Behavior of acid species during heat treatment and re-anodizing of porous alumina films formed in malonic acid

In the present work infrared spectroscopy, photoluminescence spectral measurements and the potenthiodynamic technique for studying the effect of treatment temperature on compositional and electronic properties of malonic acid alumina films were used. In the course of our studies, it has been proven that heat treatment of malonic acid films at temperatures from 250 up to 400 A degrees C leads to considerable changes in the photoluminescence properties and voltammetric response during their potentiodynamic re-anodizing. We suggest that defects, such as electron traps, in this type of porous anodic films are caused by the atoms of hydrogen (one or two) escaping from the CH2 groups of the malonic acid species as a result of the heat treatment. The sites of such defects provide pathways for easy electron migration under a high electric field increasing electroconductivity of anodic alumina films. On the contrary, no structural defects responsible for enhanced electroconductivity are observed during thermal splitting of oxalate groups in the oxalic acid alumina films.