Elertrochemical Fabrication Of Highly Ordered Porous Alumina And Its Application In The Hunmidity Sensor

High orderly porous anodic aluminum oxide (AAO) obtained by electrochemical oxidation of high purity aluminum has a wide range of applications in nanotechnology, optoelectronics, energy storage and sensor. This paper introduces the history of the development of nano-materials, preparation and research methods. Then, we will represent the sensor classification, principles and classification of humidity sensor and performance characters of humidity sensor.This article studies the electrochemical preparation process of highly ordered nanoporous anodic aluminum oxide at high field conditions, as well as its application in the humidity sensor. In the traditional condition, most of porous anodic aluminum oxide films are prepared under low field conditions. The reaction rate of this method is very slow, which limits its further application. Though the fast reaction rate of the high field anodization, the AAO films prepared by this method are not sophisticated. So we studied the porous alumina in the high field conditions. In the research, we got a complete the current-time curves at the high-field conditions. By microscopic studies, we found that there are lots of differences in the growths of alumina between the high field anodization and the low field anodization. We find different behaviors of the current transients with respect to the low-voltage anodization process. the characteristic dimension of the inter-pore distance changes with time period of anodization and at the top of the structure is twice as large as at the bottom of the pore and this effect is not observed at low-voltage anodization. These effects and the fact of pore self-ordering is explained by the presence of internal stress developed in the structure by current density change and the volume change. It is suggested that both driving forces could be controlled by the value of the applied voltage and of the pH of the solution.Since it's highly ordered pore array structure, high porosity and good response to humidity, the porous anodic aluminum oxide is often used for the humidity sensor. AAO films by electrochemical oxidation of aluminum at high-field contain high content of impurity ions. Impurity ions contribute to electronic conductivity, which makes the humidity sensor has a good sensitivity in the low humidity region. In this article, we change the surface by changing the distribution of impurities to improve the sensitivity of low humidity, and to reduce the high humidity sensitivity appropriately. Since the oxidation of oxalic acid, oxalic acid alumina films containing anions, we performed the annealing process, making the decomposition of oxalate to carbon dioxide. Because a high degree of dissociation of carbon dioxide, so it is easy to release protons in aqueous solution. According to the mechanism of proton conductivity at the high humidity, it is easy to improve the sensitivity of humidity sensors. Increased sensitivity due to low humidity, high humidity regions lower sensitivity of the sensor's linear response improved.This work was supported by the Natural Science Foundation of China (grant NO. 10874115), National Major Basic Research Project of 2010CB933702, Shanghai Nanotechnology Research Project of 0952nm01900, Shanghai Key Basic Research Project of 08JC1411000, and Research fund for the Doctoral Program of Higher Education of Chain.