Dissertations / Theses on the topic 'Electric properties'
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1
Bera, Chandan. "Thermo electric properties of nanocomposite materials." Phd thesis, Ecole Centrale Paris, 2010. http://tel.archives-ouvertes.fr/tel-00576360.
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Cette thèse présente une étude théorique du transport de chaleur dans les matériaux composites nano poreux et nano fils ainsi qu'une étude théorique des propriétés thermoélectriques de l'alliage Si0:8Ge0:2 confrontée à des mesures expérimentales réalisées pour une partie, dans le cadre de l'étude.La première étude démontre que les alliages poreux affichent des réductions de conductivité thermique à des dimensions de pores beaucoup plus grandes que les matériaux poreux non alliés de même porosité nominale. Si on considère une taille de pores de 1000nm, la conductivité thermique de l'alliage Si0:5Ge0:5 avec 0:1 de porosité est deux fois plus faible que la conductivité thermique d'un matériau non poreux, alors que les pores plus petits que 100 nm sont nécessaires pour obtenir la même réduction relative dans le Si ou Ge pur. Nos résultats indiquent que les alliages nano poreux devraient être avantageux devant les matériaux nano poreux non alliés, et ceux pour les applications nécessitant une faible conductivité thermique, tels que les nouveaux matériaux thermoélectriques.La deuxième étude théorique sur la conductance thermique de nano fils révèle l'effet de la structure sur le transport des phonons. Avec un modèle théorique qui considère la dépendance en fréquence du transport des phonons, nous sommes en mesure quantitativement de rendre compte des résultats expérimentaux sur des nano fils droits et coudés dans la gamme de température qui montre qu'un double coude sur un fil réduit sa conductance thermique de 40% à la température de 5K. Enfin, nous avons procédé à une approche théorique des propriétés thermoélectriques des alliages SiGe frittés, en les comparant aux mesures expérimentales nouvelles et antérieures, tout en évaluant leur potentiel d'amélioration. L'approche théorique a été validée par comparaison de la mobilité prévue et la conductivité thermique prévues, en faisant varier la quantité de Ge et les concentrations de dopage, dans une gamme de température comprise entre 300 et 1000K. Nos calculs suggèrent qu'une optimisation par rapport à l'état de l'art actuel est possible pour le matériau de type n et type p, conduisant potentiellement à une augmentation de 6% (5%) du ZT _a 1000K et 25% (4%) _a température ambiante. Même des améliorations plus grandes devraient être possibles si la probabilité de diffusion des phonons aux joints de grains pouvait être augmentée au-delà de sa valeur actuelle de 10%.
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Manepalli, Rahul Nagaraj. "Electron beam curing of thin film polymer dielectrics." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/11036.
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Chiatti, Olivio. "Thermo-electric properties of one-dimensional constrictions." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/20501/.
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This thesis describes low-temperature transport measurements in low-dimensional systems fabricated in high-mobility GaAs/AlGaAs heterostructures. These low-dimensional systems are formed by electrostatically constricting the electrons in the two-dimensional electron gas at the interface of the heterostructure, by applying a voltage to a pair of metallic gates known as a split-gate. At low temperatures the electrical conduction occurs without scattering. The aim is to measure the thermal conductance of these one-dimensional ballistic conductors. The thermal conductance of a split-gate device was measured as a function of gate voltage, over a wide range of temperatures and in the absence of a magnetic field. The electrons on one side of the constriction were heated with an electric current, and the temperature drop across the split-gate was measured using the thermopower of another split-gate. The measurements show that the thermal conductance displays plateaux corresponding to the one-dimensional subbands, confirming previous results. The design of the samples allows a quantitative test of the Wiedemann-Franz law in one-dimensional constrictions. The results strongly suggest that the Wiedemann-Franz law is satisfied, and new information was obtained regarding the anomaly in the conductance known as 0.7 structure, which can provide a new insight into the nature of this anomaly. It is found that the thermal conductance corresponding to the anomaly is suppressed with respect to the value expected from a single-particle picture.
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Su, Bin. "Electrical, thermomechanical and reliability modeling of electrically conductive adhesives." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/10425.
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The first part of the dissertation focuses on understanding and modeling the conduction mechanism of conductive adhesives. The contact resistance is measured between silver rods with different coating materials, and the relationship between tunnel resistivity and contact pressure is obtained based on the experimental results. Three dimensional microstructure models and resistor networks are built to simulate electrical conduction in conductive adhesives. The bulk resistivity of conductive adhesives is calculated from the computer-simulated model. The effects of the geometric properties of filler particles, such as size, shape and distribution, on electrical conductivity are studied by the method of factorial design.
The second part of the dissertation evaluates the reliability and investigates the failure mechanism of conductive adhesives subjected to fatigue loading, moisture conditioning and drop impacts. In fatigue tests it is found that electrical conduction failure occurs prior to mechanical failure. The experimental data show that electrical fatigue life can be described well by the power law equation. The electrical failure of conductive adhesives in fatigue is due to the impaired epoxy-silver interfacial adhesion. Moisture uptake in conductive adhesives is measured after moisture conditioning and moisture recovery. The fatigue life of conductive adhesives is significantly shortened after moisture conditioning and moisture recovery. The moisture accelerates the debonding of silver flakes from epoxy resin, which results in a reduced fatigue life. Drop tests are performed on test vehicles with conductive adhesive joints. The electrical conduction failure happens at the same time as joint breakage. The drop failure life is found to be correlated with the strain energy caused by the drop impact, and a power law life model is proposed for drop tests. The fracture is found to be interfacial between the conductive adhesive joints and components/substrates.
This research provides a comprehensive understanding of the conduction mechanism of conductive adhesives. The computer-simulated modeling approach presents a useful design tool for the conductive adhesive industry. The reliability tests and proposed failure mechanisms are helpful to prevent failure of conductive adhesives in electronic packages. Moreover, the fatigue and impact life models provide tools in product design and failure prediction of conductive adhesives.
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KUO, THAU-MING. "SYNTHESIS AND CHARACTERIZATION OF MONOMERS AND POLYMERS CONTAINING MULTIPLE P-ARYLENEAZO OR P-BENZOQUINODIIMINE GROUPS: CONDUCTING POLYMERS, LIQUID CRYSTAL POLYMERS, AND DIPOLAR POLYMERS." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184215.
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Aniline Black, a polymer containing p-benzoquinodiimine groups, was synthesized chemically or electrochemically by the oxidation of aniline. The polymer salts showed the conductivity of 10⁻¹-10⁻³ ohm⁻¹cm⁻¹. Polymers containing anthroquinodiimine units were also prepared by polycondensations. The syntheses of model compounds containing p-benzoquinodiimine were attempted. Multiazobisphenol monomers were synthesized. 4,4'-(3,3'-Dimethyl-4,4'-biphenylenebisazo) bisphenol 7, 4,4'-[azobis(p-phenyleneazo)] bisphenol 8, and 4,4'-(2-methoxy-1,4-phenylenebisazo) bisphenol 10 displayed liquid crystal (l.c.) properties, while model derivatives of 7, 8, and 4,4'-(4,4'-stilbenebisazo) bisphenol 9 did likewise. Monomers and derivatives of 4-[(4-hydroxyphenyl)azo]-1-naphthol 5, and 4,4'- [oxybis(p-phenyleneazo)] bisphenol 6 showed no l.c. behavior. New thermotropic polyesters based on these multiazobisphenols were synthesized. Sebacates of 5, 6, 7, 8, and 10 showed l.c. behavior, while polymers based on isophthalic or 5-t-butylisophthalic acid did not do so. Polyformals were also synthesized from these momoners, only that of 4 showed weak l.c. behavior. The correlation between the structure of these polymers and their tractabilities, electrical properties, liquid crystal behaviors was studied. Polymers and copolymers containing p-azoarylene and p-azoxyarylene groups were synthesized by oxidative coupling of various aromatic diamines. Films were cast directly from the reaction mixtures or from the polymer solution. The films were n-doped by sodium naphthalide or p-doped by iodine. They showed electrical conductivities of 10⁻⁴ to 10⁻⁵ ohm⁻¹cm⁻¹. AB monomers containing dipolar p-phenyleneazo groups were synthesized: 4-(4-hydroxy-2-methoxyphenylazo) benzoic acid 21, 4-[4-(4-hydroxy-2-methoxyphenylazo)-2-methoxyphenylazo] benzoic acid 22, and 4-(4-hydroxy-2-methoxyphenylazo)-3-nitrobenzoic acid 23. The monomers were polymerized by direct polycondensations. The polyester synthesized from 21 formed a red, transparent film. A polymethacrylate containing dipolar p-phenyleneazo groups in the side chains was also prepared by the free radical polymerization of 1- [3-methoxy-4-(p-nitrophenylazo)-phenoxy] hexyl methacrylate 28.
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McAllister, Kelly Denise. "Modification of the electronic properties of fluorinated epitaxial graphene with an electric bias." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2014. http://digitalcommons.auctr.edu/dissertations/1598.
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Ultraviolet photoemission spectroscopy measurements reveal that there is notable variation of the electron density of states in valence bands near the Fermi level. Evolution of the electronic structure of fluorinated graphene as a function ofthe applied electric bias is investigated. The experimental results demonstrate that the tailoring of electronic band structure correlates with the interlayer coupling tuned by the applied bias. The change in the work function of fluorinated graphene demonstrates the ability of fluorination to modify electron emissions characteristics of graphene.
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Patel, Kaushal Sharad. "Technique for determining through-plane modulus of thin polymer dielectrics." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/10993.
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Sen, M. "Study of magnetic, electric and thermal properties in Fe3Se4 system: Interplay of spin, charge and phonon." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2017. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/5870.
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Olsen, Casper. "Elastic and electric properties of North Sea chalk." Kgs. Lyngby : Institute of Environment & Resources, Technical University of Denmark, 2007. http://www.er.dtu.dk/publications/fulltext/2007/MR2007-123.pdf.
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Akinyeye, Richard Odunayo. "Nanostructured polypyrrole impedimetric sensors for anthropogenic organic pollutants." Thesis, University of the Western Cape, 2007. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_5301_1248150815.
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The main aim of this study was to develop a novel strategy for harnessing the properties of electroconductive polymers in sensor technology by using polymeric nanostructured blends in the preparation of high performance sensor devices.
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Simpson, Joycelyn Ovetta. "Modeling viscosity and ionic conductivity of epoxy resins using free volume concepts." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/10258.
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BOUFELFEL, ALI. "DE HAAS - VAN ALPHEN EFFECT IN QUENCHED PLATINUM CRYSTALS." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184187.
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The oscillatory de Haas-van Alphen (DHVA) magnetization has been studied in Pt crystals containing more than 100 ppm vacancies. Magnetic fields as high as 75 kG were used. The oscillations were observed at temperatures as low as 0.45 k, and found to be strongly attenuated by the vacancies in this concentration range. The emphasis of this work is on the measurement of this attenuation for the purpose of studying conduction electron scattering due to single vacancies. Dingle (scattering) temperatures due to vacancies are reported for four cyclotron orbits with the field in a (110) plane, along with a new measurement of the cyclotron effective mass (m* = 2.31 ± 0.03) for the electron orbit 33° away from <100>. Vacancies were generated by quenching Pt single crystals from temperatures as high as 1730 °C in air, using a technique which minimizes the induced strain. The vacancy contribution to the electron scattering rate was separated by measuring the Dingle temperature in both quenched and annealed specimens which had been subjected to the same quenching process. The results suggest that there is only a moderate variation in this scattering rate over the s-p-like electron sheet of the Fermi surface. However, the scattering rate for the d-like open hole sheet, which contacts the Brillouin zone, is about 49% larger than that for the electron sheet. This anisotropy is attributed mainly to the lattice distortion around a vacancy and to the difference between the hole and electron wave-function symmetries.
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Janas, Dawid. "Electrical and electrothermal properties of carbon nanotube films." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708374.
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Bathe, Abhijit. "Geotechnical properties of soils using electrical measurements." Ohio : Ohio University, 2005. http://www.ohiolink.edu/etd/view.cgi?ohiou1177436956.
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Yang, Weigang. "Electric field control of magnetic properties in multiferroic heterostructures." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/13425/.
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Recently, the use of an electric field (E-field) to control the magnetic properties of thin magnetic films has drawn intensive interest due to their important potential applications such as magnetoelectric random access memory (MERAM) devices and magnetoelectric (ME) sensor. In this thesis, the work first includes a study of the strain-mediated ME coupling strength manipulation by either changing ferromagnetic layer thickness (30-100 nm) or inserting a thin Ti buffer layer (0-10 nm). A large remanence ratio (Mr/Ms) tunability of 95% has been demonstrated in the 65 nm CoFe/PMN-PT heterostructure, corresponding to a giant ME constant (α) of 2.5 × 10-6 s/m, when an external E-field of 9 kV/cm was applied. Also, a record high remanence ratio (Mr/Ms) tunability of 100% has been demonstrated in the 50 nm CoFe/8 nm Ti/PMN-PT heterostructure, corresponding to a large ME constant α of 2.1 × 10-6 s/m, when the E-field of 16 kV/cm was applied. Furthermore, the E-field induced magnetic response was repeatable and quick even after 30 repeats were made. Secondly, a study of non-volatile magnetization change has been demonstrated in the 65 nm CoFe/24 nm Metglas/PMN-PT. In this heterostructure, the E-field created two new non-volatile remanence states, although the as-grown magnetic anisotropy was altered permanently, when the E-field between -6 kV/cm to +6 kV/cm was applied. Based on giant magnetoresistance (GMR) or anisotropic magnetoresistance (AMR), the MERAM memory cell was proposed for the fast, low-power and high-density information storage.
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Gerleman, Ian Gregory. "Thermo-electric properties of two-dimensional silicon based heterostructures." Thesis, University of Warwick, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343787.
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Altšmíd, Jakub. "Study of Electric and Dielectric Properties of Ionic Liquids." Doctoral thesis, Vysoké učení technické v Brně. Fakulta chemická, 2019. http://www.nusl.cz/ntk/nusl-409088.
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Dizertační práce je zaměřena na studium elektrických a dielektrických vlastností iontových kapalin. Iontové kapaliny mohou nacházet uplatnění v široké škále aplikací, především pak v elektrotechnice. Teoretická část se věnuje popisu základních vlastností iontových kapalin a možností jejich uplatnění v kondenzátorech a elektrochemických senzorech plynů. Experimentální část se věnuje použitým metodám charakterizace vlastností iontových kapalin, jsou zde popsány teoretické poznatky o dielektrické spektroskopii včetně metod stanovení fyzikálních vlastností a vyhodnocení experimentálních dat. Experimentální část je rozdělena na dvě základní části. První se věnuje studiu iontových kapalin pro použití jako elektrolytu v kondenzátorech, druhá část se věnuje studiu vlastností připravených experimentálních senzorů na NO2, zejména vlivem vlastností iontových kapalin na sledované parametry senzoru.
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Monari, Antonio <1976>. "Ab initio computation of electric properties and intermolecular forces." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/468/1/tesi.pdf.
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Monari, Antonio <1976>. "Ab initio computation of electric properties and intermolecular forces." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/468/.
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ARDUINO, ALESSANDRO. "Mathematical methods for magnetic resonance based electric properties tomography." Doctoral thesis, Politecnico di Torino, 2018. http://hdl.handle.net/11583/2698325.
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Magnetic resonance-based electric properties tomography (MREPT) is a recent quantitative imaging technique that could provide useful additional information to the results of magnetic resonance imaging (MRI) examinations. Precisely, MREPT is a collective name that gathers all the techniques that elaborate the radiofrequency (RF) magnetic field B1 generated and measured by a MRI scanner in order to map the electric properties inside a human body. The range of uses of MREPT in clinical oncology, patient-specific treatment planning and MRI safety motivates the increasing scientific interest in its development. The main advantage of MREPT with respect to other techniques for electric properties imaging is the knowledge of the input field inside the examined body, which guarantees the possibility of achieving high-resolution. On the other hand, MREPT techniques rely on just the incomplete information that MRI scanners can measure of the RF magnetic field, typically limited to the transmit sensitivity B1+.
In this thesis, the state of art is described in detail by analysing the whole bibliography of MREPT, started few years ago but already rich of contents. With reference to the advantages and drawbacks of each technique proposed for MREPT, the particular implementation based on the contrast source inversion method is selected as the most promising approach for MRI safety applications and is denoted by the symbol csiEPT. Motivated by this observation, a substantial part of the thesis is devoted to a thoroughly study of csiEPT. Precisely, a generalised framework based on a functional point of view is proposed for its implementation. In this way, it is possible to adapt csiEPT to various physical situations. In particular, an original formulation, specifically developed to take into account the effects of the conductive shield always employed in RF coils, shows how an accurate modelling of the measurement system leads to more precise estimations of the electric properties. In addition, a preliminary study for the uncertainty assessment of csiEPT, an imperative requirement in order to make the method reliable for in vivo applications, is performed. The uncertainty propagation through csiEPT is studied using the Monte Carlo method as prescribed by the Supplement 1 to GUM (Guide to the expression of Uncertainty in Measurement). The robustness of the method when measurements are performed by multi-channel TEM coils for parallel transmission confirms the eligibility of csiEPT for MRI safety applications.
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Hinkle, Adam R. "Tight-binding calculation of electronic properties of oligophenyl and oligoacene nanoribbons." Virtual Press, 2008. http://liblink.bsu.edu/uhtbin/catkey/1398716.
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Within recent years, allotropic structures of carbon have been produced in the forms of tubes and ribbons which offer the promise of extraordinary electronic and thermal properties. Here we present analyses of oligophenyl and oligoacene systems–infinite, one-dimensional chains of benzene rings linked along the armchair and zigzag directions. These one-dimensional structures, which are amenable to calculation by analytical means, exhibit features very similar to carbon nanotubes and nanoribbons. Using a tight-binding Hamiltonian we analytically determine the density of states, local density of states, and energy-band structure for the phenyl and the acene. We also examine the effect of disorder on the energies and the corresponding states.Department of Physics and Astronomy
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Farnsworth, Kimberly Dawn Richards. "Variable frequency microwave curing of polymer dielectrics." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/10928.
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KUPFER, JOHN CARLTON. "A SEARCH FOR CHANGES IN THE BAND STRUCTURE OF EXTREMELY STRAIN-FREE MAGNESIUM-CADMIUM CRYSTALS AS A FUNCTION OF ALLOYING, IN THE DILUTE LIMIT (DE HAAS-VAN ALPHEN, FERMI SURFACE)." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/187953.
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We report here a study of a specific doublet of de Haas-van Alphen frequencies in pure Mg and very dilute Mg(Cd) alloys with the magnetic field aligned with the c-axis. The work involved three stages. First, the use of extremely strain-free crystals, temperatures down to 40 millidegree Kelvin, large amplitude modulation, and the fast Fourier transform allowed the components of this doublet to be well resolved. This resolution allowed measurement of the changes in the cross-sectional area as a function of magnetic field orientation to verify the assignment of this doublet to the cap and monster arm junction at the top of the Brillouin zone. Third, with the magnetic field aligned with the c-axis, the splitting of this doublet offered a direct and sensitive indication of any symmetry breaking changes in the 0001 Fourier component of the ionic lattice potential in Mg upon the introduction of Cd. C. B. Friedberg's analysis of his electron interference lineshape data from the quantum interferometer in Mg had indicated that the energy of this band gap should increase by 40% with the introduction of 15 ppm Cd. Our data indicate that any change in the energy of the band gap must be at least three orders of magnitude smaller than that indicated by Friedberg. Our data are, in fact, consistent with there being no changes in the electronic band structure or the Fermi surface of Mg(Cd) alloys (with up to 0.02% (At) Cd), from that of pure Mg.
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FIGUEROA, FRANCISCO RAMON. "MONOMERS, POLYMERS AND CHARGE-TRANSFER COMPLEXES OF DITHIAFULVENES AND POLYMERS FROM 4,4'-SULFONYL DIPHENOL (2-BENZYLIDENE, 1,3-DITHIOLES, 1,3-DITHIOLIUM)." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183817.
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Monomers, polymers, charge-transfer complexes of 2-benzylidene-1,3-dithioles (Dithiafulvenes), and 1,3-dithiolium (Dithiafulvenium) salts of dithioesters and poly(dithioesters) were synthesized. The infrared, nuclear magnetic resonance (NMR) and ultra violet spectra of these materials were also reported. Condensation polymerization of piperidinium tetrathio terephthalate with α-halocarbonyl compounds using phase-transfer techniques yielded poly(dithioesters) that upon dehydrative cyclization with sulfuric acid gave poly(1,3-dithiafulvenium) salts. Polymerization of substituted dithiafulvenes with diacid chlorides, p-phenylene diisocyanate or terephthalaldehyde yielded polymers with inherent viscosities of 0.10 dL/g to 0.21 dL/g. The electric resistivity of the charge-transfer complexes of several dithiafulvenes and the electron donors TCNQ and TNF measured by the two-probe method was found to be >10⁶ Ω.cm at room temperature, hence behaving like insulators. Polyesters and polyesterimides of 4,4'-sulfonyl diphenol were synthesized. The low molecular weight polymers had viscosities of 0.12 to 0.20 dL/g. The polymers formed brittle films and their IR and NMR spectra were reported.
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Papageorge, Marc Vasilios. "Characterization of metal/ceramic interfaces on aluminum nitride." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/9352.
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Grocutt, David A. "Modelling the electronic properties of Si-based quantum structures in external electric and magnetic fields." Thesis, University of Surrey, 2010. http://epubs.surrey.ac.uk/843042/.
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A theoretical study of the electronic properties of silicon quantum dots (QDs) in applied electric and magnetic fields is presented in this work. To obtain the electronic states inside the quantum dots, a new finite-element method based technique is proposed within the effective mass approximation, in order to solve the time independent Schrodinger equation. The method allows for arbitrary shaped QDs in any material. Applied magnetic fields have been included in the most general way, such that 2-spinor wavefunctions may be obtained, which may be of more use in further work when considering many body effects within the framework of density functional theory. Applied electric fields using metal gates surrounding the QD have also been included in a new way, allowing for more realistic gate geometries. The new methods derived by the author allowed two studies to be performed. Firstly, a study of charge polarisation (localisation) inside Si double quantum dots (DQDs) in an applied magnetic field is presented, with varying DQD geometry. It is shown that the magnitude of the charge polarisation in the DQD is strongly related to the asymmetry of the DQD, and to the coupling strength between the two dots making the DQD, as well as its overall size. The applied magnetic field however, can be used to control the charge polarisation, as is demonstrated. Secondly, a study of a realistic gated Si DQD structure examined in experiments by Ferrus et al. It is demonstrated that the electric fields generated by gate potentials of the order used in the experiments have a strong ability to induce charge polarisation within the dot. The prospects for further development of the model are highlighted, to obtain more realistic simulations of electronic Si-based quantum structures.
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Ryan, Desmond Michael. "Electronic states and optical properties of quantum well heterostructures with strain and electric field effects." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/5058/.
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The aim of this work was to develop an envelope function method to calculate the electronic states and optical properties of complex quantum well heterostructures, and to demonstrate its effectiveness by application to some device structures of topical interest. In particular, structures have been considered which might form the basis of intensity modulators and polarization insensitive amplifier devices for light at a wavelength of 1.55 µm. The modulator structures considered all have the general form of two coupled quantum wells of different widths as the active region. The application of an electric field in the growth direction is intended to result in a shift in the energy and spatial localisation of the confined states and produce an increase in the absorption coefficient at longer wavelengths than the zero field absorption edge. The effectiveness of certain structures is examined in terms of field induced absorption increase at 1.55 µm. A system which shows a significant increase in absorption coefficient at this wavelength on application of a practical electric field has been identified as a possible candidate for an intensity modulator. In the case of the amplifier, the active region of the most promising structure considered consists of a stepped well which comprises two layers, one with tensile and one with compressive strain. It is known that the presence of the two oppositely strained layers can result in the TE and TM gain peaks appearing at similar photon energies. Our calculations show that a suitable choice of strain and layer widths can result in a small or zero difference between the TE and TM gains at 1.55 µm, which can be important for the polarization insensitive operation of devices in optical communications applications. In order to predict the optical properties of quantum well devices it is necessary to calculate the electron and hole states for a range of in-plane wavevectors. The calculations developed and carried out in this work are based on a multi-layer (eight band) k.p model including strain effects. The interfacial boundary conditions which result from approximations to Burt's exact envelope function theory are included in the model. The effect of an electric field is modelled by including a potential energy term in each layer Hamiltonian which is equal to the average energy shift across the layer in question due to the presence of the field. The model has been developed with flexibility in mind and has applications beyond the specific devices considered in this thesis.
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Lam, Wing Yui. "Electrical and optical properties of indium tin oxide." HKBU Institutional Repository, 2014. https://repository.hkbu.edu.hk/etd_oa/58.
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In recent years, portable devices and larger display are the trend of market, so transparent conducting oxides (TCO) draw a considerable interest due to their unique characteristics and essential role in the technology of flat panel display. Indium tin oxide (ITO) is one of the most widely used TCO in the application of display technology. In this work, properties of ITO thin film as a function of dopant ratio and density of sputtering targets had been done. It is found that the mechanism of oxygen vaccines is more dominated in electrical conduction than dopant concentration. Meanwhile, the conductivity of ITO thin film depends on the sputtering condition than the target itself. Annealing process is one of the ways to enhance the optical properties of ITO thin film. This process can change the crystal structure of film from amorphous to crystalline but limited by the presence of the oxygen. Apart from the transitional single layer of ITO thin film, a modified structure had been done by inserting a thin layer of metal (Al/Ag) into ITO which provides a highway for carrier transparent. A modified structure with Ag is successfully demonstrated and well agrees with the theory. OLED application was also done by using sandwich structure. The key of sandwich structure is the metal layer, non-reactive and highly conducting material should be selected. Upper and bottom TCO layers are purpose-built for application without affect the properties of structure. This structure also shows more robust on the flexible substrate than single layer ITO.
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Akram, Shakeel. "High temperature and high electrical resistance multilayer polyimide nanodielectrics for electric motors insulation." Thesis, Montpellier, 2020. http://www.theses.fr/2020MONTS028.
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Dans cette thèse, les films multicouches PI / nanocomposites ont été préparés selon un processus de synthèse optimisé. Les échantillons synthétisés ont été caractérisés expérimentalement et par simulations. Tout d'abord, le mécanisme de dégradation des échantillons a été exploré à l'aide d’un générateur d’impulsions. La constante diélectrique, les pertes diélectriques, la rigidité diélectrique, le courant de conduction, la charge d'espace et le courant thermo-stimulé (CTS), ont été étudiées. Ensuite, les niveaux de piège ont été calculés à l'aide des données de déclin de la charge totale et de CTS. Enfin, des modèles 3D de multicouches PI / nanocomposites basés sur les conditions aux limites obtenues à partir d'images SEM / TEM ont été construits dans COMSOL Multiphysics. Ces modèles décrivent l'impact de la dispersion des nanoparticules sur l'amplification du champ électrique. Nos résultats démontrent moins d’agglomération de nanoparticules dans les multicouches et une diminution des charges d’espace et du champ électrique interne. Ainsi, l’utilisation d’isolations multicouches devraient permettre une meilleure fiabilité des moteurs électriquesIn this thesis, the multilayer PI/nanocomposite films were prepared using an optimized synthesis process. The synthesized samples are characterized by experiments and simulations. First, the samples degradation mechanism was explored using pulse power source. Second, dielectric constant, dielectric loss, insulation lifetime, dielectric strength, conduction current, space charge and thermal stimulated current (TSC) were investigated. Third, trap levels were calculated using total charge decay data and TSC data. In the end, multilayer PI/nanocomposite 3D models based on actual boundary conditions obtained from SEM/TEM images of synthesized samples were constructed in COMSOL Multiphysics software. The impact of nanoparticle dispersion on the electric field enhancement is explicitly described in this model. Our results demonstrate that the chances of nanoparticles agglomeration are reduced by using multilayer structure. In consequence, less space charge and low electrical fields are observed in multilayer films. Using multilayer insulations would ensure reliable operation for electric motors and increase its lifetime
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Sims, William Thomas. "Linear charge-transfer polymers based on 2,5-disubstituted quinones." Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/26910.
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SWANSON, DALE DORSETT. "ELECTROCHEMICAL AND SPECTROSCOPIC STUDIES OF THIOETHER COORDINATION COMPLEXES (CYCLIC VOLTAMMETRY, OCTAHEDRAL LOW-SPIN METALS, BLUE COPPER PROTEINS, ELECTRON PARAMAGNETIC RESONANCE)." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/188102.
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The bis 1,4,7-trithiacyclononane (1,4,7-TTCN) complexes of iron, cobalt, nickel and copper are reported in this work. Their properties have been examined using computer-controlled electrochemical and spectroscopic techniques. These TTCN complexes form readily, are unusually symmetrical and support electron transfer reactions at the metal center. The cobalt(II) complex is octahedral, low spin and symmetrical. Four oxidation states of cobalt-TTCN complex are observed; two one-electron transfer processes are reversible. Copper (II) bis 1,4,7-TTCN is unusually symmetrical evidenced by both solid phase and ambient temperature aqueous phase electron paramagnetic resonance spectra. An unusually high redox potential for the copper complex indicates extraordinary stability of the Cu(I) oxidation state but evidently not at the expense of Cu(II) stability. The complex also has a high formation constant compared to other copper-thioether complexes. This unusual strength of thioether donor is attributed to ligand geometry. The 1,4,7-TTCN molecule is the only known cyclic polythioether to have all sulfur atoms endodentate. This structure contributes to thermodynamic stability of complexes as the ground state configuration of the free ligand is maintained in the complex.
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Coria, Garcia Jose Conrado. "SURFACE ENHANCED RAMAN SCATTERING OF INTERFACIAL HALIDE IONS AND WATER AT SILVER ELECTRODES IN THE PRESENCE OF LEAD (SERS, ADSORPTION, DEPOSITION)." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/275414.
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Singh, Santosh Kumar. "Silicon carbide based inverter for hybrid electric vehicles." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610181.
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Sevostianov, Igor, Mahesh Bogarapu, and Pavel Y. Tabakov. "Correlation between elastic and electric properties for cyclically loaded metals." Springer, 2002. http://hdl.handle.net/10321/639.
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Originally published in: International Journal of Fracture, Vol. 2, No. 3-4, 2005.A new method of evaluation of the elastic property deterioration due to accumulated damage is suggested and experimentally verified. It is based on the explicit correlations between two groups of anisotropic properties – conductivity and elasticity, recently established for porous/microcracked materials with anistropic microstructures. An experimental study of fatigue has been done to verify the theoretical predictions. The electrical resistance and Young''s modulus are measured as functions of the number of loading cycles in the standard fatigue tests. The agreement between the theoretical predictions and the direct experimental data is better than 10% in all cases. The results allow one to use measurements of the electric resistance to estimate the damage accumulated in methal structures and the decrease of the elastic modulus.
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Hadji-Ristic, Daniel Ilan. "Thermo-electric and transport properties of etched quantum point contacts." Thesis, Royal Holloway, University of London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444164.
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Stevenson, Timothy James. "Magnetic and electric properties of bismuth ferrite lead titanate ceramics." Thesis, University of Leeds, 2010. http://etheses.whiterose.ac.uk/1371/.
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Solid solutions of multiferroic BiFeO3 doped with ferroelectric PbTiO3 (BFPT) can be prepared by conventional mixed oxide processing to produce a range of polycrystalline ceramics ranging throughout the xBiFeO3 - (1-x)PbTiO3 series. Sintered ceramics are shown to exhibit mixed tetragonal (P4mm) and rhombohedral (R3c) phase perovskite distortions from 0.4 ≤ x < 0.75, where at x ~ 0.75 a morphotropic phase boundary exists and compositions x > 0.75 are entirely rhombohedral. From extensive use of neutron diffraction experiments, the phase coexistence is attributed to compensation for the internal strain induced upon cooling through the ferroelectric Curie point from cubic, to the distorted tetragonal perovskite phase (ܿ/ܽ = 1.17). This drives a further partial transformation to the (~4 %) lower volume rhombohedral phase as a relief mechanism. Increasing the sinter temperature and fast cooling (> 900 °C/hr) sees the monolithic samples x ≤ 0.7 disintegrate to various levels of particulate size, when a critical grain size is exceeded (7 μm), which in turn is inversely proportional to the grain boundary fracture energy. The magnetic properties studied using high resolution powder diffractometry of these two states present G-type antiferromagnetism (AFM) in both the rhombohedral and tetragonal phases; but with Tn above ambient temperature for R3c, and below for P4mm for all compositions except x = 0.3. Compositions below this PbTiO3 rich solution are never observed to support antiferromagnetic order, as the dilution of magnetic iron ions exceeds the percolation threshold via substitution with titanium ions. The rhombohedral phase is shown to exhibit an incommensurate, modulated magnetic order, with a propagation vector perpendicular to the magnetization vector, which decreases in periodicity with increasing bismuth ferrite, from 840 Å for x = 0.75. At room temperature, transforming the paramagnetic tetragonally distorted powder to a G-type AFM rhombohedral phase, is observed with the application of hydrostatic pressure. Evident from neutron experiments, using the Pearl instrument at ISIS, full transformation can be achieved with moderate pressures of 0.77 GPa, effectively ‘switching’ on the magnetic order. The monolithic samples were used at 250 K to observe the changes in simultaneous structural and G-type antiferromagnetic properties as a function of applied electric field (0 to 10 MVm-1) for the most piezoelectrically active samples, around the MPB composition (x = 0.7), using neutron diffraction at the Berlin neutron scattering centre; instrument E2. An observed increase in rhombohedral phase occurs with the application of electric field from peak analysis, which relates to a proportional increase in observed antiferromagnetic intensity (5 %). These two behaviours are proposed to be linked by the internal strain developed within the system, from increased polarisation forcing a partial phase transformation from the tetragonal to the rhombohedral phase which can support the antiferromagnetic order at room temperature.
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Cao, Jingnan, and 曹靖楠. "Thermoelectric transport properties in nanoscale systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B49799708.
Full textAbstract:
As the fast development of nanotechnology and further industrial applications, theoretical investigations upon nanoscale devices are in urgent need. Until now several formalisms have been well established in quantum transport of mesoscopic areas, including of tight-binding and first principle calculations. In this dissertation those methods were partly explored to explore transport and thermoelectric features in various models and actual devices.
The density functional theory plus non-equilibrium Green’s function serves well in the probing process of transport properties like conductance in mesoscopic systems. Atoms’ positions were treated as the only input parameters and one computation package based on NEGF-DFT loop was utilized to get the numerical results, then the corresponding thermal quantities were analysed.
The coherent transport exhibits an obvious character in transmission spectrum called transmission node, whose existence relies on the asymmetric structure of molecular junctions. In the main body of the thesis, firstly two types of model simulation were tested, and the following thermoelectric quantities showed that there’s one interesting signature in the thermopower performance, which was its temperature independence around transmission node. Through comparisons between different system parameters a rough regular pattern was obtained, that the degree of zero transmission and the energy difference around it influenced this temperature invariance feature at the same time. While these two properties were mainly determined by the natural structure of devices.
Besides model simulations the ab initio investigations were also carried out. Although the actual device was not easily altered as ideal models, some similar behaviours in the transmission and thermal curves were still found out. The temperature insensitivity was considered to appear more often in a π electron dominated molecular structure rather than ones with σ electron interactions.published_or_final_version
Physics
Master
Master of Philosophy
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Huo, Jiawei. "Theoretical study of electronic properties in strontium ruthenate." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50662132.
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Since the discovery of superconductivity in Sr2RuO4, there has been intense research interest and efforts on its unconventional pairing symmetry. Although its normal state can be qualitatively described as a quasi-two-dimensional Fermi liquid, surprisingly, Sr2RuO4 turns out to be the prime candidate of the chiral p + ip superconductor, analogous to 3He-A. Such a state is of great interest surrounding, since under a certain conditions it hosts such exotic objects as half-quantum vortices and Majorana bound states, one possible route to an enigmatic quantum computer. Nevertheless, although it is well established now that this superconducting state has odd-parity, and most likely breaks time-reversal symmetry, the negative result on the search of edge current is one of the critical challenges to its chiral p-wave order. These serious discrepancies have even triggered a debate on the primary source of its superconductivity.
Motivated by this debate, in this thesis we propose two independent methods to resolve this controversy via “smoking-gun" experiments. First, the vortex structure within the single-band and two-band models is studied within a mean-field theory. The pattern of the local density-of-state at zero bias shows significant anisotropy in the two-band model, while it is nearly isotropic in the single-band case. Also, the spin lattice relaxation rate at the vortex site is greatly enhanced in the single-band case but not in the two-band scenario. These important distinctions stem from the topology of different Fermi surfaces, and can be tested by using standard probes such as scanning tunneling microscope and nuclear magnetic resonance. In the second proposal, we focus on the two-band scenario, and apply a renormalization group theory to explain the form of spin density wave fluctuations. This theory not only reconciles the absence of long range spin density wave order with strongly enhanced fluctuations, but also unveils the mutual exclusion of these fluctuations and p-wave superconducting pairing. Such an exclusion is reflected in the suppression of the spin-spin correlation function at low energies, which can be measured in the inelastic neutron scattering experiment. This suppression, if not observed experimentally, would be a critical challenge to the two-band model, and an indirect but strong support to the assignment of the single γ-band as the primary source of the unconventional pairing.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
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Yang, Cheng-Kuang, and 楊程光. "The effect of material electric properties in electrical discharge machining." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/21143990121569687528.
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碩士清雲科技大學
機械工程研究所
94
Tungsten carbine and mold steel is the common used material in mold industry. Electrical discharge machining (EDM) is usually utilized to manufacture the special shape cavity. In general, the efficiency will be alike if the same polarity is used in EDM. And the result is different if workpiece and electrode is connected in opposite pole. Therefore, it can be shown that the material properties will affect the EDM effect. In this study, tungsten carbine, tungsten copper, copper, brass, aluminum, skd11, stainless steel and titanium are used as workpiece and tungsten, tungsten carbine, brass, copper are applied as electrode. MRR and electrode wear ratio(EWR) will be utilized as an estimate standard in different pole of EDM. And we will utilize to discuss the relationship between EWR and MRR from surface roughness, material mechanical properties and electrode erosion. And the Statistics Package for the Social Sciences (SPSS) is applied to analyze the importance of polarity, current, impact factor, resistance coefficient, electron potential and working function in EDM. In EDM, MRR is low when the high electric resistance material is used as workpiece. Furthermore, short circuit and instable discharge are easily occurred if the workpiece owing the low electron potential in EDM. And the result of surface roughness, when the MRR is low, the height on the work piece will caused the higher surface roughness. The polarity control the distribution of energy, so it is certainly the most important factor, and the electron potential, resistance coefficient and work function also the important factors in EDM method by SPSS software. Use the SPSS software can provide more precise analysis in EDM.
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Yen, Chai-Der, and 顏嘉德. "Electronic and Optical Properties of Zero-dimensional Nanographitesin Electric Fields." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/09804393572400129532.
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碩士國立成功大學
物理學系碩博士班
94
Abstract In this thesis, Tight-binding model is used to study the electronic and optical properties of zero-dimensional nanographites in electric fields. We calculate eigenvalue, width of eigenvalue, energy gap, wave function, density of states, joint density of states and optical absorption. Next, we discuss how rapid these physical properties change with values and directions of external electric fields and the geometric structure of zero-dimensional nanographites. However, the relationship between these physical properties with the dangling bond will not be discussed in the paper because the dangling bond is excluded at the beginning. With the increase of external electric fields, width of eigenvalue increases but energy gap may become very small( about 1～7meV) on some occasions. Wave function of the nearest state to Fermi level will localize on the raising points of the first and final Zigzag line. But, this phenomenon will disappear with the increase of external electric fields. These physical properties would be shown directly on joint density of states and optical absorption. Because external electric fields are able to make distributions of eigenvalue change, amplitudes of absorption peaks of joint density of states will have the alternation as well. In the mean time, absorption peaks will shift, and definitely the two different absorption peaks will combine to form one larger absorption peak. In the end, we will find optical absorption peaks will shift with the increase of external electric fields as well. Then, original optical absorption peaks will disappear and new optical absorption peaks will appear.
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Jia-WeiWang and 王家偉. "Electronic properties of curved nanographene ribbon in an electric field." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/45643424302437267029.
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Malakooti, Sadeq. "Electronic properties of DNA molecules under different electric field exposure configurations." 2014. http://liblink.bsu.edu/uhtbin/catkey/1747407.
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In recent years, the electronic behavior of DNA molecules has received much interest
ranging from interpreting experimental results to electronic based applications, including DNA
sequencing and DNA-based nanotransistors. Here we study the electronic properties of poly(G)-
poly(C) double stranded DNA molecules by means of the tight binding approximation to
understand how the molecules act under different physical conditions. For instance, the effects of
DNA tilting, stretching and compressing on the electronic properties are elucidated. Very
interesting features such as a tunable energy band gap and a metal-semiconductor transition are
disclosed for DNA under different conditions.Second order tight binding model -- Tilted DNA molecule -- Strain-dependent DNA electronics.
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Lu, Cheng-lin, and 呂政霖. "Electronic properties of quantum rings under external electric and magnetic fields." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/82435344001619231590.
Full textAbstract:
碩士國立高雄大學
應用物理學系碩士班
101
In this thesis, we investigate the electronic properties of quantum rings in magnetic and electric fields. We use the matrix method to obtain the energy spectrum and wave function. Numerical results demonstrate that the magnetic and electric fields strongly affect the physical characteristics of quantum rings. When a magnetic field is applied to the ring, the energy levels show periodic oscillations. We further consider the system including several impurities. The parameters of impurities have a great influence on the degeneracies of energy levels. On the other hand, the electric field and hindering barriers lead to anticrossing behaviors in the energy levels. Finally, we study the heat capacity of quantum-ring systems in the external fields.
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Liu, Chia-ming, and 劉家銘. "Electronic Properties of Graphene Under the Influence of Modulated Electric Fields." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/05597042885779976027.
Full textAbstract:
碩士國立成功大學
物理學系碩博士班
96
The tight-binding model is utilized to study the electronic properties of graphene under the influence of modulated electric fields. Most sub-bands that are affected by the modulated electric fields appear to be plat or dispersionless along the direction in which the electric fields are exerted except for some near the Fermi energy. The DOS at the Fermi level is proportional to V0, but not related to the wavelength of the electric fields when RE > 250. New band-edge states are generated in the following regions: ( 0 ~ V0 ) , ( 1 – V0 ~ 1 + V0 ) and ( 3 – V0 ~ 3 + V0�n). The corresponding peaks in DOS become more obvious with the increase of V0, but less evident when the wavelength is enlarged. The DOS seems to be isotropic with respect to the direction of the modulated electric fields.
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Huang, Xi-En, and 黃璽恩. "Electronic Properties of Single-Walled Carbon Nanotubes in an Electric Field." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/92858383694791940039.
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碩士國立成功大學
物理學系碩博士班
93
Abstract The sp3 tight-binding model is used to study electronic properties of single-walled carbon nanotubes in the presence of the uniform perpendicular electric field. Electronic properties strongly depend on the curvature effect, the geometric structure (radius and chiral angle), and the strength of electric field. The electric field could change energy gap, energy band curvature, the position and the number of edge state, and the state degeneracy. Furthermore, there are semiconductor-metal transitions at certain electric fields. Such effects are directly reflected in density of states (DOS). DOS exhibits a lot of prominent peaks, owing to the one-dimensional energy bands. The number, the position, and the height of pronounced peaks are determined by the field strength. The predicted results could be directly verified by the experimental measurements, such as STM and optical spectroscopy.
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許義宏. "Study of electric and magnetic properties." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/79433680854274851072.
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碩士國立彰化師範大學
物理學系
93
This thesis mainly focuses on the research of the characteristics of tunneling magnetoresistance multiplayer. Through magnetron sputtering system to manufacture magnetic multilayer. we can probe into the exchange coupling phenomenon in ferromagnetic/antiferromagnetic system. In the meantime, by using sample with different thickness, we are able to compare the influences on magnetic property of multilayer before and after anneal, and get to know the changes under different temperatures. Also, through photo-lithography and ion-milling to manufacture MTJ devices, to observe the surface texture and try to resolve the redeposition which is caused by etching process. By measuring the I-V characteristic and magnetoresistance, factors which cause device damages in the fabrication process can be found. It was discovered that the largest exchange bias of the magnetic multilayer can reach is around 180 Oe at RT. It can also reach 90 Oe at 350K. In this thesis, it’s confirmed that the sample surface texture do get improved by using special etching method. However, it’s electric property will not be as good as expected. We believe the performance can be greatly improved by applying oblique etching method with wider angle.
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何子儀. "Electric Properties of LCMO/Pb Junctions." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/73717507740807884695.
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Wang, Tz-Shiuan, and 王子軒. "Magneto-electronic properties of graphene nanoribbons in the spatially modulated electric field." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/12713049919903715954.
Full textAbstract:
碩士國立成功大學
物理學系碩博士班
96
The Peierls tight-binding model with the nearest-neighbor interactions is used to calculate the magneto-electronic structure of graphene nanoribbons under a spatially modulated electric fileld along the y-axis. A uniform perpendicular magnetic field could make all energy dispersions change into the quasi-Landau levels. Such levels are composed of the dispersionless and parabolic energy bands. A spatially modulated electric field would further induce a lot of oscillating parabolic bands with several band-edge states. It drastically modifies energy dispersions, alters subband spacings, destroys symmetry of energy spectrum about kx = 0 and Fermi level, and changes features of band-edge states (number and energy). The above-mentioned magneto-electronic structures are directly reflected in density of states (DOS). The modulation effect changes shape, number, positions, and intensities of peaks in DOS. The predicted result could be tested by the optical measurements.
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Jie-WeiGuo and 郭傑維. "The electronic properties of AB-stacked multilayer graphenes in an electric field." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/95553985505335877696.
Full textAbstract:
碩士國立成功大學
物理學系碩博士班
100
I use the tight-binding method to study the effect of AB-stacked graphite in the electric field. We found that the energy band will produce the energy gap in few-layers, and overlap in multi-layers. The overlap will become wider with the increased number of layers. The density of states of multi-layer graphene is very different compared to few-layers, the energy band will spread up and the density of states will become larger than few-layers. We also analyzed the the density of states on the Fermi energy with the changes of the electric field and the number of layers. Finally, we discuss the absorption spectra.
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Lin, Chang-Ching, and 林長青. "Electric and Magnetic Properties of Spinel CdCr2S4." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/x3ejxj.
Full textAbstract:
碩士國立中山大學
物理學系研究所
96
Multiferroic materials, showing strong coupling between ferroelectric and ferromagnetic interaction, have been the subject of intense research recently. These materials are potential candidates for the next generation in microelectronic device. CdCr2S4, one of the few multiferroics with spinel structure proposed in 2005, is in the limelight of scientific research, because of the complex interaction among lattice, spin and dipole. To investigate further, we have measured the magnetic and electric properties of single crystal CdCr2S4. The spins are coupled ferromagnetically below Curie temperature TC = 84 K. With increasing magnetic field, ferromagnetic transition is found to be shifted towards higher temperature. The magnetic hysteresis is satisfied with the characteristic of soft ferromagnet. Electric field induced permanent metal-insulator transition (MIT) and colossal magnetoresistance (CMR) are observed in the resistivity measurement. From dielectric constant measurement, two interesting dipolar ordering states have been observed. The peak near TC ~ 84 K is due to the glassy type dipolar state stimulated by the onset of ferromagnetic ordering and the other near 54 K, might be the ferroelectric ordered state induced by externally applied electric field. Both electric and magnetic field dependent physical properties have been studied and reveal significant evidences of strong spin-dipole coupling in the present system.