The Studies On Preparation And Spectral Properties Of Si Nanomaterials

Since Porous silicon (PS), which produces high-eficiency visible photoluminescence (PL) at room temperature, was firstly prepared by L.T. Canham in 1990, synthesis and characteristic of Si nanostructures and nanomaterials have been intensively investigated in recent decade for the potential applications in the optoelectronics, microelectronics and biomedical areas. Despite of the considerable number of researches, however, mechanism for the formation and PL of these nanostructures and nanomaterials remain unsolved. One of the reasons is that PS layer express very large internal surface, so it always contains an enormous quantity of impurities coming from the electrolyte and from the ambient air due to surface adsorption. The spectral and electrical properties of PS were deeply affected by their impurity content and surface passivation. Because the PL of fresh PS is unstable, weak and the surface of PS is easily contaminated, in this thesis, we seek for the new preparation of Si illuminant materials and discuss the PL mechanisms.At first, as the PL of PS is unstable with increasing of exposure time. Some techniques, such as native oxidation, plating a thin layer of silver etc, were adopted to characterize the stability and enhancement of PL.Secondly, for searching the new Si illuminant materials, this paper studied the stability of PL of laser ablated silicon plate. The silicon plates modified by laser have a lot of regular alveolate holes, which determine its PL. Compared laser ablated Si plate with PS, its PL is obviously enhanced, especially Si plate ablated by 248nm laser. It mostly because of that Si plate absorbs much suited-photons, a lot of electrons are excitated. Laser ablated Si plate contains a thin surface layer of oxidation, which also influence its PL.Thirdly, using different wavelength of pulsed laser to ablate Si plates in redistilled deionized water will obtain Si nanoparticls. When laser ablated Si plates, the surface of Si plate will be melted and/or gasified instantly and then, "chemically pure" Si colloids will be obtained. Comparing with other preparing methods, the pulse laser ablation technique has these advantage: (1) Short preparation time, usually, within 10~30 minutes and, (2) with simple operations; (3)Pure products with regular geography. Si nanoparticles are formed directly with Si atoms and Si clusters without any other chemics; (4) the laser modified rough substrate is also luminescence materials.When anions were added into the Si sol, the luminescence intensity is obviously decreased arised from the aggregation of the Si nanoparticls. From the analysis of energy spectra, it can be seen the existence of oxygen on Si particle surface. Therefore, we conclude the quantum confiment effect and the defects relevant with Si-0 are both account for the luminescence of Si sol. Because of its large surface area, it is easy to absorb other molecule. Ablated Si in the solutions of ethane, formaldehyde, gold and silver hydrogel respectively, serials of Si nanoparticles were obtained. It is found that the luminescence spectra have much relation with the surface ingredient of Si nanoparticles. Therefore, the luminescence of si nanoparticles is attributed to the quantum confinement and surface ingredient. Furthermore; laser ablated Si nanoparticles and the electrochemical etching Si nanoparticles were compared and, similar results are obtained.