Search

This article provides a perspective on the development of polymer nanodielectrics for electrical insulation applications. It includes a short history of the development of the field, barriers to implementation, a chemical toolbox available for optimizing properties, some examples of potential commercial development, and the latest advances. It offers opinions on critical research needed to fully develop the models needed to predict the behavior and to develop design tools. Key findings include the need for quantification of nanofiller dispersion, investment in long term aging data research, better scale-up methods, a data resource that brings the broad data together in a format that enables faster scientific discovery, and a commercial entity willing to take the risk in implementing these promising materials. [ABSTRACT FROM AUTHOR]

Cd3As2 provides an excellent platform for studying the physics of three-dimensional Dirac semimetals due to its stability as well as its compatibility with thin film growth. Crystals made using both bulk and thin film synthesis are unintentionally doped n-type, and other than introducing Zn to reduce the carrier concentration, no efforts have been reported to alter this intrinsic doping without major changes to the band structure. Here, group VI elements Te and Se are introduced during epitaxy to increase the electron concentration of the films. Starting from an unintentionally doped electron concentration of 1–2 × 1017 cm−3, concentrations of up to 3 × 1018 cm−3 are achieved. Analysis of Shubnikov–de Haas oscillations reveals good agreement in calculated effective mass and Fermi velocity of highly doped films with unintentionally doped single crystals with similar electron concentrations. The density functional theory is also performed to study the effects of group VI substitutions and confirms no strong perturbations in the electronic structure. This work ultimately demonstrates tunability in the carrier concentration using extrinsic dopants without substantial changes in the band structure, allowing for intentional design of Fermi-level position for device applications. [ABSTRACT FROM AUTHOR]

We report the effects of layer thickness, interface morphology, top contact, and polymer–metal combination on the performance of photovoltaic devices consisting of a fluorene–bithiophene copolymer and nanocrystalline TiO[sub 2]. Efficient photoinduced charge transfer is observed in this system, while charge recombination is relatively slow (∼100 μs–10 ms). External quantum efficiencies of 13% and monochromatic power conversion efficiencies of 1.4% at a wavelength of 440 nm are achieved in the best device reported here. The device produced an open-circuit voltage of 0.92 V, short-circuit current density of about 400 μA cm-2, and a fill factor of 0.44 under simulated air mass 1.5 illumination. We find that the short-circuit current density and the fill factor increase with decreasing polymer thickness. We propose that the performance of the indium tin oxide/TiO[sub 2]/polymer/metal devices is limited by the energy step at the polymer/metal interface and we investigate this situation using an alternative fluorene-based polymer and different top contact metals. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The dissociation of the MgH complex in GaN under low-energy electron-beam irradiation (LEEBI) and its reassociation during postirradiation annealing were measured using infrared vibration spectroscopy. The dissociation rate exhibits a pronounced dependence on the H isotope, being about 4 times greater for protium than deuterium. Reassociation occurs at temperatures < 200 °C, which may be problematic for device applications of LEEBI. We consider possible reaction paths based on atomic configurations from density-functional theory and bond-excitation mechanisms investigated in surface-desorption studies, thereby arriving at a model of the evolution consistent with the experimental results. [ABSTRACT FROM AUTHOR]

We report on a method for fabricating balanced hole and electron transport in ambipolar organic field-effect transistors (OFETs) based on the co-evaporation of zinc-phthalocyanine (ZnPc) and its fluorinated derivative (F8ZnPc). The semiconducting behaviour of the OFET can be tuned continuously from unipolar p-type, with a hole mobility in the range of (1.7 ± 0.1) × 10−4 cm2/Vs, to unipolar n-type, with an electron mobility of (1.0 ± 0.1) × 10−4 cm2/Vs. Devices of the pristine ZnPc and F8ZnPc show a current on/off ratio of 105. By co-evaporating the p-type ZnPc with the n-type F8ZnPc, we fabricate ambipolar transistors and complementary-like voltage inverters. For the ambipolar devices, the optimum balance between the hole and electron mobilities is found for the blend of 1:1.5 weight ratio with hole and electron mobilities of (8.3 ± 0.2) × 10−7 cm2/Vs and (5.5 ± 0.1) × 10−7 cm2/Vs, respectively. Finally we demonstrate application of the ambipolar devices in a complementary-like voltage inverter circuit with the performance comparable to an inverter based on separate ZnPc and F8ZnPc OFETs. [ABSTRACT FROM AUTHOR]

Discusses the simulation and measurement of corona for electrostatic pulse powered precipitators. Formulation of model; Ion and electron advection; Evolution of a Trichel pulse.

Presents information on a study which examined the characterization of gallium arsenic (GaAs) /indium GaAs quantum wells using photocurrent spectroscopy. Results; Discussion; Conclusion.

Deals with a study that presented a model for the spectral response of gallium arsenide and Al[subx]Ga[sub1-x]As p-n and p-i-n solar cells based on a standard solution of the minority-carrier equations. Application of the quantum well solar cell; Capability of the model; Strengths and weaknesses of the model; Disadvantages from the use of intercell connection.

Presents a study that investigated the effect of a collected flyash layer on electrostatic precipitator behavior. Background on the experimental apparatus and procedures used in the study; Examination of the modeling effect of precipitated dust layer; Assessment of the high-resistivity dust layer parameters used by the corona simulation.

Looks at a carrier escape study from InP/AlGaAs single quantum well structures. Indications of the photoluminescence from the InGaAs wells; Use of an estimated nonradiative efficiency of the device; Insight on the relevance to an application.

Presents a study that examined an electrostatic precipitator to determine its salient electrical behavior, particle charging and collection characteristics for pulse powering under clean plate conditions. Background on pulse energization; Analysis of the impact and interplay of particle diffusivity and electron charging; Results and implications.

The hysteresis at the spin-state transition (Tc[bar_over_tilde:_approx._equal_to]180.6 K) in [Fe(bt)2(NCS)2] has been studied by magnetic susceptibility measurements (bt=2,2’-bi-2-thiazoline). Two series of minor hysteresis loops between fixed temperatures TA=177.0, TB=183.0 K and TA=177.7, TB=183.7 K, respectively, have been obtained. Their areas are practically equal over a large range of μ2eff values. The results are consistent with the requirements of the classical Preisach model and some of its generalizations. Right and left boundary minor loops have been obtained for the widths ΔT=6.0 and ΔT=7.2 K. The areas order on two curves with almost equal maximum F/Ftotal values. A phenomenological approach is proposed to explain the results. It is based on the fact that the properties of minor loops are associated with the abrupt vs gradual character and the more or less symmetrical nature of the transition. It is pointed out that according to the Everett model, the transition should proceed by conversion of independent domains of high-spin (HS) and low-spin (LS) molecules. [ABSTRACT FROM AUTHOR]

Density-functional theory is used to examine aspects of the copper vacancy (V[SUBCu]) in cuprous oxide (Cu[SUB2]O). The normal vacancy configuration, obtained by simple removal of a Cu atom from the lattice, is found to be 0.1 eV higher in energy than a split vacancy configuration wherein a nearby Cu atom is displaced toward a normal vacancy site by half the bulk Cu-Cu separation. Jumps between the normal and split vacancy configurations are predicted to be rate limiting for V[SUBCu] diffusion with an energy barrier of 0.3 eV. Binding of V[SUBCu] to substitutional aluminum (Al[SUBCu]) and indium (In[SUBCu]) is examined. The neutral (Al[SUBCu] + 2 V[SUBCu]) complex is found to have a binding energy of 3.3 eV whereas the neutral (In[SUBCu] + 2 V[SUBCu]) complex is bound by 1.7 eV. The magnitudes of these binding energies suggest that Al[SUBCu] and In[SUBCu] should inhibit V[SUBCu] diffusion in Cu[SUB2]O. [ABSTRACT FROM AUTHOR]

Focuses on a study which investigated the electronic properties of hexagonal close packed Co[sub1-x]Cr[subx] alloys using non-spin-polarized mixed basis self-consistent pseudopotential method. Distributions of charge-density distributions; Effects of band structure; Comparison of the individual energy bands before and after stress is applied.

Discusses a study on the band structure of hexagonal-close-packed ferromagnetic cobalt using a nonlocal empirical pseudopotential method. Types of measurements performed on cobalt metal; Method; Results and discussion.

Resistance thermometers are common secondary thermometers in cryogenic applications. Bulk RuO2 thermometers are used in dilution refrigerators because of their low magnetoresistances in addition to their temperature sensitivity. Thermoelectric and thermomagnetic measurements require multiple thermometers to measure temperature differences. Here, we present a method to fabricate thin film RuO2 thermometers directly onto an experimental substrate. This enhances thermal contact between thermometers and films whose thermoelectric or thermomagnetic properties may be measured. Commercial thermometers have higher temperature sensitivities than the thermometers presented in this study, but commercial thermometers must be carefully heat sunk to the cryostat or sample to be useful. Thin film thermometers can be patterned with ultraviolet (UV) lithography. This allows both the size of the thermometer and its distance from the sample, when also patterned with UV lithography, to be on the order of micrometers. A universal calibration curve for these thin film thermometers has not been produced. The efficacy of these thermometers has been demonstrated through measurements of the Nernst effect in Nb. In this study, the thin film thermometers were calibrated using the cryostat thermometers. [ABSTRACT FROM AUTHOR]

The extreme physics of targets shocked by NIF's 192-beam laser is observed by a diverse suite of diagnostics. Many diagnostics are being developed by collaborators at other sites, but ad hoc controls could lead to unreliable and costly operations. A diagnostic control system (DCS) framework for both hardware and software facilitates development and eases integration. Each complex diagnostic typically uses an ensemble of electronic instruments attached to sensors, digitizers, cameras, and other devices. In the DCS architecture each instrument is interfaced to a low-cost WINDOWS XP processor and JAVA application. Each instrument is aggregated with others as needed in the supervisory system to form an integrated diagnostic. The JAVA framework provides data management, control services, and operator graphical user interface generation. DCS instruments are reusable by replication with reconfiguration for specific diagnostics in extensible markup language. Advantages include minimal application code, easy testing, and high reliability. Collaborators save costs by assembling diagnostics with existing DCS instruments. This talk discusses target diagnostic instrumentation used on NIF and presents the DCS architecture and framework. [ABSTRACT FROM AUTHOR]

We present a method to solve the inverse problem in pulsed photothermal radiometry (PPTR) that exploits advantages of truncated singular value decomposition (T-SVD) while imposing a non-negativity constraint to the solution. The presented method is a hybrid in the sense that it expresses the solution vector as a linear superposition of right singular vectors, but with a non-negative constraint applied to it. The weights for the superposition are determined using an optimization algorithm. In one-dimensional PPTR simulation examples, the best reconstruction results are of comparable quality to those of the conjugate gradient method. Furthermore, the hybrid method exhibits a sharper knee in the L-curve and small susceptibility to over-iteration in presence of experimental noise, thus facilitating the regularization process. As a result, the reconstructed temperature profiles are more likely to be closer to the original initial profiles. [ABSTRACT FROM AUTHOR]

Treatment of port wine stain (PWS) birthmarks in human skin by pulsed laser irradiation requires the knowledge of the maximum epidermal temperature rise and PWS depth for an attending physician to select the optimal light dosage, irradiation wavelength, and cryogen spray cooling spurt duration on an individual patient basis. Pulsed photothermal radiometry (PPTR) is a promising technique to provide such information. In this article, computer simulations are performed to evaluate the performance of PPTR depth profiling of the laser-induced temperature rise in PWS. An iterative, non-negatively constrained conjugate gradient algorithm is used to reconstruct the laser-induced temperature profile from simulated PPTR signals. Human skin is assumed to contain an epidermal melanin layer and a single homogeneous PWS layer in the dermis. The influence of structural, experimental, and algorithm parameters on the temperature profile reconstruction are discussed. Accuracy of the maximum epidermal temperature rise and PWS depth determined from the reconstructed profiles is statistically analyzed. The simulations show that when the melanin and PWS layers are physically discrete, a good reconstruction can be obtained and the maximum epidermal temperature rise and PWS depth can be determined with accuracy sufficient for the intended clinical application. Measurements and reconstructions from PWS patients are performed and the results are in agreement with the simulations. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Travel to distant conferences consumes time, energy, and human resources. An alternative, should it prove an adequate replacement for face-to-face communication, is ''teleconferencing.'' While the necessary and desirable elements of conferencing by telephone are yet to be quantified, we describe a rudimentary experimental system which provides a communication versatility that belies its simplicity. We establish a dedicated 4-wire connection between distant conference rooms. We modify conventional speakerphones (Model 4A) by disconnecting the electronic hybrid to give separate transmit (microphone) and receive (loudspeaker) leads. We give each conferee an individual instrument. In a given conference room, we sum the signals from individual transmit leads and connect the results to the transmit path of the 4-wire circuit. Similarly, we distribute the receive path of the 4-wire connection to the individual receive leads. The voice operated attenuator (variolosser) and the noise-operated gain-adjusting device (NOGAD) in each individual speakerphone are left completely intact. Complementary connections are made in the other conference room. As a result of these features, the teleconferencing system is able to provide effective, interactive conferencing among large groups of users. Because of the distributed configuration of transmitters and receivers, it copes well with room reverberation and background noise. [ABSTRACT FROM AUTHOR]

Organic photodetectors for use in medical x-ray digital imaging applications are fabricated from poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester using a solution-based, temperature assisted deposition protocol. In comparison to bulk heterojunction structures, the proposed protocol leads to much lower dark currents while still offering useful external quantum efficiency values. Devices made by this protocol lead to dark currents of around 50 pA/cm2 at -0.8 V, well within the requirements for x-ray digital imaging. When coupled to a scintillating phosphor screen the device yields a linear response of photocurrent to x-ray exposure (from 0 to 7mGy/s) for a range of operating biases. [ABSTRACT FROM AUTHOR]

We use transient photovoltage and differential charging experiments, complemented by transient absorption data, to determine charge carrier lifetimes and densities in a poly(3-hexylthiophene): methanofullerene solar cell at Voc as a function of white light-bias intensity. For a typical device, the charge carrier decay dynamics are observed to exhibit an approximately third order dependence on charge density (dn/dt∝n3). [ABSTRACT FROM AUTHOR]

We report studies of the dependence of the open-circuit voltage (VOC) of polymer/titanium dioxide hybrid devices on the ionization potential of the polymer (IP). Once corrected for differences in photocarrier generation by the polymers, the measured VOC values vary linearly with the polymer IP, with a slope of 0.8±0.1. This behavior agrees with recent studies of polymer/fullerene photovoltaic devices and is consistent with the hypothesis that VOC of an organic donor-acceptor solar cell is limited by the energy difference between the highest occupied molecular orbital of the donor (in this case, the polymer) and the lowest unoccupied electronic level of the acceptor (in this case, the conduction band edge of the TiO2). [ABSTRACT FROM AUTHOR]