Maja Remskar

Transistors with chemically synthesized layered semiconductor WS2 exhibiting 105 room temperature modulation and ambipolar behavior

We report the realization of field-effect transistors (FETs) made with chemically synthesized multilayer crystal semiconductor WS2. The Schottky-barrier FETs demonstrate ambipolar behavior and a high (∼105×) on/off current ratio at room temperature with current saturation. The behavior is attributed to the presence of an energy bandgap in the ultrathin layered semiconductor crystal material. The FETs also show clear photo response to visible light. The promising electronic and optical characteristics of the devices combined with the chemical synthesis, and flexibility of layered semiconductor crystals such as WS2 make them attractive for future electronic and optical devices.

Effects of ingested nano‐sized titanium dioxide on terrestrial isopods (Porcellio scaber)

The effects of ingested nano-sized titanium dioxide (TiO2; anatase, 15 nm) on the terrestrial isopod Porcellio scaber (Isopoda, Crustacea) after short-term (3-d) dietary exposure were studied. Activities of antioxidant enzymes, such as catalase (CAT) and glutathione-S-transferase (GST), in digestive glands were affected in a dose-independent manner, but higher-level isopod endpoints, including weight change, feeding rate, food assimilation efficiency, and survival, were not affected up to the highest tested concentration of TiO2 in food (3,000 microg/g). Exposure concentrations of 0.5, 2,000, and 3,000 microg nonsonicated TiO2/g food decreased CAT and GST activities, but intermediate concentrations (1, 10, 100, and 1,000 microg/g food) did not result in significant changes of enzyme activities. When the dispersion of TiO2 was sonicated, no effects on enzyme activities or higher-level biomarkers were observed. The experimental setup with terrestrial isopods designed for dissolved chemicals also is suitable for testing the effects of ingested nanoparticles, but the presentation of toxicity data needs to be adapted according to the mode of action of the nanoparticles and their specific characteristics.

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.

MoS2 as microtubes

We report on the existence of MoS2 hollowed microtubes, several mm in lengths and less than 0.1 μm wall thickness, grown from the vapor phase. Scanning electron microscopy studies reveal that instability of thin weakly bonded sheets against folding causes the tube growth directly or indirectly beyond the formation of turbulent gas flow. Electron diffraction of a single tube wall proves a parallel growth mode of successive layers while the crystal lattices of both tube walls are mutually rotated. A spiral growth mode is proposed.

Liquid crystal elastomer-nanoparticle systems for actuation

Liquid crystal elastomers (LCE) are currently of great interest due to conjoining of mesogenic ordering and rubber elasticity, exhibited in their large spontaneous thermally stimulated changes in shape. It has been shown that nanoparticles (nanotubes, photo-isomerisable dyes, magnetic nanoparticles…) can be incorporated into these LCE networks to create a more sensitive network to external stimuli (i.e. strain or stress, optical, electrical, electro-thermal, magnetic…). Here, we briefly summarise the current state of LCE–nanoparticle systems and explain in detail one system utilising carbon nanoparticles integrated at surfaces that may be used for electro-thermal heating of LCE systems.

Populus seed fibers as a natural source for production of oil super absorbents

The genus Populus, which includes poplars, cottonwoods and aspen trees, represents a huge natural source of fibers with exceptional physical properties. In this study, the oil absorption properties of poplar seed hair fibers obtained from Populus nigra italica when tested with high-density motor oil and diesel fuel are reported. Poplar seed hair fibers are hollow hydrophobic microtubes with an external diameter between 3 and 12 μm, an average length of 4±1 mm and average tube wall thickness of 400±100 nm. The solid skeleton of the hollow fibers consists of lignocellulosic material coated by a hydrophobic waxy coating. The exceptional chemical, physical and microstructural properties of poplar seed hair fibers enable super-absorbent behavior with high absorption capacity for heavy motor oil and diesel fuel. The absorption values of 182-211 g heavy oil/g fiber and 55-60 g heavy oil/g fiber for packing densities of 0.005 g/cm(3) and 0.02 g/cm(3), respectively, surpass all known natural absorbents. Thus, poplar seed hair fibers obtained from Populus nigra italica and other trees of the genus Populus are an extremely promising natural source for the production of oil super absorbents.

Preparation and characterization of highly oriented, photoconducting WS2 thin films

A novel combination of methods is shown to produce semiconducting WS2 thin films with properties close to those of a single crystal. The first step requires the deposition of a very thin Ni layer on a quartz substrate. On top of it an amorphous, sulphur rich, (WS3 +x) thin film is deposited by reactive rf sputtering. The final annealing step in an argon atmosphere yields 200 nm thick WS2 films. X-ray diffraction shows that the films crystallize in the 2H-WS2 phase and are perfectly oriented with the (002) basal planes parallel to the substrate. Residual W18O49 needles andβ-NiS grains are detected by transmission electron microscopy. The dc conductivity and its activation energy have values typical of bulk crystals. The optical absorption spectrum measured at Room Temperature (RT) shows excitonic peaks at the same energies as in a single crystal. RT photoconductivity measured as a function of wavelength is shown to result from interband transitions.

In vivo production of nanosized metal wear debris formed by tribochemical reaction as confirmed by high‐resolution TEM and XPS analyses

High-resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to establish the link between particles isolated from periprosthetic tissue of metal-on-metal (MOM) bearing and the solid deposit at the surface of retrieved MOM hip components. The high resolution of TEM made it possible to identify individual CoCrMo wear particles. Two shapes were observed. Needle-shaped particles ranged from 40 to 120 nm and contained both Co and Cr. Globular particles ranged up to 90 nm and contained high levels of Cr and no Co. Ti- and Ca-based particles were also identified. XPS analysis of the areas of thick solid deposit on the retrieved femoral head showed that the base alloy was covered by up to nearly 1-microm thick layer containing carbon, nitrogen, and oxygen. This layer was organic in nature, presumably protein-related. In areas with a thinner deposit, an organic-related layer was mixed with layers of metal oxides, the latter being much thinner than the extensive organic, carbon-rich layer. Outside the area of the deposit, the passive oxidized chromium layer was thinner, less than 20 nm, and carbon was bound to nonorganic oxygen.

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.