Functional applications of Al·Al2O3 nanowires : laser assisted α-Al2O3 synthesis and fabrication of micro-/nanostructured surfaces for cell compatibility studies

Abstract

Recently, one-dimensional (1D) nanostructures have attracted considerable interest of nanoscience studies as well as nanotechnology applications. Especially 1D hetero-structural nanowires with a combination of two different materials, for instance metal/metal oxide composites, hold a great potential for various photonic and electronic applications. Thus, Al·Al2O3 core-shell nanowires, which were firstly reported by Veith et al., form an interesting class of such hetero-nanostructures. This thesis describes the preparation of functional surfaces composed of 1D nanostructures by CVD of a (tBuOAlH2)2 [bis(tert-butoxyaluminum dihydride)] precursor and laser treatment of such structures. Firstly, main attention is given to understand the underlying mechanisms controlling the 1D growth of Al·Al2O3 nanostructures. By applying systematically different deposition temperatures and flow rates, various nanostructures were synthesized. At high deposition temperatures chaotic Al·Al2O3 nanowires form, whereas at low deposition temperatures worm- and loop-like nanostructures are achieved. A new mask-less local deposition method, named selective CVD (SCVD), is introduced by selective heating of the substrate with electro magnetic induction. A controlled thermal gradient leads to the observation of stepwise 1D growth of nanostructures. As a continuation the of the local deposition approach,an LCVD system has been designed and fabricated to show the possibility to grow 1D complex structures. α-Al2O3 layers were synthesized by laser induced heating of deposited Al·Al2O3 nanowires. In particular, two laser processing approaches were investigated: continuous wave (CW) laser and pulsed laser treatments. CW laser treatment is useful to produce dense and fully crystalline α-Al2O3 layers which may be employed as hard and protective coatings. Pulsed laser treatment produces a large variety of nanostructures (nanopores, nanoprotrusions, nanospheres etc.) of Al2O3 which is interesting for studying cell-surface interactions. Micro /nanostructured surfaces prepared by direct deposition of (tBuOAlH2)2 and laser treatment were tested for biocompatibility. Jurkat cells seem to adhere selectively on Al·Al2O3 nanowires which may lead to applications in cancer diagnosis and therapy. Laser treated Al·Al2O3 layers exhibit a better biocompatibility for normal human dermal fibroblast (NHDF) cells. In addition, a preliminary study on neurons showed that Al·Al2O3 nanowires provide enhanced cellular adhesion and growth which can be interesting for various applications in medical fields as well as in biosciences.