Reliable measurement of mechanical properties of thin solid films has been challenging, despite widespread usage of thin films in applications such as semiconductor, magnetic storage, and microelectromechanical systems. Some of the challenges include instrument limitations and inadequacy of theoretical models to obtain quantitative prediction of thin film properties. In this article, we propose a technique to extract the shear strength of thin films from nanoscratch experiments using a contact mechanics analysis of a sliding sphere. Based on the stress field analysis by Hamilton, the stress status around the contact point is obtained at the initiation of yield, and is used to establish a direct correlation between contact pressure/surface traction and shear strength. Nanoscratch experiments were also performed on an extremely thin diamond carbon overcoat used in supersmooth magnetic storage disks, and the shear strength was successfully obtained using the proposed technique. These results were comparable with hardness values reported in the literature, assuming Tabor’s empirical relation (hardness ≈ 3*yield strength) and Tresca yield criterion. Finally, a finite element model was developed to simulate a rigid sphere sliding over a deformable solid to further verify the validity of the proposed model. The finite element analysis confirmed that the calculation results from the proposed relation are in good agreement with experimentally measured bulk property values of shear strength.

A platinum (Pt) on pure ceria (CeO2) supported by carbon black (CB) anode was synthesized using a combined process of precipitation and coimpregnation methods. The electrochemical activity of methanol oxidation reaction on synthesized Pt-CeO2/CB anodes was investigated by cyclic voltammetry and chronoamperometry experimentation. To improve the anode property on Pt-CeO2/CB, the influence of particle morphology and particle size on anode properties was examined. The morphology and particle size of the pure CeO2 particles could be controlled by changing the preparation conditions. The anode properties (i.e., peak current density and onset potential for methanol oxidation) were improved by using nanosize CeO2 particles. This indicates that a larger surface area and higher activity on the surface of CeO2 improve the anode properties. The influence of particle morphology of CeO2 on anode properties was not very large. The onset potential for methanol oxidation reaction on Pt-CeO2/CB, which consisted of CeO2 with a high surface area, was shifted to a lower potential compared with that on the anodes, which consisted of CeO2 with a low surface area. The onset potential on Pt-CeO2/CB at 60 °C became similar to that on the commercially available Pt-Ru/carbon anode. We suggest that the rate-determining steps of the methanol oxidation reaction on Pt-CeO2/CB and commercially available Pt-Ru/carbon anodes are different, which accounts for the difference in performance. In the reaction mechanism on Pt-CeO2/CB, we conclude that the released oxygen species from the surface of CeO2 particles contribute to oxidation of adsorbed CO species on the Pt surface. This suggests that the anode performance of the Pt-CeO2/CB anode would lead to improvements in the operation of direct methanol fuel cells at 80 °C by the enhancement of diffusion of oxygen species created from the surface of nanosized CeO2 particles. Therefore, we conclude that fabrication of nanosized CeO2 with a high surface area is a key factor for development of a high-quality Pt-CeO2/CB anode in direct methanol fuel cells.

Absorption and emission properties of Tm3+ in (1-x) (Ge0.25Ga0.10S0.65)-xCsBr glass (x = 0.00–0.12) were investigated. Upon 10 mol% CsBr addition, the absorption cross sections of Tm3+ decreased accompanied by a large increase in the lifetime of the Tm3+:3H4 level to 1.23 ms since Tm3+ ions were surrounded by the Br ions of [GaS3/2Br]− units. As the concentration of Tm3+ increased, the 3H4 level lifetime decreased due to cross relaxation (Tm3+:3H4,3H6→Tm3+:3F4,3F4). Temperature dependence of the 3H4 level lifetime showed that cross relaxation in Tm3+ is a phonon-assisted energy transfer process. When Tm3+ were surrounded by Br ions, cross relaxation among Tm3+ was also suppressed due to a decrease in the transition probability among Tm3+ energy levels, a decrease in phonon energy of the host glasses, as well as an increase in the number of phonons participating in the cross relaxation process. The potential of Tm3+-doped Ge-Ga-S-CsBr glasses for S-band fiber amplifiers is also discussed.

We report on significant asymmetry phenomena, including failure mode, fracture strength, and plasticity under compression and tension, for Zr- and Ti-based composites containing ductile dendrites. The failure of the Zr-based composite always occurs in a shear mode with a small strength asymmetry and different plasticity under tension and compression. In contrast, the Ti-based composite exhibits a significant high strength asymmetry and zero tensile plasticity although its compressive plasticity is high. We propose that the ratio, α=τ0/σ0 (τ0 and σ0 are the intrinsic shear and cleavage strengths), is a substantial parameter controlling the strength asymmetry and the failure mode of various materials.

The photoluminescence spectra of the rod-shaped pure and Ti-doped MgAl2O4 single crystals, grown by the micro-pulling-down (μ-PD) method, have been systematically investigated under high-intensity pulsed Nd3+: YAG laser excitation in the ultraviolet (UV) region (266 nm). The chemical properties of the grown crystals under reducing argon atmosphere will be reported and the annealing effect under oxidizing atmosphere will be discussed. The room temperature luminescence properties of Ti-doped MgAl2O4 single crystals were performed before and after annealing as a function of the titanium concentration. Three broad bands absorption in the UV/VIS (visible) spectral regions and a broadband visible blue emission were observed from Ti-doped MgAl2O4. An estimation of the decay time value of theses emissions was determined from the time-resolved spectra and the energies of the vibrational modes of the MgAl2O4 crystal are obtained from the infrared spectra.

The room temperature tensile properties of ultrafine-grained 25-μm gold wires were evaluated as a function of calcium (Ca) doping at various strain rates ranging between 10−3 and 10−1 s−1. Paradoxically, the increased amount of Ca was found to simultaneously increase the strength and ductility of the Au wires. However, based on scanning electron microscopy and tensile characterization, the grain size distributions, strain-hardening rate, and strain rate sensitivity of Au wires did not change with Ca, thus showing that neither grain refinement nor plastic instability are likely to be responsible for the concurrent improvement of strength and ductility.

Ba5Nb4O15 has shown excellent microwave dielectric properties and is under consideration as a low-temperature cofired ceramic material for advanced radio frequency (RF) applications. By combining tape casting and liquid phase upon sintering, sintered Ba5Nb4O15 thick films stacked to form laminates were produced with aligned elongated grains. This texture engineering, correlated with crystallographic orientation, provides remarkably high temperature stability of dielectric constant up to microwave frequency. Crystallographic texture arises in Ba5Nb4O15 induced by the primary consolidation process, hot pressing, and pulsed laser deposition. The dielectric anisotropy could be efficiently obtained in the textured samples, thereby enabling significant feasibility of microwave circuit designs.

The effect of grain boundary (GB) misorientation on hot tearing susceptibility of directionally solidified (DS) nickel-based superalloys was explored. We found that the castability of second generation nickel-based superalloy CMSX-4 is inferior to DS superalloy IN792, an alloy well known for bad castability. The castability of CMSX-4 is somewhat improved at a higher solidification rate. The hot tearing tendency increases with increasing GB misorientation angle. As feeding tendency becomes greater with increasing misorientation, this points to the importance of GB cohesion for solidification cracking in the alloy. Microstructure investigation reveals that hot tearing is associated with formation of continuous gamma and gamma prime eutectic films at the GB in CMSX-4. We assume that the gamma and gamma prime eutectic, which reflects the remaining liquid at the end of solidification, prevents the impinging dendrite arms from touching and in this way decreases cohesion.

This study investigated a mechanism for controlling the shape of Cu nanocrystals fabricated using the polyol process, which considers the thermodynamic transition from a faceted surface to a rough surface and the growth mechanisms of nanocrystals with faceted or rough surfaces. The faceted surfaces were stable at relatively low temperatures because of the low entropy of perfectly faceted surfaces. Nanocrystals fabricated using a coordinative surfactant stabilized the faceted surface at a higher temperature than those fabricated using a noncoordinative surfactant. The growth rate of the surface under a given driving force was dependent on the surface structure, i.e., faceted or rough, and the growth of a faceted surface was a thermally activated process. Surface twins decreased the activation energy for growth of the faceted surface and resulted in rod- or wire-shaped nanocrystals.

Polycrystalline diamond films are deposited on p-type Si (100) and n-type SiC (6H) substrates at the low surface deposition temperatures of 370 °C–530 °C using a microwave plasma-enhanced chemical vapor deposition system in which the surface temperature during deposition is monitored and controlled. A very high growth rate up to 1.3 μm/h on SiC substrate at 530 °C surface temperature is obtained. The room temperature in-plane thermal conductivity of the low-surface-temperature–deposited thin films is measured by a traveling wave method. The diamond films of grain sizes between 3 and 7 μm and deposited at 370 °C showed a high thermal conductivity value of ∼6.5 W/cm-K, which is much higher than the single crystal SiC thermal conductivity value at room temperature. Diamond films deposited on Si and SiC single crystals at higher temperatures showed even higher thermal conductivities of 11–17 W/cm-K. The structure and microstructure of these films are characterized by x-ray diffraction, scanning electron microscopy, and Raman spectroscopy, and are related to measured thermal conductivities.

The thermal recoverability of a nanoporous silica-based system modified by a cross-linked polyelectrolyte is investigated. At room temperature, as a nominally hydrostatic pressure is applied, the gel matrix can be partially dehydrated. The released water molecules will be forced into the initially energetically unfavorable nanopores and are “locked” there. At an elevated temperature, the infiltration pressure increases slightly, which is contradictory to the experimental data of the unmodified system. More importantly, the defiltration of the confined liquid is significantly promoted, leading to a much higher system recoverability.

Electronic (UV-vis) and vibrational absorption spectroscopies were used to examine the impact of incident photon energy and local atmospheric composition on the development of photo-induced structural changes in poly[(methyl)(phenyl)silylene] thin films. The relative impact of atmosphere on the magnitude and nature of photostructural modifications in this material is found to be enhanced under 3.68 eV photon exposure where the incident photon is resonant with the lowest energy absorption of the Si-Si-conjugated backbone structure. This is in contrast to a greater overall magnitude of photo-induced structural change, with limited atmospheric dependence, observed under 5.1 eV exposure, resonant with absorption transitions associated with the π-conjugated phenyl ring side group. These results provide insight into the underlying structural mechanisms contributing to the large refractive index changes typically observed in these materials.

Many layered ternary ceramics displayed unusual thermal shock behavior, i.e., the retained strengths of as-quenched samples increased with increasing quench temperature above a critical quench temperature. However, the causation was not clear even though this phenomenon has been observed for 10 years. In this study, the thermal shock behavior of Ti3SiC2 and Ti3AlC2, two representative members of layered ternary ceramics, was investigated. The results indicated that the formation of surface oxides was responsible for this abnormal phenomenon. These results might contribute to the understanding of this unusual behavior of other layered ternary ceramics.

The Aurivillius phases in the vicinity of the Bi5AgNb4O18 compound were determined by means of solid-state reaction, x-ray diffraction, and scanning electron microscopy. The stoichiometric Aurivillius phase Bi5AgNb4O18 is compatible with Ag/Ag2O, BiAgNb2O7, and BiNbO4. Two Aurivillius-phase solid solutions were found for the A-site-deficient Bi5+x/3Ag1−xNb4O18 and the oxygen-deficient Bi5−zAgzNb3O15−z. The x value of the Bi5+x/3Ag1−xNb4O18 solid-solution limit is between 0.2 and 0.4. A single-phase non-stoichiometric compound was obtained for x = 0.2 in Bi5+x/3Ag1−xNb4O18 and z = 0.25 in Bi5−zAgzNb3O15−z. The dielectric (at 1 MHz), ferroelectric, and piezoelectric properties of the stoichiometric Aurivillius phase Bi5AgNb4O18 were as follows: TC= 772 °C, ϵr= 197 (room temperature), ϵmax = 830, tanδ ∼ 10−3(room temperature to 540 °C), Pr = 6μC/cm2, Ec = 52kV/cm, d33 = 11pC/N.

Diffusion bonding of Ti3SiC2 and nickel has been conducted at temperatures of 800 °C–1100 °C for 10–90 min under 6–20 MPa in a vacuum. The phase composition and microstructure of the joints were investigated by X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. The total diffusion path of the joining is determined to be Ni/Ni31Si12 + Ni16Ti6Si7 + TiCx/Ti3SiC2 + Ti2Ni + TiCx/ Ti3SiC2. The growth of the reaction layer follows parabolic law, and the temperature dependence of the reaction constant, k, can be expressed as k = 1.68 × 10−4 exp(−118 ± 12 kJ/RT) m/s1/2. The diffusion of nickel through the reaction zone toward Ti3SiC2 is the main controlling step in the bonding process. Joint strengths were determined through shear tests. The maximum shear strength of 121 ± 7 MPa, which is close to the shear strength of Ti3SiC2, has been obtained under the condition of 1000 °C for 10 min under 20 MPa.

We have connected viscoelastic recovery (healing) in sliding wear to free volume in polymers by using pressure-volume-temperature (P-V-T) results and the Hartmann equation of state. A linear relationship was found for all polymers studied with a wide variety of chemical structures, except for polystyrene (PS). Examination of the effect of the indenter force level applied in sliding wear on the healing shows that recovery is practically independent of that level. Strain hardening in sliding wear was observed for all materials except PS, the exception attributed to brittleness. Therefore, we have formulated a quantitative definition of brittleness in terms of elongation at break and storage modulus. Further, we provide a formula relating the brittleness to sliding wear recovery; the formula is obeyed with high accuracy by all materials including PS. High recovery values correspond to low brittleness, and vice versa. Our definition of brittleness can be used as a design criterion for choosing polymers for specific applications.