The dielectric elastomer, a particularly attractive type of electroactive polymer, uses commercial polymers such as acrylic and silicone elastomers. The technology has been limited in application by perceived lifetime issues. By addressing several lifetime issues, lifetimes of more than one million cycles, and in some cases beyond ten million cycles, were achieved with a variety of transducer configurations (including operation in generator mode) under a variety of operating conditions (including high humidity). Dielectric elastomers can produce maximum actuation strains of more than 100% and specific energy density exceeding that of known electric-field induced technology. Performance testing for dielectric elastomer actuators has typically been for peak-performance or “over-driven” conditions with short operational lifetimes (typically 100s or 1000s of cycles), particularly under conditions such as high humidity. By minimizing electric field and mechanical strain concentration factors, long lifetimes (>1 million cycles) with acrylic transducers were achieved with actuation strains as great as 40% areal strain (and up to 100% areal strain in generator mode). Actuators in a dry environment had an almost 20x increase in lifetime over actuators at ambient humidity (about 50% RH) at the same driving field conditions. Long actuation lifetimes were also achieved in a 100% RH environment and when fully submerged in salt water at reduced operating strain and field. In 100% RH, lifetimes of several million cycles were achieved at 4% strain. In underwater operation, 6 out of 11 actuators survived for >10 million cycles with an electric field limited to 32 MV/m and approximately 2% strain. The demonstrated lifecycle improvements are applicable to a variety of uses of dielectric elastomers, including haptic interface devices, pumps (implantable and external), optical positioners, and “artificial muscles” to replace small damaged muscles. Continued improvements in materials, actuator design, and packaging, combined with management of operational conditions as described here, should support new practical application of this promising technology.

A novel ZnO/TiO2 assorted photoelectrode for dye-sensitized solar cells (DSSCs) is proposed. The impacts of the ZnO/TiO2 assorted photoelectrode on the photovoltaic performance of dye-sensitized solar cells (DSSCs) were investigated. The measurements of the light transmission spectra showed the higher transmittance through ZnO/FTO than through FTO during the effective wavelength region of 536nm˜800nm for DSSCs, indicating that ZnO/TiO2 assorted photoelectrode is beneficial for the photovoltaic performance of DSSCs. The measurements on the photovoltaic characteristics of the DSSC cell indicate that the inserted ZnO layer can cause the increased open circuit voltage (Voc) more than 70 mV and fill factor (FF) but the decreased short circuit current. The enhanced Voc and FF could be attributed to the suppressed the recombination of photon-generated carriers between the ZnO/TiO2 assorted photoelectrode and electrolyte (dye) compared to TiO2 photoelectrode. However, the additional series resistance of inserted ZnO layer causes the reduced short circuit current. The optimized conversion efficiency can be achieved in the DSSC with ZnO/TiO2 assorted photoelectrode by using low series resistance of ZnO layer.

When we think of space, we typically think of a vacuum containing very little matter that lies between the Earth and other planetary and stellar bodies. However, the space above Earth's breathable atmosphere and beyond contains many things that make designing durable spacecraft a challenge. Depending on where the spacecraft is flying, it may encounter atomic oxygen, ultraviolet and other forms of radiation, charged particles, micrometeoroids and debris, and temperature extremes. These environments on their own and in combination can cause degradation and failure of polymers, composites, paints and other materials used on the exterior of spacecraft for thermal control, structure, and power generation. This article briefly discusses and gives examples of some of the degradation experienced on spacecraft and flight experiments as a result of the space environment and the use of ground and space data to predict durability.

Molecular dynamics simulations of the flow of pressurised water through carbon nanotubes of chirality (9,0), (12,0), (15,0) and (18,0) have been undertaken at 298K with a water density of approximately 1240kg/m3. Results show that the rate of filling is least in the smallest diameter nanotube, but that there is less variation in the time taken to reach maximum occupancy. The water molecules are found to undergo restructuring due to their confinement, with detailed molecular arrangement dependent on CNT diameter. Enhanced rates of flow are shown for the (15,0) nanotube, highlighting the effect of nanotube diameter on confinement and thus on flow.

The in situ X-ray reciprocal space mapping (in situ RSM) of symmetric diffraction measurements during lattice-mismatched InGaAs/GaAs(001) growth were performed to investigate the strain relaxation mechanisms. The evolution of the residual strain and crystal quality were obtained as a function of InGaAs film thickness. Based on the results, the correlation between the strain relaxation and the dislocations during the film growth were evaluated. As a result, film thickness ranges with different relaxation mechanisms were classified, and dominant dislocation behavior in each phase were deduced. From the data obtained in in situ measurements, the quantitative strain relaxation models were proposed based on a dislocation kinetic model developed by Dodson and Tsao. Good agreement between the in situ data and the model ensured the validity of the dominant dislocation behavior deduced from the present study.

Pressure induced magnetic phase transition of iron hydride was investigated with an in-situ Mössbauer spectrometer using synchrotron radiation (SR). The spectrometer is composed of a high resolution monochromator, an X-ray focusing device, a variable frequency nuclear monochromator and a diamond anvil cell. The optical system, advantages of the spectrometer and the observed high pressure magnetic phases of iron hydride are described.

Single Shockley faults (SSF) have been studied in 4H-SiC epitaxial layers by using a spatial resolved micro-photoluminescence technique. In particular the effect of the UV pumping laser has been investigated. Samples have been irradiated at different power densities in order to find a threshold for the growth of the SSF defects. A low power density (115 W/cm2) exposition at 325 nm does not affect the structural properties of the epitaxial layers. We observed a growth of this defect through the epitaxial layers when the power density is increased over the value of 115 W/cm2.

Capillary liquid flows have shown their ability to generate micro and nano-structures which can be used to synthesize material in the micro or nanometric size range. For instance, electrified capillary liquid jets issued from a Taylor are broadly used to spin micro and nanofibers when the liquid consists of a polymer solution or melt, a process termed electrospinning. In this process, the electrified capillary jet may develop a nonaxisymmetric instability, usually referred to as whipping instability, which very efficiently transforms electric energy into stretching energy, thus leading to the formation of extremely thin polymer fibers. Even though non axysimmetric instabilities of electrified jets were first investigated some decades ago, the existing theoretical models provide a qualitative understanding of the phenomenon but none of them is accurate enough when compared with experimental results. This whipping instability usually manifests itself as fast and violent lateral motion of the charged jet, which makes it difficult its characterization in the laboratory. However, this instability also develops when electrospinning is performed within a liquid bath instead of air. Although it is essentially the same phenomenon, the frequency of the whipping oscillations is much slower in the former case than in the latter, thus allowing detailed experimental characterization of the whipping instability. Furthermore, since the outer fluid is a liquid, its density and viscosity may now be used to influence the dynamics of the electrified capillary jet. In this work we present and rationalize the experimental data collecting the influence of the main parameters on the whipping characteristics of the electrified jet (frequency, amplitude, etc.).

The complementary physical properties of the distinct constituents render polymer-grafted nanocrystals (PGNPs) intriguing materials systems in which property characteristics can be tuned over a wide range from hard particulate to soft polymer-type. Here we demonstrate that dependent on the molecular weight and the graft density of the grafted polymer chains, three characteristic regimes of PGNPs are observed: (1) hard-sphere type colloidal crystalline with the formation of cracks driven by short-range interactions, (2) plastic mesocrystalline with the crazing behaviors by chain entanglement, or (3) disordered structure with soft-polymer type interactions. In addition to controlling the mechanical properties of PGNPs, grafted chains can have a key role in mediating their gradual transformation into more ordered microstructures from nanoparticles with energetically unfavorable property (i.e., activation barrier for crystallization induced by polydisperse nanoparticles [1, 2]).

Results are presented employing cross-sectional analytical transmission electron microscopy (ATEM) to examine intergranular stress corrosion cracking (IGSCC) of austenitic stainless alloys in high-temperature water environments. Microstructural, chemical and crystallographic characterization of buried interfaces at near-atomic resolutions is used to investigate corrosion/oxidation reactions, composition changes and deformation events at crack tips. Information obtained by a wide variety of high-resolution imaging and analysis methods indicates the processes occurring during crack advance and provides insights into the mechanisms controlling SCC. Examples of crack tips produced in oxidizing and hydrogenated water are presented for both Fe-base stainless steels (SSs) and Ni-base stainless alloys. Cracks in SSs show similar characteristics in both environments, with oriented oxide films at crack walls and cracks ending in few-nm-wide tips. Many of these same features are seen for alloy 182 in oxidizing water suggesting a common mechanism, generally consistent with a slip oxidation process. A distinct difference is seen at alloy 600 and alloy 182 tips produced in hydrogenated water. Penetrative attack along grain boundaries without evidence for significant plastic deformation is believed to indicate a major role of active-path corrosion/oxidation in the SCC process.

We present a study of point-defect creation in yttria-stabilized zirconia (ZrO2: Y) or YSZ exposed to various heavy ions (from C to U) covering an energy range from 100 MeV to several GeVs. It is concluded that F+-type centers (involving singly-ionized oxygen vacancies) are produced by elastic-collision processes. The ion-induced out-of-plane expansion is found to be small (< 0.2%) and to increase linearly as a function of the average F+-type center concentration with a large slope compatible with small oxygen vacancy clusters. The large defect volume and <100> axial symmetry of the F+-type centers hint that these color centers might actually be divacancies (i.e. F2 + centers).

Silica aerogels are ultra low-density, high surface area materials that are extremely good thermal insulators and have numerous technical applications. However, their mechanical properties are not ideal, as they are brittle and prone to shattering. Conversely, single-walled carbon nanotubes (SWNTs) and graphene-based materials, such as graphene oxide, have extremely high tensile strength and possess novel electronic properties. By introducing SWNTs or graphene-based materials into aerogel matrices, it is possible to produce composites with the desirable properties of both constituents. We have successfully dispersed SWNTs and graphene-based materials into silica gels. Subsequent supercritical drying results in monolithic low-density composites having improved mechanical properties. These nanocomposite aerogels have great potential for use in a wide range of applications.

We report ac electrical transport in the metallic ferromagnet La0.7Sr0.3MnO3. Both ac resistance (R) and reactance (X) were measured as a function of temperature (T= 400-100 K), frequency of the ac current (f = 100 kHz – 20 MHZ) and external dc magnetic field (H = 0-100 mT) applied parallel to the current direction. It is shown that, while R(H = 0 T) decreases smoothly around the Curie temperature (TC ) for f = 100 kHz, an abrupt increase followed by a peak close to TC occurs for f ≥ 500 kHz. The peak decreases in magnitude, broadens and shifts down in temperature with increasing values of H. The peak in R is completely suppressed under H= 100 mT resulting in a huge low-field ac magnetoresistance (R/R= -53 % for f= 2MHz) whereas the dc magnetoresistance only -31 % even at H = 7 T. While the reactance X(H = 0 T) also shows an abrupt increase at TC for f < 10 MHz, it decreases abruptly at TC for f ≥ 12 MHz. The magnetoreactance is largest (X/X= -47 %) at f = 100 kHz and it changes sign from negative to positive with increasing frequency. It is suggested that the observed huge ac magnetoresistance arises from decrease of magnetic permeability which enhances skin depth under a magnetic field. Our results indicate that the extraordinary sensitivity of the ac magnetoresistance to low dc magnetic fields can be exploited for device applications.

In this work nanoclusters of vanadium dioxide (VO2) buried in 200 nm thick SiO2 on silicon have been irradiated with increasing fluences of He ions. The projected range of He was chosen to be 650 nm in order to avoid residual He in the VO2 nanoclusters and the surrounding SiO2. The VO2 nanoclusters have been synthesized by sequential ion implantation of the elements vanadium and oxygen followed by a rapid thermal annealing step. Irradiation with He ions leads to the generation of reversible lattice point defects in the nanocrystalline VO2 precipitates. Simultaneously there is no electronic doping by He incorporation. The effect of the local- and long-range structural disorder on the metal-to-insulator phase transition has been investigated as a function of He fluence by μ-Raman spectroscopy and temperature dependent spectral ellipsometry. The disappearance of a low-frequency Raman mode indicates increasing disorder in the long-range crystal structure due to He irradiation. At the same time the thermal hysteresis of the metal-to-insulator transition narrows.

Difficulties and challenges have been widely encountered in the chemical mechanical planarization (CMP) of noble metals used as diffusion barrier films due to hardness, chemical inertness and toxic oxidation products, in particular for Ru polishing. A commercial CMC Ru polishing slurry that successfully addressed the safety concerns was based on a high pH (8.4) polymer-treated-alumina-based multi-additive slurry containing complexing reagents (carboxylic acids and salts), corrosion inhibitors, surfactants, and hydrogen peroxide as a mild, non-aggressive oxidizer. Recently, our efforts had been redirected towards the development of a new generation of low pH barrier slurries based on an entirely new concept employing unique Lewis acid type abrasives. This class of materials is well known to be highly reactive in dielectrics polishing (ceria, zirconia, titania), but far less is known about their interactions with Ru, Cu or Ta.

In this presentation, we will elaborate the unexpected discovery that hard, chemically inert, noble metals such as ruthenium can be polished easily by virtually abrasive-free and/or oxidizer-free TiO2 based slurries. Of particular importance is the finding that the polymorphic phase of TiO2 (anatase or rutile), its surface chemistry (functional groups, Lewis acid/base character), pH induced surface modification and reactivity, can all mediate the abrasive particle's adsorption properties, catalytic activity and ultimately, its slurry polishing performance.

Though atomic force microscopy (AFM) interrogates biological materials through mechanical interactions, achieving quantitative mechanical information such as modulus and adhesion at high resolution has been a challenging task. A technology for nanometer scale mechanical property mapping, peak force tapping (PFT), was developed to achieve high resolution imaging and quantitative mechanical measurements simultaneously. PFT controls instantaneous interaction force and record force spectroscopy at each pixel to calculate mechanical properties. A feedback loop maintains a constant peak force, a local maximum point in the force spectroscopy, at the level of Pico Newtons throughout the imaging process. Such high precision force controls enable application of ultra-sharp probe to image biological samples in vitro and achieve molecular resolution in protein membranes. More importantly a full suite of mechanical properties, modulus, adhesion, energy dissipation and deformation are mapped concurrent with topographic imaging. To calculate nanomechanical properties reliably cantilever spring constant and tip shape were calibrated systematically. A method to accurately determine cantilever spring constant, capable of wafer scale cantilever calibration, was developed and tested against traceable force methods. With the knowledge of tip shape, derived from morphological dilation method using a reference sample, mechanical properties measured at the nanometer scale was compared with bench mark materials ranging from 0.7 MPa to 70 GPa. The same method was also applied to OmpG membranes, Lambda DNA strings, as well as live cells. The limitation of the measurement accuracy in biology samples will be discussed.

A simple method is reported for the synthesis of monodispersed HfO2 nanoparticles by the ammonia catalyzed hydrolysis and condensation of hafnium (IV) tert-butoxide in the presence of surfactants at room temperature. Transmission electron microscopy shows faceted nanoparticles with an average diameter of 3-4 nm. As-synthesized nanoparticles are amorphous in nature and crystallize upon moderate heat treatment. The HfO2 nanoparticles have a narrow size distribution, large specific surface area and good thermal stability. Specific surface area was about 239 m2/g on as-prepared nanoparticle samples while those annealed at 500 °C have specific surface area of 221 m2/g indicating that there was no significant increase in particle size. This result was further confirmed by TEM images of nanoparticles annealed at 300 °C and 500 °C. X-ray diffraction studies of the crystallized nanoparticles revealed that HfO2 nanoparticles were monoclinic in structure. The synthetic procedure used in this work can be readily modified for large scale production of monodispersed HfO2 nanoparticles.

In a repository of high-level radioactive waste, radionuclides will leach from the waste glass and migrate into the surrounding bentonite after very long time. These processes occur simultaneously in the bentonite and should be evaluated to confirm the reliability of individual models and data for the performance assessment of high-level radioactive waste repository.

Previous study [1] reported the results of the in-diffusion experiments of Cs in compacted sodium bentonite (Kunigel V1®) in contact with fully radioactive waste glass for 15 to 300 days under aerobic conditions. And Cs migration was successfully interpreted using fundamental one dimensional diffusion model. However, migration of other radionuclides in fully radioactive waste glass were extremely slow because of low solubility, low effective diffusivity and high distribution ratio, especially multivalent elements of actinide and lanthanide.

In this study, the similar in-diffusion experiment reported by Ashida et al. [1] was carried out for about 15 years to evaluate the migration behavior of multivalent actinide and lanthanide elements. The bentonite was compacted into a stainless steel cell with 20 mm in diameter and 18 mm in length to produce dry densities of 0.5 and 1.0 Mg m-3saturated distilled water. The form of fully radioactive waste glass was borosilicate glass by using vitrified in CPF (Chemical Processing Facility). The glass sample was sliced into the disc with 4 mm in thickness and sandwiched by two pieces of the saturated bentonite sample in the diffusion cell under aerobic conditions. After 15 years, bentonite sample was sliced and immersed into the HNO3 to extract the radionuclides from the bentonite. Then profiles of Cs, Eu, Pu, Am and Cm in the bentonite sample were evaluated. The concentration profile of Cs in the bentonite was constant due to its high diffusivity.

The experimental concentrations of Am, Cm and Eu in contact with compacted sodium bentonite were good agreement with the solubilities calculated by thermodynamic data. On the other hand, the profiles of Am and Cm show two parts with different slopes which cannot be fitted by simple one-dimensional diffusion model considering single specie. Leaching and migration behavior of radio nuclides will be discussed based on the one-dimensional diffusion model considering other mechanism of several species.

[1] T. Ashida, et al. Migration behavior of cesium released from fully radioactive waste glass in compacted sodium bentonite. PNC Technical Report, TN8410 98-014(1998).

The aim of this work is the characterization of some graphite-metal couples prepared by mechanical milling (MM). The morphological and microstructural changes during MM of graphite processed with metallic powders of Cu, Ni and Ag (10 and 15 at. %) are studied. Milling is performed in a high-energy ball mill under an inert atmosphere during 1, 4 and 8 hours. The process is also repeated with a pure graphite sample in order to compare the role of metal type and concentration on the morphological characteristics of milled samples. The results show that increasing the concentration of metal particles accelerates the milling process as a result of faster work hardening and particle fracture. The results of X-ray diffraction analysis show that some crystallographic characteristics of the milled couples change as a function of milling time and metal addition. Also, SEM-EDS studies show an important effect of milling time on metal particle distribution in the prepared graphite couples.