Study On 3D Surface Modification,Optical Properties And Application Of Porous Silicon Nanomaterials

Porous silicon is a nanostructured material with high surface areas,adjustable microstructure,large adsorption capacity,biocompatibility and excellent optical performance that can be widely used in displays,optical sensors,and biological imaging.However,there are numerous reactive silicon hydrides on the surface of freshly etched porous silicon,which are susceptible to react with water and oxygen in the air.The oxidized porous silicon may affect its optical properties and stability,and reduce the applicability in applications.In this thesis,the Si-C bond was formed on the surface of n-type silicon wafer by photocatalytic reaction and the Si-O-Si bond was formed in highly doped p-type silicon by oxidation,which improved the surface stability of different doping types of porous silicon and studied the influence factors in the modification process.In addition,the porous silicon wafer loaded with thiol-functional polysilsesquioxane?SH-POSS?was prepared and was studied on optical sensing performance of copper ion(Cu²⁺).The main work is summarized as following:1.Fluorine-modified porous silicon with high stability and superhydrophobic was prepared by modifying the surface of freshly etched n-type porous silicon via photocatalytic reaction used dodecafluoroheptyl methacrylate as a functional group The structure and composition of porous silicon before and after modification were analyzed by scanning electron microscope?SEM?,Fourier transform infrared spectroscopy?FT-IR?,scanning electron microscopy-energy dispersive spectrometer?SEM-EDS?and X-ray photoelectron spectroscopy?XPS?.The effects of UV light,reactant mass fraction and reaction time on the surface properties of porous silicon were studied by water contact angle?WCA?and photoluminescence?PL?.The stability of fluorine-modified porous silicon surface in alkaline tests and air environment tests was investigated.The results indicate the dodecafluoroheptyl methacrylate was successfully grafted onto the surface of n-type porous silicon by photocatalytic reaction.Under the condition of UV light,the superhydrophobic porous silicon was prepared by reacting 40 min in a dichloride solution containing 10 wt%dodecafluoroheptyl methacrylate.The water contact angle of the fluorine-modified porous silicon surface can reach 153° and has good photoluminescence intensity.The surface of the modified porous silicon exhibited great stability in alkaline text and air environment text.In the alkaline test,After 30 minutes of the existence of alkaline droplets,the surface structure of fluorine-modified porous silicon was not dissolved,the water contact angle could keep 150°and the modified wafer could still maintain great photoluminescence intensity.In the air environment texts,the surface of the fluorine-modified porous silicon still showed hydrophobic properties and great photoluminescence intensity during one week2.The highly doped p-type porous silicon microparticles were oxidized used different concentrations of weakly alkaline buffers?borate-buffer solution and tris-buffer solution?as oxidants.The citric acid solution was introduced as the terminator to control the oxidation reaction of porous silicon.The structure and composition of porous silicon microparticles before and after oxidation were analyzed by SEM and FT-IR.The influence of UV light,oxidant types and oxidant concentration in the oxidation process was studied by PL and thermal gravimetric analyzer?TGA?.The effect of adding citric acid solution on the photoluminescence properties of porous silicon and the control of the oxidation process was studied.The oxidation mechanism of porous silicon was investigated.The results indicate the increase of the oxidation rate of porous silicon can be achieved by reacting with UV light,increasing the concentration of oxidants and increasing the pH of the oxidation solution.The addition of citric acid solution can effectively control the degree of oxidation,improve stability and especially the photoluminescence intensity of porous silicon.During the oxidation process,the silicon crystallites in the porous silicon are gradually oxidized to silicon oxide layer.The decrease of the size of microcrystalline silicon and the increase of the surface passivation layer made the photoluminescence increased at first and then decreased,the PL peak position appears blue shift with the increase of oxidation time3.The p-type porous silicon wafer after surface modification loaded with prepared thiol-functional polysilsesquioxane?SH-POSS?and was studied on detection of Cu²⁺.The composition and structure of SH-POSS and porous silicon wafers before and after loading SH-POSS were analyzed by 1H-NMR,29Si-NMR,FT-IR,SEM,and Raman spectra?Raman?.The detection of Cu²⁺ on porous silicon wafers loaded with SH-POSS was investigated by Fabry-Perot interference fringes.The results indicate SH-POSS was successfully prepared by hydrolysis-condensation reaction.The SH-POSS can be loaded into the pore structure of freshly etched porous silicon and amino-modified porous silicon.The prepared NH2-pSi-POSS can respond rapidly to Cu²⁺ concentration of 200 ppm.