[en] The phenomenon was studied by Auger electron spectroscopy in which the appearance of sulfur on a surface of tungsten is enhanced when it is bombarded by an electron beam in an ultra-high vacuum. An additional tungsten target was provided near a tungsten specimen, and the appearing rates of sulfur on the specimen were compared when the specimen and the target were respectively bombarded by an electron beam. As a result, for the specimen used here, it was confirmed that the sulfur appearance enhanced by electron bombardment was not caused by the segregation from the bulk but was resulted from the deposition from outside of the specimen. The surface distribution of sulfur showed a sharp peak at the point of bombardment; this was elucidated as being the result of the concentration of surface sulfur towards the bombarded area of the surface. (author)

[en] We have constructed a microprotrusion fabrication system consisting of a differentially pumped ion gun and a seed material supply source, both of which operate under an UHV condition. Using this system, Si (1 0 0) surfaces were bombarded by obliquely incident 3 keV Ar⁺ ions at room temperature with and without a simultaneous supply of Mo atoms. The sputtered surfaces without a Mo supply were flat or characterized by a nano-sized rippled structure, whereas those with simultaneous Mo seeding displayed densely distributed Mo-seeded cones. For a very low seeding rate of ∼7.2 x 10^-2 nm/min, the optimum sputtering rate needed to induce seed cone growth over a sputtered crater was determined to be 4.4 nm/min. The size and number density of cones thus grown at the crater center were estimated to be 65-230 nm in width and ∼3 x 10⁷ mm^-2, respectively. The controlled fabrication of such seed cones may be applicable to the development of electron sources whose basic operational mechanism is field-electron emission

[en] The synthesis of large-area monolayer tungsten disulphide (WS_2) single crystal is critical for realistic application in electronic and optical devices. Here, we demonstrate an effective approach to synthesize monolayer WS_2 crystals using tungsten hexachloride (WCl_6) as a solid precursor in atmospheric chemical vapor deposition process. In this technique, 0.05M solution of WCl_6 in ethanol was drop-casted on SiO_2/Si substrate to create an even distribution of the precursor, which was reduced and sulfurized at 750 °C in Ar atmosphere. We observed growth of triangular, star-shaped, as well as dendritic WS_2 crystals on the substrate. The crystal geometry evolves with the shape and size of the nuclei as observed from the dendritic structures. These results show that controlling the initial nucleation and growth process, large WS_2 single crystalline monolayer can be grown using the WCl_6 precursor. Our finding shows an easier and effective approach to grow WS_2 monolayer using tungsten halide solution-casting, rather than evaporating the precursor for gas phase reaction

[en] In this work, we report the synthesis of two new forms of WS₂ nanostructures - freestanding WS₂ trees and fibers on Au by chemical vapor deposition. It is observed that dislocation-driven growth causes WS₂ crystals to grow and merge in both vertical and horizontal directions to form the pyramidal tree. During the formation of WS₂ fibers, the presence of two-step growth was demonstrated. It is observed that sulphurization of WO₃ nanoparticle leads to formation of WS₂ rod in the first stage, followed by second stage in which selective growth causes some WS₂ layers grow faster compared to other ones leading to the formation of fibrous WS₂ structure. Fibers synthesized by our reported method have highly exposed WS₂ layers which can demonstrate interesting catalytic and edge related properties or can be functionalized for future applications. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

[en] Graphitized nanocarbon, such as graphene and carbon nanotube (CNT), is one of the hottest materials in nanotechnology and nanomaterials science, thus myriads of applications are expected. The subjects to be solved for realizing those applications include their controllable synthesis, namely, controllability in crystallinity, size, growth position, growth temperature and so on. In order to achieve the growth controllability, understanding of their growth process by its detailed observation in atomic dimension will be indispensable. In this talk, we will deal with a challenge to the graphene growth at temperatures as low as 150-250°C based on the findings in the in situ dynamic transmission electron microscope (TEM) observations of the graphitization process in the solid (liquid) phase reaction

[en] Highlights: • Demonstrated anisotropic etching of h-BN for nanoribbons fabrication. • Synthesis of BCN layers using mixture of solid sources and their anisotropic etching. • Raman studies confirm B and N incorporation in graphene and BCN layer formation. • SiO₂ nanoparticles incorporated during growth assisted H₂-induced etching process. • The etching process is significant to fabricate various h-BN related novel structures. Anisotropic etching of hexagonal boron nitride (h-BN) and boron–carbon–nitrogen (BCN) basal plane can be an exciting platform to develop well-defined structures with interesting properties. Here, we developed an etching process of atomically thin h-BN and BCN layers to fabricate nanoribbons (NRs) and other distinct structures by annealing in H₂ and Ar gas mixture. BCN and h-BN films are grown on Cu foil by chemical vapor deposition (CVD) using solid camphor and ammonia borane as carbon, nitrogen and boron source, respectively. Formation of micron size well-defined etched holes and NRs are obtained in both h-BN and BCN layers by the post growth annealing process. The etching process of h-BN and BCN basal plane to fabricate NRs and other structures with pronounced edges can open up new possibilities in 2D hybrid materials.

[en] Indium-doped ZnO (IZO) films with low In content (<6 at.%) were fabricated by rf helicon magnetron sputtering. The uniformity of the composites was confirmed by elemental analysis. The formation of an In-Zn-O solid solution was verified using X-ray diffraction (XRD) patterns. A wide, high-transmittance region (400-2000 nm) and >80% transmittance in the window of fiber optics telecommunication (1.30-1.55 μm) were observed. The incorporation of indium enhances the optical transmission in the designated visible and infrared wavelengths. The optical band gap shows a slight blue-shift with increasing In doping which can be explained by the Burstein-Moss effect. The Urbach tail parameter E₀ increases with increasing indium content, which coincides with the increase in the full width half maximum (FWHM) of (0002) planes in XRD patterns. A decline in crystal quality with In incorporation in IZO films is also confirmed from photoluminescence (PL) spectra. (author)

[en] Glassy carbon was Ar⁺-ion bombarded with a simultaneous Mo supply under ultrahigh vacuum conditions using a microprotrusion fabrication system that consists of a differentially pumped ion gun and a seed-material supply source. Conical protrusions were formed by sputtering with a seed supply, and carbon nanofibers (CNFs) grew on the tips even at room temperature. The length of CNFs reached up to ∼10 μm, and their diameter was almost uniform (50 nm) in the growth direction. The short CNFs aligned in the ion beam direction, whereas the long ones were non-aligned. The CNF growth on a glassy carbon surface was ascribed to the enhanced surface texturing and to the massive redeposition of C atoms onto cones, both of which are specific to the oblique ion bombardment: The former would lead to an increase in the number of possible nucleation sites for the CNF growth, and the C atoms arising from the latter process would migrate toward the conical tips, thus forming CNFs

[en] Carbon nanofibers (CNFs) with a diameter of 17 nm, and carbon nanoneedles (CNNs) with sharp tips have been synthesized on graphite substrates by ion irradiation of argon ions with the Co supplies rate of 1 and 3.4 nm/min, respectively. Energy dispersive X-ray spectrometry, combined with selected area electron diffraction patterns has been used to identify the chemical composition and crystallinity of these carbon nanostructures. The CNFs were found to be amorphous in nature, while the structures of the CNNs consisted of cubic CoC_x, orthorhombic Co₂C and Co₃C depending on the cobalt content in the CNNs. The diameter of the carbide crystals was almost as large as the diameter of the CNN. Compared to the ion-induced nickel carbides and iron carbides, the formation of single-crystalline cobalt carbides might be due to the high temperature produced by the irradiation.

[en] Highly transparent (transparency 96.5%), flexible and antireflective superhydrophobic (water contact angle >150 ) surfaces have been fabricated at room temperature by the ion irradiation method. This one-step fabrication route was fairly easy to carry out without any heat or chemical treatment and can be completed within few seconds. This novel chemical free fabricating strategy could be extended to numerous polymeric substrates to achieve transparent and flexible superhydrophobic structures for their potential applications in diverse fields. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)