Electrical Properties of Nanocomposites
TL;DR: In this article, the state-of-the-art for synthesizing composites of nanometer-sized phases (metal, semiconductor or ceramic) dispersed in a matrix has been reviewed.
Abstract: The present state-of-the-art for synthesizing composites of nanometer-sized phases (metal, semiconductor or ceramic) dispersed in a matrix has been reviewed. Both dc and ac electrical properties of different nanocomposites synthesized have been described. The theoretical models used to explain the experimental results are discussed. It appears that there is a need to have newer theoretical models developed to understand the ac electrical properties of metal-ceramic nanocomposites.
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TL;DR: In this paper, the self-organization of CdSe nanocrystallites into three-dimensional semiconductor quantum dot superiattices (colloidal crystals) is demonstrated.
Abstract: The self-organization of CdSe nanocrystallites into three-dimensional semiconductor quantum dot superiattices (colloidal crystals) is demonstrated. The size and spacing of the dots within the superlattice are controlled with near atomic precision. This control is a result of synthetic advances that provide CdSe nanocrystallites that are monodisperse within the limit of atomic roughness. The methodology is not limited to semiconductor quantum dots but provides general procedures for the preparation and characterization of ordered structures of nanocrystallites from a variety of materials.
36 citations
TL;DR: This paper reviews and enhances numerical models for determining thermal, elastic and electrical properties of carbon nanotube-reinforced polymer composites and validated by comparison with various experimental datasets reported in the recent literature.
Abstract: This paper reviews and enhances numerical models for determining thermal, elastic and electrical properties of carbon nanotube-reinforced polymer composites. For the determination of the effective ...
26 citations
TL;DR: In this paper, the presence of nickel particles of size ∼20nm in the nano-pores of an alumina-silica nanocomposite has been detected using X-ray diffraction and transmission electron micrograph.
14 citations
TL;DR: In this paper, the average particle size of molybdenum carbide is in the range of 5-15 nm and the detailed XRD analyses coupled with thermodynamic arguments show that reduction of ammonium moly bdate is predominantly by in situ generated hydrogen.
Abstract: Molybdenum carbide has been formed in the silica gel matrix by the in situ reduction of ammonium molybdate. The average particle size of molybdenum carbide is in the range of 5-15 nm. The detailed XRD analyses coupled with thermodynamic arguments show that reduction of ammonium molybdate is predominantly by in situ generated hydrogen.
2 citations
TL;DR: The low frequency (20 Hz to 1 MHz) ac conductivity and magnetoconductivity behavior of ceramic nanocomposite (Ni-SiO2) at low temperature down to 77 K are reported in this article.
Abstract: The low frequency (20 Hz to 1 MHz) ac conductivity and magnetoconductivity behaviour of ceramic nanocomposite (Ni-SiO2) at low temperature down to 77 K are reported. The frequency dependent conductivity followed the power law, σ(ω) ∝ ω
s
. The fractional exponent s is a function of temperature and was found to increase with increasing temperature. This type of variation may be attributed to small polaron hopping. A peak present in the loss tangent indicates the presence of a Debye relaxation process. The magnetoconductivity of the samples is positive, which strongly depends on frequency. A firm theoretical explanation of frequency dependent magnetoconductivity is still lacking.
1 citations
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TL;DR: In this paper, the resistivity data have been analyzed in terms of the Ziman theory of electron-phonon scattering and the effective Debye temperature Theta p has been estimated by fitting the experimental data to Ziman's equation.
Abstract: Conducting films consisting of silver particles of diameters ranging from 4 to 12 nm have been grown in glass-ceramic by subjecting the latter to a Li+ to or from Ag+ exchange followed by a suitable reduction treatment. The DC electrical resistance of these films has been measured over the temperature range 80-300 K. The resistivity data have been analysed in terms of the Ziman theory of electron-phonon scattering. The effective Debye temperature Theta p has been estimated by fitting the experimental data to Ziman's equation. Theta p is seen to vary from 98 to 192 K for silver particle sizes ranging from 4.3 to 11.0 nm. The silver particle aggregates in the present system have a fractal microstructure with fractal dimensions of around 1.6 and 1.9, respectively.
94 citations
TL;DR: In this paper, the optical absorption edge is blue shifted by ∼ 0.4 eV compared with the bulk absorption value of CdS crystal, interpreted in terms of a quantum-confinement effect of small crystal size.
Abstract: The sol–gel process has been applied successfully to the preparation of small-particle-size CdS-doped silica glasses with a significant quantum size effect. Gels prepared through the hydrolysis of a complex solution of Si(OC2H5)4 and Cd(CH3COO)2·2H2O were heated at 500°C, then reacted with H2S gas to form fine, hexagonal, CdS-microcrystal-doped glasses. The optical absorption edge is blue shifted by ∼0.4 eV compared with the bulk absorption value of CdS crystal. This result is interpreted in terms of a quantum-confinement effect of small crystal size.
92 citations
TL;DR: In this paper, the optical absorption spectra of glass-metal nanocomposite films have been measured over the wavelength range 200 to 2000 nm, and effective medium theories of Maxwell-Garnett and Bruggeman, respectively, have been used to calculate theoretically the absorption of these materials.
Abstract: Glass-metal nanocomposites incorporating ultrafine particles of iron, nickel, cobalt and manganese, respectively, in a silica glass matrix have been prepared by heat treatment of a gel derived from a sol containing silicon tetraethoxide and a suitable metal organic compound. Metal particles in all the nanocomposites are isolated and spherical-shaped with diameters ranging from 3 to 10 nm. Films of these nanocomposites with thickness of the order of a few micrometres have been prepared on glass slides by a simple dip-and-pull technique. Optical absorption spectra of the nanocomposite films have been measured over the wavelength range 200 to 2000 nm. Effective medium theories of Maxwell-Garnett and Bruggeman, respectively, have been used to calculate theoretically the optical absorption of these materials. The Maxwell-Garnett theory gives results which are in better agreement with experimental data than those obtained from Bruggeman formalism. The filling factor f as estimated from the least-squares fit of the experimental results with the Maxwell-Garnett theory has a value in the range 1 to 4%.
92 citations
TL;DR: In this paper, the electrical resistance of granular aluminum specimens with room-temperature resistivities between 1.5 and 1.3 was measured in magnetic fields up to 9 T. The results suggest the possibility of superconductivity in the insulating phase.
Abstract: The electrical resistance has been measured on granular aluminum specimens with room-temperature resistivities between 1.5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ and 1.3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}1}$ \ensuremath{\Omega} cm, from 0.3 K to room temperature, in magnetic fields up to 9 T. The results show the importance of electron correlation effects on both sides of the metal-insulator transition. The Mott hopping law is not observed in any specimen over the whole temperature range. The results suggest the possibility of superconductivity in the insulating phase.
91 citations
TL;DR: In this paper, it was shown that conduction can occur in the substrate surface by electron tunneling between the separated microparticles, and that the current carriers can be contributed to the insulator surface regions by the metallic particles.
Abstract: Electrical conduction in very thin metal films deposited onto single‐crystal sodium chloride substrates has been investigated. The conduction for annealed films is found to be thermally activated with a negative temperature coefficient of resistance. Inspection of the films in an electron microscope shows them to consist of separated microparticles. Electron tunneling through the vacuum between microparticles is generally assumed to be the mechanism of electrical conduction. In this work an attempt has been made to show that conduction can occur in the substrate surface. The conduction is believed to be electron tunneling between regions in the substrate surface immediately under the metallic particles. The current carriers can be contributed to the insulator surface regions by the metallic microparticles. In addition, an activation energy is thought to be necessary before tunneling can occur. This energy is electrostatic in nature and is dependent upon the average size and separation of the microparticle...
84 citations