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Title: Metal–semiconductor transition in atomically thin Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8} nanosheets

Abstract

Two-dimensional layered materials have attracted considerable attention since the discovery of graphene. Here we demonstrate that the layered Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8} (BSCO) can be mechanically exfoliated into single- or few-layer nanosheets. The BSCO nanosheets with four or more layers display bulk metallic characteristics, while the nanosheets with three or fewer layers have a layer-number-dependent semiconducting characteristics. Charge transport in bilayer or trilayer BSCO nanosheets exhibits Mott 2D variable-range-hopping (VRH) conduction throughout 2 K–300 K, while the charge transport in monolayers follows the Mott-VRH law above a crossover temperature of 75 K, and is governed by Efros and Shklovskii-VRH laws below 75 K. Disorder potentials and Coulomb charging both contribute to the transport gap of these nanodevices. Our study reveals a distinct layer number-dependent metal-to-semiconductor transition in a new class of 2D materials, and is of great significance for both fundamental investigations and practical devices.

Authors:
; ; ;  [1]; ;  [2];  [3];  [1];  [4];  [2];  [4]
  1. Department of Materials Science and Engineering, University of California, Los Angeles, California 90095 (United States)
  2. Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095 (United States)
  3. Department of Physics, Nagoya University, Nagoya 464-8602 (Japan)
  4. (United States)
Publication Date:
OSTI Identifier:
22303561
Resource Type:
Journal Article
Resource Relation:
Journal Name: APL Materials; Journal Volume: 2; Journal Issue: 9; Other Information: (c) 2014 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; GRAPHENE; LAYERS; METALS; NANOSTRUCTURES; SEMICONDUCTOR MATERIALS

Citation Formats

Wang, Yang, Cheng, Rui, Dong, Jianjin, Liu, Yuan, Zhou, Hailong, Yu, Woo Jong, Terasaki, Ichiro, Huang, Yu, E-mail: yhuang@seas.ucla.edu, California Nanosystems Institute, University of California, Los Angeles, California 90095, Duan, Xiangfeng, E-mail: xduan@chem.ucla.edu, and California Nanosystems Institute, University of California, Los Angeles, California 90095. Metal–semiconductor transition in atomically thin Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8} nanosheets. United States: N. p., 2014. Web. doi:10.1063/1.4892975.
Wang, Yang, Cheng, Rui, Dong, Jianjin, Liu, Yuan, Zhou, Hailong, Yu, Woo Jong, Terasaki, Ichiro, Huang, Yu, E-mail: yhuang@seas.ucla.edu, California Nanosystems Institute, University of California, Los Angeles, California 90095, Duan, Xiangfeng, E-mail: xduan@chem.ucla.edu, & California Nanosystems Institute, University of California, Los Angeles, California 90095. Metal–semiconductor transition in atomically thin Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8} nanosheets. United States. doi:10.1063/1.4892975.
Wang, Yang, Cheng, Rui, Dong, Jianjin, Liu, Yuan, Zhou, Hailong, Yu, Woo Jong, Terasaki, Ichiro, Huang, Yu, E-mail: yhuang@seas.ucla.edu, California Nanosystems Institute, University of California, Los Angeles, California 90095, Duan, Xiangfeng, E-mail: xduan@chem.ucla.edu, and California Nanosystems Institute, University of California, Los Angeles, California 90095. Mon . "Metal–semiconductor transition in atomically thin Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8} nanosheets". United States. doi:10.1063/1.4892975.
@article{osti_22303561,
title = {Metal–semiconductor transition in atomically thin Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8} nanosheets},
author = {Wang, Yang and Cheng, Rui and Dong, Jianjin and Liu, Yuan and Zhou, Hailong and Yu, Woo Jong and Terasaki, Ichiro and Huang, Yu, E-mail: yhuang@seas.ucla.edu and California Nanosystems Institute, University of California, Los Angeles, California 90095 and Duan, Xiangfeng, E-mail: xduan@chem.ucla.edu and California Nanosystems Institute, University of California, Los Angeles, California 90095},
abstractNote = {Two-dimensional layered materials have attracted considerable attention since the discovery of graphene. Here we demonstrate that the layered Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8} (BSCO) can be mechanically exfoliated into single- or few-layer nanosheets. The BSCO nanosheets with four or more layers display bulk metallic characteristics, while the nanosheets with three or fewer layers have a layer-number-dependent semiconducting characteristics. Charge transport in bilayer or trilayer BSCO nanosheets exhibits Mott 2D variable-range-hopping (VRH) conduction throughout 2 K–300 K, while the charge transport in monolayers follows the Mott-VRH law above a crossover temperature of 75 K, and is governed by Efros and Shklovskii-VRH laws below 75 K. Disorder potentials and Coulomb charging both contribute to the transport gap of these nanodevices. Our study reveals a distinct layer number-dependent metal-to-semiconductor transition in a new class of 2D materials, and is of great significance for both fundamental investigations and practical devices.},
doi = {10.1063/1.4892975},
journal = {APL Materials},
number = 9,
volume = 2,
place = {United States},
year = {Mon Sep 01 00:00:00 EDT 2014},
month = {Mon Sep 01 00:00:00 EDT 2014}
}
  • Electrical property evolution of Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} single crystals (AE = Ca, Sr and Ba) is systematically explored. When AE changes from Ca to Ba, the electrical property of Bi{sub 2}Ca{sub 2}Co{sub 2}O{sub 8+δ} and Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+δ} demonstrates semiconductor-like properties. But Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} shows the metallic behavior. Analysis of temperature-dependent resistance substantiates that from metallic Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} to semiconductor-like Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+δ} can be attributed to Anderson localization. However the semiconductor behaviour of Bi{sub 2}Sr{sub 2}Co{sub 2}O{sub 8+δ} and Bi{sub 2}Ca{sub 2}Co{sub 2}O{sub 8+δ} is related to electronic correlationsmore » effect that is inferred by large negative magnetoresistance (∼70%). The theoretical electronic structures and valence X-ray photoemission spectroscopy substantiate that there is a relative large density of state around Fermi level in Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} compared with other two compounds. It suggests that Bi{sub 2}Ba{sub 2}Co{sub 2}O{sub 8+δ} is more apt to be metal in this material system.« less
  • A cobaltite, Bi{sub 3.7}Sr{sub 11.4}Co{sub 8}O{sub 28{minus}{delta}}, with a tubular structure derived from the 2201-type has been synthesized for the first time. This oxide represents, like the homologous manganese phase, the n = 2 member of the large structural [Bi{sub 2}Sr{sub 2}MO{sub 6}]{sub n}[Sr{sub 8}M{sub 6}O{sub 16{+-}{delta}}] family (M = Cu, Co, Mn). Although its structure is similar to the Mn phase, it crystallizes in a different space group, Ammm (or Amm2), with a = 5.5232(2) {angstrom}, b = 23.465(1) {angstrom}, and c = 23.462(1) {angstrom}. The HREM study confirms that the structure consists of the stacking along b (ormore » c) of 2201-type slices with single cobalt-deficient perovskite slices [Sr{sub 8}Co{sub 6}O{sub 6-{delta}}]. But the important difference with the Mn phase concerns the nature of the Co{sub 4} pillars, which are at the intersection of two [Sr{sub 8}Co{sub 6}O{sub 16{minus}{delta}}] slices. They form four corner-sharing CoO{sub 4} tetrahedra instead of MnO{sub 6} octahedra and MnO{sub 5} pyramids. This structural difference means that the Mn and Co phases do not form a complete solid solution. The tubular series Bi{sub 4{minus}y}Sr{sub 12{minus}z}Mn{sub 8{minus}x}Co{sub x}O{sub 28{+-}{delta}} could only be obtained for 0 {le} x {le} 2.5. The magnetic properties of this oxide are very complex and are very sensitive to the oxygen content. In particular, after oxygen pressure annealing, they are characteristic of spin-state transitions with temperature close to 50 and 450 K, similar to those observed in the LaCoO{sub 3} compound.« less
  • A new cobaltite, Bi{sub 5.8}Sr{sub 15.2}Co{sub 10}O{sub 40{minus}{delta}}, with a tubular structure derived from the 2201-type has been synthesized. This oxide represents the n = 4 member of the large structural [Bi{sub 2}Sr{sub 2}MO{sub 6}]{sub n}[Sr{sub 8}M{sub 6}O{sub 16{+-}{delta}}] family (M = Cu, Mn, Co). Its average structure, similar to that of the copper-based phase, crystallizes in the space group Fmmm with cell parameters a = 5.4650(5){angstrom}, b = 34.042(2){angstrom}, and c = 23.574(1){angstrom}. Its complex crystal chemistry has been studied using XRPD and HREM techniques. This structure can be described as an intergrowth along b, of two types ofmore » (010) slices: 2202-type slices [Bi{sub 2}Sr{sub 2}CoO{sub 6}] that are four octahedron thick and cobalt-deficient perovskite-related slices [Sr{sub 8}Co{sub 6}O{sub 16{minus}{delta}}] that are one octahedra thick. The study of the magneto-transport properties of this new cobaltite shows an antiferromagnetic behavior below 80 K and a large decrease by 500 of the resistivity at room temperature by annealing under oxygen pressure.« less
  • We have studied the influence of disorder induced by oxygen on the normal state resistivity of under doped Bi{sub 2}Sr{sub 2}Cu{sub 1}O{sub 6+d}(Bi-2201) thin films, deposited in situ onto heated SrTiO{sub 3}(100) substrates by using DC magnetron sputtering for an off-stoichiometric target. The compositions and structural characterization for the deposited films were carried by (EDX), (XPS) and X-ray diffraction measurements. The effect of partial oxygen pressure in the sputtering gas on the metal-insulator transition are presented.
  • We report the growth of untwinned epitaxial thin films of Bi-Sr-Ca-Cu-O by atomically layered heteroepitaxy on SrTiO{sub 3} substrates. These films are {ital c}-axis oriented as-layered and do not exhibit 90{degree} in-plane defects, i.e., {ital a}-{ital b} twinning.'' By misorienting the surface normal from {l brace}100{r brace} by approximately 4{degree} towards {l angle}111{r angle}, the cubic symmetry of the {l brace}100{r brace} surface is adequately broken to completely align the {ital b} axis of the superconducting film with respect to the substrate. Reflection high-energy electron diffraction patterns observed during growth and post-growth x-ray diffraction analysis indicate that the incommensurate structuralmore » modulation occurs along the same direction as the step edges.« less