Understanding the interaction of group V impurities with intrinsic defects in ZnO is important for developing p-type material. We have studied N-doped ZnO thin films and N-doped bulk ZnO crystals, with positron annihilation spectroscopy, in contrast to earlier studies that have concentrated on N-implanted ZnO crystals. We show that the introduction of N impurities into ZnO, irrespective of whether it is done during the growth of thin films or bulk crystals or through implantation and subsequent thermal treatments, leads to the formation of stable vacancy clusters and negative ion-type defects. Interestingly, the stability of these vacancy clusters is found almost exclusively for N introduction, whereas single Zn vacancy defects or easily removable vacancy clusters are more typically found for ZnO doped with other impurities.

This paper describes the use of self-patterning anodic aluminum oxide (AAO) layers to enable localized metal contacts and to achieve passivation for the rear surface of silicon solar cells. There are no commercially available technologies that are capable of patterning localized contacts on silicon solar cells with low cost, high-throughput, and robust processing, especially when closely spaced small-area openings are required. In the approach described, nanoporous AAO layers were formed by anodizing aluminum over intervening dielectrics on textured silicon wafers. When the anodized test structures were fired in a belt furnace, localized contacts formed at peaks and valleys of the alkaline-textured silicon surface. Furthermore, the anodization contributed ∼35 mV increment in the implied Voc of the test structures. Low contact resistivity was demonstrated and the proposed contacting mechanism for this innovative localization suggested that the contact percentage can be controlled by varying the anodization duration and/or the surface morphology.

This paper investigates the critical loading condition that causes the emission of dislocations in silicon subjected to nanoindentation. A theoretical model is established, which follows the deformation process that with increasing the indentation load, a phase transformation takes place, followed by partial dislocations emitting from the interface between the phase-transformed zone and the originally crystalline silicon when the indentation load reaches a critical value. In the model, the emission process represents the generation of a dipole of Shockley partial dislocations. One partial dislocation of the dipole, located at the interface, is considered immobile, whereas the other partial dislocation moves into the bulk of silicon. The effects of the indenter geometry and of the location of dislocation nucleation on the critical indentation load are discussed. The model predicts that a sharp indenter leads to a relatively smaller critical indentation load. The model prediction is verified by an indentation experiment.

Microcalorimetry was used to study the adsorption of water molecules on the surface of ZnAl2O4 nanoparticles ranging from the anhydrous to the fully hydrated states. Water adsorption of ZnAl2O4 showed similar behavior to the isostructural γ-Al2O3 and revealed possible existence of hydrophobic sites on the surfaces. At the lowest measured coverage (0.49 H2O per nm2), the enthalpy of adsorption is −155.46 kJ/mol. This value decays with increasing coverage and at around 13 H2O per nm2, the heat of adsorption levels at −44 kJ/mol, suggesting further adsorbed water has liquid-like features. The anhydrous surface energy for ZnAl2O4 was calculated to be 1.36 ± 0.08 J/m2 using water adsorption microcalorimetry data. High-temperature oxide melt solution calorimetry was also used to assess the surface energy, which was 1.29 ± 0.33 J/m2. Surface energies at different hydration states are reported and showed decrease with increasing coverage, suggesting that low humidity conditions allow higher driving forces for coarsening.

Porous Al2O3 ceramics were fabricated using a rapid gelation to fix the foam structure after mechanical foaming. The slurry was made with deionized water, Al2O3 powder, a water-soluble copolymer of isobutylene and maleic anhydride, and a surfactant. The resultant gel formed at room temperature in air. The influence of the surfactant (EMAL TD) content on gelling behavior, pore structure (porosity, cell size), shrinkage behavior, and compressive strength of the resultant porous Al2O3 ceramics was evaluated. Porous Al2O3 ceramics were sintered in only one step without debinding because of the low concentration of additives (≤0.5 wt%). The porous Al2O3 ceramics had porosities from 20 to 89% and cell sizes from 60 to 220 μm. The compressive strength was 75 MPa when the porosity was 60%.

Li-stabilized Na-β″/β-Al2O3(Na1.61Li0.29Al10.70O17) nanorods were prepared by a soft chemistry process using a 1-alkyl-3-methylimidazolium bromide ([CXmim]Br, X = 4, 12, 16) ionic liquid as a template. Pure Na-β″/β-Al2O3 rods were obtained by heating at 1100 °C with [C16mim]Br as the template, resulting in nanorods of approximately 50 nm in diameter and 200–300 nm in length. It is demonstrated that alkyl chain length is the main factor determining the aspect ratio of the nanorods. The specific surface area of the powder is 81.3 m2/g, which is more than one order of magnitude higher than that of the powder prepared by a conventional solid state reaction process. The formation mechanism of the nanorods is proposed.

Large surface area, homogenous, and adhesive TiO2 coatings on stainless steel substrates were prepared by electrophoretic deposition (EPD) of colloidal dispersions of TiO2 nanoparticles in water and ethanol. Several chemical additives were used to optimize the deposition process. The best results were obtained for dispersions in water containing a mixture of Tiron and Pluronic® F127, which gave homogeneous layers, showing excellent adhesion and a large BET surface area, close to 200 m2/g. Ethanol dispersions also gave much adhesive coatings when poly(acrylic acid) was used as an additive. Nevertheless, their thickness was lower, and their surface area was less than 100 m2/g. We have shown that water splitting, occurring in the aqueous sol during the EPD, led to deposited masses lower than those expected from the Hamaker law. However, the electrolysis of water and also the small cracks in the coatings had no detrimental effects on adhesion.

An experimental study on the indentation hardness of NiTi shape memory alloys (SMAs) by using a spherical indenter tip and a finite element investigation to understand the experimental results are presented in this paper. It is shown that the spherical indentation hardness of NiTi SMAs increases with the indentation depth. The finding is contrary to the recent study on the hardness of NiTi SMAs using a sharp Berkovich indenter tip, where the interfacial energy plays a dominant role at small indentation depths. Our numerical investigation indicates that the influence of the interfacial energy is not significant on the spherical indentation hardness of SMAs. Furthermore, the depth dependency of SMA hardness under a spherical indenter is explained by the elastic spherical contact theory incorporating the deformation effect of phase transformation of SMAs. Hertz theory for purely elastic contact shows that the spherical hardness increases with the square root of the indentation depth. The phase transformation beneath the spherical tip weakens the depth effect of a purely elastic spherical hardness. This study enriches our knowledge on the basic concept of hardness for SMAs under spherical indentation at micro- and nanoscales.

The relationship between morphology and crystallography of an entangled lathy ferrite during directional solidification in Fe–Cr–Ni alloy has been investigated. During solidification, morphology of the lathy ferrite depends on the orientation relationship between the lathy ferrite and austenite. When the plane in the austenite substrate is ${(1\bar 11)_{\rm{\gamma }}}$, “Y-shaped” lathy ferrite grows in an entangled cluster and the orientation relationship between the lathy ferrite and austenite is the Nishiyama–Wassermann relationship. Lathy ferrite is preferentially elongated along ${\langle 211\rangle _{\rm{\gamma }}}$ and ${\langle 011\rangle _{\rm{\gamma }}}$ directions on ${(1\bar 11)_{\rm{\gamma }}}$ plane due to lower misfit. The included angle among the “Y-shaped” lathy ferrite is about 120° because the angle between each pair of ${[21\bar 1]_{\rm{\gamma }}}$, ${[\bar 112]_{\rm{\gamma }}}$, and ${[\bar 1\bar 2\bar 1]_{\rm{\gamma }}}$ crystal directions is equal to 120°. Formation mechanism of the perpendicular lathy ferrite has also been analyzed according to the relationship between ${\langle 211\rangle _{\rm{\gamma }}}$ and ${\langle 011\rangle _{\rm{\gamma }}}$ on ${(1\bar 11)_{\rm{\gamma }}}$ plane. This indicates that required crystal morphology of the lathy ferrite in the solidified microstructure can be obtained by controlling the crystal plane of austenite.

Metal matrix composites manufactured by the powder metallurgy route often exhibit different tensile strength due to particle geometrical reasons. The tensile strength tendency was studied in 2024 Al/30% SiCp composites as a function of relative particle size (RPS) ratio between the matrix and reinforcement particles. Dry blended composite powders, with different RPS ratios, were hot-pressed in vacuum, their microstructures were observed, and their tensile properties were measured. It was found that a decrease in RPS ratio resulted in a decrease in tensile strength, as a result of improved distribution of the SiCp. Despite their low density and heterogeneous distribution, 3-μm SiCp-reinforced composites had maximum tensile strength. The main reasons were due to the few fracture for small SiCp and the strengthening of the matrix microstructure from small particle effects. Solution treatment plus aging of the composites with the RPS ratio of 10:3 resulted in a significant improvement (42%) in strength due to the smaller diffusion path length for the alloying element.

This paper examines the onset and progression of dynamic recrystallization (DRX) phenomena under shear deformation conditions characterized by strains >1 and strain rates >102/s by purposing large strain machining (LSM) as a test of microstructure response. To accomplish this, samples are created using LSM while characterizing the deformation using digital image correlation and infrared thermography. Microstructural consequences resulting from the characterized thermomechanical conditions are examined using electron backscattered diffraction. The progression of DRX is measured by identifying the threshold of grain orientation spread demarcating the onset of recrystallization and utilizing this threshold to segregate the microstructure and quantify the extent of DRX. A model for the onset of DRX as a function of thermomechanics of deformation is presented. This characterization can help understand surface microstructures resulting from shear-based manufacturing processes, such as turning, milling, shaping, etc., that are created under analogous thermomechanical conditions.