Defence of the dissertation: 2017-01-10
Defence of the dissertation: 2017-06-09
New nanostructure materials, their order colonies, layered films, synthesis and construction of heterostructures allow scientists to develop at those days new or improved properties of materials that will determine the future of scientific and technological progress. The thesis is related to prospective studies of nanostructured TiO2 layers and film composites with other semiconductor nanoparticles based on their environmental friendliness, low cost, chemical and mechanical resistance. The aim of the work was the investigate the possibilities of anodic TiO2 film nanotubes for electrochemical decoration of lower band gap semiconductor nanoparticles. The methods for uniform decoration of anatase TiO2 nanotube (Ntb) films with Cu2O nanoparticles were proposed: with weakly acidic copper acetate electrolyte and alternating current. Growth of pure Cu2O crystals in the TiO2 Ntbs was based on thermodynamic analysis of the solution. It has been discovered that TiO2 Ntb films decorated with Cu2O nanoparticles are able to absorb not only the UV light, but visible light as well. By increasing amount of Cu2O deposited in the TiO2 nanotubes, the TiO2 Ntb – Cu2O absorption edge can be moved up to 2.1 eV. The possibility of electrochemical decoration of TiO2 Ntb film with semiconducting copper selenide nanoparticles in aqueous solutions and the peculiarities of the process were investigated. The effect of hydrogen doping of the Ti/TiO2 Ntb electrode for uniform decoration of TiO2 nanotubes with semiconducting nanoparticles was used for the first time. It was determined that TiO2 Ntb – Cu2O heterostructures are characterised by significantly lower dependence on the angle of incidence of excitation beam – this can be especially useful for solar cell circuits. Investigated optical properties and light absorption features of TiO2 Ntb decorated with copper selenide (Cu3Se2 and Cu2-xSe) nanoparticles. Optimized composition of hydrothermal processing solution and conditions for decoration of TiO2 Ntb film surfaces and nanotubes with nanoleafed MoS2. The uniform formation of crystalline MoS2 on the TiO2 surface is achieved with low concentration ammonium heptamolybdate and urea solutions within the temperature of 220 to 225 °C. It was determined that Ti/TiO2 Ntb – MoS2 electrodes catalyse hydrogen release from acidic solutions and the reaction is characterized by stability.
Processes supplying organic matter and hazardous substances to seawater are especially intensive in coastal areas and semi-enclosed seas. An understanding of the characteristics, nature of the organic matter, its cycling, distribution of pollutants and the major controlling factors in the coastal ecosystems can provide interesting insights into the occurrence of natural and anthropogenic processes in the lagoon and its drainage basin. The main task of this work was to assess the distribution pattern of organic matter and metals and to evaluate an extent of contamination of the south-eastern Baltic Sea. In this work, the stable carbon and nitrogen isotopes ratios were used in order to evaluate sources and composition of organic matter as well as the seasonal and temporal variability of organic matter. The distribution pattern of metals (Pb, Cu, Cd, Ni, Cr, Zn) in sediments of the SE Baltic Sea and the most polluted sites were evaluated by applying different geochemical indices (EF, Igeo, CF, Cd, Eir, RI). During this study, the metal (Cd, Cu, Pb and Zn) concentrations in biota tissue were assessed and the accumulation capacity of each element by mussels Macoma balthica and Dreissena polymorpha was evaluated.
Pulsed Terahertz radiation emission from the surfaces of semiconductors is typically achieved when Ti:Sapphire (λ = 800 nm) femtosecond laser pulses are impinging them at an incline angle, and the generated Terahertz pulse is registered in reflection geometry with a photoconductive antenna comprising of a short carrier lifetime material. Further improvements in terms of compactness and cost-effectiveness of these Terahertz Time-Domain Spectroscopy (THz-TDS) systems would require telecommunication wavelength, λ = 1.55 µm (0.8 eV), fiber-based femtosecond lasers activating the generating and registering semiconducting Terahertz components. The narrow-gap A3B5 semiconductors (Arsenides and Antimonides) are great candidates as surface THz emitters, since the photoexcited electrons with 0.8 eV quanta in these materials can have high excess kinetic energies and, thus, high initial velocities. In addition, their narrow forbidden energy gap induces the anisotropy of a conduction band, due to its strong interaction with a valence band. Photoconduction, consequentially, becomes anisotropic in the A3B5 narrow-gap semiconductors that are sliced along low crystallographic symmetry planes. The lateral photocurrent components provide another advantage, namely, the capability of implementing the line-of-sight optical geometry, greatly convenient for a fiber-laser-based THz-TDS system. Alternative solution enhancing the lateral photocurrent components is the external magnetic field that has a strong influence on the low effective mass electrons. Finally, a GaInAsBi-based photoconductive antenna operating as a THz detector at λ = 1.55 µm is demonstrated.