Estonian Nanotechnology Competence Center

Tartu, Estonia

Estonian Nanotechnology Competence Center

Tartu, Estonia
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Vlassov S.,University of Tartu | Polyakov B.,University of Tartu | Polyakov B.,University of Latvia | Dorogin L.M.,University of Tartu | And 7 more authors.
Solid State Communications | Year: 2011

The forces needed to overcome static friction and move 150 nm diameter Au nanoparticles on an oxidized Si substrate were measured in Normal and Shear oscillation modes inside a scanning electron microscope (SEM) in real time. The experimental setup consisted of a quartz tuning fork (QTF) mounted onto a high-precision 3D nanomanipulator used with a glued silicon or tungsten tip as a force sensor. Static friction was found to range from tens of nN to several hundred nN. Large variations in static friction values were related to differences in particle shape. Kinetic friction tended to be close to the detection limit and in most cases did not exceed several nN. The influence of thermal treatment in reducing the static friction of nanoparticles was considered. © 2011 Elsevier Ltd. All rights reserved.

Tonurist K.,University of Tartu | Thomberg T.,University of Tartu | Janes A.,University of Tartu | Kink I.,Estonian Nanotechnology Competence Center | Lust E.,University of Tartu
Electrochemistry Communications | Year: 2012

Influence of the separator material characteristics on the performance of electrical double layer capacitors (EDLCs), based on the two identical ideally polarizable microporous titanium carbide-derived carbon electrodes in room temperature ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate), has been tested by cyclic voltammetry, constant power and electrochemical impedance spectroscopy methods. Self-made separator materials have been prepared from poly(vinylidene fluoride) solutions in N,N-dimethylacetamide or N,N-dimethylformamide and acetone mixture (8:2 mass ratio) by using the electrospinning method. Noticeable influence of the separator porosity and chemical composition on the limits of ideal polarizability, specific capacitance, equivalent series resistance, phase angle, specific energy and power of the EDLCs has been obtained and discussed. © 2012 Elsevier B.V.

Polyakov B.,University of Tartu | Polyakov B.,University of Latvia | Dorogin L.M.,University of Tartu | Vlassov S.,University of Tartu | And 5 more authors.
Micron | Year: 2012

A novel method for in situ measurement of the static and kinetic friction is developed and demonstrated for zinc oxide nanowires (NWs) on oxidised silicon wafers. The experiments are performed inside a scanning electron microscope (SEM) equipped with a nanomanipulator with an atomic force microscope tip as a probe. NWs are pushed by the tip from one end until complete displacement is achieved, while NW bending is monitored by the SEM. The elastic bending profile of a NW during the manipulation process is used to calculate the static and kinetic friction forces. © 2012 Elsevier Ltd.

Vlassov S.,University of Latvia | Polyakov B.,University of Latvia | Dorogin L.M.,University of Tartu | Dorogin L.M.,Estonian Nanotechnology Competence Center | And 10 more authors.
Nano Letters | Year: 2014

The combination of two different materials in a single composite core-shell heterostructure can lead to improved or even completely novel properties. In this work we demonstrate the enhancement of the mechanical properties of silver (Ag) nanowires (NW) achieved by coating them with a silica (SiO2) shell. In situ scanning electron microscope (SEM) nanomechanical tests of Ag-SiO2 core-shell nanowires reveal an improved fracture resistance and an electron-beam induced shape restoration effect. In addition, control experiments are conducted separately on uncoated Ag NWs and on empty SiO2 shells in order to gain deeper insight into the peculiar properties of Ag-SiO2. Test conditions are simulated using finite-element methods; possible mechanisms responsible for the shape restoration and the enhanced fracture resistance are discussed. © 2014 American Chemical Society.

Sutka A.,Riga Technical University | Parna R.,University of Tartu | Mezinskis G.,Riga Technical University | Kisand V.,University of Tartu | Kisand V.,Estonian Nanotechnology Competence Center
Sensors and Actuators, B: Chemical | Year: 2014

Pure and cobalt-ion-containing nickel ferrite samples Ni 1-xCoxFe2O4 (x = 0, x = 0.01, x = 0.05 and x = 0.1) were prepared by using the sol-gel auto-combustion method. To form the desired structure after the auto-combustion process, the samples were annealed in air at 800 C for 1 h, followed by slow cooling in air (2.5 C/min) or rapid cooling by quenching in water. The influences of cobalt ion addition and the cooling rate on the electronic structure, morphology and electrical properties of Ni-Co ferrite were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The gas-sensing properties of pure and cobalt-ion-containing nickel ferrites were studied by using acetone as a test gas. The gas-response of nickel ferrite samples was strongly influenced by the cooling rate and cobalt addition. The effect was attributed to a change in the Ni3+ concentration and a restriction of the transduction of the chemical signal into an output electrical signal. It was demonstrated that the gas response of Ni1-xCo xFe2O4 tends to increase with decreasing cobalt ion content and with decreasing concentration of the point defects such as cation vacancies and Ni3+ ions. © 2013 Elsevier B.V.

Sutka A.,Riga Technical University | Sutka A.,University of Tartu | Timusk M.,University of Tartu | Timusk M.,Estonian Nanotechnology Competence Center | And 2 more authors.
International Journal of Applied Ceramic Technology | Year: 2015

We report an electrospinning approach to producing PbTiO3 polycrystalline nanofibers. The influence of the polymer concentration in the solution on the obtainable PbTiO3 nanofiber morphology was investigated. Nanofibers were characterized by high-resolution scanning electron microscopy (HR-SEM) and Raman spectroscopy. After annealing at 500°C for 3 h, the continuous structure of nanofibers remained intact. Only tetragonal PbTiO3 was identified by Raman spectroscopy. Piezoelectric behavior of PbTiO3 nanofiber mats was demonstrated by making a nanomat-based voltage generator with peak output voltage >1 V. © 2014 The American Ceramic Society.

Sutka A.,Riga Technical University | Parna R.,University of Tartu | Kleperis J.,University of Latvia | Kaambre T.,University of Tartu | And 6 more authors.
Physica Scripta | Year: 2014

Nanostructured zinc ferrites with different excess iron contents (ZnFe 2+zO4, where z = 0.00, 0.05, 0.10 and 0.15) have been synthesized using the sol-gel auto-combustion method. The effect of excess iron on the structural, optical and visible light photocatalytic activity of zinc ferrite samples has been investigated. X-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), x-ray magnetic circular dichroism (XMCD), Brunauer-Emmett-Teller theory, scanning electron microscopy (SEM), diffuse reflectance spectroscopy (UV-Vis) and photoluminescence spectroscopy were used to characterize the synthesized non-stoichiometric ZnFe2O4 powders. The XRD patterns demonstrated that the samples consist of single phase spinel structure with crystallite sizes of ∼25 nm. SEM analysis indicated that the nanosized particles grow together in porous clusters with a size of several microns. The XPS and XMCD analyses revealed that the excess iron ion substitutes Zn2+ in tetrahedral sites and in octahedral sites Fe 2+ can be found in addition to Fe3+, which could be created to restore the overall charge balance in the crystal lattice. Stoichiometric zinc ferrite (ZnFe2+zO4, z = 0.00) exhibited higher photocatalytic activity (40%) than the excess iron sample (ZnFe2+zO4, z = 0.15, i.e. 4%) under visible light irradiation for 3 h. This was explained by the formation of Fe2+ in the octahedral sites of excess iron ZnFe2O4; these species act as recombination centres. © 2014 The Royal Swedish Academy of Sciences.

Polyakov B.,University of Tartu | Polyakov B.,University of Latvia | Vlassov S.,University of Tartu | Dorogin L.M.,University of Tartu | And 4 more authors.
Surface Science | Year: 2012

The dependence of static friction on surface roughness was measured for copper oxide nanowires on silicon wafers coated with amorphous silicon. The surface roughness of the substrate was varied to different extent by the chemical etching of the substrates. For friction measurements, the nanowires (NWs) were pushed by an atomic-force microscope (AFM) tip at one end of the NW until complete displacement of the NW was achieved. The elastic bending profile of a NW during this manipulation process was used to calculate the ultimate static friction force. A strong dependence of static friction on surface roughness was demonstrated. The real contact area and interfacial shear strength were estimated using a multiple elastic asperity model, which is based on the Derjaguin-Muller-Toporov (DMT) contact mechanics. The model included vertical elastic flexure of NW rested on high asperities due to van der Waals force. © 2012 Elsevier B.V.

Estonian Nanotechnology Competence Center and University of Tartu | Date: 2010-03-25

Method of preparation of surface coating of variable transmittance and an electro-optical layered appliance including the same comprises dispersing of liquid crystal microdroplets in hydrolyzable and polymerizable precursors and applying obtained mixture on a surface by spraying. Applying the material to the surface by spraying is intrinsically related to the synthesis processes because the properties of the surrounding environment (i.e. content of water and acidity, UV radiation) and the chemical reactions that take place during spraying have considerable influence on the properties (i.e. driving voltage, thickness of obtained layer). Obtained layered appliance comprises of a matrix material with dispersed microdroplets of liquid crystal obtained by the described method, electrically conductive transparent electrodes with contacts, a dielectric material, substrate and covering layers.

Obraztsov A.N.,Moscow State University | Kopylov P.G.,Moscow State University | Loginov B.A.,Moscow Institute of Electronic Technology | Dolganov M.A.,Moscow State University | And 2 more authors.
Review of Scientific Instruments | Year: 2010

Single crystal diamond tips with perfect pyramidal geometry were obtained by a combination of chemical vapor deposition and selective oxidation of polycrystalline films. The parameters of the deposition process were chosen to provide growth of a textured film consisting of micrometer sized diamond crystallites embedded into nanodiamond ballas-like material. The heating of the film in an air environment was used for selective oxidation of the nanodiamond component. The films obtained contain free standing pyramidal single crystal diamond tips oriented by their apexes to the substrate surface. The tips were used for the fabrication of atomic force microscopy probes and their evaluation in comparison to common silicon probes. © 2010 American Institute of Physics.

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