A. Bose

Bio: A. Bose is an academic researcher from Indian Association for the Cultivation of Science. The author has contributed to research in topics: Mica & Crystal. The author has an hindex of 5, co-authored 13 publications receiving 126 citations. Previous affiliations of A. Bose include Bose Institute.

Template based growth of nanoscaled films: a brief review

Abstract: Growth of ultrathin films of metals and inorganic materials using various templates — both solid and liquid has been reviewed. Such nanoscaled films have been found to be effective in fabrication of devices and sensors. Use of crystal nanochannels of some inorganic compounds has been found to induce novel properties to the films grown within them. It is expected the latter approach will lead to the synthesis of materials with hitherto unknown properties.

Electrical properties of compacted assembly of copper oxide nanoparticles

Abstract: 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.

Synthesis of nanocomposites using glasses and mica as templates

Abstract: Various nanocomposites were synthesized using either a silica-based glass or mica crystallites as the medium. In some cases by an oxidation or a sulfidation treatment a core-shell nanostructure could be generated. Iron-iron oxide core-shell structured nanocomposites exhibited excellent humidity sensing behaviour. Gold-gold sulfide core-shell nanorods exhibited a number of optical absorption peaks which arose because of their structural characteristics. Nanoparticles of silver and silver oxide could be aligned in a polymethylmethacrylate film by an a.c. electric field of 1 MHz frequency. The composites showed large sensitivity to relative humidity. Lead sulfide nanowires of diameter, 1.2 nm, were grown within the nanochannels of Na-4 mica. These exhibited a semiconductor to metal transition at around 300 K. This arose because of high pressure generated on the nanowires. Copper sulfide nanowires grown within the Na-4 mica channels showed metallic behaviour. Silver core-silver orthosilicate shell nanostructures developed within a silicate glass medium showed discontinuous changes in resistivity at some specific temperatures. This was explained as arising due to excitation of Lamb modes at certain pressures generated because of thermal expansion mismatch of the core and the shell phases. Optical properties of iron core-iron oxide shell nanocomposites when analysed by effective medium theory led to the result of a metal non-metal transition for particle diameters below a critical value. Similar results were obtained from optical absorption data of silver nanoparticles grown in a tetrapeptide solution.

Metallic behavior of copper sulfide nanowires grown within Na-4 mica

Abstract: Copper sulfide nanowires of diameter of ∼1.2nm were grown within the crystal channels of Na-4 mica. These consist of both CuS and Cu2S strands. Electrical conduction over the temperature range of 130–300K was characterized by very low activation energies in the range of 0.008–0.004eV. The nanocomposites exhibit giant dielectric permittivity of ∼1617 which has been explained on the basis of one-dimensional metallic nanowires as predicted by the Gorkov-Eliashberg [Sov. Phys. JETP 21, 940 (1965)] and Rice-Bernasconi [Phys. Rev. Lett. 29, 113 (1972)] models.

P-type transparent conducting oxides.

Abstract: Transparent conducting oxides constitute a unique class of materials combining properties of electrical conductivity and optical transparency in a single material. They are needed for a wide range of applications including solar cells, flat panel displays, touch screens, light emitting diodes and transparent electronics. Most of the commercially available TCOs are n-type, such as Sn doped In2O3, Al doped ZnO, and F doped SnO2. However, the development of efficient p-type TCOs remains an outstanding challenge. This challenge is thought to be due to the localized nature of the O 2p derived valence band which leads to difficulty in introducing shallow acceptors and large hole effective masses. In 1997 Hosono and co-workers (1997 Nature 389 939) proposed the concept of 'chemical modulation of the valence band' to mitigate this problem using hybridization of O 2p orbitals with close-shell Cu 3d (10) orbitals. This work has sparked tremendous interest in designing p-TCO materials together with deep understanding the underlying materials physics. In this article, we will provide a comprehensive review on traditional and recently emergent p-TCOs, including Cu(+)-based delafossites, layered oxychalcogenides, nd (6) spinel oxides, Cr(3+)-based oxides (3d (3)) and post-transition metal oxides with lone pair state (ns (2)). We will focus our discussions on the basic materials physics of these materials in terms of electronic structures, doping and defect properties for p-type conductivity and optical properties. Device applications based on p-TCOs for transparent p-n junctions will also be briefly discussed.

Acceptor Levels in p-Type Cu2O: Rationalizing Theory and Experiment

Abstract: Understanding conduction in ${\mathrm{Cu}}_{2}\mathrm{O}$ is vital to the optimization of Cu-based $p$-type transparent conducting oxides. Using a screened hybrid--density-functional approach we have investigated the formation of $p$-type defects in ${\mathrm{Cu}}_{2}\mathrm{O}$ giving rise to single-particle levels that are deep in the band gap, consistent with experimentally observed activated, polaronic conduction. Our calculated transition levels for simple and split copper vacancies explain the source of the two distinct hole states seen in DLTS experiments. The necessity of techniques that go beyond the present generalized-gradient- and local-density-approximation techniques for accurately describing $p$-type defects in Cu(I)-based oxides is discussed.

Understanding the p-type defect chemistry of CuCrO2

Abstract: CuCrO2 is the most promising Cu-based delafossite for p-type optoelectronic devices. Despite this, little is known about the p-type conduction mechanism of this material, with both CuI/CuII and CrIII/CrIV hole mechanisms being proposed. In this article we examine the electronic structure, thermodynamic stability and the p-type defect chemistry of this ternary compound using density functional theory with three different approaches to the exchange and correlation; the generalized-gradient-approximation of Perdew, Burke and Ernzerhof (PBE), PBE with an additional correction for on-site Coulombic interactions (PBE + U) and the nonlocal, screened-exchange hybrid functional HSE06. The fundamental band gap of CuCrO2 is demonstrated to be indirect in nature. Under all growth conditions, the dominant intrinsic p-type defect will be the Cu vacancy, with hole formation centered solely on the Cu sublattice. Mg doping is found to be significantly lower in energy than intrinsic defect formation, explaining the large increases in conductivity seen experimentally. Cu-rich/Cr-poor growth conditions are found to be optimal for both intrinsic and extrinsic (Mg doping) defect formation, and should be adopted to maximize performance.

Modeling the polaronic nature of p-type defects in Cu2O: The failure of GGA and GGA+U

Abstract: The exact nature of the hole traps reported deep in the band gap of Cu2O has been a topic of vigorous debate, with copper vacancies and oxygen interstitials both having been proposed as the relevant defects In this article, the electronic structure of acceptor-forming defects in Cu2O, namely, copper vacancies and oxygen interstitials, is investigated using generalized gradient approximation (GGA) and GGA corrected for on-site Coulombic interactions (GGA+U) GGA produces notionally semimetallic defect complexes, which is not consistent with the experimentally known polaronic nature of conduction in Cu2O GGA+U also predicts a semimetallic defect complex for the “simple” copper vacancy but predicts the “split” vacancy and both oxygen interstitials are characterized by localized polarons, with distinct single particle levels found in the band gap For both methods, however, the positions of calculated transition levels are inconsistent with experimental ionization levels Hence neither GGA nor GGA+U are suc

Negative permeability spectra in Permalloy granular composite materials

Abstract: Complex permeability spectra of Permalloy granular composite materials have been studied in the microwave frequency range. The heat-treated Permalloy particles in the air at several hundreds of °C have a high surface electrical resistance; the eddy current effect in the high frequency permeability spectra can be suppressed in the composite structure containing the percolated particles. A negative permeability has been obtained above 5GHz due to the natural magnetic resonance in the 70vol% particle content composite material. In this content, electrical permittivity spectra show a nonmetallic characteristic. This permeability dispersion can be applied for the left-handed media.