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.
Highlights
One-dimensional nanostructures such as nanorods, nanobelts, nanowires and nanotubes have attracted intensive attention due to their unique applications in mesoscopic physics and nanoscale devices
Recent discovery of MoS2 nanopods called “mama"-tubes [2] with MoS2 fullerene-like particles in-situ grown in a confined geometry of MoS2 nanotubes and coaxial MoS2 nanotube hybrids [3] have opened a new way of synthesis of MoS2 nanotubes from MoxSyIz ternary compounds, which allows for the production of mass quantities of nanomaterials
We report on a synthesis that can be scaled up for bulk production of pure multiwall MoS2 nanotubes of lengths up to several tens micrometers and diameters up to 100 nm using groups of Mo6S4I6 nanowires as precursor crystals
Summary
One-dimensional nanostructures such as nanorods, nanobelts, nanowires and nanotubes have attracted intensive attention due to their unique applications in mesoscopic physics and nanoscale devices. A fraction (5–10 wt.%) of the total synthesized material was transported to the low-temperature zone (1010 K) of the ampoule and grew in the form of a hairy foil composed of Mo6SxIy nanowires with some traces of MoI2 at the interface with the quartz, while the material remaining at the hot zone (1123 K) appeared as a dark-brown powder The stoichiometry of this remaining powder in the form of Mo6S4I6 nanowires was determined by wave dispersive analysis using a scanning electron microscope, Jeol JSM 6500F. These nanowires were used as the precursor material for transformation into MoS2 nanotubes by annealing at 1073 K in the reactive gas composed of 98 vol% of Ar, 1 vol% of H2S, and 1 vol% of H2 for 1 h. Transport properties were measured using an Agilent 4155 semiconductor parameter analyzer using on-wafer probing of two-terminal test structures
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