Half-Heusler (HH) phases, a versatile class of alloys with promising functional properties, have recently gained attention as emerging thermoelectric materials. These materials are investigated from the perspective of thermal and electronic transport properties for enhancing the dimensionless figure of merit (ZT) at 800–1000 K. The electronic origin of thermopower enhancement is reviewed. Grain refinement and embedment of nanoparticles in HH alloy hosts were used to produce fine-grained as well as nanocomposites and monolithic nanostructured materials. Present experiments indicated that n-type Hf0.6Zr0.4NiSn0.995Sb0.005 HH alloys and p-type Hf0.3Zr0.7CoSn0.3Sb0.7/nano-ZrO2 composites can attain ZT = 1.05 and 0.8 near 900–1000 K, respectively. The observed ZT enhancements could be attributed to multiple origins; in particular, the electronic origin was identified. The prospect for higher ZT was investigated in light of a recently developed nanostructure model of lattice thermal conductivity. Tests performed on p–n couple devices from the newly developed HH materials showed good power generation efficiencies—achieving 8.7% efficiency for hot-side temperatures of about 700 °C.

We report the results of constant strain rate experiments on electroplated, single crystalline copper pillars with diameters between 75 and 525 nm. At slow strain rates, 10−3 s−1, pillar diameters with 150 nm and above show a size-dependent strength similar to previous reports. Below 150 nm, we find that the size effect vanishes as the strength transitions to a relatively size-independent regime. Strain rate sensitivity and activation volume are determined from uniaxial compression tests at different strain rates and corroborate a deformation mechanism change. These results are discussed in the framework of recent in situ transmission electron microscopy experiments observing two distinct deformation mechanisms in pillars and thin films on flexible substrates: partial dislocation nucleation from stress concentrations in smaller structures and single arm source operation in larger samples. Models attempting to explain these different size-dependent regimes are discussed in relation to these experiments and existing literature revealing further insights into the likely small-scale deformation mechanisms.

After some background discussion, this review will focus on some recent developments in the areas of theoretical studies of semiconductor electronic structure, photovoltaics, semiconducting boron nitride nanotubes, and the search for modified semiconductors and insulators with higher superconducting transition temperatures. The background discussion covers the evolution of studies of solids, which changed dramatically after the development of quantum theory. These conceptual changes resulted in methods for calculating properties of materials and theoretical frameworks for interpreting experimental measurements. In some cases, the theoretical approaches have been successful in predicting new materials and new properties. As stated above, a few examples will be given to illustrate the development of this field.

Conventionally, mean grain size is considered the most critical microstructural parameter in determining the mechanical behavior of pure metals. By systematically controlling the distribution of grain orientations in aluminum films, we show that microstructural heterogeneity alone induces large variation in the mechanical behavior of nanocrystalline metal films. Aluminum films with relatively homogeneous microstructure (all grains with identical out-of-plane orientation) show substantially less early Bauschinger effect compared to films with heterogeneous microstructure, irrespective of film thickness or grain size. On the other hand, the films with homogeneous microstructure show relatively higher yield stresses. A direct correspondence is found between the nonuniformity of plastic deformation and early Bauschinger effect, which confirms the critical role of microstructural heterogeneity.

The influence of Co content on stacking fault energy (SFE) of the γ matrix in four Ni–Co base superalloys, including newly developed alloys, has been studied by utilizing high-resolution transmission electron microscopy. The results indicated the SFE was not linear with Co content of the γ matrix. The lowest SFE could be attained at around 34.0 at.% Co. This effect was attributed to variation of electron holes, saturated Co content in the matrix, and the effect of Co on the partition coefficient of other alloying elements. A high density of twins was related to low SFE and could improve the mechanical properties.

Sn/Ni–8.0 at.%V (Ni–7.0 wt%V) couples are prepared and the interfacial reactions at 210 and 250 °C are examined. In the early stage of reaction at 250 °C, a T phase is formed as a result of fast diffusion of Sn into the Ni–8.0 at.%V substrate. With a longer reaction, the outer region of the T phase transforms to a Ni-depletion layer, which has not been observed previously. Both the T phase and the Ni-depletion layer are analyzed using transmission electronic microscopy. This newly found Ni-depletion layer is composed of Sn and nanosize “VSn2(V2Sn3)” particulates. The solid/solid reaction paths in the Sn/Ni–8.0 at.%V couples evolve from Sn/T/Ni–V, Sn/Ni3Sn4/T/Ni–V to Sn/Ni3Sn4/VSn2(V2Sn3). During the liquid/solid reactions, the paths are liquid/T/Ni–V, liquid/liquid + Ni3Sn4/T/Ni–V, liquid/liquid + Ni3Sn4/liquid + VSn2(V2Sn3)/T/Ni–V, and liquid/liquid + Ni3Sn4/liquid + VSn2(V2Sn3).

In this work, epitaxial (001) BiFeO3 thin films were deposited on SrTiO3 and TbScO3 single-crystal substrates and analyzed with high-resolution x-ray diffraction—reciprocal space mapping. A basic method was developed to extract structural details of the as-grown BiFeO3 film, including (i) epitaxial strain, (ii) ferroelastic domains, and (iii) lattice rotations. After demonstrating the method, extrinsic distortions at vertical twin walls were determined for specific BiFeO3 heterostructures. A relatively large distortion (0.20° ± 0.08°) was measured in a multidomain (12) and incoherent film, while a nearly intrinsic distortion (0.04° ± 0.03°) was measured in a two-domain coherent film. This work offers insights into the structure of multiferroic BiFeO3 thin films with a general approach that is appropriate for low symmetry epitaxial heterostructures.

Nitrogen-doped multiwalled carbon nanotubes with poly(bisphenol A carbonate) composites were prepared through simple solution blending. The scaling law, which is based on the percolation theory, is used to describe the electrical conductivities of the composites. Both direct current and alternating current conductivities are in good agreement with the unprecedented high saturated conductivities of the pristine samples (σsat = ∼734 s·cm−1, pc = 0.19 wt%). We attributed the high conductivities to the binding of nanotubes into large but tight bundles, which enable the composites to carry more charges. This is notably different from the conventional method, which focuses on forming a well-dispersed three-dimensional network resulting in the conductivities having a lower order of magnitude.

We evaluated the optical and electrical characteristics of SnO2 hybrid films with various contents (0, 0.05, 0.1, 0.15, and 0.2 at.%) of Pt nanoparticles. The Pt nanoparticles were synthesized by a methanol reduction method, and their size was restricted to an average of 3 nm using poly(N-vinyl-2-pyrrolidone) as a protecting agent. An enhancement in electrical properties was observed due to the addition of Pt nanoparticles; the lowest resistivity (1.36 × 10−2 Ω·cm) and the highest figure of merit (1.18 × 10−4 Ω−1) were obtained with SnO2 film containing 0.15 at.% Pt nanoparticles after annealing at 600 °C, and the average transmittance in the visible region was 86.61%. Well-defined 30-μm-wide direct-patterned SnO2 films containing Pt nanoparticles were formed by photochemical metal-organic deposition through a simple process including a photosensitive starting precursor, ultraviolet exposure, and removal of the unexposed area with solvent rinsing.

KMgF3:Eu nanocubes with a mean edge length of ∼12 nm were synthesized by a hydrothermal method. Result of x-ray diffraction reveals that the nanocubes are perovskite phase. Under ultraviolet excitation, the broad emission bands from trace oxygen and color centers in KMgF3 matrix were observed. In comparison with a bulk sample having the same chemical compositions, no characteristic emissions of Eu2+ were observed, which can be attributed to the overlappment of the emissions of Eu2+ and color centers in KMgF3:Eu nanocubes. In addition, the emissions of Eu3+ were also detected, and the intensity ratio of 5D0 → 7F2 to 5D0 → 7F1 changed with excitation wavelength, indicating that the material has multiple luminescence centers or emitting states.

Titanium oxide matrix was prepared by sol-gel adding fluoxetine [Prozac (C17H18NF3O)] during the reaction of gelation. This nanostructured material was studied by Fourier transform infrared (FTIR) spectroscopy, N2 adsorption, and x-ray diffraction to detect the interaction between the drug and the matrix. The complex nature of FTIR signals for the matrix and the drug did not allow observation of the interactions; however, using the density functional theory formalism, two stable complexes are suggested to be formed on the drug–matrix system. Both complexes are formed through H bond interactions involving the amine group in fluoxetine and the hydroxylated sites in titanium xerogel. They were found to be energetically stable and independent of the titanium model core cluster used in the calculations.

Epoxy–dicyandiamide (Dicy) formulations frequently contain a free accelerator for reducing the curing temperature and the time for network formation, which reduces the shelf life of these adhesives. This study compared the reaction kinetics during the storage at 60 °C for a precured epoxy adhesive (EP = diglycidyl ether of bisphenol A and Dicy, mass ratio 100:6.7, precured at 150 °C for 1 h) mixed either with free accelerator (=EPacc) or with the same concentration of accelerator immobilized in micro- or nanozeolite fillers (EPμ-filled and EPn-filled, respectively). During storage, the infrared (IR) study probed the chemical modifications. They lead to increasing cross-linking density and a loss of free volume as detected by positron annihilation lifetime spectroscopy (PALS). Cross-linking precedes to the chemical vitrification. Additionally, the glass transition and the free-volume parameters were investigated for the three EP’s as a function of temperature by PALS after thermal curing.