Experimental Study And Numerical Simulation Of Anodic Aluminum Oxide Films On Optical Properties

Porous anodic alumina（PAA）is widely used in synthesizing one-dimensional nanometer materials owing to their highly ordered arrays.However,PAA is only used as a template.There have been no reported attempts to discuss their own characters,such as optical properties and morphology characteristic.In recent years,with the deeply researching of the structural color,more attention has been paid to PAA template which has the period arrange structure like organisms.It is expected to produce the PAA thin film with better structural color by adjusting experimental conditions.Based on the above considerations,the structural morphology of PAA films prepared under different conditions is analyzed in detail,and the structural colors with high saturation are prepared by vacuum evaporation.The optical properties of PAA films are explained from both theoretical and experimental aspects.The results are as following:Porous alumina film can be formed on aluminum substrate in malonic acid and ethylene glycol mixture electrolyte solution by electrochemical method.Concentration of electrolyte affecting on thickness and hole distance of anodized aluminum film are investigated.The FE-SEM images of the anodic porous alumina show highly ordered dimple arrays measuring the maximum hole distance at the ultra-high voltage of 500 V and created bright color successfully.The reflection peak shifts gradually with the alumina hole distance toward longer wavelength,reaching622 nm in wavelength at 400 nm in hole distance in the 1.5 M/L malonic acid and ethylene glycol mixture electrolyte solution.The morphology of anodic aluminum oxide can be regulated by controlling the conditions of forming alumina,according to the factors affecting the morphology of anodized aluminum with a wide range of flexibility and controllability.Normally,the anodic aluminum oxide template with a structure of hexagonal prism closely is ordered under the steady-state voltage,and the holes are perpendicular to the substrate.However,the structure will be changed according to the voltage under non-steady-state voltage.The anodic aluminum oxide films with different morphologies are prepared by changing the voltage waveform and oxidation period,and its optical properties are analyzed.Based on the theory of equal-electric field,the reason for forming alumina is analyzed in detail from the view of space charge,which further proves the correctness about the theory of electric field theory.In 0.8 M/L malonic acid and under various viscosity of the electrolyte,tuned by addition of the propylene glycol（0,20,40,60,80,100 vol.%of the propylene glycol）,anodic aluminum oxide film with bright structure color is successfully prepared.The final confirmation of electrolyte viscosity is an important factor affecting the microstructure of anodic aluminum oxide.The barrier-layer anodic aluminum oxide films increase with the viscosity increase.Starting from the anodic aluminum oxide growth,a reasonable explanation of the above phenomenon and simulate of reflectance spectra of anodic aluminum oxide is given by Finite Difference Time Domain.The peak position is consistent with the observed color of the anodic aluminum oxide film under natural light,analyze the effect of structure color about Al substrate based on the Bragg formula and broaden the research and application of alumina.Porous anodic alumina thin films with structural color have been fabricated electrochemically in a 1:1（volume）mixture of 0.6 M/L phosphoric acid and propylene glycol at 100 V.The Au-coated films synthesized by a vacuum evaporation method display highly saturated colors,and explain the above phenomenon based on the principle of film interference.The results indicate that the pore growth rate of the PAA thin film can be slow to 0.4 nm s^-1 by adding propylene glycol.Compared to the reflectance spectra of alumina films with and without Au coated on the surface simulated by Finite Different Time Domain method,the model calculation shows good agreement with the experimental results,meanwhile error analysis is conducted.The experiments show the feasibility of this method,it can be act as a theory guidance and experiment assistance for constructing advanced nanostructured materials.