Cathodic polarization of niobium specimens that have been anodized galvanostatically up to Ea=100V, and then potentiostatically at Ea=100V has been investigated in a neutral borate solution. During potetiostatic cathodic polarization below Ec=−2.36V (vs. RHE) in both aerated and deaerated solutions, the cathodic current increased rapidly initially, and then increased gradually until it reached a steady value. Hydrogen gas evolution was observed during cathodic polarization below Ec=−2.36V with no formation of blisters and pits, suggesting that H+ reduction occurs mainly at the film surface. GD-OES spectra revealed that hydrogen species are enriched in the niobium substrate near the interface between anodic oxide films and the substrate at potentials below Ec=−2.36V, and that the trend is pronounced at lower potentials. Chemical shift was observed on Nb 3d and O 1s peaks in XPS spectra for the specimen at Ec=−3.36V, suggesting the formation of Nb2O3(OH)2. Mechanism for the reaction during cathodic polarization in a neutral solution is discussed in terms of the proton reduction at the interfaces both between oxide films / solutions and between oxide films / substrates.
This paper addresses a new method of surface patterning for thin aluminum films using photolithography, anodization, and chemical etching. Aluminum film with a thickness of about 150nm was deposited on titanium-coated silicon or slide glass substrates. Subsequently, square masks were patterned on the aluminum film using photolithography. While aluminum film was anodized in 1vol% sulfuric acid, an anodic oxide film formed in the photoresist/aluminum film interface in addition to on open surface regions. In this process, the thickness of the anodic oxide film formed under the photoresist was affected by the bath voltage and the thickness of the titanium layer. Since the thickness of the anodic oxide at open surface regions and at masked regions differed, a patterned surface was developed. In order to examine the surface morphology, the anodic oxide film was removed by chemical etching in 21vol% phosphoric acid. As result, the anodic oxide film was removed, leaving an aluminum film of convex shape on the substrate.
A titanium plate was anodized in an alkaline electrolytic bath. The anodized film was re-anodized under spark discharge in the bath with hydroxyapatite fine particles after parts of the surface of the anodized film were masked by 5mm diameter tapes. The holes on the surface of the re-anodized film were the same shape as the masking tapes and were 35μm deep.