Theories And Applications Of Raman Spectra

Raman scattering is one of the Nondestructive Testings. It is wildly used in chemistry, physics, biology, and medicine etc. Because the Raman scattering is very sensitive to the symmetries breaking of carbon structure, and with other typical advantages compare with other analyzing methods such as only a small amount of sample needed when analyzing. So Raman scattering has become the analyzing method with priority of exploring the microstructure of carbon material. In this dissertation we mainly discuss the theory of lattice vibration and the application of Raman spectra for analyzing carbon nanotubes and LaMn(1-x)FexO3. The dissertation consists of three parts as following: In part one, we discuss the theory of lattice vibration. We get the lattice wave solution of monatomic chain under the free boundary condition. The answer of dispersion relation is the same as the answer we get under the cyclic boundary condition, but they have different wave frequency. If we just consider the symmetry as the premise but don't consider the Lattice Structures, then the answer gotten under the reflecting boundary condition is the same as the answer gotten under free boundary condition. Lattice wave will be reflected when it reaches the boundary so that the reflecting boundary condition is more reasonable than cyclic boundary. We prove that the answer of stationary wave under cyclic boundary condition that has double length of the monatomic chain is the same as the answer under reflecting boundary condition. Because the traveling wave can also be caught under cyclic boundary condition so that it shows the imperfect aspect of cyclic boundary. In part two, we discuss the structures and Raman spectra of carbon nanotubes. There are three types of carbon nanotubes: armchair nanotubes, zigzag nanotubes and chiral nanotubes. Using group theory we can get the number of their vibration modes and the numbers of Raman-active and IR-active modes. Then we calculate these vibration modes and get different results from some references. In part three, we discuss Raman spectra of LaMn(1-x)FexO3. When there is a structural phase transformation in LaMn(1-x)FexO3, there will be an evident change in Raman spectrum. We investigate a series samples of LaMn(1-x)FexO3, and found that a structural phase transformation exist between x=0.2 and x=0.4 . When x<0.2, they are trigonal system. When x>0.4, they are orthorhombic system.