Ales Mrzel

Air-stable monodispersed Mo6S3I6 nanowires

We report on the properties of a new air-stable nanowire material with the chemical formula Mo6S3I6 .T he distinguishing features of the material are rapid one-step synthesis, easy isolation and controllable dispersion into small-diameter wire bundles. Elemental analysis, x-ray diffraction, thermogravimetry, differential thermal analysis, Raman scattering and electron microscopy were used to characterize the material.

The MoS2 Nanotubes with Defect-Controlled Electric Properties

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.

Field-emission properties of molybdenum disulfide nanotubes

The field-emission (FE) properties of molybdenum disulfide nanotubes (NTs) are reported for the single-tip geometry. Reproducibly stable FE currents in excess of 10 μA were measured from single NT tips in vacuum of 10−7 mbar. Valuable characteristics of the nanotube material are ease of processing and reproducibility of the FE properties.

Ferromagnetism in a cobaltocene-doped fullerene derivative below 19 K due to unpaired spins only on fullerene molecules

Abstract We report the discovery and physical properties of a new organic ferromagnet, 3-aminophenyl-methano-fullerene[60]-cobaltocene, with a Curie temperature T C of 19 K. Near- and mid-infrared spectroscopy together with electron spin resonance experiments show that spins reside entirely on the fullerene units, from which we deduce that the ferromagnetism is a consequence solely of exchange interactions between distributed p-electrons on the 3-aminophenyl-methano-fullerene[60] molecules. The ferromagnetic state of the compound is characterized by a very rapid transition to ferromagnetic order below T C , a low saturation field of H s =40 Oe and no measurable hysteresis.

The MoS2 nanotube hybrids

The MoS2 nanotube hybrids represent a family of nanomaterials, where nanotubes serve as nanoreactors and in some cases also as nanocontainers of MoS2 fullerenelike particles, which have in situ grown in a confined geometry of nanotubes. A simple temperature control of morphology, size, and inner structure of nanohybrids leads to a selective morphology such as coaxial nanotubes, “mama”-tubes with encapsulated nano-onions, the growth of MoS2 nanobuds or it facilitates a release of MoS2 nano-onions, which then form weakly bonded self-assemblies. Growth mechanism is discussed based on atomic probe electron microscopy, x-ray diffraction and high-resolution transmission electron microscopy.

Electrochemical preparation and characterisation of LizMoS2−x nanotubes

Abstract The recent synthesis of self-assembled single-wall MoS 2−x I y (x≈0 and y≈1/3) NTs bundles has given a new material, which can reversibly exchange lithium in non-aqueous electrolytes. It has been found that a relatively large amount of lithium can be inserted into the MoS 2−x I y NTs bundles (up to 3 mol of Li per MoS 2 mol). The amount of inserted lithium and, also, the reversibly extracted lithium, depends on the quality of MoS 2−x I y NTs bundles and their prior treatment. Comparing their electrochemical properties with layered 2H-MoS 2 , one finds a significant increase in the amount of inserted lithium and a decrease by about 0.7 V in the potential at which lithium insertion takes place. Furthermore the decrease of electron spin resonance (ESR) signal of lithiated nMoS 2−x I y NTs bundles exposed to the air is slower than the decrease of ESR signal of lithiated layered 2H-MoS 2 crystals which suggests that lithiated MoS 2−x I y NTs bundles are less air-sensitive than the lithiated layered 2H-MoS 2 crystals. These differences are attributed to the particular one-dimensional topology of self-assembled MoS 2−x I y NTs bundles.

Fermi electron wave packet interference images on carbon nanotubes at room temperature

We report on the structure and electronic properties of single wall carbon nanotubes tips with atomically spatial resolution. Scanning tunneling microscopy shows topographic images of closed tips with a variety of geometrical structure; these include round, conical, as well as tips with a messy shape. Standing wave pattern of the charge density is observed at the tube cap which is formed due to constructive interference between the electronic states and its reflection on the nanotube tips. Atomically resolved images show asymmetry in the charge density that decay out within 6 nm away from the cap. These distinctive tip states do not exist elsewhere on the tube and are related to the presence of topological defects at tube ends.

Molecular nitrogen in N-doped TiO2 nanoribbons

The nitrogen doping of TiO2 nanoribbons during the thermal transformation of hydrogen titanate nanoribbons (HTiNRs) between 400 and 650 °C in a dynamic ammonia atmosphere was investigated using X-ray photoelectron spectroscopy (XPS), transmission X-ray microscopy combined with near-edge X-ray absorption fine structure spectroscopy (NEXAFS-TXM), X-ray diffraction (XRD) and electron paramagnetic resonance measurements (EPR). Comprehensive structural characterizations have revealed that for a calcination temperature of 400 °C, the HTiNRs transform into pure monoclinic TiO2 β-phase (TiO2-B) whereas at higher calcination temperatures (580 and 650 °C) a mixture of TiO2-B and anatase is obtained. XPS and EPR results clearly reveal the nitrogen doping of TiO2 nanoribbons and that, depending on the calcination temperature, nitrogen atoms occupy interstitial and substitutional sites. Moreover, in samples calcined at 580 and 650 °C the presence of N2-like species in the HTiNRs was detected by NEXAFS-TXM. These species are trapped in the HTiNRs structure. EPR measurements upon light illumination have disclosed the generation of photoexcited states which implies that nitrogen has an important effect on the electronic structure of N-doped TiO2.

Field emission of point-electron source Mo6S3I6 nanowires

Th efi eld emission (FE) properties of nanowires made from the recently synthesized nanowire material Mo6S3I6 are reported. A single nanowire was mounted on an indium-coated nickel holder by dielectrophoresis in isopropyl alcohol. A careful activation or conditioning in a vacuum of 10 −7 mbar was shown to be indispensable in order to extract relatively stable FE currents in excess of 1 µ Ao riginating from only a few sites at the end of the nanowire. Measurements were performed in an FE microscope with an additional plane mesh, which enables us to record I –U characteristics in diode mode, or to observe the emission patterns in triode mode. With FE currents around 5–7 µ At he emitter degrades gradually, and to some extent irreversibly. The degradation mechanism is not a reversal of the instant site build-up.

Imaging the interlayer interactions of multiwall carbon nanotubes using scanning tunneling microscopy and spectroscopy

Using atomically-resolved scanning tunneling microscopy and spectroscopy, we probe the nature of interwall interactions within multiwall carbon nanotubes at room temperature. We find that, at low bias voltages, the tunnel current depends strongly on the atomic position, introducing visibility differences between adjacent lattice sites. Since all atoms are equally visible in analogous measurements on single-wall nanotubes, we conclude that these modulations are introduced by the interwall interactions and provide unique information about the stacking nature.