Edmunds Tamanis

Obtaining of nanostructured ZnO coatings using mechanoactivated oxidation

The concept to use nanostructured state of metal at the instant of destruction in air environment was used to obtain nanostructured Zn-ZnO coatings on glass and quartz by mechanical method. Subsequent annealing in the ambient atmosphere, annealing in vacuum and irradiation with 532-nm YAG:Nd laser were used to obtain completely oxidized, transparent ZnO coatings. The saturated with oxygen nanostructured coatings were transformed into nanostructured ZnO coatings after annealing above 773K or irradiation with laser (allowing to reach 673K) in ambient atmosphere. AFM and SEM images show that after annealing ZnO coatings have multi-shaped structure. The formation of ZnO need-like whiskers (d = 100nm, l = 2?m) was observed after laser irradiation. Obtained ZnO coatings have high microhardness (10--12GPa), strong adhesion with substrates and show green and blue luminescence at room temperature. The oxidation process is mechanoactivated due to the facilitated oxygen diffusion along deformation defects: vacancies, dislocation, microcracks, and developed network of grain boundaries.

Plant Explants Grown on Medium Supplemented with Fe3O4 Nanoparticles Have a Significant Increase in Embryogenesis

Development of nanotechnology leads to the increasing release of nanoparticles in the environment that results in accumulation of different NPs in living organisms including plants. This can lead to serious changes in plant cultures which leads to genotoxicity. The aims of the present study were to detect if iron oxide NPs pass through the flax cell wall, to compare callus morphology, and to estimate the genotoxicity in Linum usitatissimum L. callus cultures induced by different concentrations of Fe3O4 nanoparticles. Two parallel experiments were performed: experiment A, where flax explants were grown on medium supplemented with 0.5 mg/l, 1 mg/l, and 1.5 mg/l Fe3O4 NPs for callus culture obtaining, and experiment B, where calluses obtained from basal MS medium were transported into medium supplemented with concentrations of NPs identical to experiment A. Obtained results demonstrate similarly in both experiments that 25 nm Fe3O4 NPs pass into callus cells and induce low toxicity level in the callus cultures. Nevertheless, calluses from experiment A showed 100% embryogenesis in comparison with experiment B where 100% rhizogenesis was noticed. It could be associated with different stress levels and adaptation time for explants and calluses that were transported into medium with Fe3O4 NPs supplementation.

Research of Laser Cladding of the Powder Materials for Die Repair

The study of laser cladding of powder materials (H13, A11 and M2) onto the tool steel 41Cr4 and C80U was conducted with the aim to establish the influence of overlap ratio, scanning speed and powder feed rate as well as appliance of post-heat treatment on the coating quality and mechanical properties. The highest hardness was achieved for A11 and M2 cladding materials, lowest coefficient of friction – for H13 and M2 coatings. It could be recommended to apply the laser cladding at larger percentage of overlap (50%).

Controlled growth of well-aligned ZnO nanorod arrays by hydrothermal method

The application prospect of zinc oxide (ZnO) nanostructures largely relies on the ability to grow nanoobjects with necessary geometry. In this study well-aligned ZnO nanorod arrays with a high density and uniformity were successfully synthesized on the glass substrates by a hydrothermal method at low-temperature. The aqueous solutions of zinc nitrate hexahydrate and hexamethylenetetramine was used. The effect of seed layer (obtained by electrochemical method and by vacuum deposition method) on the alignment of ZnO nanorods has been investigated. The morphological properties of the ZnO nanorods were also examined in accordance with varying the magnetron sputtering angle for ZnO seeds deposition. It is also shown that the electric field can control the direction of the growth of ZnO nanorods. Morphological, structural and compositional characterizations of obtained films were carried out by scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction analysis methods.

The 'hidden image' effect in security holograms and its personalization by laser demetallization

The given work investigates principles of recording, calculation, and security aspects of ‘hidden image’ effect in digital holograms that are intended for security applications. Dot-matrix and image-matrix technologies of optical recording can be widely used for recording protective holograms with such type of security features. When a collimated laser beam falls on and then is reflected from the section of holograms, containing a protective ‘hidden image’ element, a graphic image can be seen in the projection of diffracted light on the frosted screen. The present work also discusses a method of personalizing the ‘hidden image’ effect with the help of laser demetallization. In this way the hidden image can be individualized for each hologram sticker and contain additional information such as a number, text or logotype. The attractiveness of this method is in the possibility of achieving a considerable increase of the protective characteristic of holograms and incorporating additional variable information in them, as well as in providing both visual and automatic ways of checking authenticity of a hologram.

Second harmonic generation in selenium-metal structures

The article examines the processes of second harmonic generation (SHG) when selenium-metal (Cu) film structures are illuminated by femtosecond radiation (180 fs, 80 MHz) at wavelength 800 - 1000 nm. Selenium-copper structures were obtained by successive thermal evaporation of selenium and copper onto the glass substrate in vacuum. Microanalysis of the film composition was performed to determine amount of copper in thin films. The as-evaporated selenium-copper structures were crystallised by annealing in inert atmosphere at temperature 85°C. Just evaporated as well as annealed thin films were explored. The experiment was performed by confocal microscope [1] where the femtosecond radiation from laser was injected. A photosensitivity of structures in question was then determined as functions of intensity and wavelength of the incident radiation [2]. Second harmonic intensity dependence on thickness of Cu layer was also observed. We found out that adding small amount of Cu increases reflected SH intensity.

Thermo-optical investigations of sodium-bismuth titanate single crystal

The objective of the present work is to investigate the thermo-optical (TO) properties of the relaxor-type ferroelectric sodium-bismuth titanate (SBT) single crystals as a function of temperature, using the thermal lens and optical second harmonic generation (SHG) techniques with the emphasis on the TO response near the phase transitions (PT). Symmetry-forbidden SHG signals above 538 K in the [00l] cut SBT crystal are detected. The signals are related to the coexistence of the tetragonal and rhombohedral phases. Heating of the uniaxial strain poled SBT crystal revealed remarkable changes of the TO signal near the successive PT.

Direct laser writing of conductive patterns in advanced ceramic materials

Investigations on the laser-induced reduction of advanced ceramic materials, including high-temperature supercondcutive (HTSC) ceramics, are presented. Here the oxygen content of the material is locally decreased by CW YAG:Nd laser irradiation in H2 atmosphere. Direct laser-written metallic stripes into the weakly conducting sample surface had been tested by standard 4-point-probe technique in He dewar. New data about resistance temperature dependences of 100% laser reduce dstripes of HTSC Y-Ba-Cu-O ceramics has been determined. Our experimental data are in good agreement with Matthiasens law with respect ot laser-written electrodes as YCu3 alloys. As for high resistive stripes in HTSC ceramics begin written into the surface under imcomplete reduction regime we have found similar resistance behavior to random network of Cu fine particles connected 2D through thin oxide barriers. In the case of Bi-based HTSC ceramics a controversial picture takes place - low melting temperature of Bi oxide gives rise to segregation of Bi microspheres along the stripes corresponding to incomplete electroding. Although the laser-assisted surface alloying and metallization of bioceramics has been performed.