Silicon Base Nano Materials And Ni（OH）₂Nanosheets In Hydrothermal System At Different PH Value

New kinds of materials with special characters are required in pressing because of addition of energy depletion and pollution of environment. The sizes of materials are needed to be smaller, because that the electronic devices are become samller and intelligent. And the characters of materials are neeed to be better, because that high speed developments of advance manufacture technology. One dimension nano materials have different structure, such as nanowires, nanorod, nanobelt, nanotube and so on. All of these kinds of materials have shown quite different character, such as quantum size effect, macroscopic quantum tunneling effect, coulomb blocked effect, small size effect, surface effect and so on. New kind research fields have been explored for scientist.The silicon nanotubes (SiNTs) have been synthesized by hydrothermal method with pure water. The pH value of solution which is one of important parameters of hydrothermal have not been considered. So we study the affection of pH value to the structure and morphology of nano materials mainly. The viscosity, grain size and ζ potential of precursor in solution have been studied in different pH value condition. The dispersion was better when pH value was3-6than the others. In acid environment, the silicon nanowires (SiNWs) have been synthesized. The typical experimental condition is470℃in temperature,8MPa in pressure, and4hours in reaction time. The average diameter of SiNWs with amorphous outside is80nm. The special SiNWs which would be deformed under high power electron beam illumination were composed of disposed nano particles by TEM image. The space between the nano particles is amorphous SiO. The SiNWs growth mechanism have two stage. The fist is nucleation stage, in which the size of crystal nucleus have been influence by pH value of solution. The precursor would dissolve to form silicate aggregation. When the temperature rised, the silicate aggregation would hydrolyze to form crystal nucleus. The Si-O bond located on the crystal nucleus would be broken and transform to Si-H bond, which ensure the growth of SiNWs continually. The second stage is growth stage of SiNWs, which fellow the oxide-assisted growth mechanism. The silicon would separate out from nucleus with temperature rising., The crystal silicon would separate out in direction which the diffusibility of oxygen atom was lower. The SiNTs would synthesized in neutral solution, as the SiNWs would synthesize in acid solution. The key parameter is pH value of solution in the transformation, which play an important role in nucleation and growth stage of crystal silicon nano materials. The simulation method have been used to study the mechanism of silicon nano materials growth. The nanotubes without Si-H bond on surface tend to collapse. The Si-H bond play an important role in stability of silicon nano material.In alkalescence solution, the production of experiment is silica nanospheres. The typical experiment parameter:pH is9, temperature is350℃, pressure is14MPa, soaking time is4hours. The nanosphere is smooth in surface, uniform in diameter and high purity. The diameter of nanosphere increase with the pH value of solution and temperature, and that decrease with the pressure. The photoluminescence spectrum of silica nanosphere shown that there are obviously peak located in411nm. The PL character of silica nanospheres still good when the sample place for long time. The Si-OH bond and Si-O-Si bond located on the surface of nanosphere synthesized by infra-red spectrum.The silicate monomer would increase in the alkalescence form the result of experiment with high pH value. The silicate monomer would hydrolyze to form the nucleation central, at the same time the OH-ion enter the central to form the Si-OH bond. The Si-OH bond would link each other to form Si-O-Si bond, and then the silica nanospheres generated at last. The amount of defect exist on the nanosphere surface because that the OH-take up the location of O2-, which induce the amorphous structure of nanospheres.The amorphous silica nanowires have been synthesize in neutral and alkalescence solution. The silica naowires locate on the top of reaction kettle. The diameter distribution rang are wide. The TEM image of sample shown that the nanowires are amorphous. The diameter of silica nanowires would increase with the pH value.The Ni(OH)2nanosheets have been synthesized by hydrothermal. The typical experiment condition:pH value was7, temperature was470℃and the pressure is9MPa. The thickness of Ni(OH)2nanosheets is about30nm, the diameter is about150nm. The temperature was higher than200℃is necessary condition of growth Ni(OH)2nanosheet. The aggregation of Ni(OH)2nanosheets have trend to dissolve when the temperature rise. The size of crystalline grain of Ni(OH)2nanosheets show a trend of first increase and then decrease with the pH value.In summary, the Si-H bond play an important role in growth proceeding. The pH value in solution is a crucial factor in synthesized silicon nano materials. The production is SiNWs in acid solution, and amorphous silica nanospheres in alkalescence solution. We discuss the growth mechanism of silicon nano materials in different experiment condition including temperature, pressure, reaction time and all. The Si-O bond on the surface of crystal nucleus were replaced by Si-H or Si-OH bond. The Si-H bond had advantage of stability of silicon crystal, which indicated that production is SiNWs in acid solution and amorphous nanospheres in alkalescence solution. The controllable silicon nano materials have been synthesized initially, which lay the foundation of silicon nano materials synthesis by hydrothermal method.