The fabrication methods and the basic properties of the metal-oxide nanostructures referred as nanowires are presented and reviewed in this paper, with particular emphasis to the electrical and optical properties and their useful implementation for chemical and biochemical sensing. The field of chemical sensors has benefited by the wealth of highly crystalline nanostructures produced by physical and chemical methods. Large variation in bulk electrical conductivity, structural stability upon high temperature operation, high degree of crystalline ordering, large impact of point defects and surface states have unveiled the potential for the sensing field and have opened up new perspectives of application and for the realization of novel device architectures. This paper will summarize various techniques for preparation and characterization; then, the growth mechanisms and working principles will be discussed. Finally, the challenges that this field is currently facing are presented to signify the perspectives of expansion.

New strategies for materials fabrication are of fundamental importance in the advancement of science and technology. Nanocrystals, especially with an anisotropic shape such as cubic, are candidates for building blocks for new bottom-up approaches to materials assembly, yielding a functional architecture. Such materials also receive attention because of their intrinsic size-dependent properties and resulting applications. Here, we report synthesis and characteristics of BaTiO3 and SrTiO3 nanocubes and the ordered assemblies as ferroelectric supracrystals. BaTiO3 and SrTiO3 nanocubes with narrow size distributions were obtained in an aqueous process. BaTiO3 films made up of ordered nanocube assemblies were fabricated on various substrates by evaporation-induced self-assembly method. Regardless of the substrate, the nanocubes exhibited {100} orientations and a high degree of face-to-face ordering, which remained even after heat treatment at 850 °C. Piezoresponse force microscopy was carried out on the supracrsytal films to obtain plots of the d33 piezoelectric coefficient against the poling field, and ferroelectric hysteresis curves were shown.

Lead-free positive temperature coefficient of resistance (PTC) thermistors were synthesized from (1 − x/100)BaTiO3–(x/100)(Bi1/2K1/2)TiO3-based solid solutions, using a conventional mixed-oxide fabrication route, and sintered in N2 followed by air annealing. A maximum TC of 205 °C was achieved for x = 20. An increase in x from 0 to 20 decreased the grain size by more than 92% and increased room temperature resistivity (ρRT) by 7 orders of magnitude. For x ≤ 10, PTC ratio (ρmax/ρmin) ≈ 104.5 and temperature coefficient of resistivity (α) > 10.3%/°C were achieved using Mn and Al2O3:SiO2:TiO2 (AST) additions. For x > 10, ρmax/ρmin > 103 and α > 8%/°C were only obtained in samples sintered in N2 without subsequent air annealing. Complex impedance analysis revealed three relaxation processes, attributed to a semiconducting grain core, a PTC active grain boundary interface, and a grain boundary insulating layer. Local electrical activity was investigated by hot-stage conductive mode microscopy. The existence of symmetrical grain boundary electron beam-induced current and β-conductivity contrast at the grain boundaries, consistent with the presence of an electron trapping two-dimensional grain boundary plane, compensated by positive space charge layers and a low conductivity vacancy-rich layer, was revealed for the first time within this system.

A novel combination of low-field magnetic alignment (MA) and templated grain growth (TGG) was used to fabricate highly textured diamagnetic 0.72Pb(Mg1/3Nb2/3)O3–0.28PbTiO3 (0.72PMN–0.28PT) ceramics. Samples were produced by nonaqueous slip casting of PMN–PT slurries, in which diamagnetic plate-like 0.4(Na1/2Bi1/2)TiO3–0.6PbTiO3 (0.4NBT–0.6PT) template particles were aligned by dynamic MA in a 2.2-T permanent magnet array. Template alignment improved as slurry viscosity increased, with a 32-vol% solid loading (a viscosity of ∼0.1 Pa s at 0.1 s−1) giving optimal texture quality (7.85° FWHM, f = 92 vol%) after sintering and TGG. Alignment was stable for more than 3 h during slip casting, allowing fabrication of ∼1-cm thick textured ceramics with high piezoelectric response (d33 = 1222 pC/N). The success of dynamic MA at low magnetic field (2.2 T) is attributed to an increase in driving force for alignment of large (5–10 μm) template particles relative to the randomizing effect of Brownian motion (i.e., thermal energy kBT).

ZnS/CdS semiconductor composites were synthesized successfully by combining a hydrothermal route with a homogeneous precipitation process. The as-prepared products were characterized by x-ray diffraction, scanning electron microscopy, and energy dispersive x-ray spectrometer. The results showed that the as-prepared products were composed of ZnS microspheres with a face-centered cubic phase and CdS nanoparticles with hexagonal phase, CdS nanoparticles were found to be assembled on the surfaces of the cubic ZnS microspheres. In addition, the ultraviolet-visible absorption spectroscopy and the room temperature photoluminescence (PL) spectroscopy of the ZnS microspheres and ZnS/CdS composites were also investigated. The PL testing indicated that the emission peak of as-prepared ZnS/CdS composites not only exhibited an obvious blue shift but also its intensity had a large enhancement compared to the pure ZnS microspheres. Furthermore, the photocatalytic degradation test showed that the as-prepared ZnS/CdS composites showed excellent photocatalytic degradation activity for methyl orange under UV irradiation. This enhanced activity may be related to the modification of CdS nanoparticles on the surfaces of ZnS microspheres.

Novel europium- and gadolinium-doped bismuth phosphate (Eu/BiPO4 and Gd/BiPO4) microcrystals have been synthesized by a hydrothermal route. The morphologies and optical properties of the as-prepared samples were characterized carefully. Their photocatalytic activities were determined by oxidative decomposition of methylene blue (MB) in aqueous solution. The results revealed that europium and gadolinium doping greatly improves the photocatalytic efficiency of BiPO4 microcrystals. Among these as-prepared europium and gadolinium dopant samples, 1% Eu/BiPO4 and 5% Gd/BiPO4 displayed the highest photocatalytic activity, and the degradation rates are 2 and 2.7 times greater than pure BiPO4, respectively. The photodegradation reactions of MB by Eu- and Gd-BiPO4 followed first-order kinetics. The different photocatalytic mechanisms of Eu/BiPO4 and Gd/BiPO4 photocatalysts are discussed.

Electrical properties of ZrO2 formed by simultaneous oxidation and nitridation of sputtered Zr thin films on Si have been systematically investigated. Various oxidation/nitridation temperatures (500, 700, 900, and 1100 °C) have been carried out in N2O ambient for an extended time of 20 min. Results indicated that the sample oxidized and nitrided at 700 °C possessed the highest effective dielectric constant of 18.22 and electrical breakdown field of 10.7 MV/cm at a current density of 10−6 A/cm2. This is attributed to the lowest effective oxide charge, interface-trap density, and total interface-trap density. The Fowler–Nordheim tunneling mechanism has been investigated for all samples and the highest value of barrier height extracted between the conduction band edges of oxide and semiconductor was 1.22 eV.

Sol–gel-derived aluminum (Al)-doped zinc oxide thin films have been deposited on silicon (Si) wafers and microslide glass substrates using the spin coating technique. The atomic ratio of Al:Zn in the films is 0.05, 0.1, 0.2, and 0.3. The films have been characterized using different techniques, i.e., x-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy, scanning electron microscopy, UV-visible-near infrared spectrophotometry, spectroscopic ellipsometry, and the four-probe method. The films have exhibited excellent optical transmittance (∼90%). The refractive indices of the films are in the range between 1.47 and 1.53. The thickness of the films is in the range of 103–115 nm. The films have demonstrated reflectivity of about 3% at a wave length of 600 nm. The reflectivity, transmittance, refractive index, and thickness values of the films show that the films are promising candidates for utility as antireflection coatings in silicon solar cells.

In this paper, the effect of the addition of tungsten carbide on the behavior of Fe–WC system during the mechanical alloying (MA) process has been investigated. For this purpose, raw materials containing industrial ferrotungsten and carbon black with a bit of tungsten carbide powder were milled in a high energy ball mill, and sampling was done at different times. An XRD instrument was used for estimating the probable transformation of phases and properties in the milled sample. Microstructures of specimens were studied using electron microscopy. Results showed that MA even at high milling time could not transform raw materials to other materials in a system containing ferrotungsten and carbon black. In samples with primary tungsten carbide, this was synthesized gradually at a milling time of more than 75 h, and finally, the Fe–WC composite was produced as the final product. Crystalline sizes of the synthesized carbide were in nanometer order that was confirmed by transmission electron microscopy images.

High quality CdSe nanocrystals (NCs) were synthesized via a nonorganometallic precursor and extracted in different solvents. The difference in the influence of the nature of the solvent namely ethanol, N,N-dimethyl formamide (DMF), and acetonitrile on extraction of the same type of NCs was studied with respect to quality and stability of NCs. Characterization by x-ray diffraction technique, absorption–emission spectroscopy, scanning, transmission, and atomic force microscopy demonstrated the formation of NCs of good optical property and surface composition from the synthesis method used. Different polarities of the solvent strongly influence photoluminescence (PL), surface defects, concentrations of NCs extracted, particle sizes, and surface passivation. Ethanol extraction results in small-sized NCs and good particle size distribution. DMF extraction causes lesser interfacial defects and hence prevents radiative recombinations. PL quenching was observed in all the three solvents, and this necessitates further stabilization of NCs. The stability of the so-extracted NCs was evaluated for change in their properties with respect to aging. Aging substantiated the adverse effects of acetonitrile to extract the lesser surface passivated NCs leading to Ostwald ripening and island formation. The phase and structure of NCs remain unaffected with aging or by the nature of solvent used.

The present work demonstrates an isothermal reversible variation of magnetization in nanoporous Pd67Ni33 alloy during continuous charging and discharging of the alloy electrode in 1-M KOH solution. A custom-built electrochemical cell, containing the sample as working electrode performed the in situ charging experiments inside an extraction magnetometer at a constant applied magnetic field. The metal–electrolyte response was examined by varying the electrode potential, which apart from polarizing nanoporous structure, may also lead to electrodissociation of the electrolyte medium, being aqueous in nature. The result therefore analyzed hydrogenation as the key parameter for the observed reversible magnetization in the transition metal alloy at room temperature. In addition, electrochemical reactivity due to surface oxidation at the positive potential has been discussed, considering that a change in the band structure is also possible at the negative potential regime due to hydrogenation through cyclic voltammetry study.

Under the mixed-mode loading condition, mechanical responses of the Al-terminated O-site Ni(111)/α-Al2O3(0001) interface are investigated using first-principle calculations. The displacement-controlled loadings along 22.5, 45, and 67.5° orientations with respect to the interface are applied. The tension and shear responses of the interface are elaborated according to the computational results, including the mechanical strengths, the effect of tension softening, and the failure characteristic. In addition, the stress versus displacement relationships are derived out based on the general approach suggested by [Sun et al., Mater. Sci. Eng., A170, 67 (1993)], and the deviations between the analytical and computational results are examined in particular. Furthermore, the potential function and its development of this interface are discussed in detail.

New experimental methods have been developed to optimize the accuracy and precision of the measured phase angle in nanoindentation experiments on viscoelastic materials performed with a Berkovich indenter. Measurements conducted in fused silica and sapphire form the basis of a new instrument calibration. Experimental verification of the new calibration and an enhanced test method is demonstrated in polycarbonate (PC) and polymethyl methacrylate (PMMA). In comparison to the standard continuous stiffness measurement (CSM) technique, the new calibration and test method reduces the measurement error in the phase angle of PC from 1900% to 10% and from 135% to 10% in PMMA. Scatter in phase angle measured by the new test method is nearly 10 times less than the level observed using the standard CSM technique. The effect of time dependent deformation on the measured phase angle is also documented. The experimental observations and results are applicable to a variety of dynamic nanoindentation test methods.

Indentation tests are used to determine the hardness of a material, e.g., Rockwell, Vickers, or Knoop. The indentation process is empirically observed in the laboratory during these tests; the mechanics of indentation is insufficiently understood. We have performed first molecular dynamics computer simulations of indentation resistance of polymers with a chain structure similar to that of high density polyethylene (HDPE). A coarse grain model of HDPE is used to simulate how the interconnected segments respond to an external force imposed by an indenter. Results include the time-dependent measurement of penetration depth, recovery depth, and recovery percentage, with respect to indenter force, indenter size, and indentation time parameters. The simulations provide results that are inaccessible experimentally, including continuous evolution of the pertinent tribological parameters during the entire indentation process.

Isothermal crystallization kinetics of gamma-irradiated syndiotactic polystyrene (sPS) has been investigated by differential scanning calorimetry. Amorphous sPS samples were irradiated in air with gamma ray at various doses from 0 to 800 kGy, at a rate of 30 kGy/h, and melt-crystallized at different temperatures and times. Kinetics parameters were determined using Avrami's model with Gaussian functions and a modified Arrhenius equation. Isothermally crystallized sPS irradiated in air with gamma ray exhibited multiple endothermic melting peaks corresponding to various crystalline forms, and the radiation dose had a strong effect on their melting enthalpies, crystallinities, and crystallization kinetic parameters. The amount of the α-crystalline form increased with increasing crystallization time and those of the β- and β′ forms had an opposite trend. Both crystallization half time and crystallization activation energy of the α form in gamma-irradiated sPS increased with increasing radiation dose.