The Fabrication Of Three-dimensional Ordered Macroporous Silicon And Germanium And Their Optical And Electrochemical Properties

Silicon and germanium are two common semiconductors with high refractive index and high dielectric constant, which are as the fundamental materials for the photoelectric devices. Silicon and germanium3D photonic crystal films are supposed to be with potential of complete photonic bandgap (PBG) in theory. They will combine their physical characteristics and complete PBG to get some new properties, leading to the potential application field of all-optical switches, optical communications, photonic crystals solar cells and photonic crystal LED and other aspects. In addition, nowadays silicon and germanium have with gained much attention as a promising anode material for lithium-ion batteries owing to the highest and the second highest specific capacity as the anodes. Also, the ordered macroporous structure can improve the capacity of lithiation and delithiation by offering more pathways.In this dissertation, we focus on the two typical semicondutors Si and Ge, prepared them by ionic liquid electrodeposition, which is a green chemical method. Replicated inversely the structure of polystyrene colloidal crystals,3D ordered macroporous (3DOM) silicon and germanium photonic crystal films are obtained. We discussed the process parameters of3DOM Si films preparation in the ionic liquid electrodeposition and the influence of UV introduction during the deposition. And it is analyzed that the optical properties and the bandgap characteristic of colloidal crystal templates and the3DOM photonic crystals. At last, we discuss the electrochemical properties and battery performance of three-dimensional macroporous structured Si and Ge as anode materials for lithium batteries.The electroposition in the new generation ionic liquids as electrolytes is a green, room-temperature method, which can avoid the high energy consumption, high pollution used by high temperature molten salt electrolytes.3DOM or photonic crystal silicon films have been made via ordered PS templates by electrodeposition from an ionic liquid [Py1,4]Tf2N and they are analyzed according to the process parameters. The optimum condition is found among the different size of PS templates, concentration and the deposition temperatures. The most suitable conditions for3DOM Si is with the concentration of0.1mol/L, at the room temperature or40oC, using the templates with PS sphere diameter of400-600nm. And in vertical three-electrodes cell, high ordered3DOM Si samples can be gotten with ordered area up to60μm×60μm. The mechanism of silicon electroposition is studied by chemical method, and it is a diffusion controlled process with very high charge transfer resistance. UV is introduced into the silicon and germanium electrodeposition in ionic liquids, and the deposit morphology are analyzed in details. UV can increase reactivity of the two systems SiCl4+[Py1,4]Tf2N and GeCl4+[EMIm]Tf2N, proved by the open circuit voltage and cyclic voltammetry curves. UV will significantly influence on the reduction potential for electrolyte systems. The electrodeposition with different UV irradiation conditions, it can get different morphologies of Ge films. In particular, a special nano-cube Ge structure is shown. The optimum parameters to get most obvious Ge nano-cube include under365nmUV irradiation for10-15min deposition, with the concentration of0.1mol/L. A green luminescence can be observed in germanium electrolyte system in the presence of UV. As for silicon electrodeposition, nano cube cannot be found with UV irradiation, only showing the growing nano-particles.The photonic bandgap is particularly studied by Bragg-Snell equation and modified dynamic diffraction theory with the illustration the roles of different planes in the diffraction. The bandgaps of PS templates are measured by transmission spectra and calculated by the theoreties to know the orderliness. According to the spectra, the thickness can be estimated by Fabry-Perot interference fringes. The optical properties PS/Si composite films are studied and calculated the Si refractive index contribution to estimate the oxidation degree of the silicon.3DOM Si and3DOM Ge films are investigated by optical spectra, and also the angle-resolved reflection spectra of secondary diffraction for3DOM Si. It shows a similar two-dimensional grating behavior, and the peaks have good consistency with Bragg’s law. Also, the photonic crystals can show diffraction pattern with laser irradiation, which is related with the refractive index and the structure parameters.At last,3DOM Si and Ge are in situ prepared on copper foil as negative electrodes, and their electrochemical properties and battery performance are discussed.3DOM Si shows a poor cyclic performance, at0.2C for50times, only with retaining capacity of750mAh/g, probably due to3DOM Si is very thin and vulnerable to oxidation. Compared the dense Ge with3DOM Ge electrodes, the latter one shows relatively excellent cycle performance and rate performance.3D ordered macroporous Ge exhibits a reversible capacity of1024mA h/g and retains a capacity of844mAh/g after50cycles at rate of0.2C. At different rate,3DOM Ge shows a much slower decrease of the capacity than that of the Ge electrode.3DOM Ge electrode is beneficial to buffer the volume expansion, and offer many pathways of electrons and ions.3DOM Ge electrode with high irreversible specific capacity is very promising material for next-generation lithium ion battery.