The indentation hardness of three different pure forms of silicon was investigated by two different methods. The hardness was probed by direct imaging of the residual impressions and by instrumented indentation using the Oliver–Pharr method. The forms of silicon used were a defective form of amorphous silicon, an amorphous form close to a continuous random network, and a crystalline silicon. The first form deforms via plastic flow and the latter two via phase transition. Two different unloading rates, fast and slow, were used to vary the phase transition behavior. This influenced the relative hardness as measured by instrumented indentation, which is not a reliable method to quantify hardness values in phase transforming materials. Thus, for our phase transforming silicon system, the relative hardness between samples can only be determined correctly by direct imaging, provided that the image accurately reveals the extent of the phase transformed volume.

Oxide semiconductors exhibit a range of physical properties and have potential optical, electronic, and energy applications. Transparent conducting oxides (TCOs) are currently used in products such as flat-panel displays. The prevailing n-type conductivity in these materials has historically been attributed to native defects such as oxygen vacancies. Recent calculations and experiments, however, have provided evidence that native defects are actually not responsible in majority of the cases. Hydrogen, on the other hand, does act as a shallow donor and can dramatically affect the electrical properties of oxides. In addition to contributing to n-type doping, hydrogen also passivates dangling bonds in cation vacancies and passivates acceptor dopants. Some oxides contain “hidden hydrogen,” perhaps H2 molecules, which dissociate at elevated temperatures. In this article, the many roles of hydrogen in zinc oxide, tin dioxide, titanium dioxide, indium (III) oxide, gallium (III) oxide, and strontium titanate are reviewed. The emphasis is on fundamental electronic, structural, and vibrational properties of hydrogen complexes, as determined by experiment and theory.

Large-scale industrial production of carbon nanotubes (CNTs) has recently become available, but there are relatively few reports of the investigation of these industrially produced bulk CNTs as potential electrode materials for electrochemical energy storage such as lithium-ion batteries (LIBs). Here, we report our evaluation of the electrochemical performance of the industrially produced CNTs from one manufacturer and our utilization of a kinetically controlled, vapor diffusion synthesis method combined with in-situ carbothermal reduction to homogeneously grow nanocrystalline tin (Sn) particles (∼200 nm) in the matrix of the CNTs, yielding a Sn@CNTs composite. After surface coating with a layer of carbon coating (3–4 nm), this composite was transformed to a surface-modified Sn@CNTs composite that exhibited much higher reversible capacity, initial Coulombic efficiency, and rate capacity than the pristine CNTs as anode materials for LIB.

In situ transmission electron microscopy (TEM) was carried out to investigate the dynamics of resistance switching in a solid electrolyte, Cu-Ge-S. By applying voltage to Pt-Ir/Cu-Ge-S/Pt-Ir, where Pt-Ir constituted the electrodes, a deposit containing conductive filaments composed mainly of Cu was formed around the cathode. As voltage continued to be applied, the deposit grew and finally narrow conductive filaments made contact with the anode. This corresponded to resistance switching from high- to low-resistance states (HRS and LRS). By alternating the voltage, the deposit contracted toward the cathode and detached from the anode. The resistance immediately changed from LRS to HRS. By applying voltage, the deposit containing Cu-based filaments grew and shrank, and resistance switching occurred at the electrolyte-anode interface. This conductive filament-formation model, which was recently reported, was experimentally confirmed with TEM through dynamic observations of the deposit-containing filaments.

Transparent conductive oxides (TCOs) are degenerately doped compound semiconductors with wide band gaps (Eg > 3 eV), which are used as transparent electrodes in optoelectronic devices. Reports on the influence of negative ions on the electrical properties of TCO films are reviewed and compared with our results. It was reported that the radial resistivity distributions depend (i) on the excitation mode of the magnetron (direct current or radio frequency), (ii) on the erosion state of the sputtering target, and (iii) on the density of the ceramic targets. This can be explained by the fact that the negative ions in magnetron discharges (in our case O−) are generated at the target surface and accelerated toward the growing films. Their energy and their radial distribution depend on the discharge voltage and the shape of the emitting surface, i.e., of the erosion groove. Ways for reducing the effect of negative ion bombardment are discussed.

This paper reports on the defect structures formed upon strain relaxation in pulsed laser-deposited complex oxide superlattices consisting of the ferromagnetic metal, La0.67Sr0.33MnO3, and the antiferromagnetic insulator, La0.67Sr0.33FeO3. Atomic resolution scanning transmission electron microscopy and electron energy loss spectroscopy were used to characterize the structure and chemistry of the defects. For thinner superlattices, strain relaxation occurs through the formation of 2-D stacking faults, whereas for thicker superlattices, the prolonged thermal exposure during film growth leads to the formation of nanoflowers and cracks/pinholes to reduce the overall strain energy.

Ag nanoparticles were prepared via a wet chemical reduction method and treated with tetraethoxysilane (TEOS) to form an insulating SiO2 layer on the surface (Ag@SiO2). The Ag@SiO2 nanoparticles were introduced in to the BaTiO3/poly (vinylidene fluoride) matrix to prepare the three-phase Ag@SiO2/BaTiO3/poly (vinylidene fluoride) composite, and the dielectric behavior of the composite was investigated. The results showed that the typical “conductor/polymer” percolation effect was not observed in the composite as a result of the SiO2 layer, which prevented Ag particles from contacting with each other directly and restricted the movement of electrons under external field. The high dielectric constant of 723 and a relatively low loss of 0.82 were achieved at 100 Hz with 40 vol% Ag@SiO2 and 20 vol% BaTiO3, respectively. The microcapacitor network model and “Maxwell-Wagner-Sillars” (MWS) effect were used to investigate dielectric properties of the three-phase composite.

Nanocomposite piezoelectric powders comprising polyvinylidene fluoride (PVDF) and carbon nanotubes (CNTs) were synthesized using a novel process, which combines ultrasonication and solvent-nonsolvent mixture-induced crystallization at very low temperatures ≤10 °C. The morphological and thermal properties of these composite powders were extensively studied. Scanning electron microscopy characterization showed that these composite powders have polymer particles with an average diameter of 150 nm. Fourier transform infrared spectroscopy, differential scanning calorimetry and wide-angle x-ray scattering analyses confirmed that at CNT concentrations of 0.05–20 wt% this process introduces the β-phase in both PVDF/single-walled CNT (SWCNT) and PVDF/multiwalled CNT (MWCNT) composite powders. Both types of composite powders (PVDF-multiwalled and PVDF-single-walled nanotubes) have shown piezoelectric response at different voltages up to 1% loading of multiwalled nanotubes (MWCNTs) and 0.5% loading of single-walled nanotubes (SWCNTs) in composites.

Lee and Radok [J. Appl. Mech.27, 438 (1960)] derived the solution for the indentation of a smooth rigid indenter on a linear viscoelastic half-space. They had pointed out that their solution was valid only for regimes where contact area did not decrease with time. In this article, a large number of finite element simulations and one typical experiment demonstrate that Lee-Radok solution is approximately valid for the case of reducing contact area. Based on this finding, three semiempirical methods, i.e., Step-Ramp method, Ramp-Ramp method and Sine-Sine method, are proposed for determination of shear creep compliance using the data of both loading and unloading segments. The reliability of these methods is acceptable within certain tolerance.

We report here investigations on the superstructure modulation induced by the ordering of carbon vacancies in the nonstoichiometric zirconium carbide of ZrC0.61, which was prepared by spark plasma sintering (SPS) of the mechanochemically synthesized ZrCx nanopowders. The sintered ZrC0.61 is found to exhibit an interesting microstructure of interlaced laminated sheets. In contrast to the previous long duration post annealing for realization of the ordered carbon vacancies in the rocksalt-structured transition metal carbide, the ordered carbon vacancies are directly obtained during the SPS process, and no post-annealing period is necessary. With the help of transmission electron microscopy, the superstructural nanodomains with the average size of ∼30 nm are identified.

We report a family of novel Strontium (Sr)-based bulk metallic glasses (BMGs) with good glass-forming ability and ultralow glass transition temperature (Tg) by strategic composition design. The Sr-based BMGs can be easily formed with wide composition range by a conventional copper mold cast method. The glassy alloys have many unique and diversified properties such as lowest glass transition temperature, ultralow elastic modulus, small value of Poisson’s ratio and fragility, homogeneous flow at room temperature and tunable water degradation behavior. The BMGs with novel physical and chemical properties could have potential applications for biomaterial and micromanufacture, and are model system for studying some fundamental issues such as crystallization, relaxation and deformation in metallic glass.

In this article, single-phase CuIn(SxSe1-x)2 thin films with different x have been prepared using a new two-step method consisting of partly selenizing Cu–In precursors in Se ambient, and then exposing the partly selenized films to H2S/Ar under different conditions. The x-ray diffraction indicated that the CuIn(SxSe1-x)2 films exhibited the homogeneous chalcopyrite structure. With the increase of the sulfurization temperature from 425 to 525 °C, x increases from 0 to 1, Eg increases from 0.95 to 1.42 eV, the Raman shift of the A1[Se–Se] mode increases from 173 to 197 cm−1, and the resistivity increases from 101 to 103 Ω.cm.

Small-scale testing techniques such as nanoindentation and micro-/nanocompression are promising methods for addressing mechanical properties of ion-beam-irradiated materials. We performed different proton irradiations and critically evaluated the results obtained from nanoindentation and pillar compression, both performed parallel and perpendicular to the irradiation direction. Experiments parallel to beam direction suffer from variation of material properties with penetration depth. This is improved by cross-sectional experiments, thereby probing the effect of different doses along the beam penetration depth on mechanical properties. Finally, we demonstrate that, compared with nanoindentation, miniaturized uniaxial compression experiments offer a more reliable and straightforward interpretation of the mechanical data, as they impose a nominally uniaxial stress on a well-defined volume at a specific position. Moreover, the exposed pillar geometry is not influenced by surface contamination and enables in situ observation of the governing mechanical processes, which is typically not possible during indentation experiments in a half-space geometry.

The ultimate properties of a fibrous composite system depend highly on the transverse mechanical properties of the fibers. Here, we report the size dependency of transverse elastic modulus in cellulose nanocrystals (CNCs). In addition, the mechanical properties of CNCs prepared from wood and cotton resources were investigated. Nanoindentation in an atomic force microscope (AFM) was used in combination with analytical contact mechanics modeling (Hertz model) and finite element analysis (FEA) to estimate the transverse elastic moduli (Et) of CNCs. FEA modeling estimated the results more accurately than the Hertz model. Based on the AFM–FEA calculations, wood CNCs had higher transverse elastic moduli in comparison to the cotton CNCs. Additionally, Et was shown to increase with a reduction in the CNCs’ diameter. This size-scale effect was related to the Iα/Iβ ratio and crystalline structure of CNCs.

First-principle calculations are performed to investigate the mechanical shear strength and sliding characteristic of Ni(111)/α-Al2O3(0001) interfaces. Two types of interface models are considered, i.e., Al-terminated O-site and O-terminated Al-site models. Mechanical properties such as theoretical shear strength, unstable stacking energy, and critical displacement are examined. It is found that the shear deformation of the Ni/Al2O3 interfaces takes place by a process of successive breaking and rebonding of the Al–O bonds near the Al2 or Al3 atom inside the α-Al2O3 block accompanying the sliding of Ni atomic layer, and finally the Ni/Al2O3 interfaces fail between the Ni atomic layer. Relatively, the Al–O interface possesses a superior shear resistance than the O–Al interface. In addition, the mechanical shear strength and tensile strength are discussed, together with the potential usage of these theoretical results that could offer in fabricating actual thermal barrier coating systems and in analyzing their mechanical response.

Platinum (Pt) nanoparticles were synthesized on tin dioxide (SnO2) nanowires by applying γ-ray radiolysis. The growth behavior of Pt nanoparticles was systematically investigated as a function of precursor concentration, illumination intensity and exposure time of the γ-rays. We found that these processing parameters greatly influenced the growth behavior of Pt nanoparticles in terms of size and formation density. Vapor-phase-grown SnO2 nanowires were uniformly covered with Pt nanoparticles by the radiolysis process. The Pt nanoparticle-functionalized SnO2 nanowires were tested as sensors for detecting reductive gases including carbon monoxide, toluene, and benzene. The results indicate that the γ-ray radiolysis is an efficient way of functionalizing the surface of oxide nanowires with catalytic Pt nanoparticles.

Li+ for Na+ ion-exchange-induced phase separation in borosilicate glass was investigated. A glass with a composition, 70SiO2·15B2O3·15Na2O, was prepared. The glass was transparent, and macroscopically no phase separation was observed because the immiscibility temperature for the composition was lower than the glass transition temperature. Substitution of Li+ for Na+ at the surface domain of the glass induced phase separation in the domain and subsequent heat treatment evolved interconnected silica-rich and alkali borate-rich phases through the phase separation. However, the parts in which ion exchange did not occur kept homogeneous and transparent. This phenomenon is explainable by the fact that the immiscibility temperature for the Li+-substituted composition of the original glass elevated up to a temperature higher than the ion exchange and heat treatment temperatures. The borate-rich phases leached by acid treatment for the phase-separated glass. Through these processes, we obtained monolithic glasses consisting of porous domains, and homogeneous and transparent parts.

We have used molecular dynamics simulations to examine membrane morphology and the transport of water, methanol, and hydronium in phenylated sulfonated poly(ether ether ketone ketone) (Ph-SPEEKK) and Nafion membranes at 360 K for a range of hydration levels. In Ph-SPEEKK, the average pore diameter is smaller, the sulfonate groups are more closely packed, the hydronium ions are more strongly bound to sulfonate groups, and the diffusion of water and hydronium is slower relative to the corresponding properties in Nafion at comparable hydration levels. The aromatic carbon backbone of Ph-SPEEKK is more rigid and less hydrophobic than the fluorocarbon backbone of Nafion. Water network percolation in Ph-SPEEKK occurs at a hydration level (λ) of ∼8 H2O/SO3−. At λ = 20, water, methanol, and hydronium diffusion coefficients were 1.4 × 10−5, 0.6 × 10−5, and 0.2 × 10−5 cm2/s, respectively. For λ > 20, wide pores develop leading to an increase in methanol crossover and ion transport.

The good quality single crystal ZnWO4:Yb3+ was grown by Czochralski method and the spectra were measured. The fluorescence lifetime at 1017 nm was measured to be 644 μs and the radiative lifetime was 209 μs. The laser parameters, βminIsat as well as Imin have been calculated to be 4.6%, 14.4 Kw/cm2, 0.66 Kw/cm2, respectively. The Stark-level components of the 2F7/2 and 2F5/2 were also determined. End-pumping crystal ZnWO4:Yb3+ with 975 nm laser diode, we investigated the laser output property. The highest output power at wavelength 1017 nm was obtained to be 0.5 W, corresponding to the pumping power of 10 W and the threshold was about 2 W.

PACS: 71.20.Eh; 78.20.-e; 65.60. +a, 42.55.Xi, 42.55.Ye, 42.60.Gd.

Carbon spheres (CSs) with regular shapes (Ø 300–1200 nm) and numerous oxygen groups (–OH, C6H5–C=O, and C=O) were prepared by a simple glucose hydrothermal process. CSs were studied by x-ray powder diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, x-ray photoelectron spectra, and elemental analysis. Their size was directly proportional to temperature and glucose concentration. Their shape could be controlled by temperature and reaction time. To prepare CSs (Ø 300–800 nm) with regular shapes and smooth surfaces, temperature and reaction time in the range of 180–230 °C and 3–4 h, respectively, were optimal. The chemical properties of the CSs were affected by temperature. A phase transformation from amorphous to turbostratic structure took place at T > 230 °C. The number of oxygen groups decreased as the temperature increased, and T ≤ 230 °C were optimal to prepare oxygen-rich CSs. Comparison of oxygen contents and O/C ratios indicated a further carbonization, and the degree was directly related to temperature. A possible formation mechanism for the CSs is proposed.