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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.

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The Mo6S4I6 nanowires: a A SEM image of hedgehog-like self-assemblies of identical nanowires grown up to 10 μm in length; b A TEM image revealing rigid nanocrystals with dome terminations; c A HRTEM image with rows of Mo6 clusters surrounded by sulfur and iodine atoms. A stacking fault in otherwise regular order is marked with a stepped line and associated with a disordered structure; d TED pattern of a single Mo6S4I6 nanowire in the [010] zone assigned in accordance with the proposed space group P63/m and lattice parameters of a hexagonal structure with: a = 1.88(5) nm and c = 1.18 nm.
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Figure 1: The Mo6S4I6 nanowires: a A SEM image of hedgehog-like self-assemblies of identical nanowires grown up to 10 μm in length; b A TEM image revealing rigid nanocrystals with dome terminations; c A HRTEM image with rows of Mo6 clusters surrounded by sulfur and iodine atoms. A stacking fault in otherwise regular order is marked with a stepped line and associated with a disordered structure; d TED pattern of a single Mo6S4I6 nanowire in the [010] zone assigned in accordance with the proposed space group P63/m and lattice parameters of a hexagonal structure with: a = 1.88(5) nm and c = 1.18 nm.

Mentions: Mo6S4I6 nanowires grew as hedgehog-like self-assemblies (Figure 1a) composed of nanowires of very homogeneous size, up to 100 nm in diameter and up to 20 μm in length. Considering that little information is available about this phase with no unit cell determined [18], we describe the direction of growth and assignment of the diffraction pattern in accordance with the similar Mo6S2I8 phase [19]. We find close similarities of electron and X-ray diffraction patterns of both phases, which generalize the report [20] on the stability of the Mo6S9-xIx nanowires (4.5 <x < 6) with different S and I stoichiometries, to the Mo6S4I6 phase. Nanowires of different stoichiometries grow in skeletal structures composed of one-dimensional polymer chains of Mo6–chalcogen–halogen clusters, which differ only in the site occupation by sulfur and iodine. This makes difficulties in the determination of a particular phase, especially based on X-ray results. In our studies, we used electron diffraction obtained on a single nanowire for the elucidation of the symmetry rules, X-ray diffraction for the determination of interlayer distance with sufficient accuracy, and wave dispersive analysis for the determination of the stoichiometry on a single nanowire. Due to a mixed range of selective area diffraction, one cannot exclude the presence of other Mo6S9-xIx and Mo6S10-xIx nanowires in the starting materials, like Mo6S3I6 or Mo6S2I8 [20]. Nevertheless, most of the starting materials can be attributed to one phase, i.e. Mo6S4I6, while the others incorporate impurities that cause broadening of the X-ray peaks.


The MoS 2 Nanotubes with Defect-Controlled Electric Properties
The Mo6S4I6 nanowires: a A SEM image of hedgehog-like self-assemblies of identical nanowires grown up to 10 μm in length; b A TEM image revealing rigid nanocrystals with dome terminations; c A HRTEM image with rows of Mo6 clusters surrounded by sulfur and iodine atoms. A stacking fault in otherwise regular order is marked with a stepped line and associated with a disordered structure; d TED pattern of a single Mo6S4I6 nanowire in the [010] zone assigned in accordance with the proposed space group P63/m and lattice parameters of a hexagonal structure with: a = 1.88(5) nm and c = 1.18 nm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3211322&req=5

Figure 1: The Mo6S4I6 nanowires: a A SEM image of hedgehog-like self-assemblies of identical nanowires grown up to 10 μm in length; b A TEM image revealing rigid nanocrystals with dome terminations; c A HRTEM image with rows of Mo6 clusters surrounded by sulfur and iodine atoms. A stacking fault in otherwise regular order is marked with a stepped line and associated with a disordered structure; d TED pattern of a single Mo6S4I6 nanowire in the [010] zone assigned in accordance with the proposed space group P63/m and lattice parameters of a hexagonal structure with: a = 1.88(5) nm and c = 1.18 nm.
Mentions: Mo6S4I6 nanowires grew as hedgehog-like self-assemblies (Figure 1a) composed of nanowires of very homogeneous size, up to 100 nm in diameter and up to 20 μm in length. Considering that little information is available about this phase with no unit cell determined [18], we describe the direction of growth and assignment of the diffraction pattern in accordance with the similar Mo6S2I8 phase [19]. We find close similarities of electron and X-ray diffraction patterns of both phases, which generalize the report [20] on the stability of the Mo6S9-xIx nanowires (4.5 <x < 6) with different S and I stoichiometries, to the Mo6S4I6 phase. Nanowires of different stoichiometries grow in skeletal structures composed of one-dimensional polymer chains of Mo6–chalcogen–halogen clusters, which differ only in the site occupation by sulfur and iodine. This makes difficulties in the determination of a particular phase, especially based on X-ray results. In our studies, we used electron diffraction obtained on a single nanowire for the elucidation of the symmetry rules, X-ray diffraction for the determination of interlayer distance with sufficient accuracy, and wave dispersive analysis for the determination of the stoichiometry on a single nanowire. Due to a mixed range of selective area diffraction, one cannot exclude the presence of other Mo6S9-xIx and Mo6S10-xIx nanowires in the starting materials, like Mo6S3I6 or Mo6S2I8 [20]. Nevertheless, most of the starting materials can be attributed to one phase, i.e. Mo6S4I6, while the others incorporate impurities that cause broadening of the X-ray peaks.

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.


Related in: MedlinePlus