Se-doped Nb2O5–Al2O3 composite-ceramic nanoarrays via the anodizing of Al/Nb bilayer in selenic acid

XPS characterization of metal-oxide nanocolumn arrays via anodizing Al/Nb/Mo metal layers

“…In this way, 24, 57, and 96 at.% of Al were obtained for the anodized PAA-free, re-anodized PAA-free, and re-anodized PAA-half-etched films, respectively (providing that at.%(Al+Nb+Mo)=100%). The amount of Al in the columns of the PAA-free films is comparable with the Al amounts obtained for Se-doped Nb2O5 PAAassisted nanocolumns reported in a previous work [7], ranging ~50-80 at.% Al. The extraordinarily high amount of Al in the PAA-half-etched film is explained by the dominating presence of PAA surrounding the column tops.…”

“…In the PAA-free films, also a low-intensity doublet is present, shifted to −1.8 eV from the Nb 5+ component, which is attributed to Nb 4+ cations [3] (the Nb 2+ cations in the anodized PAA-free film are most likely related with the metallic residues). The ratio of Nb 5+ :Nb 4+ cations is 96.5:3.5 and 98:2 in the anodized and re-anodized PAA-free films, respectively, suggesting the presence of a substoichiometric Nb2O5 at the surface layer of the columns, as was disclosed earlier for some other metal oxides [3,7]. On the other hand, the re-anodized PAA-half-etched film shows only the Nb 5+ doublet in the Nb 3d spectrum (Figure 3c), meaning that the column tops contain stoichiometric Nb2O5.…”

“…For selected samples, re-anodizing was carried out in a borate buffer (0.5 M H3BO3/0.05 M Na2B4O7) to a more anodic voltage, up to 180 V. The PAA overlayer was partially or fully selectively etched away in Cr2O3/H3PO4based etchant [7] to obtain the 'PAA-half-etched' or 'PAA-free' samples. Field-emission SEM, utilizing an InBeam detector for secondary electrons, was employed to examine the morphology of the anodic films.…”