Template-based fluoroethylenepropylene piezoelectrets with tubular channels for transducer applications

We describe the concept, the fabrication, and the most relevant properties of a piezoelectric-polymer system: Two fluoroethylenepropylene (FEP) films with good electret properties are laminated around a specifically designed and prepared polytetrafluoroethylene (PTFE) template at 300 degrees C. After removing the PTFE template, a two-layer FEP film with open tubular channels is obtained. For electric charging, the two-layer FEP system is subjected to a high electric field. The resulting dielectric barrier discharges inside the tubular channels yield a ferroelectret with high piezoelectricity. d(33) coefficients of up to 160 pC/N have already been achieved on the ferroelectret films. After charging at suitable elevated temperatures, the piezoelectricity is stable at temperatures of at least 130 degrees C. Advantages of the transducer films include ease of fabrication at laboratory or industrial scales, a wide range of possible geometrical and processing parameters, straightforward control of the uniformity of the polymer system, flexibility, and versatility of the soft ferroelectrets, and a large potential for device applications e.g., in the areas of biomedicine, communications, production engineering, sensor systems, environmental monitoring, etc.

Study of metal oxide-semiconductor capacitors with rf magnetron sputtering TiO(x) and TiO(x)N(y) gate dielectric layer

Metal oxide-semiconductor capacitors with TiO(x) deposited with different O(2) partial pressures (30%, 35%, and 40%) and annealed at 550, 750, and 1000 degrees C were fabricated and characterized. Fourier transform infrared, x-ray near edge spectroscopy, and elipsometry measurements were performed to characterize the TiO(x) films. TiO(x)N(y) films were also obtained by adding nitrogen to the gaseous mixture and physical results were presented. Capacitance-voltage (1 MHz) and current-voltage measurements were utilized to obtain the effective dielectric constant, effective oxide thickness, leakage current density, and interface quality. The results show that the obtained TiO(x) films present a dielectric constant varying from 40 to 170 and a leakage current density (for V(G)=-1 V, for some structures as low as 1 nA/cm(2), acceptable for complementary metal oxide semiconductor circuits fabrication), indicating that this material is a viable, in terms of leakage current density, highk substitute for current ultrathin dielectric layers. (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3043537]

Theory of small-signal ac response of a dielectric liquid containing two groups of ions

The analysis of Macdonald for electrolytes is generalized to the case in which two groups of ions are present. We assume that the electrolyte can be considered as a dispersion of ions in a dielectric liquid, and that the ionic recombination can be neglected. We present the differential equations governing the ionic redistribution when the liquid is subjected to an external electric field, describing the simultaneous diffusion of the two groups of ions in the presence of their own space charge fields. We investigate the influence of the ions on the impedance spectroscopy of an electrolytic cell. In the analysis, we assume that each group of ions have equal mobility, the electrodes perfectly block and that the adsorption phenomena can be neglected. In this framework, it is shown that the real part of the electrical impedance of the cell has a frequency dependence presenting two plateaux, related to a type of ambipolar and free diffusion coefficients. The importance of the considered problem on the ionic characterization performed by means of the impedance spectroscopy technique was discussed. (c) 2008 American Institute of Physics.

Quantum reflection: The invisible quantum barrier

We construct an invisible quantum barrier which represents the phenomenon of quantum reflection using available data on atom-wall and Bose-Einstein-condensate-wall reflection. We use the Abel equation to invert the data. The resulting invisible quantum barrier is double valued in both axes. We study this invisible barrier in the case of atom and Bose-Einstein condensate (BEC) reflection from a solid silicon surface. A time-dependent, one-spatial-dimension Gross-Pitaevskii equation is solved for the BEC case. We found that the BEC behaves very similarly to the single atom except for size effects, which manifest themselves in a maximum in the reflectivity at small distances from the wall. The effect of the atom-atom interaction on the BEC reflection and correspondingly on the invisible barrier is found to be appreciable at low velocities and comparable to the finite-size effect. The trapping of an ultracold atom or BEC between two walls is discussed.

Increase in the magnitude of the energy barrier distribution in Ni nanoparticles due to dipolar interactions

The energy barrier distribution E(b) of five samples with different concentrations x of Ni nanoparticles using scaling plots from ac magnetic susceptibility data has been determined. The scaling of the imaginary part of the susceptibility chi""(v, T) versus T ln (iota t/tau(0)) remains valid for all samples, which display Ni nanoparticles with similar shape and size. The mean value < E(b)> increases appreciably with increasing x, or more appropriately with increasing dipolar interactions between Ni nanoparticles. We argue that such an increase in < E(b)> constitutes a powerful tool for quality control in magnetic recording media technology where the dipolar interaction plays an important role. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3533911]

Barrier-free substitutional doping of graphene sheets with boron atoms: Ab initio calculations

Using ab initio methods, we propose a simple and effective way to substitutionally dope graphene sheets with boron. The method consists of selectively exposing each side of the graphene sheet to different elements. We first expose one side of the membrane to boron while the other side is exposed to nitrogen. Proceeding this way, the B atoms will be spontaneously incorporated into the graphene membrane without any activation barrier. In a second step, the system should be exposed to a H-rich environment, which will remove the CN radical from the layer and form HCN, leading to a perfect substitutional doping.

Quasi-elastic barrier distribution of the (17)O+(64)Zn system and the derivation of the (17)O nuclear matter diffuseness

The quasi-elastic excitation function for the (17)O+(64)Zn system was measured at energies near and below the Coulomb barrier, at the backward angle theta(lab) = 161 degrees. The corresponding quasi-elastic barrier distribution was derived. The excitation function for the neutron stripping reactions was also measured, at the same angle and energies, and the experimental values of the spectroscopic factors were deduced by fitting the data. A reasonably good agreement was obtained between the experimental quasi-elastic barrier distribution with the coupled-channel calculations including a very large number of channels. Of the channels investigated, three dominated the coupling matrix: two inelastic channels, (64)Zn(2(1)(+)) and (17)O(1/(+)(2)), and one-neutron transfer channel, particularly the first one. On the other hand, a very good agreement is obtained when we use a nuclear diffuseness for the (17)O nucleus larger than the one for (16)O. We verify that quasi-elastic barrier distribution is a sensitive tool for determining nuclear matter diffuseness.

Near-Barrier Fusion of the (8)B+(58)Ni Proton-Halo System

Fusion cross sections were measured for the exotic proton-halo nucleus (8)B incident on a (58)Ni target at several energies near the Coulomb barrier. This is the first experiment to report on the fusion of a protonhalo nucleus. The resulting excitation function shows a striking enhancement with respect to expectations for normal projectiles. Evidence is presented that the sum of the fusion and breakup yields saturates the total reaction cross section.

Barrier distributions for weakly bound systems

We discuss the use of reduced fusion cross sections in the derivation of fusion barrier distributions. We show that the elimination of static effects associated with system sizes and optical potentials obtained by the recently introduced fusion functions can be extended to barrier distributions. This can be a useful tool for systematic studies of breakup coupling effects in fusion processes.

Breakup coupling effects on near-barrier quasi-elastic scattering of (6,7)Li on (144)Sm

Excitation functions of quasi-elastic scattering at backward angles have been measured for the (6,7)Li + (144)Sm systems at near-barrier energies, and fusion barrier distributions have been extracted from the first derivatives of the experimental cross sections with respect to the bombarding energies. The data have been analyzed in the framework of continuum discretized coupled-channel calculations, and the results have been obtained in terms of the influence exerted by the inclusion of different reaction channels, with emphasis on the role played by the projectile breakup.

Reaction cross sections for (8)B, (7)Be, and (6)Li+(58)Ni near the Coulomb barrier: Proton-halo effects

Elastic scattering of (8)B, (7)Be, and (6)Li on a (58)Ni target has been measured at energies near the Coulomb barrier. Optical-model fits were made to the experimental angular distributions, and total reaction cross sections were deduced. A comparison with other systems provides striking evidence for proton-halo effects on (8)B reactions. As opposed to the situation for the neutron-halo nucleus (6)He, for which particle transfer dominates, the ""extra"" cross section observed for (8)B appears to result entirely from projectile breakup.

Near-barrier quasielastic scattering as a sensitive tool to derive nuclear matter diffuseness

Quasielastic excitation functions for the (16,18)O + (60)Ni systems were measured at energies near and below the Coulomb barrier, at the backward angle theta(LAB) = 161 degrees. The corresponding quasielastic barrier distributions were derived. The data were compared with predictions from coupled channel calculations using a double-folding potential as a bare potential. For the (16)O-induced scattering, good agreement was obtained for the barrier distribution by using the projectile default nuclear matter diffuseness obtained from the Sao Paulo potential systematic, that is, 0.56 fm. However, for the (18)O-induced scattering, good agreement was obtained only when the projectile nuclear matter diffuseness was changed to 0.62 fm. Therefore, in this paper we show how near-barrier quasielastic scattering can be used as a sensitive tool to derive nuclear matter diffuseness.

Structural, dielectric, and optical properties of yttrium calcium borate glasses

Structural and optical properties of stable glasses in the Y(2)O(3)-CaO-B(2)O(3) system, containing the same Y/Ca ratio as the YCa(4)O(BO(3))(3) (YCOB) crystal, were determined from Raman and reflectance infrared spectroscopy. Changes in optical functions with composition are associated with an increase in the number of non-bridging oxygen and to calcium/yttrium oxides content. Refractive indexes values (from 1.597 to 1.627 at lambda=2 mu m) are in good agreement with those of the YCOB crystal, an indication that these glasses are potential candidates for optical applications due to their ease of shaping as large bulk samples or fibers.

Microwave dielectric permittivity and photoluminescence of Eu(2)O(3) doped laser heated pedestal growth Ta(2)O(5) fibers

We report the microwave dielectric properties and photoluminescence of undoped and europium oxide doped Ta(2)O(5) fibers, grown by laser heated pedestal growth technique. The effects of Eu(2)O(3) doping (1-3 mol %) on the structural, optical, and dielectric properties were investigated. At a frequency of 5 GHz, the undoped material exhibits a dielectric permittivity of 21 and for Eu(2)O(3) doped Ta(2)O(5) samples it increases, reaching up to 36 for the highest doping concentration. Nevertheless, the dielectric losses maintain a very low value. For this wide band gap oxide, Eu(3+) optical activation was achieved and the emission is observed up to room temperature. Thus, the transparency and high permittivity make this material promising for electronic devices and microwave applications. (c) 2008 American Institute of Physics.

Density-functional description of superconducting and magnetic proximity effects across a tunneling barrier

A density-functional formalism for superconductivity and magnetism is presented. The resulting relations unify previously derived Kohn-Sham equations for superconductors and for noncollinear magnetism. The formalism, which discriminates Cooper-pair singlets from triplets, is applied to two quantum liquids coupled by tunneling through a barrier. An exact expression is derived, relating the eigenstates and eigenvalues of the Kohn-Sham equations, unperturbed by tunneling, on one side of the barrier to the proximity-induced ordering potential on the other.