Template-Based fabrication of Nanostructured Materials

Andres Johansson
Abstract & Cover

In the present thesis it has been demonstrated that the nanoporous membranes of anodic aluminium oxide have a large number of applications for fabrication of nanostructures. The AAO membrane can be manufactured in large quantities and there are numerous possibilities for tailoring the di mensions of the membrane well into the mezo-porous size range (2-50 nm). The thickness of the membrane can be monitored by changing the anodiza tion time. The inter-pore distance as well as the pore diameters can be tai lored by changing the anodization voltage. The degree of order of the pores can be determined by changing the anodization parameters, such as the elec trolyte concentration and temperature. By exposing the fabricated AAO membranes to phosphoric acid the pores can be further widened (of course the pore diameter is limited by the inter-pore distance). After the anodization the membranes can be left on the aluminium substrate or the aluminium can be etched away in mercury chloride, depending on the application of the membrane. There are numerous ways to fabricate nanoparticles, by wet-chemical techniques, by physical means in the gas phase etcetera. Two of the great challenges in the fabrications of nanoparticles are: 1. to get a narrow size distribution of the nanoparticles. 2. To get immobilized nanoparticles on different surfaces. In this thesis both these challenges were fulfilled for pal ladium nanoparticles, Prussian blue nanoparticles and for copper nanoparti cles. All fabricated by different techniques and in all cases it was possible not only to get a narrow size distribution, but also to tailor the sizes in wide ranges. Pd and Prussian blue nanoparticles were fabricated through sequen tial electroless techniques, while copper nanoparticles were made through Atomic Layer Deposition (ALD). The fabrication of monodisperse nanotubes are also described in this thesis. AAO membranes have been used as templates for deposition of Prus sian blue nanotubes as well as niobium oxide nanotubes. The Prussian blue nanotubes were polycrystalline and fabricated using the same sequential techniques as was used with Prussian blue nanoparticles. The niobium oxide nanotubes were amorphous and fabricated using ALD. In both cases the outer diameter of the nanotubes were strictly restricted by the pore diameters of the AAO membrane used as template. The thicknesses of the tube walls could be tailored in both cases and by using a template which was well or dered with respect to the pores. The produced nanotubes could be arranged in a well ordered fashion as well. By depositing nanoparticles or thin films of materials along the pore walls, the surface properties of the AAO membranes could be modified. If it is desirable to instead achieve other bulk properties, but still benefit from the well ordered pore arrangement, the pattern must be transferred to another material. Pattern transfer has been achieved using MeV ion beam lithogra phy. AAO membranes were used as masks and heavy ions were irradiated through the masks onto an underlying substrate of another material. Prior to irradiation a careful alignment of the mask with respect to the ion beam were necessary. This was possible by a technique described in this thesis, which involves a gold marker layer and Rutherford backscattering spectroscopy (RBS). After alignment and irradiation it was possible to selectively etch in the regions of the underlying substrate which had been exposed to the highly energetic ion beam. The pattern from the AAO membranes were transferred to monocrystalline TiO2 and amorphous SiO2 substrates with good results. By using this technique it was possible to transfer the pattern of the AAO membranes to other materials on large areas (several mm2 , depending on the optics). With the techniques described in this thesis individually or combining them with each other or other known techniques, it is possible to fabricate new nanomaterials. These new materials can be of use in a wide variety of application, such as in sensors and in the field of photo-cleavage of water. By depositing different thin films along the pore walls of AAO membranes interesting properties can be expected, which makes use of the large micro scopic surface and the possibility to precisely tailor the properties of the thin films deposited. A first step is to deposit bi- and multilayered structures, and thereby produce multilayered nanotubes. These nanotubes can make use of properties from all the materials deposited and will surely have interesting properties and future applications.

Source of Information
Thesis Online
Uppsala University, Department of Materials Chemistry.
(Uppsala, Sweden)
External Link
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