Electric microstructure of the surface of hydrophilic and hydrophobic anode oxide films at the aluminum surface as studied by atomic force and capacitance microscopy

The surface of hydrophilic and hydrophobic anode oxide films (AOF) at the a luminum were studied by methods of scanning probe microscopy. The surface o f the samples was also examined by a number of independent methods, such as scanning electron microscopy, water contact angle theta measurements, cont act potential (CP) measurements, and gravitometric measurements of the amou nts of water absorbed alpha and of the content M of Al2O3 in the AOF. A cha racteristic feature of the hydrophobic surface (theta = 70 degrees) is the identity of images (the same contrast) obtained in the semicontact (geometr ic relief) and capacitance (electric relief) modes. For samples with hydrop hilic surface (theta = 15 degrees) images obtained in the capacitance mode show reversed contrast over area occupied by pores (i.e., are negative with respect to the topology of the surface). This suggests that the potential of the electric field in the pores of AOFs is higher. The values of CP, alp ha, and M for the AOFs studied and experimental data obtained at elevated t emperatures make it possible to explain the phenomenon of reverse contrast by the effect of water association absorbed in the AOF pores. The adsorptio n of water in the form of multilayer liquidlike films results in a smoothin g of the surface electric field and in a hydrophobization of the surface (d isappearance of reverse contrast). Once the water multilayer film is remove d, the surface is reversibly transformed into the hydrophilic state, with t he electric nonuniformity being recovered (reverse contrast).