Strain rate effects on the mechanical behavior of nanocrystalline Au films

The effect of fabrication, film thickness, and strain rate on the mechanical behavior of Au films with 100 nm (evaporated gold) and 200 nm (electroplated gold) average grain sizes was investigated. Uniaxial tension was imposed at 10^− 3-10^− 6 s^− 1 strain rates on evaporated 0.5 μm and 0.65 μm thick Au specimens, and at 10^− 2-10^− 5 s^− 1 on electroplated 2.8 μm thick Au specimens. Strain rates between 10^− 3 and 10^− 5 s^− 1 had a marked impact on the ultimate strain of evaporated films and less significant effect on their yield and saturation stress. The ductility increased with decreasing strain rate and it varied between 2-4.5% for 500-650 nm thick films and 3.4-10.6% for 2.8 μm thick films. When compared at the same strain rate, the thick electroplated films were more ductile than the thin evaporated films, but their yield and saturation stresses were lower, possibly due to their larger grain size. Qualitatively, the stress-strain behavior was consistent at all rates except at the slowest that resulted in significantly different trends. A marked decrease of the maximum strength, effective Young's modulus, and yield strength occurred at 10^− 6 s^− 1 for thin, and at 10^− 5 s^− 1 for thick films, while for 500 nm thin films multiple stress localizations per stress-strain curve were recorded. Because of temperature, applied stress, and grain size considerations this behavior was attributed to dislocation creep taking place at a strain rate comparable to the applied strain rate.     

Grain boundary structure dependent fracture in nanocrystalline Au films

Nanocrystalline Au films were in situ strained in a high resolution transmission electron microscope, which demonstrated that the diffusion-assisted intergranular fracture was the dominant failure mode. Grain orientation with respect to grain boundaries (GBs) imposes important effect on the crack propagation and blunting. The low surface energy and high diffusion mobility of {111} planes lead to a notch-like crack. The stress concentration at the tip may help breaking {111} planes layer by layer and thus advance the crack. Cracks can be diverted from the preset path by GBs and grow into the grain interior, which has never been revealed by other experiments and molecular dynamics simulations.     

Dewetting behavior of Au films on porous substrates

Understanding the stability of thin films and their spontaneous pattern formation upon dewetting is essential to a host of physical phenomena. In this paper, we study the dewetting phenomena of Au thin films deposited on anodic aluminum oxide (AAO) membranes to analyze the stability of the metal film on porous substrates. AAO membranes, as-sputtered and dewetted Au films are all characterized by scanning electronic microscopy and X-ray diffraction. We found that both the roughness of AAO surface and modification of AAO pores exhibit remarkable influences on the dewetting behavior of Au films. The observed dewetting phenomena are explained from an energetic point of view since dewetting is a process of minimization of the system free energy.     

Microwave dielectric behavior of nanocrystalline titanium dioxide thin films

Dielectric behavior of titania thin films, deposited by DC magnetron sputtering on to borosilicate glass substrates, in the microwave region is reported. Deposition in a 100% pure oxygen DC plasma is demonstrated. The nanocrystalline films showed a crystallite size range between 16 and 50 nm. The crystallite size decreased with increase in film thickness between 150 and 700 nm and increase in rate of deposition. Refractive index decreased with increase in percentage of oxygen in the sputter gas. The dielectric constants were measured using the extended cavity perturbation technique at 8.98, 10.01 and 10.98 GHz. The dielectric constant and loss tangent showed a very small decrease with increase in frequency but exhibited a stronger dependence on processing parameters as well as crystallite size. The dielectric constant peaked at a value of 46 (±0.1) at a frequency of 8.98 GHz with 50% O₂ in the plasma, decreasing above and below it. Similarly, it peaked at a value of 46 (±0.1) for a crystallite size of 40 nm decreasing thereafter. Interestingly, the dielectric constant also showed a maximum at a bandgap of 3.36 eV at the same value. In each case the maximum dielectric constant was accompanied by a minimum in the dielectric loss. The variation in the dielectric properties can be correlated with microstructural changes as evidenced by SEM and AFM images.     

Electrical resistance as a function of temperature in pure and doped beta-tantalum films

The electrical resistance as a function of temperature has been measured for both pure and nitrogen-doped β-Ta films over the temperature range 2°?300 °K. A calibrated Auger spectroscopy system was used to analyze the film samples quantitatively for dopant and impurity concentration. The undoped film samples were prepared under conditions expected to give a high degree of purity. These samples had resistance versus temperature curves characterized by a broad maximum occuring between 100° and 250 °K and a small but well-defined resistance minimum at 15 °K. A resistance minimum effect in tantalum has not been reported previously. Adding nitrogen to the films by reactive sputtering tended to reduce the temperature at which the maximum occurred (in films from a given system), but did not affect the temperature of the minimum. Detailed data on the resistance minimum showed that below 10 °K the resistance ha d a logarithmic temperature dependence, indicating the possibility of magnetic scattering (the Kondo effect). Analysis of the films for potentially magnetic impurities revealed that Fe was present in an amount between 10 and 50 ppm.     

CdSe薄膜的溶剂热制备及其光电化学性能研究

以CdCl2.2.5H2O为镉源,以Se粉为硒源,在苄胺体系中,180℃溶荆热条件下制备了CdSe纳米晶薄膜.并用XRD、SEM、TEM、UV-vis等对产物进行了一系列的表征,结果表明在该条件下可以得到粒径在10～20nm、较为均匀的CdSe纳米晶薄膜.同时在标准的三电极体系下,测试了CdSe纳米晶薄膜电极的光电化学...     

Magnetic anisotropy of Co-Cr thin films as a function of substrate temperature during deposition

A sequence of Co78Cr22films, 500 nm in thickness, was prepared by deposition on glass in a modified Varian D.C. magnetron S-gun sputtering system. The substrate temperature during deposition, Ts, was fixed at various values with an upper limit of 300°C. Specimens were examined by VSM, TM, FMR and TEM. Msrises significantly with increasing Ts, peaking at 200°C at 370 emu/cm³. The effective volume-averaged anisotropy drops for Ts>110°C from +1.6 KOe to progressively negative values (-4.3 KOe at 300°C). From FMR we find indications of the presence, in addition to the transition and bulk layers, of a highly negative anisotropy constituent (sim-11.5KOe anisotropy field). This resonance appears at Tsvalues of 150°C and above. TEM plane and cross-section views taken on a Ts= 150°C specimen show islands composed of tilted columns within the bulk. For vertical recording, specimens prepared at Tsvalues between 50 and 100°C are recommended. On the other hand, for longitudinal recording applications, films prepared at Tsvalues above 250°C would seem to be appropriate.     

Creep behavior of nanostructured Mg alloy at ambient and low temperature

Tensile creep test at temperature <0.35 T_m was carried out to investigate the creep behavior in nanostructured Mg alloy with an average grain size of 45 nm consolidated from mechanically alloyed powders using power creep law. The stress exponent is found to be larger than one and with a threshold stress. The activation energy for the creep is measured to be 76 kJ mol⁻¹ smaller than that for grain boundary diffusion in Mg. It is deduced that creep behavior is affected by the presence of impurities and nanovoids inherited from the processing history.     

Influence of ion irradiation effects on the hydriding behavior of nanocrystalline Mg-Ni films

Mg-Ni films were grown on a silicon substrate using two magnetron sputter deposition sources and simultaneous Ar ion irradiation. X-ray diffraction microstructure and phase composition, EDX elemental composition and atomic force microscopy surface topography analysis showed that under low-energy Ar ion irradiation (bias voltages from 0 to −120 V), the Mg₂Ni phase was dominant and on the contrary with the increase of ion energy (bias voltages from −120 to −200 V), the MgNi₂ phase appeared. The Mg content changed from 63 at% down to 42 at% in films grown under bias voltages of 0 and −200 V, respectively. During hydrogenation at 8 bar, 270 °C for 3 h, films with a dominant phase of Mg₂Ni were transformed into Mg₂NiH₄. Hydrogen in MgNi₂ films was mainly in interstitials and tended to form bubbles.     

Deposition of nanocrystalline translucent h-BN films by chemical vapor deposition at high temperature

h-BN layers were deposited on α-SiC and sapphire substrates by chemical vapor deposition at high temperature (1500-1900 °C) using B₂H₆ and NH₃ diluted in Ar. Growth rates were in the 6-10 μm/h range. In all the conditions studied, the as deposited BN layers were found to be translucent to light, some having a light whitish aspect and other a more yellowish one. It was also observed that the deposit was not always adhesive. Characterizations showed that the layers were nano-crystalline with crystallite size < 10 nm. The growth rate was found to be temperature and N/B ratio dependent due to an N limited growth regime which is more pronounced above 1700 °C.     

Dependence of electrical properties on thermal temperature in nanocrystalline SnO2 thin films

Nanocrystalline SnO2 thin films were prepared by pulsed laser deposition techniques on clean glass substrates, and the films were then annealed for 30 min from 50 to 550 degrees C with a step of 50 degrees C, respectively. The investigation of X-ray diffraction confirmed that the various SnO2 thin films were consisted of nanoparticles with average grain size in the range of 23.7-28.9 nm. Root-mean-square surface roughness of the as-prepared SnO2 thin film was measured to be 25.6 nm which decreases to 16.2 nm with thermal annealing. Electrical resistivity and refractive index were measured as a function of annealing temperature, and found to lie between 1.24 to 1.45 momega-cm, and 1.502 to 1.349, respectively. The results indicate that nearly opposite actions to root-mean-square surface roughness and electrical resistivity make a unique performance with thermal annealing temperature. The post annealing shows greater tendency to affect the structural and electrical properties of SnO2 thin films which composed of nanoparticles.     

Mechanical behavior and deformation micromechanisms of polypropylene nonwoven fabrics as a function of temperature and strain rate

The mechanical behavior and the deformation and failure micromechanisms of a thermally-bonded polypropylene nonwoven fabric were studied as a function of temperature and strain rate. Mechanical tests were carried out from 248 K (below the glass transition temperature) up to 383 K at strain rates in the range ≈10⁻³ s⁻¹ to 10⁻¹ s⁻¹. In addition, individual fibers extracted from the nonwoven fabric were tested under the same conditions. Micromechanisms of deformation and failure at the fiber level were ascertained by means of mechanical tests within the scanning electron microscope while the strain distribution at the macroscopic level upon loading was determined by means of digital image correlation. It was found that the nonwoven behavior was mainly controlled by the properties of the fibers and of the interfiber bonds. Fiber properties determined the nonlinear behavior before the peak load while the interfiber bonds controlled the localization of damage after the peak load. The influence of these properties on the strength, ductility and energy absorbed during deformation is discussed from the experimental observations.     

Investigation of the effect of temperature on growth mechanism of nanocrystalline ZnS thin films

In this paper the temperature effect on the growth mechanism of ZnS thin films prepared in a chemical bath containing zinc acetate, ethylenediamine, and thioacetamide aqueous solutions has been studied in the temperature range between 25 and 75 °C. These ZnS thin films possess a nanocrystalline structure, exhibit quantum size effects due to the small crystal size and produce a blue shift in the optical spectra. This blue shift was attributed to a decrease in crystal size by using X-ray diffraction and scanning electron microscopy. The growth mechanism of the thin films is suggested to proceed by two fundamental steps: in the first step, the ZnS nanocrystallites coalesce into small grains through homogeneous nucleation in the solution phase. In the second step, eventually, these small grains or large-sized clusters diffuse and stick to the surface of the substrate to form the ZnS thin film, in a way called a cluster-by-cluster manner, resulting in particulate thin film.     

Creep compaction behavior of 3D carbon interlock fabrics with lubrication and temperature

This study aims at understanding and improving the compaction of 3D carbon interlock fabrics with water lubrication, high temperature and a combination of them. The creep compaction behavior was characterized in a mechanical testing machine under different lubrication and temperature conditions. Three different interlock fabrics were studied at high temperature in order to assess the influence of the weaving pattern on the creep compaction behavior. Finally, an experimental study was carried out to point the impact of fiber sizing on the creep compaction behavior and its evolution with temperature. The results of this work demonstrate the strong impact of temperature and lubrication on the compaction ability of 3D interlock fabrics and its link to the fiber sizing.     

Measurement of critical temperature as a function of field

The critical temperature has been measured for various magnet conductors as a function of the perpendicular applied magnetic field. The isothermal environment was provided by a variable temperature cryostat which fits into the bore of a 10 telsa solenoid. The temperature gradient across the sample volume was measured to be less than 25 millikelvins. The superconducting to normal state transition was measured resistively, using sample current densities from 0.01 to 2 A cm^?2. The maximum applied magnetic field was 10 T and varied less than 0.5% in the sample volume. The critical transport current range of the samples measured from tens to thousands of amperes in the presence of a 10 T perpendicular magnetic field at 4.2 K.     

Improved corrosion behavior of nanocrystalline Cu–20Zr films in HCl solution

Both in-plane and through-thickness linear viscoelastic properties of the single-wall carbon nanotubes (SWNT)/polyelectrolyte multilayer nanocomposite film were characterized using nanoindentation. The SWNT nanocomposite films with a SWNT loading of 4.7% by weight was made by layer-by-layer assembly (LBL). The viscoelastic functions of materials were measured using two methods: (1) the direct differentiation method from the load–displacement data; and (2) the material parameter extraction method by fitting the analytical load–displacement relation to nanoindentation data. Results from both methods agree well. The in-plane Young's moduli of the films were also measured from small-scale tensile tests; the results agree well with nanoindentation data. This investigation indicates that the in-plane and through-thickness linear viscoelastic properties are almost identical for a SWNT nanocomposite made by LBL technique, despite the preferred orientation of the SWNT in a nanocomposite film.     

Elastic constants of silver as a function of temperature

The temperature dependence of the elastic constants of silver single crystals has been determined over the range 300–1173 K with the piezoelectric ultrasonic composite oscillator technique (PUCOT). From a comparison of the present results with those available from the literature, it is deduced that the PUCOT and hence other standing-wave techniques are adequate for measuring compliances, but these techniques may have complications for computations of stiffnesses.     

Silicon dioxide as a high temperature stabilizer for silver films

Silver films cannot at present be used as high temperature reflectors because of severe agglomeration in the presence of oxygen at temperatures in excess of 200 °C. Cr₂O₃, Al₂O₃, SiO₃ and CrO_x were tested for their effectiveness as thin barrier layers, and SiO₂ is the best of those tested. The use of SiO₂ allows the process of hole healing to compete with the normal hole growth process. Hole healing does not last indefinitely but is superseded by a slower rate hole growth process with an activation energy of 49 kcal mol^-1.Because of this last mechanism, stabilized silver is less than 1% transmitting after 50 h at 650 °C in air, whereas bare silver agglomerates to 66% transmittance after only 3 min under the same conditions. Therefore 500 Å SiO₂ films can be used as long term stabilizers for silver films in oxygen atmospheres with temperatures of up to 650 °C.