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Xu EZ, Liu HM, Park K, Li Z, Losovyj Y, Starr M, Werbianskyj M, Fertig HA, Zhang SX. p-Type transition-metal doping of large-area MoS 2 thin films grown by chemical vapor deposition. Nanoscale 2017; 9:3576-3584. [PMID: 28246665 DOI: 10.1039/c6nr09495c] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Two-dimensional transition metal dichalcogenides (e.g. MoS2) have recently emerged as a promising material system for electronic and optoelectronic applications. A major challenge for these materials, however, is to realize bipolar electrical transport properties (i.e. both p-type and n-type conduction), which is critical for enhancing device performance and functionalities. Here, we demonstrate the transition metal zinc as a p-type dopant in the otherwise n-type MoS2, through systematic characterizations of large area Zn-doped MoS2 thin films grown by a one-step chemical vapor deposition (CVD) approach. Raman characterization and X-ray photoelectron spectroscopy studies identified millimeter-scale, monolayer films with 1-2% Zn as dopants. Zinc doping suppresses n-type conductivity in MoS2 and shifts its Fermi level downwards. The stability and p-type nature of Zn dopants were further confirmed by density-functional-theory calculations of formation energies and electronic band structures. The electrical transport properties of Zn-MoS2 films can be influenced by stoichiometry, and p-type gate transfer characteristics were realized by thermal treatment under a sulfur atmosphere. Our work highlights transition-metal doping followed by sulfur vacancy elimination in CVD grown films as a promising route for achieving large area p-type transition metal dichalcogenide films that are essential for practical applications in electronics and optoelectronics.
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Affiliation(s)
- E Z Xu
- Department of Physics, Indiana University, Bloomington, IN 47405, USA.
| | - H M Liu
- Department of Physics, Indiana University, Bloomington, IN 47405, USA.
| | - K Park
- Department of Physics, Virginia Tech, Blacksburg, Virginia 24061, USA
| | - Z Li
- Department of Physics, Indiana University, Bloomington, IN 47405, USA.
| | - Y Losovyj
- Department of Chemistry, Indiana University, Bloomington, IN 47405, USA
| | - M Starr
- Department of Physics, Indiana University, Bloomington, IN 47405, USA.
| | - M Werbianskyj
- Department of Physics, Indiana University, Bloomington, IN 47405, USA.
| | - H A Fertig
- Department of Physics, Indiana University, Bloomington, IN 47405, USA.
| | - S X Zhang
- Department of Physics, Indiana University, Bloomington, IN 47405, USA.
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Xu EZ, Li Z, Martinez JA, Sinitsyn N, Htoon H, Li N, Swartzentruber B, Hollingsworth JA, Wang J, Zhang SX. Diameter dependent thermoelectric properties of individual SnTe nanowires. Nanoscale 2015; 7:2869-2876. [PMID: 25623253 DOI: 10.1039/c4nr05870d] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The lead-free compound tin telluride (SnTe) has recently been suggested to be a promising thermoelectric material. In this work, we report on the first thermoelectric study of individual single-crystalline SnTe nanowires with different diameters ranging from ∼218 to ∼913 nm. Measurements of thermopower S, electrical conductivity σ and thermal conductivity κ were carried out on the same nanowires over a temperature range of 25-300 K. While the electrical conductivity does not show a strong diameter dependence, the thermopower increases by a factor of two when the nanowire diameter is decreased from ∼913 nm to ∼218 nm. The thermal conductivity of the measured NWs is lower than that of the bulk SnTe, which may arise from the enhanced phonon - surface boundary scattering and phonon-defect scattering. Temperature dependent figure of merit ZT was determined for individual nanowires and the achieved maximum value at room temperature is about three times higher than that in bulk samples of comparable carrier density.
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Affiliation(s)
- E Z Xu
- Department of Physics, Indiana University, Bloomington, Indiana 47405, USA.
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Xu EZ, Mullani NA, Gould KL, Anderson WL. A segmented attenuation correction for PET. J Nucl Med 1991; 32:161-5. [PMID: 1988625] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
A segmented attenuation correction technique has been developed for positron emission tomography which computes attenuation correction factors automatically from transmission images for use in the final image reconstruction. The technique segments the transmission image into anatomic regions by thresholding the histogram of the attenuation values corresponding to different regions such as soft tissue and lungs. Average values of attenuation are derived from these regions and new attenuation correction factors are computed by forward projection of these regions into sinograms for correction of emission images. The technique has been tested with phantom studies and with clinical cardiac studies in patients for 30- and 10-min attenuation scan times. This method for attenuation correction was linearly correlated (slope = 0.937 and r2 = 0.935) with the standard directly measured method, reducing noise in the final image, and reducing the attenuation scan time.
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Affiliation(s)
- E Z Xu
- Electrical Engineering Department, University of Houston, Texas
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