Optical Properties Of Porous Anodic Alumina Films And Its Application In Preparing Nanomaterials

Self-organized porous anodic alumina(PAA)films exhibit bright structural colour in visible regime because of the quasi-periodic microstructures with feature sizes comparable to visible wavelengths.Due to its unique optical properties,PAA films have been extensively explored as a platform for developing portable chemical sensing and biosensors devices.Currently,most sensors based on PAA films rely on expensive precision instrument to detect,imposing a cost barrier for the development of practical applications.Therefore,it is of great significance to study the optical property of PAA films for the application of portable sensors.In addition,because of its simple structure,uniform pore size distribution,high pore density,etc,PAA films can be used as template to synthesize small size nanometer materials.Unfortunately,the study that using PAA films as template to synthesize nanometer materials has not been well understand and is not perfect.Therefore,the work presented in the dissertation is focused on the following sections.(1)The influence of pretreatment conditions for Al foils on the color uniformity and brightness of PAA films has been studied.It was found that when the annealing time is 2 h,the polishing time is 5 min,the anodization of Al foils is uniform and thickness of Cr layer is 6.0 nm,we can get uniform and bright iridescent PAA films.Through a serious of experiments,some experimental conditions for the preparation of PAA films with bright iridescent have been got,which can be used for further studying their optical property.Based on these conditions,patterns with different colour combinations were fabricated by varying the time of the second anodization for different areas,which is a serious of PAA films with a “hysteresis-loop-in-a-circle,HLC” pattern.(2)The influence of different geometric parameters on the colour of PAA films has been studied.It is found that the pore depth,pore diameter,porosity,the order of sputtering Cr nanolayer and viewing angle have a great effect on the colour of PAA films.So PAA films with colour tunability have been prepared by precisely controlling the geometric parameters of PAA films(e.g.the pore depth and the porosity)and the top metal nanoparticle layers.The reason why is that the peak wavelength of reflectance spectra are shifted to longer wavelengths with increasing pore depth,decreasing pore diameter and porosity.While changing the order of widening pore diameter and sputtering Cr nanolayer,the PAA films show different color due to their different pore depths.Besides,the colour of PAA films changes dramatically after infusing organics with different refractive indices.Such change is easily discernible by naked eyes and the response time is less than 1 second,making the system potentially applicable as an easy to use “test-strip” for chemicals based on colour change.(3)One-dimensional nanowires of different materials have been prepared and studied.Ni nanorods,Co Fe alloy nanowires and Ni/Pt heterostructure nanowires have been successfully prepared by using PAA films with Cu substrate.The morphology and composition of nanostructures were analyzed by scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS).The crystal structure was characterized by X-ray diffraction(XRD).The magnetic measurement results indicate that the magnetic properties are strongly dependent on the morphology and composition of nanostructures.