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Showing papers on "Dielectric published in 2005"


Journal ArticleDOI
TL;DR: In this article, the authors review the motivations for, and recent advances in, new gate dielectric materials for incorporation into organic thin-film transistors (OTFTs) for organic electronics.
Abstract: In this contribution we review the motivations for, and recent advances in, new gate dielectric materials for incorporation into organic thin-film transistors (OTFTs) for organic electronics. After a general introduction to OTFT materials, operating principles, and processing requirements for optimizing low-cost organic electronics, this review focuses on three classes of OTFT-compatible dielectrics: i) inorganic (high-k) materials; ii) polymeric materials; and iii) self-assembled mono- and/multilayer materials. The principal goals in this active research area are tunable and reduced OTFT operating voltages, leading to decreased device power consumption while providing excellent dielectric/insulator properties and efficient low-cost solution-phase processing characteristics.

998 citations


Journal ArticleDOI
TL;DR: In this paper, the incorporation of silica nanoparticles into polyethylene increased the breakdown strength and voltage endurance significantly compared to the inclusion of micron scale fillers, and showed a decrease in dielectric permittivity for the nanocomposite over the base polymer.
Abstract: The incorporation of silica nanoparticles into polyethylene increased the breakdown strength and voltage endurance significantly compared to the incorporation of micron scale fillers. In addition, dielectric spectroscopy showed a decrease in dielectric permittivity for the nanocomposite over the base polymer, and changes in the space charge distribution and dynamics have been documented. The most significant difference between micron scale and nanoscale fillers is the tremendous increase in interfacial area in nanocomposites. Because the interfacial region (interaction zone) is likely to be pivotal in controlling properties, the bonding between the silica and polyethylene was characterized using Fourier transformed infrared (FTTR) spectroscopy, electron paramagnetic resonance (EPR), and x-ray photoelectron spectroscopy (XPS). The picture which is emerging suggests that the enhanced interfacial zone, in addition to particle-polymer bonding, plays a very important role in determining the dielectric behavior of nanocomposites.

817 citations


Journal ArticleDOI
TL;DR: The real part of the permittivity and the tan δ of sintered polycrystalline alumina at about 9 GHz have been measured in this article, where the dielectric properties have been examined as a function of purity, pore volume, and sintering grain size.
Abstract: The real part of the permittivity (E') and the tan δ of sintered alumina (Al 2 O 3 ) at about 9 GHz have been measured. The dielectric properties have been examined as a function of purity, pore volume, and sintered grain size. The tan δ is found to depend very strongly on the pore volume, purity, and grain size. e' is far less sensitive to impurities and grain size. The dependence of e' on porosity can be described by simple mixture models as expected. A model of losses in single crystals cannot be extended easily to these materials where extrinsic factors such as porosity, random crystal orientation, grain boundaries, microcracks, and impurities dominate. These factors have been studied in an attempt to describe the tan δ and e' of sintered polycrystalline alumina. In this work, the tan δ for alumina has been studied in near-theoretical density ranges between 9.1 x 10 -5 and 2.4 x 10 -5 depending on grain size.

815 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show that a variety of microwave and qubit measurements are well modeled by loss from resonant absorption of two-level defects and demonstrate that this loss can be significantly reduced by using better dielectrics and fabricating junctions of small area.
Abstract: Dielectric loss from two-level states is shown to be a dominant decoherence source in superconducting quantum bits. Depending on the qubit design, dielectric loss from insulating materials or the tunnel junction can lead to short coherence times. We show that a variety of microwave and qubit measurements are well modeled by loss from resonant absorption of two-level defects. Our results demonstrate that this loss can be significantly reduced by using better dielectrics and fabricating junctions of small area & 10 � m 2 . With a redesigned phase qubit employing low-loss dielectrics, the energy relaxation rate has been improved by a factor of 20, opening up the possibility of multiqubit gates and algorithms.

758 citations


Journal ArticleDOI
TL;DR: Electrodynamic simulations of gold nanoparticle spectra were used to investigate the sensitivity of localized surface plasmon band position to the refractive index, n, of the medium for nanoparticles of various shapes and nanoshells of various structures, and the results extended to particles of other shapes, composed of other metals, and to higher-order modes.
Abstract: Electrodynamic simulations of gold nanoparticle spectra were used to investigate the sensitivity of localized surface plasmon band position to the refractive index, n, of the medium for nanoparticles of various shapes and nanoshells of various structures Among single-component nanoparticles less than 130 nm in size, sensitivities of dipole resonance positions to bulk refractive index are found to depend only upon the wavelength of the resonance and the dielectric properties of the metal and the medium Among particle plasmons that peak in the frequency range where the real part of the metal dielectric function varies linearly with wavelength and the imaginary part is small and slowly varying, the sensitivity of the peak wavelength, λ*, to refractive index, n, is found to be a linearly increasing function of λ*, regardless of the structural features of the particle that determine λ* Quasistatic theory is used to derive an analytical expression for the refractive index sensitivity of small particle plasmo

689 citations


Journal ArticleDOI
27 Jan 2005-Nature
TL;DR: The data reveal that the specific interface structure and local asymmetries play an unexpected role in the polarization enhancement, and it is shown that even superlattices containing only single-unit-cell layers of BaTiO3 in a paraelectric matrix remain ferroelectric.
Abstract: Theoretical predictions--motivated by recent advances in epitaxial engineering--indicate a wealth of complex behaviour arising in superlattices of perovskite-type metal oxides These include the enhancement of polarization by strain and the possibility of asymmetric properties in three-component superlattices Here we fabricate superlattices consisting of barium titanate (BaTiO3), strontium titanate (SrTiO3) and calcium titanate (CaTiO3) with atomic-scale control by high-pressure pulsed laser deposition on conducting, atomically flat strontium ruthenate (SrRuO3) layers The strain in BaTiO3 layers is fully maintained as long as the BaTiO3 thickness does not exceed the combined thicknesses of the CaTiO3 and SrTiO3 layers By preserving full strain and combining heterointerfacial couplings, we find an overall 50% enhancement of the superlattice global polarization with respect to similarly grown pure BaTiO3, despite the fact that half the layers in the superlattice are nominally non-ferroelectric We further show that even superlattices containing only single-unit-cell layers of BaTiO3 in a paraelectric matrix remain ferroelectric Our data reveal that the specific interface structure and local asymmetries play an unexpected role in the polarization enhancement

596 citations


Journal ArticleDOI
TL;DR: In this article, the dielectric properties of the untreated multiwall carbon-nanotubes∕poly(vinylidene fluoride) (MWNT∕PVDF) composites are studied.
Abstract: In this letter, the dielectric properties of the untreated multiwall carbon-nanotubes∕poly(vinylidene fluoride) (MWNT∕PVDF) composites are studied. Towards low frequencies, the dielectric constant of a composite with about 2.0vol% of MWNT increases rapidly and the value of the dielectric constant is as high as 300. However, by a calculation, the percolation threshold of the MWNT∕PVDF composites is only 1.61vol% (0.0161 volume fraction) of MWNT. Both the large aspect ratio and the high conductivity of the MWNT may lead to the low percolation threshold of the MWNT∕PVDF composites. For the percolation composite, the dielectric loss value is always less than 0.4, irrespective of the frequency. Therefore, the experimental results suggest that the dielectric properties of MWNT∕PVDF composites may be improved significantly without the chemical functionalization to carbon nanotubes.

508 citations


Journal ArticleDOI
TL;DR: The results indicate markedly lower polarities than found by spectroscopy with polarity-sensitive solvatochromic dyes, and the salts are classified as moderately polar solvents.
Abstract: In a pilot study of the dielectric constant of room-temperature ionic liquids, we use dielectric spectroscopy in the megahertz/gigahertz regime to determine the complex dielectric function of five 1-alkyl-3-methylimidazolium salts, from which the static dielectric constant e is obtained by zero-frequency extrapolation. The results classify the salts as moderately polar solvents. The observed e-values at 298.15 K fall between 15.2 and 8.8, and e decreases with increasing chain length of the alkyl residue of the cation. The anion sequence is trifluoromethylsulfonate > tetrafluoroborate ≈ tetrafluorophosphate. The results indicate markedly lower polarities than found by spectroscopy with polarity-sensitive solvatochromic dyes.

496 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of the surface energy of gate dielectrics on pentacene morphology and the electrical properties of FETs are reported, using surface energy-controllable poly(imide-siloxane)s as gate-dielectric layers.
Abstract: The effects of the surface energy of polymer gate dielectrics on pentacene morphology and the electrical properties of pentacene field-effect transistors (FETs) are reported, using surface-energy-controllable poly(imide-siloxane)s as gate-dielectric layers. The surface energy of gate dielectrics strongly influences the pentacene film morphology and growth mode, producing Stranski–Krastanov growth with large and dendritic grains at high surface energy and three-dimensional island growth with small grains at low surface energy. In spite of the small grain size (≈ 300 nm) and decreased ordering of pentacene molecules vertical to the gate dielectric with low surface energy, the mobility of FETs with a low-surface-energy gate dielectric is larger by a factor of about five, compared to their high-surface-energy counterparts. In pentacene growth on the low-surface-energy gate dielectric, interconnection between grains is observed and gradual lateral growth of grains causes the vacant space between grains to be filled. Hence, the higher mobility of the FETs with low-surface-energy gate dielectrics can be achieved by interconnection and tight packing between pentacene grains. On the other hand, the high-surface-energy dielectric forms the first pentacene layer with some voids and then successive, incomplete layers over the first, which can limit the transport of charge carriers and cause lower carrier mobility, in spite of the formation of large grains (≈ 1.3 μm) in a thicker pentacene film.

447 citations


Journal ArticleDOI
TL;DR: This phenomenological theory explains the experimental observation that the spontaneous polarization is restricted to lie along the crystal b axis and predicts that the magnitude should be proportional to a magnetic order parameter.
Abstract: We show that long-range ferroelectric and incommensurate magnetic order appear simultaneously in a single phase transition in Ni3V2O8. The temperature and magnetic-field dependence of the spontaneous polarization show a strong coupling between magnetic and ferroelectric orders. We determine the magnetic symmetry using Landau theory for continuous phase transitions, which shows that the spin structure alone can break spatial inversion symmetry leading to ferroelectric order. This phenomenological theory explains our experimental observation that the spontaneous polarization is restricted to lie along the crystal b axis and predicts that the magnitude should be proportional to a magnetic order parameter.

446 citations


Journal ArticleDOI
TL;DR: In this article, the structural, thermal, microscopic, magnetization, polarization, and dielectric properties of BiFeO3 ceramics synthesized by a rapid liquid-phase sintering technique were reported.
Abstract: We have reported the structural, thermal, microscopic, magnetization, polarization, and dielectric properties of BiFeO3 ceramics synthesized by a rapid liquid-phase sintering technique. Optimum conditions for the synthesis of single-phase BiFeO3 ceramics were obtained. Temperature-dependent magnetization and hysteresis loops indicate antiferromagnetic behavior in BiFeO3 at room temperature. Although saturated ferroelectric hysteresis loops were observed in single-phase BiFeO3 ceramic synthesized at 880 °C, the reduced polarization is found to be due to the high loss and low dielectric permittivity of the ceramic, which is caused by higher leakage current.

Journal ArticleDOI
T J Lewis1
TL;DR: In this article, it is argued that the properties of the interfaces between the particles and the matrix will have an increasingly dominant role in determining dielectric performance as the particle size decreases.
Abstract: The incorporation of nanometric size particles in a matrix to form dielectric composites shows promise of materials (nanodielectrics) with new and improved properties. It is argued that the properties of the interfaces between the particles and the matrix, which will themselves be of nanometric dimensions, will have an increasingly dominant role in determining dielectric performance as the particle size decreases. The forces that determine the electrical and dielectric properties of interfaces are considered, with emphasis on the way in which they might influence composite behaviour. A number of examples are given in which interfaces at the nanometric level exercise both passive and active control over dielectric, optical and conductive properties. Electromechanical properties are also considered, and it is shown that interfaces have important electrostrictive and piezoelectric characteristics. It is demonstrated that the process of poling, namely subjecting macroscopic composite materials to electrical stress and raised temperatures to create piezoelectric materials, can be explained in terms of optimizing the collective response of the nanometric interfaces involved. If the electrical and electromechanical features are coupled to the long-established electrochemical properties, interfaces represent highly versatile active elements with considerable potential in nanotechnology.

Journal ArticleDOI
TL;DR: In this paper, an epoxy-based composite containing randomly distributed silver nanoparticles with a narrow size distribution centered around 40nm is presented, which is the basis of a prototype capacitor formed by spin coating the synthesized Ag-epoxy (40nm Ag) mixture onto a gold-deposited aluminum substrate.
Abstract: We report the synthesis of an epoxy-based composite containing randomly distributed silver nanoparticles with a narrow size distribution centered around 40nm. The surface of the Ag nanoparticles is coated with a thin layer of mercaptosuccinic acid (MSA) in order to promote formation of the Ag-epoxy while retaining flexibility of the polymer matrix. This composite is the basis of a prototype capacitor formed by spin coating the synthesized Ag-epoxy (40nm Ag) mixture onto a gold-deposited aluminum substrate. A series of Ag-epoxy composites with various Ag volume fractions was investigated in order to determine the composition associated with optimum capacitor performance. The high dielectric constant (> 300) and relatively low dielectric loss (<0.05) render this material of promising potential for embedded capacitor applications.

Journal ArticleDOI
TL;DR: It is shown that a single rectangular hole in a metallic film exhibits transmission resonances that appear near the cutoff wavelength of the hole waveguide, and this resonant transmission process is accompanied by a huge enhancement of the electric field at both entrance and exit interfaces of thehole.
Abstract: We show that a single rectangular hole in a metallic film exhibits transmission resonances that appear near the cutoff wavelength of the hole waveguide. For light polarized with the electric field pointing along the hole's short axis, it is shown that the normalized-to-area transmittance at resonance is proportional to the ratio between the long and short sides, and to the dielectric constant inside the hole. Importantly, this resonant transmission process is accompanied by a huge enhancement of the electric field at both entrance and exit interfaces of the hole.

Journal ArticleDOI
TL;DR: In this article, an isothermal energy balance is formulated for a system consisting of deformable dielectric bodies, electrodes, and the surrounding space, which is obtained in the electrostatic limit but with the possibility of arbitrarily large deformations of polarizable material.
Abstract: An isothermal energy balance is formulated for a system consisting of deformable dielectric bodies, electrodes, and the surrounding space. The formulation in this paper is obtained in the electrostatic limit but with the possibility of arbitrarily large deformations of polarizable material. The energy balance recognizes that charges may be driven onto or off of the electrodes, a process accompanied by external electrical work; mechanical loads may be applied to the bodies, thereby doing work through displacements; energy is stored in the material by such features as elasticity of the lattice, piezoelectricity, and dielectric and electrostatic interactions; and nonlinear reversible material behavior such as electrostriction may occur. Thus the external work is balanced by (I) internal energy consisting of stress doing work on strain increments, (2) the energy associated with permeating free space with an electric field, and (3) by the electric field doing work on increments of electric displacement or, equivalently, polarization. For a conservative system, the internal work is stored reversibly in the body and in the underlying and surrounding space. The resulting work statement for a conservative system is considered in the special cases of isotropic deformable dielectrics and piezoelectric materials. We identify the electrostatic stress, which provides measurable information quantifying the electrostatic effects within the system, and find that it is intimately tied to the constitutive formulation for the material and the associated stored energy and cannot be independent of them. The Maxwell stress, which is related to the force exerted by the electric field on charges in the system, cannot be automatically identified with the electrostatic stress and is difficult to measure. Two well-known and one novel formula for the electrostatic stress are identified and related to specific but differing constitutive assumptions for isotropic materials. The electrostatic stress is then obtained for a specific set of assumptions in regard to a piezoelectric material. An exploration of the behavior of an actuator composed of a deformable, electroactive polymer is presented based on the formulation of the paper.

Patent
03 Oct 2005
TL;DR: In this paper, the authors proposed a design of circuit modules and methods of construction thereof that contain composite meta-material dielectric bodies that have high effective values of real permittivity but which minimize reflective losses, through the use of host dielectrics (organic or ceramic), materials having relative permittivities substantially less than ceramic inclusions embedded therein.
Abstract: Circuit modules and methods of construction thereof that contain composite meta-material dielectric bodies that have high effective values of real permittivity but which minimize reflective losses, through the use of host dielectric (organic or ceramic), materials having relative permittivities substantially less than ceramic dielectric inclusions embedded therein. The composite meta-material bodies permit reductions in physical lengths of electrically conducting elements such as antenna element(s) without adversely impacting radiation efficiency. The meta-material structure may additionally provide frequency band filtering functions that would normally be provided by other components typically found in an RF front-end.

Journal ArticleDOI
TL;DR: In this paper, a phenomenological thermodynamic potential was constructed based on the properties of bulk BaTiO3 single crystals using an eighth-order polynomial of Landau-Devonshire expansion.
Abstract: A phenomenological thermodynamic potential was constructed based on the properties of bulk BaTiO3 single crystals. An eighth-order polynomial of Landau-Devonshire expansion was employed. It reproduces bulk properties including the three possible ferroelectric transition temperatures and their dependence on electric fields, as well as the dielectric and piezoelectric constants. Different from the existing thermodynamic potential, it is applicable to predicting the ferroelectric phase transitions and properties of BaTiO3 thin films under large compressive biaxial strains.

Journal ArticleDOI
TL;DR: This work uses a combined theoretical and experimental approach to establish a relation between crystallographic symmetry and the ability of a ferroelectric polycrystalline ceramic to switch, and shows that equiaxed polycrystal of materials that are either tetragonal or rhombohedral cannot switch; yet polycrystals of materials where these two symmetries co-exist can in fact switch.
Abstract: Ferroelectric ceramics are widely used as sensors and actuators for their electro-mechanical properties, and in electronic applications for their dielectric properties. Domain switching – the phenomenon wherein the ferroelectric material changes from one spontaneously polarized state to another under electrical or mechanical loads – is an important attribute of these materials. However, this is a complex collective process in commercially used polycrystalline ceramics that are agglomerations of a very large number of variously oriented grains. As the domains in one grain attempt to switch, they are constrained by the differently oriented neighbouring grains. Here we use a combined theoretical and experimental approach to establish a relation between crystallographic symmetry and the ability of a ferroelectric polycrystalline ceramic to switch. In particular, we show that equiaxed polycrystals of materials that are either tetragonal or rhombohedral cannot switch; yet polycrystals of materials where these two symmetries co-exist can in fact switch.

Journal ArticleDOI
25 Jul 2005-Polymer
TL;DR: In this paper, the molecular dynamics of a series of poly(dimethylsiloxane) networks filled with silica nanoparticles synthesized in situ was investigated using thermally stimulated depolarization currents, broadband dielectric relaxation spectroscopy and differential scanning calorimetry.

01 Jan 2005
TL;DR: Venkatesh et al. as mentioned in this paper presented an overview of dielectric properties measuring techniques and their application in the agri-food sector, and the concept of various measurement methodologies and their development.
Abstract: Venkatesh, M.S. and Raghavan, G.S.V. 2005. An overview of dielectric properties measuring techniques. Canadian Biosystems Engineering/Le genie des biosystemes au Canada 47: 7.15 7.30. With a need for the development of improved sensing devices for the control and automation of several agricultural, environmental, and food processes, there is an absolute need for better understanding of the dielectric properties of materials and techniques for measuring these properties. Microwave measurements and the dielectric properties of materials are finding increasing application as new electro-technology is adapted for use in the agriculture and food processing industries. The interest in dielectric properties of materials has historically been associated with the design of electrical equipment, where various dielectrics are used for insulating conductors and other components of electric equipment. Measurement of the bulk dielectric properties (dielectric constant, dielectric loss factor) is not an end unto itself. Rather, these properties are an intermediary vehicle for understanding, explaining, and empirically relating certain physico-chemical properties of the test material. Therefore, in this paper, an attempt is made to fully explore the existing knowledge of dielectric properties (complex permittivity), their role, and importance in the agri-food sector, and the concept of various measurement methodologies and their development. We have summarized the current status of research in this area with some notes on recent developments. An extensive review of the literature on measuring techniques and the comparison and potential application of dielectric properties is reported. Readers are advised to follow the appropriate literature cited for detailed and complete reference.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the kinetics of reaction, densification and grain growth for nano-powders using spark plasma sintering (SPS) and showed that the results are correlated with the microstructural features of these samples, e.g., the grain sizes present in the compacts.
Abstract: Nano-powders of BaTiO3, SrTiO3, Ba0.6Sr0.4TiO3, a mixture of the composition (BaTiO3)0.6(SrTiO3)0.4 with particle sizes in the range of 60 to 80 nm, and Bi4Ti3O12 with an average particle size of 100 nm were consolidated by spark plasma sintering (SPS). The kinetics of reaction, densification and grain growth were studied. An experimental procedure is outlined that allows the determination of a “kinetic window” within which dense nano-sized compacts can be prepared. It is shown that the sintering behaviour of the five powders varies somewhat, but is generally speaking fairly similar. However, the types of grain growth behaviour of these powders are quite different, exemplified by the observation that the kinetic window for the (BaTiO3)0.6(SrTiO3)0.4 mixture is 125 oC, ~75 oC for Bi4Ti3O12, ~25oC for BaTiO3 and SrTiO3, while it is hard to observe an apparent kinetic window for obtaining nano-sized compacts of Ba0.6Sr0.4TiO3. During the densification of the (BaTiO3)0.6(SrTiO3)0.4 mixture the reaction 0.6BaTiO3+0.4SrTiO3 → Ba0.6Sr0.4TiO3 takes place, and this reaction is suggested to have a self-pinning effect on the grain growth, which in turn explains why this powder has a large kinetic window. Notably, SPS offers a unique opportunity to more preciously investigate and monitor the sintering kinetics of nano-powders, and it allows preparation of ceramics with tailored microstructures.The dielectric properties of selected samples of (Ba, Sr)TiO3 ceramics have been studied. The results are correlated with the microstructural features of these samples, e.g. to the grain sizes present in the compacts. The ceramic with nano-sized microstructure exhibits a diffuse transition in permittivity and reduced dielectric losses in the vicinity of the Curie temperature, whereas the more coarse-grained compacts exhibit normal dielectric properties in the ferroelectric region.The morphology evolution, with increasing sintering temperature, of bismuth layer-structured ferroelectric ceramics such as Bi4Ti3O12 (BIT) and CaBi2Nb2O9 (CBNO) was investigated. The subsequent isothermal sintering experiments revealed that the nano-sized particles of the BIT precursor powder grew into elongated plate-like grains within a few minutes, via a dynamic ripening mechanism.A new processing strategy for obtaining highly textured ceramics is described. It is based on a directional dynamic ripening mechanism induced by superplastic deformation. The new strategy makes it possible to produce a textured microstructure within minutes, and it allows production of textured ferroelectric ceramics with tailored morphology and improved physical properties.The ferroelectric, dielectric, and piezoelectric properties of the textured bismuth layer-structured ferroelectric ceramics have been studied, and it was revealed that all textured samples exhibited anisotropic properties and improved performance. The highly textured Bi4Ti3O12 ceramic exhibited ferroelectric properties equal to or better than those of corresponding single crystals, and much better than those previously reported for grain-orientated Bi4Ti3O12 ceramics. Textured CaBi2Nb2O9 ceramics exhibited a very high Curie temperature, d33-values nearly three times larger than those of conventionally sintered materials, and a high thermal depoling temperature indicating that it is a very promising material for high-temperature piezoelectric applications.

Journal ArticleDOI
TL;DR: In this article, an anisotropic dielectric constant is used to provide a lefthanded behavior in waveguide geometry for optical and infrared waveguide applications, and the connection between the polaritons and the enhancement of evanescent fields is demonstrated.
Abstract: We develop an approach to build a material with negative refraction index that can be implemented for optical and infrared frequencies. In contrast to conventional designs that require simultaneously negative dielectric permittivity and magnetic permeability and rely on a resonance to achieve a nonzero magnetic response, our material is intrinsically nonmagnetic and makes use of an anisotropic dielectric constant to provide a lefthanded behavior in waveguide geometry. We demonstrate that the proposed material can support surface (polariton) waves, and show the connection between the polaritons and the enhancement of evanescent fields, also known as superlensing.

Journal ArticleDOI
TL;DR: The morphology, structure, and transport properties of pentacene thin film transistors (TFTs) are reported showing the influence of the gate dielectric surface roughness.
Abstract: The morphology, structure, and transport properties of pentacene thin film transistors (TFTs) are reported showing the influence of the gate dielectric surface roughness Upon roughening of the amorphous SiO2 gate dielectric prior to pentacene deposition, dramatic reductions in pentacene grain size and crystallinity were observed The TFT performance of pentacene films deposited on roughened substrates showed reduced free carrier mobility, larger transport activation energies, and larger trap distribution widths Spin coating roughened dielectrics with polystyrene produced surfaces with 2 A root-mean-square (rms) roughness The pentacene films deposited on these coated surfaces had grain sizes, crystallinities, mobilities, and trap distributions that were comparable to the range of values observed for pentacene films deposited on thermally grown SiO2 (roughness also ∼2 A rms)

Journal ArticleDOI
TL;DR: It is reported that through supramolecular assembly of nonpolar conjugated molecules, a remarkable ferroelectric response can be obtained in co-crystals of low-molecular-weight organic compounds.
Abstract: The research on ferroelectric materials-mostly inorganic compounds or organic polymers-is increasingly motivated by both basic scientific concerns and the potential for practical applications in electronics and optics. Ferroelectricity in organic solids would be important for the development of all-organic electronic and photonic devices. The conventional approach to making organic ferroelectrics is based on the use of polar molecules. Here we report that through supramolecular assembly of nonpolar conjugated molecules, a remarkable ferroelectric response can be obtained in co-crystals of low-molecular-weight organic compounds. Co-crystals of phenazine and chloranilic acid reveal large spontaneous polarization and sizable room-temperature dielectric constants exceeding 100. The present findings provide an approach to making potentially useful organic ferroelectric materials.

Journal ArticleDOI
TL;DR: In this paper, an improved transport model including dielectric exclusion in terms of both Born Dielectric effect and image force contribution is proposed to describe the transport properties of nanofiltration (NF) membranes.

Journal ArticleDOI
TL;DR: In this article, the frequency and temperature dependences of permittivity and impedance of the compounds ACu3Ti4O12 (A=Ca,Bi2∕3, Y2√3, La2 √3) in the ranges of 10−1-106Hz and −150-200°C were studied.
Abstract: We have studied the frequency and temperature dependences of permittivity and impedance of the compounds ACu3Ti4O12 (A=Ca,Bi2∕3,Y2∕3,La2∕3) in the ranges of 10−1–106Hz and −150–200°C. All compounds investigated display similar dielectric properties. Specifically, they all have a Debye-like relaxation and their dielectric constants are independent of frequency and temperature over a wide range. They all have two electrical responses in impedance formalism, indicating that there are two distinct contributions. We attribute them to grains and grain boundaries in the ceramic samples and explain the dielectric behaviors by Maxwell-Wagner relaxation arising at the interfaces between grains and their boundaries.

Journal ArticleDOI
TL;DR: Analysis of the complex dielectric and Raman spectra of hydrogen-bond liquids in the microwave to terahertz frequency range indicates that the cooperative relaxation, accompanied by huge polarization fluctuation, is virtually not Raman active, whereas the faster processes reflect common microscopic dynamics.
Abstract: We analyzed the complex dielectric and Raman spectra of hydrogen-bond liquids in the microwave to terahertz frequency range. As for water and methanol, the high-frequency component of the dielectric spectrum, i.e., the small deviation from the principal Debye relaxation, clearly corresponds to the Raman spectrum. This indicates that the cooperative relaxation, accompanied by huge polarization fluctuation, is virtually not Raman active, whereas the faster processes reflect common microscopic dynamics. For ethylene glycol, the shape of the Raman spectrum also resembles that of the high-frequency deviation of the dielectric spectrum, but, additionally, a weak manifestation of the cooperative relaxation arising from quadrupolar conformers is detected.

Journal ArticleDOI
TL;DR: In this article, a barrier-layer model with dielectric response based on the Maxwell-Wagner type of relaxation for ceramic CCTO is proposed, and two kinds of morphologies, i.e., terraces with ledges and bump domains, were discovered inside the grains under thermal etching conditions at 960°C for 72 min.
Abstract: CaCu 3 Ti 4 O 12 (CCTO) was prepared by solid-state reaction and identified by X-ray diffractometry. The evolution of the microstructure was observed by scanning electron microscopy (SEM). It was found that discontinuous grain growth developed during sintering, and large abnormal grains played a very significant role in the dielectric behavior. Cu ions segregated to the boundaries and CuO located at the triple-point sites of the abnormal large grains were observed by electron energy loss and energy-dispersive X-ray spectroscopy, respectively. Moreover, two kinds of morphologies, i.e., terraces with ledges and bump domains, were discovered inside the grains under the thermal etching conditions at 960°C for 72 min, which solves the contradiction related to the interpretation of the giant dielectric response between ceramic and single-crystal CCTO. Complex impedance spectroscopy was used to analyze the conductivity of ceramic CCTO, which suggests that it consists of conducting domains with two kinds of insulating barrier layers of domain and grain boundaries. The insulating domain and grain boundaries were attributed to orderly arranged dislocations and segregation of Cu ions, respectively. The conduction of CCTO was found to be related to the porosity, the grain size, and the thickness of the insulating boundary layers. For a sample sintered at 1065°C for 3 h, the anomalously low resistivity and temperature-dependent dielectric constant were due to the fact that domain boundaries were not substantially formed. The possible reasons for the development of barrier layers and the variation of the dielectric constant with the sintering time are discussed. A barrier-layer model with dielectric response based on the Maxwell-Wagner type of relaxation for ceramic CCTO is proposed. Two kinds of dielectric responses occur, depending on the microstructure: they are dominated by the domain and domain boundary and by the grain and grain boundary for large grains and fine grains, respectively.

Journal ArticleDOI
TL;DR: In this article, the authors presented the first reported data on the embedding of highly dielectric ceramic inclusions in a rubbery host medium as a means to increase the electromechanical material response for dielectrics elastomer actuation.
Abstract: This paper presents the first reported data on the embedding of highly dielectric ceramic inclusions in a rubbery host medium as a means to increase the electromechanical material response for dielectric elastomer actuation. The studied polymer/ceramic composite, consisting of a silicone matrix in which titanium dioxide powder was dispersed, exhibited, in comparison with pure silicone, a decreased elastic modulus, as well as an increased dielectric constant. The measured low frequency permittivity resulted in accordance with several classical dielectric mixing rules. The use of this material as elastomeric dielectric for planar actuators enabled a reduction of the driving electric fields, so that a transverse strain of 11% at 10 V//spl mu/m and a transverse stress of 16.5 kPa at 9 V//spl mu/m were obtained. These levels of strain and stress were respectively more than eight and four times higher than the corresponding values generated with the pure polymer matrix for analogous electrical stimuli.

Journal ArticleDOI
TL;DR: In this paper, the incorporation of nanoparticles into thermosetting resins is seen to impart desirable dielectric properties when compared with conventional (micron-sized particulates) composites.
Abstract: The incorporation of nanoparticles into thermosetting resins is seen to impart desirable dielectric properties when compared with conventional (micron-sized particulates) composites Although the improvements are accompanied by the mitigation of internal charge in the materials, the nature of the interfacial region is shown to be pivotal in determining the dielectric behaviour In particular, it is shown that the conditions and enhanced area of the interface changes the bonding that may give rise to an interaction zone, which affects the interfacial polarization through the formation of local conductivity