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  • Title: [Study of in-situ measurement system for porous alumina film based on AFM and reflectometric interference spectroscopy].
    Author: Liu C, Zhang DX, Zhang HJ.
    Journal: Guang Pu Xue Yu Guang Pu Fen Xi; 2008 Jul; 28(7):1679-83. PubMed ID: 18844188.
    Abstract:
    An in-situ measurement system for porous alumina (PA) film based on atomic force microscope (AFM) in liquid and reflectometric interference spectroscopy (RIFS) was developed. The present article briefly discusses the principle and structure of the system, and introduces its unique characteristic. The system consists of probe unit, XY scanner, Z-piezo feedback system, computer and software, fiber optic spectrometer, anodization control circuitry etc. When a white light beam illuminates the surface of the film, the reflective light beams at the front and back side of the layer are coherent, and lead to periodical amplifications and extinction in the reflective spectrum with the information of the optical thickness of the film. A fiber optic spectrometer was applied in the system which input the refractive spectrum into the computer by which the optical thickness of the film was calculated. Meanwhile according to the surface topography of PA films by AFM in liquid, the effective refractive index was calculated based on Maxwell-Garnett theory and coherent potential approximation (CPA). So the thickness of PA films could be gained at last. To checkout the feasibility and stability of the system, the real-time scanning and thickness measurement experiments were done during anodization of Al sheets in oxalic acid aqueous solution. In the experiment, the authors used 25 mm diameter aluminum (Al) sheets with 99.999% purity and 0.4 mm thickness as the anode, and graphite rod as the cathode. The pretreatment-cleaned Al sheets were anodized in an aqueous solution of 0.5 mol x L(-1) oxalic acid at the constant temperature (20 +/- 0.2) degrees C with 20 mA x cm(-2) anodization electronic current density. Real-time AFM images of PA film were successfully obtained during anodization. The pore-ratios of Al sheet were 7.81% and 13.83% at oxidizing time 150 min and 180 min respectively. Correspondingly, the effective indexes were calculated to be 1.62 and 1.60, respectively. Combining the reflective spectrum gained by the fiber optic spectrometer, the wave number differences between the two adjacent extrema were 57.69 mm(-1) and 50.00 mm(-1). Based on reflectometric interference spectroscopy, the thickness of PA films was found to be 5.35 and 6.25 microm with oxidizing time 150 min and 180 min respectively. The system has characteristics of convenient manipulation, non-destructive and high-resolution in-situ measurement. And the surface morphology, pore-ratio and effective refractive index can also be gained at the same time.
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