Zhang Yafei

ZnO nanowire network transistors based on a self-assembly method

Dense, uniform ZnO nanowire (NW) networks are prepared by using a simple and sufficient self- assembly method. In this method, ZnO NWs are modified with aminopropyltriethoxysilane (APTES) to form pos- itively charged amine-terminated surfaces. The modified ZnO NWs are adsorbed on negatively charged SiO2/Si substrates to form ZnO NW networks by the electrostatic interaction in an aqueous solution. Field-effect transistors (FETs) are fabricated and studied based on the ZnO NW networks. For a typical device with an NW density of 2.8 m 2 , it exhibits a current on/off ratio of 2.4 10 5 , a transconductance of 336 nS, and a field-effect mobility of 27.4 cm 2 /(Vs).

Progress in Carbon Nanotube Gas Sensor Research

Carbon nanotubes have become ideal candidates for fabricating nanosized gas sensors because of their excellent mechanical, electrical, physical, and chemical properties, one dimensional nanostructure, high surface adsorption capability, superior conductive performance, and electronic ballistic transport characteristics. Recently, a great deal of effort has been devoted to the development of carbon nanotube based gas sensors and rapid progress has been made. The results show that carbon nanotube gas sensors possess unique properties such as high sensitivity, fast response, small size, low energy consumption, and low operating temperature. In this review, we combine the great deal of work carried out by our group and try to summarize research progress in carbon nanotube based gas sensors for environmental monitoring, medical diagnosis, and military and defense applications. The working mechanisms and manufacturing processes of these sensors are also presented and analyzed. Despite facing enormous challenges, owing to their excellent performance, sensors based on carbon nanotubes will be substitutes for commercially traditional gas sensors.

Cu 2 O nanowires as anode materials for Li-ion rechargeable batteries

Li-ion batteries are a key technology for multiple clean energy applications. In this study, Cu2O nanowires were obtained by the reduction of cupric acetate with pyrrole. The resulting Cu2O nanowires exhibited excellent reversible capacities of 470 mAh g−1 at rate of 1 C after 100 cycles. The results show that the Cu2O nanowires had more capacity than materials previously reported. No fading was observed over 100 cycles of charging and discharging. The compound metal Cu and incorporation of the conducting polymer polypyrrole (PPy) improved the conductivity of Cu2O and enhanced the stability of the electrode during cycling. The results from this study imply that Cu2O nanowires with high capacity and good cycle retention could be excellent candidates as anode materials for Li-ion rechargeable batteries.

Preparation and Properties of GaN Films on GaAs Substrates

High-quality gallium nitride (GaN) films were prepared on Si(111) substrates by sputtering post-an nealing-reaction technique. XRD, XPS, and SEM measurement results indicate that polycrystalline GaN with hexagonal structure was successfully prepared. Intense room-temperature photoluminescence that peaked at 354 nm of the films is observed. The bandgap of these films has a blueshift with respect to bulk GaN.

Field-effect transistors with multiple channels constructed by carbon nanotubes

Single-wall carbon nanotubes (SWNTs) pre-decorated with functional molecules are directly aligned in the AC electric field, which makes SWNTs parallelly bridge the source and drain electrodes and act as the multiple conduction channels of the field-effect transistor (FET). The method avoids the mutual tanglement of SWNTs and makes them align between the source and drain electrodes abreast and dispersedly. It is indicated that aligning SWNTs in the high-volatility solvents can decrease the contaminant around the electrodes and has a function to purify the raw SWNTs. The obtained multi-channel FET not only takes on a high transconductance, but also holds the good reliability and stability.Single-wall carbon nanotubes (SWNTs) pre-decorated with functional molecules are directly aligned in the AC electric field, which makes SWNTs parallelly bridge the source and drain electrodes and act as the multiple conduction channels of the field-effect transistor (FET). The method avoids the mutual tanglement of SWNTs and makes them align between the source and drain electrodes abreast and dispersedly. It is indicated that aligning SWNTs in the high-volatility solvents can decrease the contaminant around the electrodes and has a function to purify the raw SWNTs. The obtained multi-channel FET not only takes on a high transconductance, but also holds the good reliability and stability.

Extraction of optical constants and thickness of nanometre scale TiO2 film

TiO2 thin films were deposited on glass substrates by sputtering in a conventional rf magnetron sputtering system. X-ray diffraction pattern and transmission spectrum were measured. The curves of refraction index and extinction coefficient distributions as well as the thickness of films calculated from transmission spectrum were obtained. The optimization problem was also solved using a method based on a constrained nonlinear programming algorithm.

Fabrication of SiC nanowire thin-film transistors using dielectrophoresis

The selection of solvents for SiC nanowires (NWs) in a dielectrophoretic process is discussed theoretically and experimentally. From the viewpoints of dielectrophoresis force and torque, volatility, as well as toxicity, isopropanol (IPA) is considered as a proper candidate. By using the dielectrophoretic process, SiC NWs are aligned and NW thin films are prepared. The densities of the aligned SiC NWs are 2 μm−1, 4 μm−1, 6 μm−1, which corresponds to SiC NW concentrations of 0.1 μg/μL, 0.3 μg/μL and 0.5 μg/μL, respectively. Thin-film transistors are fabricated based on the aligned SiC NWs of 6 μm−1. The mobility of a typical device is estimated to be 13.4 cm2/(Vs).

The influence of the temperature in the organic modification of single walled carbon nanotubes

In this paper, a simple method to modify single walled carbon nanotubes (SWNTs) with ODA is introduced and the effect of reaction temperature is mainly researched. The FTIR spectrum and XRD were used to investigate the organic functional groups and crystal structure of carbon nanotube before and after modification. The mole percentages of ODA decorated on SWNTs to carbon atoms in SWNTs are calculated by weighing method. The results show that the temperature plays an important role in the modification process. The amount of organic functional group on the surface of SWNTs is increase with the temperature and the mole percentage of ODA/carbon atom is in range of 2.12 to 8.64%.