Guangwei She

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.

High-performance surface-enhanced Raman scattering sensors based on Ag nanoparticles-coated Si nanowire arrays for quantitative detection of pesticides

A surface-enhanced Raman scattering (SERS) sensor made of Ag nanoparticles-coated Si nanowire (SiNW) arrays was fabricated for the quantitative detection of Carbaryl (an important nitrogen pesticide). H-terminated SiNWs were capable of reducing silver ions, leading to uniform deposition of silver nanoparticles on SiNW arrays. Such wire arrays exhibited a superior detection sensitivity of 10−17 M Rodamine 6G with high reproducibility. The sensor also enabled high sensitivity, reproducibility, and stability detection of Carbaryl. Significantly, the linear relation between the logarithmic concentrations and Raman peak intensities provided quantitative detection of Carbaryl.

Using Si and Ge Nanostructures as Substrates for Surface-Enhanced Raman Scattering Based on Photoinduced Charge Transfer Mechanism

The possibility of utilizing the Si and Ge nanostructures to promote surface-enhanced Raman scattering (SERS) is discussed. The vibronic coupling of the conduction band and valence band states of Si or Ge with the excited and ground states of the target molecule during the charge transfer (CT) process could enhance the molecular polarizability tensor. Using H-terminated silicon nanowire (H-SiNW) and germanium nanotube (H-GeNT) arrays as substrates, significant Raman enhancement of the standard probes, Rodamine 6G (R6G), dye (Bu(4)N)(2)[Ru(dcbpyH)(2)-(NCS)(2)] (N719), and 4-aminothiophenol (PATP), are demonstrated. The abundant hydrogen atoms terminated on the surface of SiNW and GeNT arrays play a critical role in promoting efficient CT and enable the SERS effect.

Highly efficient electrocatalytic hydrogen production by nickel promoted molybdenum sulfide microspheres catalysts

Ni-promoted MoS2 microspheres consisting of nanosheets have been prepared via a facile one-pot hydrothermal synthesis for the first time. The electrochemical hydrogen evolution reaction (HER) results demonstrated that the Ni-promoted MoS2 catalysts showed superior catalytic activity in the HER compared to pure MoS2 catalysts.

Silicon Nanowire-Based Fluorescent Nanosensor for Complexed Cu2+ and its Bioapplications

A silicon nanowires (SiNWs)-based fluorescent sensor for complexed Cu(2+) was realized. High sensitivity and selectivity of the present sensor facilitate its bioapplications. The sensor was successfully used to detect the Cu(2+) in liver extract. Meanwhile, real-time and in situ monitoring of Cu(2+) released from apoptotic HeLa cell was performed using the as-prepared SiNW arrays-based sensor. These results indicate that the present SiNWs-based sensor would be of potential applications in revealing the physiological and pathological roles of Cu(2+).

Electrodeposition of one-dimensional nanostructures.

Electrodeposition is a simple and flexible method for the synthesis of one-dimensional (1D) nanostructures and has attracted more and more attention in recent years. 1D nanostructures of metals, semiconductors and polymers have been successfully fabricated by electrodeposition. Templates were often used in the electrochemical process to realize the 1D growth. On the other hand, some materials with intrinsic anisotropic crystal structures can also be prepared by the template-free electrochemical method. In this paper, we review the recent patents progress and offer some prospects of future directions in electrodeposition of 1D nanostructures.

Observation of persistent photoconductance in single ZnO nanotube

Vertically aligned ZnO nanotube fabricated on an indium tin oxide substrate is found to exhibit strong persistent photoconductivity (PPC). Excitation wavelength-dependent conductance measurement on individual ZnO nanotube reveals the presence of defect states at 240 meV above the valence band edge, which are directly associated with the PPC effect. Our observations are consistent with the hypothesis that double ionization of defect-localized states is responsible for the PPC effect.

Optical modulation of persistent photoconductivity in ZnO nanowires

In this study, ZnO nanowires (ZNWs)-based optoelectric devices are found to exhibit strong persistent photoconductivity (PPC) effect. An optical modulation on the PPC effect of the ZNWs with 980 nm infrared (IR) laser has been investigated. It was found that the decay time for the PPC can be significantly shortened by IR irradiation. The modulation mechanism related with the oxygen vacancies and the subband gap excitation is proposed. Based on this mechanism, the modulation behavior of the IR can be well explained. The present optical modulation on the PPC is suggested to have potential applications in enhancing the performance of ZnO-based photodetectors.

SnO2 Nanoparticle-Coated ZnO Nanotube Arrays for High-Performance Electrochemical Sensors

Novel 1D nanostructures offer new opportunities for improving the performance of electrochemical sensors. In this study, highly ordered 1D nanostructure array electrodes composed of SnO2 nanoparticle-coated ZnO (SnO2 @ZnO) nanotubes are designed and fabricated. The composite nanotube array architecture not only endows the electrochemical electrodes with large surface areas, but also allows electrons to be quickly transferred along the nanotubes. Modifying the SnO2 @ZnO nanotube arrays with negatively charged polymer film and employing them as a working electrode, sensitive and selective electrochemical detection of an important neurotransmitter, i.e., dopamine, is realized via the cycle voltammetry (CV) and differential pulse voltammetry (DPV) techniques. Interference from ascorbic acid can be successfully eliminated. The oxidative peak currents recorded from CV linearly depend on the dopamine concentrations from 0.1 to 100 μM with a sensitivity of 2.16 × 10(-7) A μM(-1) cm(-2) and detection limit of 45.2 nM. Using the DPV technique, an improved sensitivity and detection limit of 1.94 × 10(-6) A μM(-1) cm(-2) and 17.7 nM are respectively achieved. Moreover, the SnO2 @ZnO nanotube array electrodes can be reused through simple ultrasonical cleaning and no obvious deterioration is observed in the performance.

Catalyst-free synthesis of single crystalline ZnO nanonails with ultra-thin caps

Arrays of single-crystalline ZnO nanonails with tapering diameters and ultra-thin caps have been successfully synthesized on a silicon substrate via a simple catalyst-free thermal evaporation method. Each of the ZnO nanonails consists a nanowire (stem) on the bottom and an ultra-thin symmetrical hexagonal cap on the top. Structural characterization reveals that the synthesized ZnO nanonail has a wurtzite (WZ) structure with a preferred growth direction of [0001] in the stem and in the cap. Remarkably, the ultra-thin cap shows a diameter-to-thickness ratio of over 20:1, which is much higher in magnitude than those reported in previous works. Based on the systematic morphological characterization and structural analysis, a self-catalyzed vapor–liquid–solid (VLS) mechanism followed by a vapor–solid (VS) process is proposed to explain the growth of the nanonails. Optical properties are also investigated with Raman and photoluminescence (PL) techniques, which show good crystal quality of the synthesized nanonails.