Analysis And Simulation On Light Propagation Properties Of Fullerenes And Mesoporous Materials

A photon has the advantage of faster speed compared with an electron. Unlike electron, there is no interaction among photons, thus resulting in low energy loss. In 1987,Yablonovitch and John pointed out that the materials with periodically distributed dielectric constant, which they called photonic crystals (PCs), can change the behavior of photons passing through it. There is also energy band structure for photons in photonic crystal, just as that for electrons in natural crystal (electronic crystal). Localized state will appear in presence of impurity or defect. Because photonic crystal can control the flow of photons, it has many applications and has become one of the most important research subject all over the world. For many applications involving the use of PCs it is desirable to acquire complete and absolute photonic band gaps (PBGs). In the case of such PBG structures, the wave propagation is forbidden for any direction of propagation, and independent of the polarization state. Depending on the frequency requirement of specificapplications, the engineering of the structures which are periodic for waves on both three- dimensions (3D) and two- dimensions (2D) have been achieved in the infrared, microwave, and millimeter-wave region. For wavelength shorter than infrared, only several experimental and theoretical systems have recently been demonstrated to exhibit the signature of complete band gaps, while the study on the PC crystals with PBGs shorter than visible light region is still lacking. Those are mainly because most of the materials in one hand have high absorption coefficient and their dielectric constants change constantly under prolonged irradiation with x-ray and UV light and on the other hand it is difficult to construct the structures in nanoscale by currect processing technology.The fiillerenes certainly represent a new and exciting class of materials, much work has been carried out both experimentally and theoretically. The preparation of high-quality C6o film has been achieved. The availability of multilayer film is important for further application of fiillerenes. High-quality C60 thin films have been grown successfully on various metal and semiconductor substrates, such as Ag, Cu, Si, Ge, GaAs, A1N, GaN. In recent years, much work has been done to investigate the interactions between C60 overlayers and various metal and semiconductor surfaces. Up to now, most of previous works have been limited to the study of the structural and physical properties of fullerene multilayer films, there have been few investigations ofthe optical properties of fullerene multilayer films.Since the discovery of M41S family of mesoporous silicates and aluminosilicates in 1992, numerous mesoporous or nanoporous materials with pore sizes between 2 nm and 30 nm have been synthesized because of their potential applications in catalysis, separation of large molecules, medical implants, semiconductor, magnetoelectric devices, etc. While much of the academic and industrial research on M41S materials has focused on the synthesis procedures and chemical behaviours, there have been few investigations of the optical properties of these materials. The pore size of MCM-41 type of materials can be controlled in nanometer range. It can therefore be expected that the mesoporous materials may be used as PBG crystals with a band-gap located in the nanowave ranges.However, to our knowledge these materials have not been used as photonic crystals and it is the aim of this thesis to show that fullerenes (C6o, C70and so on) and mesoporous molecular sieves (MCM-41, SBA-15) may in principle be used as one-dimensional (ID) and two-dimensional (2D) photonic crystals. Fullerenes (C60, C70 and so on) and mesoporous molecular sieves (MCM-41, SBA-15) are treated theoretically as photonic crystals. Along the main direction, ID and 2D fullerene films and mesoporous molecular sieves photonic crystal structures have been investigated. I . C6o/ A1N, C70/ A1N, C6q/ GaN multilayer thin films have been treatedtheoretically as ID photonic crystals using the transfer matrix method (TMM). The response has been studied both within and out of the periodic plane of C6O/A1N, C7O/A1N, C60/GaN multilayers. It was found that while C6O/A1N, C7O/A1N, C60/GaN multilayer films show complete PBG behavior in UV region. A fabricated C6o/A1N (or C7O/A1N) multilayers with 2 pairs of 49 nm C6o (or C70) and 21 nm AIN layers showed a high theoretical reflectivity of 90.4% at a photon energy of about 6.2 eV for C6O/A1N (or 6.09 eV for C70/AIN). These photonic crystals may be important for fabricating a photonic crystal with an incomplete band gap in UV region.II. Using the transfer matrix method we have calculated in fabricating a 2D photonic bandgap structure in the C60 and (Cs9N)2 based networks with absolute photonic bandgap for both TE and TM radiation in near infrared and visible light range. We investigate the absolute photonic band gap (PBG) formation for 2D photonic crystals (PC) consisting of air rods drilled into C60 and (C59N)2 films. The theoretical reflectance coefficients have been presented. The dielectric constants of the fullerenes and fullerrides are the major reasons that result in the different PBGs. Because the dielectric constants of the fullerrides thin films are controllable, the band-gap width and locality can be also controlled when they are used as photonic crystals.III. All of our simulation results are based on Cerius2 of molecular simulation. The structures of an unidimensional pore system (MCM-41,SBA-15) and three-dimension bcc structure (SBA-1, SBA-16, SBA-6) were constructured. We used these models to simulate X-ray diffraction patterns of MCM-41 and SBA-n type materials. The results of these simulations are close to the results of experiments patterns. In addition, we simulate X-ray diffraction patterns of different pore diameters and shape" of MCM-41. IV. The concept and analysis method of photonic crystals and band gaps are introduced into ID ordered mesoporous materials. MCM-41 type materials are treated theoretically as photonic crystal. The formation of band gaps is exhibited and confirmed by a calculation of transfer matrix technique. PBGs are found around 51-170 eV (7.29~24.3nm) in soft X-ray region. Since both pore size and lattice constant of the mesoporous silica materials can be controlled, MCM-41 materials may be used effectively as 2D photonic crystals in soft X-ray region.