Sourish Banerjee

Review Synthesis of conducting nanowires

Work reported on the synthesis of nanowires of different metals/alloys and semiconductors respectively in recent years is reviewed. The methods used mostly belong to one of the following categories: chemical, electrodeposition, physical and filling of carbon nanotubes. Electrical properties investigated for some of these nanowires indicate quantum mechanical effects to be present. Nanodevice fabrication using doped semiconducting nanowires has also been reported.

Small polaron and bipolaron transport in antimony oxide doped barium hexaferrites

Direct current electrical resistivity measurements on specimens with composition BaO (6−x) Fe2O3, x Sb2O3 with x having values of 0.0, 0.025, 0.05, 0.1, and 0.3, respectively, were carried out in the temperature range of 120–300 K. Chemical analyses showed the presence of Sb3+ and Sb5+ ions as well as Fe2+ and Fe3+ ions in the doped specimens. The doped specimens were found to have reduced resistivities. The analysis of the data shows that the electrical conductivity in this system arises due to a combined contribution of both small polaron hopping between Fe2+ and Fe3+ sites and bipolaronic transport between Sb3+ and Sb5+ sites.

Electrical properties of compacted assembly of copper oxide nanoparticles

Cu2O nanoparticles with diameters in the range 6.0-8.6nm were prepared by a chemical method. Both dc and ac electrical properties were measured on a compacted nanoparticle assembly. dc electrical resistivity in the temperature range 140-300K was found to arise due to a variable range hopping conduction mechanism. The ac resistivity variation as a function of frequency (in the range 10kHzto3MHz) and temperature (range 220–320K) was explained on the basis of the power-law exponent in percolating clusters. The interfacial amorphous phase of the nanoparticle assembly appears to control the electrical behavior of the system.

Magnetodielectric Effect in Graphene-PVA Nanocomposites

Graphene-polyvinyl alcohol (PVA) nanocomposite films with thickness of 120 μm were synthesized by solidification of PVA in a solution with dispersed graphene nanosheets. Electrical conductivity data were explained as arising due to hopping of carriers between localized states formed at the graphene-PVA interface. Dielectric permittivity data as a function of frequency indicated the occurrence of Debye-type relaxation mechanism. The nanocomposites showed a magnetodielectric effect with the dielectric constant changing by 1.8% as the magnetic field was increased to 1 T. The effect was explained as arising because of Maxwell–Wagner polarization as applied to an inhomogeneous 2D, two-component composite model. This type of nanocomposite may be suitable for applications involving nanogenerators.

Quantum confinement effect in heat treated silver oxide nanoparticles

Ag2O particles of sizes varying from 6.0 to 16 nm have been prepared by a chemical method. These have been subjected to a heat treatment at temperatures varying from 533 to 623 K. The optical absorption spectra of the heat treated particles dispersed on a glass substrate have been delineated. The absorption peak shows a maximum in wavelength as a function of heat treatment temperature. This has been explained on the basis of formation of nanometer-sized silver layer on the Ag2O particles and the consequential electron confinement within the same.

Tunneling conduction in graphene/(poly)vinyl alcohol composite

Graphene/(Poly)vinyl alcohol (PVA) composite film with thickness 60 μm was synthesized by solidification of a PVA solution comprising of dispersed graphene nanosheets. The close proximity of the graphene sheets enables the fluctuation induced tunneling of electrons to occur from one sheet to another. The dielectric data show that the present system can be simulated to a parallel resistance-capacitor network. The high frequency exponent of the frequency variation of the ac conductivity indicates that the charge carriers move in a two-dimensional space. The sample preparation technique will be helpful for synthesizing flexible conductors.

Humidity sensing by nanocomposites of silver in silicate glass ceramics

Silver nanoparticles of diameters in the range 3.4 to 13.2 nm were grown within a silicate glass ceramics containing barium titanate phase. The glass ceramics were filled with silver particles by subjecting the former to a Na+–Ag+ ion exchange process followed by a reduction treatment in hydrogen. Silver particles were formed at the interfaces of the silicate glass and the barium titanate phases, respectively. The silver particle sizes could be varied by controlling the fractal structure of the crystalline phase by prior heat treatment. Electrical resistivity measurements were carried out on cold-pressed specimens of nanocomposite powders prepared as just stated. A five order of magnitude resistivity change was recorded in the case of nanocomposite specimen with a silver particle diameter of 10.1 nm in the relative humidity range of 25% to 85%. The resistivity of the nanocomposites was found to be controlled by a variable range hopping conduction. It is believed that the silver nanoparticles provide sites...

Electrical resistivity of copper-silica nanocomposites synthesized by electrodeposition

Composites containing copper particles with nanometer dimensions in a silica gel medium have been synthesized by an electrodeposition technique. The precursor composition of the gel was in the system Cu(NO3)2–SiO2 and the copper particle diameters were in the range of 3.2–11.4 nm. The dc electrical resistivity of pellets obtained from the nanocomposite powders was measured in the temperature range of 110–300 K. A temperature dependence with a fractional exponent of 0.25 was observed. This behavior has been explained on the basis of a variable range hopping mechanism.

Magnetodielectric effect in nickel nanosheet-Na-4 mica composites

Nickel nanosheets of thickness 0.6 nm were grown within the nanochannels of Na-4 mica template. The specimens show magnetodielectric effect at room temperature with a change of dielectric constant as a function of magnetic field, the electric field frequency varying from 100 to 700 kHz. A decrease of 5% in the value of the dielectric constant was observed up to a field of 1.2 T. This is explained by an inhomogeneous two-component composite model as theoretically proposed recently. The present approach will open up synthesis of various nanocomposites for sensor applications.

Electrical resistivity of silver–silica nanocomposites

Nanoparticles of silver with diameters in the range 10.3–25.7 nm were grown within a silica gel medium by an electrodeposition technique. The dc resistivity of the nanocomposites was measured over the temperature range 100–300 K. The resistivity as a function of inverse temperature shows a maximum at around 175 K. This is explained as arising due to the presence of two conduction mechanisms, viz., an electron tunnelling between metal particles and conduction through a percolated metal structure which is fractal in nature.