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Abstract: For the direct fabrication of densely distributed one dimensional nanostructures on Si substrates, Si (100) surfaces were bombarded by obliquely incident 3keV Ar+ ions with a simultaneous supply of Mo seed atoms at various temperatures ranging from room temperature to 400°C. The surface sputtered at room-temperature with Mo seeding was characterized by the nanocones pointing in the direction of the incident ion beam. In addition, they possessed a so-called “web” at their acute-angle side. This web decreased in size with an increase in the sputtering temperature. Thus, the projections fabricated at elevated temperatures were featured by the nanorod-like structure rather than conical structure. With increasing the sputtering temperature, projections decreased in base diameter (from ∼90nm at 200°C to ∼50nm at 400°C) while they increased in both length (from ∼160nm at 200°C to ∼240nm at 400°C) and numerical density (from ∼5×107 mm−2 at 200°C to ∼1.2×108 mm−2 at 400°C). The controlled fabrication of such densely distributed one dimensional nanoprojections on Si using ion beam technique, we believe, would open up a variety of applications such as nanoelectronics and optoelectronics devices. [Copyright &y& Elsevier]

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 × 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 × 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. [Copyright &y& Elsevier]

Abstract: A compact angle-resolved secondary ion mass spectrometer with a special geometrical configuration, composing of a differentially pumped micro-beam ion gun, a tiltable sample stage and a time-of-flight (TOF) mass spectrometer, was newly developed. This system enables the measurement of angular distribution (AD) of secondary ions, which are ejected by oblique Ar+ sputtering, by a simple tilt operation of the sample stage for ejection angles ranging from 0° to 60° with keeping the ion incidence angle constant 62°±2° from the normal to the surface. Using this system, AD of secondary ions from an HfN film by 3keV Ar+-ion bombardment was measured at room temperature. Since the yield of HfN+ dimer ions was almost independent of Hf+ and N+ monomer ions, it was concluded that the HfN+ dimer ions were generated via the “as such” direct emission process. [Copyright &y& Elsevier]

Novel glass-ceramic composites with optical bandgap tunability were synthesised. Zinc silicate powder (ZS) was mixed with multi-walled carbon nanotubes (MWCNTs) at various mass fractions (0, 1, 2, and 3 wt %), followed by argon sintering. X-ray diffraction (XRD) analysis revealed the structural change from an amorphous ZS phase to a crystalline willemite phase (Zn 2 SiO 4) by adding MWCNTs, and the largest crystallite size was obtained for ZS with 2.0 wt% MWCNTs. Although the agglomeration of ZS and MWCNTs was observed by field emission scanning electron microscopy (FESEM), there was no chemical interaction between ZS and MWCNTs as confirmed by Fourier transform infrared spectroscopy (FTIR). MWCNTs enhanced the crystallisation, which led to the green emission of Zn 2 SiO 4 blue-shifting from 572 nm to 557 nm. The narrowed optical bandgap of Zn 2 SiO 4 was attributed to the MWCNT-induced exciton localised between the valence band and conduction band of Zn 2 SiO 4. The bandgap tuning effect of MWCNTs potentially paved new ways to mass fabricate zinc silicate-based semiconductors with desirable optical bandgap energy E g , which significantly benefits the sensor and laser-related industry. [ABSTRACT FROM AUTHOR]

In this work, we utilize Joule heating to convert Pt-embedded amorphous carbon nanofiber (CNF) to multiwall carbon nanotube (CNT) in a transmission electron microscope (TEM). The transformation process of Pt-embedded amorphous CNF to multiwall CNT and nano-soldering process using Pt encapsulated CNT was investigated in TEM in detail. Molten Pt-encapsulated inside CNF and CNT always flowed towards the anode, proving electromigration to be the dominant force over thermal migration. Controllable electromigration of Pt was utilized to connect the Pt-included CNT to another CNT, thus forming a seamlessly welded CNT structure. Further, two separate CNF were brought together to form Y-contact which was transformed into Y-junction CNT structure by controlled electromigration of Pt. Changes in morphology and electrical property during CNT formation and nano-soldering were probed in real time with high resolution TEM. Our method provides a procedure for the position control synthesis of CNT and its nano-soldering which can be an important step for future development of a CNT based nanoelectrical circuit. [ABSTRACT FROM AUTHOR]

A technology for converting waste materials to high quality large-area monolayer graphene film can be significant and thereby obtaining high value-added product. Here, we revealed the transformation of waste chicken fat into uniform monolayer graphene film on re-solidified Cu by a low pressure chemical vapor deposition (LPCVD) technique. The evolve gas analyzer-gas chromatography–mass spectrometry (EGA-GC–MS) analysis of chicken fat oil showed that the free fatty acid in chicken oil decomposed into a short hydrocarbon chains which makes it favorable to use as a carbon precursor for graphene synthesis. Growth of uniform monolayer graphene film on the re-solidified Cu was confirmed by Raman mapping, where 2D to G peak intensity ratio (I 2D /I G ) is 3.0 at most of the area. Thus, the use of waste from poultry industry as a carbon source instead of commonly used hydrocarbon gas sources for graphene synthesis can be an approach for green nanotechnology. [ABSTRACT FROM AUTHOR]

Visible light driven C-doped mesoporous TiO 2 (C-MTiO 2 ) nanorods have been successfully synthesized through green, low cost, and facile approach by sol-gel bio-templating method using regenerated cellulose membrane (RCM) as nanoreactor. In this study, RCM was also responsible to provide in-situ carbon sources for resultant C-MTiO 2 nanorods in acidified sol at low temperatures. The composition, crystallinity, surface area, morphological structure, and optical properties of C-MTiO 2 nanorods, respectively, had been characterized using FTIR, XRD, N 2 adsorption/desorption, TEM, UV–vis-NIR, and XPS spectroscopy. The results suggested that the growth of C-MTiO 2 nanorods was promoted by the strong interaction between the hydroxyl groups of RCMs and titanium ion. Optical and XPS analysis confirmed that carbon presence in TiO 2 nanorods were responsible for band-gap narrowing, which improved the visible light absorption capability. Photocatalytic activity measurements exhibited the capability of C-MTiO 2 nanorods in degradation of methyl orange in aqueous solution, with 96.6% degradation percentage under visible light irradiation. [ABSTRACT FROM AUTHOR]

Doping of a foreign element in sp 2 hybridized graphene lattice is of significant importance to tune the electrical and chemical properties. Here, we report on the grain structures of substitutional nitrogen-doped graphene synthesized by an atmospheric pressure (AP) solid source-based chemical vapor deposition (CVD) technique. Nitrogen-doped graphene was synthesized by mixing solid camphor and melamine as carbon and nitrogen source, respectively. The precursor materials quantity significantly affects the graphene growth on Cu foil and thereby the nitrogen doping and content. Transmission electron microscopy (TEM) analysis was performed to determine the nitrogen substitutional sites in the graphene. Dark-field (DF) TEM analysis was carried out to evaluate the graphene grain structure grown with introduction of nitrogen dopant. We obtained different grain orientations, where an individual grain size is more than 5 μm. Our findings show that graphitic nitrogen defects can be introduced in the large individual graphene grain by the developed solid source-based CVD technique. [ABSTRACT FROM AUTHOR]

Here, we reveal the structural transformation process of as-synthesized individual graphene crystals with oxidation of a copper (Cu) foil. We found that the transformation of a graphene crystal with Cu oxidation is significantly different for the thermal annealing and room temperature long-term atmospheric oxidation. Annealing creates large cracks in an individual graphene crystal due to the thermal stress and strain created by rapid oxidation of Cu surface. The cracks are further enhanced with longer annealing duration enabling oxygen diffusion through cracks, thereby accelerating oxidization of Cu. Eventually, the graphene crystals are completely damaged, leaving behind the highly oxidized Cu surface. On the other hand, in case of room temperature long-term atmospheric oxidation, oxygen diffusion occurs underneath of a graphene crystal through the reactive edge without any large cracks formation. The graphene crystals decouple from Cu surface during the oxygen diffusion and oxidation process, however no structural deformation is observed. This finding shows the significant contrast of structural change of graphene crystal and oxidation behaviors of Cu surface with thermal annealing and room temperature atmospheric oxidation. [ABSTRACT FROM AUTHOR]

Abstract: We present a direct observation of structural change in Au-incorporated carbon nanofiber (CNF) during a field emission (FE) process using an in situ transmission electron microscopy (TEM). The TEM images and their electron diffraction pattern together with electron energy loss spectroscopy (EELS) indicated that the amorphous carbon structure of CNF was transformed to hollow graphitic structure catalyzed by dispersed Au particles before FE. Thus, the in situ TEM study will be promising to reveal the formation process of nanocarbon materials by solid phase reaction depending on the catalyst metal element for metal-incorporated CNFs. [Copyright &y& Elsevier]