Remskar et al. Nanoscale Res Lett 2011, 6:26 http://www.nanoscalereslett.com/content/6/1/26 N A N O E X P R E S S Open Access The MoS Nanotubes with Defect-Controlled 2 Electric Properties Maja Remskar1*, Ales Mrzel1, Marko Virsek1, Matjaz Godec2, Matthias Krause3, Andreas Kolitsch3, Amol Singh4, Alan Seabaugh4 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. Introduction 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. In analogy to graphite, nanoparticles of many two-dimensional inor- ganic compounds are unstable against folding and can form closed cage structures which are referred to as inorganic fullerene-like particles and inorganic nano- tubes[1]. Recent discovery of MoS2 nanopods called “mama"-tubes [2] with MoS2 fullerene-like particles in-situ grown in a confined geometry of MoS2 nano- tubes and coaxial MoS2 nanotube hybrids [3] have opened a new way of synthesis of MoS2 nanotubes from MoxSyIz ternary compounds, which allows for the pro- duction of mass quantities of nanomaterials. Weak van der Waals interactions among MoS2 molecular layers enable low-strength shearing and several possible stack- ings [2,4]. Molybdenum disulfide nanostructures are receiving considerable attention because of their potential applica- tions as heterogeneous catalysts for desulfurization pro- cesses [5], hydrogen evolution [6,7], and as materials for * Correspondence: maja.remskar@ijs.si 1Jozef Stefan Institute, Jamova 39, 1000, Ljubljana, Slovenia. Full list of author information is available at the end of the article thermoelectric applications [8]. MoS2 microplatelets have been used as a solid lubricant or as an additive in oil or grease for more than 60 years. Cage-like nanos- tructures, e.g. cylindrical MoS2 nanotubes, represent a new generation of lubricants with extremely low friction resulting from the size, small enough to turn microvoids and nanovoids of the objects in mechanical contact into lubricant reservoirs, and by the curved geometry of the nanoparticles, which put them into constantly parallel orientation with the counterpart surfaces. The orienta- tion relationship has been proposed to explain the ultra- low friction measured on thin films composed of MoS2 fullerene-like particles even at high humidity [9]. Lubri- cation is strongly related to electronic properties, more precisely to the filling of Mo d 2 molecular orbitals z [10]. Control of nanotube dimensions and the density of defects that influence transport properties are of great importance in the construction of nanoscale electronic devices and multifunctional materials. The significantly lower molecular mass of MoS2 in comparison with WS2 is an advantage for many applica- tions, although MoS2 nanotubes are found to be more difficult to fabricate. Several different growth techniques are used for the synthesis of multiwall MoS2 inorganic nanotubes, like sulfurization of molybdenium oxides [11,12] and chlorides [13] in a stream of H2S gas, ther- mal decomposition of (NH4)2MoS4 [14] and by the © 2010 Remskar et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.