Preparation And Optical Properties Of Porous Aluminum Nano-array Study

Recently, the porous anodic alumina(PAA), which forms unique structure when aluminum is anodized in acidic solution, has attracted an increasing interest. As a template, it has potential applications in functional materials, such as optical components, magnetic materials, selective absorbing films, etc. The functional application of PAA establishes another new way in developing functional materials.In this thesis, the optical properties of metal/ Al₂O₃ nano-array composite structure are systematically investigated under detailed considerations to the domestic and foreign works in PAA. This work is useful in fabricating new polarizer. The thesis includes four chapters as follows.In Chapter 1, an introduction to the development of the nano-matreal, the porous anodic alumina, and the new functional materials made from PAA template is established. The main works of this thesis is also involved.Chapter 2 ,Chapter 3 and Chapter 4 are the main body of the thesis. In Chapter 2, the method and progress of making PAA are discussed in details. Then we discuss the preparations and optical properties of PAA with different branched structure.1. During the course of the second-step anodization, the anodization voltage is decreased as (?), where V₀ is the initial voltage. Then PAA with n branches pores is obtained.2. The transmission spectra indicate that three samples have better transmittance (above 80%) in the near infrared region; The phenomenon of interferometric vibraticn in the transmission spectra which agrees well with the Airy Differential Equation.3. The PAA with linear pores (n = 1) behaves better transmittance ratio and extinction ratio in the visible and near-infrared waveband than others (n > 1). We conclude that the PAA with linear spectral photometer is a good reference as a kind of template material of wire grid polarizer. In Chapter 3, the microstructure and optical properties of Cu/Al₂O₃ nano-array composite structure are systematically investigated. Porous alumina templates with different apertures are fabricated by two-step anodic oxidation processes changing the oxidation voltage. Followed, the Cu nanowires are synthesized in porous alumina by the alternating current electrochemical deposition method.1. The Cu/PAA is analyzed by SEM and XRD, the results show that the Cu nanowires are indeed synthesized in porous alumina which has the same diameter and made good structure of wire grating.2. And the transmission spectra indicate that such a micropolarizer of porous alumina film with Cu nanowires has better transmittance(above 80%) in the near infrared region. The adsorption of the light increases, the transmission of the samples decreases.3. The polarization spectra indicate that the diameter of the Cu nanowires increase with the increasing of oxidation voltage. The loss reduction of the S electric field component is lower than that of the P electric field component. The extinction ratio can be obviously improved. Then, we can obtain the Cu/PAA micropolarizers of higher efficiency by optimizing the parameters of the template.In Chapter 4, we study the microstructure, optical properties and depolarization effect of Co/Al₂O₃ nano-array composite structure. And we compare the transmitted spectra and polarized spectra of Co/ Al₂O₃ with the ones of Cu/ Al₂O₃. And we obtain Co-Cu alloy nanowire.1. CO/Al₂O₃ has good polarization in near-IR waveband. Its extinction ratio decreases with the increasing electrodeposition time. Co/ Al₂O₃ has depolarization effect in adjustable magnetic field, and the depolarization effect increases with the magnetic field when the intensity of magnetic field increases over saturation intensity.2. Compared the transmitted spectra and polarized spectra of Co/ Al₂O₃ and Cu/ Al₂O₃ , the experimental results indicate that (1) the transmittance of Cu/ Al₂O₃ is better than the one of CO/Al₂O₃ in the visible and infrared waveband; (2) the extinction ratio of the CO/Al₂O₃ is superior to the one of Cu/Al₂O₃ in near infrared waveband; (3) Co/ Al₂O₃ has depolarization effect in adjustable magnetic field, but Cu/ Al₂O₃ does not.3. Co-Cu alloy nanowire arrays are prepared by AC electrochemical deposition into PAA template with mixed CUSO₄ and COSO₄ solution as electrolyte. The XRD results show that the meatal have (111) preferred orientations during growth. Co-Cu alloy can change some characteristics of the simple metal, for example, Co.Cu/PAA has better extinction ratio in near infrared waveband than CU/Al₂O₃.