Was sind Multifunktionale Nanostrukturen?
Multifunctional nanostructures are very small entities that due to their shape, structure or physical properties can be used in multiple fields e.g. in thermoelectric, magnetic or biotechnological applications.
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Multifunctional nanostructured materials are synthesised and investigated for thermoelectronic, magnetic and biotechnological applications.
Thermoelectric Nanostructures
Thermoelectric (TE) cooling and electrical power generators devices have many advantages in comparison with conventional refrigerators or electrical power generations, for example vibration free energy conversion and micrometer feature size. Due to the relative low efficiency, the application range of the present thermoelectric devices is very limited. Theoretical predictions have shown a significant higher TE efficiency (2x to 3x) of low-dimensional TE materials, such as quantum dots (0-D) or nanowires (1-D), than in bulk materials. The efficiency enhancement is based on quantum size effects, a favourable carrier scattering mechanism, and a much lower thermal conductivity. The development of TE materials in the sub-100 nm range will lead to high-efficiency thermoelectric devices in the future. Beside the development of thermoelectric well-defined nanowires and nanotubes, we characterise the TE properties of these nanostructures. Subsequently, high performance TE devices will be developed, for example in a lab-on-a-chip microstructure.
Magnetic Nanostructures
Magnetic nanowires and nanoparticles exhibit multifunctional properties useful in a broad range of applications such as drug or gene delivery, or for magnetic imaging. Magnetic nanotubes represent a new class of anisotropic multifunctional nanoparticles. By coating the inner or outer nanotube wall with oxides, polymers, biomolecules or metals, a broad range of physical and chemical properties may be realised within a single structure. In comparison with nanowires, nanotubes have very low mass and may therefore be more suitable for applications in ferrofluids or drug delivery. We investigate novel approaches on the fabrication of multifunctional nanowires and nanotubes by using highly-ordered porous alumina templates, polymer infiltration, electrochemical and atomic layer deposition techniques. The emphasis is on the magnetic characterisation of ferromagnetic nanotubes.
Alumina Template System
The nanowires and nanotubes are produced by using a pulsed electrodeposition process with conducting materials in perfectly ordered alumina pores channel arrays or by multilayer coating of the oxide pore walls with polymers, oxides and metals. The porous alumina templates are fabricated by a lithographic guided self-assembly technique, where the feature size of the lithographic pattern is much larger than the periodicity of the pore arrays. After the growth process the nanowires and nanotubes can be transferred into solutions or integrated in microelectronic devices by a selective chemical etch of the aluminum oxide matrix.
Atomic Layer Deposition
Our research group has one main focus on the fabrication of novel nanostructures utilizing atomic layer deposition (ALD) as universal tool for functionalization and modification. ALD allows for the deposition of thin films of a wide range of materials, e.g. metal oxides, nitrides etc. In order to fabricate nanostructures from such materials, nanoscaled templates are coated by ALD and functionalized or replicated. Such templates might be biological macromolecules, like plant viruses or ferritin as well as inorganic nanostructures like nanowires, nanospheres or nanotubes.