Evidence of material mixing during local anodic oxidation nanolithography

We investigate the chemical properties of nanostructures fabricated by local anodic oxidation (LAO) on epitaxial GaAs/AlAs/GaAs layers. We find evidence for the presence of Al compounds located in the topmost surface layers of the LAO structures. Our results cannot be explained within the framework of the commonly accepted mechanism that describes the growth of the LAO oxides in terms of diffusion of oxygen-rich ions through the growing oxide. A more general mechanism that explains our experimental findings is proposed.