Spectra Study Of One-Dimensional Silica Nanomaterials

Nano scientific and technical is extraordinary concerned with developing of science and technology.Nanophase materials are extensively concerned by material field and physics field,and quickly formed the worldly nano-upsurge.In the last few years,people have untilized many methods to compose a lot of one dimension nano-composite materials. Such as nanotube,nanowire,nanostick,nanobend and nanowire array etc.And it establishes base for further research on structure and property of nanophase material. Silica is one of most abundant matter.So silica is important component of the ores and precious stones.It exists as pure silica or mixed oxide state on the earth.Nano silica is a kind of important nanophase material and unjelled white powder.It is an innocuous, smellless and unpollute nonmetallic abio-mineral.Silica nanophase material is applicated extensively in various fields.At the same time,silica is important composing of glasses, activators and micro-electronics devices composed silicon.Recently,it is regarded enough by the science field and becomes gradually an important kind of one dimension nanophase material.Silica nanotubes or nanowires are synthesized using manifold methods,such as laser ablation,sol-gel process,CVD and VLS etc.In this paper,using density-functional theory(B3LYP)at 6-31G(d)level,vibration spectrum of quasi 1D(one dimension) nanosize lines have been calculated and analyzed.Primary research work focus on three parts:(a)Effect of Polar Group on Raman Spectrum of One Dimension SiO₂ NanowireRaman vibration spectra of anhydrous(SiO₂)_n and hydrous(SiO₂)_n(n=6～20)of single-line,double-line and ring structures have been calculated using the DFT.The main research is the effects of the polar hydroxyl groups on 1D SiO₂ Nanowires.We choose two specific Raman vibration modes:radial breathing mode(RBM)and symmetrical stretching mode(SSM),further analyze their Raman vibration frequencies,depolarization ratios and polarizations to demonstrate the effects of the polar hydroxyl groups.In addition,structural symmetry reduces and charge density is redistributed due to the effects of the polar hydroxyl groups.The frequencies' variation law is successfully interpreted using the model of the harmonic oscillator combining with the cascade and parallel connection principle.Through analyzing their polarization ratios,such influences are distinct on different direction due to orientation of polar group.(b)Theoretical Study on Even-odd Oscillation of Vibrational Modes of Silica NanowireThe vibration spectrum of quasi 1D(one dimensional)nanosize lines had been calculated.The results showed that variation of vibrational frequency and intensity with number of SiO₂ units observed in IR and Raman spectra,named even-odd oscillation.For different vibration modes,even-odd oscillation extent was strong or weak because of polar group's orientation relative to silicon-oxygen two-membered ring.Moreover,analyses of Raman polarization indicated effect of hydroxyl on even-odd oscillation.(c)Theoretical Study on Raman Radial Breathing Vibration of Silica NanostructuresRaman vibration spectra of nanowires and nanotubes based on two membered ring units and three-,four-,six- and eight- membered ring units have been calculated.From Raman spectra analysis,it is found that Raman radial breathing vibration of silica nanolines and nanotubes have opposite frequency shift upon length increasing,namely, red and blue shifted.However,Raman frequencies trend to the stable values with approaching infinity.At the same time,the vibration frequencies reduce with increasing of diameter.Due to internal structure stress of nanomaterial,frequency shift is distinct for small size.Furthermore,bond length and bond angle of all kinds of structure have been analyzed to interpret them.