Ni3N was prepared by gaseous nitriding of nickel substrates using gas mixtures of high nitrogen activities, composed of NH3 and H2 at 1 atm and at temperatures between 175 °C and 550 °C. At least above 300 °C closed Ni3N layers developed, which possess distinct compressive macrostrain parallel to the surface. The observed hkl-anisotropy of the macrostrain could be ascribed to the elastic anisotropy as indicated by the single-crystal elastic constants of Ni3N obtained from first-principles calculations performed in this work. The macrostress originates from the thermal misfit between layer and substrate, developing upon cooling. The extent of macrostress is reduced by partial misfit accommodation by plastic deformation as well as by porosity.

Thermoelectric (TE) devices, both TE generators (TEGs) and TE coolers (TECs), have short service lives as TE materials undergo degradation from sublimation, oxidation and reactions in corrosive environments at high temperatures. We have investigated four high-temperature polymers (HTPs) as candidates for TE element coatings and/or TE device fillers to minimize or prevent this degradation. Two of these HTPs have shown good thermal stability in the 400–500 °C temperature range. The coatings were initially applied to bismuth telluride (Bi2Te3)-based TE materials that are used for commercial power generation devices specified for operation up to 250 °C. The HTPs protect the Bi2Te3 from both weight loss and weight gain up to 500 °C. This is clearly outside the optimum TE operation range of Bi2Te3 materials, but demonstrates the ability of the HTP coatings to protect the Bi2Te3 materials at least up to 250 °C. The properties that HTP materials demonstrated during the examination of suitability of their use for TE element coatings and/or TE device fillers using Bi2Te3are expected to hold good for higher operating temperature TE materials also.

Time stability of the solid oxide fuel cells (SOFCs) has been a significant concern toward realization of their practical applications. Its operation at elevated temperatures and in oxidizing atmospheres makes the cathode current collector one of the most vulnerable components of the SOFCs. Silver and silver-based metal oxide [lanthanum–strontium manganite (LSM) and yttria-stabilized zirconia] composites were investigated for the development of low-cost current collectors with long-term stability. While densification of pure silver limited its use as current collector, incorporation of oxide particles to the silver matrix led to formation of porous composites. However, addition of YSZ particles did not result in a stable porosity. Analysis of the impedance spectra allowed further investigations on the obtained microstructures and the formed contacts. No microstructural degradation has been observed in the porous Ag–LSM composite current collector and its electrical properties remained stable for over 5000 h of measurements at 800 °C in air.

The instrumented indentation test is an important alternative in quantifying residual stresses. Various indentation models have been developed to determine residual stresses, but no previous models can be applied to a nonequibiaxial residual stress state. To overcome this limitation, a Knoop indentation technique was developed to use the asymmetric characteristics of the Knoop indenter. With the ratio of conversion factors and equations for the relation between the load differences and the residual stress, a model of Knoop indentation was developed to determine the stress directionality p. This model was verified and compared through experiments on various biaxial tensile stress states. Imperfections in the Knoop tip change the conversion factor ratio. Using finite element simulations, this change in the conversion factor was expressed by a fitting equation.

Chemical wet etching on c-plane sapphire wafers by three etching solutions (H3PO4, H2SO4, and H3PO4/H2SO4 mixing solution) was studied. Among these etching agents, the mixing H3PO4/H2SO4 solution has the fastest etching rate (1.5 μm/min). Interestingly, we found that H2SO4 does not etch the c-plane sapphire wafer in thickness; instead, a facet pyramidal pattern is formed on the c-plane sapphire wafer. GaN light-emitting diode (LED) epitaxial structure was grown on the sapphire wafer with the pyramidal pattern and the standard flat sapphire wafer. X-ray diffraction and photoluminescence measurement show that the pyramidal pattern on the sapphire wafer improved crystalline quality but augmented the compressive stress level in the GaN LED epilayer. The horizontal LED chips fabricated on the pyramidal-patterned sapphire wafer have a larger light output than the horizontal LED chips fabricated on the standard flat sapphire wafer by 20%.

A single crystal aluminum nitride (AlN) wafer surface was investigated via the use of a novel software-based, Charge-based Deep Level Transient Spectroscopy (Q-DLTS) apparatus, both before and after surface bond termination with hydrogen plasma. The sample was cleaned and metalized with a thermoresistive evaporator to create electrical contacts and then annealed in a helium atmosphere at 825 °C. Current-voltage (I-V) measurements were performed to investigate the nature of the metal/substrate contacts. The effect of hydrogen termination was investigated and Arrhenius plots were produced from Q-DLTS spectra at temperatures ranging from −15.9 °C to 136.0 °C. Activation energies and capture cross-section values were calculated from the Q-DLTS spectra for traps existing in the AlN substrate surface. Prior to hydrogen termination, four charge traps were observed with activation energies of 0.31 eV, 0.61 eV, 0.56 eV, and 0.18 eV and capture cross sections 5.6 × 10−21 cm2, 1.1 × 10−16 cm2, 3.5 × 10−19 cm2, and 1.3 × 10−21 cm2, respectively After hydrogen termination, five charge traps were observed with activation energies of 0.31 eV, 0.61 eV, 0.52 eV, 0.19 eV, and 0.40 eV, and capture cross sections 4.9 × 10−21 cm2, 1.3 × 10−16 cm2, 2.9 × 10−19 cm2, 3.1 × 10−19 cm2, and 4.7 × 10−19 cm2, respectively. Four of these peaks after termination are matched with the peaks prior to termination and the fifth peak appears to be the result of the hydrogen termination.

Amorphous titania thin films with increasing Fe content have been prepared by RF magnetron sputtering. X-ray absorption spectroscopy revealed modifications of both local structures/environment of the Ti and Fe atoms, with formation of phases containing amorphous material and a magnetite-like phase. The temperature dependence of the electrical conductivity of the films was investigated for temperatures higher than half of the Debye temperature (T > 391 K). It was found that the electrical conductivity in the amorphous Fe/TiO2 films obeys the Meyer–Neldel rule. The origin of this behavior is explained on the basis of the multiphonon-assisted hopping model.

The analysis of nanoindentation force data are based on Sneddon’s solution for a linear elastic half space with a rigid axisymmetric indenter. Berkovich indenters commonly used in indentation experiments are normally modeled as cones. The idea of effective tip shape was presented to better explain the behavior of the unloading curve and pressure distribution under the tip in real experiments. We examine the concept of effective tip in three dimensions by importing real indenter metrology by atomic force microscope directly into finite element analysis and simulate fused silica indentation experiments. We show that fitting the elastic reloading curves overestimates the elastic modulus of fused silica. This is explained by studying the pressure distribution at maximum depth under the effective tip. While the effective tip describes the problem geometrically, it is believed that neglecting the deformed zone in the indented material is responsible for over estimating the modulus value.