Frederick C. K. Au

Field-emission characteristics of SiC nanowires prepared by chemical-vapor deposition

Silicon carbide (SiC) nanowires on a silicon substrate were prepared using hot-filament-assisted chemical-vapor deposition with a solid silicon and carbon source. The SiC nanowires show good field-emitting properties as revealed by the current–voltage characteristics. Together with its ease of preparation, these SiC nanowires are shown to have great potential in the area of electron field-emitting devices.

Electron field emission from silicon nanowires

Silicon nanowires (SiNWs) were synthesized using laser ablation. A continuous SiNW film was prepared by grinding the pieces of sponge-like SiNWs to powder, then dispersing and sticking the powder onto a Si wafer. The field emission characteristics of the SiNW film were studied based on current–voltage measurements and the Fowler–Nordheim equation. The electron field emission increased with decreasing diameter of SiNWs. A hydrogen plasma treatment of the SiNW film aimed at reducing the oxide overlayer improved the emission uniformity of the film.

Electrical properties of zinc oxide nanowires and intramolecular p–n junctions

Electrical properties of ZnO nanowires and intramolecular p–n junctions were characterized by I–V measurements. These nanowires were grown embedded in anodic aluminum oxide (AAO) templates by vapor-phase-transport growth method. The nanowires were dense, continuous, and uniform in diameter along the length of the wires. I–V measurements showed the average resistivity of the ZnO nanowires in AAO templates was about one order of magnitude higher than that of the naked single ZnO nanowire. The p–n junctions in ZnO nanowires were fabricated by a two-step growth of ZnO with and without dopant of boron (∼1 wt %) in the source. I–V results suggested that p–n junctions in ZnO nanowires were formed by the two-step method.

Uniform carbon nanoflake films and their field emissions

Films of uniformly distributed carbon nanoflakes have been prepared by using hot filament chemical vapor deposition. A large amount of carbon flakes with a thickness of less than 20 nm interlaced together to form a layer of carbon nest-like film with their sharp edges almost perpendicular to the Si substrate. Raman spectroscopy showed that the films were characteristic of pyrolytic graphite and became more disordered with the increase of substrate temperature and acetylene concentration. The growth mechanism of the carbon nanoflake films was discussed. The field emission performance has been done, showing a turn-on field of about 17 V/μm. Considering the ease of large-area preparation, the carbon nanoflake films might have a potential application in vacuum electronic devices.

Room-temperature single nanoribbon lasers

Using a single nano-object measurement methodology that enables the correlation between size/morphology/structure and photoluminescence (PL) characteristics, we show that nanoribbons are an excellent model system to study single nano-objects. In particular, we measure the PL characteristics of optically pumped individual single-crystal zinc–sulfide nanoribbons. Small collection angle measurements show that nanoribbons form excellent optical cavities and gain medium with high (full width at half maximum<0.1 nm) lasing modes free of PL background even for a low pumping power density of 9 kW/cm2. Large collection angles add a broad PL component and obscure the correct high-quality lasing of the nanowires/nanoribbons.

Thin β-SiC nanorods and their field emission properties

Abstract Beta-silicon carbide (β-SiC) nanorods (diameter, ca. 5–20 nm; length, 1 μm) have been grown on porous silicon substrates by chemical vapor deposition with an iron catalyst. The turn-on field of the grown β-SiC nanorods on a porous silicon substrate is 13–17 V/μm.

Straight β-SiC nanorods synthesized by using C–Si–SiO2

Straight beta-silicon carbide nanorods have been grown on silicon wafers using hot filament chemical vapor deposition with iron particles as catalyst. A plate made of a C–Si–SiO2 powder mixture was used as carbon and silicon sources. Hydrogen, which was the only gas fed into the deposition system, acts both as a reactant and as a mass transporting medium. The diameter of the β-SiC nanorod ranged from 20 to 70 nm, while its length was approximately 1 μm. A growth mechanism of beta-silicon carbide nanorods was proposed. The field emission properties of the beta-silicon carbide nanorods grown on the silicon substrate are also reported.

Growth and emission properties of β-SiC nanorods

Abstract A one step procedure has been developed to grow beta-silicon carbide (β-SiC) nanorods from a solid carbon and silicon source on silicon substrates using a hot filament chemical vapor deposition. The growth process was catalyzed by the impurities of metallic particles confined in the solid source plate made of a mixture of graphite and silicon powders pressed at 150°C. Hydrogen was introduced into a reaction chamber to react with the solid source. The resulting process produced, hydrocarbon and hydrosilicon radicals, which subsequently reacted on the Si substrate surface and presumably formed SiC nanorods. The nanorods consisted of a crystalline β-SiC core with an amorphous silicon oxide shell layer. The nanorods were 10–30 nm in diameter and less than 1 μm in length. Field emission characteristics of the β-SiC nanorods were investigated using current-voltage measurements and the Fowler–Nordheim equation. The silicon carbide nanorods exhibited high electron field emission with high stability. Along with the ease of preparation, these silicon carbide nanorods are believed to have potential application in electron field emitting devices.

Paramagnetic defects of silicon nanowires

The paramagnetic defects in and on Si nanowires (SiNWs) obtained by oxide-assisted growth were studied by conventional electron spin resonance spectroscopy. For the as-grown nanowires, three different defects were found: Dangling bonds or Pb-centers with g=2.0065, located at the interface of the crystalline core to the surrounding oxide, E′-centers with g=2.0005 and EX-centers with g=2.00252, located in the oxide. For the EX-centers, the characteristic hyperfine lines separated by 16.4G were detected. The as-grown SiNWs showed a spin density of about 1018cm−3. H termination of the nanowires via hydrofluoric acid decreases the spin density drastically to 3×1016cm−3. The optical absorption spectra of SiNWs determined by photothermal deflection spectroscopy are comparable to those of microcrystalline silicon and show a similar decrease of defect density upon H termination.

Microstructure and field-emission characteristics of boron-doped Si nanoparticle chains

One-dimensional boron-doped Si nanoparticle chains synthesized in bulk quantity using laser ablating SiO powder mixed with B2O3 powder have been investigated by transmission electron microscopy and measured by electron field emission. Transmission electron microscopy showed that the outer diameters of the nanoparticles in the chains were around 15 nm. High-resolution transmission electron microscopy showed that the nanoparticles had perfect lattices with an 11 nm crystalline core and a 2 nm amorphous oxide outerlayer while the distance of the interparticles was 4 nm. Field-emission measurement showed that the turn-on field of Si nanoparticle chains was 6 V/μm, which was much lower than that of undoped Si nanowires (9 V/μm). X-ray photoelectron spectroscopy confirmed that the Si nanoparticles had been heavily doped by boron.