A novel load–displacement sensing instrument has been designed and fabricated to characterize the fracture properties of brittle thin films at low temperature (approximately −30 °C) and pressure (1.6e-4 Pa) environments. In this study, the instrument was used to investigate the effects of harsh environments on the fracture behaviors of organosilicate glass (OSG) and silicon carbonitride (SiCN) thin films under four-point bend loading. Experimental results showed that the fracture strengths of film stacks are the highest when the environment contains a very low water molecule concentration. This condition can be achieved by purging the testing chamber with pure nitrogen or reducing the chamber pressure to less than 1 Pa. In contrast, cracks propagated readily along OSG/SiCN interfaces when experiments were performed in deionized water. The effects of low temperature (approximately −30 °C) and pressure on thin film fracture were also studied, and the results demonstrated that there is no observed degradation of the OSG fracture properties. X-ray photoelectron spectroscopy (XPS) technique was used to identify the chemical composition of the fracture surfaces.

The growth kinetics of Si bulk crystals and nanowires (NWs) in contact with Au–Si liquids is studied by molecular dynamics simulations using an empirical potential fitted to the Au–Si binary phase diagram. The growth speed v is predicted as a function of Si concentration xSi in the Au–Si liquid at temperature T = 1100 K and as a function of T at xSi = 75%. For both bulk crystals and NWs, the {111} surface grows by the nucleation and expansion of a single two-dimensional island at small supersaturations, whereas the {110} surface grows simultaneously at multiple sites. The top surfaces of the NWs are found to be curved near the edges. The difference in the growth velocity between NWs and bulk crystals can be explained by the shift of the liquidus curve for NWs. For both bulk crystals and NWs, the growth speed diminishes in the low temperature limit because of reduced diffusivity.

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 show that low-density nanoporous silica monoliths (aerogels), in contrast to the case of full-density silica, exhibit pronounced time-dependent deformation during indentation at room temperature. Logarithmic indentation creep and stress relaxation are revealed, with an exponential dependency of the creep constant on the applied stress. Such time-dependent deformation is attributed to stress corrosion fracture of nanoligaments that have a large surface-to-bulk atomic fraction.

Effects of the precipitated phase and the ordered phase domain of an Fe-6.5 wt%Si alloy before and after heat treatment on the bending properties were investigated in this study. The results showed that original needle-like phases were spheroidized after the heat treatment at 900 °C for 1 h followed by slow or rapid cooling. Compared with the directional solidified sample, the slow cooling sample had a higher order degree, whereas the rapid cooling samples had a lower order degree. After rapid cooling heat treatment, the fracture deflection of the sample was increased by 73.8%. Fracture analysis showed that transition from quasi-cleavage fracture to tear pit-like fracture took place in the rapid cooling sample. The bending properties of the Fe-6.5 wt%Si alloy were improved mainly due to the changes in morphology and amount of the precipitated phase as well as the reduction of order degree.

Hafnium dioxide (HfO2) thin films were synthesized on silicon and quartz substrates by thermal oxidation of metallic hafnium films in oxygen. The crystalline structure and optical properties of the HfO2 films were systematically investigated using x-ray diffraction, ultraviolet (UV)-Raman, and UV-visible spectrophotometer techniques. All the films thermally oxidized at 450 to 800 °C were mostly monoclinic. Interestingly, cubic phase coexisted with monoclinic phase in the films thermally oxidized at 500 to 600 °C. The corresponding optical band gap (Eg) varied from 5.92 to 6.08 eV for the films with a different phase ratio (cubic to monoclinic one) ranging between 0 and 1:3. These results imply that the mixed phase could have a certain effect on the increase of the Eg of HfO2 films.

A spherical indentation-based method and its numerical verification, which is capable of identifying the plastic properties, have been respectively provided by our previous work [P. Jiang, et al., J. Mater. Res.24, 1045 (2009)] and [T. Zhang, et al., J. Mater. Res.24, 3653 (2009)]. To examine its effectiveness for practical application, 10 typical metals were selected to perform experimental verifications. Here, the above method was used in combination with the Oliver–Pharr model to avoid its dependence on the previously known elastic modulus. To obtain reliable results, a reasonable calibration has been performed for the used spherical tip with imperfect shape. Finally, the present verification has shown that the deviations of yield strength and elastic modulus obtained from the indentation tests are at most 40% but are generally within 25%. And the effect of the difference in constitutive relationships between the ideal model and the actual material on the accuracy of the indentation-based method has also been illustrated.

Molecular dynamic simulations of helium atoms escaping from a helium-filled nanobubble near the surface of crystalline palladium reveal unexpected behavior. Significant deformation and cracking near the helium bubble occur initially, and then a channel forms between the bubble and the surface, providing a pathway for helium atoms to propagate toward the surface. The helium atoms erupt from the bubble in an instantaneous and volcano-like process, which leads to surface deformation consisting of cavity formation on the surface, along with modification and atomic rearrangement at the periphery of the cavity. The present simulation results show that, near the palladium surface, there is a helium-bubble-free zone, or denuded zone, with a typical thickness of about 3.0 nm. Combined with experimental measurements and continuum-scale evolutionary model predictions, the present atomic simulations demonstrate that the thickness of the denuded zone, which contains a low concentration of helium atoms, is somewhat larger than the diameter of the helium bubbles in the metal tritide. Furthermore, a relationship between the tensile strength and thickness of metal film is also determined.

Selective CdSe tip growth on CdTe tetrapod-shaped colloidal seeds has been achieved for a Cd:surfactant molar ratio of 1:2, where surfactant is oleic acid. The average length of tetrapod arms increased from 12 to 21 nm while arm width remained constant of 3 nm. Formation of CdSe tips shifts the excitonic absorption maximum to the near-infrared region and the appearance of low-intensity absorption feature corresponding to a charge-transfer band. At the same time, luminescence band splits into a narrow (about 100 meV width) CdTe excitonic subband and a 230-meV-wide charge-transfer subband, with splitting energy increasing up to 260 meV depending on CdSe tip length. The intensity ratio of charge transfer to excitonic luminescence increases exponentially with splitting energy rise. Considerable modification of the photoluminescence spectrum has been observed with temperature variation in the range of 10–60 °C.

Near-stoichiometric compositions of Ba(B′1/3B″2/3)O3 (B′ = Mg, Co, or Zn and B″ = Nb or Ta) perovskite-type materials with nonstoichiometry on Ba and B′ positions were studied by room temperature Raman spectroscopy and transmission electron microscopy. The studied materials with 1:2 ratio of B-site cations belong to the family of perovskites that has tolerance factor larger than unity, indicating formation of a strained structure. This family of materials exhibits phase transition from a completely disordered phase having space group Pm-3m to a 1:2-ordered phase with space group P-3m1. Measured Raman spectra were attributed to the presence of 1:2-cation order and are characterized by the presence of seven modes, the strongest of which at 800 cm−1 originates from collective motion of oxygen octahedra. The appearance of a mode at 670 cm−1 in Co-containing samples was ascribed to the formation of a 1:1-ordered phase and was confirmed by selected-area electron diffraction.

The thermal stability, glass-forming ability (GFA), mechanical properties and Poisson’s ratio of a Zr-based Zr75−xNi25Alx (x = 0 to 24) glassy alloy series have been investigated systematically. The large supercooled liquid region (ΔTx) of over 80 K and critical sample diameter (dc) for glass formation above 10 mm were obtained in a composition range of x = 11 to 21. The maximum dc of 15 mm was formed for an off-eutectic Zr60Ni25Al15 alloy, which had the largest ΔTx and γ value, along with the lowest density change upon crystallization. The bulk glassy alloys exhibited high compressive yield strength (σc,y) of 1662 to 2060 MPa and distinct plastic strain (εc,p) of 1.2 to 4.7%. With increasing Al content, the σc,y and Young’s modulus linearly increased, while the εc,p gradually decreased. The εc,p was found to have a good correlation with the Poisson’s ratio.

A family of ultrahigh strength Co-based bulk metallic glasses (BMGs) with critical diameters up to 2 mm is synthesized in Co65–xTaxB35 (at.%, x = 5–10) alloys by copper mold casting. The improved glass-forming ability associated with near eutectic compositions is attributed to the appropriate addition of Ta. The glassy alloys exhibit high glass transition temperature of 930–975 K, ultrahigh compressive strength of 5.6–6.0 GPa, high specific strength of 639–654 N·m/g, Vickers hardness of 15–16 GPa, and distinct plastic strain of 0.5–1.5%. The strength and the specific strength are the highest values reported for bulk metallic materials known so far. Several universal criteria correlated with the thermal properties, elastic constants, and mechanical properties were validated in the Co-based BMG system. These Co–Ta–B BMGs combining with superior mechanical properties, high thermal stability, and simple elemental composition are significant for scientific research as modeling materials and industrial application as advanced structural materials.

Improved room temperature plasticity was achieved by microalloying Cu in a series of (Fe71Nb6B23)100−xCux (x = 0, 0.25, 0.5, 0.75, and 1) glass matrix alloys with tunable size and volume fraction of precipitates composed of α-Fe and Fe23B6 phases. When ∼10-nm-sized nano-scale precipitates are formed with a size comparable to the shear bandwidth by controlling the added content of Cu, the (Fe71Nb6B23)99.5Cu0.5 alloy exhibits a maximum plastic strain of 4.3 ± 0.8% with pronounced multiple shear banding. A further increase in the size of the precipitates up to micrometer scale results in catastrophic fracture accompanied with irregular cracks, revealing that the fracture mechanism of the different alloys is controlled by the precipitate size.

The direct integration of Ge nanowires with silicon is of interest in multiple applications. In this work, we describe the growth of high-quality, vertically oriented Ge nanowires on Si (111) substrates utilizing a completely sub-Au–Si-eutectic annealing and growth procedure. With all other conditions remaining identical, annealing below the Au–Si eutectic results in successful heteroepitaxial nucleation and growth of Ge nanowires on Si substrate while annealing above the Au–Si eutectic leads to randomly oriented growth. A model is presented to elucidate the effect of the annealing temperature, in which we hypothesized that sub-Au–Si-eutectic annealing leads to the formation of a single and well-oriented interface, essential to template heteroepitaxial nucleation. These results are critically dependent on substrate preparation and lead to the creation of integrated nanowire systems with a low thermal budget process.

In this work, we have systematically explored the influence of thermo-mechanical treatment on the precipitation behavior and its strengthening in Inconel 740, a relatively new Ni-based superalloy, using specimens on which different levels of stresses were applied at 700 °C. With increasing applied stress, fraction of gamma prime precipitates increased (without significant size change) and nanoindentation hardness was enhanced. The stress effects were discussed in terms of the free energy barrier for heterogeneous nucleation and the prevailing mechanisms of precipitation strengthening.

The dependences of unit cell parameter, x-ray diffraction line width B, and microhardness H on the composition of PbTe-Bi2Te3 (0–10 mol% Bi2Te3) semiconductor alloys, subjected to different types of heat treatment, were obtained. In the concentration ranges ∼0.5–1.5 and 3–4 mol% Bi2Te3 within the homogeneity region of PbTe (0–6 mol% Bi2Te3), anomalous constancy or decrease in B and H was observed. A long room temperature aging leads to a more distinct manifestation of these effects. It is suggested that the observed peculiarities in the concentration dependences of the properties are connected with percolation effects and self-organization processes in the solid solution.

With 2 mol% Zn2+ codoping and 2 mol% K+ charge compensation, the red-emitting phosphor [K0.8Y0.63Eu3+0.08Zn0.02][Mo0.2W0.8O4] was synthesized by solid-state reaction. X-ray powder diffraction spectrum indicates that it owns single phase. Through its emission spectra, excitation spectra, and fluorescence decay curves measured, its emission mechanism was mentioned and it was calculated for its partial J-O parameters and quantum efficiency of Eu3+ 5D0 energy level under 395 nm excitation. The results indicate that Eu3+ 5D0 → 7F2 red luminescence in the host can be excited by 395 nm, but its quantum efficiency can be improved in space and it has potential applications for white light-emitting diode as the red luminescent materials.

Systematic nanoindentation experiments have been carried out to study the mechanical properties of a nanocrystalline Fe–51Ni coating exhibiting anelastic and creep characteristics. An analytical method based on the correspondence principle for linear viscoelasticity was developed. The holding displacement–time data obtained in indentation creep tests at a high loading rate of 20 mN/s were analyzed, and material parameters related to the elastic, anelastic, and creep characteristics were derived using a model containing one Maxwell unit and two Kelvin units. The anelastic deformation thus contains at least two relaxation processes having relaxation times of 0.37 and 6.8 s, respectively, and the creep deformation is described by a viscosity value of 4.2 × 104 GPa·s for the alloy in an as-deposited state. The anelastic and creep characteristics descend associated with increases of the elastic modulus and hardness values after the alloy was annealed at 673 K.

Broadband spectral conversion from visible light to near-infrared radiation in Ce3+–Nd3+/Yb3+ codoped yttrium aluminum garnet is reported. Excitation, emission spectra, and decay curves have been measured to prove the energy transfer from Ce3+ to Nd3+ or Yb3+. The energy transfer efficiencies have been estimated, and the mechanisms of the energy transfer between Ce3+ and Nd3+/Yb3+ have been proposed. Ce3+–Nd3+ codoped YAG can obtain more effective emission in the desired near-infrared region (around 1100 nm) through broadband conversion, showing potential application to improve the conversion efficiency of Si solar cells.

Silicon carbide nanowires (SiCNWs) (with diameters of tens of nanometer and aspect ratio well above 103), consisting of β-SiC one-dimensional single crystals wrapped in amorphous nitrogen-containing SiO2 sheaths, were efficiently synthesized in gram quantities by autogenous combustion synthesis using Si as a defluorination reagent of poly(tetrafluoroethylene). The combustion temperature was evaluated using the emission spectroscopy. Vapor–liquid–solid mechanism of a self-catalytic growth of the SiCNWs is proposed.