In-situ thickness measurement of porous alumina by atomic force microscopy and the reflectance wavelength measurement from 400-1000 nm

This article presents a novel method to measure the in situ thickness of porous alumina (PA) films. The PA films were prepared in oxalic acid at 30, 40, and 60 V direct current. Based on the atomic force microscope measurements, PA film porosities and refractive indexes measurements were acquired. With the observation of the reflectance spectra of PA films over the wavelength range 400-1000 nm, the nondestructive thickness measurement of the PA films were accurate and were found to be 3.66, 7.76, and 11.38 mu m, respectively. Experiments showed that when the applied voltage increased, the pores diameters and interpore distances were enlarged, and the interference pattern was stronger and exhibited a greater number of oscillations over the given wavelength range, which indicated that the PA film's thickness increased. Our results match with the theoretical predictions and analysis quite well.