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Register a new userGrowth and characterization of GaAs nanowires on carbon nanotubes composite films: toward flexible nanodevices
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Poly(ethylene imine) functionalized carbon nanotube thin films, prepared using the vacuum filtration method, were decorated with Au nanoparticles by in situ reduction of HAuCl4 under mild conditions. These Au nanoparticles were subsequently employed for the growth of GaAs nanowires (NWs) by the vapor-liquid-solid process in a gas source molecular beam epitaxy system. The process resulted in the dense growth of GaAs NWs across the entire surface of the single-walled nanotube (SWNT) films. The NWs, which were orientated in a variety of angles with respect to the SWNT films, ranged in diameter between 20 to 200 nm, with heights up to 2.5 um. Transmission electron microscopy analysis of the NW-SWNT interface indicated that NW growth was initiated upon the surface of the nanotube composite films. Photoluminescence characterization of a single NW specimen showed high optical quality. Rectifying asymmetric current-voltage behavior was observed from contacted NW ensembles and attributed to the core-shell pn-junction within the NWs. Potential applications of such novel hybrid architectures include flexible solar cells, displays, and sensors.
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We report on the synthesis of carbon nanotubes on quasicrystalline alloys. Aligned multiwalled carbon nanotubes (MWNTs) on the conducting faces of decagonal quasicrystals were synthesized using floating catalyst chemical vapor deposition. The alignment of the nanotubes was found perpendicular to the decagonal faces of the quasicrystals. A comparison between the growth and tube quality has also been made between tubes grown on various quasicrystalline and SiO2 substrates. While a significant MWNT growth was observed on decagonal quasicrystalline substrate, there was no significant growth observed on icosahedral quasicrystalline substrate. Raman spectroscopy and high resolution transmission electron microscopy (HRTEM) results show high crystalline nature of the nanotubes. Presence of continuous iron filled core in the nanotubes grown on these substrates was also observed, which is typically not seen in MWNTs grown using similar process on silicon and/or silicon dioxide substrates. The study has important implications for understanding the growth mechanism of MWNTs on conducting substrates which have potential applications as heat sinks.
GaAs nanowires were grown by metalorganic vapor phase epitaxy on evaporated metal films (Au, Au / Pd, Ag, Ni, Ga, Cu, Al, Ti). The samples were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). SEM images reveal that nanowires grow directly on the metals. TEM characterization shows crystalline nanowire (nw) structure originating from Au. Article presents state of the art about nanowire-metal interface growth and enumerates nanowire contacting methods with metals.
GaAs nanowires and GaAs/Fe3Si core/shell nanowire structures were grown by molecular-beam epitaxy on oxidized Si(111) substrates and characterized by transmission electron microscopy. The surfaces of the original GaAs NWs are completely covered by magnetic Fe3Si exhibiting nanofacets and an enhanced surface roughness compared to the bare GaAs NWs. Shell growth at a substrate temperature of T{S} = 200 {deg}C leads to regular nanofacetted Fe3Si shells. These facets, which lead to thickness inhomogeneities of the shells, consist mainly of well pronounced Fe3Si(111) planes. The crystallographic orientation of core and shell coincide, i.e. they are pseudomorphic. The nanofacetted Fe3Si shells found in the present work are probably the result of the Vollmer-Weber island growth mode of Fe3Si on the {110} side facets of the GaAs NWs.
A novel method is presented which allows the characterization of diameter selective phenomena in SWCNTs. It is based on the transformation of fullerene peapod materials into double-wall carbon nanotubes and studying the diameter distribution of the latter. The method is demonstrated for the diameter selective healing of nanotube defects and yield from C$_{70}$ peapod samples. Openings on small diameter nanotubes are closed first. The yield of very small diameter inner nanotubes from C$_{70}$ peapods is demonstrated. This challenges the theoretical models of inner nanotube formation. An anomalous absence of mid-diameter inner tubes is observed and explained by the suppressed amount of C$_{70}$ peapods due to the competition of the two almost equally stable standing and lying C$_{70}$ peapod configurations.
We show that separating metallic from semiconducting carbon nanotubes by dielectrophoresis is developing towards a bulk separation method, which allows for the first time to produce thin films of only metallic single-walled carbon nanotubes and to measure their optical absorption spectra. The data proofs that the selectivity of the separation scheme is independent from the nanotube diameter.
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