Electrical properties of compacted assembly of copper oxide nanoparticles
TL;DR: In this paper, both dc and ac electrical properties were measured on a compacted nanoparticle assembly and the dc electrical resistivity in the temperature range 140-300K was found to arise due to a variable range hopping conduction mechanism.
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.
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TL;DR: This article provides a comprehensive review on traditional and recently emergent p-TCOs, including Cu(+)-based delafossites, layered oxychalcogenides, nd (6) spinel oxides, Cr(3+-based oxides), and post-transition metal oxides with lone pair state (ns (2).
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.
311 citations
TL;DR: In this paper, the formation of $p$-type defects in transparent conducting oxides was investigated, giving rise to singleparticle levels that are deep in the band gap, consistent with experimentally observed activated, polaronic conduction.
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.
244 citations
TL;DR: In this article, the authors examined the electronic structure, thermodynamic stability and the p-type defect chemistry of CuCrO2 using density functional theory with three different approaches to the exchange and correlation.
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.
171 citations
TL;DR: For both methods, however, the positions of calculated transition levels are inconsistent with experimental ionization levels, and neither GGA nor GGA+U are successful in modeling p-type defects in Cu(2)O.
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
121 citations
TL;DR: In this article, a negative permeability has been obtained above 5GHz due to the natural magnetic resonance in the 70vol% particle content composite material and the electrical permittivity spectra show a nonmetallic characteristic.
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.
99 citations
References
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TL;DR: In this paper, the frequency dependence of the conductivity and the loss angle, and the amplification of resistance (flicker) noise are investigated. But the authors focus on the frequency of the flicker noise and do not consider the amplification effect of resistance noise.
Abstract: The Migdal-Kadanoff renormalisation scheme, which becomes exact on hierarchical lattices, is used to investigate electrical properties of 2D and 3D percolation clusters. The author studies in detail the frequency dependence of the conductivity and the loss angle, and the amplification of resistance (flicker) noise. This type of noise exhibits critical amplification, with its own exponents X and Y, which are related to the exponent b recently defined by Rammal et al. (1985).
36 citations
TL;DR: In this article, the authors demonstrate that, above the glass transition temperature T, these high-energy g boundaries undergo a reversible structural and dynamical transition from a confined amorphous solid to a confined liquid.
Abstract: Recent simulations of silicon grain boundaries equilibrated at high temperatures and subsequently cooled to zero temperature have revealed a 'confined amorphous' equilibrium structure of uniform thickness for the highenergy boundaries while low-energy boundaries are crystalline. Here we demonstrate that, above the glass transition temperature T, these high-energy g boundaries undergo a reversible structural and dynamical transition from a confined amorphous solid to a confined liquid. By contrast with the bulk glass transition, however, this equilibrium transition is continuous and thermally activated, starting at T and being complete at the melting point T, at which g m the entire film is liquid. The coexistence of the confined amorphous and liquid phases in this two-phase region of less than 1 nm thickness is shown to have a profound impact on grain-boundary self-diffusion.
36 citations
TL;DR: In this paper, nanometer-sized copper particles have been grown within a gel derived glass in the system 60 CuO, 40 SiO2 (mole), by heat treatment at temperatures in the range of 450-850'°C, copper oxide shells of thickness varying from 1.1 to 1.7 nm have been produced.
Abstract: Nanometer-sized copper particles have been grown within a gel derived glass in the system 60 CuO, 40 SiO2 (mole %). By heat treatment at temperatures in the range of 450–850 °C, copper oxide shells of thickness varying from 1.1 to 1.7 nm have been produced. DC resistivity measurements carried out over the temperature range of 30–300 °C show a drastically reduced activation energy as compared to that of a reference sample with the above composition. This is ascribed to the presence of an interfacial amorphous phase generated by the assembly of nanosized copper oxide particles.
27 citations
TL;DR: By comparing the properties of In and Pb quantum wells in a scanning tunneling microscopy subsurface imaging experiment, a 2D Mott-Hubbard correlation gap is found, induced by transverse confinement, and a self-organized 2D Anderson lattice is suggested as a new ground state.
Abstract: By comparing the properties of In and Pb quantum wells in a scanning tunneling microscopy subsurface imaging experiment, we found the existence of lateral bound states, a 2D Mott-Hubbard correlation gap, induced by transverse confinement. Its formation is attributed to spin or charge overscreening of quasi-2D excitations. The signature of the 2D confinement-deconfinement transition is also experimentally observed, with the correlation gap being pinned in the middle of the conduction band. A self-organized 2D Anderson lattice is suggested as a new ground state.
20 citations