| Femtosecond laser bombardment of a target surface can form a high temperature plasma.The plasma consists of atoms,ions and free electrons and other particles.In its life cycle,plasma is in an unstable state,and atoms or ions will transit from high energy state to low energy state and also emit a plasma spectrum.The spectrum not only carries information about a large number of target elements and their content,but also the plasma formation,evolution and expansion process.This spectrum is commonly referred to as Laser Induced Breakdown Spectroscopy(LIBS).At the same time,the transient generation of high temperature plasma outward expansion to form feathers,can be used to deposit films or nano-structures.This technology is commonly referred to as pulsed laser deposition(Pulsed Laser Deposition,PLD).Based on this idea,in this dissertation,the characteristics of plasma and its temporal and spatial evolution laws are studied by LIBS spectroscopy,and the films and nanostructures are deposited on the substrate by the characteristics of plasma homogeneous deposition.Pulsed laser deposition technology has been fully used as a powerful thin film preparation technology in the high temperature superconductivity,semiconductor,diamond and other functional films and hard ceramic film preparation,and nano-materials.With the emergence of high peak power femtosecond laser,laser induced breakdown spectroscopy and pulsed laser deposition technology move into the femtosecond era.Compared to the traditional nano/pico-second laser,femtosecond LIBS and femtosecond PLD show a more attractive prospect.The purpose of this paper is to fabricate TiO2 nanometer thin films by femtosecond PLD technology,which will lay a foundation for future research on photo-catalysis based on TiO2 nanostructures.The work of this dissertation is divided into two parts:The first part of the experimental work is to study the spatiotemporal evolution of titanium plasma spectra induced by femtosecond laser by LIBS technique,and to determine the time evolution characteristics of plasma temperature and the electron density and laser energy relationship.The second part of the experimental work is the use of femtosecond PLD technology to prepare TiO2 nanofilm materials.Through the field emission scanning electron microscopy and X-ray photoelectron spectroscopy(XPS),we study the forming mechanism and process of film,and the effects of laser energy and substrate temperature on the deposition rate and quality of the films.The effects of laser energy and substrate temperature on the deposition rate and quality of TiO2 films were investigated.Finally we use UV-Vis spectroscopy to explore its optical properties,for its application in the field of photo-catalysis.Through the above experimental study,the following conclusions are obtained:(1)The film is a fluffy structure composed of granular TiO2 particles with a particle size in the range of 1 to 100 nm.(2)The TiO2 particles were analyzed by SEM images of different deposition times,showing that the growth pattern of the TiO2 film is island-like growth,(3)The UV-Vis absorption spectrum of the sample shows that the wavelength of the film is about 400 nm,and the band gap determined by the forbidden band width calculation is about 3.1 eV,indicating that the sample is a mixed phase of rutile and anatase. |
