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The MoS 2 Nanotubes with Defect-Controlled Electric Properties

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ABSTRACT

We describe a two-step synthesis of pure multiwall MoS2 nanotubes with a high degree of homogeneity in size. The Mo6S4I6 nanowires grown directly from elements under temperature gradient conditions in hedgehog-like assemblies were used as precursor material. Transformation in argon-H2S/H2 mixture leads to the MoS2 nanotubes still grouped in hedgehog-like morphology. The described method enables a large-scale production of MoS2 nanotubes and their size control. X-ray diffraction, optical absorption and Raman spectroscopy, scanning electron microscopy with wave dispersive analysis, and transmission electron microscopy were used to characterize the starting Mo6S4I6 nanowires and the MoS2 nanotubes. The unit cell parameters of the Mo6S4I6 phase are proposed. Blue shift in optical absorbance and metallic behavior of MoS2 nanotubes in two-probe measurement are explained by a high defect concentration.

No MeSH data available.


a Scanning electron micrograph of a MoS2 nanotube between Ti/Au metal electrodes; b Current–voltage characteristics in the dark and under illumination for the MoS2 nanotube at room temperature with and without visible light illumination.
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Figure 4: a Scanning electron micrograph of a MoS2 nanotube between Ti/Au metal electrodes; b Current–voltage characteristics in the dark and under illumination for the MoS2 nanotube at room temperature with and without visible light illumination.

Mentions: Two-terminal device was fabricated from MoS2 nanotubes to measure transport properties (Figure 4a). The tubes were placed on a thermally-oxidized, heavily-doped p-Si substrate with a 90-nm-thick SiO2 overlayer. Titanium/gold contacts 20/220 nm in respective thickness were formed by electron beam evaporation using a photolithographic lift-off process with separations between the electrodes of 5 μm. Two-terminal measurements on a MoS2 nanotube, 105 nm in diameter, show a metallic (approximately ohmic) conduction. No photoconductivity was observed between measurements taken in the dark and under strong microscope illumination using a halogen lamp (Figure 4b). In addition, the wire conductivity could not be modulated independently on light illumination when backgated through the p + Si substrate in the range from -50 to +50 V with a tube bias ranging from 0 to 5 V, consistent with the metallic character of the nanotube. The nanotube conductivity is estimated to about 2 mS/cm by assuming that the wall thickness is 10 nm, which is the most frequently observed value in these nanotubes. The metallic conductivity could indicate a high density of defects, which form energy states near the Fermi level and influence also the optical absorbance spectra.


The MoS 2 Nanotubes with Defect-Controlled Electric Properties
a Scanning electron micrograph of a MoS2 nanotube between Ti/Au metal electrodes; b Current–voltage characteristics in the dark and under illumination for the MoS2 nanotube at room temperature with and without visible light illumination.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211322&req=5

Figure 4: a Scanning electron micrograph of a MoS2 nanotube between Ti/Au metal electrodes; b Current–voltage characteristics in the dark and under illumination for the MoS2 nanotube at room temperature with and without visible light illumination.
Mentions: Two-terminal device was fabricated from MoS2 nanotubes to measure transport properties (Figure 4a). The tubes were placed on a thermally-oxidized, heavily-doped p-Si substrate with a 90-nm-thick SiO2 overlayer. Titanium/gold contacts 20/220 nm in respective thickness were formed by electron beam evaporation using a photolithographic lift-off process with separations between the electrodes of 5 μm. Two-terminal measurements on a MoS2 nanotube, 105 nm in diameter, show a metallic (approximately ohmic) conduction. No photoconductivity was observed between measurements taken in the dark and under strong microscope illumination using a halogen lamp (Figure 4b). In addition, the wire conductivity could not be modulated independently on light illumination when backgated through the p + Si substrate in the range from -50 to +50 V with a tube bias ranging from 0 to 5 V, consistent with the metallic character of the nanotube. The nanotube conductivity is estimated to about 2 mS/cm by assuming that the wall thickness is 10 nm, which is the most frequently observed value in these nanotubes. The metallic conductivity could indicate a high density of defects, which form energy states near the Fermi level and influence also the optical absorbance spectra.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

We describe a two-step synthesis of pure multiwall MoS2 nanotubes with a high degree of homogeneity in size. The Mo6S4I6 nanowires grown directly from elements under temperature gradient conditions in hedgehog-like assemblies were used as precursor material. Transformation in argon-H2S/H2 mixture leads to the MoS2 nanotubes still grouped in hedgehog-like morphology. The described method enables a large-scale production of MoS2 nanotubes and their size control. X-ray diffraction, optical absorption and Raman spectroscopy, scanning electron microscopy with wave dispersive analysis, and transmission electron microscopy were used to characterize the starting Mo6S4I6 nanowires and the MoS2 nanotubes. The unit cell parameters of the Mo6S4I6 phase are proposed. Blue shift in optical absorbance and metallic behavior of MoS2 nanotubes in two-probe measurement are explained by a high defect concentration.

No MeSH data available.