The Super Capacitor Research Based On Monocrystalline Silicon Nanometer Groove

As the occurrence of reproducible clean energy which has been applied to supply power to portable electrics devices, energy buffers that can story electric energy have become more and more important. Generally speaking, the energy buffer can either be a battery or an electrochemical supercapacitor (ECS). The former has lower charging and discharging rate and the latter which has higher charging and discharging rate has drawbacks to boost the power density and scale down the size further. As a candidate, elctrostatic capacitor (ESC) which has lower capacity, but considerable power density and favorable flexibility in contrast to ECS is a promising energy buffer. Based on the idea of3D ECS structure, the effects of different etching conditions to the formation of cylindrical silicon nanoholes produced by Pt nanoparticles-assisted chemical etching are investigated and the silicon nanholes are as nanotemplates to fabricate solid state supercapacitor (SSC), of which the electrical properties are characterized preliminarily. The details include the following sections:(1) Pt nanoparticles produced by rapid thermal annealing (RTA) of sputtered Pt films are formed on the heavily doped P-type monocrystalline silicon substrate covered with thermal oxide. The effects of original Pt film thickness, annealing temperatures and annealing times to the growth of Pt nanoparticles are investigated. The results indicate that Pt nanoparticles formed by RTP for20s at800℃of4nm Pt films have higher density and are dispersed. Subsequently, the effects of etching solution compositon, original oxide thickness, Pt nanoparticles density and localization to Pt nanoperticles-assisted chemical etching of heavily doped P-type monocrystalline silicon are investigated. The results indicate that there exist two kinds of etching processes consisting of electrochemical etching which is dominated, contributing to the formation of nanoholes and the wall dissolution of nanoholes. With the H2O2concentration firmed, electrochemical polishing or porous structures will be observed on the samples if the HF concentration is modulated. Moreover, the pores are perpendicular to the substrate and the diameters of these pores increase with the reduction of the HF concentration. The addition of acetic acid or NaCl can inhibit the activity of Pt nanoparticles, thereby lowering the etching reaction and forming smaller nanoholes. The addition of ethanol is helpful for the desorption of bubbles from the sample surface, thus accelerating the etching reaction and forming bigger nanoholes. And bigger nanoholes will be observed when Pt nanoparticles with higher density are used. When Pt nanoparticles are located at specific area on the sample surface, nanoholes can also be observed at the area without Pt nanoparticles and these nanoholes are intact. The results of optical test indicate that silicon nanoholes can be used as anti-reflection layer and reflectance as low as2.5%is obtained. When the diameters of silicon nanoholes are reduced, remarkble interference is observed.(2) The properties of Pt nanoparticles-assisted chemical etching of lightly doped P-type monocrystalline silicon are investigated firstly. The results indicate that deep holes can be produed by the penetration of Pt nanoparticles into the silicon substrate under different etching conditions and micropores are formed near the top surface meanwihle. Compared with the behaviors of Pt nanoparticles-assisted etching of heavily doped P-type monocrystalline silicon, significant differences can be obtained, which means doping levels can affect the etching properties of P-type monocrystalline silicon. Subsequently, the properties of Pt nanoparticles-assisted chemical etching of heavily doped N-type monocrystalline silicon are investigated. The results indicate that micropores and mesopores are observed under different etching conditions. When the HF concentration is beyond some value, the phenomenon of the penetration of Pt nanoparticles into the silicon substrate can also be seen. In contrast to the behaviors of Pt nanoparticles-assisted etching of heavily doped P-type monocrystalline silicon, significant differences can be obtained, which means doping types can also affect the etching properties of monocrystalline silicon.(3) Based on the research of Pt nanoparticles-assisted chemical etching of heavily doped P-type monocrystalline silicon, a new kind of SCC preparation method with silicon nanoholes as nanotemplates is proposed. C-V test shows that the capacitance density of SSC is3.5uF/cm2, which is higher than that of planar capacitor (1uF/cm2).