not only a function of material properties (E, σy, and n), indenter geometry (half apex angle, indenter shape), and friction, but also relating to the indentation depth. Based on the previous research on size effect, a model of correlation between several indentation experiment parameters (hardness H, maximum load Pm, and loading curvature C) and material properties has been derived. From simulation results, a better fitting result is obtained by the established model. Furthermore, the characteristic length h∗ in Nix/Gao model has been rewritten and discussed with material properties accordingly.

Cu-based shape memory alloys (SMAs) and among these copper–zinc (Cu–Zn), copper–aluminum (Cu–Al), and copper–tin (Cu–Sn) alloys both with and without ternary additions have shown potential due to their good shape recovery, ease of fabrication, excellent conductivity of heat and electricity. However, their applications are still limited because of the shortcomings of thermal stability, brittleness, and mechanical strength, which are closely related with microstructural characteristic of Cu-based SMAs, such as coarse grain sizes, high elastic anisotropies, and the congregation of secondary phases or impurities along the grain boundaries. Efforts are being made to overcome these drawbacks with proper ternary additions, adopting alternative processing routes and also optimizing the heat treatment cycles. The present article will deal with the current status of research and commercialization of Cu-based SMAs and dwell upon the future directions in which research should be targeted and future prospects of converting the research into components for commercial use.

Microcellular injection molding, a process capable of mass-producing complex plastic parts, and particle leaching methods were combined to fabricate porous thermoplastic polyurethane tissue engineering scaffolds. Water soluble polyvinyl alcohol (PVOH) and sodium chloride (NaCl) were used as porogens to improve the porosity and interconnectivity as well as the hydrophilicity of the scaffolds. It was found in the study that the microcellular injection molding process was effective at producing high pore density and porosity. The addition of PVOH decreased the pore diameter and increased the pore density. Furthermore, scaffolds with NaCl and PVOH porogens showed more interconnected pores. The 3T3 fibroblast cell culture was used to confirm the biocompatibility of the scaffolds. Residual PVOH content after leaching increased the hydrophilicity of the scaffolds and further improved cell adhesion and proliferation. The resulting scaffolds offer an alternative scalable tissue scaffold fabrication method for soft tissue scaffold production.

To selectively detect Cu2+ ions is very important for controlling daily intake of Cu2+ ions and monitoring numerous biological processes. Fluorescence spectroscopic technique is a useful one for detection of copper ions. Previous methods always involve the use of metal Cd-based quantum dots (QDs), which suffer to the photobleaching and subsequent release of toxic metal ions. Herein, a simple method has been developed to detect Cu2+ ions by using pristine graphene QDs. Graphene QDs are synthesized by chemical oxidation of pitch graphite fibers. Our results indicate the photoluminescence (PL) of as-synthesized graphene QDs could be quenched by a group of metal ions while adding biothiol cysteine can only cause the significant recovery of the PL of graphene QDs quenched by Cu2+ ions. Our approach provides an easy and environmental friendly method for detection of Cu2+ ions and has the potential for future practical applications.

Orthorhombic SrIrO3 is a correlated metal whose electronic properties are highly susceptible to external perturbations due to the comparable interactions of spin–orbit interaction and electronic correlation. We have investigated the electronic properties of epitaxial orthorhombic SrIrO3 thin-films under compressive strain using transport measurements, optical absorption spectra, and magnetoresistance. The metastable, orthorhombic SrIrO3 thin-films are synthesized on various substrates using an epi-stabilization technique. We have observed that as in-plane lattice compression is increased, the dc-resistivity (ρ) of the thin films increases by a few orders of magnitude, and the dρ/dT changes from positive to negative values. However, optical absorption spectra show Drude-like, metallic responses without an optical gap opening for all compressively strained thin films. Transport measurements under magnetic fields show negative magnetoresistance at low temperature for compressively strained thin-films. Our results suggest that weak localization is responsible for the strain-induced metal–insulator transition for the orthorhombic SrIrO3 thin-films.

To date graphene and graphene-derived materials have created an immense research interests due to its extraordinary physical, chemical, and physiochemical properties, which delineated graphene as an outstanding material for future electronics, optics, and energy-harvesting devices. Typically, graphene has high mobility and optical transparency along with excellent mechanical properties and chemical inertness. Single-layer graphene exhibits ultrahigh optical transmissivity (∼98%), which allows passing through wide range of light wave lengths, thus designated as an ever-reported material for an optically conducting window. Furthermore, graphene's optical, electrical, and electrocatalytic properties can be tuned by applying different chemical functionalization protocols, which make it one of the most suitable candidates for advanced applications in optoelectronic and energy-harvesting devices. This review is intended to summarize the most important experimental results from the recent publications concerning the fascinating properties of graphene electrodes and their applications in various types of solar cells. Furthermore, the state of the art of different graphene synthesis processes and functionalization for the applications in solar cells are also discussed in this review.

In the work, an in situ chemical synthesis approach has been developed to fabricate SnO2/reduced graphene oxide nanocomposites in ethanol solution. X-ray diffraction, x-ray photoelectron, Fourier transform infrared and Raman spectrum revealed the formation of SnO2/reduced graphene oxide nanocomposites. Scanning electron microscopy and transmission electron microscopy showed that SnO2 nanoparticles had a crystal size of about 3–4 nm and homogeneously distributed on reduced graphene oxide matrix. The electrochemical performances of the SnO2/reduced graphene oxide nanocomposites as anode materials were measured by the galvanostatic charge/discharge cycling. The results indicated that as-synthesized SnO2/reduced graphene oxide nanocomposites had a reversible lithium storage capacity of 1051 mAh/g and an enhanced cyclability, which can be attributed to increased electrode conductivity and buffer effect to volume change in the presence of a percolated reduced graphene oxide network embedded into the metal oxide electrodes.

Electropulsing treatment (EPT) provided a promising technology to improve the microstructure and plasticity of the cold-rolled Ti–6Al–4V noticeably while only affecting the strength mildly. Thus, titanium alloy of high plasticity and good comprehensive property can be obtained by this high efficient processing method. The research found that the tensile ductility could be improved largely with the increasing frequency. In the low frequency, the maximum ductility (32.5%) could be obtained at 293 Hz-EPT. Under high-frequency EPT, plasticity has a slight decrease but the tensile strength increases in the contrary. With the help of multi-characterization, abstracting phenomena are explained and therefore the conclusion has been drawn that the whole process of increasing frequency EPT can be divided roughly into two periods: (a) recrystallization period in the low frequency, at this period athermal effect of the EPT played a leading role and (b) phase change period in the high frequency, at this period the other important factor of the EPT thermal effect was predominant. As a comparison, furnace heat treatment is conducted to prove the preferential phase transition instead of complete recrystallization under the single heating effect. The mechanism of the results can be discussed by the competitive mechanism of recrystallization process and phase change in the EPT processing.

Achieving control of crystalline quality is a key barrier to developing thermoelectric (TE) nanowires. We show that the structural properties of free-standing Bi2(Te.97Se.03)3 nanowire arrays on substrates can be improved by postdeposition annealing. Nanowires were electrochemically deposited into anodized aluminum oxide nanopore templates formed directly on metallized Si(100). The templates were chemically removed prior to annealing in a 3% H2/Ar environment to prevent microcrack formation that results from thermal stresses. Grain sizes grew exponentially with annealing temperature until reaching the full 75-nm diameter of the nanowires at 300 °C; growth was linear above this temperature since grains could grow further only in the axial directions. Crystalline quality, along with the development of the preferred (110) orientation for optimal TE properties, improved with increasing annealing temperature between 200 and 400 °C. However, continued loss of Te composition with annealing led to a mixed phase of Bi2Te3 and Bi4Te3 at 500 °C.

Poly (3-hexylthiophene) (P3HT) and aminated carbon microsphere (A-CMS) composite films with donor–acceptor architecture were prepared by spin-coating method, and the photovoltaic (PV) devices with a structure of ITO/PEDOT:PSS/P3HT:A-CMSs/Al were also fabricated. The structure and morphology of films were characterized by x-ray diffraction, Fourier transformation infrared spectrometry, ultraviolet-visible spectrophotometry, fluorescent spectrometry, and atomic force microscopy. The results indicate that A-CMSs exhibited a high LUMO energy level of −3.65 eV. The optimized blending ratio of P3HT:A-CMSs was 1:1. After annealing treatment, the intensity of absorption and the crystallization degree of the P3HT:A-CMS composite films enhanced. The polymer solar cells (PSCs) based on P3HT:A-CMS composite films showed a power conversion efficiency of 0.027% with an open circuit voltage of 0.80 V. It is suggested that A-CMS is a promising acceptor for PSCs. This would lay an experimental and theoretical foundation for the design of new acceptors for PV application.

Photoelectrochemical cells offer a more elegant, clean, and sustainable way to store solar energy as chemical energy through the splitting of water into its primitive form (H2 and O2). Among many metal oxides pointed as candidates for this application, the fundamental characteristics of hematite (α-Fe2O3), such as abundance, excellent chemical stability in an aqueous environment, and favorable optical band gap, emerged as a promising photoanode. Although attractive, the poor optoelectronic properties necessitate a large application of overpotential for split water assisted by solar irradiation, limiting the high performance of this material. Since the electrode was built using materials in nanoscale, significant advances were achieved. This review highlights new insights and recent progress in the use of a purpose-built material process to build hematite electrodes for improving photocatalytic activity. In addition, reduction on the required overpotential by effective control-treatment of morphology and surface of vertically aligned hematite nanorods will be addressed. An interesting set of results were also discussed revisiting a novel strategy recently presented in the literature and complementary advances was illustrated. These latest efforts aid in pointing out the challenges or obstacles to be overcome using this morphology and in defining new opportunities.

In this article, monolithic porous silsesquioxane materials, which are derived by sol–gel from trialkoxysilanes with substituent groups such as trimethoxysilane (HTMS), methyltrimethoxysilane (MTMS), and vinyltrimethoxysilane (VTMS), are reviewed with a special emphasis on our recent works. Careful controls over fundamental synthetic parameters such as pH, amounts of water and solvent, and kind of solvent and additives play a crucial role in the formation of monolithic gels based on random polysiloxane networks. Crystalline/amorphous precipitation is otherwise observed when the formation of isolated species including polyhedral oligomeric silsesquioxanes dominates or if phase separation of the hydrophobic networks in aqueous media is not adequately controlled. In the successfully controlled system, pore size can be varied from a few tens of nanometers to a few tens of micrometers; porous materials such as transparent aerogels and hierarchically porous monoliths have been explored. In addition, unique properties derived from trialkoxysilanes such as reactivity of the pore surface and flexible mechanical properties are demonstrated. Possibilities in the silsesquioxane materials with controlled pore structures are discussed.

This study presents the optical properties of layered ZnO/Al/ZnO composite thin films that are being explored for potential applications in solar cells and light emitting devices. The composite thin films are explored as alternatives to ZnO thin films. They are produced via radio frequency magnetron sputtering. The study clarifies the role of the aluminum mid-layer in a ZnO (25 nm)/Al/ZnO (25 nm) film structure. Multilayers with low resistivity ∼362 µΩ cm and average transmittances between ∼85 and 90% (in the visible region of the solar spectrum) are produced. The highest Haacke figure of merit of 4.72 × 10−3 Ω−1 was obtained in a multilayer with mid-layer Al thickness of 8 nm. The combined optical band gap energy of the multilayered films increased by ∼0.60 eV for mid-layer Al thicknesses between ∼1 and 10 nm. The observed shifts in the optical absorption edges to shorter wave lengths of the spectrum are shown to be in agreement with the Moss–Burstein effect.

Oxide composites are a class of materials with potential uses for nuclear, space, and coating applications. Exploiting their promise, however, requires a detailed understanding of their interfacial structure and chemistry. Using analytical microscopy, we have examined the radiation damage behavior at the interface of a model oxide bilayer, SrTiO3/MgO. The as-synthesized SrTiO3 thin film contained both (100) and (110) oriented domains. We found that after ion beam implantation the (110) domains amorphized at a lower radiation fluence than the (100) domains. Further, a persistent crystalline layer of SrTiO3 forms at the interface even as the rest of the SrTiO3 film amorphizes. We hypothesize that the enhanced amorphization susceptibility of the (110) domains is a consequence of how charged irradiation-induced defects at the interfaces interact with the charged planes of the (110) domains. These results demonstrate the complex relationship between interfacial structure and radiation damage evolution at oxide interfaces.

Gradient plasticity provides an effective theoretical framework to interpret heterogeneous and irreversible deformation processes on micron and submicron scales. By incorporating internal length scales into a plasticity framework, gradient plasticity gives access to size effects, strain heterogeneities at interfaces, and characteristic lengths of strain localization. To relate the magnitude of the internal length scale to parameters of the dislocation microstructure of the material, 3D discrete dislocation dynamics (DDD) simulations were performed for tricrystals of different dislocation source lengths (100, 200, and 300 nm). Comparing the strain profiles deduced from DDD with gradient plasticity predictions demonstrated that the internal length scale depends on the flow-stress-controlling mechanism. Different dislocation mechanisms produce different internal lengths. Furthermore, by comparing a gradient plasticity framework with interfacial yielding to the simulations it was found that, even though in the DDD simulations grain boundaries (GBs) were physically impenetrable to dislocations, on the continuum scale the assumption of plastically deformable GBs produces a better match of the DDD data than the assumption of rigid GBs. The associated effective GB strength again depends on the dislocation microstructure in the grain interior.

The well-ordered TiO2 nanotube arrays with controlled aspect ratio are fabricated via potentiostatic anodization. The aspect ratio of TiO2 nanotube array can be tuned conveniently by changing the water content in electrolyte and anodization time. The formation of well-ordered TiO2 nanotube array is good for the photogenerated electron transfer. So, the well-ordered TiO2 nanotube array photoelectrodes have been used to fabricate dye-sensitized solar cells (DSSCs). It is found that, with the optimum nanotube length and aspect ratio, DSSCs with TiO2 nanotube array photoelectrodes show better photoelectric conversion efficiency (2.60%) than that with TiO2 nanoparticles on Ti foil photoelectrode. It is elucidated by the interfacial electron transport of DSSCs, which are characterized quantitatively, using the electrochemical impedance spectra. The DSSC with optimal nanotube length and aspect ratio displays the fastest interfacial electron transfer and longer electron lifetime.

This work presents experimental data on the surface and grain boundary energies of tin dioxide nanoparticles at room temperature and high temperature conditions (quenched from 1300 °C), and a discussion of impacts on the fundamental understanding of the nondensification mechanism of SnO2 during sintering. The results were obtained using a combination of water adsorption microcalorimetry, high-temperature oxide melt drop solution calorimetry, and scanning electron transmission microscopy. At room temperature, the average surface and grain boundary energies of anhydrous SnO2 were 1.20 ± 0.02 and 0.71 ± 0.08 J m−2, respectively. At high temperature, SnO2 showed a surface energy of 0.94 ± 0.03 J m−2. This remarkable decrease was attributed to the lower oxygen pressure and was associated with a decrease in contact angle during sintering. This observation indicates a moderate but significant thermodynamic reason behind nondensification behavior of SnO2 in addition to common kinetic descriptions: high sintering temperatures and atmospheres cause smaller dihedral angles that decrease sintering stresses.

To fabricate practical light-emitting devices, identification and minimization of nonradiative processes are necessary. In this study, an electrical measurement technique for time-resolved analyses of nonradiative processes was proposed. From the comparison between a commercial light-emitting diode (LED) and rare-earth-doped semiconductors, the technique, called electrical frequency-response analysis (FRA), revealed differences in the charge behaviors in the pn junction of bulk semiconductors and impurities. Although the charge response time constant on the order of a nanosecond realized effective recombination of the electron–hole pairs in a LED, the time constant larger than a microsecond still limited the emission intensity of the rare-earth-doped semiconductors such as Er-doped Si nanocrystals and GaAs with Er and O codopants. The energy-loss processes of the Er-doped semiconductors were investigated, and countermeasures to enhance the emission intensity were proposed.

In this study, thermodynamic properties of BC2N under extreme conditions have been reported by using first-principle calculations and quasi-harmonic Debye model. Isochoric heat capacity (Cv) of BC2N at normal temperature and pressure is 23.15 kJ mol−1 K−1 and it increases with the temperature and decreases with the pressure. In the low temperature region, pressure has no obvious influence on phonons and thus the decrease of Cv is very slow. In the medium temperature region, the decrease of Cv becomes steep. The reason is that high pressure plays an important role in controlling the vibration of atoms. In the high temperature region, the decrease of Cv becomes slow. Debye temperature (θ) decreases with the temperature. However, the tendency is not obvious in the low temperature region but very clear in high temperature. Moreover, θ increases with pressure and the amplitude is larger in higher temperature. Because of the four covalent bonds with different strength and distribution asymmetric thermal expansion along different axes occurs. The value of thermal expansion coefficient along c axis is more than that of along a and b axes.