No abstract

Two types of niobia columnlike nanostructures were synthesized by anodization, reanodization, and chemical etching of sputter-deposited Al/Nb metal layers. The morphological properties of synthesized niobia columnlike nanostructures were determined by means of scanning electron microscopy. The electro-physical characteristics of niobia columnlike nanostructures were investigated in two measurement schemes. Aluminum layers of thickness 500 nm were used as contact pads. The current-voltage I-U characteristic has a nonlinear and nonsymmetrical character. The rising of temperature leads to an increase of the current. This behavior may indicate a p-n or metal-semiconductor junction. The initial resistance at 23 o C was 60 and 120 kOhms, the specific resistance to the height of the columns was 87 and 116 kOhms•nm -1 , the calculated temperature coefficient of resistance appeared to be negative and rather low: -1.39×10 -2 and -1.28×10 -2 K -1 for the niobia columnlike nanostructures reanodized at 300 and 450 V, respectively.

Reanodizing metal underlayers through porous anodic alumina has already been used extensively to fabricate ordered columns of different metal oxides. Here, we present similar 3D multilayered nanostructures with unprecedented complexity. Two-level 3D column-like nanofilms have been synthesized by anodizing an Al/Nb metal layer in aqueous oxalic acid for forming the first level, and an Al/Ta layer in aqueous tartaric acid for forming the second level of the structure. Both levels were then reanodized in aqueous boric acid. The Ta layer deposited on partially dissolved porous anodic alumina of the first level, with protruding tops of niobia columns, acquired a unique hexagonally-packed structure. The morphology of the first and second levels was determined using scanning electron microscopy. Prolonged etching for 24 h in a 50%wt aqueous phosphoric acid was used to remove the porous anodic alumina. The formation mechanism of aluminum phosphates on the second-level columns in the process of long-time cold etching is considered. The model for the growth of columns on a Ta hexagonally-packed structure of the second level is proposed and described. The described approach can be applied to create 3D two- or three-level column-like systems from various valve metals (Ta, Nb, W, Hf, V), their combinations and alloys, with adjustable column sizes and scaling. The results of optical simulation show a high sensitivity of two-level column-like 3D nanofilms to biomedical objects and liquids. Among potential applications of these two-level column-like 3D nanofilms are photonic crystals for full-color displays, chemical sensors and biosensor, solar cells and thermoresponsive shape memory polymers.

Low‐profile anodic alumina matrices of 1 μm thick with pore sizes of 105 and 160 nm are formed by two‐step anodizing of Al layers and are used as templates for the deposition of multicomponent metal oxide films on their surfaces. The metal oxide systems of Sr2FeMoO6−δ, FexMoyOz, and SnxMoyOz composites with carbon nanotubes are synthesized by electrophoretic deposition, sol–gel method, and drop method using aqueous salt solutions and are annealed at 373–473 K for 1–2 h and at 773–1123 K for 2–10 h. The morphology, microstructure, and composition of the porous alumina matrices with multicomponent metal oxides films are examined by scanning electron microscopy, energy‐dispersive X‐ray microanalysis, and X‐ray phase analysis. The use of anodic alumina matrices allows reducing the grain dimensions and gives uniformity to the microstructure and properties of the metal oxide films. The carbon nanotubes increase the working surface of the functional layer and its electrical conductivity. The variation in the synthesis conditions of deposited films and anodic alumina matrices configuration allows forming of different complex composition compounds with reproducible structure and properties.

No abstract