StatusThe thesis was presented on the 17 February, 2016
Approved by NCAA on the 21 April, 2016
Abstract– 1.39 Mb / in romanian
ThesisCZU [539.216:535.3 + 621.315.59](043)
3.85 Mb /
The thesis consistsof Introduction, four Chapters, General conclusions and recommendations. The List of References contains 211 items. The thesis includes 169 pages, 103 figures, 20 tables and 49 formulas. The obtained results are published in 39 scientific papers and reports.
Research field: nanotechnologies and new functional nanomaterials.
The purpose of the thesis: The purpose of the thesis is the elaboration of technological procedure for processing GaSe and CdSe semiconductor lamellar nanocomposites with relevant morphological, optical and photoelectrical properties, highlighting the prospects of their use in optoelectronic and photoelectric devices operating in ultraviolet, visible and near-IR spectral ranges.
The objectives of the thesis: The growth of undoped and Cd-doped GaSe single crystals using the Bridgman technique and manufacture of plane-parallel single crystal plates with smooth surfaces at the atomic level. Establishment of processing method for composite manufacturing from ε-GaSe and CdSe crystallites with micro- and nanometer dimensions. Determination of optimum technological conditions for manufacturing ε-GaSe and CdSe crystalline composites with hexagonal (wurtzite) and cubic (sphalerite) syngonies. The study of optical, photoelectrical and luminescent properties of CdSe and GaSe composites obtained by intercalation of ε-GaSe single crystals and Cd from vapour phase and CdCl2 aqueous solution. Establishment of correlation between the both polymorphic form and dimensions of GaSe and CdSe crystallites and processing method of composite manufacturing.
Novelty and scientific originality: Technological conditions for manufacturing GaSe and CdSe nanocrystalline composites with the morphology and geometrical dimensions varied by temperature, duration of thermal treatment and pressure of Cd vapours have been elaborated. Crystallographic structures of the composite components, as well as average dimensions of the crystallites were determined. Elemental composition of the crystallites was found. It was demonstrated that thermal intercalation of Cd atoms from vapour phase and aqueous solutions between layered packaging of ε-GaSe crystals forms the nucleation centres for micro- and nanocrystalline GaSe and CdSe composites with hexagonal and cubic syngonies, which were investigated by XRD, FTIR and Raman spectroscopy, as well as from single- and multiphonon vibration spectra of crystal lattice and non-controllable impurities in CdSe-GaSe composite with and without native oxygen.
Anti-Stokes photoluminescence stipulated by nanometric dimensions of composite crystallites was observed. The energy of recombination levels responsible for radiative processes in CdSe-GaSe composite obtained by thermal treatment of GaSe single crystals in Cd vapours and from CdCl2 aqueous solution was found.
The solved scientific problem: Using thermal treatment in Cd vapours, as well as CdCl2 aqueous solutions, the lamellar nanostructures from GaSe layered semiconductors and CdSe-GaSe composite with and without native oxygen are manufactured. These nanostructures have advanced anisotropic physical properties that stipulate a large area for optoelectronic applications of the materials.
Theoretical and practical significance of the thesis: The methods for variation of the morphology of crystallographic structure geometric parameters and the mechanisms of radiative recombination for GaSe lamellar single crystals-based composites are identified. The technological procedure for manufacturing the ordered lamellar structures composed of GaSe and CdSe nanocrystalline lamellas with relevant luminescent properties in the green – red spectral range is proposed. The energy of active phonons in Raman and FTIR spectra of GaSe-CdSe composite crystallites are determined. The technological procedure for manufacturing the GaSe-CdSe structures, which are photosensitive in the violet – near-IR spectral range and may have application in solar energy conversion, is proposed. The density of the surface states is found and the mechanisms of the formation of GaSe-type lamellar semiconductor composites are argued.