Tanel Tätte

Preparation of smooth siloxane surfaces for AFM visualization of immobilized biomolecules

Development of scanning probe microscopy (SPM) techniques during past decade has made possible to study bioprocesses at a molecular level. Common protocols for immobilization of biomolecules for SPM studies are based on their adsorption to alkylsiloxane monolayers on hydroxylated surfaces. The same procedure is also widely used for DNA chip and biosensor fabrication. For SPM studies of immobilized biomolecules smooth carrier surfaces are mandatory. Several studies refer to the lack of reproducibility in formation of smooth silanized surfaces. In this work a new method based on carrier treatment with linearly polymerized 3-aminopropyltrimethoxysilane for preparation of reproducibly smooth silanized surfaces is proposed.

Influence of ambient gas on the photoluminescence of sol-gel derived TiO2:Sm3+ films

Photoluminescence (PL) of TiO2:Sm3+ thin films was studied at RT. The films were prepared by the sol-gel spin-coating technique or by atomic layer deposition (ALD) followed by ion implantation. The PL was excited with a Nd:YAG pulse laser emitting at 355 nm. The spectrum of PL consists of intense Sm3+-specific emission lines with a well-pronounced fine structure. The influence of different gaseous environments (air, oxygen, nitrogen) or vacuum on the Sm3+ emission was investigated. In the case of a permanent irradiation of sol-gel films in an oxygen-containing environment, the PL intensity increased. The increase was significantly large but slow. The subsequent evacuation of the measurement chamber led to a rapid decrease of the emission below the detection limit. When the oxygen-containing gas was without any intermediate evacuation replaced by nitrogen, the PL intensity descended to an almost vacuum level. The subsequent exposure to oxygen led to a rather fast emission recovery. The ALD-prepared films exhibited a similar but markedly slower response. The fast response observed was attributed to the adsorption of oxygen on the surface, and the slower one, to the diffusion of oxygen vacancies taking place under the irradiation in the bulk.

Pinching of alkoxide jets—a route for preparing nanometre level sharp oxide fibres

The pinching phenomenon is used to shape jets of Sn(OBu)4 based viscous oligomeric melts into nanometre range sharp oxide needles. The influence of viscosity of the liquid, humidity of surrounding environment and pulling speed on formation of the needles is investigated. Optimal conditions enable reproducible preparation of needles that have tip radii down to 15–25 nm, i.e. in the range that is of considerable interest for many nanotechnological applications.

Alkoxide-based precursors for direct drawing of metal oxide micro- and nanofibres

Abstract The invention of electrospinning has solved the problem of producing micro- and nanoscaled metal oxide fibres in bulk quantities. However, until now no methods have been available for preparing a single nanofibre of a metal oxide. In this work, the direct drawing method was successfully applied to produce metal oxide (SnO2, TiO2, ZrO2, HfO2 and CeO2) fibres with a high aspect ratio (up to 10 000) and a diameter as small as 200 nm. The sol–gel processing includes consumption of precursors obtained from alkoxides by aqueous or non-aqueous polymerization. Shear thinning of the precursors enables pulling a material into a fibre. This rheological behaviour can be explained by sliding of particles owing to external forces. Transmission (propagation) of light along microscaled fibres and their excellent surface morphology suggest that metal oxide nanofibres can be directly drawn from sol precursors for use in integrated photonic systems.

Micro- and nanoscale structures by sol-gel processing

An overview of the practical output of sol-gel chemistry is demonstrated from the viewpoint of its contribution to the design of 1D and 2D materials. Different structures like thin films, fibres, needles, microtubes, -patterns and -rolls are discussed. In most cases, the advantages of sol-gel processing feasibility and cost-effectiveness are clearly evident. Accompanied by flexibility of production and good quality of the formed structures, the method offers interesting possibilities for practical applications such as sensors, opto-electronic devices, scintillators, etc.

Emission of Rare Earth Ions Incorporated into Metal Oxide Thin Films and Fibres

Photoluminescence (PL) of undoped and Sm-doped TiO 2 , ZrO 2 and HfO 2 thin films and fibers was investigated at temperatures ranging from 6 to 300 K. The thin films were grown by the atomic layer deposition (ALD) technique and doped by using the ion implantation method. The fibers were prepared by using the sol-gel method whereas an in-situ doping was used to obtain the required concentration of Sm 3+ ions in the films. In undoped as well as doped materials, PL was efficiently excited via band-to-band transitions. The emission of undoped materials was attributed to the radiative recombination of self-trapped excitons (STE). In doped materials, intense emission of Sm 3+ was recorded. It is proposed, that there exists a concurrence between the radiative recombination of bound excitonic states and the energy transfer to Sm 3+ ions, particularly at lower temperatures.

Yttria stabilized zirconia microtubes for microfluidics under extreme conditions

While the popularity of the usage of room temperature microfluidic systems is booming in different technologies such as bio-technology, micro-scale chemistry, micro-printing and many others, systems applicable under high temperature and pressure are still remarkably under-developed. The main drawback of the existing systems is the inadequate quality of the available construction materials. In this work, extrusion of metal-oxo-alkoxide sol–gel precursors through the nozzle is utilized to produce the liquid thread that is allowed to self-transform into ceramic microtubes by a chemical curing process. The focus is on YSZ (8% Y2O3 stabilized ZrO2), which exhibits a stable 100% tetragonal phase nanocrystalline structure up to 1000 °C. These tubes have excellent mechanical characteristics and can withstand 1000 atm pressure inside the tubes. Owing to these and other physical, chemical and mechanical properties, there are many potential applications for these tubes, one example being that the high optical quality of the YSZ tubes could be useful for guiding of light. Ionic conductivity with no electronic component makes these tubes suitable for ionic membrane applications like solid oxide fuel cells (SOFCs) or corresponding gas sensors. Finally, we demonstrate a single-tube-based miniature plasma jet device potentially applicable as an ion source for local surface treatment or possibly as a micro plasma propulsion device for space applications.

Study of the curing mechanism of metal alkoxide liquid threads for the synthesis of metal oxide fibers or microtubes

Curing processes enabling transformation of liquid threads into solid material have gained technological importance. Our study is focusing on the comparison of curing mechanisms for metal alkoxide-derived liquid threads. We studied the mechanisms of the formation of fine metal oxide fibers or hollow microtubes by comparing the solidification of propoxide and butoxide precursors.

Structure and Rheological Behavior of Alkoxide-Based Precursors for Drawing of Metal Oxide Micro- and Nanofibres

The aim of this study is investigation of the influence of the method of metal alkoxy precursors preparation on their rheological characteristics and spinability for metal oxide fibre drawing. The precursor samples were obtained from tin 1-butoxide Sn(OBu)4 as a result of aqueous (AQ) and non-aqueous (NAQ) (thermolysis) treatment. Small angle X-ray scattering (SAXS) data of precursors in the range of scattering vector modulus 0.07–5.3 nm-1 were recorded on a slit collimation camera KRM-1 by using Cu Kα radiation and NaI:Tl scintillation detector. Program system ATSAS [1] was used for calculation of the radius of gyration Rg and for 3D modeling of the cluster shape. The rheological characterization of samples was conducted with a help of a rotational rheometer Mars II (Haake, Karlsruhe, Germany) equipped with plate-and-plate test geometry (plate diameter 20 mm). The precursors studied in this work consist of the elongated particles of 3 – 5 nm in length and 2 nm in diameter for both AQ and NAQ prepared precursors. Rheological tests have proved that the solvent free precursors are typical non-Newtonian fluids. Precursors obtained with the help of NAQ treatment are more elastic as compared to those prepared with AQ procedure. Surface tension (ST) measurements show that the coefficient of ST of NAQ prepared precursor is 45% lower than that of AQ prepared one. Fibres with aspect ratio up to 10000 and diameter of 200 nm were directly drawn from the NAQ precursors at room temperature in standard lab atmosphere. AQ prepared precursor allows obtaining of the fibers of minimum 500 nm in diameter with maximal aspect ratio 1000.

Preparation and Characterization of CNT/TiO2 Based Transparent Fiber Electrodes

In the present work, it is shown that carbon nanotube-doped transition metal oxides are potential candidates for use as ceramic transparent electrode materials. Electrodes in shape of fibers are obtained via inexpensive and low temperature sol-gel method. Fiber electrodes are characterised by SEM-FIB and rheological analizes. Due to extraordinary electrical and optical properties of CNT-s and good chemical and physical stability of metal oxide ceramics, resulting composites could be an interesting subject for industry.