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Dielectric elastomer actuators (DEAs) are soft, electrically powered actuators that have no discrete moving parts, yet can exhibit large strains (10%–50%) and moderate stress (∼100 kPa). This Tutorial describes the physical basis underlying the operation of DEA's, starting with a simple linear analysis, followed by nonlinear Newtonian and energy approaches necessary to describe large strain characteristics of actuators. These lead to theoretical limits on actuation strains and useful non-dimensional parameters, such as the normalized electric breakdown field. The analyses guide the selection of elastomer materials and compliant electrodes for DEAs. As DEAs operate at high electric fields, this Tutorial describes some of the factors affecting the Weibull distribution of dielectric breakdown, geometrical effects, distinguishing between permanent and "soft" breakdown, as well as "self-clearing" and its relation to proof testing to increase device reliability. New evidence for molecular alignment under an electric field is also presented. In the discussion of compliant electrodes, the rationale for carbon nanotube (CNT) electrodes is presented based on their compliance and ability to maintain their percolative conductivity even when stretched. A procedure for making complaint CNT electrodes is included for those who wish to fabricate their own. Percolative electrodes inevitably give rise to only partial surface coverage and the consequences on actuator performance are introduced. Developments in actuator geometry, including recent 3D printing, are described. The physical basis of versatile and reconfigurable shape-changing actuators, together with their analysis, is presented and illustrated with examples. Finally, prospects for achieving even higher performance DEAs will be discussed. [ABSTRACT FROM AUTHOR]

The phases in the ZnO half of the ZnO-In2O3 binary system are natural superlattices consisting of a periodic stacking of single InO2 sheets separated by indium doped ZnO blocks with a spacing that depends on the composition according to the relationship In2O3(ZnO)k. Characterization by combined, atomic resolution, aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy analysis indicates that the atomic structure of each InO2 layer consists of a single continuous sheet of octahedrally coordinated InO2. The sheets are also crystallographic inversion boundaries. Analysis of the electrical conductivity, thermal conductivity, and Seebeck coefficient data at 800 °C indicates that the InO2 sheets not only decrease thermal conductivity by phonon scattering but also create potential barriers to electron transport. The origin of the potential barriers, the role of piezoelectric effects, and their dependence on superlattice spacing are discussed qualitatively. It is also argued that the crystallographically aligned InO2 sheets within individual grains are also transport barriers in randomly oriented polycrystalline materials. [ABSTRACT FROM AUTHOR]

The Raman spectrum of yttria stabilized tetragonal zirconia form 25 to 1250 degree Celsius is described. It is seen that all six Raman brand broaden and shift toward lower energy with increasing temperature and the shift associated with thermally induced volume changes mainly contributes for all bands.

Issues concerning the spectral responses of photovoltaic devices based on metal/porous silicon (PS)/silicon (Si) sandwich structures are discussed. The energy conversion efficiency of the photovoltaic devices can be increased by controlling the structure of the porous silicon films.

A thermodynamically stable series of superlattices, (ZnO)kIn2O3, form in the ZnO-In2O3 binary oxide system for InO1.5 concentrations from about 13 up to about 33 mole percent (m/o). These natural superlattices, which consist of a periodic stacking of single, two-dimensional sheets of InO6 octahedra, are found to give rise to systematic changes in the optical and vibrational properties of the superlattices. Low-frequency Raman scattering provides the evidence for the activation of acoustic phonons due to the folding of Brillouin zone. New vibrational modes at 520 and 620 cm-1, not present in either ZnO or In2O3, become Raman active. These new modes are attributed to collective plasmon oscillations localized at the two-dimensional InO1.5 sheets. Infrared reflectivity experiments, and simulations taking into account a negative dielectric susceptibility due to electron carriers in ZnO and interface modes of the dielectric layer of InO2, explain the occurrence of these new modes. We postulate that a localized electron gas forms at the ZnO/InO2 interface due to the electron band alignment and polarization effects. All our observations suggest that there are quantum contributions to the thermal and electrical conductivity in these natural superlattices. [ABSTRACT FROM AUTHOR]

Many materials show a nonlinear link between their electrical conductivity and the applied field, such as the varistor, a polycrystalline ceramic, based on doped ZnO. An analysis suggests that the the field and current density ahead of a conducting plate within a nonlinear conducting medium shows simple scaling links with distance, that rely on the nonlinearity exponent of the material.

The dependence of spectral line shape on sample-probe reactions are determined using an analytical model. The model uses a focused probe to study the discrete sampling of spatial property changes in spectra. The model reveals that probe channeling near the free surface and gradient-stimulated line broadening are the primary causes for the influence exerted by sample probe reactions on the shape of spectral lines.

Magnetostatic interactions between vortices in closely spaced planar structures are important for applications including vortex-based magnonic crystals and spin torque oscillator networks. Analytical theories that include magnetostatic interaction effects have been proposed but have not yet been rigorously tested. Here, we compare micromagnetic simulations of the dynamics of magnetic vortices confined in three disks in an equilateral triangle configuration to analytical theories that include coupling. Micromagnetic simulations show that the magnetostatic coupling between the disks leads to splitting of the gyrotropic resonance into three modes and that the frequency splitting increases with decreasing separation. The temporal profiles of the magnetization depend on the vortex polarities and chiralities; however, the frequencies depend only on the polarity combinations and will fall into one of two categories: all polarities equal or one polarity opposite to the others, where the latter leads to a larger frequency splitting. Although the magnitude of the splitting observed in the simulations is larger than what is expected based on purely dipolar interactions, a simple analytical model that assumes dipole-dipole coupling captures the functional form of the frequency splitting and the motion patterns just as well as more complex models. [ABSTRACT FROM AUTHOR]

The photoluminescence of undoped ZnO single crystals up to 1350 °C and the optical absorption of stress-relaxed, epitaxial ZnO thin films up to 1100 °C are reported. The photoluminescence intensity and power dependence with illumination flux are related to the crystal growth methods and stabilize after high temperature annealing. The observation of excitonic recombination at very high temperatures requires high illumination flux. It is found that the zero phonon line model reproduces the shift and the band gap narrowing as well as the free excitonic transition up to the cross-over with a defect level at 2.83 eV that occurs at 800 °C. A phenomenological model of the excitonic recombination band shape, taking account exciton-phonon losses and defect levels provides an excellent fit up to 2.2-2.4 eV (1100 °C). At these cross-over temperatures, an energy transfer is observed between the free exciton transition and defect transitions. However, at temperature above 1100 °C, the decrease of the band gap and the increase of thermal radiation, as well as the restrictions of our experimental set-up and particularly the illumination flux of the exciting laser, limit the analysis of the photoluminescence spectra measurements. [ABSTRACT FROM AUTHOR]

The luminescence from europium doped lanthanum trifluoride (Eu3+:LaF3) nano-crystals can be greatly enhanced by capping with β-diketonate organic ligands. Here, we report on photo-stability measurements for the case of nano-crystals capped with thenoyltrifluroacetone (TTA) and compared with those capped with an inactive ligand, oleic acid. With exposure to UV pump light, we observed significant decrease in fluorescence and change in emission spectrum of the TTA-capped nano-particles whilst the fluorescence lifetime remained approximately constant. After a dose of order 70 kJ cm-2, the luminescence level was similar to that of oleic acid capped nano-crystals. We discuss possible mechanisms. [ABSTRACT FROM AUTHOR]

The thermal diffusivity of vapor deposited thermal barrier coatings is measured using an all-optical approach. The method combines CO2 laser heating of the coating surface with detection of the temperature variation in the laser induced Cr3+ luminescence signal from the thermally grown oxide (TGO) formed under the coating during service. The thermal diffusivity is determined from the delay between a surface heating laser pulse and the heating of the TGO. Data analysis is performed using a three layer heat equation model. Various locations on several coatings were investigated with different average heating laser powers and modulation frequencies. The normalized standard deviation was found to be of the order of 20%, which is thought to be largely due to localized variations in coating thickness and density. The advantage of the method described here is that it does not require knowledge of either the thermal properties of the alloy, its temperature, or thickness, and is therefore well suited for measurement on coated parts of complex shape, such as a hot section gas turbine blade. [ABSTRACT FROM AUTHOR]

The polarization dependence of the optical absorption and R-line emission of a Cr3+-doped sapphire single crystal have been characterized. The absorption bands, U(4T2) and Y(4T1), as well as the R-line emission are determined to be dipole-like transitions associated with three incoherent dipoles oriented along the sapphire principal crystallographic axes (a,m,c). From measurements using the Muller method, it is found that the polarization of the R lines does not depend on either the polarization of the incident excitation or its wavelength. The σ emission is also an order of magnitude stronger than π emission. The R2-R1 peak separation and the ratio of the R2/R1 peak areas are found to be dependent on both the polarization and the stress directions. Stress in the basal plane breaks the symmetry of α polarization with the R2/R1 ratio increasing along the stress direction and decreasing in the perpendicular direction in the basal plane. The π emission also decreases with stress in the basal plane. However, in both polarizations the ratio R2/R1 does not depend on stress applied along the c axis. The value of the R2/R1 peak area ratio can be understood in terms of a piezoelectric-like effect on the dipole transition. [ABSTRACT FROM AUTHOR]

The effect of uniaxial stress applied along the principal crystallographic directions (a, m, and c axes) of sapphire on the lifetime of the R-line luminescence doublet is described. All the measurements were performed at room temperature on samples cut from the same sapphire single crystal containing 250 ppm Cr3+ and the luminescence excited with a laser at 532 nm. The luminescence decays were all single exponentials with lifetimes that increased linearly with compression and decreased linearly in tension. The luminescence lifetimes in compression were crystallographically dependent with the variation in the basal plane being an order of magnitude greater than that along the c axis. The measured lifetimes were independent of the polarization of the luminescence emission. The stress anisotropy of the lifetimes is shown to be dominated by the σ emission and is consistent with estimates based on the anisotropy of coupling of 4T2 with the T1u distortion. The sum of the lifetime variation measured along the three principal crystallographic directions is equal to that reported for hydrostatic stresses. This is in agreement with calculations of the orientation dependence of the stress variation in dipole oscillator strength based on crystal field analysis. [ABSTRACT FROM AUTHOR]

With repeated actuation, an increasing adhesive force develops between the gold contacts of radio-frequency microswitches until failure eventually occurs by stiction. Detailed characterization of the contact forces and the contact surfaces as a function of actuation cycles for “cold-switched” devices indicates that the increase in adhesive forces in air is attributed to mechanical creep of the polycrystalline gold contacts. The increase in adhesion is observed to be associated with an increase in contact area and depth of contact impression as well as asperity flattening. These morphological observations are related to the propensity for stiction using two nondimensional numbers, the plasticity index ψ and the adhesion parameter θ. Trajectories of the evolution of contact roughness in terms of these two numbers provide insight into the design of contacts to resist stiction. [ABSTRACT FROM AUTHOR]

Investigates the effect of microstructural disorder on current flow in varistors. Computation of currents in a network of grain boundaries each of which can be described by nonlinear electrical characteristics; Parameters of current localization; Effect of Joule heating on temperature.

Presents a study that measured the amplitude-displacement-frequency spectra for a lever of an atomic force microscope. Determination of the surface forces in air; Analysis of the displacement and frequency scans; Comparison of force microscopes and surface forces apparatus.