Evolution of Surface Morphology, Crystallite Size, and Texture of WO[sub 3] Layers Sputtered onto Si-Supported Nanoporous Alumina Templates

Abstract

Thin Al films sputtered on n-silicon wafers were anodized in two potentiodynamic steps in 0.4 M tartaric acid at 210 V and 0.4 M malonic acid at 95 V to prepare nanoporous alumina templates of type A and B, respectively. Processes at the Al/n-Si interface were closely examined to avoid field-assisted alumina dissolution during anodizing. WO 3 semiconductor layers were radiofrequency magnetron sputtered onto the as-anodized and pore-widened templates. It was revealed that the sputtered WO 3 layers covered the entire surface of type A templates while only partly penetrating into the widened pores of type B templates. The WO 3 layers crystallized at 350°C, with monoclinic phase of P2 1 /n symmetry and an average crystallite size of 28.0 nm ͑type A͒ and 32.5 nm ͑type B͒. Amorphous alumina in the Al 2 O 3 /n-Si systems did not crystallize up to 1200°C. The common trend for the WO 3 /Al 2 O 3 /n-Si systems was a preferential growth of WO 3 nanocrystallites in the ͗100͘ direction, the texture increasing with further pore widening. Besides, the crystal texture in the WO 3 layer was systematically higher on type B templates. The link between the structural features and the gas-sensing ability of the WO 3 /Al 2 O 3 /n-Si systems has been discussed.

Porous-alumina-Assisted Formation of 3-D Nanostructured Niobium Oxide Films for Advanced Sensing Applications

“…The length and diameter of nanocolumns may vary, if necessary, in the range of 450-900 nm and 30-80 nm, respectively. The initially amorphous Nb2O5 crystallized at 550 o C, while the alumina did not [5], with transformation from dielectric to a semiconductor behavior, as seen in the resistance-temperature curve of (Fig. 3a).…”

Formation of multicomponent matrix metal oxide films in anodic alumina matrixes by chemical deposition

“…Nanoporous AAM were formed by anodizing of the aluminum films in 0.4 mol/dm 3 malonic acid electrolyte with current density of 6 mA/cm 2 at anodic potential of 85 V. To improve pore regularity and enlarge the surface of the uppermost pore layer in the films, a multi-step anodizing process was developed and applied here, following generally the procedure described in Ref. [3]. The first anodizing step was performed in the above electrolyte, followed by selective dissolution of the porous alumina formed.…”

“…Formation of multicomponent matrix metal oxide films in anodic alumina matrixes by chemical deposition 3 , and others due to their high chemosensitive properties are among the most promising materials for gas sensors [1][2]. The structuring of metal oxides by applying of high ordered dielectric anodic alumina matrixes (AAM) allows to form the systems possessing a large active surface area and a heightened sensitivity to various gases [3].…”

“…The structuring of metal oxides by applying of high ordered dielectric anodic alumina matrixes (AAM) allows to form the systems possessing a large active surface area and a heightened sensitivity to various gases [3]. The formation of mixed metal oxide films with various morphology and an aspect ratio of the surface area of formed structures to their thickness can improve the selectivity of these materials [4].…”

Gas sensing properties of the nanostructured anodic Zr–W oxide film

“…3 shows the XRD pattern recorded on the annealed ZrO 2 -WO 3 anodic film. From the XRD analysis, the film is composed of two crystalline phases: monoclinic WO 3 [16] The morphology of the oxide film remains unaffected by the process of selectively dissolving the alumina overlayer, due to a well stabilized film composition, brought about by the presence of two dissimilar metal oxides.…”