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Sample records for colossal dielectric response

  1. Wireless power transfer based on dielectric resonators with colossal permittivity

    NASA Astrophysics Data System (ADS)

    Song, Mingzhao; Belov, Pavel; Kapitanova, Polina

    2016-11-01

    Magnetic resonant wireless power transfer system based on dielectric disk resonators made of colossal permittivity (ɛ = 1000) and low loss (tan δ = 2.5 × 10-4) microwave ceramic is experimentally investigated. The system operates at the magnetic dipole mode excited in the resonators providing maximal power transfer efficiency of 90% at the frequency 232 MHz. By applying an impedance matching technique, the efficiency of 50% is achieved within the separation between the resonators d = 16 cm (3.8 radii of the resonator). The separation, misalignment and rotation dependencies of wireless power transfer efficiency are experimentally studied.

  2. Origin of colossal dielectric response of CaCu3Ti4O12 studied by using CaTiO3/CaCu3Ti4O12/CaTiO3 multilayer thin films

    NASA Astrophysics Data System (ADS)

    Mitsugi, Masakazu; Asanuma, Shutaro; Uesu, Yoshiaki; Fukunaga, Mamoru; Kobayashi, Wataru; Terasaki, Ichiro

    2007-06-01

    To elucidate the origin of the colossal dielectric response (CDR) of CaCu3Ti4O12 (CCTO), multilayer thin films of CCTO interposed in insulating CaTiO3 (CTO) were synthesized using a pulsed laser deposition technique. The capacitance C of CTO/CCTO/CTO films with different layer thicknesses is measured. After removing the capacitance of CTO by extrapolating C to zero CTO thickness, the real part of dielectric constant of CCTO is estimated to be 329-435, which is much smaller than the reported value for CCTO thin films. This fact indicates that the CDR of CCTO is extrinsic and originates from an internal barrier layer capacitor.

  3. Dielectric properties of doping-free NaMn{sub 7}O{sub 12}: Origin of the observed colossal dielectric constant

    SciTech Connect

    Cabassi, R.; Bolzoni, F.; Gauzzi, A.; Gilioli, E.; Prodi, A.; Licci, F.

    2006-07-15

    The semiconducting NaMn{sub 7}O{sub 12} is a doping-free compound with several coexistent properties such as orbital ordering, charge ordering, and magnetic orderings of different types. We investigated its dielectric response by means of frequency impedance measurements in the range from 20 Hz to 1 MHz. Standard measurements on metallized samples exhibit an apparent colossal dielectric constant (CDC) with an {epsilon}{sub R} value of several thousands at low frequencies, but a careful equivalent circuit analysis allows one to ascribe the observed CDC to the effect of a depletion layer on the metal-semiconductor junctions. We bypass this effect by means of a nonstandard technique employing mica linings: the resulting dielectric behavior exhibits the presence of the charge ordering transition at T{sub CO}=176 K and shows a net bulk dielectric constant value {epsilon}{sub R}{approx_equal}68 at room temperature.

  4. Electromechanical and electro-optical functions of plasticized PVC with colossal dielectric constant

    NASA Astrophysics Data System (ADS)

    Sato, Hiromu; Hirai, Toshihiro

    2013-04-01

    A soft dielectric polymer, plasticized poly(vinyl chloride) (PVC gel), has been known as a characteristic actuator with electrotactic creep deformation. The deformation can be applied for bending and contraction. The mechanism of the deformation has been attributed to the colossal dielectric constant of the gel induced by dc field. The dielectric constant at 1 Hz, jumps from less than10 to thousand times larger value. The huge dielectric constant suggests the gel can have electro-optic function. In this paper, we introduce the gel can bend light direction by applying a dc electric field. The PVC gel can bend light direction depending on the electric field. Detailed feature of the light bending will be introduced and discussed. Bending angle can be controlled by dielectric plasticizer and electric field. The components of the gel, PVC and plasticizer themselves, did not show any effect of electro-optical function like the PVC gel. The same feature can be observed in other polymer, like poly(vinyl alcohol)-dimethyl sulphoxide gel, too.

  5. Colossal dielectric constant and relaxation behaviors in Pr:SrTiO{sub 3} ceramics

    SciTech Connect

    Liu Cheng; Liu Peng; Zhou Jianping; Su Lina; Cao Lei; He Ying; Zhang Huaiwu

    2010-05-15

    Sr{sub 1-x}Pr{sub x}TiO{sub 3} ceramics (0.00{<=}x{<=}0.03) were prepared by a traditional solid-state reaction method. Two relaxation processes (marked as A and B) of the Sr{sub 0.09}Pr{sub 0.01}TiO{sub 3} ceramics were investigated by analyzing the E{sub a} values obtained from the Arrhenius law. Colossal dielectric constant (CDC) was first obtained in Sr{sub 0.09}Pr{sub 0.01}TiO{sub 3} ceramics, whose permittivity was up to 3000 (1 kHz, room temperature), greater than that of pure SrTiO{sub 3} ceramics and samples with more Pr addition (x=0.02 and 0.03). This CDC behavior was related to the internal barrier layer capacitance mechanism.

  6. Structure and colossal dielectric permittivity of Ca2TiCrO6 ceramics

    NASA Astrophysics Data System (ADS)

    Yan-Qing, Tan; Meng, Yan; Yong-Mei, Hao

    2013-01-01

    A colossal permittivity ceramic material, Ca2TiCrO6, was successfully synthesized by the conventional solid-state reaction, and was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), x-ray photoemission spectroscopy (XPS) and x-ray diffraction (XRD). Rietveld refinement of XRD data indicated that the material crystallized in orthorhombic structure with space group pbnm. SEM displayed Ca2TiCrO6 ceramic grains packed uniformly with the size range 5-20 µm. XPS analyses indicated that elemental chromium and titanium of the material were in mixed valence. The corresponding dielectric property was tested in the frequency range 1 kHz-1 MHz and the temperature range 213-453 K, and the ceramics exhibited a relaxation-like dielectric behaviour. Importantly, the permittivity of Ca2TiCrO6 could reach 80 000 at 298 K (100 Hz) and was maintained at 40 000 up to 398 K at 1 MHz, which could be attributed to the ion disorder and mixed valence of Cr3+/Cr6+ and Ti3+/Ti4+.

  7. Dynamics of multiple phases in a colossal-magnetoresistive manganite as revealed by dielectric spectroscopy.

    PubMed

    Sheng, Zhigao; Nakamura, Masao; Kagawa, Fumitaka; Kawasaki, Masashi; Tokura, Yoshinori

    2012-07-10

    Electronic phase separation is one of the key features in correlated electron oxides. The coexistence and competition of multiple phases give rise to gigantic responses to tiny stimuli producing dramatic changes in magnetic, transport and other properties of these compounds. To probe the physical properties of each phase separately is crucial for a comprehensive understanding of phase separation phenomena and for designing their device functions. Here we unravel, using a unique p-n junction configuration, dynamic properties of multiple phases in manganite thin films. The multiple dielectric relaxations have been detected and their corresponding multiple phases have been identified, while the activation energies of dielectric responses from different phases were extracted separately. Their phase evolutions with changing both temperature and applied magnetic field have been demonstrated by dielectric response. These results provide a guideline for exploring the electronic phase separation phenomena in correlated electron oxides.

  8. Tuning of colossal dielectric constant in gold-polypyrrole composite nanotubes using in-situ x-ray diffraction techniques

    SciTech Connect

    Sarma, Abhisakh; Sanyal, Milan K.

    2014-09-15

    In-situ x-ray diffraction technique has been used to study the growth process of gold incorporated polypyrrole nanotubes that exhibit colossal dielectric constant due to existence of quasi-one-dimensional charge density wave state. These composite nanotubes were formed within nanopores of a polycarbonate membrane by flowing pyrrole monomer from one side and mixture of ferric chloride and chloroauric acid from other side in a sample cell that allows collection of x-ray data during the reaction. The size of the gold nanoparticle embedded in the walls of the nanotubes was found to be dependent on chloroauric acid concentration for nanowires having diameter more than 100 nm. For lower diameter nanotubes the nanoparticle size become independent of chloroauric acid concentration and depends on the diameter of nanotubes only. The result of this study also shows that for 50 nm gold-polypyrrole composite nanotubes obtained with 5.3 mM chloroauric acid gives colossal dielectric constant of about 10{sup 7}. This value remain almost constant over a frequency range from 1Hz to 10{sup 6} Hz even at 80 K temperature.

  9. Chemical nature of colossal dielectric constant of CaCu3Ti4O12 thin film by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Deng, Guochu; Xanthopoulos, Nicolas; Muralt, Paul

    2008-04-01

    Epitaxial CaCu3Ti4O12 thin films grown by pulsed laser deposition were studied in the as-deposited and oxygen annealed state. The first one exhibited the usual transition from dielectric to colossal dielectric behavior upon increasing the temperature to above 100K. This transition disappeared after annealing at 900°C in air. The two states significantly differ in their x-ray photoelectron spectra. The state of colossal dielectric constant corresponds to a bulk material with considerable amounts of Cu + and Ti3+, combined with Cu species enrichment at the surface. The annealed state exhibited a nearly stoichiometric composition with no Cu+ and Ti3+. The previously observed p-type conduction in the as-deposited state is thus related to oxygen vacancies compensated by the point defects of Cu+ and Ti3+.

  10. Origin of colossal dielectric permittivity of rutile Ti0.9In0.05Nb0.05O2: single crystal and polycrystalline

    PubMed Central

    Song, Yongli; Wang, Xianjie; Sui, Yu; Liu, Ziyi; Zhang, Yu; Zhan, Hongsheng; Song, Bingqian; Liu, Zhiguo; Lv, Zhe; Tao, Lei; Tang, Jinke

    2016-01-01

    In this paper, we investigated the dielectric properties of (In + Nb) co-doped rutile TiO2 single crystal and polycrystalline ceramics. Both of them showed colossal, up to 104, dielectric permittivity at room temperature. The single crystal sample showed one dielectric relaxation process with a large dielectric loss. The voltage-dependence of dielectric permittivity and the impedance spectrum suggest that the high dielectric permittivity of single crystal originated from the surface barrier layer capacitor (SBLC). The impedance spectroscopy at different temperature confirmed that the (In + Nb) co-doped rutile TiO2 polycrystalline ceramic had semiconductor grains and insulating grain boundaries, and that the activation energies were calculated to be 0.052 eV and 0.35 eV for grain and grain boundary, respectively. The dielectric behavior and impedance spectrum of the polycrystalline ceramic sample indicated that the internal barrier layer capacitor (IBLC) mode made a major contribution to the high ceramic dielectric permittivity, instead of the electron-pinned defect-dipoles. PMID:26869187

  11. Evidences of grain boundary capacitance effect on the colossal dielectric permittivity in (Nb + In) co-doped TiO2 ceramics.

    PubMed

    Li, Jinglei; Li, Fei; Li, Chao; Yang, Guang; Xu, Zhuo; Zhang, Shujun

    2015-02-06

    The (Nb + In) co-doped TiO2 ceramics were synthesized by conventional solid-state sintering (CSSS) and spark plasma sintering (SPS) methods. The phases and microstructures were studied by X-ray diffraction, Raman spectra, field-emission scanning electron microscopy and transmission electron microscopy, indicating that both samples were in pure rutile phase while showing significant difference in grain size. The dielectric and I-V behaviors of SPS and CSSS samples were investigated. Though both possess colossal permittivity (CP), the SPS samples exhibited much higher dielectric permittivity/loss factor and lower breakdown electric field when compared to their CSSS counterparts. To further explore the origin of CP in co-doped TiO2 ceramics, the I-V behavior was studied on single grain and grain boundary in CSSS sample. The nearly ohmic I-V behavior was observed in single grain, while GBs showed nonlinear behavior and much higher resistance. The higher dielectric permittivity and lower breakdown electric field in SPS samples, thus, were thought to be associated with the feature of SPS, by which reduced space charges and/or impurity segregation can be achieved at grain boundaries. The present results support that the grain boundary capacitance effect plays an important role in the CP and nonlinear I-V behavior of (Nb + In) co-doped TiO2 ceramics.

  12. Evidences of grain boundary capacitance effect on the colossal dielectric permittivity in (Nb + In) co-doped TiO2 ceramics

    PubMed Central

    Li, Jinglei; Li, Fei; Li, Chao; Yang, Guang; Xu, Zhuo; Zhang, Shujun

    2015-01-01

    The (Nb + In) co-doped TiO2 ceramics were synthesized by conventional solid-state sintering (CSSS) and spark plasma sintering (SPS) methods. The phases and microstructures were studied by X-ray diffraction, Raman spectra, field-emission scanning electron microscopy and transmission electron microscopy, indicating that both samples were in pure rutile phase while showing significant difference in grain size. The dielectric and I–V behaviors of SPS and CSSS samples were investigated. Though both possess colossal permittivity (CP), the SPS samples exhibited much higher dielectric permittivity/loss factor and lower breakdown electric field when compared to their CSSS counterparts. To further explore the origin of CP in co-doped TiO2 ceramics, the I–V behavior was studied on single grain and grain boundary in CSSS sample. The nearly ohmic I–V behavior was observed in single grain, while GBs showed nonlinear behavior and much higher resistance. The higher dielectric permittivity and lower breakdown electric field in SPS samples, thus, were thought to be associated with the feature of SPS, by which reduced space charges and/or impurity segregation can be achieved at grain boundaries. The present results support that the grain boundary capacitance effect plays an important role in the CP and nonlinear I–V behavior of (Nb + In) co-doped TiO2 ceramics. PMID:25656713

  13. Origin of magnetic and dielectric response in single phase nano crystalline BiFeO3

    NASA Astrophysics Data System (ADS)

    Feroze, Asad; Idrees, Muhammad; Nadeem, Muhammad; Siddiqi, Saadat A.; Saleem, Murtaza; Atif, Muhammad; Siddique, Muhammad; Shaukat, Saleem F.

    2016-12-01

    Stoichiometric and single phase synthesis of BiFeO3 is critical both in its particle industrial applications as well as in understanding the origin of its attractive dielectric and magnetic properties. In this study, BiFeO3 has been obtained at temperatures as low as 400 °C. Zero Fe+2/Fe+3 ratio, and absence of bismuth and oxygen non-stoichiometry have been probed by 57Fe Mössbauer spectroscopy. The appearance of different magnetic phases in 57Fe Mössbauer spectrum, MH hysteresis curve and exchange bias effect have been conferred on the basis of magneto-crystalline anisotropy and particle size distribution. Dependence of the dielectric response on the applied electric field reveals that the colossal dielectric response in BiFeO3 is dominated by extrinsic effects at grain-grain interface.

  14. Direct view at colossal permittivity in donor-acceptor (Nb, In) co-doped rutile TiO2

    NASA Astrophysics Data System (ADS)

    Mandal, Suman; Pal, Somnath; Kundu, Asish K.; Menon, Krishnakumar S. R.; Hazarika, Abhijit; Rioult, Maxime; Belkhou, Rachid

    2016-08-01

    Topical observations of colossal permittivity (CP) with low dielectric loss in donor-acceptor cations co-doped rutile TiO2 have opened up several possibilities in microelectronics and energy-storage devices. Yet, the precise origin of the CP behavior, knowledge of which is essential to empower the device integration suitably, is highly disputed in the literature. From spectromicroscopic approach besides dielectric measurements, we explore that microscopic electronic inhomogeneities along with the nano-scale phase boundaries and the low temperature polaronic relaxation are mostly responsible for such a dielectric behavior, rather than electron-pinned defect-dipoles/grain-boundary effects as usually proposed. Donor-acceptor co-doping results in a controlled carrier-hopping inevitably influencing the dielectric loss while invariably upholding the CP value.

  15. Calculation of Dielectric Response in Molecular Solids for High Capacitance Organic Dielectrics

    NASA Astrophysics Data System (ADS)

    Heitzer, Henry Matthew

    The dielectric response of a material is critically important in numerous scientific processes spanning the fields of biology, chemistry, materials science, and physics. While important across these fundamental disciplines, it remains difficult to determine theoretically the dielectric environment of a system. With recent advances in nanotechnology, biochemistry, and molecular electronics, it has become necessary to determine the dielectric response in molecular systems that are difficult to measure experimentally, such as nanoscale interfaces, highly disordered biological environments, or molecular materials that are difficult to synthesize. In these scenarios it is highly advantageous to determine the dielectric response through efficient and accurate calculations. A good example of where a theoretical prediction of dielectric response is critical is in the development of high capacitance molecular dielectrics. Molecular dielectrics offer the promise of cheap, flexible, and mass producible electronic devices when used in conjunction with organic semiconducting materials to form Organic Field Effect Transistors (OFETs). To date, molecular dielectrics suffer from poor dielectric properties resulting in low capacitances. A low capacitance dielectric material requires a much larger power source to operate the device in OFETs, leading to modest device performance. Development of better performing dielectric materials has been hindered due to the time it takes to synthesize and fabricate new molecular materials. An accurate and efficient theoretical technique could drastically decrease this time by screening potential dielectric materials and providing design rules for future molecular dielectrics. Here in, the methodology used to calculate dielectric properties of molecular materials is described. The validity of the technique is demonstrated on model systems, capturing the frequency dependence of the dielectric response and achieving quantitative accuracy compared

  16. Reply to ``Comment on `Colossal dielectric and magnetodielectric effect in Er2O3 nanoparticles embedded in a SiO2 glass matrix'''

    NASA Astrophysics Data System (ADS)

    Mukherjee, S.; Chen, C. H.; Chou, C. C.; Tseng, K. F.; Chaudhuri, B. K.; Yang, H. D.

    2011-08-01

    In our earlier paper [Mukherjee , Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.82.104107 82, 104107 (2010)], we concentrated mainly on lower calcined transparent monolithic glass samples (particle size <10 nm) where interesting high-k values with diffuse phase transition (DPT) and magnetodielectric (MD) behavior were observed. The Comment seems to focus on the sample calcined at 1200 ∘C (particle size >40 nm), where the dielectric value is observed without DPT behavior. In this Reply we argue that, contrary to the conclusion of Hreniak , the disappearance of the MD effect is not only due to structural reorganization via crystallization of a different phase, but very much depends on particle size.

  17. Magnetic-polaron-induced colossal magnetocapacitance in CdCr2S4

    NASA Astrophysics Data System (ADS)

    Xie, Y. M.; Yang, Z. R.; Zhang, Z. T.; Yin, L. H.; Chen, X. L.; Song, W. H.; Sun, Y. P.; Zhou, S. Q.; Tong, W.; Zhang, Y. H.

    2013-10-01

    The origin of colossal magnetoresistance and colossal magnetocapacitance in a CdCr2S4 system was investigated. Thermoelectric-power and electronic spin resonance spectra reveal that the magnetic polaron is responsible for the colossal magnetoresistance in the n-type sample. The existence of magnetic polarons in the paramagnetic insulting matrix forms an intrinsic Maxwell-Wagner system, leading to the appearance of colossal magnetocapacitance. Being consistent with the evolution of magnetic polarons upon cooling, the Maxwell-Wagner system is valid around insulator-metal transition, where the resistance derived from impedance spectroscopy matches perfectly with DC resistance.

  18. Dielectric Metamaterials with Toroidal Dipolar Response

    NASA Astrophysics Data System (ADS)

    Basharin, Alexey A.; Kafesaki, Maria; Economou, Eleftherios N.; Soukoulis, Costas M.; Fedotov, Vassili A.; Savinov, Vassili; Zheludev, Nikolay I.

    2015-01-01

    Toroidal multipoles are the terms missing in the standard multipole expansion; they are usually overlooked due to their relatively weak coupling to the electromagnetic fields. Here, we propose and theoretically study all-dielectric metamaterials of a special class that represent a simple electromagnetic system supporting toroidal dipolar excitations in the THz part of the spectrum. We show that resonant transmission and reflection of such metamaterials is dominated by toroidal dipole scattering, the neglect of which would result in a misunderstanding interpretation of the metamaterials' macroscopic response. Because of the unique field configuration of the toroidal mode, the proposed metamaterials could serve as a platform for sensing or enhancement of light absorption and optical nonlinearities.

  19. Dielectric relaxations and dielectric response in multiferroic BiFeO{sub 3} ceramics

    SciTech Connect

    Hunpratub, Sitchai; Thongbai, Prasit; Maensiri, Santi; Yamwong, Teerapon; Yimnirun, Rattikorn

    2009-02-09

    Single-phase multiferroic BiFeO{sub 3} ceramics were fabricated using pure precipitation-prepared BiFeO{sub 3} powder. Dielectric response of BiFeO{sub 3} ceramics was investigated over a wide range of temperature and frequency. Our results reveal that the BiFeO{sub 3} ceramic sintered at 700 deg. C exhibited high dielectric permittivity, and three dielectric relaxations were observed. A Debye-type dielectric relaxation at low temperatures (-50 to 20 deg. C) is attributed to the carrier hopping process between Fe{sup 2+} and Fe{sup 3+}. The other two dielectric relaxations at the temperature ranges 30-130 deg. C and 140-200 deg. C could be due to the grain boundary effect and the defect ordering and/or the conductivity, respectively.

  20. Local representation of the electronic dielectric response function

    DOE PAGES

    Lu, Deyu; Ge, Xiaochuan

    2015-12-11

    We present a local representation of the electronic dielectric response function, based on a spatial partition of the dielectric response into contributions from each occupied Wannier orbital using a generalized density functional perturbation theory. This procedure is fully ab initio, and therefore allows us to rigorously define local metrics, such as “bond polarizability,” on Wannier centers. We show that the locality of the bare response function is determined by the locality of three quantities: Wannier functions of the occupied manifold, the density matrix, and the Hamiltonian matrix. Furthermore, in systems with a gap, the bare dielectric response is exponentially localized,more » which supports the physical picture of the dielectric response function as a collection of interacting local responses that can be captured by a tight-binding model.« less

  1. Local representation of the electronic dielectric response function

    SciTech Connect

    Lu, Deyu; Ge, Xiaochuan

    2015-12-11

    We present a local representation of the electronic dielectric response function, based on a spatial partition of the dielectric response into contributions from each occupied Wannier orbital using a generalized density functional perturbation theory. This procedure is fully ab initio, and therefore allows us to rigorously define local metrics, such as “bond polarizability,” on Wannier centers. We show that the locality of the bare response function is determined by the locality of three quantities: Wannier functions of the occupied manifold, the density matrix, and the Hamiltonian matrix. Furthermore, in systems with a gap, the bare dielectric response is exponentially localized, which supports the physical picture of the dielectric response function as a collection of interacting local responses that can be captured by a tight-binding model.

  2. Anisotropic terahertz dielectric responses of sodium nitrate crystals.

    PubMed

    Fu, Xiaojian; Song, Youting; Sun, Changqing; Zhou, Ji

    2014-04-21

    Terahertz (THz) spectroscopy has become an effective tool to characterize the low-frequency rotational and vibrational modes of molecules. In addition, novel THz dielectric responses and optical properties on the basis of molecular rotation and vibration have attracted lots of attention because of their potential application in THz devices. In this paper, the dielectric response of low-symmetric sodium nitrate crystals in the frequency range of 0.2-1.5 THz was experimentally demonstrated. Four absorption bands at 0.23, 0.47, 0.92, and 1.15 THz were observed in the dielectric spectra and were tentatively ascribed to the rotational motion of nitrate ions. Based on the molecular rotation mechanism, the dielectric anisotropy and dielectric resonance of the crystal were discussed in detail.

  3. Electromechanical response of silicone dielectric elastomers

    NASA Astrophysics Data System (ADS)

    Cârlescu, V.; Prisăcaru, G.; Olaru, D.

    2016-08-01

    This paper presents an experimental technique to investigate the electromechanical properties of silicone dielectric elastomers actuated with high DC electric fields. A non-contact measurement technique is used to capture and monitor the thickness strain (contraction) of a circular film placed between two metallic disks electrodes. Two active fillers such as silica (10, 15 and 30 wt%) and barium titanate (5 and 15 wt%) were incorporated in order to increase the actuation performance. Thickness strain was measured at HV stimuli up to 4.5 kV and showed a quadratic dependence against applied electric field indicating that the induced strain is triggered by the Maxwell effect and/or electrostriction phenomenon as reported in literature. The actuation process evidences a rapid contraction upon HV activation and a slowly relaxation when the electrodes are short-circuit due to visco-elastic nature of elastomers. A maximum of 1.22 % thickness strain was obtained at low actuating field intensity (1.5 V/pm) comparable with those reported in literature for similar dielectric elastomer materials.

  4. The dielectric response of a colloidal spheroid.

    PubMed

    Chassagne, C; Bedeaux, D

    2008-10-01

    In this article, we present a theory for the dielectric behavior of a colloidal spheroid, based on an improved version of a previously published analytical theory [C. Chassagne, D. Bedeaux, G.J.M. Koper, Physica A 317 (2003) 321-344]. The theory gives the dipolar coefficient of a dielectric spheroid in an electrolyte solution subjected to an oscillating electric field. In the special case of the sphere, this theory is shown to agree rather satisfactorily with the numerical solutions obtained by a code based on DeLacey and White's [E.H.B. DeLacey, L.R. White, J. Chem. Soc. Faraday Trans. 2 77 (1981) 2007] for all zeta potentials, frequencies and kappa a1 where kappa is the inverse of the Debye length and a is the radius of the sphere. Using the form of the analytical solution for a sphere we were able to derive a formula for the dipolar coefficient of a spheroid for all zeta potentials, frequencies and kappa a1. The expression we find is simpler and has a more general validity than the analytical expression proposed by O'Brien and Ward [R.W. O'Brien, D.N. Ward, J. Colloid Interface Sci. 121 (1988) 402] which is valid for kappa a > 1 and zero frequency.

  5. The dielectric response to the magnetic field of electromagnetic radiation

    NASA Astrophysics Data System (ADS)

    Mukherjee, Shouvik; Mukhopadhyay, Sourabh; Datta, Prasanta Kumar

    2017-04-01

    Light–matter interaction in transparent dielectrics is revisited, including the magnetic force on bound charges in the Lorentz oscillator model. The parameter ranges of incident radiation and the medium on which the magnetic field of the electromagnetic radiation will have a significant effect are traced using Floquet theory. The analysis reveals that the threshold intensity for a significant response of the magnetic field of the radiation at the second harmonic of the incident radiation can be reduced to {10}12 {{W}}{{cm}}-2 for off resonant and even lower for resonant interaction. This phenomenon has already been observed indirectly in experiments [1, 2]. Induced magnetizing current due to the magnetic force is shown to originate from a modified dielectric response, which may be useful in future magneto-optic devices, solar energy harvesting, and studying the ultrafast dynamics in doped dielectrics.

  6. Dielectric response of polar liquids in narrow slit pores.

    PubMed

    Froltsov, Vladimir A; Klapp, Sabine H L

    2007-03-21

    Based on molecular dynamics (MD) simulations and a simple (Stockmayer) model we investigate the static and dynamic dielectric response of polar liquids confined to narrow slit pores. The MD simulations are used to calculate the time-dependent polarization fluctuations along directions parallel and perpendicular to the walls, from which the components of the frequency-dependent dielectric tensor can be derived via linear response theory. Our numerical results reveal that the system's response is strongly anisotropic. The parallel dielectric function, epsilonparallel(omega), has Debye-like character very similar to the corresponding isotropic bulk function, epsilonbulk(omega), at the same chemical potential. Indeed, the main confinement effect on epsilonparallel(omega) consists in a shift toward smaller values relative to the bulk function. On the other hand, in the perpendicular direction we observe a characteristic peak in the absorption part of the dielectric function, epsilonperpendicular(omega). This peak is absent in the bulk system and reflects strongly pronounced, damped oscillations in the polarization fluctuations normal to the walls. We discuss two possible origins of the oscillations (and the resulting absorption peak), that is collective oscillations of dipoles in clusters formed parallel to the walls, and the existence of a "dipolaron mode" previously observed in MD simulations of bulk polar fluids.

  7. Biased dielectric response in LuFe2O4

    NASA Astrophysics Data System (ADS)

    Kudasov, Yu. B.; Markelova, M.; Maslov, D. A.; Platonov, V. V.; Surdin, O. M.; Kaul, A.

    2016-12-01

    A complex permittivity at a low level of excitation signal was measured in ceramic LuFe2O4. A Debye-type relaxation response with a strong temperature dependence of a characteristic frequency was observed in accordance with earlier works. A small DC bias of about 10 V/cm led to unusual changes in the dielectric response. At frequencies, which were lower than the characteristic one, the conductivity drastically increased with slight decrease of the real part of the permittivity under the bias. In the opposite case of low frequencies, there are no traces of the DC bias effect. We show that an inhomogeneous charge distribution over surface layer (domain structure) is essential for describing the biased dielectric response in LuFe2O4.

  8. Polarization states and dielectric responses of elastically clamped ferroelectric nanocrystals

    NASA Astrophysics Data System (ADS)

    Azovtsev, A. V.; Pertsev, N. A.

    2016-12-01

    Polarization states and physical properties of ferroelectrics depend on the mechanical boundary conditions due to electrostrictive coupling between electric polarization and lattice strains. Here, we describe theoretically both equilibrium thermodynamic states and electric permittivities of ferroelectric nanocrystals subjected to the elastic three-dimensional (3D) clamping by a surrounding dielectric material. The problem is solved by the minimization of a special thermodynamic potential that describes the case of an ellipsoidal ferroelectric inclusion embedded into a linear elastic matrix. Numerical calculations are performed for BaTiO3, PbTiO3, and Pb(Zr0.5Ti0.5)O3 nanoparticles surrounded by silica glass. It is shown that, in the case of BaTiO3 and PbTiO3, elastic 3D clamping may change the order of a ferroelectric phase transition from first to second. Furthermore, the mechanical inclusion-matrix interaction shifts the temperatures of structural transitions between different ferroelectric states and even eliminates some ferroelectric phases existing in stress-free BaTiO3 and Pb(Zr0.5Ti0.5)O3 crystals. Another important effect of elastic clamping is the lowering of the symmetry of ferroelectric states in ellipsoidal inclusions, where orthorhombic and monoclinic phases may form instead of the tetragonal and rhombohedral bulk counterparts. Finally, our thermodynamic calculations show that the dielectric responses of studied perovskite ferroelectrics are sensitive to matrix-induced clamping as well. For instance, dielectric peaks occurring at structural transitions between different ferroelectric phases in BaTiO3 appear to be much higher in spherical inclusions than in the freestanding crystal. Predicted clamping-induced enhancement of certain dielectric responses at room temperature indicates that composite materials comprising nanocrystals of perovskite ferroelectrics are promising for device applications requiring the use of high-permittivity dielectrics.

  9. Thermoluminescence and dielectric response of gamma irradiated muscovite mica

    SciTech Connect

    Kaur, Sukhnandan Singh, Surinder Singh, Lakhwant; Lochab, S. P.

    2014-04-24

    The effect of gamma radiation dose on the thermoluminescence (TL) and dielectric properties of muscovite mica was studied. TL glow curves exhibited a single peak around 141 {sup 0}C and its activation energy was estimated to be about 0.89 eV. Different dielectric parameters like dielectric constant, dielectric loss and ac conductivity have been calculated in both pristine and gamma irradiated samples. These dielectric parameters have been studied as a function of irradiation dose.

  10. Thermoluminescence and dielectric response of gamma irradiated muscovite mica

    NASA Astrophysics Data System (ADS)

    Kaur, Sukhnandan; Singh, Surinder; Singh, Lakhwant; Lochab, S. P.

    2014-04-01

    The effect of gamma radiation dose on the thermoluminescence (TL) and dielectric properties of muscovite mica was studied. TL glow curves exhibited a single peak around 141 0C and its activation energy was estimated to be about 0.89 eV. Different dielectric parameters like dielectric constant, dielectric loss and ac conductivity have been calculated in both pristine and gamma irradiated samples. These dielectric parameters have been studied as a function of irradiation dose.

  11. Scaling and spatial analysis of the dielectric response of cadmium selenide nanowires

    NASA Astrophysics Data System (ADS)

    Kanai, Yosuke; Cicero, Giancarlo

    2014-10-01

    Transverse dielectric response of hexagonal cadmium selenide (CdSe) nanowires was investigated using first-principles quantum mechanical calculations. Scaling behavior of polarizability was found to closely follow a simple dielectric cylinder model even for small nanowires with a diameter of a few nanometers. The spatial dependence of the dielectric response in the nanowires was analyzed in terms of maximally localized Wannier functions in order to elucidate the model behavior. Localized d electrons at cadmium atoms were found responsible for the simple analytic scaling of the polarizability, and the dielectric response in the center of nanowire was found converged to that of bulk already for 3 nm diameter nanowires.

  12. Intrinsic dielectric properties of magnetodielectric La2CoMnO6

    NASA Astrophysics Data System (ADS)

    Silva, R. X.; Moreira, R. L.; Almeida, R. M.; Paniago, R.; Paschoal, C. W. A.

    2015-06-01

    Manganite with a double perovskite structure is an attractive material because of its interesting magnetoelectric and dielectric responses. In particular, colossal dielectric constant (CDC) behavior has been observed in La2CoMnO6 (LCMO) at radio frequencies and at room temperature. In this paper, we used infrared-reflectivity spectroscopy to study a LCMO ceramic obtained through a modified Pechini's method to determine the phonon contribution to the intrinsic dielectric response of the system and to investigate the CDC origin. The analysis of the main polar modes and of the obtained phonon parameters indicate that the CDC effect of LCMO is of pure extrinsic origin. In addition, we estimated the dielectric constant and the quality factor of the material in the microwave region to be ɛ's ˜ 16 and Qu × f ˜ 124 THz, which verifies that LCMO is appropriate for application in microwave devices and circuitry.

  13. Optical anisotropic-dielectric response of mercuric iodide

    SciTech Connect

    Yao, H.; Johs, B.; James, R.B.

    1997-10-01

    Anisotropic optical properties of mercuric iodide (HgI{sub 2}) were studied by variable-angle spectroscopic ellipsometry (VASE). Angular-dependent polarized reflectance and transmittance at three special optical-axis configurations, concerning the uniaxial anisotropic nature of the crystal, were derived to facilitate the VASE analysis. Two surface orientations of this tetragonal crystal were selected, i.e., an a-plane and a c-plane sample. Room-temperature multiple-angle spectroscopic ellipsometry measurements from both samples with three different optical configurations along with polarized transmission measurements were jointly analyzed by the VASE analysis through multiple-sample, multiple-model methods. Anisotropic dielectric functions of single-crystal HgI{sub 2}, {var_epsilon}{sub {perpendicular}}({omega}) and {var_epsilon}{sub {parallel}}({omega}), for optical electric-field vector oriented perpendicular and parallel to the c axis, respectively, were obtained in the range 1.24{endash}5.1 eV. Different absorption energy-band edges, at room temperature, were observed from the ordinary and extraordinary dielectric responses at 2.25 and 2.43 eV, respectively. This is consistent with the results related to the optical transitions between the conduction band and the heavy- and light-hole valence band indicated by theoretical studies. A surface model related to the surface roughness and defects of HgI{sub 2} was established and characterized by the VASE analysis. {copyright} {ital 1997} {ital The American Physical Society}

  14. Identification of structural relaxation in the dielectric response of water

    DOE PAGES

    Hansen, Jesper S.; Kisliuk, Alexander; Sokolov, Alexei P.; ...

    2016-06-09

    One century ago pioneering dielectric results obtained for water and n-alcohols triggered the advent of molecular rotation diffusion theory considered by Debye to describe the primary dielectric absorption in these liquids. Here, comparing dielectric, viscoelastic, and light scattering results, we unambiguously demonstrate that the structural relaxation appears only as a high-frequency shoulder in the dielectric spectra of water. In contrast, the main dielectric peak is related to a supramolecular structure, analogous to the Debye-like peak observed in monoalcohols.

  15. Dielectric response based characterization and strength prediction of cementitious materials

    NASA Astrophysics Data System (ADS)

    Manchiryal, Ram Kishore

    Electrical property based methods are powerful tools to sense the properties of cement based materials. Among the several non-invasive investigative techniques, those based on monitoring the electrical properties during the initial setting and in the subsequent hardening period have immense potential in performance prediction of concrete. Electrical impedance spectroscopy (EIS) has emerged as one of the promising techniques to non-invasively probe the microstructure and property development in cement based materials. This thesis reports the results of a systematic investigation carried out to understand the influence of material parameters on the dielectric response of cement pastes and concretes, and also a methodology to property prediction in cementitious system using electrical properties. The influence of cement type, water-to-cementing materials ratio (w/cm), and the presence of fly ash as a cement replacement material on the conductivity of cement pastes is studied. The electrical conductivity---time relationships of cement pastes and concretes are expressed using a model that facilitates the extraction of initial and final conductivities, and a characteristic time parameter. These terms are used to derive information about the microstructural changes occurring with time in cement pastes. The experimental results are subjected to a range analysis to isolate the significant factors and factor interactions that influence the initial and final conductivities as well as the time parameter from the conductivity-time model for concrete mixtures. The material parameters that influence the measured conductivity are identified and their influence quantified. The changes in dielectric constant and conductivity spectra of cement paste and concretes are attributed to the polarization phenomena. There is an observed dielectric enhancement for fly ash modified pastes. The dielectric response of concrete is very similar to that of pastes, and the effect of dilution by the

  16. Maximizing the dielectric response of molecular thin films via quantum chemical design.

    PubMed

    Heitzer, Henry M; Marks, Tobin J; Ratner, Mark A

    2014-12-23

    Developing high-capacitance organic gate dielectrics is critical for advances in electronic circuitry based on unconventional semiconductors. While high-dielectric constant molecular substances are known, the mechanism of dielectric response and the fundamental chemical design principles are not well understood. Using a plane-wave density functional theory formalism, we show that it is possible to map the atomic-scale dielectric profiles of molecule-based materials while capturing important bulk characteristics. For molecular films, this approach reveals how basic materials properties such as surface coverage density, molecular tilt angle, and π-system planarity can dramatically influence dielectric response. Additionally, relatively modest molecular backbone and substituent variations can be employed to substantially enhance film dielectric response. For dense surface coverages and proper molecular alignment, conjugated hydrocarbon chains can achieve dielectric constants of >8.0, more than 3 times that of analogous saturated chains, ∼2.5. However, this conjugation-related dielectric enhancement depends on proper molecular orientation and planarization, with enhancements up to 60% for proper molecular alignment with the applied field and an additional 30% for conformations such as coplanarity in extended π-systems. Conjugation length is not the only determinant of dielectric response, and appended polarizable high-Z substituents can increase molecular film response more than 2-fold, affording estimated capacitances of >9.0 μF/cm2. However, in large π-systems, polar substituent effects are substantially attenuated.

  17. Huge low-frequency dielectric response of (Nb,In)-doped TiO2 ceramics

    NASA Astrophysics Data System (ADS)

    Wu, Y. Q.; Zhao, X.; Zhang, J. L.; Su, W. B.; Liu, J.

    2015-12-01

    The (Nb,In)-doped TiO2 ceramics have drawn considerable attention as a type of promising giant-permittivity dielectric materials in recent years. However, a significant controversy concerning the giant dielectric mechanism currently exists, and clarifying it is vitally important from both scientific and technological viewpoints. This letter reports the results of a systematical comparison study, where two kinds of (Nb,In)-doped TiO2 ceramics with a substantial difference in dielectric loss are used. Dielectric properties and complex impedance are investigated over a broad frequency band of 3 mHz-110 MHz. A huge low-frequency dielectric response in addition to the giant dielectric relaxation appearing above 1 MHz is observed for both kinds of (Nb,In)-doped TiO2 ceramics in dielectric dispersion. The huge dielectric response observed in the low frequency range can be ascribed to a non-ohmic electrode-contact, and the dielectric relaxation appearing above 1 MHz can be attributed to an internal barrier layer capacitance effect. An electrical equivalent circuit model suggested can well describe the observed dielectric properties and electrical behaviors.

  18. The study of electrical conduction mechanisms. [dielectric response of lunar fines

    NASA Technical Reports Server (NTRS)

    Morrison, H. F.

    1974-01-01

    The dielectric response of lunar fines 74241,2 is presented in the audio-frequency range and under lunarlike conditions. Results suggest that volatiles are released during storage and transport of the lunar sample. Apparently, subsequent absorption of volatiles on the sample surface alter its dielectric response. The assumed volatile influence disappear after evacuation. A comparison of the dielectric properties of lunar and terrestrial materials as a function of density, temperature, and frequency indicates that if the lunar simulator analyzed were completely devoid of atmospheric moisture it would present dielectric losses smaller than those of the lunar sample. It is concluded that density prevails over temperature as the controlling factor of dielectric permittivity in the lunar regolith and that dielectric losses vary slowly with depth.

  19. Unusual dielectric response in cobalt doped reduced graphene oxide

    SciTech Connect

    Akhtar, Abu Jahid; Gupta, Abhisek; Kumar Shaw, Bikash; Saha, Shyamal K.

    2013-12-09

    Intensive research on cobalt doped reduced graphene oxide (Co-RGO) to investigate the modification in graphene magnetism and spin polarization due to presence of transition metal atom has been carried out, however, its dielectric spectroscopy, particularly, how capacitance changes with impurity levels in graphene is relatively unexplored. In the present work, dielectric spectroscopy along with magneto-dielectric effect are investigated in Co-RGO. Contrary to other materials, here permittivity increases abruptly with frequency in the low frequency region and continues to increase till 10{sup 7} Hz. This unusual behavior is explained on the basis of trap induced capacitance created due to impurity levels.

  20. Giant dielectric response of Haldane gap compound Y2BaNiO5

    NASA Astrophysics Data System (ADS)

    Chen, J. W.; Narsinga Rao, G.; Li, K. W.

    2012-03-01

    The dielectric properties of the Haldane gap compound Y2BaNiO5 were studied in the frequency range from 20 Hz to 1 MHz between 20 K and room temperature. This compound exhibits a high dielectric permittivity (ɛ' ˜ 104) at room temperature below 100 kHz. Both dielectric relaxation and dc resistivity ρ follow the thermally activated process with similar value of the activation energy. This indicates the close correlation between the electric conduction and the dielectric polarization. The modulus spectra reveal evidence for both grain and grain boundary relaxation times. The grain relaxation time follows thermally activated process, whereas the grain boundary relaxation time exhibits variable range hopping (VRH) behavior. The observed giant dielectric response were explained in terms of internal (grain boundary) barrier layer capacitance (IBLC) effects.

  1. Voltage-induced pinnacle response in the dynamics of dielectric elastomers

    NASA Astrophysics Data System (ADS)

    Li, Bo; Zhang, Junshi; Chen, Hualing; Li, Dichen

    2016-05-01

    A dielectric elastomer is capable of large deformation under alternating electromechanical excitation. In this paper, several dynamic properties of a dielectric elastomer are investigated, in particular the effect of strain stiffening. A theoretical model is established that shows that the bias voltage affects the amplitude and the response waveform during vibration, a curve with the shape of a pinnacle. We also describe the underlying physical mechanism by considering the molecular chain length and cross-linking density of the material. A phase portrait is presented that reveals the transitional behavior of the dielectric elastomer as it switches between soft and stiffened vibration states.

  2. Dielectric response of capacitor structures based on PZT annealed at different temperatures

    NASA Astrophysics Data System (ADS)

    Kamenshchikov, Mikhail V.; Solnyshkin, Alexander V.; Pronin, Igor P.

    2016-12-01

    Dielectric response of thin-film capacitor structures of Pt/PZT/Pt deposited by the RF magnetron sputtering method and annealed at temperatures of 540-570 °C was investigated. It was found that dielectric properties of these structures depend on the synthesis temperature. Stability of a polarized state is considered on the basis of the analysis of hysteresis loops and capacitance-voltage (C-V) characteristics. The contribution of the domain mechanism in the dielectric response of the capacitor structure comprising a ferroelectric is discussed. Extreme dependences of electrophysical characteristics of PZT films on their synthesis temperature were observed. Correlation of dielectric properties with microstructure of these films is found out.

  3. Dielectric response of Cu/amorphous BaTiO{sub 3}/Cu capacitors

    SciTech Connect

    Gonon, P.; El Kamel, F.

    2007-04-01

    Cu/amorphous BaTiO{sub 3}/Cu capacitors were tested for their dielectric properties in the 0.1 Hz-100 kHz range, from room temperature to 350 degree sign C. The amorphous barium titanate dielectric layer was deposited by rf sputtering on water-cooled copper electrodes. The room-temperature dielectric constant is around 18 and the dissipation factor is 3x10{sup -3} at 100 kHz. When increasing temperature the dielectric response displays an important frequency dispersion with the appearance of a marked loss peak at low frequencies. This dispersion is ascribed to electrode polarization effects, as evidenced by measurements performed on various film thicknesses and by using different electrodes. The electrode polarization phenomenon is discussed using a simple space charge model and is shown to be related to mobile oxygen vacancies.

  4. Dielectric response of metal/SrTiO{sub 3}/two-dimensional electron liquid heterostructures

    SciTech Connect

    Mikheev, Evgeny; Raghavan, Santosh; Stemmer, Susanne

    2015-08-17

    Maximizing the effective dielectric constant of the gate dielectric stack is important for electrostatically controlling high carrier densities inherent to strongly correlated materials. SrTiO{sub 3} is uniquely suited for this purpose, given its extremely high dielectric constant, which can reach 10{sup 4}. Here, we present a systematic study of the thickness dependence of the dielectric response and leakage of SrTiO{sub 3} that is incorporated into a vertical structure on a high-carrier-density two-dimensional electron liquid (2DEL). A simple model can be used to interpret the data. The results show a need for improved interface control in the design of metal/SrTiO{sub 3}/2DEL devices.

  5. Response analysis of dielectric elastomer spherical membrane to harmonic voltage and random pressure

    NASA Astrophysics Data System (ADS)

    Jin, Xiaoling; Wang, Yong; Chen, Michael Z. Q.; Huang, Zhilong

    2017-03-01

    Spherical membranes consisting of dielectric elastomer play important roles in flexible and stretchable devices, such as flexible actuators, sensors and loudspeakers. Executing various functions of devices depends on the dynamical behaviors of dielectric elastomer spherical membranes to external electrical and/or mechanical excitations. This manuscript concentrates on the random aspect of dielectric elastomer spherical membranes, i.e., the random response to combined excitations of harmonic voltage and random pressure. To analytically evaluate the response statistics of the stretch ratio, a specific transformation and stochastic averaging technique are successively adopted to solve the strongly nonlinear equation with respect to the stretch ratio. The stochastic differential equations for the system first integral and the phase difference between harmonic excitation and response are first derived through this transformation. The Fokker-Planck-Kolmogorov equation with respect to the stationary probability density of the system first integral and the phase difference is obtained. The stationary probability densities and the response statistics of the stretch ratio and its rate of change are then subsequently calculated. The phenomenon of stochastic jumps is found and the stochastic jump bifurcates with the variations of the frequency and the amplitude of the harmonic voltage and the intensity of the random pressure. The efficacy and accuracy of the analytical results are verified by comparing with the results from Monte Carlo simulation. Besides, the reliability of the dielectric elastomer spherical membrane is discussed briefly. The obtained results could provide options in implementing and designing dielectric elastomer structures for dynamic applications.

  6. Dielectric response and novel electromagnetic modes in three-dimensional Dirac semimetal films

    NASA Astrophysics Data System (ADS)

    Kotov, O. V.; Lozovik, Yu. E.

    2016-06-01

    Using the Kubo formalism we have calculated the local dynamic conductivity of a bulk, i.e., three-dimensional (3D), Dirac semimetal (BDS). We obtain that at frequencies lower than Fermi energy the metallic response in a BDS film manifests in the existence of surface-plasmon polaritons, but at higher frequencies the dielectric response is dominated and it occurs that a BDS film behaves as a dielectric waveguide. At this dielectric regime we predict the existence inside a BDS film of novel electromagnetic modes, a 3D analog of the transverse electric waves in graphene. We also find that the dielectric response manifests as the wide-angle passband in the mid-infrared (IR) transmission spectrum of light incident on a BDS film, which can be used for the interferenceless omnidirectional mid-IR filtering. The tuning of the Fermi level of the system allows us to switch between the metallic and the dielectric regimes and to change the frequency range of the predicted modes. This makes BDSs promising materials for photonics and plasmonics.

  7. Response delay caused by dielectric relaxation of polymer insulators for organic transistors and resolution method

    NASA Astrophysics Data System (ADS)

    Suemori, Kouji; Kamata, Toshihide

    2012-08-01

    We investigated the effect of dielectric relaxation in polymer gate insulators on the device characteristics of organic field effect transistors. Dielectric relaxation of polymer gate insulators caused an increase in drain current (ID) in a period starting immediately after the application of the gate voltage (VG) and lasting several milliseconds. This induced an apparent delay in the response of ID. Based on the observed results, we suggested an ideal gate insulator to achieve organic field effect transistors that have a fast response and high performance.

  8. Molecular motion, dielectric response, and phase transition of charge-transfer crystals: acquired dynamic and dielectric properties of polar molecules in crystals.

    PubMed

    Harada, Jun; Ohtani, Masaki; Takahashi, Yukihiro; Inabe, Tamotsu

    2015-04-08

    Molecules in crystals often suffer from severe limitations on their dynamic processes, especially on those involving large structural changes. Crystalline compounds, therefore, usually fail to realize their potential as dielectric materials even when they have large dipole moments. To enable polar molecules to undergo dynamic processes and to provide their crystals with dielectric properties, weakly bound charge-transfer (CT) complex crystals have been exploited as a molecular architecture where the constituent polar molecules have some freedom of dynamic processes, which contribute to the dielectric properties of the crystals. Several CT crystals of polar tetrabromophthalic anhydride (TBPA) molecules were prepared using TBPA as an electron acceptor and aromatic hydrocarbons, such as coronene and perylene, as electron donors. The crystal structures and dielectric properties of the CT crystals as well as the single-component crystal of TBPA were investigated at various temperatures. Molecular reorientation of TBPA molecules did not occur in the single-component crystal, and the crystal did not show a dielectric response due to orientational polarization. We have found that the CT crystal formation provides a simple and versatile method to develop molecular dielectrics, revealing that the molecular dynamics of the TBPA molecules and the dielectric property of their crystals were greatly changed in CT crystals. The TBPA molecules underwent rapid in-plane reorientations in their CT crystals, which exhibited marked dielectric responses arising from the molecular motion. An order-disorder phase transition was observed for one of the CT crystals, which resulted in an abrupt change in the dielectric constant at the transition temperature.

  9. Nodal Quasiparticle in Pseudogapped Colossal Magnetoresistive Manganites

    SciTech Connect

    Mannella, N.

    2010-06-02

    A characteristic feature of the copper oxide high-temperature superconductors is the dichotomy between the electronic excitations along the nodal (diagonal) and antinodal (parallel to the Cu-O bonds) directions in momentum space, generally assumed to be linked to the d-wave symmetry of the superconducting state. Angle-resolved photoemission measurements in the superconducting state have revealed a quasiparticle spectrum with a d-wave gap structure that exhibits a maximum along the antinodal direction and vanishes along the nodal direction. Subsequent measurements have shown that, at low doping levels, this gap structure persists even in the high-temperature metallic state, although the nodal points of the superconducting state spread out in finite Fermi arcs. This is the so-called pseudogap phase, and it has been assumed that it is closely linked to the superconducting state, either by assigning it to fluctuating superconductivity or by invoking orders which are natural competitors of d-wave superconductors. Here we report experimental evidence that a very similar pseudogap state with a nodal-antinodal dichotomous character exists in a system that is markedly different from a superconductor: the ferromagnetic metallic groundstate of the colossal magnetoresistive bilayer manganite La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7}. Our findings therefore cast doubt on the assumption that the pseudogap state in the copper oxides and the nodal-antinodal dichotomy are hallmarks of the superconductivity state.

  10. Direct measurement of the effective infrared dielectric response of a highly doped semiconductor metamaterial.

    PubMed

    Al Mohtar, Abeer; Kazan, Michel; Taliercio, Thierry; Cerutti, Laurent; Blaize, Sylvain; Bruyant, Aurélien

    2017-03-24

    We have investigated the effective dielectric response of a subwavelength grating made of highly doped semiconductors (HDS) excited in reflection, using numerical simulations and spectroscopic measurement. The studied system can exhibit strong localized surface resonances and has, therefore, a great potential for surface-enhanced infrared absorption (SEIRA) spectroscopy application. It consists of a highly doped InAsSb grating deposited on lattice-matched GaSb. The numerical analysis demonstrated that the resonance frequencies can be inferred from the dielectric function of an equivalent homogeneous slab by accounting for the complex reflectivity of the composite layer. Fourier transform infrared reflectivity (FTIR) measurements, analyzed with the Kramers-Kronig conversion technique, were used to deduce the effective response in reflection of the investigated system. From the knowledge of this phenomenological dielectric function, transversal and longitudinal energy-loss functions were extracted and attributed to transverse and longitudinal resonance modes frequencies.

  11. Direct measurement of the effective infrared dielectric response of a highly doped semiconductor metamaterial

    NASA Astrophysics Data System (ADS)

    Mohtar, Abeer Al; Kazan, Michel; Taliercio, Thierry; Cerutti, Laurent; Blaize, Sylvain; Bruyant, Aurélien

    2017-03-01

    We have investigated the effective dielectric response of a subwavelength grating made of highly doped semiconductors (HDS) excited in reflection, using numerical simulations and spectroscopic measurement. The studied system can exhibit strong localized surface resonances and has, therefore, a great potential for surface-enhanced infrared absorption (SEIRA) spectroscopy application. It consists of a highly doped InAsSb grating deposited on lattice-matched GaSb. The numerical analysis demonstrated that the resonance frequencies can be inferred from the dielectric function of an equivalent homogeneous slab by accounting for the complex reflectivity of the composite layer. Fourier transform infrared reflectivity (FTIR) measurements, analyzed with the Kramers–Kronig conversion technique, were used to deduce the effective response in reflection of the investigated system. From the knowledge of this phenomenological dielectric function, transversal and longitudinal energy-loss functions were extracted and attributed to transverse and longitudinal resonance modes frequencies.

  12. Sensing Based on Fano-Type Resonance Response of All-Dielectric Metamaterials

    PubMed Central

    Semouchkina, Elena; Duan, Ran; Semouchkin, George; Pandey, Ravindra

    2015-01-01

    A new sensing approach utilizing Mie resonances in metamaterial arrays composed of dielectric resonators is proposed. These arrays were found to exhibit specific, extremely high-Q factor (up to 15,000) resonances at frequencies corresponding to the lower edge of the array second transmission band. The observed resonances possessed with features typical for Fano resonances (FRs), which were initially revealed in atomic processes and recently detected in macro-structures, where they resulted from interference between local resonances and a continuum of background waves. Our studies demonstrate that frequencies and strength of Fano-type resonances in all-dielectric arrays are defined by interaction between local Mie resonances and Fabry-Perot oscillations of Bloch eigenmodes that makes possible controlling the resonance responses by changing array arrangements. The opportunity for obtaining high-Q responses in compact arrays is investigated and promising designs for sensing the dielectric properties of analytes in the ambient are proposed. PMID:25905701

  13. Low dielectric loss, dielectric response, and conduction behavior in Na-doped Y2/3Cu3Ti4O12 ceramics

    NASA Astrophysics Data System (ADS)

    Liang, Pengfei; Chao, Xiaolian; Yang, Zupei

    2014-07-01

    The Na-doped Y2/3Cu3Ti4O12 system has been prepared and investigated. Na doping facilitates the formation of oxygen vacancies, which is of great benefit to the growth of the grain size. Proper amount of Na substitution in NaxY(2-x)/3Cu3Ti4O12 ceramics makes the dielectric loss significantly decreased. As x = 0.050, Na0.050Y0.650Cu3Ti4O12 ceramics exhibit the lowest dielectric loss (about 0.022 at 1 kHz) and a relatively high dielectric constant (about 7500 at 1 kHz). The lowered dielectric loss is closely associated with the enhanced resistance of grain boundary. The conduction and dielectric processes of grain boundary become much more difficult after Na doping. Impedance analysis suggests that the same charge defects are responsible for the conduction and dielectric relaxation behaviors of grain boundary. Scaling behaviors indicate that the physical nature of their dielectric relaxation and conduction behavior are independent of the measurement temperature and the Na concentration.

  14. Control of optical response of a supported cluster on different dielectric substrates

    SciTech Connect

    Iida, Kenji Noda, Masashi; Nobusada, Katsuyuki

    2015-06-07

    We develop a computational method for optical response of a supported cluster on a dielectric substrate. The substrate is approximated by a dielectric continuum with a frequency-dependent dielectric function. The computational approach is based on our recently developed first-principles simulation method for photoinduced electron dynamics in real-time and real-space. The approach allows us to treat optical response of an adsorbate explicitly taking account of interactions at an interface between an adsorbate and a substrate. We calculate optical absorption spectra of supported Ag{sub n} (n = 2, 54) clusters, changing the dielectric function of a substrate. By analyzing electron dynamics in real-time and real-space, we clarify the mechanisms for variations in absorption spectra, such as peak shifts and intensity changes, relating to various experimental results for optical absorption of supported clusters. Attractive and repulsive interactions between an adsorbate and a substrate result in red and blue shifts, respectively, and the intensity decreases by energy dissipation into a substrate. We demonstrate that optical properties can be controlled by varying the dielectric function of a substrate.

  15. Domain wall contribution to the nonlinear dielectric response: effective potential model

    NASA Astrophysics Data System (ADS)

    Placeres-Jiménez, R.; Rino, J. P.; Gonçalves, A. M.; Eiras, J. A.

    2015-11-01

    Domain wall displacement has an important contribution to the different nonlinear dielectric responses observed in ferroelectrics. For a moderated alternating electric field, domain walls perform a small displacement around their equilibrium positions. Such motion of the domain walls can be modelled as a body moving in a viscous medium under the action of an effective potential W(l). From this model the dispersion relationships are derived. The exact expression for the effective potential is found assuming that the dielectric permittivity depends on the electric field strength as \\varepsilon \\propto 1/(α +β {{E}2}) . The effect of multidomain structure and polarization hysteresis are introduced through the effective field approximation {{E}\\text{eff}}\\equiv E+κ P(E) . An important merit of the model is that it allows the simulation of transient polarization processes for the arbitrary input signal, predicting a power law for the polarization and depolarization currents. An analytic expression is found for the dependence of the permittivity on the electric field strength that correctly reproduces its hysteretic behaviour. The polarization loop and nonlinear dielectric response for subswitching the alternating electric field are simulated and compared with experimental data obtained from PZT thin films. It was observed that the simulated dielectric loss was lower than the experimental one, which can be explained as a result of the interaction of domain walls with defects. Point defects are introduced into the model as a perturbation of the effective potential, showing the dependence of the dielectric loss on the concentration of the defects.

  16. Crystalline Structure, Defect Chemistry and Room Temperature Colossal Permittivity of Nd-doped Barium Titanate

    NASA Astrophysics Data System (ADS)

    Sun, Qiaomei; Gu, Qilin; Zhu, Kongjun; Jin, Rongying; Liu, Jinsong; Wang, Jing; Qiu, Jinhao

    2017-02-01

    Dielectric materials with high permittivity are strongly demanded for various technological applications. While polarization inherently exists in ferroelectric barium titanate (BaTiO3), its high permittivity can only be achieved by chemical and/or structural modification. Here, we report the room-temperature colossal permittivity (~760,000) obtained in xNd: BaTiO3 (x = 0.5 mol%) ceramics derived from the counterpart nanoparticles followed by conventional pressureless sintering process. Through the systematic analysis of chemical composition, crystalline structure and defect chemistry, the substitution mechanism involving the occupation of Nd3+ in Ba2+ -site associated with the generation of Ba vacancies and oxygen vacancies for charge compensation has been firstly demonstrated. The present study serves as a precedent and fundamental step toward further improvement of the permittivity of BaTiO3-based ceramics.

  17. Crystalline Structure, Defect Chemistry and Room Temperature Colossal Permittivity of Nd-doped Barium Titanate

    PubMed Central

    Sun, Qiaomei; Gu, Qilin; Zhu, Kongjun; Jin, Rongying; Liu, Jinsong; Wang, Jing; Qiu, Jinhao

    2017-01-01

    Dielectric materials with high permittivity are strongly demanded for various technological applications. While polarization inherently exists in ferroelectric barium titanate (BaTiO3), its high permittivity can only be achieved by chemical and/or structural modification. Here, we report the room-temperature colossal permittivity (~760,000) obtained in xNd: BaTiO3 (x = 0.5 mol%) ceramics derived from the counterpart nanoparticles followed by conventional pressureless sintering process. Through the systematic analysis of chemical composition, crystalline structure and defect chemistry, the substitution mechanism involving the occupation of Nd3+ in Ba2+ -site associated with the generation of Ba vacancies and oxygen vacancies for charge compensation has been firstly demonstrated. The present study serves as a precedent and fundamental step toward further improvement of the permittivity of BaTiO3-based ceramics. PMID:28205559

  18. Crystalline Structure, Defect Chemistry and Room Temperature Colossal Permittivity of Nd-doped Barium Titanate.

    PubMed

    Sun, Qiaomei; Gu, Qilin; Zhu, Kongjun; Jin, Rongying; Liu, Jinsong; Wang, Jing; Qiu, Jinhao

    2017-02-13

    Dielectric materials with high permittivity are strongly demanded for various technological applications. While polarization inherently exists in ferroelectric barium titanate (BaTiO3), its high permittivity can only be achieved by chemical and/or structural modification. Here, we report the room-temperature colossal permittivity (~760,000) obtained in xNd: BaTiO3 (x = 0.5 mol%) ceramics derived from the counterpart nanoparticles followed by conventional pressureless sintering process. Through the systematic analysis of chemical composition, crystalline structure and defect chemistry, the substitution mechanism involving the occupation of Nd(3+) in Ba(2+) -site associated with the generation of Ba vacancies and oxygen vacancies for charge compensation has been firstly demonstrated. The present study serves as a precedent and fundamental step toward further improvement of the permittivity of BaTiO3-based ceramics.

  19. A new method for achieving enhanced dielectric response over a wide temperature range

    DOE PAGES

    Maurya, Deepam; Sun, Fu -Chang; Pamir Alpay, S.; ...

    2015-10-19

    We report a novel approach for achieving high dielectric response over a wide temperature range. In this approach, multilayer ceramic heterostructures with constituent compositions having strategically tuned Curie points (TC) were designed and integrated with varying electrical connectivity. Interestingly, these multilayer structures exhibited different dielectric behavior in series and parallel configuration due to variations in electrical boundary conditions resulting in the differences in the strength of the electrostatic coupling. The results are explained using nonlinear thermodynamic model taking into account electrostatic interlayer interaction. We believe that present work will have huge significance in design of high performance ceramic capacitors.

  20. Insight into the dielectric response of transformer oil-based nanofluids

    NASA Astrophysics Data System (ADS)

    Dong, Ming; Dai, Jianzhuo; Li, Yang; Xie, Jiacheng; Ren, Ming; Dang, Zhimin

    2017-02-01

    The oil-based nanofluids with greater dielectric strength have attracted much attention as a crucial insulating materials in high-voltage oil-immersed power equipment. In fact, the different microstructures of the transformer oil-based nanofluids (TNFs) would result in different dielectric properties. In this work, the broadband dielectric spectroscopy measurement was used to establish the linkage between the electric double layer (EDL) and dielectric response properties of TNFs which was performed at 298K temperature and with frequency range from 10-2Hz˜106Hz. The modified Havriliak-Negami (HN) model function was used to analyze the measured results. The results demonstrate that both the real and imaginary parts of dielectric spectra of two kinds of oil are composed of the conductivity and polarization process. Compared with pure oil, two polarization process could be observed for the TNFs, explained by the EDL structure reasonably. The introduction of the EDL structure provides an idea to account for the insulating strength improvement of TNFs for the first time.

  1. An inorganic-organic hybrid crystal with a two-step dielectric response and thermochromic luminescence.

    PubMed

    Duan, Hai-Bao; Yu, Shan-Shan; Liu, Shao-Xian; Zhang, Hui

    2017-02-14

    An iodoplumbate-based hybrid crystal [C2-Apy][PbI3] (1) (C2-Apy(+) = 1-ethyl-4-aminopyridinium) was synthesized and characterized structurally. Single crystal X-ray diffraction revealed that 1 crystallizes in the orthorhombic system with the space group Pnma at 150 K. Inorganic components form straight and face-sharing octahedral [PbI3]∞ chains and organic components form C2-Apy(+) cations that are incorporated into the space between the inorganic chains. A temperature-dependent single crystal structure indicates that there exists an order-disorder transition of the cation. The dynamic motion of the cation strongly influences the dielectric and emission features of 1. 1 shows a two-step dielectric response. The first step dielectric response at a low frequency is caused by direct current conduction and electrode polarization which have been proved by impedance spectra. The second dielectric response at a high frequency (10 kHz to 10 MHz) is related to the order-disorder transition of the alkyl chain and the dynamic motion of pyridyl rings. In addition, 1 shows multi-band emission, and different emission bands show different trends with the temperature change, which makes 1 exhibit thermochromic luminescence properties.

  2. Electric and magnetic response in dielectric dark states for low loss subwavelength optical meta atoms

    SciTech Connect

    Jain, Aditya; Moitra, Parikshit; Koschny, Thomas; Valentine, Jason; Soukoulis, Costas M.

    2015-07-14

    Artificially created surfaces or metasurfaces, composed of appropriately shaped subwavelength structures, namely, meta-atoms, control light at subwavelength scales. Historically, metasurfaces have used radiating metallic resonators as subwavelength inclusions. However, while resonant optical metasurfaces made from metal have been sufficiently subwavelength in the propagation direction, they are too lossy for many applications. Metasurfaces made out of radiating dielectric resonators have been proposed to solve the loss problem, but are marginally subwavelength at optical frequencies. We designed subwavelength resonators made out of nonradiating dielectrics. The resonators are decorated with appropriately placed scatterers, resulting in a meta-atom with an engineered electromagnetic response. A metasurface that yields an electric response is fabricated, experimentally characterized, and a method to obtain a magnetic response at optical frequencies is theoretically demonstrated. In conclusion, this design methodology paves the way for metasurfaces that are simultaneously subwavelength and low loss.

  3. Electric and magnetic response in dielectric dark states for low loss subwavelength optical meta atoms

    DOE PAGES

    Jain, Aditya; Moitra, Parikshit; Koschny, Thomas; ...

    2015-07-14

    Artificially created surfaces or metasurfaces, composed of appropriately shaped subwavelength structures, namely, meta-atoms, control light at subwavelength scales. Historically, metasurfaces have used radiating metallic resonators as subwavelength inclusions. However, while resonant optical metasurfaces made from metal have been sufficiently subwavelength in the propagation direction, they are too lossy for many applications. Metasurfaces made out of radiating dielectric resonators have been proposed to solve the loss problem, but are marginally subwavelength at optical frequencies. We designed subwavelength resonators made out of nonradiating dielectrics. The resonators are decorated with appropriately placed scatterers, resulting in a meta-atom with an engineered electromagnetic response. Amore » metasurface that yields an electric response is fabricated, experimentally characterized, and a method to obtain a magnetic response at optical frequencies is theoretically demonstrated. In conclusion, this design methodology paves the way for metasurfaces that are simultaneously subwavelength and low loss.« less

  4. Generalized regular singular-point description of low-frequency dielectric responses

    NASA Astrophysics Data System (ADS)

    Frenning, Göran; Nilsson, Martin; Strømme, Maria

    2004-07-01

    This paper presents a generalized regular singular-point (GRSP) model developed to account for dielectric spectra of the wide range of materials having a frequency response containing more than two power-law regions. In fact, the model is valid for an unlimited number of such regions, and is shown to provide a good description of the entire dielectric spectrum of tablets made of microcrystalline cellulose, including two relaxation peaks and power-law responses at low and high frequencies. This finding puts the GRSP model in a unique position, since no model existing in the literature is able to describe the totality of features present in the spectrum, without resorting to a superposition of more elementary responses.

  5. Interpreting the nonlinear dielectric response of glass-formers in terms of the coupling model

    NASA Astrophysics Data System (ADS)

    Ngai, K. L.

    2015-03-01

    Nonlinear dielectric measurements at high electric fields of glass-forming glycerol and propylene carbonate initially were carried out to elucidate the dynamic heterogeneous nature of the structural α-relaxation. Recently, the measurements were extended to sufficiently high frequencies to investigate the nonlinear dielectric response of faster processes including the so-called excess wing (EW), appearing as a second power law at high frequencies in the loss spectra of many glass formers without a resolved secondary relaxation. While a strong increase of dielectric constant and loss is found in the nonlinear dielectric response of the α-relaxation, there is a lack of significant change in the EW. A surprise to the experimentalists finding it, this difference in the nonlinear dielectric properties between the EW and the α-relaxation is explained in the framework of the coupling model by identifying the EW investigated with the nearly constant loss (NCL) of caged molecules, originating from the anharmonicity of the intermolecular potential. The NCL is terminated at longer times (lower frequencies) by the onset of the primitive relaxation, which is followed sequentially by relaxation processes involving increasing number of molecules until the terminal Kohlrausch α-relaxation is reached. These intermediate faster relaxations, combined to form the so-called Johari-Goldstein (JG) β-relaxation, are spatially and dynamically heterogeneous, and hence exhibit nonlinear dielectric effects, as found in glycerol and propylene carbonate, where the JG β-relaxation is not resolved and in D-sorbitol where it is resolved. Like the linear susceptibility, χ1(f), the frequency dispersion of the third-order dielectric susceptibility, χ3(f), was found to depend primarily on the α-relaxation time, and independent of temperature T and pressure P. I show this property of the frequency dispersions of χ1(f) and χ3(f) is the characteristic of the many-body relaxation dynamics of

  6. Dielectric response variation and the strength of van der Waals interactions.

    PubMed

    Hopkins, Jaime C; Dryden, Daniel M; Ching, Wai-Yim; French, Roger H; Parsegian, V Adrian; Podgornik, Rudolf

    2014-03-01

    Small changes in the dielectric response of a material result in substantial variations in the Hamaker coefficient of the van der Waals interactions, as demonstrated in a simplified approximate model as well as a realistic example of amorphous silica with and without an exciton peak. Variation of the dielectric response spectra at one particular frequency influences all terms in the Matsubara summation, making the total change in the Hamaker coefficient depend on the spectral changes not only at that frequency but also at the rest of the spectrum, properly weighted. The Matsubara terms most affected by the addition of a single peak are not those close to the position of the added peak, but are distributed doubly non-locally over the entire range of frequencies. A possibility of eliminating van der Waals interactions or at least drastically reducing them by spectral variation in a narrow regime of frequencies thus seems very remote.

  7. Inorganic backbone ionomers: Design and dielectric response of single-ion conducting polymers

    NASA Astrophysics Data System (ADS)

    Bartels, Joshua

    analysis of the static dielectric constant and show excellent agreement with x-ray scattering and DFT calculations, each ionomer strongly favoring the formation of quadrupoles. Finally a polysiloxane ionomer was considered and was mixed with three anion and/or cation solvating additives, tetraglyme, tetraethylene glycol, and branched poly(ethylenimine). The EP model of the dielectric response gives the conducting ion concentration and the mobility of conducting ions and shows an increase in conducting ion concentration with both anion solvating and cation solvating additives. The static dielectric constant indicates an increased preference for ion pairs when anion receptors are present. Most interestingly, the additive that best decreased the glass transition temperature and increased the static dielectric constant did not result in the best dc conductivity. The best dc conductivity resulted from tetraglyme because it solvated cations without interacting with the polymer. High ion conductivities have not been observed in polymer systems that decouple charge transport from polymer motion, and therefore low Tg ionomers are the natural path forward for commercially viable ionomers. Inorganic backbone polymers impart a low Tg without bringing any strong disadvantage to ionomers. These materials are very important for developing superior ion conductors and should be pursued in future ionomer research.

  8. Slow Debye-type peak observed in the dielectric response of polyalcohols

    NASA Astrophysics Data System (ADS)

    Bergman, Rikard; Jansson, Helén; Swenson, Jan

    2010-01-01

    Dielectric relaxation spectroscopy of glass forming liquids normally exhibits a relaxation scenario that seems to be surprisingly general. However, the relaxation dynamics is more complicated for hydrogen bonded liquids. For instance, the dielectric response of monoalcohols is dominated by a mysterious Debye-like process at lower frequencies than the structural α-relaxation that is normally dominating the spectra of glass formers. For polyalcohols this process has been thought to be absent or possibly obscured by a strong contribution from conductivity and polarization effects at low frequencies. We here show that the Debye-like process, although much less prominent, is also present in the response of polyalcohols. It can be observed in the derivative of the real part of the susceptibility or directly in the imaginary part if the conductivity contribution is reduced by covering the upper electrode with a thin Teflon layer. We report on results from broadband dielectric spectroscopy studies of several polyalcohols: glycerol, xylitol, and sorbitol. The findings are discussed in relation to other experimental observations of ultraslow (i.e., slower than the viscosity related α-relaxation) dynamics in glass formers.

  9. Dielectric response of electron-doped ionic superconductor LixZrNCl

    NASA Astrophysics Data System (ADS)

    Botana, Antia S.; Pickett, Warren E.

    2014-09-01

    When electron doped, the layered transition metal nitrides TNCl (T =group IVB transition metal ion) become impressive superconductors with critical temperature Tc=15-26 K. Here we take the most studied member ZrNCl as a representative and calculate the dielectric response ɛ (ω) versus frequency and concentration of doped electronic carriers. The static dielectric constant ɛ∞=5 is reproduced extremely well. We establish that the differences between rigid band modeling and virtual crystal treatment are small, and compare also with actual lithium doping using supercells. We obtain the variations upon changing the doping level of the reflectivity and energy loss function as well, many of which are found not to be correlated with the observed (non)variation of Tc(x). The main plasmon peaks appear where the electron gas model suggests, in the range 1.2-2.0 eV for x varying from 0.16 to 0.50.

  10. Lattice strain accompanying the colossal magnetoresistance effect in EuB6.

    PubMed

    Manna, Rudra Sekhar; Das, Pintu; de Souza, Mariano; Schnelle, Frank; Lang, Michael; Müller, Jens; von Molnár, Stephan; Fisk, Zachary

    2014-08-08

    The coupling of magnetic and electronic degrees of freedom to the crystal lattice in the ferromagnetic semimetal EuB(6), which exhibits a complex ferromagnetic order and a colossal magnetoresistance effect, is studied by high-resolution thermal expansion and magnetostriction experiments. EuB(6) may be viewed as a model system, where pure magnetism-tuned transport and the response of the crystal lattice can be studied in a comparatively simple environment, i.e., not influenced by strong crystal-electric field effects and Jahn-Teller distortions. We find a very large lattice response, quantified by (i) the magnetic Grüneisen parameter, (ii) the spontaneous strain when entering the ferromagnetic region, and (iii) the magnetostriction in the paramagnetic temperature regime. Our analysis reveals that a significant part of the lattice effects originates in the magnetically driven delocalization of charge carriers, consistent with the scenario of percolating magnetic polarons. A strong effect of the formation and dynamics of local magnetic clusters on the lattice parameters is suggested to be a general feature of colossal magnetoresistance materials.

  11. On the dielectric response of complex layered oxides: Mica-type silicates and layered double hydroxides

    NASA Astrophysics Data System (ADS)

    Mehrotra, Vivek; Giannelis, Emmanuel P.

    1992-08-01

    The dielectric properties of mica-type silicates and layered double hydroxides have been studied in the pristine and various intercalated forms in the frequency range 101-107 Hz. A relaxation peak has been observed for the pristine silicate, whereas the pristine layered double hydroxide exhibits an anomalous low-frequency dispersion. The dielectric response is rationalized in terms of structural ordering and fluctuation of charge carriers as well as models invoking fractal time processes and fractal structure. The response is also related to the structure and mobility of the intercalated water molecules. In both pristine hosts, the predominant conduction mechanism is proton hopping between sites generated by a network of intercalated water molecules. Silicate intercalated with the insulating form of polyaniline exhibits an almost frequency-independent response. In the case of conducting polyaniline intercalated silicate, where polarons are the majority charge carriers, an anomalous low-frequency dispersion is observed and the response is typical of a metal-insulator composite. Finally, impedance measurements have been used to calculate the spatial disorder and/or surface irregularity of the host layers, expressed by the fractal dimension ds. The changes observed in ds upon intercalation of high-charge ions are correlated to the stacking disorder of the host layers.

  12. Contributions to the second order dielectric response of an electron liquid

    NASA Astrophysics Data System (ADS)

    Bachlechner, Martina E.; Miesenboeck, Helga M.; Macke, Wilhelm

    1988-06-01

    The dielectric response function χ of a uniform electron gas is investigated up to the second order of the Coulomb interaction with different methods. When examining all polarisation diagrams with two interaction lines, it is confirmed that previous work in the Green's function formalism does not contain all second order processes and the importance of the corrections is pointed out. It is further shown, how the evaluation of χ with Green's function can be greatly simplified when taking into account the symmetry of the expressions.

  13. Dielectric Response of Glass-Forming Liquids in the Nonlinear Regime

    NASA Astrophysics Data System (ADS)

    Samanta, Subarna

    Broadband dielectric spectroscopy is a powerful technique for understanding the dynamics in supercooled liquids. It generates information about the timescale of the orientational motions of molecular dipoles within the liquid. However, dynamics of liquids measured in the non-linear response regime has recently become an area of significant interest, because additional information can be obtained compared with linear response measurements. The first part of this thesis describes nonlinear dielectric relaxation experiments performed on various molecular glass forming-liquids, with an emphasis on the response at high frequencies (excess wing). A significant nonlinear dielectric effect (NDE) was found to persist in these modes, and the magnitude of this NDE traces the temperature dependence of the activation energy. A time resolved measurement technique monitoring the dielectric loss revealed that for the steady state NDE to develop it would take a very large number of high amplitude alternating current (ac) field cycles. High frequency modes were found to be 'slaved' to the average structural relaxation time, contrary to the standard picture of heterogeneity. Nonlinear measurements were also performed on the Johari-Goldstein beta-relaxation process. High ac fields were found to modify the amplitudes of these secondary modes. The nonlinear features of this secondary process are reminiscent of those found for the excess wing regime, suggesting that these two contributions to dynamics have common origins. The second part of this thesis describes the nonlinear effects observed from the application of high direct current (dc) bias fields superposed with a small amplitude sinusoidal ac field. For several molecular glass formers, the application of a dc field was found to slow down the system via reduction in configurational entropy (Adam-Gibbs relation). Time resolved measurements indicated that the rise of the non-linear effect is slower than its decay, as observed in the

  14. Effect of initial stretch ratio on the electromechanical responses of dielectric elastomer actuators

    NASA Astrophysics Data System (ADS)

    Dai, Huliang; Zou, Jiangjiang; Wang, Lin

    2016-05-01

    In this paper, the dynamic responses of a dielectric elastomer actuator (DEA) subjected to an electrical load are investigated. Various dynamical behaviors of the DEA system have been observed. For example, when the DEAs are under a constant electric field, the oscillation is periodic. For DEAs under harmonic electric excitation, however, quasiperiodic and chaotic oscillations may occur. Of particular interest is that the initial stretch ratio has significant influence on the electromechanical behavior of the DEA, showing that chaotic divergent oscillation (i.e., extreme contraction with respect to the height of the DEA) could occur within a certain parameter region of the initial stretch ratios.

  15. Interpreting the nonlinear dielectric response of glass-formers in terms of the coupling model

    SciTech Connect

    Ngai, K. L.

    2015-03-21

    Nonlinear dielectric measurements at high electric fields of glass-forming glycerol and propylene carbonate initially were carried out to elucidate the dynamic heterogeneous nature of the structural α-relaxation. Recently, the measurements were extended to sufficiently high frequencies to investigate the nonlinear dielectric response of faster processes including the so-called excess wing (EW), appearing as a second power law at high frequencies in the loss spectra of many glass formers without a resolved secondary relaxation. While a strong increase of dielectric constant and loss is found in the nonlinear dielectric response of the α-relaxation, there is a lack of significant change in the EW. A surprise to the experimentalists finding it, this difference in the nonlinear dielectric properties between the EW and the α-relaxation is explained in the framework of the coupling model by identifying the EW investigated with the nearly constant loss (NCL) of caged molecules, originating from the anharmonicity of the intermolecular potential. The NCL is terminated at longer times (lower frequencies) by the onset of the primitive relaxation, which is followed sequentially by relaxation processes involving increasing number of molecules until the terminal Kohlrausch α-relaxation is reached. These intermediate faster relaxations, combined to form the so-called Johari-Goldstein (JG) β-relaxation, are spatially and dynamically heterogeneous, and hence exhibit nonlinear dielectric effects, as found in glycerol and propylene carbonate, where the JG β-relaxation is not resolved and in D-sorbitol where it is resolved. Like the linear susceptibility, χ{sub 1}(f), the frequency dispersion of the third-order dielectric susceptibility, χ{sub 3}(f), was found to depend primarily on the α-relaxation time, and independent of temperature T and pressure P. I show this property of the frequency dispersions of χ{sub 1}(f) and χ{sub 3}(f) is the characteristic of the many

  16. Dielectric and electrical studies of Pr{sup 3+} doped nano CaSiO{sub 3} perovskite ceramics

    SciTech Connect

    Kulkarni, Sandhya; Nagabhushana, B.M.; Parvatikar, Narsimha; Koppalkar, Anilkumar; Shivakumara, C.; Damle, R.

    2014-02-01

    Highlights: • CaSiO{sub 3}:Pr{sup 3+} was prepared by facile low temperature solution combustion method. • The crystalline phase of the product is obtained by adopting sintering method. • Samples prepared at 500 °C and calcined at 900 °C for 3 h showed β-phase. • The Pr{sup 3+} doped CaSiO{sub 3} shows “unusual results”. • The electrical microstructure has been accepted to be of internal barrier layer capacitor. - Abstract: CaSiO{sub 3} nano-ceramic powder doped with Pr{sup 3+} has been prepared by solution combustion method. The powder Ca{sub 0.95}Pr{sub 0.05}SiO{sub 3} is investigated for its dielectric and electrical properties at room temperature to study the effect of doping. The sample is characterized by X-ray diffraction and infrared spectroscopy. The size of either of volume elements of CaSiO{sub 3}:Pr{sup 3+} estimated from transmission electron microscopy is about 180–200 nm. The sample shows colossal dielectric response at room temperature. This colossal dielectric behaviour follows Debye-type relaxation and can be explained by Maxwell–Wagner (MW) polarization. However, analysis of impedance and electric modulus data using Cole–Cole plot shows that it deviates from ideal Debye behaviour resulting from the distribution of relaxation times. The distribution in the relaxation times may be attributed to existence of electrically heterogeneous grains, insulating grain boundary, and electrode contact regions. Doping, thus, results in substantial modifications in the dielectric and electrical properties of the nano-ceramic CaSiO{sub 3}.

  17. Dielectric function beyond the random-phase approximation: kinetic theory versus linear response theory.

    PubMed

    Reinholz, H; Röpke, G

    2012-03-01

    Calculating the frequency-dependent dielectric function for strongly coupled plasmas, the relations within kinetic theory and linear response theory are derived and discussed in comparison. In this context, we give a proof that the Kohler variational principle can be extended to arbitrary frequencies. It is shown to be a special case of the Zubarev method for the construction of a nonequilibrium statistical operator from the principle of the extremum of entropy production. Within kinetic theory, the commonly used energy-dependent relaxation time approach is strictly valid only for the Lorentz plasma in the static case. It is compared with the result from linear response theory that includes electron-electron interactions and applies for arbitrary frequencies, including bremsstrahlung emission. It is shown how a general approach to linear response encompasses the different approximations and opens options for systematic improvements.

  18. Ab-initio optical properties and dielectric response of open-shell spinel zinc ferrite

    NASA Astrophysics Data System (ADS)

    Ziaei, Vafa; Bredow, Thomas

    2017-02-01

    In the present work, we predict the optical properties and the dielectric response spectrum of the spinel zinc ferrite Zn2Fe4O8, and show in particular the impact of many-body effects on the absorption spectrum, using advanced many-body perturbation approach. The excitonic effects remarkably redistribute the spectral weights causing a red-shift of 1.6 eV of the maximum of the independent particle G 0 W 0 (IP- G 0 W 0) towards the electron-hole affected spectrum. The excitation spectrum of the zinc ferrite exhibits a low lying doubly degenerated bound dark exciton at 1.84 eV with a fully symmetric excited-state density, and a narrow optical gap setting on at 1.93 eV. We further analyse the electronic transitions and exciton density distributions giving insights to the nature of excitations. The dielectric response of Zn2Fe4O8 shows a particular sensitivity to the excitations higher than the electronic band gap, however it abruptly becomes passive to the incoming electro-magnetic wave and propagates to the negative regions at high energy regimes.

  19. Why the dipolar response in dielectrics and spin-glasses is unavoidably universal

    PubMed Central

    Cuervo-Reyes, Eduardo

    2016-01-01

    Materials response to electric or magnetic fields is often dominated by the dynamics of dipoles in the system. This is for instance the case of polar dielectrics and many transition metal compounds. An essential and not yet well understood fact is that, despite their structural diversity, dielectric solids exhibit a striking universality of frequency and time responses, sharing many aspects with the behaviour of spin-glasses. In this article I propose a stochastic approach to dipole dynamics within which the “universal frequency response” derives naturally with Debye’s relaxation mechanism as a special case. This formulation reveals constraints to the form of the relaxation functions, which are essential for a consistent representation of the dynamical slowing-down at the spin-glass transition. Relaxation functions with algebraic-, and exponential-tails, as well as damped oscillations, are shown to have a unified representation in which the stable limit of the distribution of waiting-times between dipole flips determines the present type of dynamics. PMID:27366866

  20. Electronic Structure, Dielectric Response, and Surface Charge Distribution of RGD (1FUV) Peptide

    NASA Astrophysics Data System (ADS)

    Adhikari, Puja; Wen, Amy M.; French, Roger H.; Parsegian, V. Adrian; Steinmetz, Nicole F.; Podgornik, Rudolf; Ching, Wai-Yim

    2014-07-01

    Long and short range molecular interactions govern molecular recognition and self-assembly of biological macromolecules. Microscopic parameters in the theories of these molecular interactions are either phenomenological or need to be calculated within a microscopic theory. We report a unified methodology for the ab initio quantum mechanical (QM) calculation that yields all the microscopic parameters, namely the partial charges as well as the frequency-dependent dielectric response function, that can then be taken as input for macroscopic theories of electrostatic, polar, and van der Waals-London dispersion intermolecular forces. We apply this methodology to obtain the electronic structure of the cyclic tripeptide RGD-4C (1FUV). This ab initio unified methodology yields the relevant parameters entering the long range interactions of biological macromolecules, providing accurate data for the partial charge distribution and the frequency-dependent dielectric response function of this peptide. These microscopic parameters determine the range and strength of the intricate intermolecular interactions between potential docking sites of the RGD-4C ligand and its integrin receptor.

  1. Electronic structure, dielectric response, and surface charge distribution of RGD (1FUV) peptide.

    PubMed

    Adhikari, Puja; Wen, Amy M; French, Roger H; Parsegian, V Adrian; Steinmetz, Nicole F; Podgornik, Rudolf; Ching, Wai-Yim

    2014-07-08

    Long and short range molecular interactions govern molecular recognition and self-assembly of biological macromolecules. Microscopic parameters in the theories of these molecular interactions are either phenomenological or need to be calculated within a microscopic theory. We report a unified methodology for the ab initio quantum mechanical (QM) calculation that yields all the microscopic parameters, namely the partial charges as well as the frequency-dependent dielectric response function, that can then be taken as input for macroscopic theories of electrostatic, polar, and van der Waals-London dispersion intermolecular forces. We apply this methodology to obtain the electronic structure of the cyclic tripeptide RGD-4C (1FUV). This ab initio unified methodology yields the relevant parameters entering the long range interactions of biological macromolecules, providing accurate data for the partial charge distribution and the frequency-dependent dielectric response function of this peptide. These microscopic parameters determine the range and strength of the intricate intermolecular interactions between potential docking sites of the RGD-4C ligand and its integrin receptor.

  2. Thermal analysis and temperature dependent dielectric responses of Co doped anatase TiO{sub 2} nanoparticles

    SciTech Connect

    Alamgir; Khan, Wasi; Ahammed, Nashiruddin; Naqvi, A. H.; Ahmad, Shabbir

    2015-05-15

    Nanoparticles (NPs) of pure and 5 mol % cobalt doped TiO{sub 2} synthesized through acid modified sol-gel method were characterized to understand their thermal, structural, morphological, and temperature dependent dielectric properties. Thermogravimetric analysis (TGA) has been used for thermal studies and indicates the weight loss in two steps due to the removal of residual organics. X-ray diffraction study was employed to confirm the formation of single anatase phase with tetragonal symmetry for both pure and 5 mol % Co doped TiO{sub 2} NPs. The average crystallite size of both samples was calculated from the Scherrer’s formula and was found in the range from 9-11 nm. TEM micrographs of these NPs reflect their shape and distribution. The dielectric constant (ε′), dielectric loss (tanδ) and ac conductivity (σ{sub ac}) were also studied as a function of temperature at different frequencies. Electrical responses of the synthesized NPs have been analyzed carefully in the framework of relevant models. It is also noticed that the dielectric constant (ε′) of the samples found to decrease with increasing frequency but increases with increasing temperature up to a particular value and then sharply decreases. Temperature variation of dielectric constant exhibits step like escalation and shows relaxation behavior. Study of dielectric properties shows dominant dependence on the grain size as well as Co ion incorporation in TiO{sub 2}.

  3. Peculiarities of the dielectric response of natural zeolite composites prepared by using zeolite and silicon powders

    NASA Astrophysics Data System (ADS)

    Ozturk Koc, S.; Orbukh, V. I.; Eyvazova, G. M.; Lebedeva, N. N.; Salamov, B. G.

    2016-03-01

    We present the real and imaginary part of the dielectric permittivity of natural zeolite composites prepared by using zeolite and silicon powders. The dielectric response (DR) dependences on the frequency (3-300 GHz) of electric field and different Si concentrations (5-33%) are non-monotonic and a maximum peak is observed. This peak position is practically independent on the frequency and its maximum is observed in zeolite composites which included 9% of the Si-powder. Also the maximum peak is decreased by about an order of magnitude when frequency increases from 500 Hz to 5 kHz. Addition of the conductive Si-particles to zeolite-powder leads to two opposite effects. Firstly, the movement of electrons in the Si-particles provides increase of DR. Secondly, cations which leaving from zeolite pores can be neutralized by the particles of Si in the intercrystalline-space. Such a peculiar mechanism for recombination of Si electrons and cations from pores leads to a reduction of DR for large silicon concentrations. Due to the fact that the contribution of free carriers in the decreasing of the DR as the frequency increases, it is consistent with the suggestion that the maximum peak decreases with increasing frequency.

  4. Ac-conductivity and dielectric response of new zinc-phosphate glass/metal composites

    NASA Astrophysics Data System (ADS)

    Maaroufi, A.; Oabi, O.; Lucas, B.

    2016-07-01

    The ac-conductivity and dielectric response of new composites based on zinc-phosphate glass with composition 45 mol%ZnO-55 mol%P2O5, filled with metallic powder of nickel (ZP/Ni) were investigated by impedance spectroscopy in the frequency range from 100 Hz to 1 MHz at room temperature. A high percolating jump of seven times has been observed in the conductivity behavior from low volume fraction of filler to the higher fractions, indicating an insulator - semiconductor phase transition. The measured conductivity at higher filler volume fraction is about 10-1 S/cm and is frequency independent, while, the obtained conductivity for low filler volume fraction is around 10-8 S/cm and is frequency dependent. Moreover, the elaborated composites are characterized by high dielectric constants in the range of 105 for conductive composites at low frequencies (100 Hz). In addition, the distribution of the relaxation processes was also evaluated. The Debye, Cole-Cole, Davidson-Cole and Havriliak-Negami models in electric modulus formalism were used to model the observed relaxation phenomena in ZP/Ni composites. The observed relaxation phenomena are fairly simulated by Davidson-Cole model, and an account of the interpretation of results is given.

  5. Optical dielectric response of gallium nitride studied by variable angle spectroscopy ellipsometry

    SciTech Connect

    Yao, H.; Yan, C.H.; Jenkinson, H.A.; Zavada, J.M.; Speck, J.S.; Denbaars, S.P.

    1997-12-31

    Variable angle spectroscopic ellipsometry (VASE) and transmission measurements have been employed to study the dielectric response of gallium nitride (GaN) thin films -- an important material for light emitting diodes (LEDs) and laser diodes applications. The GaN films were grown by atmosphere pressure metal organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates ({alpha}-Al{sub 2}O{sub 3}). Room temperature VASE measurements were made, in the range of 0.75 to 5.5eV, at the angle of incidence of 73, 75, and 77 degree, respectively. Evidence of anisotropy is observed especially in the spectral range under the band gap ({approximately}3.4 eV), reflecting the nature of wurtzite crystal structure of GaN. The ordinary dielectric function {var_epsilon}{sub {perpendicular}}({omega}) of GaN were obtained through the analysis of transmission and VASE data in the range below and above the band gap. The thickness of these GaN films is also determined via the analysis.

  6. Solvation dynamics and the dielectric response in a glass-forming solvent: from picoseconds to seconds

    NASA Astrophysics Data System (ADS)

    Richert, R.; Stickel, F.; Fee, R. S.; Maroncelli, M.

    1994-10-01

    We have measured the response times of solvation dynamics in the range 100 ps to 100 s and the dielectric relaxation covering 10 decades in frequency for the glass-forming solvent 2-methyltetrahydrofuran. In this wide range of solvent viscosities, from the glass transition to beyond the melting point, the mean relaxation times for the two techniques which monitor dipolar orientation are identical within our resolution. For two characteristic decay traces recorded on the time scales of 10 ns and 1 s we compare the observed Stokes-shift dynamics with various theoretical approaches. The decay pattern is reproduced by the dipolar dynamic-mean-spherical-approximation, whereas the absolute time scale of the solvation is mapped by the dielectric polarization itself. For the solvent under study we find almost perfect agreement between experiment and the dipolar dMSA theory if the time scale of the predicted curve is rescaled by a factor of (epsilon(sub infinity)/epsilon(sub s))(exp 1/2).

  7. Inducing transparency with large magnetic response and group indices by hybrid dielectric metamaterials.

    PubMed

    Chen, Cheng-Kuang; Lai, Yueh-Chun; Yang, Yu-Hang; Chen, Chia-Yun; Yen, Ta-Jen

    2012-03-26

    We present metamaterial-induced transparency (MIT) phenomena with enhanced magnetic fields in hybrid dielectric metamaterials. Using two hybrid structures of identical-dielectric-constant resonators (IDRs) and distinct-dielectric-constant resonators (DDRs), we demonstrate a larger group index (ng~354), better bandwidth-delay product (BDP~0.9) than metallic-type metamaterials. The keys to enable these properties are to excite either the trapped mode or the suppressed mode resonances, which can be managed by controlling the contrast of dielectric constants between the dielectric resonators in the hybrid metamaterials.

  8. Stable dielectric response of low-loss aromatic polythiourea thin films on Pt/SiO2 substrate

    NASA Astrophysics Data System (ADS)

    Eršte, A.; Fulanović, L.; Čoga, L.; Lin, M.; Thakur, Y.; Zhang, Q. M.; Bobnar, V.

    2016-03-01

    We have investigated dielectric properties of aromatic polythiourea (ArPTU, a polar polymer containing high dipolar moments with very low defect levels) thin films that were developed on Pt/SiO2 substrate. The detected response is compared to the response of commercially available polymers, such as high density polyethylene (HDPE) and polypropylene (PP), which are at present used in foil capacitors. Stable values of the dielectric constant ɛ‧≈5 (being twice higher than in HDPE and PP) over broad temperature and frequency ranges and dielectric losses as low as in commercial systems suggest ArPTU as a promising candidate for future use in a variety of applications.

  9. Low-frequency optical dielectric response and rigidity transitions in network glasses

    SciTech Connect

    Gonzalez-Leal, J. M.; Angel, J. A.; Marquez, E.; Jimenez-Garay, R.; Krecmer, P.

    2006-11-15

    Self-organization occurring in As{sub x}S{sub 1-x} and As{sub x}Se{sub 1-x} glass alloy films reflects in their low-frequency optical dielectric response, and valuable information about the building blocks conforming their structure, can be derived from the analysis of the refractive-index dispersion data. The experimental results are discussed in the framework of the single-oscillator approach proposed by Wemple and DiDomenico, which provides a meaningful parametrization of the phenomena ruling the coupling between the photon-probe and the electron plasma in the near-infrared spectral region. Rigidity transitions occurring in both binary glassy systems are discussed in terms of the differences observed in the oscillator parameters, and these electronic evidences are linked to those arguments found in the literature, based on calorimetric and Raman measurements, that point to a segregated-phase view of glass materials.

  10. The polarization response function and the dielectric permittivity of a plasma

    SciTech Connect

    Gnavi, G.; Gratton, F.

    1984-09-01

    We give a simple direct derivation of the polarization response function h for linear electrostatic excitations of a plasma (without magnetic field) considering the effect of a percussion on the electrons. The physical meaning of the procedure is discussed, thus bringing into light basic facts of the plasma dielectric behavior. The result h = S/sub p/ fo(x/t) (where f/sub o/ is the electron distribution function in velocity space and /sub p/ the plasma frequency) is obtained without passing through the Vlasov-Poisson equations as in the standard theory. We show that the equivalence between the present method and the classic Landau analysis rests on properties of the Fourier transform applied on velocity space.

  11. Dielectric response of high permittivity polymer ceramic composite with low loss tangent

    SciTech Connect

    Subodh, G.; Deepu, V.; Mohanan, P.; Sebastian, M. T.

    2009-08-10

    The present communication investigates the dielectric response of the Sr{sub 9}Ce{sub 2}Ti{sub 12}O{sub 36} ceramics loaded high density polyethylene and epoxy resin. Sr{sub 9}Ce{sub 2}Ti{sub 12}O{sub 36} ceramic filled polyethylene and epoxy composites were prepared using hot blending and mechanical mixing, respectively. 40 vol % ceramic loaded polyethylene has relative permittivity of 12.1 and loss tangent of 0.004 at 8 GHz, whereas the corresponding composite using epoxy as matrix has permittivity and loss tangent of 14.1 and 0.022, respectively. The effective medium theory fits relatively well for the observed permittivity of these composites.

  12. Microfabricated, silicon devices with nanowells and nanogap electrodes: a platform for dielectric spectroscopy with silane-tunable response

    NASA Astrophysics Data System (ADS)

    Seifi Fini, Hassan; Suganuma, Yoshinori; Dhirani, Al-Amin

    2015-05-01

    Combining the advantages of nanogap devices and impedance spectroscopy can potentially provide a platform for dielectric spectroscopy with widely ranging applications—from fundamental studies at the nanoscale and surfaces to label free and selective sensors. The present study characterizes the impedance response of a microfabricated, silicon-based device with a large array of nanowells surrounded by annular, nanogap detection regions. Device impedance is measured versus frequency over 5 orders in a variety of organic solvents with dielectric constants ranging over 2 orders. The study finds two key results. First, an equivalent R/C circuit model is found to compare favorably with device impedance response over these wide ranges of parameters. Importantly, the model correlates with structure of the nanogap device, which suggests that such a structure-impedance response approach can help guide modeling of other devices geometries. Second, the model points to—and data confirm—correlation between nanogap device response and dielectric constant of materials in the nanogaps, particularly at low frequencies. In addition, the correlation is significantly modified by robust, silane functionalization of the devices due to a large surface-to-volume ratio of the nanogaps. These results demonstrate that nanogap impedance spectroscopy using microfabricated/silanized silicon devices is a robust and versatile platform for dielectric spectroscopy of materials on the nanoscale and on surfaces.

  13. Annealing effect on the dielectric response of novel polymer/nano-quasicrystalline composites

    NASA Astrophysics Data System (ADS)

    Venkatesh, Ch.; Rao, V. V.

    2013-06-01

    In the earlier paper (Ch. Venkatesh et al. Solid State Comm., 2010), a dielectric percolation has been reported in composites of nano-quasicrystalline (nQc) Al-Cu-Fe (filler) and polyvinylidene fluoride (PVDF) (matrix). Though a high value of dielectric constant is observed near to the percolation threshold, these composites show higher dielectric loss values at lower frequencies. An effect of annealing has been investigated on the same composites which lead to decrement in dielectric loss values appreciably. The low dielectric loss values have been attributed due to the formation of thick grain boundaries in polymer matrix which completely surrounds the nQc cluster that weakens the effective tunneling of charge carriers near the filler-polymer interfacial region. Finally, a dielectric constant of 500 with tanδ<1 at 1 KHz is observed which may make the composite useful for low loss capacitive applications.

  14. The effects of halide anions on the dielectric response of potassium halide solutions in visible, UV and far UV region.

    PubMed

    Shagieva, F M; Boinovich, L B

    2013-06-07

    Based on the experimentally measured dispersion of refractive indices, we studied the effects of halide anions on the dielectric response of potassium halide solutions in the visible, UV and far UV regions. It was shown that a specific ion effect according to the Hofmeister series is clearly demonstrated for the visible range of spectra. For the near-, mid-, and far UV ranges of spectra, the specific ion effect essentially depends on solution concentration and temperature. The influence of ions on the behavior of dynamic dielectric permittivity of a solution is discussed on the basis of ion/water and ion/ion electrostatic and electrodynamic interactions and hydration shell structure.

  15. Electrical conductivity, dielectric response and space charge dynamics of an electroactive polymer with and without nanofiller reinforcement

    NASA Astrophysics Data System (ADS)

    Kochetov, R.; Tsekmes, I. A.; Morshuis, P. H. F.

    2015-07-01

    Electroactive polymers have gained considerable attention over the last 20 years for exhibiting a large displacement in response to electrical stimulation. The promising fields of application include wave energy converters, muscle-like actuators, sensors, robotics, and biomimetics. For an electrical engineer, electroactive polymers can be seen as a dielectric elastomer film or a compliant capacitor with a highly deformable elastomeric medium. If the elastomer is pre-stretched and pre-charged, a reduction of the tensile force lets the elastomer revert to its original form and increases the electrical potential. The light weight of electroactive polymers, low cost, high intrinsic breakdown strength, cyclical way of operation, reliable performance, and high efficiency can be exploited to utilize the elastomeric material as a transducer. The energy storage for a linear dielectric polymer is determined by its relative permittivity and the applied electric field. The latter is limited by the dielectric breakdown strength of the material. Therefore, to generate a high energy density of a flexible capacitor, the film must be used at the voltage level close to the material’s breakdown or inorganic particles with high dielectric permittivity which can be introduced into the polymer matrix. In the present study, silicone-titania elastomer nanocomposites were produced and the influence of nanoparticles on the macroscopic dielectric properties of the neat elastomer including space charge dynamics, complex permittivity, and electrical conductivity, were investigated.

  16. Dielectric properties and frequency response of self-assembled monolayers of alkanethiols.

    PubMed

    Wang, Bing; Luo, Jianglong; Wang, Xiaoping; Wang, Haiqian; Hou, J G

    2004-06-08

    This paper presents dielectric properties of alkanethiol self-assembled monolayers (SAMs) under an ac electric field. Using a Hg-SAM/SAM-Hg junction, we measured the ac impedance of alkanethiol SAMs using a sinusoidal perturbation of 30 mV (peak-to-peak) with frequency ranging from 1 Hz to 1 MHz at zero bias. Semicircles at higher frequencies and at middle frequencies along with Warburg lines at lower frequencies were observed in complex plane impedance plots, that is, Nyquist plots. The frequency response of SAMs was analyzed by modeling the junction using an equivalent circuit and fitting the Nyquist plots. The semicircles at higher frequencies are attributed to the effect of the SAM/SAM interfaces, and the ones at middle frequencies are attributed to the effect of alkanethiol SAMs. The comparison in the plots of the imaginary part of the impedance Z against frequency for the bare Hg electrodes (in pure ethanal) and the SAM-covered Hg electrodes (in alkanethiol solution) supports the analysis. The Warburg lines are attributed to a certain ionic impurity. The dielectric loss spectra are further analyzed. Chain-length-dependent peaks, which correspond to different relaxation mechanisms, at higher frequencies and middle frequencies were observed in the spectra of the dissipation factor (tan delta vs frequency). The peaks move to small frequency with the increase of chain length of alkanethiols. Using a correlation of peak position with the chain length, we then derived active energies of 39-99 meV for alkanethiol SAMs of C7-C18 under an ac electric field.

  17. Theory of tailorable optical response of two-dimensional arrays of plasmonic nanoparticles at dielectric interfaces

    PubMed Central

    Sikdar, Debabrata; Kornyshev, Alexei A.

    2016-01-01

    Two-dimensional arrays of plasmonic nanoparticles at interfaces are promising candidates for novel optical metamaterials. Such systems materialise from ‘top–down’ patterning or ‘bottom–up’ self-assembly of nanoparticles at liquid/liquid or liquid/solid interfaces. Here, we present a comprehensive analysis of an extended effective quasi-static four-layer-stack model for the description of plasmon-resonance-enhanced optical responses of such systems. We investigate in detail the effects of the size of nanoparticles, average interparticle separation, dielectric constants of the media constituting the interface, and the nanoparticle position relative to the interface. Interesting interplays of these different factors are explored first for normally incident light. For off-normal incidence, the strong effects of the polarisation of light are found at large incident angles, which allows to dynamically tune the reflectance spectra. All the predictions of the theory are tested against full-wave simulations, proving this simplistic model to be adequate within the quasi-static limit. The model takes seconds to calculate the system’s optical response and makes it easy to unravel the effect of each system parameter. This helps rapid rationalization of experimental data and understanding of the optical signals from these novel ‘metamaterials’, optimised for light reflection or harvesting. PMID:27652788

  18. Theory of tailorable optical response of two-dimensional arrays of plasmonic nanoparticles at dielectric interfaces.

    PubMed

    Sikdar, Debabrata; Kornyshev, Alexei A

    2016-09-22

    Two-dimensional arrays of plasmonic nanoparticles at interfaces are promising candidates for novel optical metamaterials. Such systems materialise from 'top-down' patterning or 'bottom-up' self-assembly of nanoparticles at liquid/liquid or liquid/solid interfaces. Here, we present a comprehensive analysis of an extended effective quasi-static four-layer-stack model for the description of plasmon-resonance-enhanced optical responses of such systems. We investigate in detail the effects of the size of nanoparticles, average interparticle separation, dielectric constants of the media constituting the interface, and the nanoparticle position relative to the interface. Interesting interplays of these different factors are explored first for normally incident light. For off-normal incidence, the strong effects of the polarisation of light are found at large incident angles, which allows to dynamically tune the reflectance spectra. All the predictions of the theory are tested against full-wave simulations, proving this simplistic model to be adequate within the quasi-static limit. The model takes seconds to calculate the system's optical response and makes it easy to unravel the effect of each system parameter. This helps rapid rationalization of experimental data and understanding of the optical signals from these novel 'metamaterials', optimised for light reflection or harvesting.

  19. Theory of tailorable optical response of two-dimensional arrays of plasmonic nanoparticles at dielectric interfaces

    NASA Astrophysics Data System (ADS)

    Sikdar, Debabrata; Kornyshev, Alexei A.

    2016-09-01

    Two-dimensional arrays of plasmonic nanoparticles at interfaces are promising candidates for novel optical metamaterials. Such systems materialise from ‘top–down’ patterning or ‘bottom–up’ self-assembly of nanoparticles at liquid/liquid or liquid/solid interfaces. Here, we present a comprehensive analysis of an extended effective quasi-static four-layer-stack model for the description of plasmon-resonance-enhanced optical responses of such systems. We investigate in detail the effects of the size of nanoparticles, average interparticle separation, dielectric constants of the media constituting the interface, and the nanoparticle position relative to the interface. Interesting interplays of these different factors are explored first for normally incident light. For off-normal incidence, the strong effects of the polarisation of light are found at large incident angles, which allows to dynamically tune the reflectance spectra. All the predictions of the theory are tested against full-wave simulations, proving this simplistic model to be adequate within the quasi-static limit. The model takes seconds to calculate the system’s optical response and makes it easy to unravel the effect of each system parameter. This helps rapid rationalization of experimental data and understanding of the optical signals from these novel ‘metamaterials’, optimised for light reflection or harvesting.

  20. Small- and strong-signal dielectric response in a single-crystal film of partially deuterated betaine phosphite

    NASA Astrophysics Data System (ADS)

    Balashova, E. V.; Krichevtsov, B. B.; Lemanov, V. V.

    2011-06-01

    Poly- and single-crystal films of betaine phosphite deuterated to ˜20% have been grown by evaporation on NdGaO3 (001) substrates with a preliminarily deposited planar interdigital structure of electrodes. The small-signal dielectric response in the 0.1-100.0-kHz frequency range has revealed a strong anomaly in capacitance upon the transition of the films to the ferroelectric state. Application of a bias field brings about suppression and a slight shift of the dielectric anomaly toward higher temperatures. The strong-signal dielectric response has been studied by the Sawyer-Tower method over the frequency range 0.06-3.00 kHz both in the para- and ferroelectric phases. In contrast to the case of a plane-parallel capacitor, in the planar structure studied, the dielectric hysteresis loops exhibit a very small coercivity at low frequencies, which grows with increasing frequency. This difference should be assigned to different domain structures formed in a planeparallel capacitor and in a planar structure in a saturating field. The growth of hysteresis with increasing frequency in a planar structure is considered to be associated with the domain wall motion.

  1. Colossal Tooling Design: 3D Simulation for Ergonomic Analysis

    NASA Technical Reports Server (NTRS)

    Hunter, Steve L.; Dischinger, Charles; Thomas, Robert E.; Babai, Majid

    2003-01-01

    The application of high-level 3D simulation software to the design phase of colossal mandrel tooling for composite aerospace fuel tanks was accomplished to discover and resolve safety and human engineering problems. The analyses were conducted to determine safety, ergonomic and human engineering aspects of the disassembly process of the fuel tank composite shell mandrel. Three-dimensional graphics high-level software, incorporating various ergonomic analysis algorithms, was utilized to determine if the process was within safety and health boundaries for the workers carrying out these tasks. In addition, the graphical software was extremely helpful in the identification of material handling equipment and devices for the mandrel tooling assembly/disassembly process.

  2. Depolarized light scattering and dielectric response of a peptide dissolved in water

    SciTech Connect

    Martin, Daniel R.; Fioretto, Daniele; Matyushov, Dmitry V.

    2014-01-21

    The density and orientational relaxation of bulk water can be separately studied by depolarized light scattering (DLS) and dielectric spectroscopy (DS), respectively. Here, we ask the question of what are the leading collective modes responsible for polarization anisotropy relaxation (DLS) and dipole moment relaxation (DS) of solutions involving mostly hydrophobic solute-water interfaces. We study, by atomistic molecular dynamics simulations, the dynamics and structure of hydration water interfacing N-Acetyl-leucine-methylamide dipeptide. The DLS response of the solution is consistent with three relaxation processes: bulk water, rotations of single solutes, and collective dipole-induced-dipole polarizability of the solutes, with the time-scale of 130–200 ps. No separate DLS response of the hydration shell has been identified by our simulations. Density fluctuations of the hydration layer, which largely contribute to the response, do not produce a dynamical process distinct from bulk water. We find that the structural perturbation of the orientational distribution of hydration waters by the dipeptide solute is quite significant and propagates ∼3−5 hydration layers into the bulk. This perturbation is still below that produced by hydrated globular proteins. Despite this structural perturbation, there is little change in the orientational dynamics of the hydration layers, compared to the bulk, as probed by both single-particle orientational dynamics and collective dynamics of the dipole moment of the shells. There is a clear distinction between the perturbation of the interfacial structure by the solute-solvent interaction potential and the perturbation of the interfacial dynamics by the corresponding forces.

  3. Surface plasmon response of metal spherical nanoshells coated with dielectric overlayer

    NASA Astrophysics Data System (ADS)

    Cheng, Peihong; Bao, Jilong; Wu, Ligang; Li, Xue; Zhao, Hongxia; Zhu, Renxiang; Wang, Jinxia; Li, Dongsheng

    2013-11-01

    Surface Plasmon Resonance (SPR) characteristics of metal spherical nanoshells coated with different dielectric overlayers were investigated in this Letter. Besides band position, it is found that the line width of the symmetric dipole SP resonance is affected by the overlayer coating when the coupling strength of the inner surface cavity mode and outer surface sphere mode is strong. When the surrounding dielectric constant is comparative to that of core silica, narrowest damping width is expected. The computation results also demonstrate that the quality factors and electromagnetic field distribution are dependent on the overlayer coating. Consequently, an appropriate dielectric overlayer coating may be an important way of tuning SP characteristics of metal nanoshells.

  4. A complete dielectric response model for liquid water: a solution of the Bethe ridge problem.

    PubMed

    Emfietzoglou, Dimitris; Cucinotta, Francis A; Nikjoo, Hooshang

    2005-08-01

    We present a complete yet computationally simple model for the dielectric response function of liquid water over the energy-momentum plane, which, in contrast to earlier models, is consistent with the recent inelastic X-ray scattering spectroscopy data at both zero and finite momentum transfer values. The model follows Ritchie's extended-Drude algorithm and is particularly effective at the region of the Bethe ridge, substantially improving previous models. The present development allows for a more accurate simulation of the inelastic scattering and energy deposition process of low-energy electrons in liquid water and other biomaterials. As an example, we calculate the stopping power of liquid water for electrons over the 0.1-10 keV range where direct experimental measurements are still impractical and the Bethe stopping formula is inaccurate. The new stopping power values are up to 30-40% lower than previous calculations. Within the range of validity of the first Born approximation, the new values are accurate to within the experimental uncertainties (a few percent). At the low end, the introduction of Born corrections raises the uncertainty to perhaps approximately 10%. Thus the present model helps extend the ICRU electron stopping power database for liquid water down to about two orders of magnitude with a comparable level of uncertainty.

  5. Study of the heating effect contribution to the nonlinear dielectric response of a supercooled liquid

    NASA Astrophysics Data System (ADS)

    Brun, C.; Crauste-Thibierge, C.; Ladieu, F.; L'Hôte, D.

    2010-12-01

    We present a detailed study of the heating effects in dielectric measurements carried out on a liquid. Such effects come from the dissipation of the electric power in the liquid and give contribution to the nonlinear third harmonics susceptibility χ _3, which depends on the frequency and temperature. This study is used to evaluate a possible "spurious" contribution to the recently measured nonlinear susceptibility of an archetypical glassforming liquid (glycerol). Those measurements have been shown to give a direct evaluation of the number of dynamically correlated molecules temperature dependence close to the glass transition temperature T_g ≈ 190 K [Crauste-Thibierge et al., Phys. Rev. Lett. 104, 165703 (2010)]. We show that the heating contribution is totally negligible (i) below 204 K at any frequency; (ii) for any temperature at the frequency where the third harmonics response χ _3 is maximum. Besides, this heating contribution does not scale as a function of f/f_{α }, with f_{α }(T) the relaxation frequency of the liquid. In the high frequency range, when f/f_{α } ≥ 1, we find that the heating contribution is damped because the dipoles cannot follow instantaneously the temperature modulation due to the heating phenomenon. An estimate of the magnitude of this damping is given.

  6. Dielectric response of wurtzite gallium nitride in the terahertz frequency range

    NASA Astrophysics Data System (ADS)

    Hibberd, M. T.; Frey, V.; Spencer, B. F.; Mitchell, P. W.; Dawson, P.; Kappers, M. J.; Oliver, R. A.; Humphreys, C. J.; Graham, D. M.

    2016-12-01

    We report on the characterization of the intrinsic, anisotropic, dielectric properties of wurtzite gallium nitride in the spectral range of 0.5-11 THz, using terahertz time-domain spectroscopy. The ordinary (ε˜⊥) and extraordinary (ε˜∥) components of the complex dielectric function were determined experimentally for a semi-insulating, m-plane gallium nitride single crystal, providing measurements of the refractive indices (n⊥,∥) and absorption coefficients (α⊥,∥) . These material parameters were successfully modeled by considering the contribution of the optical phonon modes, measured using Raman spectroscopy, to the dielectric function, giving values for the relative static dielectric constants of ε0⊥ = 9.22 ± 0.02 and ε0∥ = 10.32 ± 0.03 for wurtzite gallium nitride.

  7. Non-debye dielectric response in monolithic layers of silver stearate

    NASA Astrophysics Data System (ADS)

    Kastro, R. A.; Goryaev, M. A.; Smirnov, A. P.

    2017-02-01

    This paper reports on the results of investigations of the electrophysical properties of silver stearate by the methods of dielectric spectroscopy and differential scanning calorimetry (DSC). The mechanisms of charge transfer and dielectric relaxation in silver stearate have been established. It has been found that there is a critical temperature T = 338 K, which is probably related to the low-temperature phase transition in the system under investigation.

  8. Dielectric Response at THz Frequencies of Mg Water Complexes Interacting with O3 Calculated by Density Functional Theory

    DTIC Science & Technology

    2012-10-24

    vibrational modes in the absorption spectra of various materials. A series of studies have focused on the general concept of constructing dielectric response...has a total of 3N-6 normal mode vibrations . The Schrodinger equation for the harmonic oscillations of these normal modes has known solutions. The...and m is the effective mass contributed by those atoms vibrating in the normal mode . A molecule in stable equilibrium is characterized by all

  9. High-performance colossal permittivity materials of (Nb + Er) co-doped TiO2 for large capacitors and high-energy-density storage devices.

    PubMed

    Tse, Mei-Yan; Wei, Xianhua; Hao, Jianhua

    2016-09-21

    The search for colossal permittivity (CP) materials is imperative because of their potential for promising applications in the areas of device miniaturization and energy storage. High-performance CP materials require high dielectric permittivity, low dielectric loss and relatively weak dependence of frequency- and temperature. In this work, we first investigate the CP behavior of rutile TiO2 ceramics co-doped with niobium and erbium, i.e., (Er0.5Nb0.5)xTi1-xO2. Excellent dielectric properties were observed in the materials, including a CP of up to 10(4)-10(5) and a low dielectric loss (tan δ) down to 0.03, which are lower than that of the previously reported co-doped TiO2 CP materials when measured at 1 kHz. Stabilities of frequency and temperature were also accomplished via doping Er and Nb. Valence states of the elements in the material were analyzed using X-ray photoelectron spectroscopy. The Er induced secondary phases were observed using elemental mapping and energy-dispersive spectrometry. Consequently, this work may provide comprehensive guidance to develop high-performance CP materials for fully solid-state capacitor and energy storage applications.

  10. Photo-induced change of dielectric response in BaCoSiO{sub 4} stuffed tridymite

    SciTech Connect

    Taniguchi, Hiroki Okamura, Takuma; Yamamoto, Takafumi; Okazaki, Ryuji; Terasaki, Ichiro; Moriwake, Hiroki; Kuwabara, Akihide; Itoh, Mitsuru

    2014-04-28

    The photodielectric effect is demonstrated in Mott-insulator BaCoSiO{sub 4} with a stuffed-tridymite-type structure under irradiation of visible light at 365 nm. The real part of dielectric permittivity is enhanced by ∼300% with little increase of tan δ in a low-frequency region. Results of diffuse reflectance spectroscopy, first-principles calculations and dielectric measurements suggest that the photodielectric effect stems from a response of photo-excited electrons in an unoccupied upper-Hubbard band for 3d-orbitals of cobalt, which have significantly small mobility due to the unique configuration of Co ions in the stuffed-tridymite-type structure.

  11. Colossal Ultraviolet Photoresponsivity of Few-Layer Black Phosphorus.

    PubMed

    Wu, Jing; Koon, Gavin Kok Wai; Xiang, Du; Han, Cheng; Toh, Chee Tat; Kulkarni, Eeshan S; Verzhbitskiy, Ivan; Carvalho, Alexandra; Rodin, Aleksandr S; Koenig, Steven P; Eda, Goki; Chen, Wei; Neto, A H Castro; Özyilmaz, Barbaros

    2015-08-25

    Black phosphorus has an orthorhombic layered structure with a layer-dependent direct band gap from monolayer to bulk, making this material an emerging material for photodetection. Inspired by this and the recent excitement over this material, we studied the optoelectronics characteristics of high-quality, few-layer black phosphorus-based photodetectors over a wide spectrum ranging from near-ultraviolet (UV) to near-infrared (NIR). It is demonstrated for the first time that black phosphorus can be configured as an excellent UV photodetector with a specific detectivity ∼3 × 10(13) Jones. More critically, we found that the UV photoresponsivity can be significantly enhanced to ∼9 × 10(4) A W(-1) by applying a source-drain bias (VSD) of 3 V, which is the highest ever measured in any 2D material and 10(7) times higher than the previously reported value for black phosphorus. We attribute such a colossal UV photoresponsivity to the resonant-interband transition between two specially nested valence and conduction bands. These nested bands provide an unusually high density of states for highly efficient UV absorption due to the singularity of their nature.

  12. Colossal magnetocaloric effect in magneto-auxetic systems

    NASA Astrophysics Data System (ADS)

    Dudek, M. R.; Wojciechowski, K. W.; Grima, J. N.; Caruana-Gauci, R.; Dudek, K. K.

    2015-08-01

    We show that a mechanically driven magnetocaloric effect (MCE) in magneto-auxetic systems (MASs) in the vicinity of room temperature is possible and the effect can be colossal. Even at zero external magnetic field, the magnetic entropy change in this reversible process can be a few times larger in magnitude than in the case of the giant MCE discovered by Pecharsky and Gschneidner in Gd5(Si2Ge2). MAS represent a novel class of metamaterials having magnetic insertions embedded within a non-magnetic matrix which exhibits a negative Poisson’s ratio. The auxetic behaviour of the non-magnetic matrix may either enhance the magnetic ordering process or it may result in a transition to the disordered phase. In the MAS under consideration, a spin 1/2 system is chosen for the magnetic component and the well-known Onsager solution for the two-dimensional square lattice Ising model at zero external magnetic field is used to show that the isothermal change in magnetic entropy accompanying the auxetic behaviour can take a large value at room temperature. The practical importance of our findings is that MCE materials used in present engineering applications may be further enhanced by changing their geometry such that they exhibit auxetic behaviour.

  13. Spin and orbital order separation in colossal magnetoresistive transition

    NASA Astrophysics Data System (ADS)

    Hossain, M. A.; Burkhardt, M. H.; Weschke, E.; Schierle, E.; Golden, M. S.; Tomioka, Y.; Tokura, Y.; StöHr, J.; D&üRr, H. A.

    2013-03-01

    Understanding the Colossal magnetoresistive (CMR) process in manganites is one of the grand challenges of modern physics. While the metallic ferromagnetic phase is relatively well understood, the triggering mechanism of the metal-insulator transition is not clear and it is believed that lattice strain in term of polarons play an important role in the mysterious insulating phase. Lattice strain occurs in the charge-orbitally ordered insulating phase via the Jahn-Teller type distortion and therefore, to understand the CMR it is critical to understand the interplay of ferromagnetism and orbital order during the CMR transition itself. In this letter, with high magnetic field dependent Resonant Soft X-ray Scattering measurements, we show that during the CMR process, an insulating antiferromagnetic phase, which is extremely susceptible to magnetic field and temperature, directly competes with metallic ferromagnetism while the robust CE type spin and orbitally ordered regions act as a catalyst to seed these antiferromagnetic regions. This allows us to construct a picture of the competing forces at the heart of CMR.

  14. Relaxor-like dielectric response of spin liquid CuCrO{sub 2}

    SciTech Connect

    Mazumder, N. Roy, R.; Ghorai, U. K.; Saha, S.; Chattopadhyay, K. K.

    2014-04-24

    Broadband dielectric analysis (10{sup −2}-10{sup 7} Hz) of layered triangular lattice CuCrO{sub 2} is performed (123 K - 473 K) and analyzed in connection with recently observed spin frustration in this multiferroic [M. Poienar et al. Phys. Rev. B 81, 104411, (2010); M. Frontzek et al. Phys. Rev. B 84, 094448, (2011)]. Most unexpectedly, this well known delafossite has found to have nontrivial charge degrees of freedom, being characterized by a relaxor-like dielectric relaxation around 375 K with FWHM of ∼100K. The result strongly suggests the existence of intermolecular Coulomb interaction between charge disproportionation induced electric dipoles.

  15. Cryogenic temperature relaxor-like dielectric responses and magnetodielectric coupling in Aurivillius Bi5Ti3FeO15 multiferroic thin films

    NASA Astrophysics Data System (ADS)

    Bai, Wei; Yin, Wenhao; Yang, Jing; Tang, Kai; Zhang, Yuanyuan; Lin, Tie; Meng, Xiangjian; Duan, Chun-Gang; Tang, Xiaodong; Chu, Junhao

    2014-08-01

    Dielectric responses and magnetodielectric (MD) behavior of Aurivillius Bi5Ti3FeO15 multiferroics were systemically studied at cryogenic temperatures. Dielectric anomaly at ˜145 K was found by the temperature dependent dielectric spectroscopy, and relaxor-like relaxation dynamics was further confirmed unambiguously. Besides the two abnormal MD transitions at about 98 K and 220 K, remarkable MD couplings were observed near relaxation peak over the whole frequency range of 102-106 Hz. Finally, the possible mechanisms of the relaxation and MD properties were discussed in association with the occurrence of local Fe-O nano-clusters because of the antisite disorder defects in Aurivillius multiferroic phases.

  16. Room-temperature magneto-dielectric response in multiferroic ZnFe2O4/PMN-PT bilayer thin films

    NASA Astrophysics Data System (ADS)

    Garg, T.; Kulkarni, A. R.; Venkataramani, N.

    2016-08-01

    The magneto-dielectric response in multiferroic ZnFe2O4/PMN-PT bilayer thin films prepared on a glass substrate using RF magnetron sputtering has been investigated in this work. PMN-PT thin films (i.e. PMN-PT/LCMO/Pt/Ti/glass) deposited on glass were used as a substrate for deposition of ZnFe2O4 thin films. ZnFe2O4 thin films were annealed ex situ at different temperatures. Structural, magnetic, ferroelectric, dielectric and magneto-dielectric studies were carried out on these multiferroic bilayer thin films. Structural studies revealed the presence of each layer in its respective single phase. Magnetic and ferroelectric studies revealed the ferromagnetic and ferroelectric behaviors of these bilayers. To quantify the magnetoelectric coupling, the dielectric constant of the bilayer was measured at room temperature as a function of frequency with and without the applied magnetic field. The magneto-dielectric response MD(%) was calculated by finding the relative change in dielectric constant at 1 kHz as a percentage. The observed MD response was correlated with magnetization of the ferrite layer. An MD response of 2.60% was found for a bilayer film annealed at 350 °C. At this particular annealing temperature, the ZnFe2O4 layer also has the highest saturation magnetization of 1900 G.

  17. Colossal terahertz nonlinearity of tunneling van der Waals gap (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Bahk, Young-Mi; Kang, Bong Joo; Kim, Yong Seung; Kim, Joon-Yeon; Kim, Won Tae; Kim, Tae Yun; Kang, Taehee; Rhie, Ji Yeah; Han, Sanghoon; Park, Cheol-Hwan; Rotermund, Fabian; Kim, Dai-Sik

    2016-09-01

    We manufactured an array of three angstrom-wide, five millimeter-long van der Waals gaps of copper-graphene-copper composite, in which unprecedented nonlinearity was observed. To probe and manipulate van der Waals gaps with long wavelength electromagnetic waves such as terahertz waves, one is required to fabricate vertically oriented van der Waals gaps sandwiched between two metal planes with an infinite length in the sense of being much larger than any of the wavelengths used. By comparison with the simple vertical stacking of metal-graphene-metal structure, in our structure, background signals are completely blocked enabling all the light to squeeze through the gap without any strays. When the angstrom-sized van der Waals gaps are irradiated with intense terahertz pulses, the transient voltage across the gap reaches up to 5 V with saturation, sufficiently strong to deform the quantum barrier of angstrom gaps. The large transient potential difference across the gap facilitates electron tunneling through the quantum barrier, blocking terahertz waves completely. This negative feedback of electron tunneling leads to colossal nonlinear optical response, a 97% decrease in the normalized transmittance. Our technology for infinitely long van der Waals gaps can be utilized for other atomically thin materials than single layer graphene, enabling linear and nonlinear angstrom optics in a broad spectral range.

  18. Colossal injection of catalyst atoms into silicon nanowires.

    PubMed

    Moutanabbir, Oussama; Isheim, Dieter; Blumtritt, Horst; Senz, Stephan; Pippel, Eckhard; Seidman, David N

    2013-04-04

    The incorporation of impurities during the growth of nanowires from the vapour phase alters their basic properties substantially, and this process is critical in an extended range of emerging nanometre-scale technologies. In particular, achieving precise control of the behaviour of group III and group V dopants has been a crucial step in the development of silicon (Si) nanowire-based devices. Recently it has been demonstrated that the use of aluminium (Al) as a growth catalyst, instead of the usual gold, also yields an effective p-type doping, thereby enabling a novel and efficient route to functionalizing Si nanowires. Besides the technological implications, this self-doping implies the detachment of Al from the catalyst and its injection into the growing nanowire, involving atomic-scale processes that are crucial for the fundamental understanding of the catalytic assembly of nanowires. Here we present an atomic-level, quantitative study of this phenomenon of catalyst dissolution by three-dimensional atom-by-atom mapping of individual Al-catalysed Si nanowires using highly focused ultraviolet-laser-assisted atom-probe tomography. Although the observed incorporation of the catalyst atoms into nanowires exceeds by orders of magnitude the equilibrium solid solubility and solid-solution concentrations in known non-equilibrium processes, the Al impurities are found to be homogeneously distributed in the nanowire and do not form precipitates or clusters. As well as the anticipated effect on the electrical properties, this kinetics-driven colossal injection also has direct implications for nanowire morphology. We discuss the observed strong deviation from equilibrium using a model of solute trapping at step edges, and identify the key growth parameters behind this phenomenon on the basis of a kinetic model of step-flow growth of nanowires. The control of this phenomenon provides opportunities to create a new class of nanoscale devices by precisely tailoring the shape and

  19. Joining Chemical Pressure and Epitaxial Strain to Yield Y-doped BiFeO3 Thin Films with High Dielectric Response

    PubMed Central

    Scarisoreanu, N. D.; Craciun, F.; Birjega, R.; Ion, V.; Teodorescu, V. S.; Ghica, C.; Negrea, R.; Dinescu, M.

    2016-01-01

    BiFeO3 is one of the most promising multiferroic materials but undergoes two major drawbacks: low dielectric susceptibility and high dielectric loss. Here we report high in-plane dielectric permittivity (ε’ ∼2500) and low dielectric loss (tan δ < 0.01) obtained on Bi0.95Y0.05FeO3 films epitaxially grown on SrTiO3 (001) by pulsed laser deposition. High resolution transmission electron microscopy and geometric phase analysis evidenced nanostripe domains with alternating compressive/tensile strain and slight lattice rotations. Nanoscale mixed phase/domain ensembles are commonly found in different complex materials with giant dielectric/electromechanical (ferroelectric/ relaxors) or magnetoresistance (manganites) response. Our work brings insight into the joined role of chemical pressure and epitaxial strain on the appearance of nanoscale stripe structure which creates conditions for easy reorientation and high dielectric response, and could be of more general relevance for the field of materials science where engineered materials with huge response to external stimuli are a highly priced target. PMID:27157090

  20. Nanostructure and free volume effects in enhancing the dielectric response of strongly dipolar polymers

    NASA Astrophysics Data System (ADS)

    Dong, Rui; Thakur, Yash; Ranjan, Vivek; Buongiorno Nardelli, Marco; Zhang, Qiming; Bernholc, Jerry

    Materials for capacitive energy storage with high energy density and low loss are desired in many fields. We perform multiscale simulations to investigate several members of the aromatic polyurea family. We find that the disordered structures with misaligned chains have considerably larger dielectric constants, due to significant increase in the free volume, which leads to easier reorientation of dipolar groups in the presence of an electric field. Large segment motion is still not allowed below the glass transition temperature, upholding the very low loss at high field and elevated temperature that we observe experimentally. Optimization of the nanostructure and free volume effects thus provides a new, very promising pathway for the design of high-performance dielectrics for capacitive energy storage.

  1. A multi-physical model of actuation response in dielectric gels

    NASA Astrophysics Data System (ADS)

    Li, Bo; Chang, LongFei; Asaka, Kinji; Chen, Hualing; Li, Dichen

    2016-12-01

    Actuation deformation of a dielectric gel is attributed to: the solvent diffusion, the electrical polarization and material hyperelasticity. A multi-physical model, coupling electrical and mechanical quantities, is established, based on the thermodynamics. A set of constitutive relations is derived as an equation of state for characterization. The model is applied to specific cases as effective validations. Physical and chemical parameters affect the performance of the gel, showing nonlinear deformation and instability. This model offers guidance for engineering application.

  2. Peculiarities of the dielectric response of the silver-modified-zeolite porous microstructure

    NASA Astrophysics Data System (ADS)

    Bunyatova, U.; Ozturk Koc, S.; Orbukh, V. I.; Eyvazova, G. M.; Agamaliev, Z. A.; Lebedeva, N. N.; Koçum, İ. C.; Salamov, B. G.; Ozer, M.

    2016-10-01

    The aim of this study was to characterize electrical conductivity and dielectrical properties of the silver-exchanged zeolite - natural clinoptilolite from Western part of Turkey and Azerbaijan in the range of frequencies from 200 Hz to 1 MHz and at room temperature. For a better understanding the effect of concentration and content of silver in the nanoporous zeolite volume on the conductivity, a study of the dielectric properties of an un-modified and silver-modified zeolite plates with different amounts of Ag ions and Ag nanoparticles is performed. Un-modified and three different types of the silver ion-exchanged modified clinoptilolite plates were prepared. It was found, that with increasing silver concentration, resistance of zeolite plate monotonically decreases at the same time a capacitance is increases. It is suggested an explanation of the observed frequency dependence of the capacitance and resistance of zeolite plates on the silver concentrations may be explain on the basis of an electrode-dielectric interface gap model. At the same time, the observed phenomenon can be explained by considering the fact that with increasing content of silver the conductivity increases. These results show that Ag nanoparticles play significant role for performance improvement in plasma electronic devices with zeolite cathode.

  3. Time-dependent non-equilibrium dielectric response in QM/continuum approaches

    SciTech Connect

    Ding, Feizhi; Lingerfelt, David B.; Li, Xiaosong E-mail: li@chem.washington.edu; Mennucci, Benedetta E-mail: li@chem.washington.edu

    2015-01-21

    The Polarizable Continuum Models (PCMs) are some of the most inexpensive yet successful methods for including the effects of solvation in quantum-mechanical calculations of molecular systems. However, when applied to the electronic excitation process, these methods are restricted to dichotomously assuming either that the solvent has completely equilibrated with the excited solute charge density (infinite-time limit), or that it retains the configuration that was in equilibrium with the solute prior to excitation (zero-time limit). This renders the traditional PCMs inappropriate for resolving time-dependent solvent effects on non-equilibrium solute electron dynamics like those implicated in the instants following photoexcitation of a solvated molecular species. To extend the existing methods to this non-equilibrium regime, we herein derive and apply a new formalism for a general time-dependent continuum embedding method designed to be propagated alongside the solute’s electronic degrees of freedom in the time domain. Given the frequency-dependent dielectric constant of the solvent, an equation of motion for the dielectric polarization is derived within the PCM framework and numerically integrated simultaneously with the time-dependent Hartree fock/density functional theory equations. Results for small molecular systems show the anticipated dipole quenching and electronic state dephasing/relaxation resulting from out-of-phase charge fluctuations in the dielectric and embedded quantum system.

  4. Dielectric response of II-VI semiconductor core-shell ensembles: Study of the lossless optical condition

    NASA Astrophysics Data System (ADS)

    de la Cruz, R. M.; Kanyinda-Malu, C.

    2014-09-01

    We theoretically investigate optical properties of II-VI core-shell distribution mixtures made of two type-I sized-nanoshells as a plausible negative dielectric function material. The nonlocal optical response of the semiconductor QD is described by using a resonant excitonic dielectric function, while the shell response is modeled with Demangeot formula. Achieving the zero-loss at an optical frequency ω, i.e., ɛeff =ɛeff‧ + iɛeff″ with ɛeff‧ < 0 and ɛeff″ = 0, is of fundamental importance in nanophotonics. Resonant states in semiconductors provide a source for negative dielectric function provided that the dipole strength and the oscillator density are adequate to offset the background. Furthermore, the semiconductor offers the prospect of pumping, either optically or electrically, to achieve a gain mechanism that can offset the loss. We analyse optimal conditions that must be satisfied to achieve semiconductor-based negative index materials. By comparing with II-VI semiconductor quantum dots (QDs) previously reported in the literature, the inclusion of phonon and shell contributions in the ɛeff along with the finite barrier Effective Mass Approximation (EMA) approach, we found similar qualitative behaviours for the ɛeff. The lossless optical condition along with ɛeff‧ < 0 is discussed in terms of sizes, volume fractions and embedding medium of the mixtures' distributions. Furthermore, we estimated optical power to maintain nanocrystals density in excited states and this value is less than that previously obtained in II-VI semiconductor QDs.

  5. Impedance response and dielectric relaxation in co-precipitation derived ferrite (Ni,Zn)Fe2O4 ceramics

    NASA Astrophysics Data System (ADS)

    Chen, D. G.; Tang, X. G.; Liu, Q. X.; Jiang, Y. P.; Ma, C. B.; Li, R.

    2013-06-01

    Dielectric spectra and magnetization hysteresis loops were used to investigate the grain size effect with temperature on the electrical and magnetic response of co-precipitation derived spinel (Ni0.5Zn0.5)Fe2O4 (NZFO) ceramics. Remarkable dielectric relaxation phenomena of non-Debye type have been observed in each NZFO ceramics as confirmed by two kinds of Cole-Cole plots of the 1100 °C sintered samples, mainly due to the electron-hopping mechanism between n-type and p-type carriers and interfacial ion effect when applied an increase of temperature. The high and low response of grain and grain-boundary regions were determined by modeling the impedance experimental results on two equivalent RC circuits taking into account grain deep trap states. By employing the modified Arrhenius equation, activation energy values of different sintering temperatures were calculated and analyzed in combination with oxygen vacancy. In addition, the magnetization of various sintering temperature samples is dominated by cation distribution and surface effect in different particle ranges.

  6. Temperature dependence of the dielectric response of anodized Al-Al2O3-metal capacitors

    NASA Astrophysics Data System (ADS)

    Hickmott, T. W.

    2003-03-01

    The temperature dependence of capacitance, CM, and conductance, GM, of Al-Al2O3-metal capacitors with Cu, Ag, and Au electrodes has been measured between 100 and 340 K at seven frequencies between 10 kHz and 1 MHz. Al2O3 films between 15 and 64 nm thick were formed by anodizing evaporated Al films in borate-glycol or borate-H2O electrolyte. The interface capacitance at the Al2O3-metal interface, CI, which is in series with the capacitance CD due to the Al2O3 dielectric, is determined from plots of 1/CM versus insulator thickness. CI is not fixed for a given metal-insulator interface but depends on the vacuum system used to deposit the metal electrode. CI is nearly temperature independent. When CI is taken into account the dielectric constant of Al2O3 determined from capacitance measurements is ˜8.3 at 295 K. The dielectric constant does not depend on anodizing electrolyte, insulator thickness, metal electrode, deposition conditions for the metal electrode or measurement frequency. By contrast, GM of Al-Al2O3-metal capacitors depends on both the deposition conditions of the metal and on the metal. For Al-Al2O3-Cu capacitors, GM is larger for capacitors with large values of 1/CI that result when Cu is evaporated in an oil-pumped vacuum system. For Al-Al2O3-Ag capacitors, GM does not depend on the Ag deposition conditions.

  7. Terahertz dielectric response of photoexcited carriers in Si revealed via single-shot optical-pump and terahertz-probe spectroscopy

    SciTech Connect

    Minami, Yasuo; Horiuchi, Kohei; Masuda, Kaisei; Takeda, Jun; Katayama, Ikufumi

    2015-10-26

    We have demonstrated accurate observations of terahertz (THz) dielectric response due to photoexcited carriers in a Si plate via single-shot optical-pump and THz-probe spectroscopy. In contrast to conventional THz time-domain spectroscopy, this spectroscopic technique allows single-shot detection of the THz response of materials at a given delay time between the pump and THz pulses, thereby sufficiently extending the time interval between the pump pulses. As a result, we can accurately measure the dielectric properties of materials, while avoiding artifacts in the response caused by the accumulation of long-lived photoexcited carriers. Using our single-shot scheme, the transmittance of a Si plate was measured in the range of 0.5–2.5 THz with different pump fluences. Based on a Drude model analysis, the optically induced complex dielectric constant, plasma frequency, and damping rate in the THz region were quantitatively evaluated.

  8. Broadband effective magnetic response of inorganic dielectric resonator-based metamaterial for microwave applications

    NASA Astrophysics Data System (ADS)

    Yahiaoui, R.; Chung, U.-C.; Burokur, S. N.; de Lustrac, A.; Elissalde, C.; Maglione, M.; Vigneras, V.; Mounaix, P.

    2014-03-01

    A single-sized dielectric cylinder-based metamaterial is fabricated from TiO2 nanoparticles, using a bottom-up approach. The sub-elements constituting the metalayer are embedded in a nonmagnetic transparent host matrix in the microwave regime and arranged in a square lattice. We demonstrate numerically and experimentally a broadband magnetic activity. The key feature to achieve this performance remains in the high aspect ratio of the metamaterial building blocks. This is a very promising step towards complex electromagnetic functions, involving low-cost metamaterials with simple fabrication.

  9. Experimental study on the dielectric properties of polyacrylate dielectric elastomer

    NASA Astrophysics Data System (ADS)

    Qiang, Junhua; Chen, Hualing; Li, Bo

    2012-02-01

    The dielectric constant of elastomeric dielectric material is an essential physical parameter, whose value may affect the electromechanical deformation of a dielectric elastomer actuator. Since the dielectric constant is influenced by several external factors as reported before, and no certain value has been confirmed to our knowledge, in the present paper, on the basis of systematical comparison of recent past literature, we conducted extensive works on the measurement of dielectric properties of VHB films, involving five influencing factors: prestretch (both equal and unequal biaxial), electrical frequency, electrode material, stress relaxation time and temperature. Experimental results directly show that the dielectric response changes according to these factors, based on which we investigate the significance of each factor, especially the interaction of two external conditions on the dielectric constant of deformable dielectric, by presenting a physical picture of the mechanism of polarization.

  10. Griffiths phase and colossal magnetoresistance in Nd0.5Sr0.5MnO3 oxygen-deficient thin films

    NASA Astrophysics Data System (ADS)

    Solin, N. I.; Korolyov, A. V.; Medvedev, Yu. V.; Nikolaenko, Yu. M.; Khokhlov, V. A.; Prokhorov, A. Yu.; Levchenko, G. G.

    2013-05-01

    This work is devoted to study the influence of the Griffiths phase in colossal magnetoresistance manganites. Griffiths-phase-like behavior of the paramagnetic susceptibility χ0 is observed in Nd0.5Sr0.5MnO3 oxygen-deficient thin films fabricated by magnetron sputtering deposition. In Nd0.5Sr0.5MnO3-δ films with oxygen deficiency for ТG≈260-280 K>T>TC=138 K (ТG and ТС—Griffiths and Curie temperatures, respectively), paramagnetic matrix consists of a magnetic phase with short-range order (˜1-1.5 nm) (which is responsible for the colossal magnetoresistance (CMR) above ТС), and is embedded in this matrix region with long-range ferromagnetic order (≫10 nm), responsible for the Griffiths phase-like behavior of the paramagnetic susceptibility. Electrical resistivity is caused by carrier tunneling between the localized states and obeys the Efros-Shklovskii law. Magnetic resistivity is caused by change of the localized state sizes under the magnetic field. The temperature and magnetic field dependencies of size of the phase inhomogeneity inclusions, found from measurements of magneto-transport properties, can be satisfactorily described by the model of thermodynamic phase separation into metallic droplets of small radius in a paramagnetic matrix. Intrinsic nanoscale inhomogeneities caused by thermodynamic phase separation, rather than the Griffiths phase, determine the electrical resistivity and colossal magnetoresistance of the films. In half-doped manganites, the nature of long-range ordered magnetic phases may be related, besides the chemical heterogeneity, to proximity to a ferromagnetic-antiferromagnetic boundary at the phase diagram as well. The results are in good agreement with the model of existence of an analog of Griffiths phase temperature in half-doped manganites.

  11. Enhanced dielectric and piezoelectric responses in Zn1-xMgxO thin films near the phase separation boundary

    NASA Astrophysics Data System (ADS)

    Kang, Xiaoyu; Shetty, Smitha; Garten, Lauren; Ihlefeld, Jon F.; Trolier-McKinstry, Susan; Maria, Jon-Paul

    2017-01-01

    Dielectric and piezoelectric properties for Zn1-xMgxO (ZMO) thin films are reported as a function of MgO composition up to and including the phase separation region. Zn1-xMgxO (0.25 ≤ x ≤ 0.5) thin films with c-axis textures were deposited by pulsed laser deposition on platinized sapphire substrates. The films were phase pure wurtzite for MgO concentrations up to 40%; above that limit, a second phase with rocksalt structure evolves with strong {100} texture. With increasing MgO concentration, the out-of-plane (d33,f) and in-plane (e31,f) piezoelectric coefficients increase by 360% and 290%, respectively. The increase in piezoelectric coefficients is accompanied by a 35% increase in relative permittivity. Loss tangent values fall monotonically with increasing MgO concentration, reaching a minimum of 0.001 for x ≥ 0.30, at which point the band gap is reported to be 4 eV. The enhanced piezoelectric response, the large band gap, and the low dielectric loss make Zn1-xMgxO an interesting candidate for thin film piezoelectric devices, and demonstrate that compositional phase transformations provide opportunities for property engineering.

  12. Enhanced dielectric and piezoelectric responses in Zn1-xMgxO thin films near the phase separation boundary

    DOE PAGES

    Kang, Xiaoyu; Shetty, Smitha; Garten, Lauren; ...

    2017-01-23

    Dielectric and piezoelectric properties for Zn1-xMgxO (ZMO) thin films are reported as a function of MgO composition up to and including the phase separation region. Zn1-xMgxO (0.25 ≤ x ≤ 0.5) thin films with c-axis textures were deposited by pulsed laser deposition on platinized sapphire substrates. The films were phase pure wurtzite for MgO concentrations up to 40%; above that limit, a second phase with rocksalt structure evolves with strong {100} texture. With increasing MgO concentration, the out-of-plane (d33,f) and in-plane (e31,f) piezoelectric coefficients increase by 360% and 290%, respectively. The increase in piezoelectric coefficients is accompanied by a 35%more » increase in relative permittivity. Loss tangent values fall monotonically with increasing MgO concentration, reaching a minimum of 0.001 for x ≥ 0.30, at which point the band gap is reported to be 4 eV. As a result, the enhanced piezoelectric response, the large band gap, and the low dielectric loss make Zn1-xMgxO an interesting candidate for thin film piezoelectric devices, and demonstrate that compositional phase transformations provide opportunities for property engineering.« less

  13. The ac-magnetic susceptibility and dielectric response of complex spin ordering processes in Mn₃O₄

    SciTech Connect

    Thota, Subhash E-mail: wilfrid.prellier@ensicaen.fr; Singh, Kiran; Simon, Ch.; Prellier, Wilfrid E-mail: wilfrid.prellier@ensicaen.fr; Nayak, Sanjib; Kumar, Jitendra

    2014-09-14

    We report a meticulous study of the ac-magnetization dynamics (χ{sub ac}(T)), relative dielectric permittivity ε{sub r}(T), and magneto-dielectric (Δε{sub r}/ε{sub r}(H)) response of various complex magnetic transitions that occur below the ferrimagnetic Néel temperature T{sub N} of Mn₃O₄. Besides the known sequence of transitions at T{sub N}~42.75 K, T₁~39 K, and T₂~34 K, the existence of a new anomaly reported recently at 38 K (T*) has been successfully probed by χ{sub ac}(T) and ε{sub r}(T) measurements. The effect of external dc-bias fields (H{sub DC}) and driving frequency (f) on the above mentioned transitions has been investigated in consonance with the ε{sub r}(T) and Δε{sub r}/ε{sub r}(T,H) results. For the first time, we observed a clear hysteresis of about 5.15 K in the zero-field ε{sub r}(T) across the incommensurate-to-commensurate transition T₂~34 K, which provides evidence to the first-order nature of this transition. The Arrott plot (H/M vs. M²}) criterion has been used to distinguish the nature of all the sequential transitions that take place below T{sub N}.

  14. Slow dielectric response of Debye-type in water and other hydrogen bonded liquids

    NASA Astrophysics Data System (ADS)

    Jansson, Helén; Bergman, Rikard; Swenson, Jan

    2010-05-01

    The slow dynamics of some hydrogen bonded glass-forming liquids has been investigated by broadband dielectric spectroscopy. We show that the polyalcohols glycerol, xylitol, and sorbitol, and mixtures of glycerol and water, and in fact, even pure water exhibit a process of Debye character at longer time-scales than the glass transition and viscosity related α-relaxation. Even if it is less pronounced, this process displays many similarities to the well-studied Debye-like process in monoalcohols. It can be observed in both the negative derivative of the real part of the permittivity or in the imaginary part of the permittivity, if the conductivity contribution is reduced. In the present study the conductivity contribution has been suppressed by use of a thin Teflon film placed between the sample and one of the electrodes. The new findings might have important implications for the structure and dynamics of hydrogen bonded liquids in general, and for water in particular.

  15. Propagation of electromagnetic waves in stratified media with nonlinearity in both dielectric and magnetic responses.

    PubMed

    Kim, Kihong; Phung, D K; Rotermund, F; Lim, H

    2008-01-21

    We develop a generalized version of the invariant imbedding method, which allows us to solve the electromagnetic wave equations in arbitrarily inhomogeneous stratified media where both the dielectric permittivity and magnetic permeability depend on the strengths of the electric and magnetic fields, in a numerically accurate and efficient manner. We apply our method to a uniform nonlinear slab and find that in the presence of strong external radiation, an initially uniform medium of positive refractive index can spontaneously change into a highly inhomogeneous medium where regions of positive or negative refractive index as well as metallic regions appear. We also study the wave transmission properties of periodic nonlinear media and the influence of nonlinearity on the mode conversion phenomena in inhomogeneous plasmas. We argue that our theory is very useful in the study of the optical properties of a variety of nonlinear media including nonlinear negative index media fabricated using wires and split-ring resonators.

  16. Dielectric response of pure and doped-GaSe crystals studied by an indigenously developed broadband THz-TDS system

    NASA Astrophysics Data System (ADS)

    Das, Amit C.; Bhattacharya, S.; Mandal, K. C.; Mondal, S.; Jewariya, M.; Ozaki, T.; Bhaktha, S. N. B.; Datta, P. K.

    2016-04-01

    Publisher's Note: This paper, originally published on 12 July 2016, was replaced with a corrected/revised version on 26 July 2016. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance. We have developed a terahertz time domain spectroscopy system (THz TDS). For THz generation, optical rectification process and for detection, electro-optic sampling processes are used. Identical < 110 > cut ZnTe crystals are used for both generation and detection of THz radiation.This spectroscopy system can be used for the noninvasive and contactless electrical and optical characterizations of various samples. In this work spectroscopic measurements of pure, Chromium and Indium doped GaSe crystals within 0.4 THz to 3 THz range are taken by the developed set-up to study the dielectric response of the samples.

  17. Strong domain configuration dependence of the nonlinear dielectric response in (K,Na)NbO{sub 3}-based ceramics

    SciTech Connect

    Huan, Yu; Wang, Xiaohui Li, Longtu; Koruza, Jurij

    2015-11-16

    The nonlinear dielectric response in (Na{sub 0.52}K{sub 0.4425}Li{sub 0.0375})(Nb{sub 0.92−x}Ta{sub x}Sb{sub 0.08})O{sub 3} ceramics with different amounts of Ta was measured using subcoercive electric fields and quantified by the Rayleigh model. The irreversible extrinsic contribution, mainly caused by the irreversible domain wall translation, was strongly dependent on the domain configuration. The irreversible extrinsic contributions remained approximately the same within the single-phase regions, either orthorhombic or tetragonal, due to the similar domain morphology. However, in the polymorphic phase transition region, the domain wall density was increased by minimized domain size, as observed by transmission electron microscopy. This resulted in constrained domain wall motion due to self-clamping and reduced the irreversible extrinsic contribution.

  18. Spectroscopic and dielectric response of zinc bismuth phosphate glasses as a function of chromium content

    SciTech Connect

    Rao, P. Srinivasa; Babu, P. Ramesh; Vijay, R.; Narendrudu, T.; Veeraiah, N.; Rao, D. Krishna

    2014-09-15

    Graphical abstract: 20ZnF{sub 2}–(20 − x)Bi{sub 2}O{sub 3}–60P{sub 2}O{sub 5}:xCr{sub 2}O{sub 3} (0 ≤ x ≤2 mol%) glasses are prepared by melt quenching technique. The optical absorption spectra of present glasses are analyzed as a function of chromium content. The absorption bands are assigned to {sup 4}A{sub 2g}(F) ⟶ {sup 4}T{sub 1g}(F), {sup 4}A{sub 2g}(F) ⟶ {sup 4}T{sub 2g}(F), {sup 4}A{sub 2g}(F) ⟶ {sup 2}T{sub 1g}(G) and {sup 4}A{sub 2g}(F) ⟶ {sup 2}E{sub g}(G) transitions of Cr{sup 3+} ions. - Highlights: • ZnF{sub 2}–Bi{sub 2}O{sub 3}–P{sub 2}O{sub 5}:Cr{sub 2}O{sub 3} glasses were prepared by melt quenching and annealing. • Spectroscopic and dielectric properties of chromium ions were investigated. • ESR and optical absorption spectra indicate the co-existence of Cr{sup 6+} ions with Cr{sup 5+} ions and Cr{sup 3+} ions. • Cr{sup 3+} ions act as modifiers and influence the semiconducting nature of the glass system. - Abstract: 20ZnF{sub 2}–(20 − x)Bi{sub 2}O{sub 3}–60P{sub 2}O{sub 5}:xCr{sub 2}O{sub 3} (0 ≤ x ≤2 mol%) glasses are prepared by melt quenching technique. Amorphous nature of these samples is confirmed by X-ray diffraction (XRD) analysis. FTIR study reveals bands due to CrO{sub 6}(o{sub d}) and CrO{sub 4}{sup 2−}(T{sub d}) units along with conventional phosphate groups. The optical absorption and ESR studies of present glasses are analyzed as a function of chromium content. The absorption bands are assigned to {sup 4}A{sub 2g}(F) ⟶ {sup 4}T{sub 1g}(F), {sup 4}A{sub 2g}(F) ⟶ {sup 4}T{sub 2g}(F), {sup 4}A{sub 2g}(F) ⟶ {sup 2}T{sub 1g}(G) and {sup 4}A{sub 2g}(F) ⟶ {sup 2}E{sub g}(G) transitions of Cr{sup 3+} ions. The highest concentration of Cr{sup 3+} ions (in octahedral sites, with network modifying positions) is found in the sample with 2.0 mol% of Cr{sub 2}O{sub 3}. The analysis of dielectric properties indicates a gradual increase in semiconducting character with increase in the concentration of

  19. Dielectric Response to Impurity Ions in GALLIUM(1 -X)ALUMINUM(X)ARSENIDE/GALLIUM-ARSENIDE/GALLIUM(1- X)aluminum(x) Arsenide Quantum Wells.

    NASA Astrophysics Data System (ADS)

    Elabsy, Abdelsalam Mohamed

    The present work considers the dielectric response to donor and acceptor ions by the valence electrons in GaAs quantum wells (QWs) of infinite and finite depths. It is found that, as far as the binding energy for a donor is concerned, the dielectric response of the GaAs QWs leads to deviations with respect to the hydrogenic theory. The effect of the nonparabolicity of the GaAs conduction band on the binding energy for a hydrogenic donor placed at on- and off-center positions in a GaAs QW, leads to substantially enhanced binding. A model of the kinetic energy operator, adapted by Morrow and Brownstein for an electron in the presence of an abrupt heterojunction, has also been used to calculate the binding energy for a donor placed at the center of the GaAs QW. It is found that the binding energy considering the linearized screening theory is larger than that for the hydrogenic theory. It is also found that an acceptor ion binding a heavy hole is much more affected by the dielectric response of the valence electrons of the GaAs than that associated with a light hole. It is clear from this work that consideration of the dielectric response of the valence electrons of a GaAs QW is an important factor in investigating the energy states of impurities.

  20. Instantaneous charge and dielectric response to terahertz pulse excitation in TTF-CA

    NASA Astrophysics Data System (ADS)

    Gomi, Hiroki; Yamagishi, Naoto; Mase, Tomohito; Inagaki, Takeshi J.; Takahashi, Akira

    2017-03-01

    We present the results of exact numerical calculations of the dielectric properties of tetrathiafulvalene-p -chloranil (TTF-CA) using the extended Hubbard model. The electronic polarization P¯el of the ionic ground state is obtained by directly calculating the adiabatic flow of current. The direction of P¯el is opposite to polarization P¯ion owing to ionic displacement, and | P¯el| is much larger than | P¯ion| , showing that, in the ionic phase, TTF-CA is an electric ferroelectric. Furthermore, we numerically calculate the dynamics induced by THz pulse excitation. In the ionic phase, there exists an almost exact linear relationship between Δ ρ (t ) and E (t ) , and between Δ Pel(t ) and E (t ) in the realistic range of the excitation magnitude, where Δ ρ (t ) [Δ Pel(t ) ] is the charge transfer (electric polarization) variation induced by the THz pulse and E (t ) is the electric field of the pulse at time t . The absolute value of Δ ρ (t ) in the neutral phase is much smaller than that in the ionic phase. These results are consistent with those of experiments and originate from the adiabatic nature of the THz pulse excited state.

  1. Dielectric Response of a Quantum Dot Measured with an Aluminum Single Electron Transistor

    NASA Astrophysics Data System (ADS)

    Berman, D.; Zhitenev, N. B.; Ashoori, R. C.; Melloch, M. R.

    1997-03-01

    We demonstrate the first use of an aluminum single electron transistor (SET) as a charge sensor coupled to a semiconductor structure. A quantum dot is electrostatically defined with metal gates on top of a GaAs/AlGaAs heterostructure. The SET functions both as one of the defining gates for the quantum dot and as an electrometer. The quantum dot acts as a dielectric between two capacitor plates, one of which is the SET, and the other is an opposing gate to which we apply an ac excitation and a dc voltage V_g. We vary the conductance of a single tunnel barrier (resistances in the range of 10^3-10^12 Ω) which connects the dot to a charge reservoir and measure the capacitance C between the opposing gate and the SET. Due to the effect of screening, C(V_g) displays periodically occurring dips for those Vg at which a single electron can move in and out of the dot. The oscillations are gradually washed out as the coupling strength to the lead increases beyond 2e^2/h. For sufficiently small couplings, electrons do not tunnel into the dot during one cycle of ac excitation. Surprisingly, the capacitance of such an effectively sealed dot also displays oscillations with electron number. These however are opposite in sign to the oscillations seen for moderate coupling.

  2. Control-focused, nonlinear and time-varying modelling of dielectric elastomer actuators with frequency response analysis

    NASA Astrophysics Data System (ADS)

    Jacobs, William R.; Wilson, Emma D.; Assaf, Tareq; Rossiter, Jonathan; Dodd, Tony J.; Porrill, John; Anderson, Sean R.

    2015-05-01

    Current models of dielectric elastomer actuators (DEAs) are mostly constrained to first principal descriptions that are not well suited to the application of control design due to their computational complexity. In this work we describe an integrated framework for the identification of control focused, data driven and time-varying DEA models that allow advanced analysis of nonlinear system dynamics in the frequency-domain. Experimentally generated input-output data (voltage-displacement) was used to identify control-focused, nonlinear and time-varying dynamic models of a set of film-type DEAs. The model description used was the nonlinear autoregressive with exogenous input structure. Frequency response analysis of the DEA dynamics was performed using generalized frequency response functions, providing insight and a comparison into the time-varying dynamics across a set of DEA actuators. The results demonstrated that models identified within the presented framework provide a compact and accurate description of the system dynamics. The frequency response analysis revealed variation in the time-varying dynamic behaviour of DEAs fabricated to the same specifications. These results suggest that the modelling and analysis framework presented here is a potentially useful tool for future work in guiding DEA actuator design and fabrication for application domains such as soft robotics.

  3. Origin of soft-mode stiffening and reduced dielectric response in SrTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Ostapchuk, T.; Petzelt, J.; Železný, V.; Pashkin, A.; Pokorný, J.; Drbohlav, I.; Kužel, R.; Rafaja, D.; Gorshunov, B. P.; Dressel, M.; Ohly, Ch.; Hoffmann-Eifert, S.; Waser, R.

    2002-12-01

    The problem of the reduced dielectric response in thin films of high-permittivity materials is analyzed by studying the soft-mode response in several SrTiO3 thin films by means of Fourier transform far infrared, monochromatic submillimeter, and micro-Raman spectroscopies. A 300-nm-thick metalorganic chemical vapor deposition film, quasiepitaxially grown on a (0001) sapphire substrate with a perfect <111> orientation, displays a ferroelectric transition near 125 K induced by a tensile residual stress, appearing apparently simultaneously with the antiferrodistortive transition. On the other hand, polycrystalline chemical solution deposition films grown on (0001) sapphire, and also tensile stressed, show a harder soft mode response without the appearance of macroscopic ferroelectricity. This effect, which increases with the film thickness, is explained by a strong depolarizing field induced by the percolated porosity and cracks (in the 10-nm scale) along the boundaries of columnar grains (normal to the probe field direction). Brick-wall model calculations showed that 0.2 vol. % of such a porosity type reduces the permittivity from 30000 to less than 1000. The activation of the forbidden IR modes in the Raman spectra in the whole 80-300-K temperature range studied is explained by the effect of polar grain boundaries, in analogy with the bulk ceramics.

  4. Model of dissipative dielectric elastomers

    NASA Astrophysics Data System (ADS)

    Chiang Foo, Choon; Cai, Shengqiang; Jin Adrian Koh, Soo; Bauer, Siegfried; Suo, Zhigang

    2012-02-01

    The dynamic performance of dielectric elastomer transducers and their capability of electromechanical energy conversion are affected by dissipative processes, such as viscoelasticity, dielectric relaxation, and current leakage. This paper describes a method to construct a model of dissipative dielectric elastomers on the basis of nonequilibrium thermodynamics. We characterize the state of the dielectric elastomer with kinematic variables through which external loads do work, and internal variables that measure the progress of the dissipative processes. The method is illustrated with examples motivated by existing experiments of polyacrylate very-high-bond dielectric elastomers. This model predicts the dynamic response of the dielectric elastomer and the leakage current behavior. We show that current leakage can be significant under large deformation and for long durations. Furthermore, current leakage can result in significant hysteresis for dielectric elastomers under cyclic voltage.

  5. Spin relaxation signature of colossal magnetic anisotropy in platinum atomic chains

    NASA Astrophysics Data System (ADS)

    Bergman, Anders; Hellsvik, Johan; Bessarab, Pavel F.; Delin, Anna

    2016-11-01

    Recent experimental data demonstrate emerging magnetic order in platinum atomically thin nanowires. Furthermore, an unusual form of magnetic anisotropy - colossal magnetic anisotropy (CMA) - was earlier predicted to exist in atomically thin platinum nanowires. Using spin dynamics simulations based on first-principles calculations, we here explore the spin dynamics of atomically thin platinum wires to reveal the spin relaxation signature of colossal magnetic anisotropy, comparing it with other types of anisotropy such as uniaxial magnetic anisotropy (UMA). We find that the CMA alters the spin relaxation process distinctly and, most importantly, causes a large speed-up of the magnetic relaxation compared to uniaxial magnetic anisotropy. The magnetic behavior of the nanowire exhibiting CMA should be possible to identify experimentally at the nanosecond time scale for temperatures below 5 K. This time-scale is accessible in e.g., soft x-ray free electron laser experiments.

  6. Spin relaxation signature of colossal magnetic anisotropy in platinum atomic chains

    PubMed Central

    Bergman, Anders; Hellsvik, Johan; Bessarab, Pavel F.; Delin, Anna

    2016-01-01

    Recent experimental data demonstrate emerging magnetic order in platinum atomically thin nanowires. Furthermore, an unusual form of magnetic anisotropy – colossal magnetic anisotropy (CMA) – was earlier predicted to exist in atomically thin platinum nanowires. Using spin dynamics simulations based on first-principles calculations, we here explore the spin dynamics of atomically thin platinum wires to reveal the spin relaxation signature of colossal magnetic anisotropy, comparing it with other types of anisotropy such as uniaxial magnetic anisotropy (UMA). We find that the CMA alters the spin relaxation process distinctly and, most importantly, causes a large speed-up of the magnetic relaxation compared to uniaxial magnetic anisotropy. The magnetic behavior of the nanowire exhibiting CMA should be possible to identify experimentally at the nanosecond time scale for temperatures below 5 K. This time-scale is accessible in e.g., soft x-ray free electron laser experiments. PMID:27841287

  7. Variation of Topology in Magnetic Bubbles in a Colossal Magnetoresistive Manganite.

    PubMed

    Yu, Xiuzhen; Tokunaga, Yusuke; Taguchi, Yasujiro; Tokura, Yoshinori

    2017-01-01

    The emergence of zero-bias bubbles (≈100 nm in diameter) with various Bloch lines and their triangular lattice is revealed in a colossal magnetoresistive material, La1-x Srx MnO3 , by means of Lorentz transmission electron microscopy (LTEM). The magnetization dynamics, and accompanying changes of the topological number of bubbles via the field-driven motion of the Bloch lines, are demonstrated by in situ LTEM observations.

  8. Microwave responses and general model of nanotetraneedle ZnO: Integration of interface scattering, microcurrent, dielectric relaxation, and microantenna

    NASA Astrophysics Data System (ADS)

    Fang, Xiao-Yong; Cao, Mao-Sheng; Shi, Xiao-Ling; Hou, Zhi-Ling; Song, Wei-Li; Yuan, Jie

    2010-03-01

    Based on the unique geometrical structure of nanotetra-ZnO needle (T-ZnON), we investigate the microwave responses of T-ZnON, including interface scattering, microcurrent attenuation, microantenna radiation, and dielectric relaxation, and build an energy attenuation model. The associated quantitative formula is deduced for calculating the microwave absorption properties of T-ZnON/SiO2 nanocomposite (T-ZnON/SiO2) in the range 8-14 GHz according to the present energy attenuation model. Very good agreement between the calculated and experimental results is obtained in a wide frequency range. The maximum deviation less than 0.5 dB in the range 8-14 GHz is obtained. Using the aforementioned model, we analyze the contribution of microwave responses to the energy attenuation in the frequency range 2-18 GHz, and the results reveal that interface scattering and microcurrent attenuation make the contribution most important. In addition, we calculate the effects of the volume fraction, conductivity, permittivity, needle length of T-ZnON, and thickness of T-ZnON/SiO2 on the reflectivity. The results show that the microwave absorption is evidently dependent on these effect factors, and the optimal microwave absorption band and the strongest microwave absorption peak of T-ZnON/SiO2 would appear when these physical parameters are changed.

  9. Atomic-scale control of TiO6 octahedra through solution chemistry towards giant dielectric response

    PubMed Central

    Hu, Wanbiao; Li, Liping; Li, Guangshe; Liu, Yun; Withers, Ray L.

    2014-01-01

    The structures of many important functional oxides contain networks of metal-oxygen polyhedral units i.e. MOn. The correlation between the configurations and connectivities of these MOn to properties is essentially important to be well established to conduct the design, synthesis and application of new MOn-based functional materials. In this paper, we report on an atomic-scale solution-chemistry approach that for the first time enables TiO6 octahedral network control starting from metastable brookite TiO2 through simultaneously tuning pH values and interfering ions (Fe3+, Sc3+, and Sm3+). The relationship between solution chemistry and the resultant configuration/connectivity of TiO6 octahedra in TiO2 and lepidocrocite titanate is mapped out. Apart from differing crystalline phases and morphologies, atomic-scale TiO6 octahedral control also endows numerous defect dipoles for giant dielectric responses. The structural and property evolutions are well interpreted by the associated H+/OH− species in solution and/or defect states associated with Fe3+ occupation within TiO6 octahedra. This work therefore provides fundamental new insights into controlling TiO6 octahedral arrangement essential for atomic-scale structure-property design. PMID:25301286

  10. Dielectric response of doped Bi12TiO20: Ru crystals in an alternating electric field

    NASA Astrophysics Data System (ADS)

    Avanesyan, V. T.; Paima, K. I.

    2016-08-01

    The results of examination of AC dependences of capacitance and dielectric loss tangent of sillenite Bi12TiO20 crystals doped with ruthenium on frequency are presented. Non-Debye dispersion of dielectric coefficients is found in the frequency interval of 5 × 102-105 Hz, and a resonance phenomenon is observed. Polarization processes in the studied samples are attributed to relaxators associated with metal-oxygen vacancies and structural elements incorporating 6 s 2 lone-pair electrons.

  11. Resonances in the optical response of a slab with time-periodic dielectric function {epsilon}(t)

    SciTech Connect

    Zurita-Sanchez, Jorge R.; Halevi, P.

    2010-05-15

    We demonstrate that the optical response of a periodically modulated dynamic slab exhibits infinite resonances for frequencies {omega}=({Omega}/2)(2l+1), namely, odd multiples of one-half of the modulating frequency {Omega} of the dielectric function {epsilon}(t). These frequencies coincide partially with the usual condition of parametric amplification. However, the resonances occur only for certain normalized slab thicknesses L{sub R}. These resonances follow from detailed numerical studies based on our recent paper [Zurita-Sanchez, Halevi, and Cervantes-Gonzalez, Phys. Rev. A 79, 053821 (2009)]. As the thickness L nearly matches a resonance thickness L{sub R}, the amplitudes of counterpropagating modes in the slab obey a condition implying that both have the same modulus and their phases match a condition related to L{sub R} and the bulk wave vectors. When this condition is met, the electric field profile inside the slab is a superposition of standing waves with odd and even symmetries, and the reflection and transmission coefficients can reach great values and become infinite at exact resonance. Numerical simulations of the optical response are shown for a sinusoidal {epsilon}(t) with either moderate or strong modulation. As expected, as the modulation strength increases, higher-order harmonics {omega}-n{Omega} (n=0,{+-}1,{+-}2,...) become more noticeable, and short-wavelength bulk modes contribute significantly. However, we found that, regardless of the excitation frequency {omega}=({Omega}/2)(2l+1), the dominant spectral component of the generated fields is {Omega}/2. Also, as the excitation frequency increases, the parity of the standing waves is conserved.

  12. Dielectric responses and multirelaxation behaviors of pure and doped CaCu3Ti4O12 ceramics

    NASA Astrophysics Data System (ADS)

    Fang, Liang; Shen, Mingrong; Zheng, Fengang; Li, Zhenya; Yang, Jing

    2008-09-01

    Pure and Co/Fe doped CaCu3Ti4O12 (CCTO) ceramics were prepared by solid state reaction method. The electrical properties of ceramics were found to be dependent on the type of dopant materials. A multirelaxation mechanism should be considered for the common observed (50-200 K) dielectric relaxation of CCTO ceramic. In relatively high temperature range, this relaxation followed the Arrhenius behavior with activation energy of 68 meV, which was ascribed to the Maxwell-Wagner (MW)-type relaxation associated with grains. In lower temperature range, this relaxation exhibited variable-ranger-hopping behavior due to the dipolar effects. The dielectric relaxation mechanism of Co doped CCTO ceramic was similar to that of pure CCTO ceramic, while that of Fe doped CCTO ceramic was quite different. Two dielectric relaxations were identified in the temperature range from 4 to 300 K. A dielectric relaxation at room temperature with an activation energy of 390.3 meV was attributed to the MW-type relaxation associated with grain boundaries. Another dielectric relaxation at low temperatures (100-200 K) with an activation energy of 265 meV was originated from the carrier hopping process between Fe2+ and Fe3+.

  13. Terahertz dielectric response of ferroelectric Ba(x)Sr(1-x)TiO3 thin films.

    PubMed

    Kang, Seung Beom; Kwak, Min Hwan; Choi, Muhan; Kim, Sungil; Kim, Taeyong; Cha, Eun Jong; Kang, Kwang Yong

    2011-11-01

    Terahertz time-domain spectroscopy has been used to investigate the dielectric and optical properties of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films for nominal x-values of 0.4, 0.6, and 0.8 in the frequency range of 0.3 to 2.5 THz. The ferroelectric thin films were deposited at approximately 700 nm thickness on [001] MgO substrate by pulsed laser deposition. The measured complex dielectric and optical constants were compared with the Cole-Cole relaxation model. The results show that the Cole-Cole relaxation model fits well with the data throughout the frequency range and the dielectric relaxation behavior of ferroelectric Ba(x)Sr(1-x)TiO(3) thin films varies with the films compositions. Among the compositions of Ba(x)Sr(1-x)TiO(3) films with different Ba/Sr ratios, Ba(0.6)Sr(0.4)TiO(3) has the highest dielectric constants and the shortest dielectric relaxation time.

  14. Toward carbon-nanotube-based theranostic agents for microwave detection and treatment of breast cancer: enhanced dielectric and heating response of tissue-mimicking materials.

    PubMed

    Mashal, Alireza; Sitharaman, Balaji; Li, Xu; Avti, Pramod K; Sahakian, Alan V; Booske, John H; Hagness, Susan C

    2010-08-01

    The experimental results reported in this paper suggest that single-walled carbon nanotubes (SWCNTs) have the potential to enhance dielectric contrast between malignant and normal tissue for microwave detection of breast cancer and facilitate selective heating of malignant tissue for microwave hyperthermia treatment of breast cancer. In this study, we constructed tissue-mimicking materials with varying concentrations of SWCNTs and characterized their dielectric properties and heating response. At SWCNT concentrations of less than 0.5% by weight, we observed significant increases in the relative permittivity and effective conductivity. In microwave heating experiments, we observed significantly greater temperature increases in mixtures containing SWCNTs. These temperature increases scaled linearly with the effective conductivity of the mixtures. This work is a first step towards the development of functionalized, tumor-targeting SWCNTs as theranostic (integrated therapeutic and diagnostic) agents for microwave breast cancer detection and treatment.

  15. PREFACE: Dielectrics 2011

    NASA Astrophysics Data System (ADS)

    Vaughan, Alun; Lewin, Paul

    2011-08-01

    In 2011, the biennial meeting of the Dielectrics Group of the IOP, Dielectrics 2011, was held for the first time in a number of years at the University of Kent at Canterbury. This conference represents the most recent in a long standing series that can trace its roots back to a two-day meeting that was held in the spring of 1968 at Gregynog Hall of the University of Wales. In the intervening 43 years, this series of meetings has addressed many topics, including dielectric relaxation, high field phenomena, biomaterials and even molecular electronics, and has been held at many different venues within the UK. However, in the early 1990s, a regular venue was established at the University of Kent at Canterbury and, it this respect, this year's conference can be considered as "Dielectrics coming home". The format for the 2011 meeting followed that established at Dielectrics 2009, in breaking away from the concept of a strongly themed event that held sway during the mid 2000s. Rather, we again adopted a general, inclusive approach that was based upon four broad technical areas: Theme 1: Insulation/HV Materials Theme 2: Dielectric Spectroscopy Theme 3: Modelling Dielectric Response Theme 4: Functional Materials The result was a highly successful conference that attracted more than 60 delegates from eight countries, giving the event a truly international flavour, and which included both regular and new attendees; it was particularly pleasing to see the number of early career researchers at the meeting. Consequently, the organizing committee would like to thank our colleagues at the IOP, the invited speakers, our sponsors and all the delegates for making the event such a success. Finally, we look forward to convening again in 2013, when we will be returning to The University of Reading. Prof Alun Vaughan and Prof Paul Lewin, Editors

  16. Ru(4+) induced colossal magnetoimpedance in Ru doped perovskite manganite at room temperature.

    PubMed

    Singh, Brajendra

    2016-05-14

    We have demonstrated Ru(4+) induced colossal magnetoimpedance (MI) at room temperature in a ∼1 Tesla magnetic field with a pulsed laser deposited La0.7Ca0.3Mn0.7Ru0.3O3 thin film. This composition showed a large negative ∼12% MI in the low frequency range (<5 MHz), a colossal positive MI > 120% in the intermediate frequency range (5 MHz to ∼13 MHz) and a negative MI in the high frequency range (∼13 MHz to 40 MHz) at room temperature. XAS data confirmed the predominant Ru valence state was 4+ in La0.7Ca0.3Mn0.7Ru0.3O3. Ru(4+) induced (i) charge carrier localization and (ii) reduced hole carrier density enhances the MI in this composition, which otherwise was not significant in mixed valences Mn(3+)/Mn(4+) containing La0.7Ca0.3MnO3 and Ru(4+)/Ru(5+) and Mn(3+)/Mn(4+) mixed valences containing Ru = 0.1 and Ru = 0.2 compositions in La0.7Ca0.3Mn1-xRuxO3 (0 ≤x≤ 0.3) thin films.

  17. Fast response and low power consumption 1×2 thermo-optic switch based on dielectric-loaded surface plasmon polariton waveguides

    NASA Astrophysics Data System (ADS)

    Qi, Zhipeng; Hu, Guohua; Yun, Binfeng; Zhang, Xiong; Cui, Yiping

    2016-08-01

    In this paper, we present a 1 × 2 thermo-optic (TO) switch based on the integration of the dielectric-loaded surface plasmon polariton (SPP) waveguides with the silicon nanowires. Liquid-curable fluorinated resin (LFR) made of perfluorinated polymer was adopted as the ridge, which has a TO coefficient twice more than that of polymethyl methacrylate, leading to a significant decrease in the power consumption. It was shown that the response time of the dielectric-loaded SPP waveguide could be improved through optimizing the dimensions of the LFR polymer ridge without loss of relative high figure of merit and large confinement factor. Performance characteristics of such a 1 × 2 TO switch operating at a telecom wavelength of 1550 nm was investigated theoretically from the analysis of both heat and optical fields. The results reveal that a switching power as low as 7 mW and an extremely short switching time (with rise time of 3 μs and fall time of 6.7 μs) could be achieved with the proposed dielectric-loaded SPP-based 1 × 2 TO switch. In addition, the crosstalk could be enhanced to at least 40 dB with the applied power of 7 mW at the wavelength of 1550 nm, and it could be retained to be above 20 dB in the wavelength spectrum of 1500-1600 nm during the on/off state.

  18. Toward a better understanding of dielectric responses of van der Waals liquids: The role of chemical structures

    NASA Astrophysics Data System (ADS)

    Jedrzejowska, Agnieszka; Wojnarowska, Zaneta; Adrjanowicz, Karolina; Ngai, K. L.; Paluch, Marian

    2017-03-01

    Exhaustive analysis of dielectric relaxation data of van der Waals glass-forming liquids revealed a strong correlation between the width of the frequency dispersion of the α-relaxation and the dielectric strength Δ ɛ , originating from the dipole-dipole interaction contribution to the intermolecular potential [M. Paluch et al., Phys. Rev. Lett. 116, 025702 (2016)]. The two van der Waals liquids, 4-vinyl-1,3-dioxolan-2-one (VPC) and 4-ethyl-1,3-dioxolan-2-one (EPC), have chemical structures modified from that of propylene carbonate. All three glass-formers have very similar values of dipole moments, exactly the same dielectric strength, and hence identical frequency dispersion of the α-relaxation in all three glass-formers is expected if the correlation holds. Based on this expectation, we performed dielectric relaxation measurements of the VPC and EPC at ambient and elevated pressures. The results obtained show not only identical α-relaxation frequency dispersion for the three glass-formers but also the excess wing which is the unresolved Johari-Goldstein β-relaxation. On the other hand, the other thermodynamics related parameters of the α-relaxation dynamics, including the glass transition temperature Tg, the fragility index mP, and activation volume Δ Va c t, are not uniformly the same for all three glass-formers.

  19. Computationally efficient dielectric calculations of molecular crystals

    SciTech Connect

    Schwarz, Kathleen A.; Sundararaman, Ravishankar; Arias, T. A.

    2015-06-07

    The microscopic dielectric response is a key quantity for electronic materials such as organic semiconductors. Calculations of this response for molecular crystals are currently either expensive or rely on extreme simplifications such as multipole expansions which lack microscopic detail. We present an alternate approach using a microscopic analogue of the Clausius-Mossotti equation, which constructs the dielectric response of a crystal from an eigenvalue decomposition of the dielectric response of individual molecules. This method can potentially be used to examine the effects of defects, disorder, and surfaces on the dielectric properties of molecular solids.

  20. Ultraviolet to near infrared response of optically sensitive nonvolatile memories based on platinum nano-particles and high-k dielectrics on a silicon on insulator substrate

    NASA Astrophysics Data System (ADS)

    Mikhelashvili, V.; Meyler, B.; Shneider, Y.; Yofis, S.; Salzman, J.; Atiya, G.; Cohen-Hyams, T.; Ankonina, G.; Kaplan, W. D.; Lisiansky, M.; Roizin, Y.; Eisenstein, G.

    2013-02-01

    An optically triggered nonvolatile memory based on platinum nano-particles embedded within a SiO2 and HfO2 dielectric stack on a silicon on insulator (SOI) substrate is presented. The memory cell exhibits a very wide spectral response, from 220 nm to 950 nm; much wider than common photo-detectors fabricated on SOI. It offers several functionalities including a low programming voltage and wide hysteresis of the capacitance-voltage characteristics, an illumination and voltage sweep amplitude dependent hysteresis of the current-voltage characteristics, and plasmonic enhanced, efficient broad-band photo detection.

  1. PREFACE: Dielectrics 2013

    NASA Astrophysics Data System (ADS)

    Hadjiloucas, Sillas; Blackburn, John

    2013-11-01

    pleased to express our thanks to the Conference Department of the Institute of Physics for their invaluable support in organizing this event. We are especially grateful to Dawn Stewart for her responsive and day-to-day handling of this conference, as well as Claire Garland for help in planning and managing this international event. We would also like to thank Dr Steve Welch, Director at ESP Central Ltd, representing the interest of the Electronics, Sensors, Photonics Knowledge Transfer Network, as well as Paul Naylor and Susan Matos for their contribution towards the KTN session of the Conference. Finally, we would like to thank Solartron Analytical, Ametek and Princeton Applied Research for demonstrating precision electrochemical impedance spectroscopy measurement techniques at the conference. We hope that the wider Dielectrics community will find these proceedings of interest and will use them as reference text in their future work. Programme committee R Pethig, University of Edinburgh J Blackburn, National Physical Laboratory J Swingler, Heriot Watt University S Hadjiloucas, University of Reading A West, University of Sheffiled M Hughes, University of Surrey S Dodd, University of Leicester D Almond, University of Bath M Cain, National Physical Laboratory D J Swaffield, University of Southampton N Green, University of Southampton A Vaughan, University of Southampton Sillas Hadjiloucas and John Blackburn (Summer 2013)

  2. Coexistence of colossal stress and texture gradients in sputter deposited nanocrystalline ultra-thin metal films

    SciTech Connect

    Kuru, Yener; Welzel, Udo; Mittemeijer, Eric J.

    2014-12-01

    This paper demonstrates experimentally that ultra-thin, nanocrystalline films can exhibit coexisting colossal stress and texture depth gradients. Their quantitative determination is possible by X-ray diffraction experiments. Whereas a uniform texture by itself is known to generally cause curvature in so-called sin{sup 2}ψ plots, it is shown that the combined action of texture and stress gradients provides a separate source of curvature in sin{sup 2}ψ plots (i.e., even in cases where a uniform texture does not induce such curvature). On this basis, the texture and stress depth profiles of a nanocrystalline, ultra-thin (50 nm) tungsten film could be determined.

  3. First Order Colossal Magnetoresistance Transitions in the Two-Orbital Model for Manganites

    SciTech Connect

    Sen, Cengiz; Alvarez, Gonzalo; Dagotto, Elbio R

    2010-01-01

    Large-scale Monte Carlo simulation results for the two-orbital model for manganites, including Jahn- Teller lattice distortions, are presented here. At hole density x 1=4 and in the vicinity of the region of competition between the ferromagnetic metallic and spin-charge-orbital ordered insulating phases, the colossal magnetoresistance (CMR) phenomenon is observed with a magnetoresistance ratio 10 000%. Our main result is that this CMR transition is found to be of first order in some portions of the phase diagram, in agreement with early results from neutron scattering, specific heat, and magnetization, thus solving a notorious discrepancy between experiments and previous theoretical studies. The first order characteristics of the transition survive, and are actually enhanced, when weak quenched disorder is introduced.

  4. Colossal Aggregations of Giant Alien Freshwater Fish as a Potential Biogeochemical Hotspot

    PubMed Central

    Boulêtreau, Stéphanie; Cucherousset, Julien; Villéger, Sébastien; Masson, Rémi; Santoul, Frédéric

    2011-01-01

    The ubiquity and fascinating nature of animal aggregations are widely recognised. We report here consistent and previously undocumented occurences of aggregations of a giant alien freshwater fish, the Wels catfish (Silurus glanis). Aggregative groups were on average composed of 25 (±10 SD, ranging from 15 to 44) adults with estimated average total biomass of 651 kg (386 – 1132) and biomass density of 23 kg m−2 (14 – 40). Aggregations always occurred within the same location. No foraging, reproductive or anti-predator behaviour were observed during the aggregations. A mass-balance model estimated that these colossal aggregations of an alien species can locally release, through excretion only, up to 70 mg P m−2 h−1 and 400 mg N m−2 h−1, potentially representing the highest biogeochemical hotspots reported in freshwater ecosystems and another unexpected ecological effect of alien species. PMID:21998687

  5. Spin correlations and colossal magnetoresistance in HgCr2Se4

    NASA Astrophysics Data System (ADS)

    Lin, Chaojing; Yi, Changjiang; Shi, Youguo; Zhang, Lei; Zhang, Guangming; Müller, Jens; Li, Yongqing

    2016-12-01

    This study aims to unravel the mechanism of colossal magnetoresistance (CMR) observed in n -type HgCr2Se4 , in which low-density conduction electrons are exchange-coupled to a three-dimensional Heisenberg ferromagnet with a Curie temperature TC≈105 K. Near room temperature the electron transport exhibits an ordinary semiconducting behavior. As temperature drops below T*≃2.1 TC , the magnetic susceptibility deviates from the Curie-Weiss law, and concomitantly the transport enters an intermediate regime exhibiting a pronounced CMR effect before a transition to metallic conduction occurs at T

  6. Metal-insulator transition above room temperature in maximum colossal magnetoresistance manganite thin films

    NASA Astrophysics Data System (ADS)

    Chen, X. J.; Habermeier, H.-U.; Zhang, H.; Gu, G.; Varela, M.; Santamaria, J.; Almasan, C. C.

    2005-09-01

    It has been suggested that the maximum magnitude of colossal magnetoresistance occurs in mixed-valent manganites with a tolerance factor t=0.96 [Zhou, Archibald, and Goodenough, Nature (London) 381, 770 (1996)]. However, at t≈0.96 most manganites have relatively low values of the metal-insulator transition temperature TMI(˜60-150K) . Here, we report that a 50 Å La0.9Sr0.1MnO3 thin film with t=0.96 grown on a (100) SrTiO3 substrate has a metal-insulator transition above room temperature, which represents a doubling of TMI compared with its value in the bulk material. We show that this spectacular increase of TMI is a result of the epitaxially compressive strain-induced reduction of the Jahn-Teller distortion.

  7. Colossal magnetoresistance in a Mott insulator via magnetic field-driven insulator-metal transition

    SciTech Connect

    Zhu, M.; Peng, J.; Zou, T.; Prokes, K.; Mahanti, S. D.; Hong, Tao; Mao, Z. Q.; Liu, G. Q.; Ke, X.

    2016-05-25

    Here, we present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca3Ru2O7. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattice-charge coupling. This study further provides a model approach to search for CMR systems other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases.

  8. Origin of colossal magnetoresistance in LaMnO3 manganite.

    PubMed

    Baldini, Maria; Muramatsu, Takaki; Sherafati, Mohammad; Mao, Ho-kwang; Malavasi, Lorenzo; Postorino, Paolo; Satpathy, Sashi; Struzhkin, Viktor V

    2015-09-01

    Phase separation is a crucial ingredient of the physics of manganites; however, the role of mixed phases in the development of the colossal magnetoresistance (CMR) phenomenon still needs to be clarified. We report the realization of CMR in a single-valent LaMnO3 manganite. We found that the insulator-to-metal transition at 32 GPa is well described using the percolation theory. Pressure induces phase separation, and the CMR takes place at the percolation threshold. A large memory effect is observed together with the CMR, suggesting the presence of magnetic clusters. The phase separation scenario is well reproduced, solving a model Hamiltonian. Our results demonstrate in a clean way that phase separation is at the origin of CMR in LaMnO3.

  9. Colossal aggregations of giant alien freshwater fish as a potential biogeochemical hotspot.

    PubMed

    Boulêtreau, Stéphanie; Cucherousset, Julien; Villéger, Sébastien; Masson, Rémi; Santoul, Frédéric

    2011-01-01

    The ubiquity and fascinating nature of animal aggregations are widely recognised. We report here consistent and previously undocumented occurences of aggregations of a giant alien freshwater fish, the Wels catfish (Silurus glanis). Aggregative groups were on average composed of 25 (± 10 SD, ranging from 15 to 44) adults with estimated average total biomass of 651 kg (386 - 1132) and biomass density of 23 kg m(-2) (14 - 40). Aggregations always occurred within the same location. No foraging, reproductive or anti-predator behaviour were observed during the aggregations. A mass-balance model estimated that these colossal aggregations of an alien species can locally release, through excretion only, up to 70 mg P m(-2) h(-1) and 400 mg N m(-2) h(-1), potentially representing the highest biogeochemical hotspots reported in freshwater ecosystems and another unexpected ecological effect of alien species.

  10. Spin seebeck effect and thermal colossal magnetoresistance in graphene nanoribbon heterojunction.

    PubMed

    Ni, Yun; Yao, Kailun; Fu, Huahua; Gao, Guoying; Zhu, Sicong; Wang, Shuling

    2013-01-01

    Spin caloritronics devices are very important for future development of low-power-consumption technology. We propose a new spin caloritronics device based on zigzag graphene nanoribbon (ZGNR), which is a heterojunction consisting of single-hydrogen-terminated ZGNR (ZGNR-H) and double-hydrogen-terminated ZGNR (ZGNR-H2). We predict that spin-up and spin-down currents flowing in opposite directions can be induced by temperature difference instead of external electrical bias. The thermal spin-up current is considerably large and greatly improved compared with previous work in graphene. Moreover, the thermal colossal magnetoresistance is obtained in our research, which could be used to fabricate highly-efficient spin caloritronics MR devices.

  11. Spin Seebeck Effect and Thermal Colossal Magnetoresistance in Graphene Nanoribbon Heterojunction

    PubMed Central

    Ni, Yun; Yao, Kailun; Fu, Huahua; Gao, Guoying; Zhu, Sicong; Wang, Shuling

    2013-01-01

    Spin caloritronics devices are very important for future development of low-power-consumption technology. We propose a new spin caloritronics device based on zigzag graphene nanoribbon (ZGNR), which is a heterojunction consisting of single-hydrogen-terminated ZGNR (ZGNR-H) and double-hydrogen-terminated ZGNR (ZGNR-H2). We predict that spin-up and spin-down currents flowing in opposite directions can be induced by temperature difference instead of external electrical bias. The thermal spin-up current is considerably large and greatly improved compared with previous work in graphene. Moreover, the thermal colossal magnetoresistance is obtained in our research, which could be used to fabricate highly-efficient spin caloritronics MR devices. PMID:23459307

  12. Colossal magnetoresistance in a Mott insulator via magnetic field-driven insulator-metal transition

    DOE PAGES

    Zhu, M.; Peng, J.; Zou, T.; ...

    2016-05-25

    Here, we present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca3Ru2O7. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattice-charge coupling. This study further provides a model approach to search for CMR systemsmore » other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases.« less

  13. Magnetically-driven colossal supercurrent enhancement in InAs nanowire Josephson junctions.

    PubMed

    Tiira, J; Strambini, E; Amado, M; Roddaro, S; San-Jose, P; Aguado, R; Bergeret, F S; Ercolani, D; Sorba, L; Giazotto, F

    2017-04-12

    The Josephson effect is a fundamental quantum phenomenon where a dissipationless supercurrent is introduced in a weak link between two superconducting electrodes by Andreev reflections. The physical details and topology of the junction drastically modify the properties of the supercurrent and a strong enhancement of the critical supercurrent is expected to occur when the topology of the junction allows an emergence of Majorana bound states. Here we report charge transport measurements in mesoscopic Josephson junctions formed by InAs nanowires and Ti/Al superconducting leads. Our main observation is a colossal enhancement of the critical supercurrent induced by an external magnetic field applied perpendicular to the substrate. This striking and anomalous supercurrent enhancement cannot be described by any known conventional phenomenon of Josephson junctions. We consider these results in the context of topological superconductivity, and show that the observed critical supercurrent enhancement is compatible with a magnetic field-induced topological transition.

  14. Thermal, dielectrical and mechanical response of α and β-poly(vinilydene fluoride)/Co-MgO nanocomposites

    PubMed Central

    2011-01-01

    Nanocomposites of the self-forming core-shell Co-MgO nanoparticles, which were of approximately 100 nm in diameter, and poly(vinylidene fluoride) (PVDF) polymer have been prepared. When the polymer is crystallized in the α-phase, the introduction of the nanoparticles leads to nucleation of the γ-phase of PVDF, increasing also the melting temperature of the polymer. With the introduction of the Co-MgO particles, the dielectric constant of the material slightly increases and the storage modulus decreases with respect to the values obtained for the pure polymer. PMID:21711778

  15. Strong magnetic-dielectric-lattice coupling in transition metal hydroxyhalides and ferroelectric response in rhombohedral Co2(OD)3X (X=Cl, Br)

    NASA Astrophysics Data System (ADS)

    Zheng, X. G.; Fujihala, M.; Kitajima, S.; Maki, M.; Kato, K.; Takata, M.; Xu, C. N.

    2013-05-01

    Hydroxyl salts of the type M2(OH)3X, and M(OH)X, where M represents a transition metal ion and X represents a halogen ion, widely exist as minerals and were recently reported to be geometrically frustrated magnets. Here, we report the finding of ferroelectric response in them. First, we observed strong magnetic-lattice-dielectric couplings in all of them as witnessed during their magnetic transitions at low temperatures. Secondly, we identified apparent ferroelectric responses in the deuterated hydroxyl salts of high crystal symmetries, i.e., rhombohedral Co2(OD)3Cl and Co2(OD)3Br, at high temperatures of 220-230 K through an isotope effect. The present work shows that multiferroicity may be a potentially universal phenomenon in magnetic hydroxyl salts. Meanwhile, it provides the first link between magnetic geometric frustration and hydrogen-bonded soft-mode ferroelectrics.

  16. Giant dielectric response and low dielectric loss in Al{sub 2}O{sub 3} grafted CaCu{sub 3}Ti{sub 4}O{sub 12} ceramics

    SciTech Connect

    Rajabtabar-Darvishi, A.; Bayati, R. E-mail: mbayati@ncsu.edu; Sheikhnejad-Bishe, O.; Wang, L. D.; Li, W. L.; Sheng, J.; Fei, W. D. E-mail: mbayati@ncsu.edu

    2015-03-07

    This study sheds light on the effect of alumina on dielectric constant and dielectric loss of novel CaCu{sub 3}Ti{sub 4}O{sub 12} composite ceramics. Alumina, at several concentrations, was deposited on the surface of CaCu{sub 3}Ti{sub 4}O{sub 12} particles via sol-gel technique. The dielectric constant significantly increased for all frequencies and the dielectric loss substantially decreased for low and intermediate frequencies. These observations were attributed to the change in characteristics of grains and grain boundaries. It was found that the insulating properties of the grain boundaries are improved following the addition of Al{sub 2}O{sub 3}. The relative density of CaCu{sub 3}Ti{sub 4}O{sub 12}/Al{sub 2}O{sub 3} composite ceramics decreased compared to the pure CaCu{sub 3}Ti{sub 4}O{sub 12} and the grain size was greatly changed with the alumina content affecting the dielectric properties. With the addition of alumina into CaCu{sub 3}Ti{sub 4}O{sub 12}, tighter interfaces formed. The 6%- and 10%-alumina ceramics showed the minimum dielectric loss and the maximum dielectric constant, respectively. Both the dielectric constant and loss tangent decreased in the 20%-alumina ceramic due to the formation of CuO secondary phase. It was revealed that Al serves as an electron acceptor decreasing the electron concentration, if Al{sup 3+} ions substitute for Ti{sup 4+} ions, and as an electron donor increasing the electron concentration, if Al{sup 3+} ions substitute for Ca{sup 2+} ions. We established a processing-microstructure-properties paradigm which opens new avenues for novel applications of CaCu{sub 3}Ti{sub 4}O{sub 12}/Al{sub 2}O{sub 3} composite ceramics.

  17. Broadband local dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Labardi, M.; Lucchesi, M.; Prevosto, D.; Capaccioli, S.

    2016-05-01

    A route to extend the measurement bandwidth of local dielectric spectroscopy up to the MHz range has been devised. The method is based on a slow amplitude modulation at a frequency Ω of the excitation field oscillating at a frequency ω and the coherent detection of the modulated average electric force or force gradient at Ω. The cantilever mechanical response does not affect the measurement if Ω is well below its resonant frequency; therefore, limitations on the excitation field frequency are strongly reduced. Demonstration on a thin poly(vinyl acetate) film is provided, showing its structural relaxation spectrum on the local scale up to 45 °C higher than glass temperature, and nanoscale resolution dielectric relaxation imaging near conductive nanowires embedded in the polymer matrix was obtained up to 5 MHz frequency, with no physical reason to hinder further bandwidth extension.

  18. Dielectric metasurfaces

    NASA Astrophysics Data System (ADS)

    Valentine, Jason

    While plasmonics metasurfaces have seen much development over the past several years, they still face throughput limitations due to ohmic losses. On the other hand, dielectric resonators and associated metasurfaces can eliminate the issue of ohmic loss while still providing the freedom to engineer the optical properties of the composite. In this talk, I will present our recent efforts to harness this freedom using metasurfaces formed from silicon and fabricated using CMOS-compatible techniques. Operating in the telecommunications band, I will discuss how we have used this platform to realize a number of novel functionalities including wavefront control, near-perfect reflection, and high quality factor resonances. In many cases the optical performance of these silicon-based metasurfaces can surpass their plasmonic counterparts. Furthermore, for some cases the surfaces are more amenable to large-area fabrication techniques.

  19. Electrode effects in dielectric spectroscopy measurements on (Nb +In) co-doped TiO2

    NASA Astrophysics Data System (ADS)

    Crandles, David; Yee, Susan; Savinov, Maxim; Nuzhnyy, Dimitri; Petzelt, Jan; Kamba, Stanislav; Prokes, Jan

    Recently, several papers reported the discovery of giant permittivity and low dielectric loss in (Nb+In) co-doped TiO2. A series of tests was performed which included the measurement of the frequency dependence of the dielectric permittivity and ac conductivity of co-doped (Nb+In)TiO2 as a function of electrode type, sample thickness and temperature. The data suggest that the measurements are strongly affected by the electrodes. The consistency between four contact van der Pauw dc conductivity measurements and bulk conductivity values extracted from two contact ac conductivity measurements suggest that the values of colossal permittivity are, at least in part, a result of Schottky barrier depletion widths that depend on electrode type and temperature. Nserc, Czech Science Foundation (Project 15-08389S).

  20. Dielectric constant of water in the interface

    NASA Astrophysics Data System (ADS)

    Dinpajooh, Mohammadhasan; Matyushov, Dmitry V.

    2016-07-01

    We define the dielectric constant (susceptibility) that should enter the Maxwell boundary value problem when applied to microscopic dielectric interfaces polarized by external fields. The dielectric constant (susceptibility) of the interface is defined by exact linear-response equations involving correlations of statistically fluctuating interface polarization and the Coulomb interaction energy of external charges with the dielectric. The theory is applied to the interface between water and spherical solutes of altering size studied by molecular dynamics (MD) simulations. The effective dielectric constant of interfacial water is found to be significantly lower than its bulk value, and it also depends on the solute size. For TIP3P water used in MD simulations, the interface dielectric constant changes from 9 to 4 when the solute radius is increased from ˜5 to 18 Å.

  1. All-dielectric metamaterials

    NASA Astrophysics Data System (ADS)

    Jahani, Saman; Jacob, Zubin

    2016-01-01

    The ideal material for nanophotonic applications will have a large refractive index at optical frequencies, respond to both the electric and magnetic fields of light, support large optical chirality and anisotropy, confine and guide light at the nanoscale, and be able to modify the phase and amplitude of incoming radiation in a fraction of a wavelength. Artificial electromagnetic media, or metamaterials, based on metallic or polar dielectric nanostructures can provide many of these properties by coupling light to free electrons (plasmons) or phonons (phonon polaritons), respectively, but at the inevitable cost of significant energy dissipation and reduced device efficiency. Recently, however, there has been a shift in the approach to nanophotonics. Low-loss electromagnetic responses covering all four quadrants of possible permittivities and permeabilities have been achieved using completely transparent and high-refractive-index dielectric building blocks. Moreover, an emerging class of all-dielectric metamaterials consisting of anisotropic crystals has been shown to support large refractive index contrast between orthogonal polarizations of light. These advances have revived the exciting prospect of integrating exotic electromagnetic effects in practical photonic devices, to achieve, for example, ultrathin and efficient optical elements, and realize the long-standing goal of subdiffraction confinement and guiding of light without metals. In this Review, we present a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index metamaterials and anisotropic metamaterials. Finally, we discuss current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics, as well as biomimetic metasurfaces.

  2. All-dielectric metamaterials.

    PubMed

    Jahani, Saman; Jacob, Zubin

    2016-01-01

    The ideal material for nanophotonic applications will have a large refractive index at optical frequencies, respond to both the electric and magnetic fields of light, support large optical chirality and anisotropy, confine and guide light at the nanoscale, and be able to modify the phase and amplitude of incoming radiation in a fraction of a wavelength. Artificial electromagnetic media, or metamaterials, based on metallic or polar dielectric nanostructures can provide many of these properties by coupling light to free electrons (plasmons) or phonons (phonon polaritons), respectively, but at the inevitable cost of significant energy dissipation and reduced device efficiency. Recently, however, there has been a shift in the approach to nanophotonics. Low-loss electromagnetic responses covering all four quadrants of possible permittivities and permeabilities have been achieved using completely transparent and high-refractive-index dielectric building blocks. Moreover, an emerging class of all-dielectric metamaterials consisting of anisotropic crystals has been shown to support large refractive index contrast between orthogonal polarizations of light. These advances have revived the exciting prospect of integrating exotic electromagnetic effects in practical photonic devices, to achieve, for example, ultrathin and efficient optical elements, and realize the long-standing goal of subdiffraction confinement and guiding of light without metals. In this Review, we present a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index metamaterials and anisotropic metamaterials. Finally, we discuss current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics, as well as biomimetic metasurfaces.

  3. Mathematical models for the reflection coefficients of lossy dielectric half-spaces with application to transient responses of chirped pulses

    NASA Technical Reports Server (NTRS)

    Evans, D. D.

    1977-01-01

    Reflection coefficients are found at normal incidence for a large class of homogeneous lossy half-spaces with a one-dimensionally inhomogeneous or stratified lossy layer on top. Solutions are in terms of Hankel functions of complex argument to decrease cancellation error at high frequencies. One special case is that of layers on a homogeneous half-space where the dielectric constant in each layer may vary in a quite general manner. A Wronskian is used to insure the critical computations are correct. The reflection of chirped pulses is considered. Solutions are obtained by applying the fast Fourier transform. It is found that for a typical relatively long normalized 'long' pulse the power reflected as a function of time is essentially the power reflection coefficient for the frequencies swept out, whereas for a relatively short 'long' pulse, with the same relative change in frequency and the same number of oscillations there is only the uniform attenuation by the power reflection coefficient of the center frequency. By a 'long' pulse we mean a pulse whose spatial length is long compared to the thickness of the reflecting layer.

  4. Wigner Crystal and Colossal Magnetoresistance in InSb Doped with Mn

    PubMed Central

    Obukhov, S. A.; Tozer, S. W.; Coniglio, W. A.

    2015-01-01

    We report magnetotransport investigation of nonmagnetic InSb single crystal doped with manganese at Mn concentration NMn ~ 1,5 × 1017 cm−3 in the temperature range T = 300 K–40 mK, magnetic field B = 0–25T and hydrostatic pressure P = 0–17 kbar. Resistivity saturation was observed in the absence of magnetic field at temperatures below 200 mK while applied increasing external magnetic field induced colossal drop of resistivity (by factor 104) at B ~ 4T with further gigantic resistivity increase (by factor 104) at 15T. Under pressure, P = 17 kbar, resistivity saturation temperature increased up to 1,2 K. Existing models are discussed in attempt to explain resistivity saturation, dramatic influence of magnetic field and pressure on resistivity with the focus on possible manifestation of three dimensional Wigner crystal formed in InSb by light electrons and heavy holes. PMID:26307952

  5. Chemical Ordering Modulated Electronic Phase Separation and Macroscopic Properties in Colossal Magnetoresistance Manganites

    NASA Astrophysics Data System (ADS)

    Zhu, Yinyan; Du, Kai; Yin, Lifeng; Shen, Jian; Low-dimensional material physics Team

    Using unit cell by unit cell superlattice growth technique, we determine the role of chemical ordering of the Pr dopant in a colossal magnetoresistance (La1-yPry)1-x CaxMnO3 (LPCMO) system, which has been well known for its large length scale electronic phase separation (EPS) phenomena. Our experimental results show that the chemical ordering of Pr leads to dramatic reduction of the length scale of EPS. Moreover, compared to the conventional Pr-disordered LPCMO system, the Pr-ordered LPCMO system has ~100 K higher metal-insulator transition temperature. We have further investigated the n-dependence of the physical properties of the (LCMO)2n/(PCMO)n superlattices. Magnetic and transport measurements indicate that the physical properties change nonmonotonically with increasing n, reaching a minimum for both the Curie temperature and the meta-insulator transition temperature. The crossover thickness thus reflects the characteristic correlation length scale along the vertical direction of the superlattice. For superlattices with n smaller than the correlation length, we combine MFM studies and model calculations to explain the weakened ferromagnetism and metallicity with increasing n.

  6. Colossal positive magnetoresistance in surface-passivated oxygen-deficient strontium titanite

    PubMed Central

    David, Adrian; Tian, Yufeng; Yang, Ping; Gao, Xingyu; Lin, Weinan; Shah, Amish B.; Zuo, Jian-Min; Prellier, Wilfrid; Wu, Tom

    2015-01-01

    Modulation of resistance by an external magnetic field, i.e. magnetoresistance effect, has been a long-lived theme of research due to both fundamental science and device applications. Here we report colossal positive magnetoresistance (CPMR) (>30,000% at a temperature of 2 K and a magnetic field of 9 T) discovered in degenerate semiconducting strontium titanite (SrTiO3) single crystals capped with ultrathin SrTiO3/LaAlO3 bilayers. The low-pressure high-temperature homoepitaxial growth of several unit cells of SrTiO3 introduces oxygen vacancies and high-mobility carriers in the bulk SrTiO3, and the three-unit-cell LaAlO3 capping layer passivates the surface and improves carrier mobility by suppressing surface-defect-related scattering. The coexistence of multiple types of carriers and inhomogeneous transport lead to the emergence of CPMR. This unit-cell-level surface engineering approach is promising to be generalized to others oxides, and to realize devices with high-mobility carriers and interesting magnetoelectronic properties. PMID:25975606

  7. Achievement of High-Response Organic Field-Effect Transistor NO₂ Sensor by Using the Synergistic Effect of ZnO/PMMA Hybrid Dielectric and CuPc/Pentacene Heterojunction.

    PubMed

    Han, Shijiao; Cheng, Jiang; Fan, Huidong; Yu, Junsheng; Li, Lu

    2016-10-21

    High-response organic field-effect transistor (OFET)-based NO₂ sensors were fabricated using the synergistic effect the synergistic effect of zinc oxide/poly(methyl methacrylate) (ZnO/PMMA) hybrid dielectric and CuPc/Pentacene heterojunction. Compared with the OFET sensors without synergistic effect, the fabricated OFET sensors showed a remarkable shift of saturation current, field-effect mobility and threshold voltage when exposed to various concentrations of NO₂ analyte. Moreover, after being stored in atmosphere for 30 days, the variation of saturation current increased more than 10 folds at 0.5 ppm NO₂. By analyzing the electrical characteristics, and the morphologies of organic semiconductor films of the OFET-based sensors, the performance enhancement was ascribed to the synergistic effect of the dielectric and organic semiconductor. The ZnO nanoparticles on PMMA dielectric surface decreased the grain size of pentacene formed on hybrid dielectric, facilitating the diffusion of CuPc molecules into the grain boundary of pentacene and the approach towards the conducting channel of OFET. Hence, NO₂ molecules could interact with CuPc and ZnO nanoparticles at the interface of dielectric and organic semiconductor. Our results provided a promising strategy for the design of high performance OFET-based NO₂ sensors in future electronic nose and environment monitoring.

  8. Achievement of High-Response Organic Field-Effect Transistor NO2 Sensor by Using the Synergistic Effect of ZnO/PMMA Hybrid Dielectric and CuPc/Pentacene Heterojunction

    PubMed Central

    Han, Shijiao; Cheng, Jiang; Fan, Huidong; Yu, Junsheng; Li, Lu

    2016-01-01

    High-response organic field-effect transistor (OFET)-based NO2 sensors were fabricated using the synergistic effect the synergistic effect of zinc oxide/poly(methyl methacrylate) (ZnO/PMMA) hybrid dielectric and CuPc/Pentacene heterojunction. Compared with the OFET sensors without synergistic effect, the fabricated OFET sensors showed a remarkable shift of saturation current, field-effect mobility and threshold voltage when exposed to various concentrations of NO2 analyte. Moreover, after being stored in atmosphere for 30 days, the variation of saturation current increased more than 10 folds at 0.5 ppm NO2. By analyzing the electrical characteristics, and the morphologies of organic semiconductor films of the OFET-based sensors, the performance enhancement was ascribed to the synergistic effect of the dielectric and organic semiconductor. The ZnO nanoparticles on PMMA dielectric surface decreased the grain size of pentacene formed on hybrid dielectric, facilitating the diffusion of CuPc molecules into the grain boundary of pentacene and the approach towards the conducting channel of OFET. Hence, NO2 molecules could interact with CuPc and ZnO nanoparticles at the interface of dielectric and organic semiconductor. Our results provided a promising strategy for the design of high performance OFET-based NO2 sensors in future electronic nose and environment monitoring. PMID:27775653

  9. Correlation between upconversion photoluminescence and dielectric response in Ba-substituted (Sr1-xBax)4(La0.85Ho0.025Yb0.125)2Ti4Nb6O30

    NASA Astrophysics Data System (ADS)

    Wei, T.; Wang, X. D.; Zhao, C. Z.; Liu, M. F.; Liu, J. M.

    2014-06-01

    The filled tetragonal tungsten bronze (Sr1-xBax)4(La0.85Ho0.025Yb0.125)2Ti4Nb6O30 (SBLTNx: Ho-Yb) ceramics with different Ba substitution levels (x) are prepared. The upconversion photoluminescence (UC-PL) and dielectric permittivity are investigated. The substitution of Sr2+ ions at the A2-sites by larger Ba2+ ions results in substantial variation of the UC-PL intensity as a function of substitution level x. Furthermore, the dielectric response to the substitution of Sr2+ by Ba2+ suggests a close correlation between the UC-PL intensity and dielectric permittivity. The origin for this correlation is discussed based on the random stress field (RSF) model.

  10. Metal-dielectric composite for dispersion free optics

    NASA Astrophysics Data System (ADS)

    Balasubrahmaniyam, M.; Patra, Anuradha; Ganesan, A. R.; Kasiviswanathan, S.

    2013-02-01

    Bergman formulation has been used to extract effective dielectric function of Au nanoparticles (AuNPs) embedded metal oxide (MO) composite thin films. The extracted composite dielectric function helps further understanding ofthe resonance features in optical far-field responses. Detailed analysis on the extracted dielectric functions point towards the possibility of using them for dispersion free optics.

  11. Non-Debye relaxation in the dielectric response of nematic liquid crystals: surface and memory effects in the adsorption-desorption process of ionic impurities.

    PubMed

    de Paula, J L; Santoro, P A; Zola, R S; Lenzi, E K; Evangelista, L R; Ciuchi, F; Mazzulla, A; Scaramuzza, N

    2012-11-01

    We demonstrate theoretically that the presence of ions in insulating materials such as nematic liquid crystals may be responsible for the dielectric spectroscopy behavior observed experimentally. It is shown that, at low frequencies, an essentially non-Debye relaxation process takes place due to surface effects. This is accomplished by investigating the effects of the adsorption-desorption process on the electrical response of an electrolytic cell when the generation and recombination of ions is present. The adsorption-desorption is governed by a non-usual kinetic equation in order to incorporate memory effects related to a non-Debye relaxation and the roughness of the surface. The analysis is carried out by searching for solutions to the drift-diffusion equation that satisfy the Poisson equation relating the effective electric field to the net charge density. We also discuss the effect of the mobility of the ions, i.e., situations with equal and different diffusion coefficients for positive and negative ions, on the impedance and obtain an exact expression for the admittance. The model is compared with experimental results measured for the impedance of a nematic liquid crystal sample and a very good agreement is obtained.

  12. Non-Debye relaxation in the dielectric response of nematic liquid crystals: Surface and memory effects in the adsorption-desorption process of ionic impurities

    NASA Astrophysics Data System (ADS)

    de Paula, J. L.; Santoro, P. A.; Zola, R. S.; Lenzi, E. K.; Evangelista, L. R.; Ciuchi, F.; Mazzulla, A.; Scaramuzza, N.

    2012-11-01

    We demonstrate theoretically that the presence of ions in insulating materials such as nematic liquid crystals may be responsible for the dielectric spectroscopy behavior observed experimentally. It is shown that, at low frequencies, an essentially non-Debye relaxation process takes place due to surface effects. This is accomplished by investigating the effects of the adsorption-desorption process on the electrical response of an electrolytic cell when the generation and recombination of ions is present. The adsorption-desorption is governed by a non-usual kinetic equation in order to incorporate memory effects related to a non-Debye relaxation and the roughness of the surface. The analysis is carried out by searching for solutions to the drift-diffusion equation that satisfy the Poisson equation relating the effective electric field to the net charge density. We also discuss the effect of the mobility of the ions, i.e., situations with equal and different diffusion coefficients for positive and negative ions, on the impedance and obtain an exact expression for the admittance. The model is compared with experimental results measured for the impedance of a nematic liquid crystal sample and a very good agreement is obtained.

  13. Dielectric Properties of Piezoelectric Polyimides

    NASA Technical Reports Server (NTRS)

    Ounaies, Z.; Young, J. A.; Simpson, J. O.; Farmer, B. L.

    1997-01-01

    Molecular modeling and dielectric measurements are being used to identify mechanisms governing piezoelectric behavior in polyimides such as dipole orientation during poling, as well as degree of piezoelectricity achievable. Molecular modeling on polyimides containing pendant, polar nitrile (CN) groups has been completed to determine their remanent polarization. Experimental investigation of their dielectric properties evaluated as a function of temperature and frequency has substantiated numerical predictions. With this information in hand, we are then able to suggest changes in the molecular structures, which will then improve upon the piezoelectric response.

  14. Quasi-intrinsic colossal permittivity in Nb and In co-doped rutile TiO2 nanoceramics synthesized through a oxalate chemical-solution route combined with spark plasma sintering.

    PubMed

    Han, HyukSu; Dufour, Pascal; Mhin, Sungwook; Ryu, Jeong Ho; Tenailleau, Christophe; Guillemet-Fritsch, Sophie

    2015-07-14

    Nb and In co-doped rutile TiO2 nanoceramics (n-NITO) were successfully synthesized through a chemical-solution route combined with a low temperature spark plasma sintering (SPS) technique. The particle morphology and the microstructure of n-NITO compounds were nanometric in size. Various techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG)/differential thermal analysis (DTA), Fourier transform infrared (FTIR), and Raman spectroscopy were used for the structural and compositional characterization of the synthesized compound. The results indicated that the as-synthesized n-NITO oxalate as well as sintered ceramic have a co-doped single phase of titanyl oxalate and rutile TiO2, respectively. Broadband impedance spectroscopy revealed that novel colossal permittivity (CP) was achieved in n-NITO ceramics exhibiting excellent temperature-frequency stable CP (up to 10(4)) as well as low dielectric loss (∼5%). Most importantly, detailed impedance data analyses of n-NITO compared to microcrystalline NITO (μ-NITO) demonstrated that the origin of CP in NITO bulk nanoceramics might be related with the pinned electrons in defect clusters and not to extrinsic interfacial effects.

  15. High frequency dielectric response and magnetic studies of Zn1-xTbxFe2O4 nanocrystalline ferrites synthesized via micro-emulsion technique

    NASA Astrophysics Data System (ADS)

    Azhar Khan, Muhammad; Sabir, Muhammad; Mahmood, Azhar; Asghar, M.; Mahmood, K.; Afzal Khan, M.; Ahmad, Iqbal; Sher, Muhammad; Farooq Warsi, Muhammad

    2014-06-01

    Tb3+-doped nanocrystalline zinc ferrites with a nominal composition of Zn1-xTbxFe2O4 (x=0, 0.03, 0.06, 0.09, 0.12 and 0.15) were prepared by micro-emulsion method and were annealed at 600 °C for 8.5 h. The synthesized samples were characterized by thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometer (VSM) and dielectric measurement techniques. The powder XRD patterns confirm the single phase cubic spinel structure, indicated that doping nanoferrites with small concentrations of terbium ions allowed their entrance to the spinel lattice and the crystallite size is found in the range of 16-24 nm. The dielectric constant (ε) and dielectric loss (tanδ) of all the samples were measured in the frequency range 100 MHz-3 GHz at room temperature. The dielectric constant and dielectric loss of the samples are found to decrease with increase in frequency and Tb3+ content. The reduction in the dielectric parameters is attributed to the obstruction incorporated in electron exchange mechanism caused by the lockup among iron and terbium cations. The magnetic properties revealed that these terbium doped nanocrystalline zinc ferrites exhibit ferrimagnetic behavior. The high saturation magnetization and coercivity along with smaller dielectric parameters having Tb-contents suggests that the materials are suitable for applications in memory devices and high frequency applications.

  16. Colossal Kerr nonlinearity based on electromagnetically induced transparency in a five-level double-ladder atomic system.

    PubMed

    Hamedi, H R; Gharamaleki, Ali Hamrah; Sahrai, Mostafa

    2016-08-01

    The paper is aimed at modeling the enhanced Kerr nonlinearity in a five-level double-ladder-type atomic system based on electromagnetically induced transparency (EIT) by using the semi-classical density matrix method. We present an analytical model to explain the origin of Kerr nonlinearity enhancement. The scheme also results in a several orders of magnitude increase in the Kerr nonlinearity in comparison with the well-known four- and three-level atomic systems. In addition to the steady-state case, the time-dependent Kerr nonlinearity and the switching feature of EIT-based colossal Kerr nonlinearity is investigated for the proposed system.

  17. Response to ``Comment on `Slow Debye-type peak observed in the dielectric response of polyalcohols' '' [J. Chem. Phys. 134, 037101 (2011)

    NASA Astrophysics Data System (ADS)

    Bergman, R.; Jansson, H.; Swenson, J.

    2011-01-01

    In our recent article [R. Bergman et al., J. Chem. Phys. 132, 044504 (2010)] we investigated some polyalcohols, i.e., glycerol, xylitol, and sorbitol by dielectric spectroscopy. In the study, a low-frequency peak of Debye character that normally is hidden by the large low-frequency dispersion due to conductivity was revealed by analyzing the real part of the permittivity and by using a thin Teflon film to suppress the low-frequency dispersion. We agree with the comment by Paluch et al. [J. Chem. Phys. 134, 037101 (2011)] that the Teflon film setup will indeed create a peak due to the dc conductivity. However, due to the fact that the location of the peak was almost identical in measurement with and without Teflon, we unfortunately mainly showed the data measured with Teflon, despite that it could also be observed in the real part of the permittivity without using the Teflon setup, as shown in our original article [R. Bergman et al., J. Chem. Phys. 132, 044504 (2010)]. Here, we show that the low-frequency peak of Debye character can also be observed by subtracting the dc conductivity. Furthermore, we show that the modulus representation used in Paluch et al. [J. Chem. Phys. 134, 037101 (2011).] is also not suitable for detecting processes hidden by the conductivity.

  18. Dielectric behavior of Ar{sup +} implanted CR-39 polymer

    SciTech Connect

    Shekhawat, Nidhi; Sharma, Annu; Aggarwal, Sanjeev; Deshpande, S. K.; Nair, K. G. M.

    2012-06-05

    The frequency dependent dielectric response of Ar{sup +} implanted CR-39 specimens has been studied. Samples were implanted with 130 keV Ar{sup +} ions to various doses ranging from 5x10{sup 14} to 1x10{sup 16} cm{sup -2}. The frequency response of dielectric constant (e) and dielectric loss has been studied both in the pristine and argon ion implanted samples of CR-39 polymer in the frequency range 10{sup 4} to 10{sup 8} Hz. Structural changes produced in CR-39 specimens due to implantation have been studied using Attenuated total reflectance (ATR) Fourier transform infrared spectroscopic technique. Results of dielectric analysis indicate the lowering in dielectric constant ({epsilon}') and similar behavior of dielectric loss with increase in ion fluence. An attempt has been made to correlate these changes produced in the dielectric properties of implanted specimens with the structural changes produced due to implantation.

  19. Experimental evidence for the formation of CoFe{sub 2}C phase with colossal magnetocrystalline-anisotropy

    SciTech Connect

    El-Gendy, Ahmed A. E-mail: ecarpenter2@vcu.edu; Bertino, Massimo; Qian, Meichun; Khanna, Shiv N. E-mail: ecarpenter2@vcu.edu; Clifford, Dustin; Carpenter, Everett E. E-mail: ecarpenter2@vcu.edu

    2015-05-25

    Attainment of magnetic order in nanoparticles at room temperature is an issue of critical importance for many different technologies. For ordinary ferromagnetic materials, a reduction in size leads to decreased magnetic anisotropy and results in superparamagnetic relaxations. If, instead, anisotropy could be enhanced at reduced particle sizes, then it would be possible to attain stable magnetic order at room temperature. Herein, we provide experimental evidence substantiating the synthesis of a cobalt iron carbide phase (CoFe{sub 2}C) of nanoparticles. Structural characterization of the CoFe{sub 2}C carbide phase was performed by transmission electron microscopy, electron diffraction and energy electron spectroscopy. X-ray diffraction was also performed as a complimentary analysis. Magnetic characterization of the carbide phase revealed a blocking temperature, T{sub B}, of 790 K for particles with a domain size as small as 5 ± 1 nm. The particles have magnetocrystalline anisotropy of 4.6 ± 2 × 10{sup 6 }J/m{sup 3}, which is ten times larger than that of Co nanoparticles. Such colossal anisotropy leads to thermally stable long range magnetic order. Moreover, the thermal stability constant is much larger than that of the commonly used FePt nanoparticles. With thermal stability and colossal anisotropy, the CoFe{sub 2}C nanoparticles have huge potential for enhanced magnetic data storage devices.

  20. Impact of metallophilicity on "colossal" positive and negative thermal expansion in a series of isostructural dicyanometallate coordination polymers.

    PubMed

    Korcok, Jasmine L; Katz, Michael J; Leznoff, Daniel B

    2009-04-08

    Five isostructural dicyanometallate coordination polymers containing metallophilic interactions (In[M(CN)(2)](3) (M = Ag, Au), KCd[M(CN)(2)](3), and KNi[Au(CN)(2)](3)) were synthesized and investigated by variable-temperature powder X-ray diffraction to probe their thermal expansion properties. The compounds have a trigonal unit cell and show positive thermal expansion (PTE) in the ab plane, where Kagome sheets of M atoms reside, and negative thermal expansion (NTE) along the trigonal c axis, perpendicular to these sheets. The magnitude of thermal expansion is unusually large in all cases (40 x 10(-6) K(-1) < |alpha| < 110 x 10(-6) K(-1)). The system with the weakest metallophilic interactions, In[Ag(CN)(2)](3), shows the most "colossal" thermal expansion of the series (alpha(a) = 105(2) x 10(-6) K(-1), alpha(c) = -84(2) x 10(-6) K(-1) at 295 K), while systems containing stronger Au-Au interactions show relatively reduced thermal expansion. Thus, it appears that strong metallophilic interactions hinder colossal thermal expansion behavior. Additionally, the presence of K(+) counterions also reduces the magnitude of thermal expansion.

  1. Nonlinear electroelastic deformations of dielectric elastomer composites: I-Ideal elastic dielectrics

    NASA Astrophysics Data System (ADS)

    Lefèvre, Victor; Lopez-Pamies, Oscar

    2017-02-01

    This paper puts forth homogenization solutions for the macroscopic elastic dielectric response-under finite deformations and finite electric fields-of ideal elastic dielectric composites with two-phase isotropic particulate microstructures. Specifically, solutions are presented for three classes of microstructures: (i) an isotropic iterative microstructure wherein the particles are infinitely polydisperse in size, (ii) an isotropic distribution of polydisperse spherical particles of a finite number of different sizes, and (iii) an isotropic distribution of monodisperse spherical particles. The solution for the iterative microstructure, which corresponds to the viscosity solution of a Hamilton-Jacobi equation in five "space" variables, is constructed by means of a novel high-order WENO finite-difference scheme. On the other hand, the solutions for the microstructures with spherical particles are constructed by means of hybrid finite elements. Prompted by the functional features shared by all three obtained solutions, a simple closed-form approximation is proposed for the macroscopic elastic dielectric response of ideal elastic dielectric composites with any type of (non-percolative) isotropic particulate microstructure. As elaborated in a companion paper, the proposed approximate solution proves particularly useful as a fundamental building block to generate approximate solutions for the macroscopic elastic dielectric response of dielectric elastomer composites made up of non-Gaussian dielectric elastomers filled with nonlinear elastic dielectric particles.

  2. Time-resolved optical studies of colossal magnetoresistance and charge-density wave materials

    NASA Astrophysics Data System (ADS)

    Ren, Yuhang

    This thesis presents measurements of collective modes and ultrafast carrier relaxation dynamics in charge-density-wave (CDW) conductors and colossal magnetoresistance (CMR) manganites. A femtosecond laser pump pulse excites a broad frequency spectrum of low-energy collective modes and electron-hole pairs thereby changing its optical properties. The low-energy collective excitations and quasiparticle relaxation and recombination processes are monitored by measuring the resulting photoinduced absorption as a function of probe pulse wavelength and time delay. A general model was developed for the photogeneration and detection mechanism of collective modes based on light absorption in two-color pump-probe experiments. A broad spectrum of collective modes (phasons and amplitudons) with frequencies down to a few GHz is excited and propagates normal to the surface into the material. The dispersion of the long-wavelength phason and amplitudon can be measured by changing the probe wavelength. The first pump-probe spectroscopy was performed from the ultraviolet to mid-infrared wavelength range to study low-frequency collective excitations, including temperature evolution, dispersion, damping, and anisotropy of amplitude mode and transverse phason in quasi-one dimensional CDW conductors, K 0.3MoO3 and K0.33MoO3 on ultrafast time scale. The transverse phason exhibits an acoustic-like dispersion relation in the frequency range from 5--40 GHz. The phason velocity is strongly anisotropic with a very weak temperature dependence. In contrast, the amplitude mode exhibits a weak (optic-like) dispersion relation with a frequency of 1.66 THz at 30 K. The studies were extended to doped perovskite manganite thin films and single crystals. A low-energy collective mode is observed and discussed in terms of the opening of a pseudogap resulting from charge/orbital ordering phases. The softening of the collective mode is necessary to explain by combining a cooperative Jahn-Teller type

  3. Electrode effects in dielectric spectroscopy measurements on (Nb+In) co-doped TiO2

    NASA Astrophysics Data System (ADS)

    Crandles, D. A.; Yee, S. M. M.; Savinov, M.; Nuzhnyy, D.; Petzelt, J.; Kamba, S.; Prokeš, J.

    2016-04-01

    Recently, several papers reported the discovery of giant permittivity and low dielectric loss in (Nb+In) co-doped TiO2. A series of tests was performed which included the measurement of the frequency dependence of the dielectric permittivity and alternating current (ac) conductivity of co-doped (Nb+In)TiO2 as a function of electrode type, sample thickness, and temperature. The data suggest that the measurements are strongly affected by the electrodes. The consistency between four-contact van der Pauw direct current conductivity measurements and bulk conductivity values extracted from two-contact ac conductivity measurements suggest that the values of colossal permittivity are, at least in part, a result of Schottky barrier depletion widths that depend on electrode type and temperature.

  4. Soft Dielectrics: Heterogeneity and Instabilities

    NASA Astrophysics Data System (ADS)

    Rudykh, Stephan; Debotton, Gal; Bhattacharya, Kaushik

    2012-02-01

    Dielectric Elastomers are capable of large deformations in response to electrical stimuli. Heterogeneous soft dielectrics with proper microstructures demonstrate much stronger electromechanical coupling than their homogeneous constituents. In turn, the heterogeneity is an origin for instability developments leading to drastic change in the composite microstructure. In this talk, the electromechanical instabilities are considered. Stability of anisotropic soft dielectrics is analyzed. Ways to achieve giant deformations and manipulating extreme material properties are discussed. 1. S. Rudykh and G. deBotton, ``Instabilities of Hyperelastic Fiber Composites: Micromechanical Versus Numerical Analyses.'' Journal of Elasticity, 2011. http://dx.doi.org/2010.1007/s10659-011-9313-x 2. S. Rudykh, K. Bhattacharya and G. deBotton, ``Snap-through actuation of thick-wall electroactive balloons.'' International Journal of Non-Linear Mechanics, 2011. http://dx.doi.org/10.1016/j.ijnonlinmec.2011.05.006 3. S. Rudykh and G. deBotton, ``Stability of Anisotropic Electroactive Polymers with Application to Layered Media.'' Zeitschrift f"ur angewandte Mathematik und Physik, 2011. http://dx.doi.org/10.1007/s00033-011-0136-1 4. S. Rudykh, A. Lewinstein, G. Uner and G. deBotton, ``Giant Enhancement of the Electromechanical Coupling in Soft Heterogeneous Dielectrics.'' 2011 http://arxiv.org/abs/1105.4217v1

  5. Dielectrically Loaded HTS Spiral Antenna

    NASA Astrophysics Data System (ADS)

    Ramasamy, J.; Hanna, D.; Vlasov, Y. A.; Larkins, G. L.; Moeckly, B. H.

    2004-06-01

    The objective of this work is to fabricate, test, and study a dielectrically loaded high temperature superconductor (HTS) spiral antenna that would operate in the frequency band of 10 MHz to 200 MHz. The antenna is formed by depositing and patterning a YBa2Cu3O7 (YBCO) thin film on top of 4-inch-diameter sapphire and Yittria Stabilized ZrO2 substrates. The presence of the HTS material guarantees low conductor loss in the antenna. A thick epitaxial layer of strontium titanate (STO) is then deposited on top of the YBCO for high dielectric constant loading. This set-up can be simulated using the Fidelity software routine, a Finite Difference Time Domain based program from Zeland, Inc. We have simulated the performance of this antenna structure, first in free space and then after loading with the dielectric slabs. Important parameters such as feed point impedance and antenna gain are studied for different simulation conditions. The dielectric ensures reduced feed point impedance as well as improvement of the low frequency response of the antenna.

  6. Dielectric Actuation of Polymers

    NASA Astrophysics Data System (ADS)

    Niu, Xiaofan

    Dielectric polymers are widely used in a plurality of applications, such as electrical insulation, dielectric capacitors, and electromechanical actuators. Dielectric polymers with large strain deformations under an electric field are named dielectric elastomers (DE), because of their relative low modulus, high elongation at break, and outstanding resilience. Dielectric elastomer actuators (DEA) are superior to traditional transducers as a muscle-like technology: large strains, high energy densities, high coupling efficiency, quiet operation, and light weight. One focus of this dissertation is on the design of DE materials with high performance and easy processing. UV radiation curing of reactive species is studied as a generic synthesis methodology to provide a platform for material scientists to customize their own DE materials. Oligomers/monomers, crosslinkers, and other additives are mixed and cured at appropriate ratios to control the stress-strain response, suppress electromechanical instability of the resulting polymers, and provide stable actuation strains larger than 100% and energy densities higher than 1 J/g. The processing is largely simplified in the new material system by removal of the prestretching step. Multilayer stack actuators with 11% linear strain are demonstrated in a procedure fully compatible with industrial production. A multifunctional DE derivative material, bistable electroactive polymer (BSEP), is invented enabling repeatable rigid-to-rigid deformation without bulky external structures. Bistable actuation allows the polymer actuator to have two distinct states that can support external load without device failure. Plasticizers are used to lower the glass transition temperature to 45 °C. Interpenetrating polymer network structure is established inside the BSEP to suppress electromechanical instability, providing a breakdown field of 194 MV/m and a stable bistable strain as large as 228% with a 97% strain fixity. The application of BSEP

  7. Electrical conduction in polymer dielectrics

    NASA Technical Reports Server (NTRS)

    Cotts, D. B.

    1985-01-01

    The use of polymer dielectrics with moderate resistivities could reduce or eliminate problems associated with spacecraft charging. The processes responsible for conduction and the properties of electroactive polymers are reviewed, and correlations drawn between molecular structure and electrical conductivity. These structure-property relationships led to the development of several new electroactive polymer compositions and the identification of several systems that have the requisite thermal, mechanical, environmental and electrical properties for use in spacecraft.

  8. Extending applications of dielectric elastomer artificial muscle

    NASA Astrophysics Data System (ADS)

    Chiba, Seiki; Waki, Mikio; Kornbluh, Roy; Pelrine, Ron

    2007-04-01

    Dielectric elastomers have demonstrated high energy density and high strains as well as high electromechanical efficiency and fast speeds of response. These properties, combined with their projected low cost make them attractive for a variety of actuator applications including linear actuators, diaphragm pumps, rotary motors, and haptic displays. Dielectric elastomers have also been shown to offer high energy density, high efficiency, and large strains when operated as generators. Dielectric elastomers have reached a stage of development where standardized products can be applied to new applications. In some cases, dielectric elastomer devices are improvements over existing devices. In other cases, however, dielectric elastomers can enable new types of devices that cannot be made with existing technologies, such as new types of loudspeakers and power generating devices. A new dipole loudspeaker system was developed using a commercially available push-pull diaphragm configuration. This same transducer configuration was used to develop a new power generating system. This generator system enables a power generation of 0.06 to 0.12 W by manually displacing the device by 5 to 6 mm once a second. By introducing a voltage step-down conversion circuit, the device was able to power wireless communications, allowing the control of devices separated by a distance of a few meters. These two devices are examples of the new applications that are enabled as the dielectric elastomer technology commercially emerges. Future improvements to dielectric elastomers could enable new capabilities in clean electrical power generation from ocean waves, for example.

  9. Resonant dielectric metamaterials

    DOEpatents

    Loui, Hung; Carroll, James; Clem, Paul G; Sinclair, Michael B

    2014-12-02

    A resonant dielectric metamaterial comprises a first and a second set of dielectric scattering particles (e.g., spheres) having different permittivities arranged in a cubic array. The array can be an ordered or randomized array of particles. The resonant dielectric metamaterials are low-loss 3D isotropic materials with negative permittivity and permeability. Such isotropic double negative materials offer polarization and direction independent electromagnetic wave propagation.

  10. Inductive dielectric analyzer

    NASA Astrophysics Data System (ADS)

    Agranovich, Daniel; Polygalov, Eugene; Popov, Ivan; Ben Ishai, Paul; Feldman, Yuri

    2017-03-01

    One of the approaches to bypass the problem of electrode polarization in dielectric measurements is the free electrode method. The advantage of this technique is that, the probing electric field in the material is not supplied by contact electrodes, but rather by electromagnetic induction. We have designed an inductive dielectric analyzer based on a sensor comprising two concentric toroidal coils. In this work, we present an analytic derivation of the relationship between the impedance measured by the sensor and the complex dielectric permittivity of the sample. The obtained relationship was successfully employed to measure the dielectric permittivity and conductivity of various alcohols and aqueous salt solutions.

  11. Temperature-controlled colossal magnetoresistance and perfect spin Seebeck effect in hybrid graphene/boron nitride nanoribbons.

    PubMed

    Zhu, Lin; Li, Ruimin; Yao, Kailun

    2017-02-01

    Thermal spin transport properties of graphene and hexagonal boron nitride nanoribbon heterojunctions have been investigated using density functional theory calculations combined with the Keldysh nonequilibrium Green's function approach. The results showed that the perfect spin Seebeck effect and analogy negative differential thermoelectric resistance occurred in the device under a temperature difference without a gate or bias voltage. An intriguing thermally induced colossal magnetoresistance without gate regulation was also observed, which can be switched between a positive and negative value with temperature control. It was also found that the unit number of zigzag graphene nanoribbons and boron nitride nanoribbons can tune the electronic band structure and the energy gap of the heterostructure, and then modulate the thermal spin transport properties. The results suggest that graphene and hexagonal boron nitride nanoribbon heterostructures may have potential applications in graphene-based nanodevices.

  12. Dielectric screening in semiconductors

    NASA Astrophysics Data System (ADS)

    Harrison, Walter A.; Klepeis, John E.

    1988-01-01

    Intra-atomic and interatomic Coulomb interactions are incorporated into bond-orbital theory, based upon universal tight-binding parameters, in order to treat the effects of charge redistribution in semiconductor bonds. The dielectric function ɛ(q) is obtained for wave numbers in a [100] direction. The screening of differences in average hybrid energy across a heterojunction is calculated in detail, indicating that the decay length for the potential depends upon the relative values of Madelung and intra-atomic Coulomb terms. The parameters used here predict an imaginary decay length and thus an oscillating potential near the interface. The same theory is applied to point defects by imbedding a cluster in a matrix lattice, taking charges in that lattice to be consistent with continuum theory. Illustrating the theory with a phosphorus impurity in silicon, it is seen that the impurity and its neighboring atoms have charges on the order of only one-tenth of an electronic charge, alternating in sign from neighbor to neighbor as for planar defects. Although there are shifts in the term values on the order of a volt, the difference in these shifts for neighboring atoms is much smaller so that the effect on the bonds is quite small. This behavior is analogous to the response of a dielectric continuum to a point charge: The medium is locally neutral except at the center of the cluster and there are slowly varying potentials e2/ɛr. Because of this slow variation, free-atom term values should ordinarily suffice for the calculation of bond properties and bond lengths at impurities. Corrections are larger for homovalent substitutions such as carbon in silicon.

  13. Phase transition and enhanced magneto-dielectric response in BiFeO{sub 3}-DyMnO{sub 3} multiferroics

    SciTech Connect

    Tripathy, Satya N. Pradhan, Dillip K.; Pradhan, Dhiren K.; Palai, Ratnakar; Katiyar, Ram S.; Mishra, Karuna K.; Sen, Shrabanee; Paulch, Marian; Scott, James F.

    2015-04-14

    We report systematic studies on crystal structure and magneto-dielectric properties of (1 − x) BiFeO{sub 3}-x DyMnO{sub 3} (0.0 ≤ x ≤ 0.2) nanoceramics synthesized by auto-combustion method. Rietveld refinement of X-ray diffraction data indicates a structural transition from R3c to R3c + Pn2{sub 1}a at x = 0.1. Field emission scanning electron micrographs display a decrease in grain size with increase in x. The presence of dielectric anomalies around antiferromagnetic transition temperature implies the magnetoelectric coupling. Dielectric measurements showed decrease in magnetic ordering temperature with increasing x in agreement with differential scanning calorimetry results. A significant increase in magnetization has been found with increasing DyMnO{sub 3} substitution. Magneto-impedance spectroscopy reveals a significant change (∼18%) in dielectric permittivity at H = 2 T for x = 0.2.

  14. Dielectric anisotropy in polar solvents under external fields

    NASA Astrophysics Data System (ADS)

    Buyukdagli, Sahin

    2015-08-01

    We investigate dielectric saturation and increment in polar liquids under external fields. We couple a previously introduced dipolar solvent model to a uniform electric field and derive the electrostatic kernel of interacting dipoles. This procedure allows an unambiguous definition of the liquid dielectric permittivity embodying non-linear dielectric response and correlation effects. We find that the presence of the external field results in a dielectric anisotropy characterized by a two-component dielectric permittivity tensor. The increase of the electric field amplifies the permittivity component parallel to the field direction, i.e. dielectric increment is observed along the field. However, the perpendicular component is lowered below the physiological permittivity {{\\varepsilon}w}≈ 77 , indicating dielectric saturation perpendicular to the field. By comparison with Molecular Dynamics simulations from the literature, we show that the mean-field level dielectric response theory underestimates dielectric saturation. The inclusion of dipolar correlations at the weak-coupling level intensify the mean-field level dielectric saturation and improves the agreement with simulation data at weak electric fields. The correlation-corrected theory predicts as well the presence of a metastable configuration corresponding to the antiparallel alignment of dipoles with the field. This prediction can be verified by solvent-explicit simulations where solvent molecules are expected to be trapped transiently in this metastable state.

  15. All-Dielectric Multilayer Cylindrical Structures for Invisibility Cloaking

    PubMed Central

    Mirzaei, Ali; Miroshnichenko, Andrey E.; Shadrivov, Ilya V.; Kivshar, Yuri S.

    2015-01-01

    We study optical response of all-dielectric multilayer structures and demonstrate that the total scattering of such structures can be suppressed leading to optimal invisibility cloaking. We use experimental material data and a genetic algorithm to reduce the total scattering by adjusting the material and thickness of various layers for several types of dielectric cores at telecommunication wavelengths. Our approach demonstrates 80-fold suppression of the total scattering cross-section by employing just a few dielectric layers. PMID:25858295

  16. Terahertz Artificial Dielectric Lens

    NASA Astrophysics Data System (ADS)

    Mendis, Rajind; Nagai, Masaya; Wang, Yiqiu; Karl, Nicholas; Mittleman, Daniel M.

    2016-03-01

    We have designed, fabricated, and experimentally characterized a lens for the THz regime based on artificial dielectrics. These are man-made media that mimic properties of naturally occurring dielectric media, or even manifest properties that cannot generally occur in nature. For example, the well-known dielectric property, the refractive index, which usually has a value greater than unity, can have a value less than unity in an artificial dielectric. For our lens, the artificial-dielectric medium is made up of a parallel stack of 100 μm thick metal plates that form an array of parallel-plate waveguides. The convergent lens has a plano-concave geometry, in contrast to conventional dielectric lenses. Our results demonstrate that this lens is capable of focusing a 2 cm diameter beam to a spot size of 4 mm, at the design frequency of 0.17 THz. The results further demonstrate that the overall power transmission of the lens can be better than certain conventional dielectric lenses commonly used in the THz regime. Intriguingly, we also observe that under certain conditions, the lens boundary demarcated by the discontinuous plate edges actually resembles a smooth continuous surface. These results highlight the importance of this artificial-dielectric technology for the development of future THz-wave devices.

  17. The influence of the semiconductor and dielectric properties on surface flashover in silicon-dielectric systems

    SciTech Connect

    Gradinaru, G.; Madangarli, V.P.; Sudarshan, T.S. . Dept. of Electrical and Computer Engineering)

    1994-07-01

    New experimental results on surface flashover are reported for high field silicon-dielectric systems. Different conditions of the lateral surface, contacts and ambient dielectrics have been studied. The strong influence of the semiconductor quality, and that of the dielectric properties, on the prebreakdown and breakdown response of the system, is demonstrated. All experimental results strongly support the conclusion that surface flashover in silicon systems is a physical process totally different from semiconductor surface breakdown. This conclusion has important practical application in the improvement of the performance of photoconductive power switches, severely limited by premature breakdown effects.

  18. Highly efficient omnidirectional structural color tuning method based on dielectric-metal-dielectric structure.

    PubMed

    Fang, Bo; Yang, Chenying; Shen, Weidong; Zhang, Xing; Zhang, Yueguang; Liu, Xu

    2017-02-01

    A novel and convenient scheme is proposed to achieve angle insensitive color filtering across a large color gamut by simply altering the thickness of the dielectric layer of a dielectric-metal-dielectric grating structure. The plasmonic filter presents a great feature of angle resolved spectrum response up to 60° and is independent of the azimuthal angle and the polarization state as well so as to construct an omnidirectional filter for practical applications. The color tuning feature of the proposed filter with varied dielectric thickness is attributed to the modulation of the condition for the localized surface plasmon resonance, which bears responsibility for the omnidirectional property of this plasmonic filter. This color-tuning method with a single mold size required can have wide applications in fields of display, colorful decoration, printing, and so forth.

  19. Dielectric Characterization of Mylar and The Effects of Doping Processes.

    SciTech Connect

    Belcher, Cami Beth

    2016-11-01

    Mylar® polymer is a bi-axially oriented polyethylene terephthalate (PET) polymer film used widely as a dielectric, specifically in capacitors. The dielectric characteristics of Mylar have been well studied and documented over the years; however, many of the mechanisms responsible for dielectric breakdown and failure are not understood for modified versions of the material. Previous studies on Mylar confirm that factors such as temperature, humidity, and voltage ramp rates can also have a significant effect on the dielectric properties and measurement of the dielectric properties. This study seeks to determine how dielectric properties, including permittivity, dielectric loss, and breakdown strength, are affected by doping of the polymer. To do this, two types of Mylar films, virgin film and film doped with a small-molecule electron-acceptor, are tested. Both types of materials are tested under a variety of environmental and experimental conditions, including testing at elevated temperatures, varying relative humidity, and varying ramp rates in dielectric breakdown testing. Analysis of permittivity, dielectric loss, and breakdown strength will be presented comparing virgin and doped Mylar to gain insight into the effects of doping with electron-acceptor molecules on dielectric properties under these varying environmental and test conditions.

  20. A new dielectric metamaterial building block with a strong magnetic response in the sub-1.5-micrometer region: silicon colloid nanocavities.

    PubMed

    Shi, Lei; Tuzer, T Umut; Fenollosa, Roberto; Meseguer, Francisco

    2012-11-20

    A new dielectric metamaterial building block based on high refractive index silicon spherical nanocavities with Mie resonances appearing in the near infrared optical region is prepared and characterized. It is demonstrated both experimentally and theoretically that a single silicon nanocavity supports well-defined and robust magnetic resonances, even in a liquid medium environment, at wavelength values up to six times larger than the cavity radius.

  1. Dielectric responses of modified BaTiO3 ceramics in multilayer ceramic capacitors to the combined uniaxial stress and dc bias field

    NASA Astrophysics Data System (ADS)

    Yang, Gang; Yue, Zhenxing; Gui, Zhilun; Li, Longtu

    2008-10-01

    Dielectric measurements of modified BaTiO3 in a multilayer ceramic capacitor (MLCC) show that the application of external uniaxial stress perpendicular to electric field in a MLCC can lead to a slight increase in the dielectric permittivity. The additional application of a dc bias results in a significantly suppressed dielectric permittivity in the temperature range from 228 to 453 K. These observations can be explained as a result of domain wall movements in grains with a core-shell structure, due to the combined stress and dc bias field. As the dc bias increased up to 5.6 MV/m, the Curie peak, which has diffuse phase transition characteristics in the absence of dc bias, becomes sharper, and two new peaks are induced at about 250 and 315 K. Furthermore, the first order paraelectric-ferroelectric phase transition of the modified BaTiO3 ceramic becomes stronger with increasing dc bias when a uniaxial stress is also applied.

  2. Diffractive coherence in multilayer dielectric gratings

    SciTech Connect

    Shore, B.W.; Feit, M.D.; Perry, M.D.; Boyd, R.D.; Britten, J.A.; Li, Lifeng

    1995-05-26

    Successful operation of large-scale high-power lasers, such as those in use and planned at LLNL and elsewhere, require optical elements that can withstand extremely high fluences without suffering damage. Of particular concern are dielectric diffraction gratings used for beam sampling and pulse compression. Laser induced damage to bulk dielectric material originates with coupling of the electric field of the radiation to bound electrons, proceeding through a succession of mechanisms that couple the electron kinetic energy to lattice energy and ultimately to macroscopic structural changes (e.g. melting). The constructive interference that is responsible for the diffractive behavior of a grating or the reflective properties of a multilayer dielectric stack can enhance the electric field above values that would occur in unstructured homogeneous material. Much work has been done to model damage to bulk matter. The presence of nonuniform electric fields, resulting from diffractive coherence, has the potential to affect damage thresholds and requires more elaborate theory. We shall discuss aspects of work directed towards understanding the influence of dielectric structures upon damage, with particular emphasis on computations and interpretation of electric fields within dielectric gratings and multilayer dielectric stacks, noting particularly the interference effects that occur in these structures.

  3. Colossal negative thermal expansion with an extended temperature interval covering room temperature in fine-powdered Mn0.98CoGe

    NASA Astrophysics Data System (ADS)

    Lin, Jianchao; Tong, Peng; Zhang, Kui; Tong, Haiyun; Guo, Xinge; Yang, Cheng; Wu, Ying; Wang, Meng; Lin, Shuai; Chen, Li; Song, Wenhai; Sun, Yuping

    2016-12-01

    MnM'X (M' = Co, Ni; X = Ge, Si, etc.) alloys usually present a large volumetric change during the Martensitic (MA) transformation. This offers a great opportunity for exploring new negative thermal expansion (NTE) materials if the temperature interval of NTE can be extended. Here, we report colossal NTE in fine-powdered Mn0.98CoGe prepared by repeated thermal cycling (TC) through the MA transition or ball milling. Both treatments can expand the MA transformation, and thus broaden the NTE temperature window (ΔT). For the powders that have gone through TC for ten times, ΔT reaches 90 K (309 K-399 K), and the linear expansion coefficient (αL) is about -141 ppm/K, which rank among the largest values of colossal NTE materials. The difference between two kinds of treatments and the possible mechanisms of the extended MA transformation window are discussed based on the introduced strain.

  4. Dielectric comparison of lunar and terrestrial fines at lunar conditions

    NASA Technical Reports Server (NTRS)

    Alvarez, R.

    1974-01-01

    The dielectric properties of lunar fines 74241,2 in the audio-frequency range under lunarlike conditions are presented. Results suggest that volatiles are released during storage and transport of the lunar sample. Apparently, subsequent adsorption of volatiles on the sample surface alters its dielectric response. The assumed volatile influence disappears after evacuation. A comparison of the dielectric properties of lunar and terrestrial materials as a function of density, temperature, and frequency indicates that if the terrestrial sample analyzed were completely devoid of atmospheric moisture, it would present dielectric losses smaller than those of the lunar sample. It is concluded that density prevails over temperature as the controlling factor of dielectric permittivity in the lunar regolith and that dielectric losses vary slowly with depth.

  5. Improved Dielectric Films For Capacitors

    NASA Technical Reports Server (NTRS)

    Yen, Shiao-Ping S.; Lewis, Carol R.; Cygan, Peter J.; Jow, T. Richard

    1994-01-01

    Dielectric films made from blends of some commercially available high-dielectric-constant cyanoresins with each other and with cellulose triacetate (CTA) have both high dielectric constants and high breakdown strengths. Dielectric constants as high as 16.2. Films used to produce high-energy-density capacitors.

  6. Fabrication of Polyurethane Dielectric Actuators

    DTIC Science & Technology

    2005-01-01

    a summary of a 3 year Technology Investment Fund Project entitled “Dielectric Polymer Actuators for Active/ Passive Vibration Isolation”, which was...completed in March 2005. The purpose of this project was to investigate dielectric polymer materials for potential use in active/ passive vibration...devices and systems based on dielectric polymer actuators. Keywords: dielectric actuators, electroactive polymers , Technology Investment Fund 1

  7. Multi-susceptibile Single-Phased Ceramics with Both Considerable Magnetic and Dielectric Properties by Selectively Doping

    PubMed Central

    Liu, Chuyang; Zhang, Yujing; Jia, Jingguo; Sui, Qiang; Ma, Ning; Du, Piyi

    2015-01-01

    Multiferroic ceramics with extraordinary susceptibilities coexisting are vitally important for the multi-functionality and integration of electronic devices. However, multiferroic composites, as the most potential candidates, will introduce inevitable interface deficiencies and thus dielectric loss from dissimilar phases. In this study, single-phased ferrite ceramics with considerable magnetic and dielectric performances appearing simultaneously were fabricated by doping target ions in higher valence than that of Fe3+, such as Ti4+, Nb5+ and Zr4+, into BaFe12O19. In terms of charge balance, Fe3+/Fe2+ pair dipoles are produced through the substitution of Fe3+ by high-valenced ions. The electron hopping between Fe3+ and Fe2+ ions results in colossal permittivity. Whilst the single-phased ceramics doped by target ions exhibit low dielectric loss naturally due to the diminishment of interfacial polarization and still maintain typical magnetic properties. This study provides a convenient method to attain practicable materials with both outstanding magnetic and dielectric properties, which may be of interest to integration and multi-functionality of electronic devices. PMID:25835175

  8. Colossal Room-Temperature Electrocaloric Effect in Ferroelectric Polymer Nanocomposites Using Nanostructured Barium Strontium Titanates.

    PubMed

    Zhang, Guangzu; Zhang, Xiaoshan; Yang, Tiannan; Li, Qi; Chen, Long-Qing; Jiang, Shenglin; Wang, Qing

    2015-07-28

    The electrocaloric effect (ECE) refers to conversion of thermal to electrical energy of polarizable materials and could form the basis for the next-generation refrigeration and power technologies that are highly efficient and environmentally friendly. Ferroelectric materials such as ceramic and polymer films exhibit large ECEs, but each of these monolithic materials has its own limitations for practical cooling applications. In this work, nanosized barium strontium titanates with systematically varied morphologies have been prepared to form polymer nanocomposites with the ferroelectric polymer matrix. The solution-processed polymer nanocomposites exhibit an extraordinary room-temperature ECE via the synergistic combination of the high breakdown strength of a ferroelectric polymer matrix and the large change of polarization with temperature of ceramic nanofillers. It is found that a sizable ECE can be generated under both modest and high electric fields, and further enhanced greatly by tailoring the morphology of the ferroelectric nanofillers such as increasing the aspect ratio of the nanoinclusions. The effect of the geometry of the nanofillers on the dielectric permittivity, polarization, breakdown strength, ECE and crystallinity of the ferroelectric polymer has been systematically investigated. Simulations based on the phase-field model have been carried out to substantiate the experimental results. With the remarkable cooling energy density and refrigerant capacity, the polymer nanocomposites are promising for solid-state cooling applications.

  9. Cast dielectric composite linear accelerator

    DOEpatents

    Sanders, David M.; Sampayan, Stephen; Slenes, Kirk; Stoller, H. M.

    2009-11-10

    A linear accelerator having cast dielectric composite layers integrally formed with conductor electrodes in a solventless fabrication process, with the cast dielectric composite preferably having a nanoparticle filler in an organic polymer such as a thermosetting resin. By incorporating this cast dielectric composite the dielectric constant of critical insulating layers of the transmission lines of the accelerator are increased while simultaneously maintaining high dielectric strengths for the accelerator.

  10. Nonlinear electroelastic deformations of dielectric elastomer composites: II - Non-Gaussian elastic dielectrics

    NASA Astrophysics Data System (ADS)

    Lefèvre, Victor; Lopez-Pamies, Oscar

    2017-02-01

    This paper presents an analytical framework to construct approximate homogenization solutions for the macroscopic elastic dielectric response - under finite deformations and finite electric fields - of dielectric elastomer composites with two-phase isotropic particulate microstructures. The central idea consists in employing the homogenization solution derived in Part I of this work for ideal elastic dielectric composites within the context of a nonlinear comparison medium method - this is derived as an extension of the comparison medium method of Lopez-Pamies et al. (2013) in nonlinear elastostatics to the coupled realm of nonlinear electroelastostatics - to generate in turn a corresponding solution for composite materials with non-ideal elastic dielectric constituents. Complementary to this analytical framework, a hybrid finite-element formulation to construct homogenization solutions numerically (in three dimensions) is also presented. The proposed analytical framework is utilized to work out a general approximate homogenization solution for non-Gaussian dielectric elastomers filled with nonlinear elastic dielectric particles that may exhibit polarization saturation. The solution applies to arbitrary (non-percolative) isotropic distributions of filler particles. By construction, it is exact in the limit of small deformations and moderate electric fields. For finite deformations and finite electric fields, its accuracy is demonstrated by means of direct comparisons with finite-element solutions. Aimed at gaining physical insight into the extreme enhancement in electrostriction properties displayed by emerging dielectric elastomer composites, various cases wherein the filler particles are of poly- and mono-disperse sizes and exhibit different types of elastic dielectric behavior are discussed in detail. Contrary to an initial conjecture in the literature, it is found (inter alia) that the isotropic addition of a small volume fraction of stiff (semi

  11. Pattern formation in dielectric barrier discharges with different dielectric materials

    SciTech Connect

    Dong, L. F.; Fan, W. L.; Wang, S.; Ji, Y. F.; Liu, Z. W.; Chen, Q.

    2011-03-15

    The influence of dielectric material on the bifurcation and spatiotemporal dynamics of the patterns in dielectric barrier discharge in argon/air at atmospheric pressure is studied. It is found that pattern bifurcation sequences are different with different dielectric materials. The spatiotemporal dynamics of the hexagonal pattern in dielectric barrier discharge depends on the dielectric material. The hexagon pattern with glass dielectric is an interleaving of two rectangular sublattices appearing at different moments. The hexagon pattern with quartz dielectric is composed of one set of hexagonal lattice discharging twice in one half cycle of the applied voltage, one is at the rising edge and the other at the falling edge. It results in that the accumulation of wall charges in individual microdischarges in a hexagon pattern with quartz dielectric is greater than that with glass dielectric, which is in agreement with the electron density measurement by Stark broadening of Ar I 696.54 nm.

  12. Pyroelectric and dielectric properties of ferroelectric films with interposed dielectric buffer layers

    NASA Astrophysics Data System (ADS)

    Espinal, Y.; Kesim, M. T.; Misirlioglu, I. B.; Trolier-McKinstry, S.; Mantese, J. V.; Alpay, S. P.

    2014-12-01

    The dielectric and pyroelectric properties of c-domain ferroelectric films with linear dielectric buffer layers were investigated theoretically. Computations were carried out for multilayers consisting of PbZr0.2Ti0.8O3 with Al2O3, SiO2, Si3N4, HfO2, and TiO2 buffers on metalized Si. It is shown that the dielectric and pyroelectric properties of such multilayers can be increased by the presence of the buffer compared to ferroelectric monolayers. Calculations for PbZr0.2Ti0.8O3 films with 1% Al2O3 interposed between electrodes on Si show that the dielectric and pyroelectric coefficients are 310 and 0.070 μC cm-2 °C-1, respectively. Both values are higher than the intrinsic response of PbZr0.2Ti0.8O3 monolayer on Si.

  13. PREFACE: Dielectrics 2009: Measurement Analysis and Applications

    NASA Astrophysics Data System (ADS)

    Vaughan, Alun; Williams, Graham

    2009-07-01

    2001 the Annual Meetings focused on numerous topics, including relaxation and conduction processes in liquids, solids, liquid crystals, synthetic polymers and biopolymers, piezoelectric materials, electrets and ferroelectrets, interfacial phenomena, high field conduction and breakdown phenomena in solids, liquids and gases and, importantly, the remarkable developments in dielectric instrumentation during this period. These activities reflected the need, and willingness, to move dielectrics researches with the times. As examples of the variety and diversity of these meetings we may refer briefly to the 1981, 1989 and 1996 Meetings. The 1981 Oxford Meeting on High Field Phenomena in Dielectrics included strong themes on fundamental and practical effects of high E-fields on the dielectric and conduction behaviour of liquids and solids, electrical treeing and dielectric breakdown, non-linear dielectric effects, electrets, thin-film devices and electro-rheology. The late 1980's had seen large initiatives in the UK and globally in the general area of Molecular Electronics so, in timely fashion, this was the subject of the 1989 Meeting in Bangor. The 1996 Smart Dielectrics Meeting at Canterbury reported subsequent advances in designer materials having electro-responsive and electro-optical properties. The programme concerned electro- and photo-active materials, mainly organic, in the form of polar dielectrics, polyelectrolytes, organic semi- and photo-conductors, photo-refractive polymer films, organic ferroelectric films, liquid crystalline polymer films, piezo- and pyro-electric polymer films, electroluminescent polymers, electro-rheological fluids and non-linear optical polymer films as described by leading international scientists. The physico-chemical functions of the materials were demonstrated and interpreted in terms of fundamental molecular properties. An Archive, containing full details of all the Meetings of the DDG and the Dielectrics Society, has been placed on

  14. Fermi surfaces, spin-mixing parameter, and colossal anisotropy of spin relaxation in transition metals from ab initio theory

    NASA Astrophysics Data System (ADS)

    Zimmermann, Bernd; Mavropoulos, Phivos; Long, Nguyen H.; Gerhorst, Christian-Roman; Blügel, Stefan; Mokrousov, Yuriy

    2016-04-01

    The Fermi surfaces and Elliott-Yafet spin-mixing parameter (EYP) of several elemental metals are studied by ab initio calculations. We focus first on the anisotropy of the EYP as a function of the direction of the spin-quantization axis [B. Zimmermann et al., Phys. Rev. Lett. 109, 236603 (2012), 10.1103/PhysRevLett.109.236603]. We analyze in detail the origin of the gigantic anisotropy in 5 d hcp metals as compared to 5 d cubic metals by band structure calculations and discuss the stability of our results against an applied magnetic field. We further present calculations of light (4 d and 3 d ) hcp crystals, where we find a huge increase of the EYP anisotropy, reaching colossal values as large as 6000 % in hcp Ti. We attribute these findings to the reduced strength of spin-orbit coupling, which promotes the anisotropic spin-flip hot loops at the Fermi surface. In order to conduct these investigations, we developed an adapted tetrahedron-based method for the precise calculation of Fermi surfaces of complicated shape and accurate Fermi-surface integrals within the full-potential relativistic Korringa-Kohn-Rostoker Green function method.

  15. Successive Magnetic-Field-Induced Transitions and Colossal Magnetoelectric Effect in Ni3TeO6

    DOE PAGES

    Kim, Jae Wook; Artyukhin, Sergei; Mun, Eun Deok; ...

    2015-09-24

    In this paper, we report the discovery of a metamagnetic phase transition in a polar antiferromagnet Ni3TeO6 that occurs at 52 T. The new phase transition accompanies a colossal magnetoelectric effect, with a magnetic-field-induced polarization change of 0.3 μC/cm2, a value that is 4 times larger than for the spin-flop transition at 9 T in the same material, and also comparable to the largest magnetically induced polarization changes observed to date. Via density-functional calculations we construct a full microscopic model that describes the data. We model the spin structures in all fields and clarify the physics behind the 52 Tmore » transition. The high-field transition involves a competition between multiple different exchange interactions which drives the polarization change through the exchange-striction mechanism. Finally, the resultant spin structure is rather counterintuitive and complex, thus providing new insights on design principles for materials with strong magnetoelectric coupling.« less

  16. Electric field induced metal-insulator transition and colossal magnetoresistance in CdCr2S4

    NASA Astrophysics Data System (ADS)

    Sun, C. P.; Lin, C. C.; Her, J. L.; Taran, S.; Chou, C. C.; Chan, C. L.; Huang, C. L.; Berger, H.; Yang, H. D.

    2008-03-01

    Multiferroic ordering existing in a single material is a recent hot topic in the field of condensed matter physics due to its potential application in device control. The chromium chalcogenide spinel CdCr2S4 is one of the attractive materials investigated by Hemberger et al. recently.[1] Based on the electrical measurement, there is no discontinuity through the ferromagnetic ordering at TC ˜ 85K.[2] We measure the temperature dependent resistance under various electric fields to investigate the electrical properties of the present material. To our knowledge, we first observe the electric field induced metal-insulator transition in this material around TC. Moreover, a colossal magnetoresistance (CMR), which is comparable to that of manganese-based CMR material, is also observed near TC. The origin for these properties is discussed. [1] J. Hemberger, P. Lunkenheimer, R. Fichtl, H.-A. Krug von Nidda, V. Tsurkan, A. Loidl, Nature 434, 364 (2006). [2] P. K. Baltzer, H. W. Lehmann, and M. Robbins, Phys. Rev. Lett. 15, 493 (1965).

  17. Colossal low-frequency resonant magnetomechanical and magnetoelectric effects in a three-phase ferromagnetic/elastic/piezoelectric composite

    NASA Astrophysics Data System (ADS)

    Liu, Guoxi; Li, Xiaotian; Chen, Jianguo; Shi, Huaduo; Xiao, Wenlei; Dong, Shuxiang

    2012-10-01

    Colossal low-frequency resonant magnetomechanical (MM) and magnetoelectric (ME) coupling effects have been found in a three-phase composite made of Pb(Zr,Ti)O3 ceramic fibers/phosphor copper-sheet unimorph and NdFeB magnets. The experimental results revealed that the ferromagnetic/elastic/piezoelectric three-phase composite with a cantilever beam structure could show huge bending MM coefficient of ˜145.9 × 10-3/Oe (unit in bending radian per Oe) and ME voltage coefficient of ˜16 000 V/cm.Oe at the first-order bending resonance frequency of ˜5 Hz. The achieved results related to ME effect are at least one order of magnitude higher over those of other ME materials and devices reported ever. The extremely strong MM and ME couplings in the three-phase composite are due to strong magnetic force moment effect induced by the interaction between NdFeB magnets and the applied magnetic field, and further resonant enhancement via the strain-mediated phosphor copper-sheet with a relatively high mechanical quality factor.

  18. Effect of temperature, high pressure and freezing/thawing of dry-cured ham slices on dielectric time domain reflectometry response.

    PubMed

    Rubio-Celorio, Marc; Garcia-Gil, Núria; Gou, Pere; Arnau, Jacint; Fulladosa, Elena

    2015-02-01

    Dielectric Time Domain Reflectometry (TDR) is a useful technique for the characterization and classification of dry-cured ham according to its composition. However, changes in the behavior of dielectric properties may occur depending on environmental factors and processing. The effect of temperature, high pressure (HP) and freezing/thawing of dry-cured ham slices on the obtained TDR curves and on the predictions of salt and water contents when using previously developed predictive models, was evaluated in three independent experiments. The results showed that at temperatures below 20 °C there is an increase of the predicted salt content error, being more important in samples with higher water content. HP treatment caused a decrease of the reflected signal intensity due to the major mobility of available ions promoting an increase of the predicted salt content. Freezing/thawing treatment caused an increase of the reflected signal intensity due to the microstructural damages and the loss of water and ions, promoting a decrease of the predicted salt content.

  19. Dielectric relaxation and magnetodielectric response in DyMn{sub 0.5}Cr{sub 0.5}O{sub 3}

    SciTech Connect

    Yuan, B.; Yang, J. Zuo, X. Z.; Zhu, X. B.; Dai, J. M.; Song, W. H.; Kan, X. C.; Zu, L.; Sun, Y. P.

    2015-09-28

    We investigate the structural, magnetic, and magnetodielectric properties of DyMn{sub 0.5}Cr{sub 0.5}O{sub 3}. The sample can be indexed with an orthorhombic phase with B site disordered space group Pbnm. The valence state of both Mn and Cr ions are suggested to be +3 based on the results of x-ray photoelectron spectroscopy. Two thermally excited dielectric relaxation at temperatures T{sub N2} < T< 300 K and large magnetodielectric effect (MDC = 20%–30%) due to the disordered arrangement of Mn{sup 3+}/Cr{sup 3+} ions associated with electron hopping between them are observed. The absence of any noticeable magnetoresistance effect (MR < 0.5%) demonstrates that the observed magnetodielectric effect is an intrinsic behavior. These results suggest that DyMn{sub 0.5}Cr{sub 0.5}O{sub 3} is a magnetodielectric compound, whose dielectric properties are dependence of the applied magnetic field, which exhibits such effects near room temperature and holds great promise for future device applications.

  20. A single dielectric nanolaser

    NASA Astrophysics Data System (ADS)

    Huang, Tsung-Yu; Yen, Ta-Jen

    2016-09-01

    To conquer Ohmic losses from metal and enhance pump absorption efficiency of a nanolaser based on surface plasmon polariton, we theoretically calculate the first magnetic and electric scattering coefficient of a dielectric sphere under a plane wave excitation with a dielectric constant of around 12. From this calculation, we could retrieve both negative effective permittivity and permeability of the sphere simultaneously at frequencies around 153 THz in the aids of Lewin's theory and the power distribution clearly demonstrate the expected negative Goos-Hänchen effect, which usually occurred in a negative refractive waveguide, thus creating two energy vortices to trap incident energy and then promoting the pump absorption efficiency. Meanwhile, a magnetic lasing mode at 167.3 THz is demonstrated and reveals a magnetic dipole resonance mode and a circulating energy flow within the dielectric sphere, providing a possible stopped light feedback mechanism to enable the all-dielectric nanolaser. More importantly, the corresponding mode volume is reduced to 0.01λ3 and a gain threshold of 5.1×103 is obtained. To validate our design of all-dielectric nanolaser, we employ finite-difference-time-domain simulation software to examine the behavior of the nanolaser. From simulation, we could obtain a pinned-down population inversion of 0.001 and a lasing peak at around 166.5 THz, which is very consistent with the prediction of Mie theory. Finally, according to Mie theory, we can regard the all-dielectric nanolaser as the excitation of material polariton and thus could make an analogue between lasing modes of the dielectric and metallic nanoparticles.

  1. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Effective Anisotropic Dielectric Properties of Crystal Composites

    NASA Astrophysics Data System (ADS)

    Wei, En-Bo; Gu, Guo-Qing; Poon, Ying-Ming; Franklin, G. Shin

    2010-02-01

    Transformation field method (TFM) is developed to estimate the anisotropic dielectric properties of crystal composites having arbitrary shapes and dielectric properties of crystal inclusions, whose principal dielectric axis are different from those of anisotropic crystal matrix. The complicated boundary-value problem caused by inclusion shapes is circumvented by introducing a transformation electric field into the crystal composites regions, and the effective anisotropic dielectric responses are formulated in terms of the transformation field. Furthermore, the numerical results show that the effective anisotropic dielectric responses of crystal composites periodically vary as a function of the rotating angle between the principal dielectric axes of inclusion and matrix crystal materials. It is found that at larger inclusion volume fraction the inclusion shapes induce profound effect on the effective anisotropic dielectric responses.

  2. Dielectric elastomer actuators for facial expression

    NASA Astrophysics Data System (ADS)

    Wang, Yuzhe; Zhu, Jian

    2016-04-01

    Dielectric elastomer actuators have the advantage of mimicking the salient feature of life: movements in response to stimuli. In this paper we explore application of dielectric elastomer actuators to artificial muscles. These artificial muscles can mimic natural masseter to control jaw movements, which are key components in facial expressions especially during talking and singing activities. This paper investigates optimal design of the dielectric elastomer actuator. It is found that the actuator with embedded plastic fibers can avert electromechanical instability and can greatly improve its actuation. Two actuators are then installed in a robotic skull to drive jaw movements, mimicking the masseters in a human jaw. Experiments show that the maximum vertical displacement of the robotic jaw, driven by artificial muscles, is comparable to that of the natural human jaw during speech activities. Theoretical simulations are conducted to analyze the performance of the actuator, which is quantitatively consistent with the experimental observations.

  3. Dielectric Constant of Suspensions

    NASA Astrophysics Data System (ADS)

    Mendelson, Kenneth S.; Ackmann, James J.

    1997-03-01

    We have used a finite element method to calculate the dielectric constant of a cubic array of spheres. Extensive calculations support preliminary conclusions reported previously (K. Mendelson and J. Ackmann, Bull. Am. Phys. Soc. 41), 657 (1996).. At frequencies below 100 kHz the real part of the dielectric constant (ɛ') shows oscillations as a function of the volume fraction of suspension. These oscillations disappear at low conductivities of the suspending fluid. Measurements of the dielectric constant (J. Ackmann, et al., Ann. Biomed. Eng. 24), 58 (1996). (H. Fricke and H. Curtis, J. Phys. Chem. 41), 729 (1937). are not sufficiently sensitive to show oscillations but appear to be consistent with the theoretical results.

  4. Superdirective dielectric nanoantennas

    NASA Astrophysics Data System (ADS)

    Krasnok, Alexander E.; Simovski, Constantin R.; Belov, Pavel A.; Kivshar, Yuri S.

    2014-06-01

    We introduce the novel concept of superdirective nanoantennas based on the excitation of higher-order magnetic multipole moments in subwavelength dielectric nanoparticles. Our superdirective nanoantenna is a small Si nanosphere containing a notch, and is excited by a dipole located within the notch. In addition to extraordinary directivity, this nanoantenna demonstrates efficient radiation steering at the nanoscale, resulting from the subwavelength sensitivity of the beam radiation direction to variation of the source position inside the notch. We compare our dielectric nanoantenna with a plasmonic nanoantenna of similar geometry, and reveal that the nanoantenna's high directivity in the regime of transmission is not associated with strong localization of near fields in the regime of reception. Likewise, the absence of hot spots inside the nanoantenna leads to low dissipation in the radiation regime, so that our dielectric nanoantenna has significantly smaller losses and high radiation efficiency of up to 70%.

  5. Dielectric assist accelerating structure

    NASA Astrophysics Data System (ADS)

    Satoh, D.; Yoshida, M.; Hayashizaki, N.

    2016-01-01

    A higher-order TM02 n mode accelerating structure is proposed based on a novel concept of dielectric loaded rf cavities. This accelerating structure consists of ultralow-loss dielectric cylinders and disks with irises which are periodically arranged in a metallic enclosure. Unlike conventional dielectric loaded accelerating structures, most of the rf power is stored in the vacuum space near the beam axis, leading to a significant reduction of the wall loss, much lower than that of conventional normal-conducting linac structures. This allows us to realize an extremely high quality factor and a very high shunt impedance at room temperature. A simulation of a 5 cell prototype design with an existing alumina ceramic indicates an unloaded quality factor of the accelerating mode over 120 000 and a shunt impedance exceeding 650 M Ω /m at room temperature.

  6. Controlling birefringence in dielectrics

    NASA Astrophysics Data System (ADS)

    Danner, Aaron J.; Tyc, Tomáš; Leonhardt, Ulf

    2011-06-01

    Birefringence, from the very essence of the word itself, refers to the splitting of light rays into two parts. In natural birefringent materials, this splitting is a beautiful phenomenon, resulting in the perception of a double image. In optical metamaterials, birefringence is often an unwanted side effect of forcing a device designed through transformation optics to operate in dielectrics. One polarization is usually implemented in dielectrics, and the other is sacrificed. Here we show, with techniques beyond transformation optics, that this need not be the case, that both polarizations can be controlled to perform useful tasks in dielectrics, and that rays, at all incident angles, can even follow different trajectories through a device and emerge together as if the birefringence did not exist at all. A number of examples are shown, including a combination Maxwell fisheye/Luneburg lens that performs a useful task and is achievable with current fabrication materials.

  7. Thermally switchable dielectrics

    DOEpatents

    Dirk, Shawn M.; Johnson, Ross S.

    2013-04-30

    Precursor polymers to conjugated polymers, such as poly(phenylene vinylene), poly(poly(thiophene vinylene), poly(aniline vinylene), and poly(pyrrole vinylene), can be used as thermally switchable capacitor dielectrics that fail at a specific temperature due to the non-conjugated precursor polymer irreversibly switching from an insulator to the conjugated polymer, which serves as a bleed resistor. The precursor polymer is a good dielectric until it reaches a specific temperature determined by the stability of the leaving groups. Conjugation of the polymer backbone at high temperature effectively disables the capacitor, providing a `built-in` safety mechanism for electronic devices.

  8. A dielectric affinity microbiosensor

    NASA Astrophysics Data System (ADS)

    Huang, Xian; Li, Siqi; Schultz, Jerome S.; Wang, Qian; Lin, Qiao

    2010-01-01

    We present an affinity biosensing approach that exploits changes in dielectric properties of a polymer due to its specific, reversible binding with an analyte. The approach is demonstrated using a microsensor comprising a pair of thin-film capacitive electrodes sandwiching a solution of poly(acrylamide-ran-3-acrylamidophenylboronic acid), a synthetic polymer with specific affinity to glucose. Binding with glucose induces changes in the permittivity of the polymer, which can be measured capacitively for specific glucose detection, as confirmed by experimental results at physiologically relevant concentrations. The dielectric affinity biosensing approach holds the potential for practical applications such as long-term continuous glucose monitoring.

  9. Multilayer dielectric diffraction gratings

    DOEpatents

    Perry, Michael D.; Britten, Jerald A.; Nguyen, Hoang T.; Boyd, Robert; Shore, Bruce W.

    1999-01-01

    The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described.

  10. Multilayer dielectric diffraction gratings

    DOEpatents

    Perry, M.D.; Britten, J.A.; Nguyen, H.T.; Boyd, R.; Shore, B.W.

    1999-05-25

    The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described. 7 figs.

  11. Millimeter wave and terahertz dielectric properties of biological materials

    NASA Astrophysics Data System (ADS)

    Khan, Usman Ansar

    Broadband dielectric properties of materials can be employed to identify, detect, and characterize materials through their unique spectral signatures. In this study, millimeter wave, submillimeter wave, and terahertz dielectric properties of biological substances inclusive of liquids, solids, and powders were obtained using Dispersive Fourier Transform Spectroscopy (DFTS). Two broadband polarizing interferometers were constructed to test materials from 60 GHz to 1.2 THz. This is an extremely difficult portion of the frequency spectrum to obtain a material's dielectric properties since neither optical nor microwave-based techniques provide accurate data. The dielectric characteristics of liquids such as cyclohexane, chlorobenzene, benzene, ethanol, methanol, 1,4 dioxane, and 10% formalin were obtained using the liquid interferometer. Subsequently the solid interferometer was utilized to determine the dielectric properties of human breast tissues, which are fixed and preserved in 10% formalin. This joint collaboration with the Tufts New England Medical Center demonstrated a significant difference between the dielectric response of tumorous and non-tumorous breast tissues across the spectrum. Powders such as anthrax, flour, talc, corn starch, dry milk, and baking soda have been involved in a number of security threats and false alarms around the globe in the last decade. To be able to differentiate hoax attacks and serious security threats, the dielectric properties of common household powders were also examined using the solid interferometer to identify the powders' unique resonance peaks. A new sample preparation kit was designed to test the powder specimens. It was anticipated that millimeter wave and terahertz dielectric characterization will enable one to clearly distinguish one powder from the other; however most of the powders had relatively close dielectric responses and only Talc had a resonance signature recorded at 1.135 THz. Furthermore, due to

  12. Optimal Super Dielectric Material

    DTIC Science & Technology

    2015-09-01

    electrically insulating materials filled to the point of incipient wetness (paste consistency) with liquids containing dissolved ions. This work...109. This strongly supports the fundamental hypothesis of SDM: In the presence of an electric field any electrically insulating, porous material...ABSTRACT The results of this study establish that powder-based super dielectric materials (SDM) are a large family of porous electrically

  13. Ionic Structure at Dielectric Interfaces

    NASA Astrophysics Data System (ADS)

    Jing, Yufei

    The behavior of ions in liquids confined between macromolecules determines the outcome of many nanoscale assembly processes in synthetic and biological materials such as colloidal dispersions, emulsions, hydrogels, DNA, cell membranes, and proteins. Theoretically, the macromolecule-liquid boundary is often modeled as a dielectric interface and an important quantity of interest is the ionic structure in a liquid confined between two such interfaces. The knowledge gleaned from the study of ionic structure in such models can be useful in several industrial applications, such as biosensors, lithium-ion batteries double-layer supercapacitors for energy storage and seawater desalination. Electrostatics plays a critical role in the development of such functional materials. Many of the functions of these materials, result from charge and composition heterogeneities. There are great challenges in solving electrostatics problems in heterogeneous media with arbitrary shapes because electrostatic interactions remains unknown but depend on the particular density of charge distributions. Charged molecules in heterogeneous media affect the media's dielectric response and hence the interaction between the charges is unknown since it depends on the media and on the geometrical properties of the interfaces. To determine the properties of heterogeneous systems including crucial effects neglected in classical mean field models such as the hard core of the ions, the dielectric mismatch and interfaces with arbitrary shapes. The effect of hard core interactions accounts properly for short range interactions and the effect of local dielectric heterogeneities in the presence of ions and/or charged molecules for long-range interactions are both analyzed via an energy variational principle that enables to update charges and the medium's response in the same simulation time step. In particular, we compute the ionic structure in a model system of electrolyte confined by two planar dielectric

  14. Correlation between upconversion photoluminescence and dielectric response in Ba-substituted (Sr{sub 1−x}Ba{sub x}){sub 4}(La{sub 0.85}Ho{sub 0.025}Yb{sub 0.125}){sub 2}Ti{sub 4}Nb{sub 6}O{sub 30}

    SciTech Connect

    Wei, T.; Wang, X. D.; Zhao, C. Z.; Liu, M. F.; Liu, J. M.

    2014-06-30

    The filled tetragonal tungsten bronze (Sr{sub 1−x}Ba{sub x}){sub 4}(La{sub 0.85}Ho{sub 0.025}Yb{sub 0.125}){sub 2}Ti{sub 4}Nb{sub 6}O{sub 30} (SBLTNx: Ho-Yb) ceramics with different Ba substitution levels (x) are prepared. The upconversion photoluminescence (UC-PL) and dielectric permittivity are investigated. The substitution of Sr{sup 2+} ions at the A{sub 2}-sites by larger Ba{sup 2+} ions results in substantial variation of the UC-PL intensity as a function of substitution level x. Furthermore, the dielectric response to the substitution of Sr{sup 2+} by Ba{sup 2+} suggests a close correlation between the UC-PL intensity and dielectric permittivity. The origin for this correlation is discussed based on the random stress field (RSF) model.

  15. Magnetorefractive effect in manganites with a colossal magnetoresistance in the visible spectral region

    SciTech Connect

    Sukhorukov, Yu. P. Telegin, A. V.; Granovsky, A. B. Gan'shina, E. A.; Zhukov, A.; Gonzalez, J.; Caicedo, J. M.; Bessonov, V. D.; Kaul', A. R.; Gorbenko, O. Yu.; Korsakov, I. E.

    2012-01-15

    The magnetotransmission, magnetoreflection, and magnetoresistance of the La{sub 0.7}Ca{sub 0.3}MnO{sub 3} and La{sub 0.9}Ag{sub 0.1}MnO{sub 3} epitaxial films have been investigated. It has been found that the films exhibit a significant magnetorefractive effect in the case of reflection and transmission of light in the fundamental absorption region both in the vicinity of the Curie temperature and at low temperatures. It has been shown that the magnetorefractive effect in the infrared spectral region of the manganites is determined by a high-frequency response to magnetoresistance, whereas the magnetorefractive effect in the visible spectral region of these materials is associated with a change in the electronic structure in response to a magnetic field, which, in turn, leads to a change in the electron density of states, the probability of interband optical transitions, and the shift of light absorption bands. The obtained values of the magnetotransmittance and magnetoreflectance in the visible spectral region are less than those observed in the infrared region of the spectrum, but they are several times greater than the linear magneto-optical effects. As a result, the magnetorefractive effect, which is a nongyrotropic phenomenon, makes it possible to avoid the use of light analyzers and polarizers in optical circuits.

  16. Magnetorefractive effect in manganites with a colossal magnetoresistance in the visible spectral region

    NASA Astrophysics Data System (ADS)

    Sukhorukov, Yu. P.; Telegin, A. V.; Granovsky, A. B.; Gan'shina, E. A.; Zhukov, A.; Gonzalez, J.; Herranz, G.; Caicedo, J. M.; Yurasov, A. N.; Bessonov, V. D.; Kaul', A. R.; Gorbenko, O. Yu.; Korsakov, I. E.

    2012-01-01

    The magnetotransmission, magnetoreflection, and magnetoresistance of the La0.7Ca0.3MnO3 and La0.9Ag0.1MnO3 epitaxial films have been investigated. It has been found that the films exhibit a significant magnetorefractive effect in the case of reflection and transmission of light in the fundamental absorption region both in the vicinity of the Curie temperature and at low temperatures. It has been shown that the magnetorefractive effect in the infrared spectral region of the manganites is determined by a high-frequency response to magnetoresistance, whereas the magnetorefractive effect in the visible spectral region of these materials is associated with a change in the electronic structure in response to a magnetic field, which, in turn, leads to a change in the electron density of states, the probability of interband optical transitions, and the shift of light absorption bands. The obtained values of the magnetotransmittance and magnetoreflectance in the visible spectral region are less than those observed in the infrared region of the spectrum, but they are several times greater than the linear magneto-optical effects. As a result, the magnetorefractive effect, which is a nongyrotropic phenomenon, makes it possible to avoid the use of light analyzers and polarizers in optical circuits.

  17. The effects of vacuum ultraviolet radiation on low-k dielectric films

    SciTech Connect

    Sinha, H.; Ren, H.; Nichols, M. T.; Lauer, J. L.; Shohet, J. L.; Tomoyasu, M.; Russell, N. M.; Jiang, G.; Antonelli, G. A.; Fuller, N. C.; Engelmann, S. U.; Lin, Q.; Ryan, V.; Nishi, Y.

    2012-12-01

    Plasmas, known to emit high levels of vacuum ultraviolet (VUV) radiation, are used in the semiconductor industry for processing of low-k organosilicate glass (SiCOH) dielectric device structures. VUV irradiation induces photoconduction, photoemission, and photoinjection. These effects generate trapped charges within the dielectric film, which can degrade electrical properties of the dielectric. The amount of charge accumulation in low-k dielectrics depends on factors that affect photoconduction, photoemission, and photoinjection. Changes in the photo and intrinsic conductivities of SiCOH are also ascribed to the changes in the numbers of charged traps generated during VUV irradiation. The dielectric-substrate interface controls charge trapping by affecting photoinjection of charged carriers into the dielectric from the substrate. The number of trapped charges increases with increasing porosity of SiCOH because of charge trapping sites in the nanopores. Modifications to these three parameters, i.e., (1) VUV induced charge generation, (2) dielectric-substrate interface, and (3) porosity of dielectrics, can be used to reduce trapped-charge accumulation during processing of low-{kappa} SiCOH dielectrics. Photons from the plasma are responsible for trapped-charge accumulation within the dielectric, while ions stick primarily to the surface of the dielectrics. In addition, as the dielectric constant was decreased by adding porosity, the defect concentrations increased.

  18. Magneto-Optical Activity in High Index Dielectric Nanoantennas

    PubMed Central

    de Sousa, N.; Froufe-Pérez, L. S.; Sáenz, J. J.; García-Martín, A.

    2016-01-01

    The magneto-optical activity, namely the polarization conversion capabilities of high-index, non-absorbing, core-shell dielectric nanospheres is theoretically analyzed. We show that, in analogy with their plasmonic counterparts, the polarization conversion in resonant dielectric particles is linked to the amount of electromagnetic field probing the magneto-optical material in the system. However, in strong contrast with plasmon nanoparticles, due to the peculiar distribution of the internal fields in resonant dielectric spheres, the magneto-optical response is fully governed by the magnetic (dipolar and quadrupolar) resonances with little effect of the electric ones. PMID:27488903

  19. Antenna with Dielectric Having Geometric Patterns

    NASA Technical Reports Server (NTRS)

    Dudley, Kenneth L. (Inventor); Elliott, Holly A. (Inventor); Cravey, Robin L. (Inventor); Connell, John W. (Inventor); Ghose, Sayata (Inventor); Watson, Kent A. (Inventor); Smith, Jr., Joseph G. (Inventor)

    2013-01-01

    An antenna includes a ground plane, a dielectric disposed on the ground plane, and an electrically-conductive radiator disposed on the dielectric. The dielectric includes at least one layer of a first dielectric material and a second dielectric material that collectively define a dielectric geometric pattern, which may comprise a fractal geometry. The radiator defines a radiator geometric pattern, and the dielectric geometric pattern is geometrically identical, or substantially geometrically identical, to the radiator geometric pattern.

  20. Potential energy mapping of the excited-states of (η6-arene)Cr(CO)3 complexes: the evolution toward CO-loss or haptotropic shift processes.

    PubMed

    Long, Conor

    2012-06-28

    The potential energy profiles of the optically accessible excited states of two model (η(6)-arene)Cr(CO)(3) systems were explored using Time-Dependent Density Functional Theory. Two photochemical reactions were investigated, CO-loss and the haptotropic or ring-slip of the arene ligand. In both cases the photochemical reaction requires the surmounting of a small thermal barrier in the lowest energy excited state. In the case of (η(6)-benzene)Cr(CO)(3) only one excited state is populated following 400 nm excitation and this leads to the release of CO. The calculated energy barrier to this process is 13 kJ mol(-1). In the case of (η(6)-thiophenol)Cr(CO)(3) two excited states are accessible one leading to CO-loss while the other results in the ring-slip process. The calculated barrier to the ring-slip process is 11 kJ mol(-1). The calculations are consistent with the results of picosecond time-resolved infrared studies.

  1. Colossal negative thermal expansion induced by magnetic phase competition on frustrated lattices in Laves phase compound (Hf,Ta)Fe2

    NASA Astrophysics Data System (ADS)

    Li, B.; Luo, X. H.; Wang, H.; Ren, W. J.; Yano, S.; Wang, C.-W.; Gardner, J. S.; Liss, K.-D.; Miao, P.; Lee, S.-H.; Kamiyama, T.; Wu, R. Q.; Kawakita, Y.; Zhang, Z. D.

    2016-06-01

    Competition between ferromagnetic and antiferromagnetic phases on frustrated lattices in hexagonal Laves phase compound Hf0.86Ta0.14Fe2 is investigated by using neutron diffraction as a function of temperature and magnetic fields and density-functional-theory calculations. At 325 K, the compound orders into the 120° frustrated antiferromagnetic state with a well-reduced magnetic moment, and an in-plane lattice contraction simultaneously sets in. With further cooling down, however, the accumulated distortion in turn destabilizes this susceptible frustrated structure. The frustration is completely relieved at 255 K when the first-order transition to the ferromagnetic state takes place, where a colossal negative volumetric thermal expansion, -123 ×10-6 /K, is obtained. Meanwhile, the antiferromagnetic state can be suppressed by few-tesla magnetic fields, which results in a colossal positive magnetostriction. Such delicate competition is attributed to the giant magnetic fluctuation inherent in the frustrated antiferromagnetic state. Therefore, the magnetoelastic instability is approached even under a small perturbation.

  2. Temperature switchable polymer dielectrics.

    SciTech Connect

    Kholwadwala, Fenil Manish; Johnson, Ross Stefan; Dirk, Shawn M.

    2010-06-01

    Materials with switchable states are desirable in many areas of science and technology. The ability to thermally transform a dielectric material to a conductive state should allow for the creation of electronics with built-in safety features. Specifically, the non-desirable build-up and discharge of electricity in the event of a fire or over-heating would be averted by utilizing thermo-switchable dielectrics in the capacitors of electrical devices (preventing the capacitors from charging at elevated temperatures). We have designed a series of polymers that effectively switch from a non-conductive to a conductive state. The thermal transition is governed by the stability of the leaving group after it leaves as a free entity. Here, we present the synthesis and characterization of a series of precursor polymers that eliminate to form poly(p-phenylene vinylene) (PPV's).

  3. Temperature switchable polymer dielectrics.

    SciTech Connect

    Johnson, Ross Stefan

    2010-08-01

    Materials with switchable states are desirable in many areas of science and technology. The ability to thermally transform a dielectric material to a conductive state should allow for the creation of electronics with built-in safety features. Specifically, the non-desirable build-up and discharge of electricity in the event of a fire or over-heating would be averted by utilizing thermo-switchable dielectrics in the capacitors of electrical devices (preventing the capacitors from charging at elevated temperatures). We have designed a series of polymers that effectively switch from a non-conductive to a conductive state. The thermal transition is governed by the stability of the leaving group after it leaves as a free entity. Here, we present the synthesis and characterization of a series of precursor polymers that eliminate to form poly(p-phenylene vinylene) (PPV's).

  4. DIELECTRIC WALL ACCELERATOR TECHNOLOGY

    SciTech Connect

    Sampayan, S; Caporaso, G; Chen, Y; Harris, J; Hawkins, S; Holmes, C; Nelson, S; Poole, B; Rhodes, M; Sanders, D; Sullivan, J; Wang, L; Watson, J

    2007-10-18

    The dielectric wall accelerator (DWA) is a compact pulsed power device where the pulse forming lines, switching, and vacuum wall are integrated into a single compact geometry. For this effort, we initiated a extensive compact pulsed power development program and have pursued the study of switching (gas, oil, laser induced surface flashover and photoconductive), dielectrics (ceramics and nanoparticle composites), pulse forming line topologies (asymmetric and symmetric Blumleins and zero integral pulse forming lines), and multilayered vacuum insulator (HGI) technology. Finally, we fabricated an accelerator cell for test on ETAII (a 5.5 MeV, 2 kA, 70 ns pulsewidth electron beam accelerator). We review our past results and report on the progress of accelerator cell testing.

  5. Dielectric Signatures of Annealing in Glacier Ice

    NASA Astrophysics Data System (ADS)

    Grimm, R. E.; Stillman, D. E.; MacGregor, J. A.

    2015-12-01

    We analyzed the dielectric spectra of 49 firn and ice samples from ice sheets and glaciers to better understand how differing ice formation and evolution affect electrical properties. The dielectric relaxation of ice is well known and its characteristic frequency increases with the concentration of soluble impurities in the ice lattice. We found that meteoric ice and firn generally possess two such relaxations, indicating distinct crystal populations or zonation. Typically, one population is consistent with that of relatively pure ice, and the other is significantly more impure. However, high temperatures (e.g., temperate ice), long residence times (e.g., ancient ice from Mullins Glacier, Antarctica), or anomalously high impurity concentrations favor the development of a single relaxation. These relationships suggest that annealing causes two dielectrically distinct populations to merge into one population. The dielectric response of temperate ice samples indicates increasing purity with increasing depth, suggesting final rejection of impurities from the lattice. Separately, subglacially frozen samples from the Vostok 5G ice core possess a single relaxation whose variable characteristic frequency likely reflects the composition of the source water. Multi-frequency electrical measurements on cores and in the field can track annealing of glacier ice.

  6. Immunohistochemistry Successfully Uncovers Intratumoral Heterogeneity and Widespread Co-Losses of Chromatin Regulators in Clear Cell Renal Cell Carcinoma

    PubMed Central

    Devarajan, Karthik; Parsons, Theodore; Wang, Qiong; Liao, Lili; Cho, Eun-Ah; O'Neill, Raymond; Solomides, Charalambos; Peiper, Stephen C.; Testa, Joseph R.; Uzzo, Robert; Yang, Haifeng

    2016-01-01

    Recent studies have shown that intratumoral heterogeneity (ITH) is prevalent in clear cell renal cell carcinoma (ccRCC), based on DNA sequencing and chromosome aberration analysis of multiple regions from the same tumor. VHL mutations were found to be universal throughout individual tumors when it occurred (ubiquitous), while the mutations in other tumor suppressor genes tended to be detected only in parts of the tumors (subclonal). ITH has been studied mostly by DNA sequencing in limited numbers of samples, either by whole genome sequencing or by targeted sequencing. It is not known whether immunohistochemistry (IHC) can be used as a tool to study ITH. To address this question, we examined the protein expression of PBRM1, and PBRM1-related proteins such as ARID1A, SETD2, BRG1, and BRM. Altogether, 160 ccRCC (40 per stage) were used to generate a tissue microarray (TMA), with four foci from each tumor included. Loss of expression was defined as 0–5% of tumor cells with positive nuclear staining in an individual focus. We found that 49/160 (31%), 81/160 (51%), 23/160 (14%), 24/160 (15%), and 61/160 (38%) of ccRCC showed loss of expression of PBRM1, ARID1A, SETD2, BRG1, and BRM, respectively, and that IHC could successfully detect a high prevalence of ITH. Phylogenetic trees were constructed that reflected the ITH. Striking co-losses among proteins were also observed. For instance, ARID1A loss almost always accompanied PBRM1 loss, whereas BRM loss accompanied loss of BRG1, PBRM1 or ARID1A. SETD2 loss frequently occurred with loss of one or more of the other four proteins. Finally, in order to learn the impact of combined losses, we compared the tumor growth after cells acquired losses of ARID1A, PBRM1, or both in a xenograft model. The results suggest that ARID1A loss has a greater tumor-promoting effect than PBRM1 loss, indicating that xenograft analysis is a useful tool to investigate how these losses impact on tumor behavior, either alone or in combination. PMID

  7. Dielectric spectroscopy of polyaniline

    SciTech Connect

    Calleja, R.D.; Matveeva, E.M.

    1993-12-31

    Polyaniline films (PANI) are being considered as attractive new galvanic sources, electrochromic displays, chemical sensors, etc. So far much work has been done to study their optical, electrochemical and electrical properties. However, there are still doubts about the basic electric conductivity mechanisms of PANI. The aim of this paper is to study the influence of water molecules and acid anions on the properties of PANI films by dielectric spectroscopy.

  8. Angle-resolved photoemission studies on bi-layer colossal magnetoresistive oxides lanthanum(2-2x)strontium(1+2x)manganese(2)oxide(7)

    NASA Astrophysics Data System (ADS)

    Sun, Zhe

    In recent years the studies of manganites have flourished initially because of their Colossal Magnetoresistance (CMR) effect. However the scientific community quickly realized that the fundamental physics is abundant, exotic and challenging. Strong correlations of charge, lattice, spin and orbital degrees of freedom have been found to be responsible for many interesting physical phenomena. Of manganites, La2-2xSr 1+2xMn2O 7 has naturally layered crystal structure. The reduced two-dimensional character amplifies fluctuations of electronic, magnetic, and orbital degrees of freedom and interactions of them, which provides good opportunities for an understanding of the rich physics in manganites. In crystals, electrons have intrinsic charge, spin and orbital degrees of freedom, and the electron-phonon interaction has been an active topic for many decades, thus studies of electrons will definitely shed light on important physics in manganites. Angle-resolved photoemission spectroscopy (ARPES) is an ideal probe of electrons, and so by performing ARPES measurements on La2-2 xSr1+2xMn2 O7 we have obtained abundant knowledge of the physics of strong correlations of various degrees of freedom. We have made many new discoveries by exploring the physics in this com-pound. For the first time we resolved bi-layer split band structure of the prototype of bi-layer manganites, which was predicted by theoretical calculations long time ago. We observed minority-spin states in La2-2 xSr1+2xMn 2O7 (x = 0.36--0.39), which gives direct evidence that this system is not a half-metal in this doping iv range. We gave the first direct measurement of electron-phonon coupling strength in manganites and identified the phonon branches to which electrons couple. In addition to band insulator and Mott insulator there is another type of insulator, in which metallic domains and insulating domains coexist and phase separation and percolation effect play important roles in the metal

  9. Tunable dielectric properties of ferrite-dielectric based metamaterial.

    PubMed

    Bi, K; Huang, K; Zeng, L Y; Zhou, M H; Wang, Q M; Wang, Y G; Lei, M

    2015-01-01

    A ferrite-dielectric metamaterial composed of dielectric and ferrite cuboids has been investigated by experiments and simulations. By interacting with the electromagnetic wave, the Mie resonance can take place in the dielectric cuboids and the ferromagnetic precession will appear in the ferrite cuboids. The magnetic field distributions show the electric Mie resonance of the dielectric cuboids can be influenced by the ferromagnetic precession of ferrite cuboids when a certain magnetic field is applied. The effective permittivity of the metamaterial can be tuned by modifying the applied magnetic field. A good agreement between experimental and simulated results is demonstrated, which confirms that these metamaterials can be used for tunable microwave devices.

  10. Tunable Dielectric Properties of Ferrite-Dielectric Based Metamaterial

    PubMed Central

    Bi, K.; Huang, K.; Zeng, L. Y.; Zhou, M. H.; Wang, Q. M.; Wang, Y. G.; Lei, M.

    2015-01-01

    A ferrite-dielectric metamaterial composed of dielectric and ferrite cuboids has been investigated by experiments and simulations. By interacting with the electromagnetic wave, the Mie resonance can take place in the dielectric cuboids and the ferromagnetic precession will appear in the ferrite cuboids. The magnetic field distributions show the electric Mie resonance of the dielectric cuboids can be influenced by the ferromagnetic precession of ferrite cuboids when a certain magnetic field is applied. The effective permittivity of the metamaterial can be tuned by modifying the applied magnetic field. A good agreement between experimental and simulated results is demonstrated, which confirms that these metamaterials can be used for tunable microwave devices. PMID:25993433

  11. The dielectric breakdown limit of silicone dielectric elastomer actuators

    NASA Astrophysics Data System (ADS)

    Gatti, Davide; Haus, Henry; Matysek, Marc; Frohnapfel, Bettina; Tropea, Cameron; Schlaak, Helmut F.

    2014-02-01

    Soft silicone elastomers are used in a generation of dielectric elastomer actuators (DEAs) with improved actuation speed and durability compared to the commonly used, highly viscoelastic polyacrylate 3M VHB™ films. The maximum voltage-induced stretch of DEAs is ultimately limited by their dielectric breakdown field strength. We measure the dependence of dielectric breakdown field strength on thickness and stretch for a silicone elastomer, when voltage-induced deformation is prevented. The experimental results are combined with an analytic model of equi-biaxial actuation to show that accounting for variable dielectric field strength results in different values of optimal pre-stretch and thickness that maximize the DEA actuation.

  12. Principles of dielectric blood coagulometry as a comprehensive coagulation test.

    PubMed

    Hayashi, Yoshihito; Brun, Marc-Aurèle; Machida, Kenzo; Nagasawa, Masayuki

    2015-10-06

    Dielectric blood coagulometry (DBCM) is intended to support hemostasis management by providing comprehensive information on blood coagulation from automated, time-dependent measurements of whole blood dielectric spectra. We discuss the relationship between the series of blood coagulation reactions, especially the aggregation and deformation of erythrocytes, and the dielectric response with the help of clot structure electron microscope observations. Dielectric response to the spontaneous coagulation after recalcification presented three distinct phases that correspond to (P1) rouleau formation before the onset of clotting, (P2) erythrocyte aggregation and reconstitution of aggregates accompanying early fibrin formation, and (P3) erythrocyte shape transformation and/or structure changes within aggregates after the stable fibrin network is formed and platelet contraction occurs. Disappearance of the second phase was observed upon addition of tissue factor and ellagic acid for activation of extrinsic and intrinsic pathways, respectively, which is attributable to accelerated thrombin generation. A series of control experiments revealed that the amplitude and/or quickness of dielectric response reflect platelet function, fibrin polymerization, fibrinolysis activity, and heparin activity. Therefore, DBCM sensitively measures blood coagulation via erythrocytes aggregation and shape changes and their impact on the dielectric permittivity, making possible the development of the battery of assays needed for comprehensive coagulation testing.

  13. Dielectric Nonlinear Transmission Line (Postprint)

    DTIC Science & Technology

    2011-12-01

    Technical Paper 3. DATES COVERED (From - To) 2011 4. TITLE AND SUBTITLE Dielectric Nonlinear Transmission Line (POSTPRINT) 5a. CONTRACT NUMBER...14. ABSTRACT A parallel plate nonlinear transmission line (NLTL) was constructed. Periodic loading of nonlinear dielectric slabs provides the...846-9101 Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. 239.18 Dielectric Nonlinear Transmission Line David M. French, Brad W. Hoff

  14. Dielectric properties of lunar surface

    NASA Astrophysics Data System (ADS)

    Yushkova, O. V.; Kibardina, I. N.

    2017-03-01

    Measurements of the dielectric characteristics of lunar soil samples are analyzed in the context of dielectric theory. It has been shown that the real component of the dielectric permittivity and the loss tangent of rocks greatly depend on the frequency of the interacting electromagnetic field and the soil temperature. It follows from the analysis that one should take into account diurnal variations in the lunar surface temperature when interpreting the radar-sounding results, especially for the gigahertz radio range.

  15. Molecular Donor-Bridge-Acceptor Strategies for High-Capacitance Organic Dielectric Materials.

    PubMed

    Heitzer, Henry M; Marks, Tobin J; Ratner, Mark A

    2015-06-10

    Donor-bridge-acceptor (DBA) systems occupy a rich history in molecular electronics and photonics. A key property of DBA materials is their typically large and tunable (hyper)polarizabilities. While traditionally, classical descriptions such as the Clausius-Mossotti formalism have been used to relate molecular polarizabilities to bulk dielectric response, recent work has shown that these classical equations are inadequate for numerous materials classes. Creating high-dielectric organic materials is critically important for utilizing unconventional semiconductors in electronic circuitry. Employing a plane-wave density functional theory formalism, we investigate the dielectric response of highly polarizable DBA molecule-based thin films. Such films are found to have large dielectric response arising from cooperative effects between donor and acceptor units when mediated by a conjugated bridge. Moreover, the dielectric response can be systematically tuned by altering the building block donor, acceptor, or bridge structures and is found to be nonlinearly dependent on electric field strength. The computed dielectric constants are largely independent of the density functional employed, and qualitative trends are readily evident. Remarkably large computed dielectric constants >15.0 and capacitances >6.0 μF/cm(2) are achieved for squaraine monolayers, significantly higher than in traditional organic dielectrics. Such calculations should provide a guide for designing high-capacitance organic dielectrics that should greatly enhance transistor performance.

  16. The Colossal Cosmic Eye

    NASA Astrophysics Data System (ADS)

    2005-09-01

    Eighty-five million years ago on small planet Earth, dinosaurs ruled, ignorant of their soon-to-come demise in the great Jurassic extinction, while mammals were still small and shy creatures. The southern Andes of Bolivia, Chile, and Argentina were not yet formed and South America was still an island continent. Eighty-five million years ago, our Sun and its solar system was 60,000 light years away from where it now stands [1]. Eighty-five million years ago, in another corner of the Universe, light left the beautiful spiral galaxy NGC 1350, for a journey across the universe. Part of this light was recorded at the beginning of the year 2000 AD by ESO's Very Large Telescope, located on the 2,600m high Cerro Paranal in the Chilean Andes on planet Earth. Astronomers classify NGC 1350 as an Sa(r) type galaxy, meaning it is a spiral with large central regions. In fact, NGC 1350 lies at the border between the broken-ring spiral type and a grand design spiral with two major outer arms. It is about 130,000 light-years across and, hence, is slightly larger than our Milky Way. The rather faint and graceful outer arms originate at the inner main ring and can be traced for almost half a circle when they each meet the opposite arm, giving the impression of completing a second outer ring, the "eye". The arms are given a blue tint as a result of the presence of very young and massive stars. The amount of dust, seen as small fragmented dust spirals in the central part of the galaxy and producing a fine tapestry that bear resemblance with blood vessels in the eye, is also a signature of the formation of stars.

  17. Residual ferroelectricity in barium strontium titanate thin film tunable dielectrics

    SciTech Connect

    Garten, L. M. Trolier-McKinstry, S.; Lam, P.; Harris, D.; Maria, J.-P.

    2014-07-28

    Loss reduction is critical to develop Ba{sub 1−x}Sr{sub x}TiO{sub 3} thin film tunable microwave dielectric components and dielectric energy storage devices. The presence of ferroelectricity, and hence the domain wall contributions to dielectric loss, will degrade the tunable performance in the microwave region. In this work, residual ferroelectricity—a persistent ferroelectric response above the global phase transition temperature—was characterized in tunable dielectrics using Rayleigh analysis. Chemical solution deposited Ba{sub 0.7}Sr{sub 0.3}TiO{sub 3} films, with relative tunabilities of 86% over 250 kV/cm at 100 kHz, demonstrated residual ferroelectricity 65 °C above the ostensible paraelectric transition temperature. Frequency dispersion observed in the dielectric temperature response was consistent with the presence of nanopolar regions as one source of residual ferroelectricity. The application of AC electric field for the Rayleigh analysis of these samples led to a doubling of the dielectric loss for fields over 10 kV/cm at room temperature.

  18. Modeling and control of a dielectric elastomer actuator

    NASA Astrophysics Data System (ADS)

    Gupta, Ujjaval; Gu, Guo-Ying; Zhu, Jian

    2016-04-01

    The emerging field of soft robotics offers the prospect of applying soft actuators as artificial muscles in the robots, replacing traditional actuators based on hard materials, such as electric motors, piezoceramic actuators, etc. Dielectric elastomers are one class of soft actuators, which can deform in response to voltage and can resemble biological muscles in the aspects of large deformation, high energy density and fast response. Recent research into dielectric elastomers has mainly focused on issues regarding mechanics, physics, material designs and mechanical designs, whereas less importance is given to the control of these soft actuators. Strong nonlinearities due to large deformation and electromechanical coupling make control of the dielectric elastomer actuators challenging. This paper investigates feed-forward control of a dielectric elastomer actuator by using a nonlinear dynamic model. The material and physical parameters in the model are identified by quasi-static and dynamic experiments. A feed-forward controller is developed based on this nonlinear dynamic model. Experimental evidence shows that this controller can control the soft actuator to track the desired trajectories effectively. The present study confirms that dielectric elastomer actuators are capable of being precisely controlled with the nonlinear dynamic model despite the presence of material nonlinearity and electromechanical coupling. It is expected that the reported results can promote the applications of dielectric elastomer actuators to soft robots or biomimetic robots.

  19. Low Dielectric Polymers

    NASA Technical Reports Server (NTRS)

    Venumbaka, Sreenivasulu R.; Cassidy, Patrick E.

    2002-01-01

    This report summarizes results obtained from research funded through Research Cooperative Agreement No. NCC-1-01033-"Low Dielectric Polymers" (from 5/10/01 through 5/09/02). Results are reported in three of the proposed research areas (Tasks 1-3 in the original proposal): (1) Repeat and confirm the preparation and properties of the new alkyl-substituted PEK, 6HC17-PEK, (2) Prepare and evaluate polymers derived from a highly fluorinated monomer, and (3) Prepare and evaluate new silicon and/or fluorine-containing polymers expected to retain useful properties at low temperature.

  20. Inorganic optical dielectric films

    NASA Astrophysics Data System (ADS)

    Woollam, John A.

    1996-07-01

    Dielectric coatings have been in use for a very long time, yet today they represent a steadily growing wold-wide industry. A wide range of materials, and applications from the near ultraviolet into the infrared are in use, or under development. This paper is a brief survey, including references to the literature, and a discussion of materials diagnostics. Discussed is the microstructure, optical constants and their relationship as determined especially by optical measurements. This paper emphasizes the materials science aspects rather than applications.

  1. Boron nitride as two dimensional dielectric: Reliability and dielectric breakdown

    SciTech Connect

    Ji, Yanfeng; Pan, Chengbin; Hui, Fei; Shi, Yuanyuan; Lanza, Mario; Zhang, Meiyun; Long, Shibing; Lian, Xiaojuan; Miao, Feng; Larcher, Luca; Wu, Ernest

    2016-01-04

    Boron Nitride (BN) is a two dimensional insulator with excellent chemical, thermal, mechanical, and optical properties, which make it especially attractive for logic device applications. Nevertheless, its insulating properties and reliability as a dielectric material have never been analyzed in-depth. Here, we present the first thorough characterization of BN as dielectric film using nanoscale and device level experiments complementing with theoretical study. Our results reveal that BN is extremely stable against voltage stress, and it does not show the reliability problems related to conventional dielectrics like HfO{sub 2}, such as charge trapping and detrapping, stress induced leakage current, and untimely dielectric breakdown. Moreover, we observe a unique layer-by-layer dielectric breakdown, both at the nanoscale and device level. These findings may be of interest for many materials scientists and could open a new pathway towards two dimensional logic device applications.

  2. The use of nonlinear dielectric spectroscopy to monitor the bioelectromagnetic effects of a weak pulsed magnetic field in real time.

    PubMed

    Davies, E; Woodward, A; Kell, D

    2000-01-01

    Nonlinear dielectric spectroscopy (NLDS) was used to detect interaction of a pulsed magnetic field (PMF) with membrane protein dynamics in aggregating Dictyostelium discoideum amoebae. In the experiments reported here, a strong nonlinear dielectric response of Dictyostelium discoideum cells is shown, and a distinctive nonlinear dielectric response of cells previously exposed to PMF is shown. The method of NLDS is shown to be capable of monitoring and charting the dynamic frequency response of the cell to an electromagnetic field.

  3. Research on the Crystal Growth and Dielectric Properties of High Permittivity Ferroelectric Materials.

    DTIC Science & Technology

    1984-05-01

    allow many of the underlying mechanisms controlling the microwave dielectric response to be identified. 2 C5988A/Jbs 0D Rockwell International Science...compared to infrared and optical sensors, and re- duced weight and size when compared to conventional microwave radars, have led to increased emphasis... method . Dielectric values along the a- axis are much lower, typically 470 at room temperature and unaffected by poling. Dielectric losses (tan 6) are

  4. Precision time-domain dielectric spectrometer

    NASA Astrophysics Data System (ADS)

    Mopsik, F. I.

    1984-01-01

    A description is given for an automated method for determining dielectric constant and loss by the measurement of the time response of the dielectric to a step voltage. Attention is paid to the circuits necessary to achieve high accuracy (0.1%) and high sensitivity (tan δ=10-5) over audio and subaudio frequencies (104 to 10-4 Hz). These include a 100-V step generator accurate to 5 ppm, a charge detector with a time-independent bias current of 30 fA, and a clock that can control sampling time from 5 μs to 10 s. In addition, a numerical Laplace transform, based on a cubic spline, is described that preserves the accuracy of the time data when they are transformed into the frequency domain.

  5. Miniaturization of dielectric liquid microlens in package

    PubMed Central

    Yang, Chih-Cheng; Tsai, C. Gary; Yeh, J. Andrew

    2010-01-01

    This study presents packaged microscale liquid lenses actuated with liquid droplets of 300–700 μm in diameter using the dielectric force manipulation. The liquid microlens demonstrated function focal length tunability in a plastic package. The focal length of the liquid lens with a lens droplet of 500 μm in diameter is shortened from 4.4 to 2.2 mm when voltages applied change from 0 to 79 Vrms. Dynamic responses that are analyzed using 2000 frames∕s high speed motion cameras show that the advancing and receding times are measured to be 90 and 60 ms, respectively. The size effect of dielectric liquid microlens is characterized for a lens droplet of 300–700 μm in diameter in an aspect of focal length. PMID:21267438

  6. Spacecraft dielectric material properties and spacecraft charging

    NASA Technical Reports Server (NTRS)

    Frederickson, A. R.; Wall, J. A.; Cotts, D. B.; Bouquet, F. L.

    1986-01-01

    The physics of spacecraft charging is reviewed, and criteria for selecting and testing semiinsulating polymers (SIPs) to avoid charging are discussed and illustrated. Chapters are devoted to the required properties of dielectric materials, the charging process, discharge-pulse phenomena, design for minimum pulse size, design to prevent pulses, conduction in polymers, evaluation of SIPs that might prevent spacecraft charging, and the general response of dielectrics to space radiation. SIPs characterized include polyimides, fluorocarbons, thermoplastic polyesters, poly(alkanes), vinyl polymers and acrylates, polymers containing phthalocyanine, polyacene quinones, coordination polymers containing metal ions, conjugated-backbone polymers, and 'metallic' conducting polymers. Tables summarizing the results of SIP radiation tests (such as those performed for the NASA Galileo Project) are included.

  7. Microfabrication of stacked dielectric elastomer actuator fibers

    NASA Astrophysics Data System (ADS)

    Corbaci, Mert; Walter, Wayne; Lamkin-Kennard, Kathleen

    2016-04-01

    Dielectric elastomer actuators (DEA) are one of the best candidate materials for next generation of robotic actuators, soft sensors and artificial muscles due to their fast response, mechanical robustness and compliance. However, high voltage requirements of DEAs have impeded their potential to become widely used in such applications. In this study, we propose a method for fabrication of silicon based multilayer DEA fibers composed of microlevel dielectric layers to improve the actuation ratios of DEAs at lower voltages. A multi-walled carbon nanotube - polydimethylsiloxane (MWCNT/PDMS) composite was used to fabricate mechanically compliant, conductive parallel plates and electrode connections for the DEA actuators. Active surface area and layer thickness were varied to study the effects of these parameters on actuation ratio as a function of applied voltage. Different structures were fabricated to assess the flexibility of the fabrication method for specific user-end applications.

  8. Tailoring the dipole properties in dielectric polymers to realize high energy density with high breakdown strength and low dielectric loss

    NASA Astrophysics Data System (ADS)

    Thakur, Yash; Lin, Minren; Wu, Shan; Cheng, Zhaoxi; Jeong, D.-Y.; Zhang, Q. M.

    2015-03-01

    High energy density polymer materials are desirable for a broad range of modern power electronic systems. Here, we report the development of a new class of polymer dielectrics based on polyurea and polythiourea, which possess high thermal stability. By increasing the dipole density, the dielectric constant of meta-phenylene polyurea and methylene polythiourea can be increased to 5.7, compared with aromatic polyurea and aromatic polythiourea, which have a dielectric constant in the range of 4.1-4.3. The random dipoles with high dipolar moment and amorphous structure of these polyurea and polythiourea based polymers provide strong scattering to the charge carriers, resulting in low losses even at high electric fields. Consequently, this new class of polymers exhibit a linear dielectric response to the highest field measured (>700 MV/m) with a high breakdown strength, achieving high energy density (>13 J/cm3) with high efficiency (>90%).

  9. Voltage sensor and dielectric material

    DOEpatents

    Yakymyshyn, Christopher Paul; Yakymyshyn, Pamela Jane; Brubaker, Michael Allen

    2006-10-17

    A voltage sensor is described that consists of an arrangement of impedance elements. The sensor is optimized to provide an output ratio that is substantially immune to changes in voltage, temperature variations or aging. Also disclosed is a material with a large and stable dielectric constant. The dielectric constant can be tailored to vary with position or direction in the material.

  10. Microwave Propagation in Dielectric Fluids.

    ERIC Educational Resources Information Center

    Lonc, W. P.

    1980-01-01

    Describes an undergraduate experiment designed to verify quantitatively the effect of a dielectric fluid's dielectric constant on the observed wavelength of microwave radiation propagating through the fluid. The fluid used is castor oil, and results agree with the expected behavior within 5 percent. (Author/CS)

  11. Low dielectric polyimide fibers

    NASA Technical Reports Server (NTRS)

    Dorogy, William E., Jr. (Inventor); St.clair, Anne K. (Inventor)

    1994-01-01

    A high temperature resistant polyimide fiber that has a dielectric constant of less than 3 is presented. The fiber was prepared by first reacting 2,2-bis (4-(4aminophenoxy)phenyl) hexafluoropropane with 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane dianhydride in an aprotic solvent to form a polyamic acid resin solution. The polyamic acid resin solution is then extruded into a coagulation medium to form polyamic acid fibers. The fibers are thermally cured to their polyimide form. Alternatively, 2,2-bis(4-(4-aminophenoxy)phenyl) hexafluoropropane is reacted with 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride to form a polyamic acid, and the polyamic acid is chemically converted to its polyimide form. The polyimide is then dissolved in a solvent to form a polyimide resin solution, and the polyimide resin is extruded into a coagulation medium to form a polyimide wet gel filament. In order to obtain polyimide fibers of increased tensile properties, the polyimide wet gel filaments are stretched at elevated temperatures. The tensile properties of the fibers were measured and found to be in the range of standard textile fibers. Polyimide fibers obtained by either method will have a dielectric constant similar to that of the corresponding polymer, viz., less than 3 at 10 GHz.

  12. Folded dielectric elastomer actuators

    NASA Astrophysics Data System (ADS)

    Carpi, Federico; Salaris, Claudio; DeRossi, Danilo

    2007-04-01

    Polymer-based linear actuators with contractile ability are currently demanded for several types of applications. Within the class of dielectric elastomer actuators, two basic configurations are available today for such a purpose: the multi-layer stack and the helical structure. The first consists of several layers of elementary planar actuators stacked in series mechanically and parallel electrically. The second configuration relies on a couple of helical compliant electrodes alternated with a couple of helical dielectrics. The fabrication of both these configurations presents some specific drawbacks today, arising from the peculiarity of each structure. Accordingly, the availability of simpler solutions may boost the short-term use of contractile actuators in practical applications. For this purpose, a new configuration is here described. It consists of a monolithic structure made of an electroded sheet, which is folded up and compacted. The resulting device is functionally equivalent to a multi-layer stack with interdigitated electrodes. However, with respect to a stack the new configuration is advantageously not discontinuous and can be manufactured in one single phase, avoiding layer-by-layer multi-step procedures. The development and preliminary testing of prototype samples of this new actuator made of a silicone elastomer are presented here.

  13. Dielectric laser accelerators

    NASA Astrophysics Data System (ADS)

    England, R. Joel; Noble, Robert J.; Bane, Karl; Dowell, David H.; Ng, Cho-Kuen; Spencer, James E.; Tantawi, Sami; Wu, Ziran; Byer, Robert L.; Peralta, Edgar; Soong, Ken; Chang, Chia-Ming; Montazeri, Behnam; Wolf, Stephen J.; Cowan, Benjamin; Dawson, Jay; Gai, Wei; Hommelhoff, Peter; Huang, Yen-Chieh; Jing, Chunguang; McGuinness, Christopher; Palmer, Robert B.; Naranjo, Brian; Rosenzweig, James; Travish, Gil; Mizrahi, Amit; Schachter, Levi; Sears, Christopher; Werner, Gregory R.; Yoder, Rodney B.

    2014-10-01

    The use of infrared lasers to power optical-scale lithographically fabricated particle accelerators is a developing area of research that has garnered increasing interest in recent years. The physics and technology of this approach is reviewed, which is referred to as dielectric laser acceleration (DLA). In the DLA scheme operating at typical laser pulse lengths of 0.1 to 1 ps, the laser damage fluences for robust dielectric materials correspond to peak surface electric fields in the GV /m regime. The corresponding accelerating field enhancement represents a potential reduction in active length of the accelerator between 1 and 2 orders of magnitude. Power sources for DLA-based accelerators (lasers) are less costly than microwave sources (klystrons) for equivalent average power levels due to wider availability and private sector investment. Because of the high laser-to-particle coupling efficiency, required pulse energies are consistent with tabletop microJoule class lasers. Combined with the very high (MHz) repetition rates these lasers can provide, the DLA approach appears promising for a variety of applications, including future high-energy physics colliders, compact light sources, and portable medical scanners and radiative therapy machines.

  14. Colossal magnetoresistance in amino-functionalized graphene quantum dots at room temperature: manifestation of weak anti-localization and doorway to spintronics.

    PubMed

    Roy, Rajarshi; Thapa, Ranjit; Kumar, Gundam Sandeep; Mazumder, Nilesh; Sen, Dipayan; Sinthika, S; Das, Nirmalya S; Chattopadhyay, Kalyan K

    2016-04-21

    In this work, we have demonstrated the signatures of localized surface distortions and disorders in functionalized graphene quantum dots (fGQD) and consequences in magneto-transport under weak field regime (∼1 Tesla) at room temperature. Observed positive colossal magnetoresistance (MR) and its suppression is primarily explained by weak anti-localization phenomenon where competitive valley (inter and intra) dependent scattering takes place at room temperature under low magnetic field; analogous to low mobility disordered graphene samples. Furthermore, using ab-initio analysis we show that sub-lattice sensitive spin-polarized ground state exists in the GQD as a result of pz orbital asymmetry in GQD carbon atoms with amino functional groups. This spin polarized ground state is believed to help the weak anti-localization dependent magneto transport by generating more disorder and strain in a GQD lattice under applied magnetic field and lays the premise for future graphene quantum dot based spintronic applications.

  15. Current dependence of colossal anisotropic magnetoresistance in La 0.3 Pr 0.4 Ca 0.3 MnO 3 microbridges

    NASA Astrophysics Data System (ADS)

    Jeon, J.; Jung, J.; Chow, K. H.

    2016-09-01

    The effect of the bias current on the in-plane colossal anisotropic magnetoresistance (C-AMR) is investigated in spatially confined La 0.3 Pr 0.4 Ca 0.3 MnO 3 microbridges. Dramatic increases of the C-AMR are found when the bias current is reduced. For example, in one of the samples, the C-AMR changed from ˜900% to over ˜24 000% as the current is decreased from 1 μA to 10 nA. The results indicate that the bias current can be used to manipulate the C-AMR in spatially confined manganite thin films via changes to the nature of the anisotropic percolation within the samples.

  16. A New Concept for Non-Volatile Memory: The Electric-Pulse Induced Resistive Change Effect in Colossal Magnetoresistive Thin Films

    NASA Technical Reports Server (NTRS)

    Liu, S. Q.; Wu, N. J.; Ignatiev, A.

    2001-01-01

    A novel electric pulse-induced resistive change (EPIR) effect has been found in thin film colossal magnetoresistive (CMR) materials, and has shown promise for the development of resistive, nonvolatile memory. The EPIR effect is induced by the application of low voltage (< 4 V) and short duration (< 20 ns) electrical pulses across a thin film sample of a CMR material at room temperature and under no applied magnetic field. The pulse can directly either increase or decrease the resistance of the thin film sample depending on pulse polarity. The sample resistance change has been shown to be over two orders of magnitude, and is nonvolatile after pulsing. The sample resistance can also be changed through multiple levels - as many as 50 have been shown. Such a device can provide a way for the development of a new kind of nonvolatile multiple-valued memory with high density, fast write/read speed, low power-consumption, and potential high radiation-hardness.

  17. Magnetically tunable dielectric, impedance and magnetoelectric response in MnFe2O4/(Pb1-xSrx)TiO3 composites thin films

    NASA Astrophysics Data System (ADS)

    Bala, Kanchan; Kotnala, R. K.; Negi, N. S.

    2017-02-01

    We have synthesized piezomagnetic-piezoelectric composites thin films MnFe2O4/(Pb1-xSrx)TiO3, where x=0.1, 0.2, and 0.3, using the metalorganic deposition (MOD) reaction method. The structural and microstructural analysis using the X-ray diffraction (XRD), AFM, and SEM reveals the presence of homogenous growth of both pervoskite and spinel phases in the composite films. Our results show that all the composites films exhibit good multiferroic as well as considerable magnetoelectric coupling. The impedance (Z‧ and Z″) and electrical modulus (M‧ and M″) Nyquist plots show distinct electrical responses with the magnetic field. Our analyses suggest that this electrical response arises due to the coexistence of the high resistive phase and the comparatively conductive phase in the MFO/PST composite films. The maximum magnetoelectric coefficient (α) is found to be 4.29 V Oe-1 cm-1 and 2.82 V Oe-1 cm-1 for compositions x=0.1 and 0.2. These values are substantially larger than those reported for bilayer composites thin films in literature and make them interesting for room temperature device applications.

  18. Magnetic origin of dielectric transition in BiFeO{sub 3}

    SciTech Connect

    Ray, J.; Biswal, A. K.; Vishwakarma, P. N.; Babu, P. D.; Siruguri, V.

    2014-04-24

    Magnetic relaxation measurements at 5K, 50K and 120K on BiFeO{sub 3} prepared by sol-gel auto combustion method shows stretched -exponential decay. These results shows the two factors viz, cooperative dynamics and rate of dynamics of spin, may be responsible for the low temperature magnetic-glassy behavior, concluded from bifurcation of zero field cooled (ZFC) and field cooled (FC) data of dc magnetization. Temperature dependent dielectric measurement shows a possible phase transition, seen in the dielectric-relaxation time and dielectric constant in the range 200 – 240K. Comparison of dielectric and magnetization data indicates a possibility of magneto-electric coupling.

  19. A dielectric omnidirectional reflector

    PubMed

    Fink; Winn; Fan; Chen; Michel; Joannopoulos; Thomas

    1998-11-27

    A design criterion that permits truly omnidirectional reflectivity for all polarizations of incident light over a wide selectable range of frequencies was used in fabricating an all-dielectric omnidirectional reflector consisting of multilayer films. The reflector was simply constructed as a stack of nine alternating micrometer-thick layers of polystyrene and tellurium and demonstrates omnidirectional reflection over the wavelength range from 10 to 15 micrometers. Because the omnidirectionality criterion is general, it can be used to design omnidirectional reflectors in many frequency ranges of interest. Potential uses depend on the geometry of the system. For example, coating of an enclosure will result in an optical cavity. A hollow tube will produce a low-loss, broadband waveguide, whereas a planar film could be used as an efficient radiative heat barrier or collector in thermoelectric devices.

  20. The Dielectric Wall Accelerator

    SciTech Connect

    Caporaso, George J.; Chen, Yu-Jiuan; Sampayan, Stephen E.

    2009-01-01

    The Dielectric Wall Accelerator (DWA), a class of induction accelerators, employs a novel insulating beam tube to impress a longitudinal electric field on a bunch of charged particles. The surface flashover characteristics of this tube may permit the attainment of accelerating gradients on the order of 100 MV/m for accelerating pulses on the order of a nanosecond in duration. A virtual traveling wave of excitation along the tube is produced at any desired speed by controlling the timing of pulse generating modules that supply a tangential electric field to the tube wall. Because of the ability to control the speed of this virtual wave, the accelerator is capable of handling any charge to mass ratio particle; hence it can be used for electrons, protons and any ion. The accelerator architectures, key technologies and development challenges will be described.

  1. Multilayer optical dielectric coating

    DOEpatents

    Emmett, John L.

    1990-01-01

    A highly damage resistant, multilayer, optical reflective coating includes alternating layers of doped and undoped dielectric material. The doping levels are low enough that there are no distinct interfaces between the doped and undoped layers so that the coating has properties nearly identical to the undoped material. The coating is fabricated at high temperature with plasma-assisted chemical vapor deposition techniques to eliminate defects, reduce energy-absorption sites, and maintain proper chemical stoichiometry. A number of differently-doped layer pairs, each layer having a thickness equal to one-quarter of a predetermined wavelength in the material are combined to form a narrowband reflective coating for a predetermined wavelength. Broadband reflectors are made by using a number of narrowband reflectors, each covering a portion of the broadband.

  2. An acoustic dielectric and mechanical spectrometer.

    PubMed

    Hu, Ruifen; Stevenson, Adrian C; Lowe, Christopher R

    2012-06-21

    In this report, the dielectric constant of glycerol solutions (0-70% (w/w)) and the mechanical transitions of poly(2-hydroxylethyl methacrylate-co-methacrylic acid) films (600-800 nm, 1.5-10 mol% cross-linker) have been investigated by the magnetic acoustic resonance sensor (MARS), which is an electrode-free acoustic sensor and operates over a continuous frequency spectrum (6-200 MHz). When a glycerol solution was loaded, the response of the MARS decayed exponentially as the operating frequency was increased. The decay rate against frequency as a function of the glycerol concentration reflects the change of the dielectric property of the glycerol solutions. In addition, mechanical relaxation of the poly(2-hydroxylethyl methacrylate-co-methacrylic acid) film has been observed on the MARS and the corresponding viscoelastic transition frequency has been estimated. The viscoelastic transition frequency increased as the polymer was more highly cross-linked. The MARS system behaved as a dielectric and mechanical spectrometer, monitoring the electrical and mechanical properties of viscoelastic materials or on the solid-liquid interfaces simultaneously, which has prospective application in studies of biomaterials, molecular interactions and drug deliveries.

  3. Attosecond clocking of scattering dynamics in dielectrics

    NASA Astrophysics Data System (ADS)

    Kling, Matthias

    2016-05-01

    In the past few years electronic-device scaling has progressed rapidly and miniaturization has reached physical gate lengths below 100 nm, heralding the age of nanoelectronics. Besides the effort in size scaling of integrated circuits, tremendous progress has recently been made in increasing the switching speed where strong-field-based ``dielectric-electronics'' may push it towards the petahertz frontier. In this contest, the investigation of the electronic collisional dynamics occurring in a dielectric material is of primary importance to fully understand the transport properties of such future devices. Here, we demonstrate attosecond chronoscopy of electron collisions in SiO2. In our experiment, a stream of isolated aerodynamically focused SiO2 nanoparticles of 50 nm diameter was delivered into the laser interaction region. Photoemission is initiated by an isolated 250 as pulse at 35 eV and the electron dynamics is traced by attosecond streaking using a delayed few-cycle laser pulse at 700 nm. Electrons were detected by a kilohertz, single-shot velocity-map imaging spectrometer, permitting to separate frames containing nanoparticle signals from frames containing the response of the reference gas only. We find that the nanoparticle photoemission exhibits a positive temporal shift with respect to the reference. In order to understand the physical origin of the shift we performed semi-classical Monte-Carlo trajectory simulations taking into account the near-field distributions in- and outside the nanoparticles as obtained from Mie theory. The simulations indicate a pronounced dependence of the streaking time shift near the highest measured electron energies on the inelastic scattering time, while elastic scattering only shows a small influence on the streaking time shift for typical dielectric materials. We envision our approach to provide direct time-domain access to inelastic scattering for a wide range of dielectrics.

  4. High dielectric constant 0-3 ceramic-polymer composites

    NASA Astrophysics Data System (ADS)

    Shan, Xiaobing

    0-3 ceramic-polymer composites using both nano-size and micro-size CaCu3Ti4O12 ceramic particles were studied. The micro-size ceramic particles were prepared from the CaCu3Ti 4O12 pellets by milling. The CaCu3Ti4O 12 ceramics were prepared using conventional solid-state reaction under different conditions, such as molding pressure, milling media and time, and calcination temperature and time. Based on the analysis of the dielectric spectrum, it was found that the dielectric responses of CaCu3Ti 4O12 ceramics are determined by three different processes. The effect of thickness of the ceramics on the dielectric properties was observed and studied. Although the dielectric response at low frequency increases with decreasing thickness, the dielectric behavior for the high frequency relaxation process is weakly dependent on thickness. 0-3 composites with different concentrations (0-50 vo% CaCu3Ti 4O12 ceramics) were prepared using solution casting. However, a clear polymer-rich layer was found in as-cast film due to the poor wettability between ceramic and polymer matrix. The HP was used to modify the morphology of the composites. Different configurations were studied for the HP process. Composites with a dielectric constant of 510 at 1 kHz were obtained in 50vol% CaCu3Ti4O12 composite with CC HP at room temperature. It was found that the relaxation time of the major relaxation process obtained in the composite changes with processing condition, such as annealing, HP and concentration. It indicates that the interfacial layers between ceramic particles and polymer matrix play an important role on the dielectric response of the composite. As for the HP samples, it was interestingly observed that as HP time changes, there is a critical HP time at which the composite exhibits a much higher dielectric constant. Based on the dielectric spectrum of the composites at different temperatures, it was concluded that the loss of the composites at low frequency is controlled by a

  5. A comparative study of nano-SiO2 and nano-TiO2 fillers on proton conductivity and dielectric response of a silicotungstic acid-H3PO4-poly(vinyl alcohol) polymer electrolyte.

    PubMed

    Gao, Han; Lian, Keryn

    2014-01-08

    The effects of nano-SiO2 and nano-TiO2 fillers on a thin film silicotungstic acid (SiWA)-H3PO4-poly(vinyl alcohol) (PVA) proton conducting polymer electrolyte were studied and compared with respect to their proton conductivity, environmental stability, and dielectric properties, across a temperature range from 243 to 323 K. Three major effects of these fillers have been identified: (a) barrier effect; (b) intrinsic dielectric constant effect; and (c) water retention effect. Dielectric analyses were used to differentiate these effects on polymer electrolyte-enabled capacitors. Capacitor performance was correlated to electrolyte properties through dielectric constant and dielectric loss spectra. Using a single-ion approach, proton density and proton mobility of each polymer electrolyte were derived as a function of temperature. The results allow us to deconvolute the different contributions to proton conductivity in SiWA-H3PO4-PVA-based electrolytes, especially in terms of the effects of fillers on the dynamic equilibrium of free protons and protonated water in the electrolytes.

  6. Response of the capacitance and dielectric loss of the SrRuO3/SrTiO3/SrRuO3 film heterostructures to variations in temperature and electric field

    NASA Astrophysics Data System (ADS)

    Boikov, Yu. A.; Danilov, V. A.

    2016-10-01

    Three-layer epitaxial heterostructures with a 750-nm-thick intermediate strontium titanate layer between two strontium ruthenate conductive thin-film electrodes have been grown by laser deposition. Photolithography and ion etching have been used to form film parallel-plate capacitors based on the grown heterostructures. The capacitance ( C) and dielectric loss tangent (tanδ) of the parallel-plate capacitors have been measured in the temperature range T = 4.2-300 K at an applied bias voltage of up to ±2.5 V and without it. At T > 100 K, the temperature dependence of the dielectric permittivity (ɛ) of the SrTiO3 intermediate layer is well approximated by the Curie-Weiss law taking into account the capacitance induced by the penetration of an electric field into the oxide electrodes. At T ≈ 20 K, the dielectric permittivity ɛ of the SrTiO3 intermediate layer decreases by approximately 20% in an electric field of 25 kV/cm. The dielectric loss tangent of the film capacitor heterostructures decreases monotonically with a decrease in the temperature in the range from 300 to 80 K and almost does not depend on the electric field strength. However, in the range from 80 to 4.2 K, the dielectric loss tangent increases nonmonotonically (abruptly) with a decrease in the temperature and decreases significantly in an applied electric field.

  7. Dielectric loss in microstrip lines

    NASA Technical Reports Server (NTRS)

    Simpson, T. L.; Tseng, B.

    1976-01-01

    A technique is presented for calculating dielectric loss in microstrip lines. Numerical results for several different substrates are included. These are compared with other available results and experimental data.

  8. Dielectric inspection of erythrocyte morphology

    NASA Astrophysics Data System (ADS)

    Hayashi, Yoshihito; Oshige, Ikuya; Katsumoto, Yoichi; Omori, Shinji; Yasuda, Akio; Asami, Koji

    2008-05-01

    We performed a systematic study of the sensitivity of dielectric spectroscopy to erythrocyte morphology. Namely, rabbit erythrocytes of four different shapes were prepared by precisely controlling the pH of the suspending medium, and their complex permittivities over the frequency range from 0.1 to 110 MHz were measured and analyzed. Their quantitative analysis shows that the characteristic frequency and the broadening parameter of the dielectric relaxation of interfacial polarization are highly specific to the erythrocyte shape, while they are insensitive to the cell volume fraction. Therefore, these two dielectric parameters can be used to differentiate erythrocytes of different shapes, if dielectric spectroscopy is applied to flow-cytometric inspection of single blood cells. In addition, we revealed the applicability and limitations of the analytical theory of interfacial polarization to explain the experimental permittivities of non-spherical erythrocytes.

  9. Extrinsic mechanism for giant dielectric response in Ba{sub 0.70}Sr{sub 0.30}(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} ceramic

    SciTech Connect

    Patel, Piyush Kumar Yadav, K. L. Durgesh

    2014-04-24

    To obtain the high dielectric constant, the effect of sintering process on the electrical properties of Ba{sub 0.70}Sr{sub 0.30}(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} ceramics were investigated. X-ray diffraction pattern of the samples at room temperature shows a monoclinic structure. Microstructure analysis shows well-grown and dense microstructure in all the samples. We found giant dielectric constant (∼3.59 × 10{sup 5}) with low dielectric loss (∼0.49) at room temperature for 2 hr sintered sample at 1250 °C. The extrinsic phenomena like interfacial polarization due to space charge accumulation at grain boundaries are discussed.

  10. Interconnect Between a Waveguide and a Dielectric Waveguide Comprising an Impedance Matched Dielectric Lens

    NASA Technical Reports Server (NTRS)

    Decrossas, Emmanuel (Inventor); Chattopadhyay, Goutam (Inventor); Chahat, Nacer (Inventor); Tang, Adrian J. (Inventor)

    2016-01-01

    A lens for interconnecting a metallic waveguide with a dielectric waveguide is provided. The lens may be coupled a metallic waveguide and a dielectric waveguide, and minimize a signal loss between the metallic waveguide and the dielectric waveguide.

  11. Dielectric properties of marsh vegetation

    NASA Astrophysics Data System (ADS)

    Kochetkova, Tatiana D.; Suslyaev, Valentin I.; Shcheglova, Anna S.

    2015-10-01

    The present work is devoted to the measurement of the dielectric properties of mosses and lichens in the frequency range from 500 MHz to 18 GHz. Subjects of this research were three species of march vegetation - moss (Dicranum polysetum Michx), groundcedar (Diphasiastrum complanatum (L.) Holub) and lichen (Cladonia stellaris). Samples of vegetation were collected in Tomsk region, Western Siberia, Russia. Complex dielectric permittivity was measured in coaxial section by Agilent Technologies vector network analyzer E8363B. Green samples was measured for some moisture contents from 100% to 3-5 % during a natural drying. The measurements were performed at room temperature, which remained within 21 ÷ 23 ° C. The frequency dependence of the dielectric constant for the three species of marsh vegetation differ markedly. Different parts of the complex permittivity dependency on moisture were fitted by line for all frequency points. Two break point were observed corresponding to the transition of water in the vegetation in various phase states. The complex permittivity spectra of water in the vegetation allow determining the most likely corresponding dielectric model of water in the vegetation by the method of hypothesis testing. It is the Debye's model. Parameters of Debye's model were obtained by numerical methods for all of three states of water. This enables to calculate the dielectric constant of water at any frequency range from 500 MHz to 18 GHz and to find the parameters of the dielectric model of the vegetation.

  12. Designing Multipolar Resonances in Dielectric Metamaterials

    PubMed Central

    Butakov, Nikita A.; Schuller, Jon A.

    2016-01-01

    Dielectric resonators form the building blocks of nano-scale optical antennas and metamaterials. Due to their multipolar resonant response and low intrinsic losses they offer design flexibility and high-efficiency performance. These resonators are typically described in terms of a spherical harmonic decomposition with Mie theory. In experimental realizations however, a departure from spherical symmetry and the use of high-index substrates leads to new features appearing in the multipolar response. To clarify this behavior, we present a systematic experimental and numerical characterization of Silicon disk resonators. We demonstrate that for disk resonators on low-index quartz substrates, the electric and magnetic dipole modes are easily identifiable across a wide range of aspect-ratios, but that higher order peaks cannot be unambiguously associated with any specific multipolar mode. On high-index Silicon substrates, even the fundamental dipole modes do not have a clear association. When arranged into arrays, resonances are shifted and pronounced preferential forward and backward scattering conditions appear, which are not as apparent in individual resonators and may be associated with interference between multipolar modes. These findings present new opportunities for engineering the multipolar scattering response of dielectric optical antennas and metamaterials, and provide a strategy for designing nano-optical components with unique functionalities. PMID:27929038

  13. Designing Multipolar Resonances in Dielectric Metamaterials

    NASA Astrophysics Data System (ADS)

    Butakov, Nikita A.; Schuller, Jon A.

    2016-12-01

    Dielectric resonators form the building blocks of nano-scale optical antennas and metamaterials. Due to their multipolar resonant response and low intrinsic losses they offer design flexibility and high-efficiency performance. These resonators are typically described in terms of a spherical harmonic decomposition with Mie theory. In experimental realizations however, a departure from spherical symmetry and the use of high-index substrates leads to new features appearing in the multipolar response. To clarify this behavior, we present a systematic experimental and numerical characterization of Silicon disk resonators. We demonstrate that for disk resonators on low-index quartz substrates, the electric and magnetic dipole modes are easily identifiable across a wide range of aspect-ratios, but that higher order peaks cannot be unambiguously associated with any specific multipolar mode. On high-index Silicon substrates, even the fundamental dipole modes do not have a clear association. When arranged into arrays, resonances are shifted and pronounced preferential forward and backward scattering conditions appear, which are not as apparent in individual resonators and may be associated with interference between multipolar modes. These findings present new opportunities for engineering the multipolar scattering response of dielectric optical antennas and metamaterials, and provide a strategy for designing nano-optical components with unique functionalities.

  14. Abnormal percolative transport and colossal electroresistance induced by anisotropic strain in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/PMN-PT heterostructure

    NASA Astrophysics Data System (ADS)

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Zhang, Hong-Rui; Liu, Yao; Zhang, Ying; Wang, Shuan-Hu; Wu, Rong-Rong; Zhang, Ming; Bao, Li-Fu; Sun, Ji-Rong; Shen, Bao-Gen

    2014-11-01

    Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5 K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems.

  15. Abnormal percolative transport and colossal electroresistance induced by anisotropic strain in (011)-Pr(0.7)(Ca(0.6)Sr(0.4))(0.3)MnO₃/PMN-PT heterostructure.

    PubMed

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Zhang, Hong-Rui; Liu, Yao; Zhang, Ying; Wang, Shuan-Hu; Wu, Rong-Rong; Zhang, Ming; Bao, Li-Fu; Sun, Ji-Rong; Shen, Bao-Gen

    2014-11-17

    Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr(0.7)(Ca(0.6)Sr(0.4))(0.3)MnO3/0.7Pb(Mg(1/3)Nb(2/3))O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5 K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems.

  16. Terahertz Magnetic Mirror Realized with Dielectric Resonator Antennas.

    PubMed

    Headland, Daniel; Nirantar, Shruti; Withayachumnankul, Withawat; Gutruf, Philipp; Abbott, Derek; Bhaskaran, Madhu; Fumeaux, Christophe; Sriram, Sharath

    2015-11-25

    Single-crystal silicon is bonded to a metal-coated substrate and etched in order to form an array of microcylinder passive terahertz dielectric resonator antennas (DRAs). The DRAs exhibit a magnetic response, and hence the array behaves as an efficient artificial magnetic conductor (AMC), with potential for terahertz antenna and sensing applications.

  17. Resonant dielectric nanostructures: a low-loss platform for functional nanophotonics

    NASA Astrophysics Data System (ADS)

    Decker, Manuel; Staude, Isabelle

    2016-10-01

    This review overviews the state of the art of research into high-index dielectric nanoresonators and their use in functional photonic nanostructures at optical frequencies. We start by providing the motivations for this research area and by putting it into context with the more well-established subfields of nanophotonics, in particular nanoplasmonics. Following the introduction, fundamental concepts regarding the optical properties of subwavelength dielectric nanoresonators are established. To this end, we provide a brief summary of the Mie theory, before focussing on optically induced magnetic response in Mie-resonant dielectric nanoparticles. We discuss the influence of the nanoparticle’s shape on its optical response, and provide an overview of directional effects that can occur when light is scattered by a Mie-resonant nanoparticle. We then dedicate a few words to technology-related aspects, including an overview of fabrication methods for Mie-resonant dielectric nanoparticles. Next, recent progress on all-dielectric nanoantennas is presented, focussing on strategies to locally enhance optical near-fields and to achieve directional emission patterns. We then turn to all-dielectric metasurfaces and their potential applications. We touch on dielectric metamaterial reflectors and Fano-resonant dielectric metasurfaces, before discussing graded Mie-resonant dielectric metasurfaces for wavefront control applications in more detail. Following this, an overview of the recent progress in active, tunable and nonlinear dielectric nanostructures is provided. Finally, prospects and challenges are discussed, particularly the realization of highly efficient Mie-resonant nanostructures at visible frequencies, the integration of Mie-resonant nanostructures with active and functional materials, and the construction of three-dimensional high-index dielectric nanostructures.

  18. Dipolar correlations and the dielectric permittivity of water.

    PubMed

    Sharma, Manu; Resta, Raffaele; Car, Roberto

    2007-06-15

    The static dielectric properties of liquid and solid water are investigated within linear response theory in the context of ab initio molecular dynamics. Using maximally localized Wannier functions to treat the macroscopic polarization we formulate a first-principles, parameter-free, generalization of Kirkwood's phenomenological theory. Our calculated static permittivity is in good agreement with experiment. Two effects of the hydrogen bonds, i.e., a significant increase of the average local moment and a local alignment of the molecular dipoles, contribute in almost equal measure to the unusually large dielectric constant of water.

  19. Temperature-dependent dielectric properties of a thermoplastic gelatin

    NASA Astrophysics Data System (ADS)

    Landi, Giovanni; Neitzert, Heinz C.; Sorrentino, Andrea

    2016-05-01

    The frequency and the temperature dependence of the dielectric properties of a thermoplastic gelatin based bio-material have been investigated. At lower frequencies the dielectric response is strongly affected by charge carrier accumulation at the electrodes which modifies the dominating hopping conduction mechanism. The variation of the ac conductivity with frequency obeys a Jonscher type power law except for a small deviation in the low frequency range due to the electrode polarization effect. The master curve of the ac conductivity data shows that the conductivity relaxation of the gelatin is temperature independent.

  20. Efficient Third Harmonic Generation from Metal-Dielectric Hybrid Nanoantennas.

    PubMed

    Shibanuma, Toshihiko; Grinblat, Gustavo; Albella, Pablo; Maier, Stefan A

    2017-03-16

    High refractive index dielectric nanoantennas are expected to become key elements for nonlinear nano-optics applications due to their large nonlinearities, low energy losses, and ability to produce high electric field enhancements in relatively large nanoscale volumes. In this work, we show that the nonlinear response from a high-index dielectric nanoantenna can be significantly improved by adding a metallic component to build a metal-dielectric hybrid nanostructure. We demonstrate that the plasmonic resonance of a Au nanoring can boost the anapole mode supported by a Si nanodisk, strongly enhancing the electric field inside the large third-order susceptibility dielectric. As a result, a high third harmonic conversion efficiency, which reaches 0.007% at a third harmonic wavelength of 440 nm, is obtained. In addition, by suitably modifying geometrical parameters of the hybrid nanoantenna, we tune the enhanced third harmonic emission throughout the optical regime. Coupling metallic and dielectric nanoantennas to expand the potential of subwavelength structures opens new paths for efficient nonlinear optical effects in the visible range on the nanoscale.

  1. Dielectric properties of polyfunctional alcohols: 2,3-butanediol

    NASA Astrophysics Data System (ADS)

    Zhuravlev, V. I.

    2016-08-01

    Using a variety theoretical approaches within the Debye, Davidson-Cole, and Forsman models, and an approach based on the Dissado-Hill theory, dielectric spectra of 2,3-butanediol in the temperature range of 298 to 423 K are analyzed. It is shown that the dielectric spectra of 2,3-butanediole are described by the Davidson-Cole equation, and the βDC parameter depends strongly on temperature. The spectrum of dielectric relaxation of 2,3-butanediol within the Debye theory is presented as the sum of two areas of dispersion, and conclusions are drawn regarding possible mechanisms of dispersion responsible for the obtained fields. The relaxation times of 2,3-butanediol, calculated using different equations describing the nonlinear behavior of relaxation times, are compared. The dipole moments of clusters are obtained for the first time using the Dissado-Hill cluster model, and a preliminary analysis of them is performed.

  2. Polarization processes in rocks: 1. Complex Dielectric Permittivity method

    NASA Astrophysics Data System (ADS)

    Levitskaya, Tsylya M.; Sternberg, Ben K.

    1996-07-01

    This is the first part of a review of research performed in the former USSR. Experimental data were used from several regions of the USSR, including Russia, Ukraine, and Georgia. Many of the publications are available in U.S. libraries. Some of them are translated into English. This part contains results from applying the Complex Dielectric Permittivity method (Dielectric Spectroscopy) for studying the electrical response of rocks in alternating fields with frequencies from 100 Hz to 100 MHz. Data on dielectric properties of sedimentary rocks of different lithology and with various porosities, salinities of saturating solution, and hydrocarbon content are reviewed here. Measurement methods, including means for avoiding or reducing the electrode polarization, are also considered. It is shown that wet rocks exhibit a Maxwell-Wagner polarization process at frequencies 105-107 Hz, caused by charge accumulation on the pore boundaries.

  3. A Wireless Multi-Sensor Dielectric Impedance Spectroscopy Platform

    PubMed Central

    Ghaffari, Seyed Alireza; Caron, William-O.; Loubier, Mathilde; Rioux, Maxime; Viens, Jeff; Gosselin, Benoit; Messaddeq, Younes

    2015-01-01

    This paper describes the development of a low-cost, miniaturized, multiplexed, and connected platform for dielectric impedance spectroscopy (DIS), designed for in situ measurements and adapted to wireless network architectures. The platform has been tested and used as a DIS sensor node on ZigBee mesh and was able to interface up to three DIS sensors at the same time and relay the information through the network for data analysis and storage. The system is built from low-cost commercial microelectronics components, performs dielectric spectroscopy ranging from 5 kHz to 100 kHz, and benefits from an on-the-fly calibration system that makes sensor calibration easy. The paper describes the microelectronics design, the Nyquist impedance response, the measurement sensitivity and accuracy, and the testing of the platform for in situ dielectric impedance spectroscopy applications pertaining to fertilizer sensing, water quality sensing, and touch sensing. PMID:26393587

  4. A Wireless Multi-Sensor Dielectric Impedance Spectroscopy Platform.

    PubMed

    Ghaffari, Seyed Alireza; Caron, William-O; Loubier, Mathilde; Rioux, Maxime; Viens, Jeff; Gosselin, Benoit; Messaddeq, Younes

    2015-09-17

    This paper describes the development of a low-cost, miniaturized, multiplexed, and connected platform for dielectric impedance spectroscopy (DIS), designed for in situ measurements and adapted to wireless network architectures. The platform has been tested and used as a DIS sensor node on ZigBee mesh and was able to interface up to three DIS sensors at the same time and relay the information through the network for data analysis and storage. The system is built from low-cost commercial microelectronics components, performs dielectric spectroscopy ranging from 5 kHz to 100 kHz, and benefits from an on-the-fly calibration system that makes sensor calibration easy. The paper describes the microelectronics design, the Nyquist impedance response, the measurement sensitivity and accuracy, and the testing of the platform for in situ dielectric impedance spectroscopy applications pertaining to fertilizer sensing, water quality sensing, and touch sensing.

  5. Hydration dependence of conformational dielectric relaxation of lysozyme.

    PubMed

    Knab, Joseph; Chen, Jing-Yin; Markelz, Andrea

    2006-04-01

    Dielectric response of hen egg white lysozyme is measured in the far infrared (5-65 cm-1, 0.15-1.95 THz, 0.6-8.1 meV) as a function of hydration. The frequency range is associated with collective vibrational modes of protein tertiary structure. The observed frequency dependence of the absorbance is broad and glass-like. For the entire frequency range, there is a slight increase in both the absorbance and index of refraction with increasing hydration for <0.27 h (mass of H2O per unit mass protein). At 0.27 h, the absorbance and index begin to increase more rapidly. This transition corresponds to the point where the first hydration shell is filled. The abrupt increase in dielectric response cannot be fully accounted for by the additional contribution to the dielectric response due to bulk water, suggesting that the protein has not yet achieved its fully hydrated state. The broad, glass-like response suggests that at low hydrations, the low frequency conformational hen egg white lysozyme dynamics can be described by a dielectric relaxation model where the protein relaxes to different local minima in the conformational energy landscape. However, the low frequency complex permittivity does not allow for a pure relaxational mechanism. The data can best be modeled with a single low frequency resonance (nu approximately 120 GHz=4 cm-1) and a single Debye relaxation process (tau approximately .03-.04 ps). Terahertz dielectric response is currently being considered as a possible biosensing technique and the results demonstrate the required hydration control necessary for reliable biosensor applications.

  6. Temperature dependent reversible p-n-p type conduction switching with colossal change in thermopower of semiconducting AgCuS.

    PubMed

    Guin, Satya N; Pan, Jaysree; Bhowmik, Arghya; Sanyal, Dirtha; Waghmare, Umesh V; Biswas, Kanishka

    2014-09-10

    Semiconductors have been fundamental to various devices that are typically operated with electric field, such as transistors, memories, sensors, and resistive switches. There is growing interest in the development of novel inorganic materials for use in transistors and semiconductor switches, which can be operated with a temperature gradient. Here, we show that a crystalline semiconducting noble metal sulfide, AgCuS, exhibits a sharp temperature dependent reversible p-n-p type conduction switching, along with a colossal change in the thermopower (ΔS of ~1757 μV K(-1)) at the superionic phase transition (T of ~364 K). In addition, its thermal conductivity is ultralow in 300-550 K range giving AgCuS the ability to maintain temperature gradients. We have developed fundamental understanding of the phase transition and p-n-p type conduction switching in AgCuS through temperature dependent synchrotron powder X-ray diffraction, heat capacity, Raman spectroscopy, and positron annihilation spectroscopy measurements. Using first-principles calculations, we show that this rare combination of properties originates from an effective decoupling of electrical conduction and phonon transport associated with electronic states of the rigid sulfur sublattice and soft vibrations of the disordered cation sublattices, respectively. Temperature dependent p-n-p type conduction switching makes AgCuS an ideal material for diode or transistor devices that operate reversibly on temperature or voltage changes near room temperature.

  7. A Variable Temperature Synchrotron X-ray Diffraction Study of Colossal Magnetoresistant NdMnAsO0.95F0.05

    PubMed Central

    Wildman, E. J.; Mclaughlin, A. C.

    2016-01-01

    The recent discovery of high temperature superconductivity in Fe arsenides has invigorated research into transition metal pnictides. Colossal magnetoresistance (CMR) has recently been reported for NdMnAsO1-xFx for x = 0.05–0.08, with a maximum magnetoresistance achieved at low temperature (MR9T(3 K)) = −95%). This appears to be a novel mechanism of CMR, which is as a result of a second order phase transition in field from an insulating antiferromagnet to a semiconducting paramagnet. Here we report a variable temperature synchrotron X-ray powder diffraction study of the CMR oxypnictide NdMnAsO0.95F0.05 between 4 K–290 K. An excellent fit to the tetragonal unit cell with space group P4/nmm is obtained over the entire temperature range, with no change in crystal structure detected down to 4 K. A coupling of the lattice and magnetic order is observed, where subtle discontinuities in the temperature variation of a and the c/a ratio are apparent as the Nd spins order antiferromagnetically and the Mn moments reorient into the basal plane at TSR. The results suggest that very small changes in lattice parameters effect the coupling between lattice, electronic and magnetic degrees of freedom. PMID:26875693

  8. Colossal magnetoresistance accompanying a structural transition in a highly two-dimensional metallic state of Ca3 Ru2 O7

    NASA Astrophysics Data System (ADS)

    Ohmichi, E.; Yoshida, Y.; Ikeda, S. I.; Shirakawa, N.; Osada, T.

    2004-09-01

    We report the high-field magnetoresistivity, magnetization, and magnetostriction data of a bilayered ruthenate Ca3Ru2O7 grown by a floating-zone method. The samples used in this study show metallic inplane conduction, but nonmetallic interplane conduction, below 30K ; these results are suggestive of a highly two-dimensional metallic ground state. We demonstrate here the existence of two types of field-induced metamagnetic transitions at 6 and 15T , accompanied by the colossal magnetoresistance effect in the interplane conduction [ρc(20T)/ρc(0T)<10-3] . Interestingly, the higher-field transition is accompanied by large inplane lattice shrinkage that is sufficient to cause orbital polarization in nearly threefold t2g orbitals. The lattice change due to the magnetic field coincides with the discontinuity at 48K observed in the thermal contraction data, suggesting that the high-temperature crystal structure is restored by the application of a magnetic field. In this paper, we will discuss this anomalous coupling between spin, charge, and lattice in Ca3Ru2O7 in terms of structural distortions.

  9. Changes of the local distortions and colossal magnetoresistive properties of La(0.7)Ca(0.3)MnO(3) induced by Ti or Ga defects

    SciTech Connect

    Bridges, F.; Cao, D.; Anderson, M.; Ramirez, A.P.; Olapinski, M.; Subramanian, M.A.; Booth, C.H.; Kwei, G.

    2002-07-12

    The magnetoresistive properties of La0.7Ca0.3MnO3 change rapidly when Ti or Ga are substituted on the Mn site for concentrations, x, from 1 to 10 percent. The samples exhibit colossal magnetoresistance (CMR) and the resistivity increases dramatically with dopant concentration. The temperature of the resistivity peak, TR, shifts rapidly to lower temperatures with increasing x and the ferromagnetic transition broadens. However, the transition temperature, Tc, is only slightly suppressed. Consequently, TR occurs well below Tc for x above 2 percent. Investigations of these materials using Mn XAFS show that changes in the local structure, parametrized by the pair-distribution width, sigma, correlate well with Tc and the sample magnetization. For a given dopant, the resistivity peak occurs when sigma{sup 2} decreases below a critical value. Both dopants produce extended defects which increases the resistivity of the nearby materials considerably. The data suggest that even at x {approx}4 percent, most of the sites are slightly distorted at low T.

  10. Elastomer dielectric for pulse power

    NASA Astrophysics Data System (ADS)

    Bradely, L. P.; Orham, E. L.; Stowers, I. F.; Braucht, J. R.

    1980-05-01

    Selected elastomer dielectrics are characterized as high voltage insulators for use in pulse power systems. Silicone, ethylene propylene rubber and polyurethene were tested, but most of the data is for silicone. The particular power system developed uses a formed silicone insulator 76 cm in dia. and 3 mm thick as the major insulator between capacitors, railgap switches, load, and return conductor. The capacitor array is dc charged to 50 kv. The use of an elastomer dielectric made possible the construction of a pulser one order of magnitude smaller than previously constructed pulsers having the same current characteristics. Also, use of the elastomer dielectrics in pulse powr systems leads to improved production techniques and system reliability.

  11. USDA/ARS and dielectric properties research

    Technology Transfer Automated Retrieval System (TEKTRAN)

    An overview of the research is presented, including RF dielectric heating for seed treatment, insect control, product conditioning, and moisture and quality sensing applications, equipment used, dielectric properties measurement techniques, broad- frequency- range data obtained, and research results...

  12. Capacitive Cells for Dielectric Constant Measurement

    ERIC Educational Resources Information Center

    Aguilar, Horacio Munguía; Maldonado, Rigoberto Franco

    2015-01-01

    A simple capacitive cell for dielectric constant measurement in liquids is presented. As an illustrative application, the cell is used for measuring the degradation of overheated edible oil through the evaluation of their dielectric constant.

  13. Dielectric spectroscopy of ionic microgel suspensions.

    PubMed

    Mohanty, P S; Nöjd, S; Bergman, M J; Nägele, G; Arrese-Igor, S; Alegria, A; Roa, R; Schurtenberger, P; Dhont, J K G

    2016-12-06

    The determination of the net charge and size of microgel particles as a function of their concentration, as well as the degree of association of ions to the microgel backbone, has been pursued in earlier studies mainly by scattering and rheology. These methods suffer from contributions due to inter-particle interactions that interfere with the characterization of single-particle properties. Here we introduce dielectric spectroscopy as an alternative experimental method to characterize microgel systems. The advantage of dielectric spectroscopy over other experimental methods is that the polarization due to mobile charges within a microgel particle is only weakly affected by inter-particle interactions. Apart from electrode polarization effects, experimental spectra on PNIPAM-co-AA [poly(N-isopropylacrylamide-co-acrylic acid)] ionic microgel particles suspended in de-ionized water exhibit three well-separated relaxation modes, which are due to the polarization of the mobile charges within the microgel particles, the diffuse double layer around the particles, and the polymer backbone. Expressions for the full frequency dependence of the electrode-polarization contribution to the measured dielectric response are derived, and a theory is proposed for the polarization resulting from the mobile charges within the microgel. Relaxation of the diffuse double layer is modeled within the realm of a cell model. The net charge and the size of the microgel particles are found to be strongly varying with concentration. A very small value of the diffusion coefficient of ions within the microgel is found, due to a large degree of chemical association of protons to the polymer backbone.

  14. CVD Diamond Dielectric Accelerating Structures

    SciTech Connect

    Schoessow, P.; Kanareykin, A.; Gat, R.

    2009-01-22

    The electrical and mechanical properties of diamond make it an ideal candidate material for use in dielectric accelerating structures: high RF breakdown field, extremely low dielectric losses and the highest available thermoconductive coefficient. Using chemical vapor deposition (CVD) cylindrical diamond structures have been manufactured with dimensions corresponding to fundamental TM{sub 01} mode frequencies in the GHz to THz range. Surface treatments are being developed to reduce the secondary electron emission (SEE) coefficient below unity to reduce the possibility of multipactor. The diamond CVD cylindrical waveguide technology developed here can be applied to a variety of other high frequency, large-signal applications.

  15. Dielectric barrier discharges applied for optical spectrometry

    NASA Astrophysics Data System (ADS)

    Brandt, S.; Schütz, A.; Klute, F. D.; Kratzer, J.; Franzke, J.

    2016-09-01

    The present review reflects the importance of dielectric barrier discharges for optical spectrometric detection in analytical chemistry. In contrast to usual discharges with a direct current the electrodes are separated by at least one dielectric barrier. There are two main features of the dielectric barrier discharges: they can serve as dissociation and excitation devices as well as ionization sources, respectively. This article portrays various application fields of dielectric barrier discharges in analytical chemistry used for elemental and molecular detection with optical spectrometry.

  16. Dielectric nanostructures with high laser damage threshold

    NASA Astrophysics Data System (ADS)

    Ngo, C. Y.; Hong, L. Y.; Deng, J.; Khoo, E. H.; Liu, Z.; Wu, R. F.; Teng, J. H.

    2017-02-01

    Dielectric-based metamaterials are proposed to be the ideal candidates for low-loss, high-efficiency devices. However, to employ dielectric nanostructures for high-power applications, the dielectric material must have a high laser-induced damaged threshold (LIDT) value. In this work, we investigated the LIDT values of dielectric nanostructures for high-power fiber laser applications. Consequently, we found that the fabricated SiO2 nanostructured lens can withstand laser fluence exceeding 100 J/cm2.

  17. Effect of thermal stresses on the dielectric properties of strontium titanate thin films

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Weiss, C. V.; Alpay, S. P.

    2011-07-01

    We develop a quantitative thermodynamic model to understand the role of thermal stresses on the dielectric permittivity and tunability of (001)-textured polycrystalline monodomain strontium titanate (SrTiO3) films. This methodology is used to compute the dielectric constant and tunability of SrTiO3 films on Si, c-sapphire, LaAlO3, and MgO substrates. Results show that dielectric properties of SrTiO3 depend strongly on the growth/processing temperature TG. For substrates such as MgO that induce compressive in-plane thermal stresses, the dielectric response of SrTiO3 is enhanced. However, for SrTiO3 films on IC-compatible substrates (Si and c-sapphire), thermal stresses can significantly degrade the dielectric permittivity and tunability.

  18. The behavior of dielectric elastomer actuators connected in series and parallel

    NASA Astrophysics Data System (ADS)

    Li, Guorui; Liang, Yiming; Yang, Xuxu; Cheng, Tingyu; Huang, Zhilong; Li, Tiefeng

    2016-04-01

    Dielectric elastomer membrane has the ability of shrinking the thickness and expanding surface area when a voltage is applied through its thickness. Dielectric elastomer has been widely studied and used as dielectric elastomer actuator (DEA), dielectric elastomer generator (DEG) and dielectric elastomer sensor (DES). We study the behavior of several DEAs connected in series and parallel, and find that the different connecting models can achieve different responses of the DEAs. DEAs connected in series can enhance the actuation, while DEA connected in parallel can enhance the actuation force. In our experiment, DEAs connected in series and parallel are loaded in actuation direction under a dead load providing pre-stretch. We discuss the results of the experiments and give the conclusions.

  19. Low-κ' dielectric properties of UV-treated bi-axially oriented polypropylene films

    NASA Astrophysics Data System (ADS)

    Dervos, C. T.; Tarantili, P. A.; Athanassopoulou, M. D.

    2009-07-01

    A 40 µm multilayer bi-axially oriented polypropylene (BOPP) film, was fabricated by the tenter process and its dielectric response was investigated after applying combined action of UV, humidity and heat. Dissipation factor (tan δ) and relative dielectric constant measurements were performed via the capacitance method for frequencies 20Hz-1 GHz. These results show that the relative dielectric constant (κ') reduces towards ultra low values (1.8) with an increasing number of applied UV-condensation cycles without any subsequent increase in the dielectric loss. Having no added physical porosity and absence of fluorine atoms, the irradiated BOPP structures offer significant advantages over poly(tetrafluoroethylene) PTFE due to reduced polarization effects, lower dielectric constant values and chemical stability to the adjacent copper or aluminium conductors. Possible application fields are dry type high-voltage capacitors and insulation within electronic components.

  20. Improved gas sensing and dielectric properties of Fe doped hydroxyapatite thick films: Effect of molar concentrations

    SciTech Connect

    Mene, Ravindra U.; Mahabole, Megha P.; Mohite, K.C.; Khairnar, Rajendra S.

    2014-02-01

    Highlights: • We report improved gas sensing and dielectric characteristics of Fe ion exchanged HAp films. • Fe doped HAp film shows maximum gas response at relatively lower temperature. • Response and gas uptake capacity of sensors is improved for appropriate amount of Fe ions in HAp matrix. • Fe-HAp films exhibit remarkable improvement in dielectric properties compared to pure HAp. • Fe doped HAp films show significant improvement in gas sensing as well as in dielectric properties. - Abstract: In the present work Fe doped hydroxyapatite (Fe-HAp) thick films has been successfully utilized to improve the gas sensing as well as its dielectric properties. Initially, HAp nano powder is synthesized by chemical precipitation process and later on Fe ions are doped in HAp by ion exchange process. Structural and morphological modifications are observed by means of X-ray diffraction and scanning electron microscopy analysis. The sensing parameters such as operating temperature, response/recovery time and gas uptake capacity are experimentally determined. The Fe-HAp (0.05 M) film shows improved CO and CO{sub 2} gas sensing capacity at lower operating temperature compared to pure HAp. Moreover, variation of dielectric constant and dielectric loss for pure and Fe-HAp thick films are studied as a function of frequency in the range of 10 Hz–1 MHz. The study reveals that Fe doped HAp thick films improve the sensing and dielectric characteristics as compared to pure HAp.

  1. Cellulose Triacetate Dielectric Films For Capacitors

    NASA Technical Reports Server (NTRS)

    Yen, Shiao-Ping S.; Jow, T. Richard

    1994-01-01

    Cellulose triacetate investigated for use as dielectric material in high-energy-density capacitors for pulsed-electrical-power systems. Films of cellulose triacetate metalized on one or both sides for use as substrates for electrodes and/or as dielectrics between electrodes in capacitors. Used without metalization as simple dielectric films. Advantages include high breakdown strength and self-healing capability.

  2. Thermally stable dielectric responses in uniaxially (001)-oriented CaBi4Ti4O15 nanofilms grown on a Ca2Nb3O10− nanosheet seed layer

    PubMed Central

    Kimura, Junichi; Takuwa, Itaru; Matsushima, Masaaki; Shimizu, Takao; Uchida, Hiroshi; Kiguchi, Takanori; Shiraishi, Takahisa; Konno, Toyohiko J.; Shibata, Tatsuo; Osada, Minoru; Sasaki, Takayoshi; Funakubo, Hiroshi

    2016-01-01

    To realize a high-temperature capacitor, uniaxially (001)-oriented CaBi4Ti4O15 films with various film thicknesses were prepared on (100)cSrRuO3/Ca2Nb3O10− nanosheet/glass substrates. As the film thickness decreases to 50 nm, the out-of-plane lattice parameters decrease while the in-plane lattice ones increase due to the in-plane tensile strain. However, the relative dielectric constant (εr) at room temperature exhibits a negligible degradation as the film thickness decreases to 50 nm, suggesting that εr of (001)-oriented CaBi4Ti4O15 is less sensitive to the residual strain. The capacitance density increases monotonously with decreasing film thickness, reaching a value of 4.5 μF/cm2 for a 50-nm-thick nanofilm, and is stable against temperature changes from room temperature to 400 °C irrespective of film thickness. This behaviour differs from that of the widely investigated perovskite-structured dielectrics. These results show that (001)-oriented CaBi4Ti4O15 films derived using Ca2Nb3O10− nanosheets as seed layers can be made candidates for high-temperature capacitor applications by a small change in the dielectric properties against film thickness and temperature variations. PMID:26875929

  3. Origin of giant dielectric permittivity and weak ferromagnetic behavior in (1-x)LaFeO3-xBaTiO3 (0.0 ≤ x ≤ 0.25) solid solutions

    NASA Astrophysics Data System (ADS)

    Sreenivasu, T.; Tirupathi, P.; Prabahar, K.; Suryanarayana, B.; Chandra Mouli, K.

    The solid solutions of (1-x) LaFeO3-xBaTiO3 (0.0≤x≤0.25) have been synthesized successfully by the conventional solid-state reaction method. Room temperature (RT) X-ray diffraction studies reveal the stabilization of orthorhombic phase with Pbnm space group. Complete solubility in the perovskite series was demonstrated up to x=0.25. The dielectric permittivity shows colossal dielectric constant (CDC) at RT. The doping of BaTiO3 in LaFeO3 exhibit pronounced CDC up to a composition x=0.15, further it starts to decrease. The frequency-dependent dielectric loss exhibits polaronic conduction, which can attribute to presence of multiple valence of iron. The relaxation frequency and polaronic conduction mechanism was shifted towards RT as function of x. Moreover, large magnetic moment with weak ferromagnetic behavior is observed in doped LaFeO3 solid solution, which might be the destruction of spin cycloid structure due to insertion of Ti in Fe-O-Fe network of LaFeO3.

  4. van der Waals interactions between excited-state atoms and dispersive dielectric surfaces

    NASA Astrophysics Data System (ADS)

    Fichet, M.; Schuller, F.; Bloch, D.; Ducloy, M.

    1995-02-01

    van der Waals interactions between atoms and dielectric surfaces are reinvestigated. To describe the nonretarded interaction potential between a dispersive dielectric surface and an atom in an arbitrary internal energy state, we derive a general expression in terms of an integral, over real frequency, of the combined atom and surface polarizabilities. It is shown that, for excited atoms, the expression is equivalent to the one obtained by Wylie and Sipe [Phys. Rev. A 32, 2030 (1985)]. We thus demonstrate how to extend this approach to excited atoms interacting with birefringent dielectrics. For isotropic dielectrics, a method of integration in closed form allows us to derive an approximate formula for the van der Waals interaction constant in terms of resonance frequencies and oscillator strengths of both the atom and the dielectric. Frequency-dependent ``dielectric reflection'' coefficients are introduced for virtual atomic dipole couplings either in absorption or in emission. In absorption, the reflection coefficient is always positive and smaller than unity. In emission, it may take arbitrary values, positive or negative (corresponding to van der Waals repulsion). Such a behavior is shown to be related to resonant excitation exchange between the atomic system and the dielectric medium, when an atomic transition frequency gets in resonance with a dielectric absorption band. Numerical calculations performed for the cesium-sapphire system are shown to be in good agreement with data obtained by selective-reflection spectroscopy. Finally, experimental tests of the birefringent character of the sapphire response are discussed.

  5. Dielectric THz waveguides

    NASA Astrophysics Data System (ADS)

    Dupuis, Alexandre

    In this thesis we have explored a wide variety of dielectric waveguides that rely on many different waveguiding mechanisms to guide THz (far-infrared) radiation. We have explored both theoretically and experimentally a large number of waveguide designs with the aim of reducing propagation and bending losses. The different waveguides can be classified into two fundamentally different strategies for reducing the propagation loss: small-core single-mode evanescent-field fibers or large hollow-core multi-mode tubes. Our focus was first set on exploring the small-core evanescent-field fiber strategy for reducing propagation losses. Following initial theoretical work in our group, much effort was spent on the fabrication and measurement of evanescent porous subwavelength diameter plastic fibers, in an attempt to further reduce the propagation losses. The fabrication of such fibers is a challenge and many novel techniques were devised to enable fiber drawing without hole collapse. The first method sealed the holes of an assembly of polymer tubes and lead to fibers of relatively low porosity (˜25% air within the core) due to reduction in hole size during fiber drawing. The second method was a novel sacrificial polymer technique whereby drawing a completely solid fiber prevented any hole collapse and the subsequent dissolution of the sacrificial polymer revealed the holes in the fiber. The third method was a combination of preform casting using glass molds and drawing with pressurized air within the holes. This led to fibers of record porosity (86% air). The measurement of these porous fibers began with a collaboration with a group from the university of Sherbrooke. At the time, the only available detector was a frequency integrating liquid-helium-cooled bolometer (powermeter). A novel directional coupler method for measuring the losses of subwavelength fibers was developed whereby an evanescent coupler is formed by bringing a probe fiber in proximity to the sample fiber

  6. Scattering from Thin Dielectric Disks

    NASA Technical Reports Server (NTRS)

    Levine, D. M.; Schneider, A.; Lang, R. H.; Carter, H. G.

    1984-01-01

    A solution was obtained for scattering from thin dielectric disks by approximating the currents induced inside the disk with the currents which would exist inside a dielectric slab of the same thickness, orientation and dielectric properties. This approximation reduces to an electrostatic approximation when the disk thickness, T, is small compared to the wavelength of the incident radiation and the approximation yields a conventional physical optics solution when the dimension, A, characteristic of the geometrical cross section of the disk (e.g., the diameter of a circular disk) is large compared to wavelength. When the ratio A/T is sufficiently large the disk will always be in one or the other of these regimes (T lambda or kA1. Consequently, when A/T is large this solution provides a conventional approximation for the scattered fields which can be applied at all frequencies. As a check on this conclusion, a comparison was made between the theoretical and measured radar cross section of thin dielectric disks. Agreement was found for thin disks with both large and small values of kA.

  7. Counteracting Gravitation In Dielectric Liquids

    NASA Technical Reports Server (NTRS)

    Israelsson, Ulf E.; Jackson, Henry W.; Strayer, Donald M.

    1993-01-01

    Force of gravity in variety of dielectric liquids counteracted by imposing suitably contoured electric fields. Technique makes possible to perform, on Earth, variety of experiments previously performed only in outer space and at great cost. Also used similarly in outer space to generate sort of artificial gravitation.

  8. Dielectric elastomer actuators with granular coupling

    NASA Astrophysics Data System (ADS)

    Carpi, Federico; Frediani, Gabriele; Nanni, Massimo; De Rossi, Danilo

    2011-04-01

    So-called 'hydrostatically coupled' dielectric elastomer actuators (HC-DEAs) have recently been shown to offer new opportunities for actuation devices made of electrically responsive elastomeric insulators. HC-DEAs include an incompressible fluid that mechanically couples a dielectric elastomer based active part to a passive part interfaced to the load, so as to enable hydrostatic transmission. Drawing inspiration from that concept, this paper presents a new kind of actuators, analogous to HC-DEAs, except for the fact that the fluid is replaced by fine powder. The related technology, here referred to as 'granularly coupled' DEAs (GC-DEAs), relies entirely on solid-state materials. This permits to avoid drawbacks (such as handling and leakage) inherent to usage of fluids, especially those in liquid phase. The paper presents functionality and actuation performance of bubble-like GC-DEAs, in direct comparison with HC-DEAs. For this purpose, prototype actuators made of two pre-stretched membranes of acrylic elastomer, coupled via talcum powder (for GC-DEA) or silicone grease (for HC-DEA), were manufactured and comparatively tested. As compared to HC-DEAs, GC-DEAs showed a higher maximum stress, the same maximum relative displacement, and nearly the same bandwidth. The paper presents characterization results and discusses advantages and drawbacks of GC-DEAs, in comparison with HC-DEAs.

  9. Dielectric barrier discharges in analytical chemistry.

    PubMed

    Meyer, C; Müller, S; Gurevich, E L; Franzke, J

    2011-06-21

    The present review reflects the importance of dielectric barrier discharges in analytical chemistry. Special about this discharge is-and in contrast to usual discharges with direct current-that the plasma is separated from one or two electrodes by a dielectric barrier. This gives rise to two main features of the dielectric barrier discharges; it can serve as dissociation and excitation device and as ionization mechanism, respectively. The article portrays the various application fields for dielectric barrier discharges in analytical chemistry, for example the use for elemental detection with optical spectrometry or as ionization source for mass spectrometry. Besides the introduction of different kinds of dielectric barrier discharges used for analytical chemistry from the literature, a clear and concise classification of dielectric barrier discharges into capacitively coupled discharges is provided followed by an overview about the characteristics of a dielectric barrier discharge concerning discharge properties and the ignition mechanism.

  10. Colossal magnetoresistance in amino-functionalized graphene quantum dots at room temperature: manifestation of weak anti-localization and doorway to spintronics

    NASA Astrophysics Data System (ADS)

    Roy, Rajarshi; Thapa, Ranjit; Kumar, Gundam Sandeep; Mazumder, Nilesh; Sen, Dipayan; Sinthika, S.; Das, Nirmalya S.; Chattopadhyay, Kalyan K.

    2016-04-01

    In this work, we have demonstrated the signatures of localized surface distortions and disorders in functionalized graphene quantum dots (fGQD) and consequences in magneto-transport under weak field regime (~1 Tesla) at room temperature. Observed positive colossal magnetoresistance (MR) and its suppression is primarily explained by weak anti-localization phenomenon where competitive valley (inter and intra) dependent scattering takes place at room temperature under low magnetic field; analogous to low mobility disordered graphene samples. Furthermore, using ab-initio analysis we show that sub-lattice sensitive spin-polarized ground state exists in the GQD as a result of pz orbital asymmetry in GQD carbon atoms with amino functional groups. This spin polarized ground state is believed to help the weak anti-localization dependent magneto transport by generating more disorder and strain in a GQD lattice under applied magnetic field and lays the premise for future graphene quantum dot based spintronic applications.In this work, we have demonstrated the signatures of localized surface distortions and disorders in functionalized graphene quantum dots (fGQD) and consequences in magneto-transport under weak field regime (~1 Tesla) at room temperature. Observed positive colossal magnetoresistance (MR) and its suppression is primarily explained by weak anti-localization phenomenon where competitive valley (inter and intra) dependent scattering takes place at room temperature under low magnetic field; analogous to low mobility disordered graphene samples. Furthermore, using ab-initio analysis we show that sub-lattice sensitive spin-polarized ground state exists in the GQD as a result of pz orbital asymmetry in GQD carbon atoms with amino functional groups. This spin polarized ground state is believed to help the weak anti-localization dependent magneto transport by generating more disorder and strain in a GQD lattice under applied magnetic field and lays the premise for

  11. Two-phase mixed media dielectric with macro dielectric beads for enhancing resistivity and breakdown strength

    DOEpatents

    Falabella, Steven; Meyer, Glenn A; Tang, Vincent; Guethlein, Gary

    2014-06-10

    A two-phase mixed media insulator having a dielectric fluid filling the interstices between macro-sized dielectric beads packed into a confined volume, so that the packed dielectric beads inhibit electro-hydrodynamically driven current flows of the dielectric liquid and thereby increase the resistivity and breakdown strength of the two-phase insulator over the dielectric liquid alone. In addition, an electrical apparatus incorporates the two-phase mixed media insulator to insulate between electrical components of different electrical potentials. And a method of electrically insulating between electrical components of different electrical potentials fills a confined volume between the electrical components with the two-phase dielectric composite, so that the macro dielectric beads are packed in the confined volume and interstices formed between the macro dielectric beads are filled with the dielectric liquid.

  12. Colossal thermoelectric power in charge ordered lanthanum calcium manganites (La0.5Ca0.5MnO3)

    NASA Astrophysics Data System (ADS)

    Joy, Lija K.; Shanmukharao Samatham, S.; Thomas, Senoy; Ganesan, V.; Al-Harthi, Salim; Liebig, A.; Albrecht, M.; Anantharaman, M. R.

    2014-12-01

    Lanthanum calcium manganites (La0.5Ca0.5MnO3) with a composition close to charge ordering, synthesized by high energy ball milling, was found to exhibit colossal thermoelectric power. Thermoelectric power (TEP) data was systematically analyzed by dividing the entire temperature range (5 K-300 K) into three different regimes to explore different scattering mechanisms involved. Mandal's model has been applied to explain TEP data in the region below the Curie temperature (TC). It has been found that the variation of thermoelectric power with temperature is pronounced when the system enters the charge ordered region at T < 200 K. For temperatures lower than 120 K, due to the co-existence of charge ordered state with a spin-glass state, the variation of thermoelectric power is maximum and exhibited a peak value of -80 mV/K at 58 K. This has been explained by incorporating Kondo properties of the spin-glass along with magnon scattering. FC-ZFC magnetization measurements indicate the existence of a glassy state in the region corresponding to a maximum value of thermoelectric power. Phonon drag contribution instead of spin-glass contribution is taken into account to explain TEP in the region 120 K < T < TC. Mott's polaronic contribution of charge carriers are considered to interpret TEP in the high temperature region (T > TC). The optimal Mn4+-Mn3+ concentration in charge ordered La0.5Ca0.5MnO3 was examined by X-ray Photoelectron Spectroscopy analysis which confirms the charge ordered nature of this compound.

  13. Temperature dependent evolution of the electronic and local atomic structure in the cubic colossal magnetoresistive manganite La1-xSrxMnO3

    SciTech Connect

    Arenholz, Elke; Mannella, N.; Booth, C.H.; Rosenhahn, A.; Sell, B.C.; Nambu, A.; Marchesini, S.; Mun, B. S.; Yang, S.-H.; Watanabe, M.; Ibrahim, K.; Arenholz, E.; Young, A.; Guo, J.; Tomioka, Y.; Fadley, C.S.

    2007-12-06

    We have studied the temperature-dependent evolution of the electronic and local atomic structure in the cubic colossal magnetoresistive manganite La{sub 1-x}Sr{sub x}MnO{sub 3} (x= 0.3-0.4) with core and valence level photoemission (PE), x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES), resonant inelastic x-ray scattering (RIXS), extended x-ray absorption fine structure (EXAFS) spectroscopy and magnetometry. As the temperature is varied across the Curie temperature T{sub c}, our PE experiments reveal a dramatic change of the electronic structure involving an increase in the Mn spin moment from {approx} 3 {micro}B to {approx} 4 {micro}B, and a modification of the local chemical environment of the other constituent atoms indicative of electron localization on the Mn atom. These effects are reversible and exhibit a slow-timescale {approx}200 K-wide hysteresis centered at T{sub c}. Based upon the probing depths accessed in our PE measurements, these effects seem to survive for at least 35-50 {angstrom} inward from the surface, while other consistent signatures for this modification of the electronic structure are revealed by more bulk sensitive spectroscopies like XAS and XES/RIXS. We interpret these effects as spectroscopic fingerprints for polaron formation, consistent with the presence of local Jahn-Teller distortions of the MnO{sub 6} octahedra around the Mn atom, as revealed by the EXAFS data. Magnetic susceptibility measurements in addition show typical signatures of ferro-magnetic clusters formation well above the Curie temperature.

  14. Colossal thermoelectric power in charge ordered lanthanum calcium manganites (La{sub 0.5}Ca{sub 0.5}MnO{sub 3})

    SciTech Connect

    Joy, Lija K.; Anantharaman, M. R.; Shanmukharao Samatham, S.; Ganesan, V.; Thomas, Senoy; Al-Harthi, Salim; Liebig, A.; Albrecht, M.

    2014-12-07

    Lanthanum calcium manganites (La{sub 0.5}Ca{sub 0.5}MnO{sub 3}) with a composition close to charge ordering, synthesized by high energy ball milling, was found to exhibit colossal thermoelectric power. Thermoelectric power (TEP) data was systematically analyzed by dividing the entire temperature range (5 K–300 K) into three different regimes to explore different scattering mechanisms involved. Mandal's model has been applied to explain TEP data in the region below the Curie temperature (T{sub C}). It has been found that the variation of thermoelectric power with temperature is pronounced when the system enters the charge ordered region at T < 200 K. For temperatures lower than 120 K, due to the co-existence of charge ordered state with a spin-glass state, the variation of thermoelectric power is maximum and exhibited a peak value of −80 mV/K at 58 K. This has been explained by incorporating Kondo properties of the spin-glass along with magnon scattering. FC-ZFC magnetization measurements indicate the existence of a glassy state in the region corresponding to a maximum value of thermoelectric power. Phonon drag contribution instead of spin-glass contribution is taken into account to explain TEP in the region 120 K < T < T{sub C}. Mott's polaronic contribution of charge carriers are considered to interpret TEP in the high temperature region (T > T{sub C}). The optimal Mn{sup 4+}-Mn{sup 3+} concentration in charge ordered La{sub 0.5}Ca{sub 0.5}MnO{sub 3} was examined by X-ray Photoelectron Spectroscopy analysis which confirms the charge ordered nature of this compound.

  15. Tailoring dielectric properties of ferroelectric-dielectric multilayers

    SciTech Connect

    Kesim, M. T.; Zhang, J.; Cole, M. W.; Misirlioglu, I. B.

    2014-01-13

    We develop a nonlinear thermodynamic model for multilayer ferroelectric heterostructures that takes into account electrostatic and electromechanical interactions between layers. We concentrate on the effect of relative layer fractions and in-plane thermal stresses on dielectric properties of Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3}-, BaTiO{sub 3}-, and PbZr{sub 0.2}Ti{sub 0.8}O{sub 3} (PZT)-SrTiO{sub 3} (STO) multilayers on Si and c-sapphire. We show that dielectric properties of such multilayers can be significantly enhanced by tailoring the growth/processing temperature and the STO layer fraction. Our computations show that large tunabilities (∼90% at 400 kV/cm) are possible in carefully designed barium strontium titanate-STO and PZT-STO even on Si for which there exist substantially large in-plane strains.

  16. Abnormal percolative transport and colossal electroresistance induced by anisotropic strain in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/PMN-PT heterostructure

    PubMed Central

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Zhang, Hong-Rui; Liu, Yao; Zhang, Ying; Wang, Shuan-Hu; Wu, Rong-Rong; Zhang, Ming; Bao, Li-Fu; Sun, Ji-Rong; Shen, Bao-Gen

    2014-01-01

    Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5 K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems. PMID:25399635

  17. Total absorption in ultra-thin lossy layer on transparent substrate using dielectric resonance structure

    NASA Astrophysics Data System (ADS)

    Matsui, T.; Iizuka, H.

    2017-03-01

    A resonant sub-wavelength structure made of a high-refractive-index dielectric material exhibits a resonator-like response and provides unity reflection. We show that near-unity absorption is obtained by using a sub-wavelength resonant structure, which consists of periodic high-refractive-index nano-blocks, when an ultra-thin absorption layer is attached to a transparent dielectric substrate. The resonant structure does not necessarily touch the absorption layer and, therefore, a coating film can be inserted between the absorption layer and the periodic structure. Our results significantly extend application scenarios of detectors and optoelectronic devices that can be implemented on transparent dielectric substrates.

  18. Terahertz carrier dynamics and dielectric properties of GaN epilayers with different carrier concentrations

    NASA Astrophysics Data System (ADS)

    Guo, H. C.; Zhang, X. H.; Liu, W.; Yong, A. M.; Tang, S. H.

    2009-09-01

    Using terahertz time-domain spectroscopy, we measured the complex conductivity and dielectric function of n-type GaN with various carrier concentrations on sapphire substrate. The measured complex conductivity, which is due to the free carriers, is well fitted by simple Drude model. The contribution from the lattice vibration to the complex dielectric function increases with the decrease in free carrier concentration. A better fitting of the frequency-dependent complex dielectric response was obtained by considering both of the Drude and the classical damped oscillator model.

  19. Dielectric relaxation and charged domain walls in (K,Na)NbO3-based ferroelectric ceramics

    NASA Astrophysics Data System (ADS)

    Esin, A. A.; Alikin, D. O.; Turygin, A. P.; Abramov, A. S.; Hreščak, J.; Walker, J.; Rojac, T.; Bencan, A.; Malic, B.; Kholkin, A. L.; Shur, V. Ya.

    2017-02-01

    The influence of domain walls on the macroscopic properties of ferroelectric materials is a well known phenomenon. Commonly, such "extrinsic" contributions to dielectric permittivity are discussed in terms of domain wall displacements under external electric field. In this work, we report on a possible contribution of charged domain walls to low frequency (10-106 Hz) dielectric permittivity in K1-xNaxNbO3 ferroelectric ceramics. It is shown that the effective dielectric response increases with increasing domain wall density. The effect has been attributed to the Maxwell-Wagner-Sillars relaxation. The obtained results may open up possibilities for domain wall engineering in various ferroelectric materials.

  20. Dielectric properties modelling of cellular structures with PDMS for micro-sensor applications

    NASA Astrophysics Data System (ADS)

    Kachroudi, Achraf; Basrour, Skandar; Rufer, Libor; Sylvestre, Alain; Jomni, Fathi

    2015-12-01

    Electro-active polymers are emerging in the fields of actuators and micro-sensors because their good dielectric and mechanical properties makes them suitable for such applications. In this work, we focus on micro-structured (cellular) polymer materials (referred as piezoelectrets or ferroelectrets) that need prior charging to attain piezoelectric behaviour. The development of such applications requires an in-depth knowledge of the intrinsic dielectric properties of such structures and models to enable the accurate prediction of a given micro-structured material’s dielectric properties. Various polymers including polypropylene, polytetrafluoroethylene, fluoroethylenepropylene, cyclo-olefines and poly(ethylene terephthalate) in a cellular form have been studied by researchers over the last fifteen years. However, there is still a lack of information on the intrinsic dielectric properties of the most recently used dielectric polymer (polydimethylsiloxane, PDMS) over wide frequency and temperature ranges. In this work, we shall propose an exhaustive equivalent electrical circuit model and explain how it can be used to predict the micro-structured PDMS complex permittivity versus frequency and temperature. The results obtained from the model were found to be in good agreement with experimental data for various micro-structured PDMS materials. Typically, for micro-sensor applications, the dielectric constant and dielectric losses are key factors which need to be minimized. We have developed a configuration which enables both to be strongly reduced with a reduction of 16% in the dielectric constant of a micro-structured PDMS compared with the bulk material. In addition, the phenomena responsible for dielectric losses variations with frequency and temperature are discussed and correlated with the theoretical model. Our model is thus proved to be a powerful tool for the control of the dielectric properties of micro-structured PDMS material for micro-sensor applications.

  1. Vibron and phonon hybridization in dielectric nanostructures.

    PubMed

    Preston, Thomas C; Signorell, Ruth

    2011-04-05

    Plasmon hybridization theory has been an invaluable tool in advancing our understanding of the optical properties of metallic nanostructures. Through the prism of molecular orbital theory, it allows one to interpret complex structures as "plasmonic molecules" and easily predict and engineer their electromagnetic response. However, this formalism is limited to conducting particles. Here, we present a hybridization scheme for the external and internal vibrations of dielectric nanostructures that provides a straightforward understanding of the infrared signatures of these particles through analogy to existing hybridization models of both molecular orbitals and plasmons extending the range of applications far beyond metallic nanostructures. This method not only provides a qualitative understanding, but also allows for the quantitative prediction of vibrational spectra of complex nanoobjects from well-known spectra of their primitive building blocks. The examples of nanoshells illustrate how spectral features can be understood in terms of symmetry, number of nodal planes, and scale parameters.

  2. Haptic interfaces using dielectric electroactive polymers

    NASA Astrophysics Data System (ADS)

    Ozsecen, Muzaffer Y.; Sivak, Mark; Mavroidis, Constantinos

    2010-04-01

    Quality, amplitude and frequency of the interaction forces between a human and an actuator are essential traits for haptic applications. A variety of Electro-Active Polymer (EAP) based actuators can provide these characteristics simultaneously with quiet operation, low weight, high power density and fast response. This paper demonstrates a rolled Dielectric Elastomer Actuator (DEA) being used as a telepresence device in a heart beat measurement application. In the this testing, heart signals were acquired from a remote location using a wireless heart rate sensor, sent through a network and DEA was used to haptically reproduce the heart beats at the medical expert's location. A series of preliminary human subject tests were conducted that demonstrated that a) DE based haptic feeling can be used in heart beat measurement tests and b) through subjective testing the stiffness and actuator properties of the EAP can be tuned for a variety of applications.

  3. Tunable electromechanical actuation in silicone dielectric film

    NASA Astrophysics Data System (ADS)

    Lamberti, Andrea; Di Donato, Marco; Chiappone, Annalisa; Giorgis, Fabrizio; Canavese, Giancarlo

    2014-10-01

    Dielectric elastomer actuator films were fabricated on transparent conductive electrode using bi-component poly(dimethyl)siloxane (PDMS). PDMS is a well-known material in microfluidics and soft lithography for biomedical applications, being easy to process, low cost, biocompatible and transparent. Moreover its mechanical properties can be easily tuned by varying the mixing ratio between the oligomer base and the crosslinking agent. In this work we investigate the chemical composition and the electromechanical properties of PDMS thin film verifying for the first time the tuneable actuation response by simply modifying the amount of the curing agent. We demonstrate that, for a 20:1 ratio of base:crosslinker mixture, a striking 150% enhancement of Maxwell strain occurs at 1 Hz actuating frequency.

  4. Acoustic transducer based on dielectric elastomers

    NASA Astrophysics Data System (ADS)

    Graf, Christian; Maas, Jügen

    2012-04-01

    Dielectric electroactive polymers are thin films based on elastomeric material coated with compliant and conductive electrodes. By applying an electrical field, the polymer performs large deformations, which can be utilized to generate sound waves. When using such kind of electrostatic loudspeakers, no additional resonating sound boxes are required and the vibrating mass is very lightweight, resulting in an excellent impulse and wide-band frequency response. For the loudspeaker's operation both an electrical bias voltage and a mechanical bias stress have to be applied. In this contribution different possibilities are presented to generate the mechanical bias stress. The design of an appropriate power electronics for the acoustic transducer, which is build of standard components, is also described. Finally, the loudspeaker concepts are evaluated by experiments in an anechoic room.

  5. Dielectric decrement of electrolyte solutions

    NASA Astrophysics Data System (ADS)

    Felderhof, B. U.

    We calculate the dielectric decrement of ionic solutions in a continuum model. We show that apart from a familiar static contribution there are three kinetic contributions to the effect, two of which are related by a symmetry relation. The third contribution is due to frequency dispersion of the friction coefficient and for small ions reduces the total effect considerably. We find that the total effect as calculated from the continuum model is too small to account for the experimental data.

  6. 'Photonic jets' from dielectric microaxicons

    SciTech Connect

    Geints, Yu E; Zemlyanov, A A; Panina, E K

    2015-08-31

    We consider a specific spatially localised light structure, namely, a 'photonic jet' formed in the near field upon scattering of an optical wave in a dielectric micron particle. Dimensional parameters and intensity of a photonic jet from microaxicons of different spatial orientation are studied theoretically. It is found for the first time that an axicon-generated photonic jet has in this case a substantially larger length compared with the case of a jet formed on a spherical particle. (scattering of light)

  7. Techniques for Microwave Dielectric Measurements.

    DTIC Science & Technology

    1986-03-01

    the complex dielectric constant. The theory is developed on the premise that the electromagnetic (EM) fields are unchanged in form and only slightly...values of these shifts, the validity of the theory can come into doubt. It is also true that as the sample is made smaller, the tolerances on the accuracy...Complex Permittivity in Re- entrant Cavity: Part A - Theoretical Analysis of the Method," Microwave Theory Tech., Vol. MTT-28 (1980), pp. 225-28

  8. Asymmetric Dielectric Elastomer Composite Material

    NASA Technical Reports Server (NTRS)

    Stewart, Brian K. (Inventor)

    2014-01-01

    Embodiments of the invention provide a dielectric elastomer composite material comprising a plurality of elastomer-coated electrodes arranged in an assembly. Embodiments of the invention provide improved force output over prior DEs by producing thinner spacing between electrode surfaces. This is accomplished by coating electrodes directly with uncured elastomer in liquid form and then assembling a finished component (which may be termed an actuator) from coated electrode components.

  9. Complex Amorphous Dielectrics

    SciTech Connect

    van Dover, Robert Bruce

    2014-11-22

    This work focused on synthesizing a wide range of oxides containing two or more metals, and measuring their properties. Many simple metal oxides such as zirconium oxide, have been extensively studied in the past. We developed a technique in which we create a large number of compositions simultaneously and examine their behavior to understand trends and identify high performance materials. Superior performance generally comes in the form of increased responsiveness; in the materials we have studied this may mean more electrical charge for a given voltage in a capacitor, faster switching for a given drive in a transistor, more current for a given voltage in an ionic conductor, or more current for a given illumination in a solar cell. Some of the materials we have identified may find use in decreasing the power needed to operate integrated circuits, other materials could be useful for solar power or other forms of energy conversion.

  10. Dielectric and Electromechanical Properties of Polyurethane and Polydimethylsiloxane Blends and their Nanocomposites

    NASA Astrophysics Data System (ADS)

    Cakmak, Enes

    Conventional means of converting electrical energy to mechanical work are generally considered too noisy and bulky for many contemporary technologies such as microrobotic, microfluidic, and haptic devices. Dielectric electroactive polymers (D-EAPs) constitude a growing class of electroactive polymers (EAP) that are capable of producing mechanica work induced by an applied electric field. D-EAPs are considered remarkably efficient and well suited for a wide range of applications, including ocean-wave energy harvesters and prosthetic devices. However, the real-world application of D-EAPs is very limited due to a number of factors, one of which is the difficulty of producing high actuation strains at acceptably low electric fields. D-EAPs are elastomeric polymers and produce large strain response induced by external electric field. The electromechanical properties of D-EAPs depend on the dielectric properties and mechanical properties of the D-EAP. In terms of dielectric behavior, these actuators require a high dielectric constant, low dielectric loss, and high dielectric strength to produce an improved actuation response. In addition to their dielectric properties, the mechanical properties of D-EAPs, such as elastic moduli and hysteresis, are also of importance. Therefore, material properties are a key feature of D-EAP technology. DE actuator materials reported in the literature cover many types of elastomers and their composites formed with dielectric fillers. Along with polymeric matrix materials, various ceramic, metal, and organic fillers have been employed in enhancing dielectric behavior of DEs. This work describes an effort to characterize elastomer blends and composites of different matrix and dielectric polymer fillers according to their dielectric, mechanical, and electromechanical responses. This dissertation focuses on the development and characterization of polymer-polymer blends and composites from a high-k polyurethane (PU) and polydimethylsiloxane

  11. Microwave dielectric spectrum of rocks

    NASA Technical Reports Server (NTRS)

    Ulaby, F. T.; Bengal, T.; East, J.; Dobson, M. C.; Garvin, J.; Evans, D.

    1988-01-01

    A combination of several measurement techniques was used to investigate the dielectric properties of 80 rock samples in the microwave region. The real part of the dielectric constant, epsilon', was measured in 0.1 GHz steps from 0.5 to 18 GHz, and the imaginary part, epsilon'', was measured at five frequencies extending between 1.6 and 16 GHz. In addition to the dielectric measurements, the bulk density was measured for all the samples and the bulk chemical composition was determined for 56 of the samples. The study shows that epsilon' is frequency-dependent over the 0.5 to 18 GHz range for all rock samples, and that the bulk density rho accounts for about 50 percent of the observed variance of epsilon'. For individual rock types (by genesis), about 90 percent of the observed variance may be explained by the combination of density and the fractional contents of SiO2, Fe2O3, MgO, and TiO2. For the loss factor epsilon'', it was not possible to establish statistically significant relationships between it and the measured properties of the rock samples (density and chemical composition).

  12. Scattering from thin dielectric disks

    NASA Technical Reports Server (NTRS)

    Le Vine, D. M.; Schneider, A.; Lang, R. H.; Carter, H. G.

    1985-01-01

    A solution was obtained for scattering from thin dielectric disks by approximating the currents induced inside the disk with the currents which would exist inside a dielectric slab of the same thickness, orientation and dielectic properties. This approximation reduces to an electrostatic approximation when the disk thickness, T, is small compared to the wavelength of the incident radiation and the approximation yields a conventional physical optics solution when the dimension, A, characteristic of the geometrical cross section of the disk (e.g., the diameter of a circular disk) is large compared to wavelength. When the ratio A/T sufficiently large the disk will always be in one or the other of these regimes, T lambda or kA1. Consequently, when A/T is large this solution provides a conventional approximation for the scattered fields which can be applied at all frequencies. As a check on this conclusion, a comparison was made between the theoretical and measured radar cross section of thin dielectric disks. Agreement was found for thin disks with both large and small values of kA.

  13. Multipolar Coupling in Hybrid Metal–Dielectric Metasurfaces

    DOE PAGES

    Guo, Rui; Rusak, Evgenia; Staude, Isabelle; ...

    2016-03-02

    In this paper, we study functional hybrid metasurfaces consisting of metal–dielectric nanoantennas that direct light from an incident plane wave or from localized light sources into a preferential direction. The directionality is obtained by carefully balancing the multipolar contributions to the scattering response from the constituents of the metasurface. The hybrid nanoantennas are composed of a plasmonic gold nanorod acting as a feed element and a silicon nanodisk acting as a director element. In order to experimentally realize this design, we have developed a two-step electron-beam lithography process in combination with a precision alignment step. Finally, the optical response ofmore » the fabricated sample is measured and reveals distinct signatures of coupling between the plasmonic and the dielectric nanoantenna elements that ultimately leads to unidirectional radiation of light.« less

  14. Multipolar Coupling in Hybrid Metal–Dielectric Metasurfaces

    SciTech Connect

    Guo, Rui; Rusak, Evgenia; Staude, Isabelle; Dominguez, Jason; Decker, Manuel; Rockstuhl, Carsten; Brener, Igal; Neshev, Dragomir N.; Kivshar, Yuri S.

    2016-03-02

    In this paper, we study functional hybrid metasurfaces consisting of metal–dielectric nanoantennas that direct light from an incident plane wave or from localized light sources into a preferential direction. The directionality is obtained by carefully balancing the multipolar contributions to the scattering response from the constituents of the metasurface. The hybrid nanoantennas are composed of a plasmonic gold nanorod acting as a feed element and a silicon nanodisk acting as a director element. In order to experimentally realize this design, we have developed a two-step electron-beam lithography process in combination with a precision alignment step. Finally, the optical response of the fabricated sample is measured and reveals distinct signatures of coupling between the plasmonic and the dielectric nanoantenna elements that ultimately leads to unidirectional radiation of light.

  15. Dielectric properties of conductive ionomers

    NASA Astrophysics Data System (ADS)

    Klein, Robert James

    Ion and polymer dynamics of ion-containing polymers were investigated, with the majority of results obtained from application of a physical model of electrode polarization (EP) to dielectric spectroscopy data. The physical model of MacDonald, further developed by Coelho, was extended for application to tan delta (the ratio of dielectric loss to dielectric constant) as a function of frequency. The validity of this approach was confirmed by plotting the characteristic EP time as a function of thickness and comparing the actual and predicted unrelaxed dielectric constant for a poly(ethylene oxide) (PEO)-based ionomer neutralized by lithium, sodium, and cesium. Results were obtained for ion mobility and mobile ion concentration for a neat PEO-based ionomer, two (methoxyethoxy-ethoxy phosphazene) (MEEP) -based ionomers, two MEEP-based salt-doped polymers, sulfonated polystyrene (SPS) neutralized by sodium with a high sulfonation fraction, and SPS neutralized by zinc with a low sulfonation fraction. Additionally, the conductivity parameters of six plasticized forms of a neat PEO-based ionomer were characterized, but the method apparently failed to correctly evaluate bulk ionic behavior. In all cases except the SPS ionomers ion mobility follows a Vogel-Fulcher-Tammann (VFT) temperature dependence. In all cases, mobile ion concentration follows an Arrhenius temperature dependence. Fitting parameters from these two relationships yielded direct information about the state of ionic diffusion and ion pairing in each system. Combination of these two functionalities predicts a relationship for conductivity that is significantly different than the VFT relation typically used in the literature to fit conductivity. The most outstanding result was the extremely small fraction of ions found to be mobile. For ionomers it can be concluded that the primary reason for low conductivities arises from the low fraction of mobile ions. The local and segmental dynamics of the neat and

  16. A high-performance dielectric elastomer consisting of bio-based polyester elastomer and titanium dioxide powder

    NASA Astrophysics Data System (ADS)

    Yang, Dan; Tian, Ming; Dong, Yingchao; Kang, Hailan; Gong, Daolin; Zhang, Liqun

    2013-10-01

    A bio-based polyester elastomer containing many polar groups was combined with high-dielectric-constant titanium dioxide (TiO2) powder to form a dielectric elastomer composite for the first time. The effects of the titanium dioxide filler on the elastic modulus, dielectric properties, and electromechanical responses of the polyester dielectric elastomer were studied. We found that the dielectric constant of composites increased with increasing content of TiO2. Nevertheless, the elastic modulus of the composites did not increase with increasing content of TiO2, and the polyester elastomer filled with 6 vol. % of TiO2 exhibited the lowest elastic modulus, which led to a high prestrain-free actuated strain of 11.8% at a low electric field of just 9.8 kV/mm. The actuated strain is better than other dielectric elastomers reported in the literature. The high electromechanical performance was attributed to the increase in dielectric constant and decrease in elastic modulus of the composite from those of the pure polyester elastomer. The decrease in elastic modulus was explained in detail by the competing effects of crosslink density and filler network. In addition, a dramatic increase in dielectric constant of the composite was observed and discussed through several dielectric mixing rules. Finally, the polyester elastomer and titanium dioxide are both environment-friendly, making possible the composite to be used in biological and medical devices.

  17. A self-healing dielectric elastomer actuator

    NASA Astrophysics Data System (ADS)

    Hunt, Stacy; McKay, Thomas G.; Anderson, Iain A.

    2014-03-01

    Dielectric elastomer actuators that can provide muscle-like actuation are unable to self-heal like real muscle tissue. This severely limits dielectric elastomer reliability and robustness. This paper describes a way to instill self-healing into the DE by using a two-phase dielectric consisting of an open-cell silicone sponge saturated with silicone oil. When the dielectric is breached, the oil is able to flow back into any void, re-establishing the dielectric structure. The sponge holds the oil in place and provides dimensional stability, while the oil ensures the integrity of the dielectric layer. The operation of this has been demonstrated in a prototype DE actuator that continued to function despite being perforated multiple times with a sharp object.

  18. Dielectric relaxation of high-k oxides

    PubMed Central

    2013-01-01

    Frequency dispersion of high-k dielectrics was observed and classified into two parts: extrinsic cause and intrinsic cause. Frequency dependence of dielectric constant (dielectric relaxation), that is the intrinsic frequency dispersion, could not be characterized before considering the effects of extrinsic frequency dispersion. Several mathematical models were discussed to describe the dielectric relaxation of high-k dielectrics. For the physical mechanism, dielectric relaxation was found to be related to the degree of polarization, which depended on the structure of the high-k material. It was attributed to the enhancement of the correlations among polar nanodomain. The effect of grain size for the high-k materials' structure mainly originated from higher surface stress in smaller grain due to its higher concentration of grain boundary. PMID:24180696

  19. Decomposition of the total momentum in a linear dielectric into field and matter components

    SciTech Connect

    Crenshaw, Michael E.

    2013-11-15

    The long-standing resolution of the Abraham–Minkowski electromagnetic momentum controversy is predicated on a decomposition of the total momentum of a closed continuum electrodynamic system into separate field and matter components. Using a microscopic model of a simple linear dielectric, we derive Lagrangian equations of motion for the electric dipoles and show that the dielectric can be treated as a collection of stationary simple harmonic oscillators that are driven by the electric field and produce a polarization field in response. The macroscopic energy and momentum are defined in terms of the electric, magnetic, and polarization fields that travel through the dielectric together as a pulse of electromagnetic radiation. We conclude that both the macroscopic total energy and the macroscopic total momentum are entirely electromagnetic in nature for a simple linear dielectric in the absence of significant reflections. -- Highlights: •The total momentum in a dielectric is identified by conservation principles. •The total momentum in a dielectric cannot be decomposed into field and matter parts. •A component of momentum in a dielectric is due to motion of the polarization field.

  20. Dielectric relaxation, resonance and scaling behaviors in Sr3Co2Fe24O41 hexaferrite

    NASA Astrophysics Data System (ADS)

    Tang, Rujun; Jiang, Chen; Qian, Wenhu; Jian, Jie; Zhang, Xin; Wang, Haiyan; Yang, Hao

    2015-08-01

    The dielectric properties of Z-type hexaferrite Sr3Co2Fe24O41 (SCFO) have been investigated as a function of temperature from 153 to 503 K between 1 and 2 GHz. The dielectric responses of SCFO are found to be frequency dependent and thermally activated. The relaxation-type dielectric behavior is observed to be dominating in the low frequency region and resonance-type dielectric behavior is found to be dominating above 108 Hz. This frequency dependence of dielectric behavior is explained by the damped harmonic oscillator model with temperature dependent coefficients. The imaginary part of impedance (Z″) and modulus (M″) spectra show that there is a distribution of relaxation times. The scaling behaviors of Z″ and M″ spectra further suggest that the distribution of relaxation times is temperature independent at low frequencies. The dielectric loss spectra at different temperatures have not shown a scaling behavior above 108 Hz. A comparison between the Z″ and the M″ spectra indicates that the short-range charges motion dominates at low temperatures and the long-range charges motion dominates at high temperatures. The above results indicate that the dielectric dispersion mechanism in SCFO is temperature independent at low frequencies and temperature dependent at high frequencies due to the domination of resonance behavior.

  1. Dielectric relaxation, resonance and scaling behaviors in Sr3Co2Fe24O41 hexaferrite.

    PubMed

    Tang, Rujun; Jiang, Chen; Qian, Wenhu; Jian, Jie; Zhang, Xin; Wang, Haiyan; Yang, Hao

    2015-08-28

    The dielectric properties of Z-type hexaferrite Sr3Co2Fe24O41 (SCFO) have been investigated as a function of temperature from 153 to 503 K between 1 and 2 GHz. The dielectric responses of SCFO are found to be frequency dependent and thermally activated. The relaxation-type dielectric behavior is observed to be dominating in the low frequency region and resonance-type dielectric behavior is found to be dominating above 10(8) Hz. This frequency dependence of dielectric behavior is explained by the damped harmonic oscillator model with temperature dependent coefficients. The imaginary part of impedance (Z″) and modulus (M″) spectra show that there is a distribution of relaxation times. The scaling behaviors of Z″ and M″ spectra further suggest that the distribution of relaxation times is temperature independent at low frequencies. The dielectric loss spectra at different temperatures have not shown a scaling behavior above 10(8) Hz. A comparison between the Z″ and the M″ spectra indicates that the short-range charges motion dominates at low temperatures and the long-range charges motion dominates at high temperatures. The above results indicate that the dielectric dispersion mechanism in SCFO is temperature independent at low frequencies and temperature dependent at high frequencies due to the domination of resonance behavior.

  2. Electrical conductivity and dielectric studies of MnO2 doped V2O5

    NASA Astrophysics Data System (ADS)

    Tan, Foo Khoon; Hassan, Jumiah; Wahab, Zaidan Abd.; Azis, Raba'ah Syahidah

    The investigation on electrical conductivity and dielectric properties of mixed oxide of manganese (Mn) and vanadium (V) was carried out to study the mixed oxides response to different frequencies and different measuring temperatures. The frequency and temperature dependence of AC conductivity, dielectric constant and dielectric loss factor of mixed oxides were studied in the frequency range of 40 Hz-1 MHz and a temperature range of 30-250 °C. Since the mixed oxides are multi phase materials, hence the properties of the pure oxides are also presented in this study to discuss the multi phase behaviour of the mixed oxides. The XRD pattern shows the Mn-V oxide is multiphase and quantitative phase analysis was performed to determine the relative phases. The overall results indicate that with increasing temperature, the AC conductivity, dielectric constant, dielectric loss factor and loss tangent of the Mn-V mixed oxide increases. However, it shows an overlap in the dielectric constant at 225 °C and 250 °C due to the V2O5 phase in the mixed oxide. From the AC activation energy, the mixed oxides underwent conduction mechanism transition from band to hopping in the investigated frequency range. The MnV2O6 has relatively good resistivity, therefore the mixed oxide sintered at 550 °C with the highest composition of MnV2O6 gives the highest dielectric constant of 9845 at 1 kHz, and at 250 °C.

  3. Dielectric relaxation, resonance and scaling behaviors in Sr3Co2Fe24O41 hexaferrite

    PubMed Central

    Tang, Rujun; Jiang, Chen; Qian, Wenhu; Jian, Jie; Zhang, Xin; Wang, Haiyan; Yang, Hao

    2015-01-01

    The dielectric properties of Z-type hexaferrite Sr3Co2Fe24O41 (SCFO) have been investigated as a function of temperature from 153 to 503 K between 1 and 2 GHz. The dielectric responses of SCFO are found to be frequency dependent and thermally activated. The relaxation-type dielectric behavior is observed to be dominating in the low frequency region and resonance-type dielectric behavior is found to be dominating above 108 Hz. This frequency dependence of dielectric behavior is explained by the damped harmonic oscillator model with temperature dependent coefficients. The imaginary part of impedance (Z″) and modulus (M″) spectra show that there is a distribution of relaxation times. The scaling behaviors of Z″ and M″ spectra further suggest that the distribution of relaxation times is temperature independent at low frequencies. The dielectric loss spectra at different temperatures have not shown a scaling behavior above 108 Hz. A comparison between the Z″ and the M″ spectra indicates that the short-range charges motion dominates at low temperatures and the long-range charges motion dominates at high temperatures. The above results indicate that the dielectric dispersion mechanism in SCFO is temperature independent at low frequencies and temperature dependent at high frequencies due to the domination of resonance behavior. PMID:26314913

  4. Enhanced performance in capacitive force sensors using carbon nanotube/polydimethylsiloxane nanocomposites with high dielectric properties.

    PubMed

    Jang, Hyeyoung; Yoon, Hyungsuk; Ko, Youngpyo; Choi, Jaeyoo; Lee, Sang-Soo; Jeon, Insu; Kim, Jong-Ho; Kim, Heesuk

    2016-03-14

    Force sensors have attracted tremendous attention owing to their applications in various fields such as touch screens, robots, smart scales, and wearable devices. The force sensors reported so far have been mainly focused on high sensitivity based on delicate microstructured materials, resulting in low reproducibility and high fabrication cost that are limitations for wide applications. As an alternative, we demonstrate a novel capacitive-type force sensor with enhanced performance owing to the increased dielectric properties of elastomers and simple sensor structure. We rationally design dielectric elastomers based on alkylamine modified-multi-walled carbon nanotube (MWCNT)/polydimethylsiloxane (PDMS) composites, which have a higher dielectric constant than pure PDMS. The alkylamine-MWCNTs show excellent dispersion in a PDMS matrix, thus leading to enhanced and reliable dielectric properties of the composites. A force sensor array fabricated with alkylamine-MWCNT/PDMS composites presents an enhanced response due to the higher dielectric constant of the composites than that of pure PDMS. This study is the first to report enhanced performance of capacitive force sensors by modulating the dielectric properties of elastomers. We believe that the disclosed strategy to improve the sensor performance by increasing the dielectric properties of elastomers has great potential in the development of capacitive force sensor arrays that respond to various input forces.

  5. Synthesis, dielectric behavior and impedance measurement studies of Cr-substituted Zn-Mn ferrites

    SciTech Connect

    Hankare, P.P.; Patil, R.P.; Garadkar, K.M.; Sasikala, R.; Chougule, B.K.

    2011-03-15

    Graphical abstract: Variation of dielectric constant with frequency. Research highlights: {yields} Sol-gel route synthesized spherical crystalline nanoparticles of ZnMn{sub 1-x}Cr{sub x}FeO{sub 4}. {yields} XRD, DTA, FTIR, SEM, dielectric and impedance study. {yields} The ferrites show concentration dependence of ac electrical conductivity. {yields} Impedance response is dominated by grain boundary behavior. -- Abstract: Nanocrystalline ZnMn{sub 1-x}Cr{sub x}FeO{sub 4} (1.0 {>=} x {>=} 0) ferrites were synthesized by sol-gel technique. X-ray diffraction (XRD) confirmed the formation of single phasic cubic spinel lattice for all the compositions studied. Lattice parameter shows a decreasing trend with an increase in Cr content in the compositions. Formation of spherical nanoparticles was revealed by scanning electron microscopy (SEM) analysis. Infrared spectroscopic studies revealed two main absorption bands in the range 400-800 cm{sup -1} arising due to tetrahedral (A) and octahedral (B) site vibrations. Dielectric constant, dielectric loss tangent, ac conductivity and complex impedance were measured as a function of frequency in the range 20 Hz to 1 MHz. Frequency dependence of dielectric constant shows dielectric dispersion due to the Maxwell-Wagner type of interfacial polarization. The role of chromium in modifying structural and dielectric properties of these ferrites has been explained.

  6. Exploring Strategies for High Dielectric Constant and Low Loss Polymer Dielectrics

    NASA Astrophysics Data System (ADS)

    Zhu, Lei

    Polymer dielectrics having high dielectric constant, high temperature capability, and low loss are attractive for a broad range of applications such as film capacitors, gate dielectrics, artificial muscles, and electrocaloric cooling. Unfortunately, it is generally observed that higher polarization or dielectric constant tends to cause significantly enhanced dielectric loss. It is therefore highly desired that the fundamental physics of all types of polarization and loss mechanisms be thoroughly understood for dielectric polymers. In this presentation, we intend to explore advantages and disadvantages for different types of polarization. Among a number of approaches, dipolar polarization is promising for high dielectric constant and low loss polymer dielectrics, if the dipolar relaxation peak can be pushed to above the gigahertz range. In particular, dipolar glass, paraelectric, and relaxor ferroelectric polymers are discussed for the dipolar polarization approach. This work is supported by NSF Polymers Program (DMR-1402733).

  7. Exploring Strategies for High Dielectric Constant and Low Loss Polymer Dielectrics.

    PubMed

    Zhu, Lei

    2014-11-06

    Polymer dielectrics having high dielectric constant, high temperature capability, and low loss are attractive for a broad range of applications such as film capacitors, gate dielectrics, artificial muscles, and electrocaloric cooling. Unfortunately, it is generally observed that higher polarization or dielectric constant tends to cause significantly enhanced dielectric loss. It is therefore highly desired that the fundamental physics of all types of polarization and loss mechanisms be thoroughly understood for dielectric polymers. In this Perspective, we intend to explore advantages and disadvantages for different types of polarization. Among a number of approaches, dipolar polarization is promising for high dielectric constant and low loss polymer dielectrics, if the dipolar relaxation peak can be pushed to above the gigahertz range. In particular, dipolar glass, paraelectric, and relaxor ferroelectric polymers are discussed for the dipolar polarization approach.

  8. A microwave dielectric resonant oscillatory circuit

    NASA Astrophysics Data System (ADS)

    Sigov, A. S.; Shvartsburg, A. B.

    2016-07-01

    Bias currents in a thin dielectric nonconducting torus are investigated, and the resonant mode of excitation of these currents is established. The similarity of the frequency spectrum of such a dielectric element to the spectra of a classical Thomson oscillatory circuit and a metamaterial with negative permittivity is demonstrated. The resonant frequency of electromagnetic oscillations of the ring dielectric circuit and magnetic and electric fields of such a circuit under resonant excitation are determined.

  9. Dielectric anomalies of both chiral and achiral nematogens near the isotropic to mesogenic phase transition

    NASA Astrophysics Data System (ADS)

    Godfrey, Garrett J.

    The dielectric properties of nematic liquid crystals were studied in both the achiral and chiral limits. For achiral nematics, the literature documents that pretransitional curvature occurs for polar molecules on both sides of the nematic and isotropic phase transition. This curvature is due to anti-parallel dimer formation. However, past models have failed to quantitatively describe pretransitional curvature. Through a generalization of the order parameter, a macroscopic model has been developed to mathematically describe the pretransitional curvature on the isotropic side of the transition. The new model was fitted to dielectric data from the literature. Meaningful parameter estimates were extracted. The dielectric response of chiral nematic systems has not been well studied in the literature. A system with tunable chirality was dielectrically studied by mixing two highly chiral liquid crystals: cholesteryl oleyl carbonate (left handed) and cholesteryl chloride (right handed). An apparatus was designed and built to systematically measure the dielectric response of the mixtures. Optical cross-polarized microscopy was used to identify the transition temperatures of each phase. The transition temperatures were then correlated with the dielectric response. The initial intentions of studying chiral systems was two-fold: to see how chirality played a role in the pretransitional curvature, and to see if the blue phases were dielectrically distinguishable. While the initial intentions were null and indecisive, respectively, interesting results were obtained. First, the phase transitions were monotropic for the highest chirality mixtures. Second, the estimated discontinuity at the isotropic to mesogenic transition followed theoretical predictions that had not been tested for dielectric measurements.

  10. Decoherence in Josephson qubits from dielectric loss.

    PubMed

    Martinis, John M; Cooper, K B; McDermott, R; Steffen, Matthias; Ansmann, Markus; Osborn, K D; Cicak, K; Oh, Seongshik; Pappas, D P; Simmonds, R W; Yu, Clare C

    2005-11-18

    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 . 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.

  11. Relaxation processes in non-Debye dielectrics

    NASA Astrophysics Data System (ADS)

    Turik, A. V.; Bogatin, A. S.; Andreev, E. V.

    2011-12-01

    The specific features of the relaxation processes in non-Debye dielectrics have been investigated. The nature of the difference between the relaxation frequencies of the dielectric constant and dielectric loss (conductivity) has been explained. It has been shown that the average relaxation frequency of the conductivity is considerably (in some cases, by several orders of magnitude) higher than the relaxation frequency of the dielectric constant owing to an increase in the conductivity spectra of the statistical weight of the relaxation processes with short relaxation times.

  12. Model dielectric functions and conservation laws

    NASA Astrophysics Data System (ADS)

    Shirley, Eric L.

    2003-03-01

    There continues to be a need for calculating dielectric screening of charges in solids. Most work has been done in the random-phase approximation (RPA) with minor variations, which proves to be quite accurate for many applications. However, this is still a time-consuming and computationally intensive approach, and model dielectric functions can be valuable for this reason. This talk discusses several conservation laws related to dielectric screening and a model dielectric function that obeys such laws. Shortcomings of model functions that are difficult to overcome will be touched on, and a possible means of combining results from RPA and model calculations will be addressed.

  13. Dielectric behaviors of typical benzene monosubstitutes, bromobenzene and benzonitrile.

    PubMed

    Shikata, Toshiyuki; Sugimoto, Natsuki; Sakai, Yuji; Watanabe, Junji

    2012-10-18

    The dielectric behaviors of typical benzene monosubstitutes, bromobenzene (Br-Bz) and benzonitrile (NC-Bz), were investigated up to 3 THz in the pure liquid state over a temperature range from 10 to 60 °C to understand differences in molecular motions of these simple, planar molecules bearing rather different electric dipole moments: 1.72 and 4.48 D for Br-Bz and NC-Bz in gaseous state, respectively. Temperature dependence of spin-lattice relaxation time (T(1)) for (13)C NMR and viscosities for these liquids were also determined to obtain information for molecular motions. Moreover, depolarized Rayleigh scattering (DRS) experiments were carried out for both liquids at 20 °C to determine frequency dependencies of optical susceptibilities up to 8 THz directly relating to rotational motions of their molecular planes. Most Br-Bz molecules rotate freely over a temperature range examined, showing a Kirkwood correlation factor close to g(K) ∼ 1.0 at dielectric Debye-type relaxation times (ca. 18 ps at 20 °C) essentially identical to microscopic (dielectric) relaxation times evaluated from T(1)(13)C NMR data. A small amount of Br-Bz molecules forms dimeric intermolecular associations in an antiparallel configuration of dipole moments. On the other hand, NC-Bz molecules form stable dimers in the antiparallel dipole configuration at a population much higher than that of Br-Bz because of a markedly greater dipole moment than that of Br-Bz. A major dielectric relaxation mechanism for NC-Bz found at ca. 70 ps at 20 °C results from the dissociation process of dimers with a lifetime longer than a rotational relaxation time, observable as a minor dielectric relaxation mechanism at ca. 12 ps at 20 °C, of individual monomeric NC-Bz molecules without the formation of dimers. The formation of stable dimers in an antiparallel configuration is responsible for the observed small g(K) values, ca. 0.5, and disagreement between major (or minor) dielectric relaxation times and

  14. Printing low-voltage dielectric elastomer actuators

    NASA Astrophysics Data System (ADS)

    Poulin, Alexandre; Rosset, Samuel; Shea, Herbert R.

    2015-12-01

    We demonstrate the fabrication of fully printed thin dielectric elastomer actuators (DEAs), reducing the operation voltage below 300 V while keeping good actuation strain. DEAs are soft actuators capable of strains greater than 100% and response times below 1 ms, but they require driving voltage in the kV range, limiting the possible applications. One way to reduce the driving voltage of DEAs is to decrease the dielectric membrane thickness, which is typically in the 20-100 μm range, as reliable fabrication becomes challenging below this thickness. We report here the use of pad-printing to produce μm thick silicone membranes, on which we pad-print μm thick compliant electrodes to create DEAs. We achieve a lateral actuation strain of 7.5% at only 245 V on a 3 μm thick pad-printed membrane. This corresponds to a ratio of 125%/kV2, by far the highest reported value for DEAs. To quantify the increasing stiffening impact of the electrodes on DEA performance as the membrane thickness decreases, we compare two circular actuators, one with 3 μm- and one with 30 μm-thick membranes. Our experimental measurements show that the strain uniformity of the 3 μm-DEA is indeed affected by the mechanical impact of the electrodes. We developed a simple DEA model that includes realistic electrodes of finite stiffness, rather than assuming zero stiffness electrodes as is commonly done. The simulation results confirm that the stiffening impact of the electrodes is an important parameter that should not be neglected in the design of thin-DEAs. This work presents a practical approach towards low-voltage DEAs, a critical step for the development of real world applications.

  15. Preferential Solvation of a Highly Medium Responsive Pentacyanoferrate(II) Complex in Binary Solvent Mixtures: Understanding the Role of Dielectric Enrichment and the Specificity of Solute-Solvent Interactions.

    PubMed

    Papadakis, Raffaello

    2016-09-08

    In this work, the preferential solvation of an intensely solvatochromic ferrocyanide(II) dye involving a 4,4'-bipyridine-based ligand was examined in various binary solvent mixtures. Its solvatochromic behavior was rationalized in terms of specific and nonspecific solute-solvent interactions. An exceptional case of solvatochromic inversion was observed when going from alcohol/water to amide/water mixtures. These effects were quantified using Onsager's solvent polarity function. Furthermore, the sensitivity of the solvatochromism of the dye was determined using various solvatochromic parameters such as π* expressing the dipolarity/polarizability of solvents and α expressing the hydrogen-bond-donor acidity of solvents. This analysis was useful for the rationalization of the selective solvation phenomena occurring in the three types of alcohol/water and amide/water mixtures studied. Furthermore, two preferential solvation models were employed for the interpretation of the experimental spectral results in binary solvent mixtures, namely, the model of Suppan on dielectric enrichment [J. Chem. Soc. Faraday Trans. 1 1987, 83, 495-509] and the model of Bosch, Rosés, and co-workers [J. Chem. Soc., Perkin Trans. 2, 1995, 8, 1607-1615]. The first model successfully predicted the charge transfer energies of the dye in formamide/water and N-methylformamide/water mixtures, but in the case of MeOH/water mixtures, the prediction was less accurate because of the significant contribution of specific solute-solvent interactions in that case. The second model gave more insights for both specific solute-solvent as well as solvent-solvent interactions in the cybotactic region. The role of dielectric enrichment and specific interactions was discussed based on the findings.

  16. Dielectric properties of uncooked chicken breast muscles from ten to one thousand eight hundred megahertz.

    PubMed

    Zhuang, H; Nelson, S O; Trabelsi, S; Savage, E M

    2007-11-01

    The dielectric properties, consisting of the dielectric constant (epsilon') and loss factor (epsilon''), were measured with an open-ended coaxial-line probe and impedance analyzer for uncooked broiler breast muscle pectoralis major and pectoralis minor, deboned at 2- and 24-h postmortem, over the frequency range from 10 to 1,800 MHz at temperatures ranging from 5 to 85 degrees C. The dielectric property profiles of chicken breast muscle are dependent upon the radio-wave and microwave frequencies and temperature. Increasing frequency from 10 to 1,800 MHz results in decreasing values of the dielectric constant and loss factor regardless of temperature in this range, chicken breast muscle type, or deboning time. However, the response to temperature varies with the frequency, muscle type, and deboning time. There are no differences in the dielectric constant and loss factor values at frequencies of 26 or 1,800 MHz between samples deboned at 2- and at 24-h postmortem. However, the muscle type significantly affects the average values of the dielectric constant and loss factor, with pectoralis minor having significantly higher average values. Both the deboning time and muscle type significantly affect the average values of the loss tangent (tan delta = dielectric loss factor/dielectric constant) at 26 and 1,800 MHz, with pectoralis minor having higher values than pectoralis major and 2-h samples having higher values than 24-h samples. Our quality measurements also show there are significant differences in chicken meat quality characteristics, including color, pH, drip loss, water holding capacity, and texture (Warner-Bratzler shear force value) between the different muscle types and between different deboning times in the same test. These results suggest that there is a probable potential for using dielectric property measurements to assess the quality of chicken meat.

  17. Techniques for Measuring the Dielectric Properties of Agricultural Products

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dielectrics and dielectric properties of materials are defined generally, and methods for measuring dielectric properties of agricultural products are described for several frequency ranges from audio frequencies through microwave frequencies. These include measurement with impedance and admittance...

  18. Characterisation of water behaviour in cellulose ether polymers using low frequency dielectric spectroscopy.

    PubMed

    McCrystal, C B; Ford, J L; He, R; Craig, D Q M; Rajabi-Siahboomi, A R

    2002-08-28

    The behaviour of water in hydroxypropylmethylcellulose (HPMC) K100LV, K4M, K15M, K100M, E4M, F4M and HPC polymers was characterised using low frequency dielectric spectroscopy (LFDS). Dielectric responses of 25% (w/w) HPMC K15M gels and deionised water were found to be similar at +22 and 0 degrees C. However, at -30 degrees C, a dielectric response typical of a solid was apparent. The melting of frozen water within gels was detected as increases in the magnitude of the dielectric response with increase in temperature. More than one phase transition was visible in the majority of gels studied which may be related to the presence of different states of water melting at different temperatures. In addition to polymer concentration, both polymer molecular weight and substitution level influenced the nature of the transitions. The magnitude of the dielectric response was increased in all HPMC gel systems in comparison to the response seen in deionised water. Drug addition affected the transitions occurring during the melting of ice in the gels. This may be related to the presence of ionic species in the systems. LFDS studies on cellulose ether gels have provided some interesting evidence for the existence of more than one state of water within such gel systems. The results are in good agreement with thermal analysis findings in similar gel systems.

  19. Synthesis and dielectric studies of poly (vinyl pyrrolidone) / titanium dioxide nanocomposites

    NASA Astrophysics Data System (ADS)

    Vasudevan, Prathibha; Thomas, Sunil; V, Arunkumar K.; S, Karthika; V, Unnikrishnan N.

    2015-02-01

    In this paper, we present the synthesis of poly vinyl pyrrolidone (PVP) / titanium dioxide nanocomposites via sol- gel technique. The structural and dielectric properties of the samples were also analysed in this work. PVP doped with varying concentrations of TiO2 are prepared by the sol-gel route. The prepared composites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and impedance spectroscopy. XRD and TEM confirm the presence of TiO2 nanoparticles in the composites. The dielectric response and the AC electrical conductivity of the samples are investigated for the frequency range 1 kHz-2MHz at room temperature. The dielectric studies show low values for dielectric constant and loss at high frequencies.

  20. Surface plasmon coupling enhanced dielectric environment sensitivity in a quasi-three-dimensional metallic nanohole array.

    PubMed

    Li, Yuanyuan; Pan, Jian; Zhan, Peng; Zhu, Shining; Ming, Naiben; Wang, Zhenlin; Han, Wenda; Jiang, Xunya; Zi, Jian

    2010-02-15

    An enhanced dielectric environment response is observed in a kind of metallic nanohole arrays which are prepared by metal deposition on a sacrificial two dimensional colloidal crystal template. The periodic metallic structures are composed of interlinked metallic half-shells supported on a planar dielectric substrate. When putting in dielectric matrix of different refractive index, the measured sensitivity of the quasi-three-dimensional metallic nanohole array can reach a value of 1192 nm per refractive index unit which shows a five-fold increase as compared with the metallic structures supported on the template. The observed boost in sensitivity is found to originate from a substantially reduced substrate effect, resulting in a pronounced surface plasmon coupling of which its strength is independent of the dielectric environment, a characteristics absent in conventional planar metallic subwavelength hole arrays. These findings are analyzed theoretically and confirmed by numerical simulations.

  1. Probing a dielectric resonator acting as passive sensor through a wireless microwave link

    NASA Astrophysics Data System (ADS)

    Friedt, J.-M.; Boudot, R.; Martin, G.; Ballandras, S.

    2014-09-01

    Dielectric resonators, generally used for frequency filtering in oscillator loops, can be used as passive cooperative targets for wireless sensor applications. In the present work, we demonstrate such an approach by probing their spectral characteristics using a microwave RADAR system. The unique spectral response and energy storage capability of resonators provide unique responses allowing to separate the sensor response from clutter. Although the dielectric resonator is not designed for high temperature sensitivity, the accurate determination of the resonance frequency allows for a remote estimate of the temperature with Kelvin resolution.

  2. Interaction of two dielectric macroparticles

    SciTech Connect

    Munirov, V. R.; Filippov, A. V.

    2013-11-15

    The electrostatic interaction of two charged dielectric spherical particles with a nonuniform freecharge distribution over their surfaces in an external homogeneous electric field is considered. An exact solution for the electric field potential is obtained, and an analytical expression for the interaction force between these two particles is found. The case of a uniform free-charge distribution is considered in detail, and the region of parameters in the plane “the ratio of the radii vs. the ratio of the charges,” where repulsion between two like-charged particles turns into attraction as the interparticle distance decreases is established.

  3. Dielectric cure monitoring: Preliminary studies

    NASA Technical Reports Server (NTRS)

    Goldberg, B. E.; Semmel, M. L.

    1984-01-01

    Preliminary studies have been conducted on two types of dielectric cure monitoring systems employing both epoxy resins and phenolic composites. An Audrey System was used for 23 cure monitoring runs with very limited success. Nine complete cure monitoring runs have been investigated using a Micromet System. Two additional measurements were performed to investigate the Micromet's sensitivity to water absorption in a post-cure carbon-phenolic material. While further work is needed to determine data significance, the Micromet system appears to show promise as a feedback control device during processing.

  4. Inhibiting electro-thermal breakdown of acrylic dielectric elastomer actuators by dielectric gel coating

    NASA Astrophysics Data System (ADS)

    La, Thanh-Giang; Lau, Gih-Keong

    2016-01-01

    Electrical breakdown of dielectric elastomer actuators (DEA) is very localized; a spark and a pinhole (puncture) in dielectric ends up with short-circuit. This letter shows that prevention of electrothermal breakdown helps defer failure of DEAs even with conductive-grease electrodes. Dielectric gel encapsulation or coating (Dow Corning 3-4170) helps protect acrylic elastomer (VHB 4905), making it thermally more stable and delaying its thermal oxidation (burn) from 218 °C to 300 °C. Dielectric-gel-coated acrylic DEAs can withstand higher local leak-induced heating and thus achieve higher dielectric strengths than non-coated DEAs do.

  5. Microelectrode-based dielectric spectroscopy of glucose effect on erythrocytes.

    PubMed

    Colella, L; Beyer, C; Fröhlich, J; Talary, M; Renaud, P

    2012-06-01

    The dielectric response of biconcave erythrocytes exposed to D-glucose and L-glucose has been investigated using a double array of planar interdigitated microelectrodes on a glass microchip. Erythrocytes are analyzed under physiological conditions suspended in hypo-osmolar balanced solutions containing different glucose concentrations (0-20 mM). The glucose effect on the cellular dielectric properties is evaluated by analyzing the spectra using two different approaches, the equivalent circuit model and a modified model for ellipsoidal particles. The results show that at elevated glucose concentration (15 mM) the membrane capacitance increases by 36%, whereas the cytosol conductivity slightly decreases with a variation of about 15%. On the contrary, no variation has been registered with L-glucose, a biologically inactive enantiomer of D-glucose. The paper discusses the possible mechanism controlling the membrane dielectric response. As the external D-glucose increases, the number of activated glucose transporter in the erythrocyte membrane raises and the transition from sugar-free state to sugar-bounded state induces a change in the dipole moments and in the membrane capacitance.

  6. Crosslinked polymeric dielectric materials and electronic devices incorporating same

    NASA Technical Reports Server (NTRS)

    Marks, Tobin J. (Inventor); Facchetti, Antonio (Inventor); Wang, Zhiming (Inventor); Choi, Hyuk-Jin (Inventor); Suh, legal representative, Nae-Jeong (Inventor)

    2012-01-01

    Solution-processable dielectric materials are provided, along with precursor compositions and processes for preparing the same. Composites and electronic devices including the dielectric materials also are provided.

  7. High thermal conductivity lossy dielectric using a multi layer configuration

    DOEpatents

    Tiegs, Terry N.; Kiggans, Jr., James O.

    2003-01-01

    Systems and methods are described for loss dielectrics. A loss dielectric includes at least one high dielectric loss layer and at least one high thermal conductivity-electrically insulating layer adjacent the at least one high dielectric loss layer. A method of manufacturing a loss dielectric includes providing at least one high dielectric loss layer and providing at least one high thermal conductivity-electrically insulating layer adjacent the at least one high dielectric loss layer. The systems and methods provide advantages because the loss dielectrics are less costly and more environmentally friendly than the available alternatives.

  8. A simple method for reducing inevitable dielectric loss in high-permittivity dielectric elastomers

    NASA Astrophysics Data System (ADS)

    Madsen, F. B.; Yu, L.; Mazurek, P.; Skov, A. L.

    2016-07-01

    Commercial viability of dielectric elastomers (DEs) is currently limited by a few obstacles, including high driving voltages (in the kV range). Driving voltage can be lowered by either decreasing the Young’s modulus or increasing the dielectric permittivity of silicone elastomers, or a combination thereof. A decrease in the Young’s modulus, however, is often accompanied by a loss in mechanical stability, whereas increases in dielectric permittivity are usually followed by a large increase in dielectric loss followed by a decrease in breakdown strength and thereby the lifetime of the DE. A new soft elastomer matrix, with high dielectric permittivity and a low Young’s modulus, aligned with no loss of mechanical stability, was prepared through the use of commercially available chloropropyl-functional silicone oil mixed into a tough commercial liquid silicone rubber silicone elastomer. The addition of chloropropyl-functional silicone oil in concentrations up to 30 phr was found to improve the properties of the silicone elastomer significantly, as dielectric permittivity increased to 4.4, dielectric breakdown increased up to 25% and dielectric losses were reduced. The chloropropyl-functional silicone oil also decreased the dielectric losses of an elastomer containing dielectric permittivity-enhancing TiO2 fillers. Commercially available chloropropyl-functional silicone oil thus constitutes a facile method for improved silicone DEs, with very low dielectric losses.

  9. Physics of drug delivery: dielectric spectroscopy to probe mucoadhesion

    NASA Astrophysics Data System (ADS)

    Stromme, Maria

    2003-04-01

    This work presents how dielectric spectroscopy can be used as a tool to obtain insight about properties on the nano-scale of interfaces of pharmaceutical interest. An outline for studying the adhesion in terms of a compatibility factor between pharmaceutical gels and biological tissue is put forward. The proposed compatibility factor is calculated from the high frequency response (kHz region) of the gel and porcine nasal mucosa separately, and from that of the combined system. It gives an assessment of the possibilities of intimate surface contact, which is generally considered to be the first step in the mucoadhesion process. The results from dielectric spectroscopy were compared to measurements using a tensile strength method and it was found that the gels with the highest compatibility factors were the same as those pointed out as having the highest mucoadhesion using the tensile strength method.

  10. Graphene Nanoplatelet-Polystyrene Nanocomposite: Dielectric and Charge Storage Behaviors

    NASA Astrophysics Data System (ADS)

    Al-Saleh, Mohammed H.; Abdul Jawad, Saadi

    2016-07-01

    Graphene nanoplatelet (GNP)-polystyrene nanocomposites filled with up to 20 wt.% GNPs were prepared by melt mixing. The microstructure, direct-current (dc) electrical percolation behavior, and dielectric characteristics were investigated as functions of frequency. In addition, the effects of dc bias on the complex impedance and charge transport mechanisms were explored. The dc electrical percolation curve showed a gradually transition from the insulating to conducting state. At 15 wt.% GNP loading and frequency greater than 104 Hz, the nanocomposite exhibited dielectric constant and loss factor of 180 and 0.11, respectively, revealing remarkable storage capabilities at high frequencies. For nanocomposites filled with 12 wt.% to 20 wt.% GNPs, the alternating-current conductivity was found to follow the universal dynamic response behavior, implying electron conduction due to tunneling in addition to direct contact between GNPs.

  11. The Current State of Silicone-Based Dielectric Elastomer Transducers.

    PubMed

    Madsen, Frederikke B; Daugaard, Anders E; Hvilsted, Søren; Skov, Anne L

    2016-03-01

    Silicone elastomers are promising materials for dielectric elastomer transducers (DETs) due to their superior properties such as high efficiency, reliability and fast response times. DETs consist of thin elastomer films sandwiched between compliant electrodes, and they constitute an interesting class of transducer due to their inherent lightweight and potentially large strains. For the field to progress towards industrial implementation, a leap in material development is required, specifically targeting longer lifetime and higher energy densities to provide more efficient transduction at lower driving voltages. In this review, the current state of silicone elastomers for DETs is summarised and critically discussed, including commercial elastomers, composites, polymer blends, grafted elastomers and complex network structures. For future developments in the field it is essential that all aspects of the elastomer are taken into account, namely dielectric losses, lifetime and the very often ignored polymer network integrity and stability.

  12. Optical bistability in photonic crystal microrings with nonlinear dielectric materials.

    PubMed

    Ogusu, Kazuhiko; Takayama, Kosuke

    2008-05-12

    We study the linear resonance properties of several types of microrings in a two-dimensional photonic crystal (PC) consisting of a square lattice with air holes in dielectric using the plane-wave expansion method and the FDTD method. Moreover we investigate the nonlinear responses, especially optical bistability when an intense optical pulse is incident into the microrings. In this paper, Ag-As-Se chalcogenide glass is assumed as nonlinear dielectric, which has a high third-order nonlinearity. Although line-defect waveguides in an air-hole-type PC are usually multimoded, we can obtain interesting unique properties such as counter rotation of intracavity fields, transmission to all output ports, and unstable nonlinear oscillations in the multimoded PC microring. We can improve the resonance characteristics by partly introducing single-mode waveguides into microrings and can obtain stable optical bistability.

  13. Dielectric function for doped graphene layer with barium titanate

    NASA Astrophysics Data System (ADS)

    Martinez Ramos, Manuel; Garces Garcia, Eric; Magana, Fernado; Vazquez Fonseca, Gerardo Jorge

    2015-03-01

    The aim of our study is to calculate the dielectric function for a system formed with a graphene layer doped with barium titanate. Density functional theory, within the local density approximation, plane-waves and pseudopotentials scheme as implemented in Quantum Espresso suite of programs was used. We considered 128 carbon atoms with a barium titanate cluster of 11 molecules as unit cell with periodic conditions. The geometry optimization is achieved. Optimization of structural configuration is performed by relaxation of all atomic positions to minimize their total energies. Band structure, density of states and linear optical response (the imaginary part of dielectric tensor) were calculated. We thank Dirección General de Asuntos del Personal Académico de la Universidad Nacional Autónoma de México, partial financial support by Grant IN-106514 and we also thank Miztli Super-Computing center the technical assistance.

  14. Dielectric Spectroscopy of Fresh Chicken Breast Meat

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Technical abstract The dielectric properties of fresh chicken breast meat were measured at temperatures from 5 to 85 degrees °C over the frequency range from 10 MHz to 1.8 GHz by dielectric spectroscopy techniques with an open-ended coaxial-line probe and impedance analyzer. Samples were cut from ...

  15. Dielectric Spectroscopy of Fresh Chicken Breast Meat

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The dielectric properties of fresh chicken breast meat were measured at temperatures from 5 to 85 'C over the frequency range from 10 MHz to 1.8 GHz by dielectric spectroscopy techniques with an open-ended coaxial-line probe and impedance analyzer. Samples were cut from both the Pectoralis major an...

  16. Graphene-Dielectric Integration for Graphene Transistors

    PubMed Central

    Liao, Lei; Duan, Xiangfeng

    2010-01-01

    Graphene is emerging as an interesting electronic material for future electronics due to its exceptionally high carrier mobility and single-atomic thickness. Graphene-dielectric integration is of critical importance for the development of graphene transistors and a new generation of graphene based electronics. Deposition of dielectric materials onto graphene is of significant challenge due to the intrinsic material incompatibility between pristine graphene and dielectric oxide materials. Here we review various strategies being researched for graphene-dielectric integration. Physical vapor deposition (PVD) can be used to directly deposit dielectric materials on graphene, but often introduces significant defects into the monolayer of carbon lattice; Atomic layer deposition (ALD) process has also been explored to to deposit high-κ dielectrics on graphene, which however requires functionalization of graphene surface with reactive groups, inevitably leading to a significant degradation in carrier mobilities; Using naturally oxidized thin aluminum or polymer as buffer layer for dielectric deposition can mitigate the damages to graphene lattice and improve the carrier mobility of the resulted top-gated transistors; Lastly, a physical assembly approach has recently been explored to integrate dielectric nanostructures with graphene without introducing any appreciable defects, and enabled top-gated graphene transistors with the highest carrier mobility reported to date. We will conclude with a brief summary and perspective on future opportunities. PMID:21278913

  17. Polycarbonate based three-phase nanocomposite dielectrics

    NASA Astrophysics Data System (ADS)

    Sain, P. K.; Goyal, R. K.; Prasad, Y. V. S. S.; Bhargava, A. K.

    2016-08-01

    Three-phase polycarbonate (PC) matrix nanocomposites are prepared using the solution method. One of the nanocomposite fillers is dielectric and the other is conducting. Lead zirconate titanate (PZT) is used as the dielectric filler. The conducting fillers, nano-Cu and multi-walled carbon nanotubes (MWCNTs), are used to make two different nanocomposites, MWCNT-PZT-PC and Cu-PZT-PC. The prepared nanocomposites are characterized using density measurement, x-ray diffractometry, scanning electron microscopy, energy dispersive x-ray spectroscopy, and differential scanning calorimetry. Percolation is absent in both three-phase nanocomposites within the study’s concentration window of conducting fillers. The dielectric properties of the nanocomposites are evaluated using a precision impedance analyser. The dielectric constant of the Cu-PZT-PC nanocomposite increases to 14 (a dissipation factor of 0.17), whereas in the case of the MWCNT-PZT-PC nanocomposite it increases to 8.5 (a dissipation factor of 0.002). The melting point of both nanocomposites decreases with respect to the control PC. The frequency (1 kHz to 1 MHz) and temperature (room temperature to 200 °C) dependence of the dielectric constant and dissipation factor are examined. For the Cu-PZT-PC nanocomposites, the dielectric constant decreases with increasing frequency, whereas in the case of the MWCNT-PZT-PC nanocomposites the dielectric constant is almost constant. The dielectric constant and dissipation factor exhibit a slight temperature dependence.

  18. Dielectric spectroscopy of watermelons for quality sensing

    NASA Astrophysics Data System (ADS)

    Nelson, Stuart O.; Guo, Wen-chuan; Trabelsi, Samir; Kays, Stanley J.

    2007-07-01

    Dielectric properties of four small-sized watermelon cultivars, grown and harvested to provide a range of maturities, were measured with an open-ended coaxial-line probe and an impedance analyser over the frequency range from 10 MHz to 1.8 GHz. Probe measurements were made on the external surface of the melons and also on tissue samples from the edible internal tissue. Moisture content and soluble solids content (SSC) were measured for internal tissue samples, and SSC (sweetness) was used as the quality factor for correlation with the dielectric properties. Individual dielectric constant and loss factor correlations with SSC were low, but a high correlation was obtained between the SSC and permittivity from a complex-plane plot of dielectric constant and loss factor, each divided by SSC. However, SSC prediction from the dielectric properties by this relationship was not as high as expected (coefficient of determination about 0.4). Permittivity data (dielectric constant and loss factor) for the melons are presented graphically to show their relationships with frequency for the four melon cultivars and for external surface and internal tissue measurements. A dielectric relaxation for the external surface measurements, which may be attributable to a combination of bound water, Maxwell-Wagner, molecular cluster or ion-related effects, is also illustrated. Coefficients of determination for complex-plane plots, moisture content and SSC relationship, and penetration depth are also shown graphically. Further studies are needed for determining the practicality of sensing melon quality from their dielectric properties.

  19. Nanostructured high-performance dielectric block copolymers.

    PubMed

    Liu, Wenmei; Liao, Xiaojuan; Li, Yawei; Zhao, Qiuhua; Xie, Meiran; Sun, Ruyi

    2015-10-25

    A new type of insulating-conductive block copolymer was synthesized by metathesis polymerization. The copolymer can self-assemble into unique nanostructures of micelles or hollow spheres. It exhibits a high dielectric constant, low dielectric loss, and high stored/released energy density due to the strong dipolar and nano-interfacial polarization contributions.

  20. Dielectric Loss Measurements on Raw Materials.

    ERIC Educational Resources Information Center

    Mwanje, J.

    1980-01-01

    Describes an experiment used to study dielectric properties of materials. Values of the dielectric loss tangent can be determined at low frequencies from Lissajous figures formed on an oscilloscope. Some mineral rock specimens show Debye-type relaxation peaks at frequencies in the region of 1 to 500 Hz. (Author/DS)

  1. Dielectric bow-tie nanocavity.

    PubMed

    Lu, Qijing; Shu, Fang-Jie; Zou, Chang-Ling

    2013-12-15

    We propose a novel dielectric bow-tie (DBT) nanocavity consisting of two opposing tip-to-tip triangle semiconductor nanowires, whose end faces are coated by silver nanofilms. Based on the advantages of the dielectric slot and tip structures, and the high reflectivity of the silver mirror, light can be confined in this nanocavity with low loss. We demonstrate that at 4.5 K (300 K) around the resonance wavelength of 1550 nm, the mode excited in this nanocavity has a deep subwavelength mode volume of 2.8×10(-4) μm³ and a high quality factor of 4.9×10(4) (401.3), corresponding to an ultrahigh Purcell factor of 1.6×10(7) (1.36×10(5)). This DBT nanocavity may find applications for integrated nanophotonic circuits, such as high-efficiency single photon sources, thresholdless nanolasers, and strong coupling in cavity quantum electrodynamics experiments.

  2. Ion implanted dielectric elastomer circuits

    NASA Astrophysics Data System (ADS)

    O'Brien, Benjamin M.; Rosset, Samuel; Anderson, Iain A.; Shea, Herbert R.

    2013-06-01

    Starfish and octopuses control their infinite degree-of-freedom arms with panache—capabilities typical of nature where the distribution of reflex-like intelligence throughout soft muscular networks greatly outperforms anything hard, heavy, and man-made. Dielectric elastomer actuators show great promise for soft artificial muscle networks. One way to make them smart is with piezo-resistive Dielectric Elastomer Switches (DES) that can be combined with artificial muscles to create arbitrary digital logic circuits. Unfortunately there are currently no reliable materials or fabrication process. Thus devices typically fail within a few thousand cycles. As a first step in the search for better materials we present a preliminary exploration of piezo-resistors made with filtered cathodic vacuum arc metal ion implantation. DES were formed on polydimethylsiloxane silicone membranes out of ion implanted gold nano-clusters. We propose that there are four distinct regimes (high dose, above percolation, on percolation, low dose) in which gold ion implanted piezo-resistors can operate and present experimental results on implanted piezo-resistors switching high voltages as well as a simple artificial muscle inverter. While gold ion implanted DES are limited by high hysteresis and low sensitivity, they already show promise for a range of applications including hysteretic oscillators and soft generators. With improvements to implanter process control the promise of artificial muscle circuitry for soft smart actuator networks could become a reality.

  3. Dielectric breakdown of additively manufactured polymeric materials

    SciTech Connect

    Monzel, W. Jacob; Hoff, Brad W.; Maestas, Sabrina S.; French, David M.; Hayden, Steven C.

    2016-01-11

    Dielectric strength testing of selected Polyjet-printed polymer plastics was performed in accordance with ASTM D149. This dielectric strength data is compared to manufacturer-provided dielectric strength data for selected plastics printed using the stereolithography (SLA), fused deposition modeling (FDM), and selective laser sintering (SLS) methods. Tested Polyjet samples demonstrated dielectric strengths as high as 47.5 kV/mm for a 0.5 mm thick sample and 32.1 kV/mm for a 1.0 mm sample. As a result, the dielectric strength of the additively manufactured plastics evaluated as part of this study was lower than the majority of non-printed plastics by at least 15% (with the exception of polycarbonate).

  4. Dielectric breakdown of additively manufactured polymeric materials

    DOE PAGES

    Monzel, W. Jacob; Hoff, Brad W.; Maestas, Sabrina S.; ...

    2016-01-11

    Dielectric strength testing of selected Polyjet-printed polymer plastics was performed in accordance with ASTM D149. This dielectric strength data is compared to manufacturer-provided dielectric strength data for selected plastics printed using the stereolithography (SLA), fused deposition modeling (FDM), and selective laser sintering (SLS) methods. Tested Polyjet samples demonstrated dielectric strengths as high as 47.5 kV/mm for a 0.5 mm thick sample and 32.1 kV/mm for a 1.0 mm sample. As a result, the dielectric strength of the additively manufactured plastics evaluated as part of this study was lower than the majority of non-printed plastics by at least 15% (with themore » exception of polycarbonate).« less

  5. Microwave dielectric properties of boreal forest trees

    NASA Technical Reports Server (NTRS)

    Xu, G.; Ahern, F.; Brown, J.

    1993-01-01

    The knowledge of vegetation dielectric behavior is important in studying the scattering properties of the vegetation canopy and radar backscatter modelling. Until now, a limited number of studies have been published on the dielectric properties in the boreal forest context. This paper presents the results of the dielectric constant as a function of depth in the trunks of two common boreal forest species: black spruce and trembling aspen, obtained from field measurements. The microwave penetration depth for the two species is estimated at C, L, and P bands and used to derive the equivalent dielectric constant for the trunk as a whole. The backscatter modelling is carried out in the case of black spruce and the results are compared with the JPL AIRSAR data. The sensitivity of the backscatter coefficient to the dielectric constant is also examined.

  6. Self-stabilizing dielectric elastomer generators

    NASA Astrophysics Data System (ADS)

    Zanini, P.; Rossiter, J.; Homer, M.

    2017-03-01

    Dielectric elastomer generators (DEGs) are an emerging technology for the conversion of mechanical into electrical energy. Despite many advantageous characteristics, there are still issues to overcome, including the need for charging at every cycle to produce an electrical output. Self-priming circuits (SPCs) are one possible solution, storing part of the electric energy output of one cycle to supply as input for the next, producing a voltage boost effect. Until now, studies regarding SPCs neglect to consider how the increasing voltage will create an electromechanical response and affect the DEG when driven by an oscillatory mechanical load. In the present work we model this force-based actuation, including coupling between the DEG and SPC, in order to predict the dynamics of the system. In such cases, the DEG has a mechanical response when charged (actuator behaviour), and as the voltage increases, this actuation-like effect increases the capacitance values that bound the cycle. We show how this inherent nonlinearity yields a reduction in the DEG’s capacitance swing and reduces the performance of the SPC, but also self-stabilizes the system. This stability is useful in the design of robust DEG energy harvesters that can operate near to, but not enter, failure mode.

  7. Numerical investigation of dielectric barrier discharges

    NASA Astrophysics Data System (ADS)

    Li, Jing

    1997-12-01

    A dielectric barrier discharge (DBD) is a transient discharge occurring between two electrodes in coaxial or planar arrangements separated by one or two layers of dielectric material. The charge accumulated on the dielectric barrier generates a field in a direction opposite to the applied field. The discharge is quenched before an arc is formed. It is one of the few non-thermal discharges that operates at atmospheric pressure and has the potential for use in pollution control. In this work, a numerical model of the dielectric barrier discharge is developed, along with the numerical approach. Adaptive grids based on the charge distribution is used. A self-consistent method is used to solve for the electric field and charge densities. The Successive Overrelaxation (SOR) method in a non-uniform grid spacing is used to solve the Poisson's equation in the cylindrically-symmetric coordinate. The Flux Corrected Transport (FCT) method is modified to solve the continuity equations in the non-uniform grid spacing. Parametric studies of dielectric barrier discharges are conducted. General characteristics of dielectric barrier discharges in both anode-directed and cathode-directed streamer are studied. Effects of the dielectric capacitance, the applied field, the resistance in external circuit and the type of gases (O2, air, N2) are investigated. We conclude that the SOR method in an adaptive grid spacing for the solution of the Poisson's equation in the cylindrically-symmetric coordinate is convergent and effective. The dielectric capacitance has little effect on the g-factor of radical production, but it determines the strength of the dielectric barrier discharge. The applied field and the type of gases used have a significant role on the current peak, current pulse duration and radical generation efficiency, discharge strength, and microstreamer radius, whereas the external series resistance has very little effect on the streamer properties. The results are helpful in

  8. Dielectric behaviour of BaTiO3-based ceramic multilayer capacitors under high dc bias field

    NASA Astrophysics Data System (ADS)

    Yang, Gang; Yue, Zhenxing; Zhao, Jianqiang; Wen, Hai; Wang, Xiaohui; Li, Longtu

    2006-08-01

    The dielectric behaviour of X7R-MLCCs with different active layers under high dc bias field (up to 6.25 MV m-1) has been investigated in the whole measurement temperature range from 213 to 453 K. The results show that as the dc bias field increases, the dielectric permittivity in the whole measurement range and the frequency dispersion at lower temperature are both suppressed, while dielectric loss initially decreases till the temperature reaches about 423 K and subsequently remains invariable. These results are attributed to the response of the core-shell structure in grains to the applied dc bias field. Furthermore, the dielectric permittivity of X7R-MLCCs with more dielectric layers is more significantly affected because of a more powerful pinning effect of the residual stress between the dielectric layer and the Ni electrode on the migration of the domain walls and the influence of created interfaces on dielectric properties of the dielectric materials close to the interface. The Curie peaks for two samples shift towards higher temperature at a rate 0.55 × 10-5 K m V-1 in the presence of the dc bias field. It is more significant that an interesting field-induced transition from paraelectric phase to ferroelectric phase in the shell part was found at about 323 K and Curie temperature.

  9. Relaxor Behavior and Dielectric Relaxation in Lead-Free Solid Solutions of (1 - x)(Bi0.5Na0.5TiO3)- x(SrNb2O6)

    NASA Astrophysics Data System (ADS)

    Bajpai, P. K.; Singh, K. N.; Tamrakar, Preeti

    2016-02-01

    Lead-free compositions (1 - x) (Bi0.5Na0.5TiO3)- x(SrNb2O6) (BNT-SN) are synthesized by a simple solid state reaction route. SN diffuse in distorted perovskite BNT for low concentrations of SN ( x ≤ 0.03) and are stabilized in rhombohedral perovskite phase with experimentally observed relative density of the ceramics >92%. A temperature-dependent dielectric response exhibits a broad dielectric peak that shows frequency-dependent shifts towards higher temperatures reflecting typical relaxor behavior. Modified Curie-Weiss law and Lorentz-type empirical relationships are used to fit the dielectric data that exhibit almost complete diffuse phase transition characteristics. In addition, significant dielectric dispersion is observed in a low-frequency regime in both components of the dielectric response and a small dielectric relaxation peak is observed. Cole-Cole plots indicate the poly-dispersive nature of the dielectric relaxation.

  10. Spontaneous emission in dielectric nanoparticles

    NASA Astrophysics Data System (ADS)

    Pukhov, K. K.; Basiev, T. T.; Orlovskii, Yu. V.

    2008-09-01

    An analytical expression is obtained for the radiative-decay rate of an excited optical center in an ellipsoidal dielectric nanoparticle (with sizes much less than the wavelength) surrounded by a dielectric medium. It is found that the ratio of the decay rate A nano of an excited optical center in the nanoparticle to the decay rate A bulk of an excited optical center in the bulk sample is independent of the local-field correction and, therefore, of the adopted local-field model. Moreover, the expression implies that the ratio A nano/ A bulk for oblate and prolate ellipsoids depends strongly on the orientation of the dipole moment of the transition with respect to the ellipsoid axes. In the case of spherical nanoparticles, a formula relating the decay rate A nano and the dielectric parameters of the nanocomposite and the volumetric content c of these particles in the nanocomposite is derived. This formula reduces to a known expression for spherical nanoparticles in the limit c ≪ 1, while the ratio A nano/ A bulk approaches unity as c tends to unity. The analysis shows that the approach used in a number of papers {H. P. Christensen, D. R. Gabbe, and H. P. Jenssen, Phys. Rev. B 25, 1467 (1982); R. S. Meltzer, S. P. Feofilov, B. Tissue, and H. B. Yuan, Phys. Rev. B 60, R14012 (1999); R. I. Zakharchenya, A. A. Kaplyanskii, A. B. Kulinkin, et al., Fiz. Tverd. Tela 45, 2104 (2003) [Phys. Solid State 45, 2209 (2003)]; G. Manoj Kumar, D. Narayana Rao, and G. S. Agarwal, Phys. Rev. Lett. 91, 203903 (2003); Chang-Kui Duan, Michael F. Reid, and Zhongqing Wang, Phys. Lett. A 343, 474 (2005); K. Dolgaleva, R. W. Boyd, and P. W. Milonni, J. Opt. Soc. Am. B 24, 516 (2007)}, for which the formula for A nano is derived merely by substituting the bulk refractive index by the effective refractive index of the nanocomposite must be revised, because the resulting ratio A nano/ A bulk turns out to depend on the local-field model. The formulas for the emission and absorption cross

  11. Functionalized carbon nanotubes as a filler for dielectric elastomer composites with improved actuation performance

    NASA Astrophysics Data System (ADS)

    Galantini, Fabia; Bianchi, Sabrina; Castelvetro, Valter; Gallone, Giuseppe

    2013-05-01

    Among the broad class of electro-active polymers, dielectric elastomer actuators represent a rapidly growing technology for electromechanical transduction. In order to further develop this applied science, the high driving voltages currently needed must be reduced. For this purpose, one of the most widely considered approaches is based on making elastomeric composites with highly polarizable fillers in order to increase the dielectric constant while maintaining both low dielectric losses and high-mechanical compliance. In this work, multi-wall carbon nanotubes were first functionalized by grafting either acrylonitrile or diurethane monoacrylate oligomers, and then dispersed into a polyurethane matrix to make dielectric elastomer composites. The procedures for the chemical functionalization of carbon nanotubes and proper characterizations of the obtained products are provided in detail. The consequences of the use of chemically modified carbon nanotubes as a filler, in comparison to using unmodified ones, were studied in terms of dielectric, mechanical and electromechanical response. In particular, an increment of the dielectric constant was observed for all composites throughout the investigated frequency spectrum, but only in the cases of modified carbon nanotubes did the loss factor remain almost unchanged with respect to the simple matrix, indicating that conductive percolation paths did not arise in such systems. An effective improvement in the actuation strain was observed for samples loaded with functionalized carbon nanotubes.

  12. Saturation effects on the joint elastic-dielectric properties of carbonates

    NASA Astrophysics Data System (ADS)

    Han, Tongcheng; Clennell, Michael Ben; Pervukhina, Marina; Josh, Matthew

    2016-06-01

    We used a common microstructural model to investigate the cross-property relations between elastic wave velocities and dielectric permittivity in carbonate rocks. A unified model based on validated self-consistent effective medium theory was used to quantify the effects of porosity and water saturation on both elastic properties (compressional and shear wave velocities) and electromagnetic properties (dielectric permittivity). The results of the forward models are presented as a series of cross-plots covering a wide range of porosities and water saturations and for microstructures that correspond to different predominant aspect ratios. It was found that dielectric permittivity correlated approximately linearly with elastic wave velocity at each saturation stage, with slopes varying gradually from positive at low saturation conditions to negative at higher saturations. The differing sensitivities of the elastic and dielectric rock properties to changes in porosity, pore morphology and water saturation can be used to reduce uncertainty in subsurface fluid saturation estimation when co-located sonic and dielectric surveys are available. The joint approach is useful for cross-validation of rock physics models for analysing pore structure and saturation effects on elastic and dielectric responses.

  13. Perovskite phase formation, microstructure and improvement of dielectric properties in iron-containing ferroelectrics

    NASA Astrophysics Data System (ADS)

    Fang, Bijun; Geng, Baoyou; Wei, Xianwen; Shan, Yuejin; Tezuka, Keitaro; Imoto, Hideo

    2006-08-01

    Pure perovskite-phase lead iron scandium niobate, Pb(Fe1/4Sc1/4Nb1/2)O3 (PFScN), ceramics have been prepared by a conventional solid-state reaction method via a B-site oxide mixing route. Although synthesis conditions have been tailored to optimization, strong frequency dispersion of the dielectric properties cannot be improved by modifying ceramic processing, which is considered as correlating to the nature of iron-containing ferroelectrics. Sintering in an O2 atmosphere and MnO2 and Li2CO3 dopings tend to decrease the dielectric loss of the iron-containing dielectrics. The strong frequency dispersion of the dielectric response and the abnormally recurrent increase of the dielectric constant and loss in the paraelectric region are correspondingly suppressed. This improvement of dielectric properties in the iron-containing ferroelectrics is interpreted by an electron compensation mechanism, in which the generation of donor electrons is based on different ionization paths.

  14. Dielectric relaxations and alternating current conductivity in manganese substituted cobalt ferrite

    SciTech Connect

    Kolekar, Y. D.; Sanchez, L. J.; Ramana, C. V.

    2014-04-14

    Manganese (Mn) substituted cobalt ferrites (CoFe{sub 2-x}Mn{sub x}O{sub 4}, referred to CFMO) have been synthesized by the solid state reaction method and their dielectric properties and ac conductivity have been evaluated as a function of applied frequency and temperature. X-ray diffraction measurements indicate that CFMO crystallize in the inverse cubic spinel phase with a lattice constant ∼8.38 Å. Frequency dependent dielectric measurements at room temperature obey the modified Debye model with relaxation time of 10{sup −4} s and spreading factor of 0.35(±0.05). The frequency (20 Hz–1 MHz) and temperature (T = 300–900 K) dependent dielectric constant analyses indicate that CFMO exhibit two dielectric relaxations at lower frequencies (1–10 kHz), while completely single dielectric relaxation for higher frequencies (100 kHz–1 MHz). The dielectric constant of CFMO is T-independent up to ∼400 K, at which point increasing trend prevails. The dielectric constant increase with T > 400 K is explained through impedance spectroscopy assuming a two-layer model, where low-resistive grains separated from each other by high-resistive grain boundaries. Following this model, the two electrical responses in impedance formalism are attributed to the grain and grain-boundary effects, respectively, which also satisfactorily accounts for the two dielectric relaxations. The capacitance of the bulk of the grain determined from impedance analyses is ∼10 pF, which remains constant with T, while the grain-boundary capacitance increases up to ∼3.5 nF with increasing T. The tan δ (loss tangent)-T also reveals the typical behavior of relaxation losses in CFMO.

  15. Dielectric investigation of some woven fabrics

    NASA Astrophysics Data System (ADS)

    Cerovic, Dragana D.; Dojcilovic, Jablan R.; Asanovic, Koviljka A.; Mihajlidi, Tatjana A.

    2009-10-01

    In this paper, we have investigated the temperature dependence of dielectric properties (relative dielectric permeabilities and dielectric tangents of losses) for woven fabrics of hemp, jute, flax, cotton, polyester (PES), cotton-PES mixture, and wool. The measurements have been carried out at a temperature range from -50 to 50 °C in the electric periodic field at a frequency 1 MHz in vacuum. For the same specimens, the values of the dielectric properties have also been measured at an air temperature of 21 °C and at relative humidities of 40%, 60%, and 80%. At different frequencies from 80 kHz to 5 MHz, the dielectric properties have been measured at a relative humidity of 40% and at a temperature of 21 °C. An investigation of the dielectric properties of woven fabrics can provide a better understanding of the relation between the dielectric properties of woven fabrics and the different raw material compositions, temperatures, relative air humidities, and frequencies for specimens. Hence, this investigation helps to improve textile material properties.

  16. Dielectric Heaters for Testing Spacecraft Nuclear Reactors

    NASA Technical Reports Server (NTRS)

    Sims, William Herbert; Bitteker, Leo; Godfroy, Thomas

    2006-01-01

    A document proposes the development of radio-frequency-(RF)-driven dielectric heaters for non-nuclear thermal testing of the cores of nuclear-fission reactors for spacecraft. Like the electrical-resistance heaters used heretofore for such testing, the dielectric heaters would be inserted in the reactors in place of nuclear fuel rods. A typical heater according to the proposal would consist of a rod of lossy dielectric material sized and shaped like a fuel rod and containing an electrically conductive rod along its center line. Exploiting the dielectric loss mechanism that is usually considered a nuisance in other applications, an RF signal, typically at a frequency .50 MHz and an amplitude between 2 and 5 kV, would be applied to the central conductor to heat the dielectric material. The main advantage of the proposal is that the wiring needed for the RF dielectric heating would be simpler and easier to fabricate than is the wiring needed for resistance heating. In some applications, it might be possible to eliminate all heater wiring and, instead, beam the RF heating power into the dielectric rods from external antennas.

  17. New trends in Brunner's relation: dielectric levels

    NASA Astrophysics Data System (ADS)

    Trouiller, Yorick; Didiergeorges, Anne; Fanget, Gilles L.; Laviron, Cyrille; Comboure, Corinne; Quere, Yves

    1999-07-01

    The goal of this paper is to understand the optical phenomena at dielectric levels. The purpose is also to quantify the impact of dielectric and resist thickness variations on the CD range with and without Bottom Anti Reflective COating (BARC). First we will show how all dielectric levels can be reduced to the stack metal/oxide/BARC/resist, and what are the contributions to resists and dielectric thickness range for each levels. Then a simple model will be developed to understand CD variation in this tack: by extending the Perot/Fabry model to the dielectric levels, developed by Brunner for the gate level, we can obtain a simple relation between the CD variation and all parameters. Experimentally CD variation for Damascene line level on 0.18micrometers technology has been measured depending on oxide thickness and resist thickness and can confirm this model. UV5 resist, AR2 BARC from Shipley and Top ARC from JSR have been used for these experiments. The main conclusions are: (1) Depending on your dielectric deposition and CMP processes, if resist thickness is controlled, a standard BARC process used for the gate is adapted to remove oxide thickness variation influence providing the optimized resist thickness is used. (2) If both resist thickness and dielectric thickness are uncontrolled, a more absorbent BARC is required.

  18. Microwave dielectric behavior of vegetation material

    NASA Technical Reports Server (NTRS)

    Elrayes, Mohamed A.; Ulaby, Fawwaz T.

    1987-01-01

    The microwave dielectric behavior of vegetation was examined through the development of theoretical models involving dielectric dispersion by both bound and free water and supported by extensive dielectric measurements conducted over a wide range of conditions. The experimental data were acquired using an open-ended coaxial probe that was developed for sensing the dielectric constant of thin layers of materials, such as leaves, from measurements of the complex reflection coefficient using a network analyzer. The probe system was successfully used to record the spectral variation of the dielectric constant over a wide frequency range extending from 0.5 to 20.4 GHz at numerous temperatures between -40 to +40 C. The vegetation samples were measured over a wide range of moisture conditions. To model the dielectric spectrum of the bound water component of the water included in vegetation, dielectric measurements were made for several sucrose-water solutions as analogs for the situation in vegetation. The results were used in conjunction with the experimental data for leaves to determine some of the constant coefficients in the theoretical models. Two models, both of which provide good fit to the data, are proposed.

  19. Tuning sound with soft dielectrics

    NASA Astrophysics Data System (ADS)

    Bortot, Eliana; Shmuel, Gal

    2017-04-01

    Soft dielectric tubes undergo large deformations when subjected to radial voltage. Using the theory of nonlinear electroelasticity, we investigate how voltage-controlled deformations of these tubes in an array alter acoustic wave propagation through it. We show that the propagation is annihilated across a certain audible frequency range, referred to as a sonic band gap. We carry out a numerical study, to find that the band gap depends nonlinearly on the voltage, owing to geometrical and material nonlinearities. By analyzing different mechanical constraints, we demonstrate that snap-through instabilities resulting from these nonlinearities can be harnessed to achieve sharp transitions in the gap width. Our conclusions hint at a new strategy to adaptively filter sound using a simple control parameter—an applied voltage.

  20. Dielectric-constant gas thermometry

    NASA Astrophysics Data System (ADS)

    Gaiser, Christof; Zandt, Thorsten; Fellmuth, Bernd

    2015-10-01

    The principles, techniques and results from dielectric-constant gas thermometry (DCGT) are reviewed. Primary DCGT with helium has been used for measuring T-T90 below the triple point of water (TPW), where T is the thermodynamic temperature and T90 is the temperature on the international temperature scale of 1990 (ITS-90), and, in an inverse regime with T as input quantity, for determining the Boltzmann constant at the TPW. Furthermore, DCGT allows the determination of several important material properties including the polarizability of neon and argon as well as the virial coefficients of helium, neon, and argon. With interpolating DCGT (IDCGT), the ITS-90 has been approximated in the temperature range from 4 K to 25 K. An overview and uncertainty budget for each of these applications of DCGT is provided, accompanied by corroborating evidence from the literature or, for IDCGT, a CIPM key comparison.

  1. Virtual gap dielectric wall accelerator

    DOEpatents

    Caporaso, George James; Chen, Yu-Jiuan; Nelson, Scott; Sullivan, Jim; Hawkins, Steven A

    2013-11-05

    A virtual, moving accelerating gap is formed along an insulating tube in a dielectric wall accelerator (DWA) by locally controlling the conductivity of the tube. Localized voltage concentration is thus achieved by sequential activation of a variable resistive tube or stalk down the axis of an inductive voltage adder, producing a "virtual" traveling wave along the tube. The tube conductivity can be controlled at a desired location, which can be moved at a desired rate, by light illumination, or by photoconductive switches, or by other means. As a result, an impressed voltage along the tube appears predominantly over a local region, the virtual gap. By making the length of the tube large in comparison to the virtual gap length, the effective gain of the accelerator can be made very large.

  2. Femtosecond optomagnetism in dielectric antiferromagnets

    NASA Astrophysics Data System (ADS)

    Bossini, D.; Rasing, Th

    2017-02-01

    Optical femtosecond manipulation of magnetic order is attractive for the development of new concepts for ultrafast magnetic recording. Theoretical and experimental investigations in this research area aim at establishing a physical understanding of magnetic media in light-induced non-equilibrium states. Such a quest requires one to adjust the theory of magnetism, since the thermodynamical concepts of elementary excitations and spin alignment determined by the exchange interaction are not applicable on the femtosecond time-scale after the photo-excitation. Here we report some key milestones concerning the femtosecond optical control of spins in dielectric antiferromagnets, whose spin dynamics is by nature faster than that of ferromagnets and can be triggered even without any laser heating. The recent progress of the opto-magnetic effect in the sub-wavelength regime makes this exciting research area even more promising, in terms of both fundamental breakthroughs and technological perspectives.

  3. Standards for dielectric elastomer transducers

    NASA Astrophysics Data System (ADS)

    Carpi, Federico; Anderson, Iain; Bauer, Siegfried; Frediani, Gabriele; Gallone, Giuseppe; Gei, Massimiliano; Graaf, Christian; Jean-Mistral, Claire; Kaal, William; Kofod, Guggi; Kollosche, Matthias; Kornbluh, Roy; Lassen, Benny; Matysek, Marc; Michel, Silvain; Nowak, Stephan; O'Brien, Benjamin; Pei, Qibing; Pelrine, Ron; Rechenbach, Björn; Rosset, Samuel; Shea, Herbert

    2015-10-01

    Dielectric elastomer transducers consist of thin electrically insulating elastomeric membranes coated on both sides with compliant electrodes. They are a promising electromechanically active polymer technology that may be used for actuators, strain sensors, and electrical generators that harvest mechanical energy. The rapid development of this field calls for the first standards, collecting guidelines on how to assess and compare the performance of materials and devices. This paper addresses this need, presenting standardized methods for material characterisation, device testing and performance measurement. These proposed standards are intended to have a general scope and a broad applicability to different material types and device configurations. Nevertheless, they also intentionally exclude some aspects where knowledge and/or consensus in the literature were deemed to be insufficient. This is a sign of a young and vital field, whose research development is expected to benefit from this effort towards standardisation.

  4. Near-infrared trapped mode magnetic resonance in an all-dielectric metamaterial.

    PubMed

    Zhang, Jianfa; MacDonald, Kevin F; Zheludev, Nikolay I

    2013-11-04

    Optical responses in conventional metamaterials based on plasmonic metal nanostructures are inevitably accompanied by Joule losses, which obstruct practical applications by limiting resonance quality factors and compromising the efficiency of metamaterial devices. Here we experimentally demonstrate a fully-dielectric metamaterial that exhibits a 'trapped mode' resonance at optical frequencies, founded upon the excitation by incident light of anti-parallel displacement currents in meta-molecules comprising pairs of parallel, geometrically dissimilar dielectric nano-bars. The phenomenon is demonstrated in the near-infrared part of the spectrum using silicon, showing that in principle strong, lossless resonant responses are possible anywhere in the optical spectral range.

  5. Photoinduced Giant Dielectric Constant in Lead Halide Perovskite Solar Cells.

    PubMed

    Juarez-Perez, Emilio J; Sanchez, Rafael S; Badia, Laura; Garcia-Belmonte, Germá; Kang, Yong Soo; Mora-Sero, Ivan; Bisquert, Juan

    2014-07-03

    Organic-inorganic lead trihalide perovskites have emerged as an outstanding photovoltaic material that demonstrated a high 17.9% conversion efficiency of sunlight to electricity in a short time. We have found a giant dielectric constant (GDC) phenomenon in these materials consisting on a low frequency dielectric constant in the dark of the order of ε0 = 1000. We also found an unprecedented behavior in which ε0 further increases under illumination or by charge injection at applied bias. We observe that ε0 increases nearly linearly with the illumination intensity up to an additional factor 1000 under 1 sun. Measurement of a variety of samples of different morphologies, compositions, and different types of contacts shows that the GDC is an intrinsic property of MAPbX3 (MA = CH3NH3(+)). We hypothesize that the large dielectric response is induced by structural fluctuations. Photoinduced carriers modify the local unit cell equilibrium and change the polarizability, assisted by the freedom of rotation of MA. The study opens a way for the understanding of a key aspect of the photovoltaic operation of high efficiency perovskite solar cells.

  6. Antenna dielectric sealing process characterization. Final report

    SciTech Connect

    Busby, M.L.; Yerganian, S.S.

    1994-04-01

    An antenna assembly experienced leak test failures during TMS testing. The leaks were occurring between the dielectric and housing. The antenna assembly dielectric is sealed into a nickel-plated aluminum housing using a tin catalyzed condensation cure silicone (RTV). In preparation for sealing, the dielectric and housing are chemically cleaned and then plasma cleaned. The surfaces to be sealed are primed, RTV is applied, and the RTV is cured in a humidity chamber. This report is an evaluation of the production process and includes FEM analysis and process characterization and control (PC&C) data.

  7. Exploring Hamiltonian dielectric solvent molecular dynamics

    NASA Astrophysics Data System (ADS)

    Bauer, Sebastian; Tavan, Paul; Mathias, Gerald

    2014-09-01

    Hamiltonian dielectric solvent (HADES) is a recent method [7,25], which enables Hamiltonian molecular dynamics (MD) simulations of peptides and proteins in dielectric continua. Sample simulations of an α-helical decapeptide with and without explicit solvent demonstrate the high efficiency of HADES-MD. Addressing the folding of this peptide by replica exchange MD we study the properties of HADES by comparing melting curves, secondary structure motifs and salt bridges with explicit solvent results. Despite the unoptimized ad hoc parametrization of HADES, calculated reaction field energies correlate well with numerical grid solutions of the dielectric Poisson equation.

  8. Epoxy Foam Encapsulants: Processing and Dielectric Characterization

    SciTech Connect

    Linda Domeier; Marion Hunter

    1999-01-01

    The dielectric performance of epoxy foams was investigated to determine if such materials might provide advantages over more standard polyurethane foams in the encapsulation of electronic assemblies. Comparisons of the dielectric characteristics of epoxy and urethane encapsulant foams found no significant differences between the two resin types and no significant difference between as-molded and machined foams. This study specifically evaluated the formulation and processing of epoxy foams using simple methylhydrosiloxanes as the flowing agent and compared the dielectric performance of those to urethane foams of similar density.

  9. Dielectric gas mixtures containing sulfur hexafluoride

    DOEpatents

    Cooke, Chathan M.

    1979-01-01

    Electrically insulating gaseous media of unexpectedly high dielectric strength comprised of mixtures of two or more dielectric gases are disclosed wherein the dielectric strength of at least one gas in each mixture increases at less than a linear rate with increasing pressure and the mixture gases are present in such proportions that the sum of their electrical discharge voltages at their respective partial pressures exceeds the electrical discharge voltage of each individual gas at the same temperature and pressure as that of the mixture.

  10. Dielectric constants of soils at microwave frequencies

    NASA Technical Reports Server (NTRS)

    Geiger, F. E.; Williams, D.

    1972-01-01

    A knowledge of the complex dielectric constant of soils is essential in the interpretation of microwave airborne radiometer data of the earth's surface. Measurements were made at 37 GHz on various soils from the Phoenix, Ariz., area. Extensive data have been obtained for dry soil and soil with water content in the range from 0.6 to 35 percent by dry weight. Measurements were made in a two arm microwave bridge and results were corrected for reflections at the sample interfaces by solution of the parallel dielectric plate problem. The maximum dielectric constants are about a factor of 3 lower than those reported for similar soils at X-band frequencies.

  11. Porous low dielectric constant materials for microelectronics.

    PubMed

    Baklanov, Mikhail R; Maex, Karen

    2006-01-15

    Materials with a low dielectric constant are required as interlayer dielectrics for the on-chip interconnection of ultra-large-scale integration devices to provide high speed, low dynamic power dissipation and low cross-talk noise. The selection of chemical compounds with low polarizability and the introduction of porosity result in a reduced dielectric constant. Integration of such materials into microelectronic circuits, however, poses a number of challenges, as the materials must meet strict requirements in terms of properties and reliability. These issues are the subject of the present paper.

  12. Tunable Dielectric Materials and Devices for Broadband Wireless Communications

    NASA Technical Reports Server (NTRS)

    Mueller, Carl H.; Miranda, Felix A.; Dayton, James A. (Technical Monitor)

    1998-01-01

    Wireless and satellite communications are a rapidly growing industries which are slated for explosive growth into emerging countries as well as countries with advanced economies. The dominant trend in wireless communication systems is towards broadband applications such as multimedia file transfer, video transmission and Internet access. These applications require much higher data transmission rates than those currently used for voice transmission applications. To achieve these higher data rates, substantially larger bandwidths and higher carrier frequencies are required. A key roadblock to implementing these systems at K-band (18-26.5 GHz) and Ka-band (26.5-40 GHz) is the need to develop hardware which meets the requirements for high data rate transmission in a cost effective manner. In this chapter, we report on the status of tunable dielectric thin films for devices, such as resonators, filters, phased array antennas, and tunable oscillators, which utilize nonlinear tuning in the control elements. Paraelectric materials such as Barium Strontium Titanate ((Ba, Sr)TiO3) have dielectric constants which can be tuned by varying the magnitude of the electric field across the material. Therefore, these materials can be used to control the frequency and/or phase response of various devices such as electronically steerable phased array antennas, oscillators, and filters. Currently, tunable dielectric devices are being developed for applications which require high tunability, low loss, and good RF power-handling capabilities at microwave and millimeter-wave frequencies. These properties are strongly impacted by film microstructure and device design, and considerable developmental work is still required. However, in the last several years enormous progress has occurred in this field, validating the potential of tunable dielectric technology for broadband wireless communication applications. In this chapter we summarize how film processing techniques, microwave test

  13. Dielectric fluctuations in force microscopy: noncontact friction and frequency jitter.

    PubMed

    Yazdanian, Showkat M; Marohn, John A; Loring, Roger F

    2008-06-14

    Electric force microscopy, in which a charged probe oscillates tens to hundreds of nanometers above a sample surface, provides direct mechanical detection of relaxation in molecular materials. Noncontact friction, the damping of the probe's motions, reflects the dielectric function at the resonant frequency of the probe, while fluctuations in the probe frequency are induced by slower molecular motions. We present a unified theoretical picture of both measurements, which relates the noncontact friction and the power spectrum of the frequency jitter to dielectric properties of the sample and to experimental geometry. Each observable is related to an equilibrium correlation function associated with electric field fluctuations, which is determined by two alternative, complementary strategies for a dielectric continuum model of the sample. The first method is based on the calculation of a response function associated with the polarization of the dielectric by a time-varying external charge distribution. The second approach employs a stochastic form of Maxwell's equations, which incorporate a fluctuating electric polarization, to compute directly the equilibrium correlation function in the absence of an external charge distribution. This approach includes effects associated with the propagation of radiation. In the experimentally relevant limit that the tip-sample distance is small compared to pertinent wavelengths of radiation, the two methods yield identical results. Measurements of the power spectrum of frequency fluctuations of an ultrasensitive cantilever together with measurements of the noncontact friction over a poly(methylmethacrylate) film are used to estimate the minimum experimentally detectable frequency jitter. The predicted jitter for this polymer is shown to exceed this threshold, demonstrating the feasibility of the measurement.

  14. Dielectric fluctuations in force microscopy: Noncontact friction and frequency jitter

    PubMed Central

    Yazdanian, Showkat M.; Marohn, John A.; Loring, Roger F.

    2008-01-01

    Electric force microscopy, in which a charged probe oscillates tens to hundreds of nanometers above a sample surface, provides direct mechanical detection of relaxation in molecular materials. Noncontact friction, the damping of the probe’s motions, reflects the dielectric function at the resonant frequency of the probe, while fluctuations in the probe frequency are induced by slower molecular motions. We present a unified theoretical picture of both measurements, which relates the noncontact friction and the power spectrum of the frequency jitter to dielectric properties of the sample and to experimental geometry. Each observable is related to an equilibrium correlation function associated with electric field fluctuations, which is determined by two alternative, complementary strategies for a dielectric continuum model of the sample. The first method is based on the calculation of a response function associated with the polarization of the dielectric by a time-varying external charge distribution. The second approach employs a stochastic form of Maxwell’s equations, which incorporate a fluctuating electric polarization, to compute directly the equilibrium correlation function in the absence of an external charge distribution. This approach includes effects associated with the propagation of radiation. In the experimentally relevant limit that the tip-sample distance is small compared to pertinent wavelengths of radiation, the two methods yield identical results. Measurements of the power spectrum of frequency fluctuations of an ultrasensitive cantilever together with measurements of the noncontact friction over a poly(methylmethacrylate) film are used to estimate the minimum experimentally detectable frequency jitter. The predicted jitter for this polymer is shown to exceed this threshold, demonstrating the feasibility of the measurement. PMID:18554042

  15. Mechanistic Study of Plasma Damage of Low k Dielectric Surfaces

    SciTech Connect

    Bao Junjing; Shi Hualiang; Huang Huai; Ho, P. S.; Liu Junjun; Goodner, M. D.; Moinpour, M.; Kloster, G. M.

    2007-10-31

    Plasma damage to low k dielectric materials was investigated from a mechanistic point of view. Low k dielectric films were treated by plasma Ar, O{sub 2}, N{sub 2}/H{sub 2}, N{sub 2} and H{sub 2} in a standard RIE chamber and the damage was characterized by Angle Resolved X-ray Photoelectron Spectroscopy (ARXPS), X-Ray Reflectivity (XRR), Fourier Transform Infrared Spectroscopy (FTIR) and Contact Angle measurements. Both carbon depletion and surface densification were observed on the top surface of damaged low k materials while the bulk remained largely unaffected. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. A downstream hybrid plasma source with separate ions and atomic radicals was employed to study their respective roles in the plasma damage process. Ions were found to play a more important role in the plasma damage process. The dielectric constant of low k materials can increase up to 20% due to plasma damage and we attributed this to the removal of the methyl group making the low k surface hydrophilic. Annealing was generally effective in mitigating moisture uptake to restore the k value but the recovery was less complete for higher energy plasmas. Quantum chemistry calculation confirmed that physisorbed water in low k materials induces the largest increase of dipole moments in comparison with changes of surface bonding configurations, and is primarily responsible for the dielectric constant increase.

  16. Effect of combined external uniaxial stress and dc bias on the dielectric property of BaTiO3-based dielectrics in multilayer ceramic capacitor: thermodynamics and experiments

    NASA Astrophysics Data System (ADS)

    Yang, Gang; Yue, Zhenxing; Sun, Tieyu; Gou, Huanlin; Li, Longtu

    2008-02-01

    The dielectric properties of (Nb, Y)-doped BaTiO3 in a multilayer ceramic capacitor (MLCC) under combined external uniaxial compressive stress and dc bias field were investigated at room temperature by using a modified Ginsburg-Landau-Devonshire thermodynamic theory and the dielectric measurement. It is found that although dc bias decreases the dielectric properties dominantly, the influence of the external uniaixial compressive stress should not be neglected. When applied along a direction perpendicular to the internal electrode layer in the MLCC, the external uniaixal compressive stress will strengthen the negative effect of dc bias. In contrast, the external uniaxial compressive stress along a direction parallel to the internal electrode layer in the MLCC will increase the dielectric permittivity under dc bias field, i.e. improve the ɛ-V response of the MLCC. Furthermore, although there is a difference between the calculated permittivity and the measured permittivity, the effects of the combined external uniaxial compressive stress and dc bias field on the dielectric permittivity described through two approaches are in good agreement.

  17. Semimetallization of dielectrics in strong optical fields

    DOE PAGES

    Kwon, Ojoon; Paasch-Colberg, Tim; Apalkov, Vadym; ...

    2016-02-18

    At the heart of ever growing demands for faster signal processing is ultrafast charge transport and control by electromagnetic fields in semiconductors. Intense optical fields have opened fascinating avenues for new phenomena and applications in solids. Because the period of optical fields is on the order of a femtosecond, the current switching and its control by an optical field may pave a way to petahertz optoelectronic devices. Lately, a reversible semimetallization in fused silica on a femtosecond time scale by using a few-cycle strong field (~1 V/Å) is manifested. The strong Wannier-Stark localization and Zener-type tunneling were expected to drivemore » this ultrafast semimetallization. Wider spread of this technology demands better understanding of whether the strong field behavior is universally similar for different dielectrics. Here we employ a carrier-envelope-phase stabilized, few-cycle strong optical field to drive the semimetallization in sapphire, calcium fluoride and quartz and to compare this phenomenon and show its remarkable similarity between them. The similarity in response of these materials, despite the distinguishable differences in their physical properties, suggests the universality of the physical picture explained by the localization of Wannier-Stark states. Lastly, our results may blaze a trail to PHz-rate optoelectronics.« less

  18. Spectral curve fitting of dielectric constants

    NASA Astrophysics Data System (ADS)

    Ruzi, M.; Ennis, C.; Robertson, E. G.

    2017-01-01

    Optical constants are important properties governing the response of a material to incident light. It follows that they are often extracted from spectra measured by absorbance, transmittance or reflectance. One convenient method to obtain optical constants is by curve fitting. Here, model curves should satisfy Kramer-Kronig relations, and preferably can be expressed in closed form or easily calculable. In this study we use dielectric constants of three different molecular ices in the infrared region to evaluate four different model curves that are generally used for fitting optical constants: (1) the classical damped harmonic oscillator, (2) Voigt line shape, (3) Fourier series, and (4) the Triangular basis. Among these, only the classical damped harmonic oscillator model strictly satisfies the Kramer-Kronig relation. If considering the trade-off between accuracy and speed, Fourier series fitting is the best option when spectral bands are broad while for narrow peaks the classical damped harmonic oscillator and the Triangular basis fitting model are the best choice.

  19. Semimetallization of dielectrics in strong optical fields

    SciTech Connect

    Kwon, Ojoon; Apalkov, Vadym; Kim, Bum -Kyu; Kim, Ju -Jin; Stockman, Mark I.; Kim, D.

    2016-02-18

    At the heart of ever growing demands for faster signal processing is ultrafast charge transport and control by electromagnetic fields in semiconductors. Intense optical fields have opened fascinating avenues for new phenomena and applications in solids. Because the period of optical fields is on the order of a femtosecond, the current switching and its control by an optical field may pave a way to petahertz optoelectronic devices. Lately, a reversible semimetallization in fused silica on a femtosecond time scale by using a few-cycle strong field (~1 V/Å) is manifested. The strong Wannier-Stark localization and Zener-type tunneling were expected to drive this ultrafast semimetallization. Wider spread of this technology demands better understanding of whether the strong field behavior is universally similar for different dielectrics. Here we employ a carrier-envelope-phase stabilized, few-cycle strong optical field to drive the semimetallization in sapphire, calcium fluoride and quartz and to compare this phenomenon and show its remarkable similarity between them. The similarity in response of these materials, despite the distinguishable differences in their physical properties, suggests the universality of the physical picture explained by the localization of Wannier-Stark states. Lastly, our results may blaze a trail to PHz-rate optoelectronics.

  20. Semimetallization of dielectrics in strong optical fields

    NASA Astrophysics Data System (ADS)

    Kwon, Ojoon; Paasch-Colberg, Tim; Apalkov, Vadym; Kim, Bum-Kyu; Kim, Ju-Jin; Stockman, Mark I.; Kim, D.

    2016-02-01

    At the heart of ever growing demands for faster signal processing is ultrafast charge transport and control by electromagnetic fields in semiconductors. Intense optical fields have opened fascinating avenues for new phenomena and applications in solids. Because the period of optical fields is on the order of a femtosecond, the current switching and its control by an optical field may pave a way to petahertz optoelectronic devices. Lately, a reversible semimetallization in fused silica on a femtosecond time scale by using a few-cycle strong field (~1 V/Å) is manifested. The strong Wannier-Stark localization and Zener-type tunneling were expected to drive this ultrafast semimetallization. Wider spread of this technology demands better understanding of whether the strong field behavior is universally similar for different dielectrics. Here we employ a carrier-envelope-phase stabilized, few-cycle strong optical field to drive the semimetallization in sapphire, calcium fluoride and quartz and to compare this phenomenon and show its remarkable similarity between them. The similarity in response of these materials, despite the distinguishable differences in their physical properties, suggests the universality of the physical picture explained by the localization of Wannier-Stark states. Our results may blaze a trail to PHz-rate optoelectronics.

  1. Semimetallization of dielectrics in strong optical fields

    PubMed Central

    Kwon, Ojoon; Paasch-Colberg, Tim; Apalkov, Vadym; Kim, Bum-Kyu; Kim, Ju-Jin; Stockman, Mark I.; Kim, D.

    2016-01-01

    At the heart of ever growing demands for faster signal processing is ultrafast charge transport and control by electromagnetic fields in semiconductors. Intense optical fields have opened fascinating avenues for new phenomena and applications in solids. Because the period of optical fields is on the order of a femtosecond, the current switching and its control by an optical field may pave a way to petahertz optoelectronic devices. Lately, a reversible semimetallization in fused silica on a femtosecond time scale by using a few-cycle strong field (~1 V/Å) is manifested. The strong Wannier-Stark localization and Zener-type tunneling were expected to drive this ultrafast semimetallization. Wider spread of this technology demands better understanding of whether the strong field behavior is universally similar for different dielectrics. Here we employ a carrier-envelope-phase stabilized, few-cycle strong optical field to drive the semimetallization in sapphire, calcium fluoride and quartz and to compare this phenomenon and show its remarkable similarity between them. The similarity in response of these materials, despite the distinguishable differences in their physical properties, suggests the universality of the physical picture explained by the localization of Wannier-Stark states. Our results may blaze a trail to PHz-rate optoelectronics. PMID:26888147

  2. Dielectric and specific heat relaxations in vapor deposited glycerol

    NASA Astrophysics Data System (ADS)

    Kasina, A.; Putzeys, T.; Wübbenhorst, M.

    2015-12-01

    conclusively explains the extraordinary high kinetic stability of the MROL state, its specific calorimetric signature, the enhanced strength, and apparent slow-down of the dielectric α-relaxation. In this new picture, the incredibly slow and strengthened dielectric response is ascribed to driven rotational diffusion of whole RPCs, a mechanism that perfectly couples to the relaxation time of the "normal" glycerol fraction. First considerations based on the strength and the retardation of the dielectric RPCs' response yield independently a size estimate for the RPCs in the order of 4-5 nm. Finally, we have discussed possible crystallisation and reorganisation effects, which give rise to pronounced out-of phase components of the specific heat at higher temperatures.

  3. Estimating the extent of surface oxidation by measuring the porosity dependent dielectrics of oxygenated porous silicon [rapid communication

    NASA Astrophysics Data System (ADS)

    Pan, L. K.; Sun, Chang Q.; Li, C. M.

    2005-02-01

    Surface oxidation and porosity variation play significant roles in the dielectric performance of porous silicon (PS) yet discriminating the contribution of these events is a challenge. Here we present an analytical solution that covers contributions from the components of silicon oxide surface, silicon backbone and voids using a serial-parallel capacitance structure. Agreement between modeling predictions and measurement has been realized, which turns out an effective method that enables us to estimate the extent of surface oxidation of a specimen by measuring the porosity dependent dielectric response of the chemically passivated PS, and provides guidelines that could be useful for designing dielectric porous structures with surface oxidation.

  4. A model for the scattering of high-frequency electromagnetic fields from dielectrics exhibiting thermally-activated electrical losses

    NASA Technical Reports Server (NTRS)

    Hann, Raiford E.

    1991-01-01

    An equivalent circuit model (ECM) approach is used to predict the scattering behavior of temperature-activated, electrically lossy dielectric layers. The total electrical response of the dielectric (relaxation + conductive) is given by the ECM and used in combination with transmission line theory to compute reflectance spectra for a Dallenbach layer configuration. The effects of thermally-activated relaxation processes on the scattering properties is discussed. Also, the effect of relaxation and conduction activation energy on the electrical properties of the dielectric is described.

  5. Metal-dielectric hybrid surfaces as integrated optoelectronic interfaces

    DOEpatents

    Narasimhan, Vijay K.; Hymel, Thomas M.; Lai, Ruby A.; Cui, Yi

    2017-01-03

    An optoelectronic device has a hybrid metal-dielectric optoelectronic interface including an array of nanoscale dielectric resonant elements (e.g., nanopillars), and a metal film disposed between the dielectric resonant elements and below a top surface of the resonant elements such that the dielectric resonant elements protrude through the metal film. The device may also include an anti-reflection coating. The device may further include a metal film layer on each of the dielectric resonant elements.

  6. Laboratory measurement of the complex dielectric constant of soils

    NASA Technical Reports Server (NTRS)

    Wiebe, M. L.

    1971-01-01

    The dielectric constant of a material is an extremely important parameter when considering passive radiometric remote sensing applications. This is because the emitted energy measured by a microwave radiometer is dependent on the dielectric constant of the surface being scanned. Two techniques of measuring dielectric constants are described. The first method involves a dielectric located in air. The second method uses basically the same theoretical approach, but the dielectric under consideration is located inside a section of waveguide.

  7. Dielectric Measurements of Millimeter-Wave Materials

    NASA Astrophysics Data System (ADS)

    Afsar, M. N.

    1984-12-01

    It is no longer necessary to use extrapolated microwave dielectric data when designing millimeter-wave components, devices, and systems. Precision measurements can now be made to generate highly accurate millimeter-wave (5 to 1/2 mm) continuous spectra on complex refractive index, complex dielectric permittivity, and loss tangent for a variety of materials such as common ceramics, semiconductors, crystalline, and glassy materials. The continuous spectra reveal an increase in dielectric loss with increase in frequency in this wavelength range for most materials. Reliable measurements also reveal that the method of preparation of nominally identical specimens can change the dielectric losses by many factors. These broad-band measurements were carried out employing dispersive Fourier transform spectroscopy applied to a modular two-beam polarization interferometer. Data obtained with Fabry-Perot open resonator methods at wavelengths of 5 mm and longer will also be compared.

  8. Characterization of photonic nanojets in dielectric microdisks

    NASA Astrophysics Data System (ADS)

    Liu, Cheng-Yang; Chen, Chien-Jung

    2015-09-01

    The direct imaging of photonic nanojets in different dielectric microdisks illuminated by a laser source is reported. The SiO2 and Si3N4 microdisks are of height 650 nm with diameters ranging from 3 μm to 8 μm. The finite-difference time-domain calculation is used to execute the numerical simulation for the photonic nanojets in the dielectric microdisks. The photonic nanojet measurements are performed with a scanning optical microscope system. The photonic nanojets with high intensity spots and low divergence are observed in the dielectric microdisks illuminated from the side with laser source of wavelengths 405 nm, 532 nm and 671 nm. The experimental results of key parameters are compared to the simulations and in agreement with theoretical results. Our studies show that photonic nanojets can be efficiently created by a dielectric microdisk and straightforwardly applied to nano-photonics circuit.

  9. Chemically prepared lead magnesium niobate dielectrics

    SciTech Connect

    Tuttle, B.A.; Voigt, J.A.; Sipola, D.L.; Olson, W.R.; Goy, D.M.

    1998-11-01

    A chemical solution powder synthesis technique has been developed that produces first, uniform powders of lead magnesium niobate (PMN) with 60 to 80 nm crystallite size. The synthesis technique was based on the dissolution of lead acetate and alkoxide precursors in acetic acid followed by precipitation with oxalic acid/propanol solutions. Lead magnesium niobate ceramics fabricated from these chemically derived powders had smaller, more uniform grain size and higher dielectric constants than ceramics fabricated from mixed oxide powders that were processed under similar thermal conditions. Chem-prep PMN dielectrics with peak dielectric constants greater than 22,000 and polarizations in excess of 29 {micro}C/cm{sup 2} were obtained for 1,100 C firing treatments. Substantial decreases in dielectric constant and polarization were measured for chemically prepared PMN ceramics fired at lower temperatures, consistent with previous work on mixed oxide materials.

  10. Composite Dielectric Materials for Electrical Switching

    SciTech Connect

    Modine, F.A.

    1999-04-25

    Composites that consist of a dielectric host containing a particulate conductor as a second phase are of interest for electrical switching applications. Such composites are "smart" materials that can function as either voltage or current limiters, and the difference in fimction depends largely upon whether the dielectric is filled to below or above the percolation threshold. It also is possible to combine current and voltage limiting in a single composite to make a "super-smart" material.

  11. Transition Control with Dielectric Barrier Discharge Plasmas

    DTIC Science & Technology

    2013-01-01

    AFRL-AFOSR-UK-TR-2013-0007 Transition Control with Dielectric Barrier Discharge Plasmas Professor Cameron Tropea...Discharge Plasmas 5a. CONTRACT NUMBER FA8655-11-1-3067 5b. GRANT NUMBER Grant 11-3067 5c. PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S...15. SUBJECT TERMS EOARD, Plasma Aerodynamic, transition control, Dielectric Barrier 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

  12. Low-loss coupling to dielectric resonators

    NASA Technical Reports Server (NTRS)

    Hearn, C. P.; Bradshaw, E. S.; Trew, R. J.; Hefner, B. B., Jr.

    1991-01-01

    A compilation is presented of experimental observations and arguments concerning the use of dielectric resonators in applications requiring both tight coupling (beta greater than 10) and high unloaded Q, such as low loss bandpass filters. The microstrip coupled dielectric resonator is the primary focus, but an alternative coupling technique is discussed and comparatively evaluated. It is concluded that coupling factors as large as 65 are achievable.

  13. Deep-Dielectric Charging - A Review.

    DTIC Science & Technology

    1985-05-24

    L. L., Kristiansen, M. , Marx, J., and Bowling, A. (1983) Pulse flashover of solid dielectrics in vacuum , IEEE Trans. Elect. Insul . , EI- 18:3 10-314...electric field pattern. These processes are expected to occur on spacecraft having exposed insulating surfaces which, at times, may be subject to energetic...dielectric near the surface where the electric field strength exceeds the experimentally determined prebreakdown level-1 of Z10 V cm for polymers. As an

  14. Low-Dielectric-Constant Polyimide Fibers

    NASA Technical Reports Server (NTRS)

    Dorogy, William E., Jr.; Proctor, K. Mason; St. Clair, Anne K.

    1994-01-01

    In experiments performed at NASA Langley Research Center, low-dielectric-constant polyimide fibers produced by use of resin extrusion. These fibers also have high thermal stability and good tensile properties. Useful in industrial and aerospace applications in which fibers required to have dielectric constants less than 3, high thermal stability, and tensile properties in range of those of standard textile fibers. Potential applications include use in printed circuit-boards and in aircraft composites.

  15. Method of casting patterned dielectric structures

    DOEpatents

    Poco, John F.; Hrubesh, Lawrence W.

    2001-01-01

    A pattern of dielectric structures are formed directly on a substrate in a single step using sol-gel chemistry and molding procedures. The resulting dielectric structures are useful in vacuum applications for electronic devices. Porous, lightweight structures having a high aspect ratio that are suitable for use as spacers between the faceplate and baseplate of a field emission display can be manufactured using this method.

  16. Radiative transfer in a plane stratified dielectric

    NASA Technical Reports Server (NTRS)

    Wilheit, T. T., Jr.

    1975-01-01

    A model is developed for calculating radiative transfer in a stratified dielectric. This model is used to show that the reflectivity of a stratified dielectric is primarily determined by gradients in the real part of the refractive index over distances on the order of 1/10 wavelength in the medium. The effective temperature of the medium is determined by the thermodynamic temperature profile over distances of the order delta T.

  17. Dispersion Characteristics of a Dielectric Loaded Waveguide,

    DTIC Science & Technology

    1984-07-30

    NATIONAL BUREAU OF STANOAODS-1963-A ., ’I A NSWC TR 84-338 00 In ’DISPERSION CHARACTERISTICS OF A SDIELECTRIC LOADED WAVEGUIDE By H. CROSBY J. CHOE Y...4. TITLE (and Subtitle) S. TYPE OF REPORT & PERIOD COVERED DISPERSION CHARACTERISTICS OF A DIELECTRIC LOADED WAVEGUIDE S. PERFORMING ORG. REPORT...SUPPLEMENTARY NOTES S. KEY WORDS (Continue on reverse aide it necessary and Identify by block number) Dielectric Loaded Waveguide ) " Resonant Cavity) a

  18. High Dielectric Constant Polymer Film Capacitors (PREPRINT)

    DTIC Science & Technology

    2010-02-01

    film, and the test of our first generation prototype capacitors . High-K Polymeric Dielectrics Commercial polypropylene (PP) capacitor film has a...1994). 2. Maurizio Rabuffi and Guido Picci, “Status Quo and Future Prospects for Metallized Polypropylene Energy Storage Capacitors ”, IEEE Trans...AFRL-RZ-WP-TP-2010-2126 HIGH DIELECTRIC CONSTANT POLYMER FILM CAPACITORS (PREPRINT) Shihai Zhang, Brian Zellers, Dean Anderson, Paul

  19. Strain tunable ferroelectric and dielectric properties of BaZrO{sub 3}

    SciTech Connect

    Zhang, Yajun; Liu, Man; Shimada, Takahiro; Kitamura, Takayuki; Wang, Jie

    2014-06-14

    The crucial role of epitaxial (in-plane) strain on the structural, electronic, energetic, ferroelectric, and dielectric properties of BaZrO{sub 3} (BZO) is investigated using density-functional theory calculations. We demonstrate that the BZO crystal subjected to a critical compressive (or tensile) strain exhibits non-trivial spontaneous polarization that is higher than that of well-known ferroelectrics BaTiO{sub 3}, while the BZO crystal is essentially paraelectric in the absence of strain. The electronic structure and Born-effective-charge analyses elucidate that the strain-induced paraelectric-to-ferroelectric transition is driven by the orbital hybridization of d-p electrons between zirconium and oxygen. Through the strain-induced paraelectric-to-ferroelectric phase transition, the dielectric response of BZO is significantly enhanced by the in-plane strain. The tensile strain increases the in-plane dielectric constant by a factor of seven with respect to that without the strain, while the compression tends to enhance the out-of-plane dielectric response. Therefore, strain engineering makes BZO an important electromechanical material due to the diversity in ferroelectric and dielectric properties.

  20. Linear and nonlinear optical properties of hybrid metallic–dielectric plasmonic nanoantennas

    PubMed Central

    Hentschel, Mario; Metzger, Bernd; Knabe, Bastian

    2016-01-01

    Summary We study the linear and nonlinear optical properties of hybrid metallic–dielectric plasmonic gap nanoantennas. Using a two-step-aligned electron beam lithography process, we demonstrate the ability to selectively and reproducibly fill the gap region of nanoantennas with dielectric nanoparticles made of lithium niobate (LiNbO3) with high efficiency. The linear optical properties of the antennas are modified due to the large refractive index of the material. This leads to a change in the coupling strength as well as an increase of the effective refractive index of the surrounding. The combination of these two effects causes a red- or blue-shift of the plasmonic modes, respectively. We find that the nonlinear optical properties of the combined system are only modified in the range of one order of magnitude. The observed changes in our experiments in the nonlinear emission can be traced to the changed dielectric environment and thus the modified linear optical properties. The intrinsic nonlinearity of the dielectric used is in fact small when compared to the nonlinearity of the metallic part of the hybrid antennas. Thus, the nonlinear signals generated by the antenna itself are dominant in our experiments. We demonstrate that the well-known nonlinear response of bulk dielectric materials cannot always straightforwardly be used to boost the nonlinear response of nanoscale antenna systems. Our results significantly deepen the understanding of these interesting hybrid systems and offer important guidelines for the design of nanoscale, nonlinear light sources. PMID:26925359

  1. Temperature dependent dielectric and electric modulus properties of ZnS nano particles

    NASA Astrophysics Data System (ADS)

    Ali, Hassan; Falak, Attia; Rafiq, M. A.; Khan, Usman; Karim, Shafqat; Nairan, Adeela; Jing, Tang; Sun, Yue; Sun, Sibai; Qian, Chenjiang; Xu, Xiulai

    2017-03-01

    A comprehensive study of the dielectric and electric modulus properties of Zinc Sulfide (ZnS) semiconductor nanoparticles has been conducted using impedance spectroscopy in the frequency range of 200 Hz to 2 MHz and over the temperature range of 300 K to 400 K. Microscopic analysis confirms the formation of spherical nanoparticles with an average size of ∼20 nm. Maxwell–Wagner–Sillars (MWS) interfacial polarization is responsible for the increase in dielectric permittivity and dielectric loss at lower frequencies. Increase in dielectric permittivity and dielectric loss has been observed with a rise in temperature. The electric modulus complex plane plot reveals the presence of the grain (bulk) effect and non-Debye type relaxation processes in the material. The non-Debye type processes have also been confirmed by the asymmetric relaxation peaks of the imaginary part of the electric modulus. The frequency dependent maximum of the imaginary part of the electric modulus follows the Arrhenius law with an activation energy of 0.13 eV. The modulus analysis also establishes that the hopping mechanism is responsible for electrical conduction in the ZnS nanoparticles.

  2. Linear and nonlinear optical properties of hybrid metallic-dielectric plasmonic nanoantennas.

    PubMed

    Hentschel, Mario; Metzger, Bernd; Knabe, Bastian; Buse, Karsten; Giessen, Harald

    2016-01-01

    We study the linear and nonlinear optical properties of hybrid metallic-dielectric plasmonic gap nanoantennas. Using a two-step-aligned electron beam lithography process, we demonstrate the ability to selectively and reproducibly fill the gap region of nanoantennas with dielectric nanoparticles made of lithium niobate (LiNbO3) with high efficiency. The linear optical properties of the antennas are modified due to the large refractive index of the material. This leads to a change in the coupling strength as well as an increase of the effective refractive index of the surrounding. The combination of these two effects causes a red- or blue-shift of the plasmonic modes, respectively. We find that the nonlinear optical properties of the combined system are only modified in the range of one order of magnitude. The observed changes in our experiments in the nonlinear emission can be traced to the changed dielectric environment and thus the modified linear optical properties. The intrinsic nonlinearity of the dielectric used is in fact small when compared to the nonlinearity of the metallic part of the hybrid antennas. Thus, the nonlinear signals generated by the antenna itself are dominant in our experiments. We demonstrate that the well-known nonlinear response of bulk dielectric materials cannot always straightforwardly be used to boost the nonlinear response of nanoscale antenna systems. Our results significantly deepen the understanding of these interesting hybrid systems and offer important guidelines for the design of nanoscale, nonlinear light sources.

  3. Thin film dielectric composite materials

    DOEpatents

    Jia, Quanxi; Gibbons, Brady J.; Findikoglu, Alp T.; Park, Bae Ho

    2002-01-01

    A dielectric composite material comprising at least two crystal phases of different components with TiO.sub.2 as a first component and a material selected from the group consisting of Ba.sub.1-x Sr.sub.x TiO.sub.3 where x is from 0.3 to 0.7, Pb.sub.1-x Ca.sub.x TiO.sub.3 where x is from 0.4 to 0.7, Sr.sub.1-x Pb.sub.x TiO.sub.3 where x is from 0.2 to 0.4, Ba.sub.1-x Cd.sub.x TiO.sub.3 where x is from 0.02 to 0.1, BaTi.sub.1-x Zr.sub.x O.sub.3 where x is from 0.2 to 0.3, BaTi.sub.1-x Sn.sub.x O.sub.3 where x is from 0.15 to 0.3, BaTi.sub.1-x Hf.sub.x O.sub.3 where x is from 0.24 to 0.3, Pb.sub.1-1.3x La.sub.x TiO.sub.3+0.2x where x is from 0.23 to 0.3, (BaTiO.sub.3).sub.x (PbFeo.sub.0.5 Nb.sub.0.5 O.sub.3).sub.1-x where x is from 0.75 to 0.9, (PbTiO.sub.3).sub.- (PbCo.sub.0.5 W.sub.0.5 O.sub.3).sub.1-x where x is from 0.1 to 0.45, (PbTiO.sub.3).sub.x (PbMg.sub.0.5 W.sub.0.5 O.sub.3).sub.1-x where x is from 0.2 to 0.4, and (PbTiO.sub.3).sub.x (PbFe.sub.0.5 Ta.sub.0.5 O.sub.3).sub.1-x where x is from 0 to 0.2, as the second component is described. The dielectric composite material can be formed as a thin film upon suitable substrates.

  4. Dielectric loss against piezoelectric power harvesting

    NASA Astrophysics Data System (ADS)

    Liang, Junrui; Shu-Hung Chung, Henry; Liao, Wei-Hsin

    2014-09-01

    Piezoelectricity is one of the most popular electromechanical transduction mechanisms for constructing kinetic energy harvesting systems. When a standard energy harvesting (SEH) interface circuit, i.e., bridge rectifier plus filter capacitor, is utilized for collecting piezoelectric power, the previous literature showed that the power conversion can be well predicted without much consideration for the effect of dielectric loss. Yet, as the conversion power gets higher by adopting power-boosting interface circuits, such as synchronized switch harvesting on inductor (SSHI), the neglect of dielectric loss might give rise to deviation in harvested power estimation. Given the continuous progress on power-boosting interface circuits, the role of dielectric loss in practical piezoelectric energy harvesting (PEH) systems should receive attention with better evaluation. Based on the integrated equivalent impedance network model, this fast track communication provides a comprehensive study on the susceptibility of harvested power in PEH systems under different conditions. It shows that, dielectric loss always counteracts piezoelectric power harvesting by causing charge leakage across piezoelectric capacitance. In particular, taking corresponding ideal lossless cases as references, the counteractive effect might be aggravated under one of the five conditions: larger dielectric loss tangent, lower vibration frequency, further away from resonance, weaker electromechanical coupling, or using power-boosting interface circuit. These relationships are valuable for the study of PEH systems, as they not only help explain the role of dielectric loss in piezoelectric power harvesting, but also add complementary insights for material, structure, excitation, and circuit considerations towards holistic evaluation and design for practical PEH systems.

  5. Dielectric silicone elastomers with mixed ceramic nanoparticles

    SciTech Connect

    Stiubianu, George; Bele, Adrian; Cazacu, Maria; Racles, Carmen; Vlad, Stelian; Ignat, Mircea

    2015-11-15

    Highlights: • Composite ceramics nanoparticles (MCN) with zirconium dioxide and lead zirconate. • Dielectric elastomer films wDith PDMS matrix and MCN as dielectric filler. • Hydrophobic character—water resistant and good flexibility specific to siloxanes. • Increased value of dielectric constant with the content of MCN in dielectric films. • Increased energy output from uniaxial deformation of the dielectric elastomer films. - Abstract: A ceramic material consisting in a zirconium dioxide-lead zirconate mixture has been obtained by precipitation method, its composition being proved by wide angle X-ray powder diffraction and energy-dispersive X-ray spectroscopy. The average diameter of the ceramic particles ranged between 50 and 100 nm, as revealed by transmission electron microscopy images. These were surface treated and used as filler for a high molecular mass polydimethylsiloxane-α,ω-diol (Mn = 450,000) prepared in laboratory, the resulted composites being further processed as films and crosslinked. A condensation procedure, unusual for polydimethylsiloxane having such high molecular mass, with a trifunctional silane was approached for the crosslinking. The effect of filler content on electrical and mechanical properties of the resulted materials was studied and it was found that the dielectric permittivity of nanocomposites increased in line with the concentration of ceramic nanoparticles.

  6. Model for chaotic dielectric microresonators

    NASA Astrophysics Data System (ADS)

    Keating, J. P.; Novaes, M.; Schomerus, H.

    2008-01-01

    We develop a random-matrix model of two-dimensional dielectric resonators which combines internal wave chaos with the deterministic Fresnel laws for reflection and refraction at the interfaces. The model is used to investigate the statistics of the laser threshold and linewidth (lifetime and Petermann factor of the resonances) when the resonator is filled with an active medium. The laser threshold decreases for increasing refractive index n and is smaller for TM polarization than for TE polarization, but is almost independent of the number of out-coupling modes N . The Petermann factor in the linewidth of the longest-living resonance also decreases for increasing n and scales as N , but is less sensitive to polarization. For resonances of intermediate lifetime, the Petermann factor scales linearly with N . These qualitative parametric dependencies are consistent with the random-matrix theory of resonators with small openings. However, for a small refractive index where the resonators are very open, the details of the statistics become nonuniversal. This is demonstrated by comparison with a particular dynamical model.

  7. Laser produced nanocavities in dielectrics

    NASA Astrophysics Data System (ADS)

    Hallo, Ludovic; Bourgeade, Antoine; Mezel, Candice; Tikhonchuk, Vladimir; Gamaly, Eugene

    2006-10-01

    Tight focusing of the laser pulses opens a possibility to modify the properties of transparent materials and create high-density memories and photonic crystals. It was demonstrated recently [1,2] a formation of sub-wavelength holes by focusing a 100 ns, 100 fs laser pulses inside samples of sapphir and glass. This paper presents the results of numerical simulations of the interaction of sub-ps laser pulses with transparent dielectrics. It contains two parts : a 2D model of the laser energy deposition, based on the solution of full Maxwell equations coupled to a ionisation model accounting for the multiphotonic and avalanche ionisation, and the 3-body recombination. The second part presents the 2D hydrodynamic simulations of the shock wave propagation and the cavity formation with initial conditions provided by 2D absorption model. It is shown that the cavity parameters are very sensitive to the properties of the EOS in the phase transition domain. [1] E.G. Gamaly, S. Juodkazis, K. Nishimura, H. Misawa, B. Luther-Davies, L. Hallo, Ph. Nicola"i, V. T. Tikhonchuk, Phys. Rev. B 73, 214101 (2006). [2] S. Juodkazis, K. Nishimura, S. Tanaka, H. Misawa, E.G. Gamaly, B. Luther-Davies, L. Hallo, Ph. Nicola"i, V. T. Tikhonchuk, Phys. Rev. Lett. 96, 166101 (2006).

  8. Enhanced performance in capacitive force sensors using carbon nanotube/polydimethylsiloxane nanocomposites with high dielectric properties

    NASA Astrophysics Data System (ADS)

    Jang, Hyeyoung; Yoon, Hyungsuk; Ko, Youngpyo; Choi, Jaeyoo; Lee, Sang-Soo; Jeon, Insu; Kim, Jong-Ho; Kim, Heesuk

    2016-03-01

    Force sensors have attracted tremendous attention owing to their applications in various fields such as touch screens, robots, smart scales, and wearable devices. The force sensors reported so far have been mainly focused on high sensitivity based on delicate microstructured materials, resulting in low reproducibility and high fabrication cost that are limitations for wide applications. As an alternative, we demonstrate a novel capacitive-type force sensor with enhanced performance owing to the increased dielectric properties of elastomers and simple sensor structure. We rationally design dielectric elastomers based on alkylamine modified-multi-walled carbon nanotube (MWCNT)/polydimethylsiloxane (PDMS) composites, which have a higher dielectric constant than pure PDMS. The alkylamine-MWCNTs show excellent dispersion in a PDMS matrix, thus leading to enhanced and reliable dielectric properties of the composites. A force sensor array fabricated with alkylamine-MWCNT/PDMS composites presents an enhanced response due to the higher dielectric constant of the composites than that of pure PDMS. This study is the first to report enhanced performance of capacitive force sensors by modulating the dielectric properties of elastomers. We believe that the disclosed strategy to improve the sensor performance by increasing the dielectric properties of elastomers has great potential in the development of capacitive force sensor arrays that respond to various input forces.Force sensors have attracted tremendous attention owing to their applications in various fields such as touch screens, robots, smart scales, and wearable devices. The force sensors reported so far have been mainly focused on high sensitivity based on delicate microstructured materials, resulting in low reproducibility and high fabrication cost that are limitations for wide applications. As an alternative, we demonstrate a novel capacitive-type force sensor with enhanced performance owing to the increased

  9. Polymer dielectric materials for organic thin-film transistors: Interfacial control and development for printable electronics

    NASA Astrophysics Data System (ADS)

    Kim, Choongik

    Organic thin-film transistors (OTFTs) have been extensively studied for organic electronics. In these devices, organic semiconductor-dielectric interface characteristics play a critical role in influencing OTFT operation and performance. This study begins with exploring how the physicochemical characteristics of the polymer gate dielectric affects the thin-film growth mode, microstructure, and OTFT performance parameters of pentacene films deposited on bilayer polymer (top)-SiO2 (bottom) dielectrics. Pentacene growth mode varies considerably with dielectric substrate, and correlations are established between pentacene film deposition temperature, the thin-film to bulk microstructural phase transition, and OTFT device performance. Furthermore, the primary influence of the polymer dielectric layer glass transition temperature on pentacene film microstructure and OTFT response is shown for the first time. Following the first study, the influence of the polymer gate dielectric viscoelastic properties on overlying organic semiconductor film growth, film microstructure, and TFT response are investigated in detail. From the knowledge that nanoscopically-confined thin polymer films exhibit glass transition temperatures that deviate substantially from those of the corresponding bulk materials, pentacene (p-channel) and cyanoperylene (n-channel) films grown on polymer gate dielectrics at temperatures well-below their bulk glass transition temperatures (Tg(b)) have been shown to exhibit morphological/microstructural transitions and dramatic OTFT performance discontinuities at well-defined temperatures (defined as the polymer "surface glass transition temperature," or Tg(s)). These transitions are characteristic of the particular polymer architecture and independent of film thickness or overall film cooperative chain dynamics. Furthermore, by analyzing the pentacene films grown on UV-curable polymer dielectrics with different curing times (hence, different degrees of

  10. Response

    ERIC Educational Resources Information Center

    Higgins, Chris

    2012-01-01

    This article presents the author's response to the reviews of his book, "The Good Life of Teaching: An Ethics of Professional Practice." He begins by highlighting some of the main concerns of his book. He then offers a brief response, doing his best to address the main criticisms of his argument and noting where the four reviewers (Charlene…

  11. Changing the optical and electrical properties of a crown dielectric surface using a 532 nm diode laser

    NASA Astrophysics Data System (ADS)

    Khairuzzaman, Md

    The optical response of a dielectric surface to a given laser radiation can be modified when this surface receives a supplemental uniform energy from an external source such as from the uniform electric field set up by a capacitor voltage. A low capacitor voltage across the dielectric can shift the wavelength of the probe laser as perceived by the dielectric surface toward smaller values. This shift is due to an increase of the vibrational frequency of the electric dipoles located on the dielectric surface. The change in the polarization properties of the dielectric surface suggests the usage of this configuration as an optoelectronic switch driven by a relatively small capacitor voltage. Another goal of this work is to observe the coupling between two lasers through a simultaneous interaction on the surface of a crown dielectric material. We analyze the destructive interference pattern between a weak probe laser and a stronger coupling laser in an electromagnetic induced transparency (EIT)-type configuration. We compare our destructive interference pattern obtained with crown glass illuminated with a diode laser of 532 nm, with previous results where a flint dielectric material was illuminated with the same radiation in similar experimental conditions.

  12. Fruit and Vegetable Quality Assessment via Dielectric Sensing

    PubMed Central

    El Khaled, Dalia; Novas, Nuria; Gazquez, Jose A.; Garcia, Rosa M.; Manzano-Agugliaro, Francisco

    2015-01-01

    The demand for improved food quality has been accompanied by a technological boost. This fact enhances the possibility of improving the quality of horticultural products, leading towards healthier consumption of fruits and vegetables. A better electrical characterization of the dielectric properties of fruits and vegetables is required for this purpose. Moreover, a focused study of dielectric spectroscopy and advanced dielectric sensing is a highly interesting topic. This review explains the dielectric property basics and classifies the dielectric spectroscopy measurement techniques. It comprehensively and chronologically covers the dielectric experiments explored for fruits and vegetables, along with their appropriate sensing instrumentation, analytical modelling methods and conclusions. An in-depth definition of dielectric spectroscopy and its usefulness in the electric characterization of food materials is presented, along with the various sensor techniques used for dielectric measurements. The collective data are tabulated in a summary of the dielectric findings in horticultural field investigations, which will facilitate more advanced and focused explorations in the future. PMID:26131680

  13. Fruit and Vegetable Quality Assessment via Dielectric Sensing.

    PubMed

    El Khaled, Dalia; Novas, Nuria; Gazquez, Jose A; Garcia, Rosa M; Manzano-Agugliaro, Francisco

    2015-06-29

    The demand for improved food quality has been accompanied by a technological boost. This fact enhances the possibility of improving the quality of horticultural products, leading towards healthier consumption of fruits and vegetables. A better electrical characterization of the dielectric properties of fruits and vegetables is required for this purpose. Moreover, a focused study of dielectric spectroscopy and advanced dielectric sensing is a highly interesting topic. This review explains the dielectric property basics and classifies the dielectric spectroscopy measurement techniques. It comprehensively and chronologically covers the dielectric experiments explored for fruits and vegetables, along with their appropriate sensing instrumentation, analytical modelling methods and conclusions. An in-depth definition of dielectric spectroscopy and its usefulness in the electric characterization of food materials is presented, along with the various sensor techniques used for dielectric measurements. The collective data are tabulated in a summary of the dielectric findings in horticultural field investigations, which will facilitate more advanced and focused explorations in the future.

  14. Temperature and moisture dependent dielectric properties of legume flours associated with dielectric heating

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dielectric properties of flour samples from four legumes (chickpea, green pea, lentil, and soybean) at four different moisture contents were measured using an open-ended coaxial probe and impedance analyzer at frequencies of 10 to 1800 MHz and temperatures of 20 to 90°C. The dielectric constant and ...

  15. Temperature and Moisture Dependent Dielectric Properties of Legume Flours Associated with Dielectric Heating

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dielectric property data are important in developing thermal treatments using radio frequency (RF) and microwave (MW) energy and essential to estimate the heating uniformity in electromagnetic fields. Dielectric properties of flour samples from four legumes (chickpea, green pea, lentil, and soybean)...

  16. A percolation cluster model of the temperature dependent dielectric properties of hydrated proteins

    NASA Astrophysics Data System (ADS)

    Suherman, Phe Man; Smith, Geoff

    2003-02-01

    This study investigates the temperature dependence of the low frequency dielectric properties (0.1 Hz-1 MHz) of hydrated globular proteins (namely, ovalbumin, lysozyme and pepsin). The study aims to reveal the mechanisms of water-protein interaction from the dielectric response of these model proteins. Two principle dielectric responses were observed for each hydrated protein, namely, an anomalous low frequency dispersion and a dielectric loss peak at higher frequency (called the varepsilon3 dispersion). The low frequency response conformed to a fractional power low of frequency, while the higher frequency response conformed to a Davidson-Cole model. The strength of both processes reached a maximum at a certain temperature within the experimental temperature range. This temperature is referred to as the percolation threshold (PT) and is thought to be associated with the percolation of protons between hydrogen-bonded water molecules. The relaxation times of the varepsilon3 dispersion conformed to Arrhenius behaviour at temperatures below the PT, from which an activation energy (DeltaH) could be calculated. This activation energy is thought to be a measure of the concentration of available charged sites through which proton transport is facilitated. The structural fractal dimension in the hydrated protein system was also calculated, and enabled the approximation of the pathway for charge percolation in the protein matrix.

  17. Cu-Induced Dielectric Breakdown of Porous Low-Dielectric-Constant Film

    NASA Astrophysics Data System (ADS)

    Cheng, Yi-Lung; Lee, Chih-Yen; Huang, Yao-Liang; Sun, Chung-Ren; Lee, Wen-Hsi; Chen, Giin-Shan; Fang, Jau-Shiung; Phan, Bach Thang

    2017-02-01

    Dielectric breakdown induced by Cu ion migration in porous low-k dielectric films has been investigated in alternating-polarity bias conditions using a metal-insulator-metal capacitor with Cu top metal electrode. The experimental results indicated that Cu ions migrated into the dielectric film under stress with positive polarity, leading to weaker dielectric strength and shorter time to failure (TTF). In the alternating-polarity test, the measured TTFs increased with decreasing stressing frequency, implying backward migration of Cu ions during reverse-bias stress. Additionally, compared with a direct-current stress condition, the measured TTFs were higher as the frequency was decreased to 10-2 Hz. The electric-field acceleration factor for porous low-k dielectric film breakdown in the alternating-polarity test was also found to increase. This Cu backward migration effect is effective when the stressing time under negative polarity is longer than 0.1 s.

  18. Spectral and angular characteristics of dielectric resonator metasurface at optical frequencies

    SciTech Connect

    Zou, Longfang; López-García, Martin; Oulton, Ruth; Klemm, Maciej; Withayachumnankul, Withawat; Fumeaux, Christophe; Shah, Charan M.; Mitchell, Arnan; Bhaskaran, Madhu; Sriram, Sharath

    2014-11-10

    The capability of manipulating light at subwavelength scale has fostered the applications of flat metasurfaces in various fields. Compared to metallic structure, metasurfaces made of high permittivity low-loss dielectric resonators hold the promise of high efficiency by avoiding high conductive losses of metals at optical frequencies. This letter investigates the spectral and angular characteristics of a dielectric resonator metasurface composed of periodic sub-arrays of resonators with a linearly varying phase response. The far-field response of the metasurface can be decomposed into the response of a single grating element (sub-array) and the grating arrangement response. The analysis also reveals that coupling between resonators has a non-negligible impact on the angular response. Over a wide wavelength range, the simulated and measured angular characteristics of the metasurface provide a definite illustration of how different grating diffraction orders can be selectively suppressed or enhanced through antenna sub-array design.

  19. Effect of flip-flop motion on dielectric spectra of highly ordered liquid crystals

    NASA Astrophysics Data System (ADS)

    Osiecka, N.; Massalska-Arodź, M.; Galewski, Z.; Chłedowska, K.; Bąk, A.

    2015-11-01

    This paper presents studies of dielectric response of chosen Schiff bases, which have similar molecular structures with different isomerizations of an azomethine bridging group, alkyloxy chain length with n =5 or n =6 carbon atoms, and a bromine or chlorine halogen terminal atom. Significant differences in the values of the maximum of dielectric absorption related to flip-flop molecular jumps in hexagonal smectic-BCry phases have been found despite small differences of molecular dipole moments in these substances. This phenomenon is discussed in relation to the possibilities of the creation of dimers and to steric factors favoring motions.

  20. Physical restrictions on the Casimir interaction of metal-dielectric metamaterials: An effective-medium approach

    SciTech Connect

    Silveirinha, Mario G.; Maslovski, Stanislav I.

    2010-11-15

    Using an effective-medium approach, we demonstrate that the Casimir interaction of structured metal-dielectric metamaterial slabs which effectively behave as either uniform nongyrotropic materials or bi-isotropic materials is attractive at all distances, independent of the emergence of artificial magnetism or strong magnetoelectric coupling, when the slabs stand in a vacuum. In particular, it is shown that the magnetic response of a metal-dielectric metamaterial is always diamagnetic at imaginary frequencies, and this explains in simple physical terms the impossibility of Casimir repulsion.