Valter Reedo 1,2 , Martin Järvekülg 1,2 , A. Lukner 1 , K. Keevend 1 , A. Lõhmus 1 , U. Mäeorg 2

1. Elaboration of micro-dimensional optical oxide materials from the Ti, Zr and Hf alkoxides Valter Reedo1,2, Martin Järvekülg1,2, A. Lukner1 , K. Keevend1, A. Lõhmus1, U. Mäeorg2 1Institute of Physics, University of Tartu, Riia 142, EE-51014 Tartu, Estonia, 2Institute of Organic and Bioorganic Chemistry, University of Tartu, Jakobi 2, 51014 Tartu, Estonia • INTRODUCTION • Nano- and microscale structures have exceptional properties and have • great potential as the building blocks of nano- and microdevices systems of • high efficiency. • In present work we report preparation of nano-dimensional ZrO2, TiO2 and HfO2 rare earth doped and un-doped thin films, fibres, powders and micro-structured surfaces. These rare earth doped oxides are valuable sensors (e.g. for monitoring of ambient gas content at high temperatures or for detection of high energy particles). • We observed, for the first time, the self formation of ZrO2, TiO2 and HfO2 micro-tubes from precursor solution. We also work on in-situ conversion of prepared oxide materials to metal carbides for elaboration of new approach for obtaining of hard alloys. • AIM OF THE WORK • Elabortion of method for preparation of rare earth doped and un-doped thin films, fibres, powders and micro-structured surfaces starting from the Zr, Ti, Hf alkoxides. • Finding novel methods for manipulation of viscose alkoxide polymer to develop new micro-dimensional structures. • Characterization of obtained low-dimensional oxide structures for finding new properties and fenomenons. THIN FILMSBY DIP-COATING AN D SPIN-COATING Prepared films were smooth and ~50 nm in thickness.The morphology of spin-coated Sm3+ doped and undoped films (fig 1.) show that formed crystallites are different in size (20-30 nm for doped and 90-120 nm for undoped films). This indicates that growth of nano-crystallites is influenced by addition of dopant in TiO2 materials. In collaboration with S. Slange and A. Lukner we have observed gas-sensing property on Sm3+ doped spin-coated and dip-coated TiO2 thin film (fig 2.). This makes this material potentially valuable for gas sensing applications. Figure 2. The PL intensity responses of Sm-doped TiO2 powders for different oxygen concentrations in ambient atmosphere Figure 1. AFM image of a) Sm3+ doped TiO2 b) undoped TiO2. FIBERS BY ROAD BULLING Fibers were prepared by glass road spinning technique from solvent free precursors. Prepared HfO2, ZrO2 and TiO2 fibers were 50-100μm in diameter. Luminescence spectrum was measured for Sm3+ doped TiO2 fibers (Fig 6.). INTRODUCTION OF SOL-GEL TECHNIQUE Relatively simple and low-cost sol-gel technique was used for preparation of low-dimensional ZrO2, TiO2 and HfO2 undoped and rare earth doped oxide materials. Below is brought a brief overview of this technique. POWDERS BY RAPID HYDROLYSIS AND CONDENSATION In collaboration with A. Lukner we have observed different behaviorof Sm3+ spectra intensity by heat treatment for TiO2 thin films and powdwes (fig 4.). This gives us tool for manipulation of photoluminescence properties of material. Water, dopant Alkoxides + Water Precursor stadium (viscose material) + Solvents Figure 4. The spectra intensity change in post preparation annealing for films(B) and for powders (C) Hydrolysis, Polymerization Controlled gelation and hydrolysis Figure 6. Photoluminescence of Sm3+doped TiO2fiber. Figure 7. Photosof hafnia fibers Figure 5. SEM image of Sm3+ doped TiO2 powder. MICRO-STRUCTURED OXIDE SURFACES Micro-structured HfO2 surfaces (Fig 8.) were prepared by sol-gel molding technique [1]. SELF-FORMATION OF OXIDE MICRO-TUBES BY CONTROLLED GELATION AND HYDROLYSIS. Varying catalyst concentration in the sol resulted in self-formation of solid tubular low-dimensional structures. Most of these were in the form of tubes with ~1mm in length and ~30-4μm in diameter. Nanoscale fiber-like solid particles could also be detected. 50 μm Figure 8. Micro-structured HfO2 surfaces. • CONCLUSIONS • Sol-gel method can be applied for elaborating various low-dimentional TiO2,ZrO2 and HfO2 samples. • Fibers, films and micro molded surfaces are transparent and the material is suitable for hosting rare-earth dopants, which make them potentially valuable for different optical uses. • A novel method for manufacturing micro- and possibly nanoscale tubes and fibers was found. Further studies are underway to clarify cognitive aspect of the materials and to determine there industrial potential. Figure 6. Self formed zirconia microtubes. REFERENCES AKNOWLEDGEMENTS This work has been supported by ETF6537, ETF6660, ETF6163, SF0382149s02, Estonian Nanotechnology Competence Center and Doctoral school of material science and material technology. [1] T. M. Gale, C. Grimkiewicz, S. Obi, M. Schniper, J. Söchtig, H. Thiele, S. Westenhöfer, Optics and Lasers in Engineering 43 (2005) 373-386. [2] S. Hasegawa, Y. Sasaki and S. Matsuhara, Sensors and Actuators, (1993) 509-510.