Preparation And Application Of Ni/SiNW Nanocomposites

In last decades, there has been a tremendous interest and a challenge to fabricate, characterize and apply materials of nanoscal dimensions. Silicon based nanomaterials now become the intensive focus of research owning to their unique properties in physics and chemistry compared with bulk silicon and compatibility with silicon IC technology as well as fabrication of nanoscale devices.In order to fabricate an incorporate integrated power and multidimensional Nano-micro sensor systems on chip, the mainly works are listed as following:First, the mechanism and fabrication of the SiNWs with Metal-Assisted Chemical Etching and the Ni/SiNWs constructed with electroless plating were investigated. The properties of SiNWs and Ni/SiNWs were characterized by SEM (Scanning electron microscope), EDS (Energydispersive spectroscopy), RCL Didital Bridge (Resistance R, Capacitance C and Inductance L) and Raman spectroscopy, respectively. These properties are being exploited for the fabrication of noval semiconductor devices.Second, the Ni/SiNW nanocomposites toward the fabrication of capacitive humidity sensors were studied. The humidity detection system was constructed by different saturated aqueous solution in a closed glass vessel at the ambient temperature of 25℃based on Lab View virtual instrument. The sensor exhibited high sensitivity (～0.207 nF/1% RH), fast response time (39 s) and recovery time (24 s) as well as low hysteresis when the humidity level changed from 11.3% to 97.3% RH. The results demonstrated that the Ni/SiNWs nanocomposites are the potential sensing material for high performance humidity sensors.Third, the prototypical electrochemical methanol sensor based on a Pd-Ni/SiNWs nanocomposite catalytic electrode was successfully constructed. The Pd-Ni/SiNWs arrays were prepared by electroless Pd-Ni co-plated on the surface of SiNWs. The performances of the prototype sensor were characterized by cyclic voltammetry and fixed potential amperometry techniques. The sensor exhibits a good sensitivity of 7.48 mA mM-1 cm-2 with R=0.98 and the corresponding detection limit of 6μmol L-1 (signal-to-noise-ratio=3, S/N= 3) for cyclic voltammetry. Meanwhile, the electrode also displays a sensitivity of 0.76 mA mM-1 cm-2 with R=0.97 and the corresponding detection limit of 10μmol L-1 (S/N= 3) for a fixed potential amperometry at-0.25 V versus an Ag/AgCl reference electrode in 1 M KOH. The results demonstrated that the Pd-Ni/SiNWs catalytic electrode has potential as an efficient and integrated sensor for methanol detection.Fourth, an electrochemical capacitors based on NiO/SiNW composites were investigated. The NiO/SiNW nanocomposites were fabricated by annealing Ni/SiNW composites at different temperatures in an oxygen atmosphere. The electrochemical behaviors of these electrodes were investigated with electrochemical technique. The results indicated that when the NiO/SiNW composites were annealed at 400℃, the maximum specific capacitance value was 681 F g-1(or 183 F cm-3), and the probing of the cycling life indicated that only about 3% of the capacity was lost after 1000 charge/discharge cycles. Therefore, the NiO/SiNW nanocomposites would be one of the optimal electrode materials for integrated electrochemical capacitors.Fifth, thermoelectric devices based on Ni/SiNW nanocomposite arrays were constructed. Single-polished N-type heavily Sb-doped silicon wafers with <100>-orientation and resistivity of 0.01-0.05Ω·cm were used as the substrates. The thermoelectric prototype was prepared by coating Ni films onto the SiNWs with electroless plating which possesses the exchange capability of photo-thermoelectric. The Seebeck coefficient is-273μV K-1(@300 K). The thermoelectric power is～7 mW cm-2 under the temperature difference of 200 K and the value of ZT is estimated from 0.08 to 0.2. When the lens with 130 mm diameter focuses the sunlight, the photo-thermoelectric power of the prototype is 18 mW. The results demonstrated that the Ni/SiNW nanocomposite arrays are a promising material for the new energy devices.In conclusion, it is very attractive for the development of an incorporate integrated power and multidimensional Nano-micro sensor systems on chip owing to the simple processing and low cost. It is must bring a better economic benefit and social value.