Low Dimensional Si-Based Nano-Composites And Optoelectronic Application

Si is regarded as an electrical and photovoltaic material has made a great success. As its low band gap,low toxic,silicon has been used in a lot of areas including photovoltaic areas,electrical areas,biosensor areas,and so on.Quantum confinement effect play an important role in the property of semiconductors.Silicon based low dimensional nanomaterials would be exhibite a lot of new properties and expand its applications in some new areas.We report a new solution route for the preparation of zero dimensional SiO₂-capped silicon nanocrystals(Si NCs).The Si NCs terminated with SiO₂ are fully characterized by transmission electron microscopy,X-ray diffraction,UV-Vis absorption,photoluminescence decay and Fourier transform infrared spectra.The photoluminescence spectra reveal that the Si NCs solution emits green luminescence at 535 and 578 nm excited at 490 nm.The origin of the green luminescence of Si NCs is studied.Our theoretical calculations reveal that the green emission is due to the surface related localized states rather than the purely quantum-confined states,which agrees well with the experimental results.A self-trapped exciton model is proposed to take into account the stepwise localization of electron and hole at the Si-SiO₂ interface.From the localization energies the effective Bohr radii of the localized electrons and holes are estimated to be about 1.71 and 1.57 nm,respectively.By exploiting a simple solution approach,we bound the ethoxy-terminated Si nanopartilces to surface functionalized multi-walled carbon nanotubes(MWCNTs) via covalent bonds.Quenching of photoluminescence(PL) of the Si nanoparticles was observed once conjugated to the MWCNTs.The structure of the material was characterized by TEM and FTIR.F(o|¨)ster resonance energy transfer from the Si nanoparticles to the MWCNTs may response for the PL quenching by analyzing the time-resolved PL decay and calculation.The results suggest novel potential applications of the unique Si/MWCNT nanocomposites in optoelectronics devices.Similarly,we prepared the two dimensional Si NPs-graphene composite by self-assemble method.The charge transfer process was observed by Kelvin Probe Force Microscopy.We prepared Si nanowires(NWs) as one-dimensional material and the Si NW arrays as three dimentional materials by metal-assistant chemical erosion method. And following the sol-gel process to prepare Si/ZnO core/shell nanowire array.We characterize these materials by Scanning electron microscopy(SEM),transmission electron microscopy(TEM) and x-ray diffraction(XRD).The diameter of the Si nanowires was about 100 nm,and the shell of ZnO was about 20-30 nm.The Reflectance spectra of as prepared Si/ZnO planar,Si/ZnO core/shell NWs and the bare Si substrate exhibited that the reflectivity of a bare Si surface is about 41%over the range of 300-800 nm,while 23%and 8%for the Si/ZnO planar and Si/ZnO NW arrays,revealing that ZnO film and nanowire structrure can effectively decrease reflection.The photoelectrochemical properties of the Si/ZnO planar and NW arrays were investigated using a three-electrode configuration,The photoconversion efficiency for Si/ZnO NW arrays could be 0.47%when illumination with light intensity 20 mW/cm².The relation between the intensity of illumination and the photoconversion efficiency was also discussed.For the low dimensional Si based functional materials.We have discussed the silicon materials used in not only light emitting area,photovoltaic area,but also in photocatalyst area.