Xia Fan

p-Type ZnO nanowire arrays.

Well-aligned ZnO nanowire (NW) arrays with durable and reproducible p-type conductivity were synthesized on alpha-sapphire substrates by using N2O as a dopant source via vapor-liquid-solid growth. The nitrogen-doped ZnO NWs are single-crystalline and grown predominantly along the [110] direction, in contrast to the [001] direction of undoped ZnO NWs. Electrical transport measurements reveal that the nondoped ZnO NWs exhibit n-type conductivity, whereas the nitrogen-doped ZnO NWs show compensated highly resistive n-type and finally p-type conductivity upon increasing N2O ratio in the reaction atmosphere. The electrical properties of p-type ZnO NWs are stable and reproducible with a hole concentration of (1-2) x 10(18) cm(-3) and a field-effect mobility of 10-17 cm2 V(-2) s(-1). Surface adsorptions have a significant effect on the transport properties of NWs. Temperature-dependent PL spectra of N-doped ZnO NWs show acceptor-bound-exciton emission, which corroborates the p-type conductivity. The realization of p-type ZnO NWs with durable and controlled transport properties is important for fabrication of nanoscale electronic and optoelectronic devices.

Controlled synthesis of oriented single-crystal ZnO nanotube arrays on transparent conductive substrates

Large-scale arrays of highly oriented single-crystal ZnO nanotubes (ZNTs) are successfully fabricated on transparent conductive substrates by a simple method from an aqueous solution at a low temperature (typically 85°C). The tubular morphology of the ZnO nanostructures is formed by a defect-selective chemical etching of the electrodeposited ZnO nanorods. The size of the ZNT arrays is determined by that of ZnO nanorod arrays which can be readily controlled by tuning several electrodeposition parameters. The present method can be employed to prepare ZNT arrays on flexible, conductive substrates, as well as on patterned conductive substrates.

The fabrication and optical properties of highly crystalline ultra-long Cu-doped ZnO nanowires

We demonstrate the bulk synthesis of single crystalline Cu-doped ZnO nanowires using (CuI+ZnI2) powders at 600 °C. These mass nanowires are characterized through x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction, and high-resolution TEM; they have uniform diameters of about 65 nm and are several tens of microns in length. The growth of ZnCuO nanowires is suggested for self-catalyzed vapour–liquid–solid. In particular, the PL spectra of these nanowires show emission peaks that strongly shift to long wavelength with increasing Cu, and the doping quantity is found to be responsible for the different characteristics; the PL mechanism is explained in detail.

A surface-enhanced Raman spectroscopy substrate for highly sensitive label-free immunoassay

Large-scale uniform silicon nanowires (SiNWs) array was fabricated by chemical etching on n-Si(111) wafer. Silver nanoparticles (AgNPs) were loaded on their surfaces. The AgNPs on SiNWs (AgNPs@SiNWs) array exhibit strong surface-enhanced Raman effect. On the substrate surfaces, characteristic Raman signals are generated with trace amount of mouse immunoglobulin G (mIgG), goat-anti-mouse immunoglobulin G (gamIgG), and immune complexes formed from 4ng each of mIgG and gamIgG. The shifted positions and changed intensities in Raman bands indicate the occurrence of immunoreactions. This AgNPs@SiNWs array is a unique substrate for surface-enhanced Raman spectroscopy to show the immune reagents and immunoreactions at higher sensitivity.

Tuning Electrical and Photoelectrical Properties of CdSe Nanowires via Indium Doping

As an important II–VI semiconductor material, CdSe has attracted considerable attention due to its unique properties such as a direct band-gap ( 1.7 eV at room temperature) and excellent photoelectrical characteristics that make it a promising material for applications in photodetectors and photovoltaics. Thus far, 1D CdSe nanostructures, such as nanowires (NWs), nanotubes, nanosaws, nanosheets, and nanoribbons, have been successfully synthesized by using various methods including electrochemistry, solution chemical reactions, self-catalysis thermal evaporation, and laser ablation-assisted chemical vapor deposition (CVD). Besides their usage in single-electron transistors and electrochromic and charge-coupling devices, CdSe nanostructures also show application potential in biomolecular labeling, phosphors, and light-emitting diodes. Notably, photodetectors and field-effect transistors (FETs) based on a single CdSe nanoribbon have been recently realized. Nevertheless, the practical applications of CdSe nanostructures are hindered by poor materials properties, due mainly to lack of control over conductivity. Doping is an efficient approach to tune the electrical properties of semiconductors, and has been widely utilized in the semiconductor industry. Indeed, CdSe films and bulk crystals with tunable conductivity have been realized by using indium as n-type dopant. Doping of CdSe nanostruc-

Single zinc-doped indium oxide nanowire as driving transistor for organic light-emitting diode

Zn-doped In2O3 nanowires (NWs) were prepared by simple chemical vapor deposition and were systematically characterized. Field-effect transistors (FETs) constructed from the Zn-doped In2O3 nanowires exhibit excellent performance characteristics such as high mobility, “high-on-state” current of 105A and large on/off current ratio of 107. Single-NW-FETs can successfully drive an organic light-emitting diode, revealing the application potential of Zn-doped In2O3 NW-FETs in high-performance displays.

p-type conduction in nitrogen-doped ZnS nanoribbons

We report reproducible p-type transport properties in nitrogen-doped ZnS nanoribbons (NRs) synthesized by applying ammonia gas as the acceptor source. Field-effect transistors fabricated from individual ZnS NRs revealed the p-type behavior of ZnS NRs and significant enhancement in p-type transport properties upon annealing in argon ambient. Annealing-induced conversion of highly insulating to p-type conducting ZnS NRs was attributed to activation of N acceptors from the passivated states of NS–H bonding.

Effects of ambient pressure on silicon nanowire growth

Growth of silicon nanowires (SiNWs) by thermal evaporation of SiO in a closed system was studied. The yield of SiNWs obtained in the present closed system was much higher than that from the previous open systems. As the ambient pressure increased, the yield of SiNWs decreased and the diameter of the SiNWs increased, but the surface of the SiNWs was roughened. Transmission electron microscopic examination showed that the originally smooth surface of SiNWs was roughened by the formation of Si nano-particles. The implication of these results on the growth mechanism of the SiNWs is discussed.

Dye degradation induced by hydrogen-terminated silicon nanowires under ultrasonic agitations

A method for degradation of environmentally hazardous dyes using silicon nanowires (SiNWs) has been developed. Environmentally unfriendly methyl red was degraded with assistance of H-terminated SiNWs under ultrasonic agitation. The hydrogenated surfaces of SiNWs are shown to be responsible for the surface reaction and decay of methyl red. The rate of degradation increases with the amount of SiNWs and agitation power. SiNWs after their application can be recycled and reactivated for further uses by a simple heating in hydrogen plasmas.

Formation of ZnS/SiO2 nanocables

Nanometer-sized coaxial cables with a single-crystal ZnS core and a thin amorphous SiO2 shell were synthesized by simple thermal evaporation in vacuum. As-fabricated ZnS/SiO2 nanocables were studied using scanning electron microscopy, x-ray diffraction and transmission electron microscopy. The ZnS/SiO2 nanocables have diameters of ∼50nm, lengths of several tens of micrometers, and shell thickness of ∼4nm. The core of the nanocable has a wurtzite structure with a growth direction along [001]. The nanocables show strong photoluminescence with two peaks related to band gap and defect-related emission.