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

Elaboration of micro-dimensional optical oxide materials from the Ti, Zr and Hf alkoxides

INTRODUCTIONNano- 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.

AKNOWLEDGEMENTS

This work has been supported byETF6537, ETF6660, ETF6163, SF0382149s02, Estonian Nanotechnology Competence Center and Doctoral school of material science and material technology.

THIN FILMS BY DIP-COATING AN D SPIN-COATING

Figure 1. AFM image of a) Sm3+ doped TiO2 b) undoped TiO2.

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.

Figure 5. SEM image of Sm3+ doped TiO2 powder.

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 oxygenconcentrations in ambient atmosphere

POWDERS BY RAPID HYDROLYSIS AND CONDENSATION

Figure 4. The spectra intensity change in post preparation annealing for films (B) and for powders (C)

In collaboration with A. Lukner we have observed different behavior of 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.

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.).

Figure 6. Photoluminescence of Sm3+ doped TiO2 fiber.

Figure 7. Photos of hafnia fibers

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 ~30-4 μm in diameter. Nanoscale fiber-like solid particles could also be detected.

INTRODUCTION OF SOL-GEL TECHNIQUERelatively 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.

REFERENCES

Hydrolysis, Polymerization

Precursor stadium

(viscose material)

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.

MICRO-STRUCTURED OXIDE SURFACESMicro-structured HfO2 surfaces (Fig 8.)were prepared by sol-gel molding technique [1].

[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.

50 μm

Figure 8. Micro-structured HfO2 surfaces.

+ Solvents

+ Water

Controlled gelation andhydrolysis

AlkoxidesWater, dopant