Browsing by Author "Dimov D."
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Item Directed modification of the properties of vacuum deposited polymer layers by energy-stimulated processes(2008-05-01) Dimov D.; Spassova E.; Georgiev A.; Karamancheva I.; Assa J.; Danev G.Vacuum deposited thin layers were investigated for obtaining nanocomposite films based on a polyimide matrix and copper phthalocyanine particles as ``guests``. The paper presents a study related to energy-stimulated processes using microwave treatment as an alternative to the classical thermal processing. FTIR spectroscopy investigations demonstrated the possibility for a considerable shortening of the entire treatment process. The best results were obtained by combining the thermal and microwave treatments (15 min microwave + 15 min thermal treatment). © 2008 IOP Publishing Ltd.Item Effect of InP/ZnS quantum dots aggregation on the kinetics of birefringence recorded in thin azopolymer composite films(2024-09-01) Stoilova A.; Dimov D.; Trifonova Y.; Mateev G.; Lilova V.; Nazarova D.; Nedelchev L.The article describes the preparation of new thin film composite materials based on the azopolymer (poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt]) doped with three different concentration of InP/ZnS quantum dots with size of 7.5 nm. Clusters of aggregated InP/ZnS were microscopically observed in the fabricated composite samples. Birefringence (Δn) was induced in the films at two different wavelengths of the pump laser (355 nm and 444 nm) and the obtained higher values of Δnmax for the samples doped with quantum dots up to 2 wt% in comparison to the non-doped film and the sample with the highest nanocrystals concentration are discussed, based on the measured fluorescence spectra, in terms of possible local energy transfer between the azobenzene chromophores and the InP/ZnS quantum dots.Item Ion - Beam assisted process in the physical deposition of organic thin layers(2010-01-01) Dimov D.; Georgiev A.; Spassova E.; Assa J.; Danev G.A novel method was developed for physical deposition of thin polyimide layers by applying an argon plasma assisted process. The influence was investigated of the plasma on the combined molecular flux of the two thermally evaporated precursors - oxydianiline and pyromellitic dianhydride. The effects observed on the properties of the deposited films are explained with the increased energy of the precursor molecules resulting from the ion-molecular collisions. As could be expected, molecules with higher energy possess higher mobility and thus determine the modification of the films structure and their electrical properties. © 2010 IOP Publishing Ltd.Item OPTICAL PROPERTIES OF ELECTROSPRAY DEPOSITED PAZO POLYMER FILMS DOPED WITH GeTe4-Cu CHALCOGENIDE PARTICLES(2022-01-01) Stoilova A.; Lilova V.; Ivanova V.; Trifonova Y.; Dimov D.Composite films based on the azopolymer poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] doped with GeTe4-Cu chalcogenide particles have been prepared through electrospray deposition. Polarization microscopy was applied to study the films morphology. The transmittance coefficient (T), the reflectance coefficient (R), the refractive index (n), the extinction coefficient (k), the optical absorption coefficient (α) and the optical band gap (Formula presented) of the composite films and of the pure azo polymer film were determined. A significant change in the optical properties of the composite films in comparison to the non-doped azo polymer film has been observed.Item Physical deposition of thin polyimide layers by applying an argon plasma assisted process(2010-01-01) Dimov D.; Georgiev A.; Spassova E.; Assa J.; Dineff P.; Danev G.A novel method for physical deposition of thin polyimide layers by applying an argon plasma assisted process has been developed. The influence of the plasma on the combined molecular flux of the two thermally evaporated precursors - 4,4'- oxydianiline and pyromellitic dianhydride was investigated. The process parameters were changed in the limlts 0,4 - 2 A for the anode current and 80 - 170 V for the anode voltage. Their influence was studied using FTIR spectroscopy and electron microscopy techniques. It was proposed that the plasma flux crossing the molecular flows of the polyimide precursors enhances the imidization process by partly activating the precursor molecules in the gas phase. © 2010 IOP Publishing Ltd.Item Tautomeric influence on the photoinduced birefringence of 4-substituted phthalimide 2-hydroxy Schiff bases in PMMA matrix(2021-05-01) Blagoeva B.; Stoilova A.; Dimov D.; Yordanov D.; Nazarova D.; Georgiev A.; Antonov L.The photoinduced birefringence of two 4-substituted phthalimide 2-hydroxy Schiff bases, containing salicylic (4) and 2-hydroxy-1-naphthyl (5) moieties has been investigated in PMMA matrix. Their optical behaviour as nanocomposite films was revealed by combined use of DFT quantum chemical calculations (in ground and excited state) and experimental optical spectroscopy (UV–Vis and fluorescence). The results have shown that solid-state reversible switching takes place by enol/keto tautomerization and Z/E isomerization. Birefringence study was performed in the PMMA nanocomposite films using pump lasers at λrec = 355 nm and λrec = 442 nm. Fast response time and high stability of anisotropy up to 58% for (4) and 95% for (5) after turning off the excitation laser, was observed, which makes these materials appropriate candidates for cutting-edge optical information technology materials. The possibility for multiple cycles of recording, reading and optical erasure of the photoinduced birefringence at λrec = 442 nm in 5 has been demonstrated. The obtained results have shown that the maximum value of the measured birefringence is close to the anisotropic characteristics of the most frequently used azo materials.Item Thin dye layers - Vacuum deposition and structure(2012-01-01) Dimov D.; Assa J.; Georgiev A.; Kazakov R.; Karashanova D.; Danev G.; Spassova E.Vacuum-deposited layers of zinc phthalocyanine and perylene-3,4,9,10- tetracarboxylic dianhydride were obtained with regard to the development of converters of solar radiation into electricity, namely, organic solar cells. It was shown that there were no differences in the composition of the initial dyes and the deposited ones, which is a proof of their thermal stability and a prerequisite for the reproducibility of the composition of the single and mixed layers under study. The results obtained are interpreted in view of the possible applicability of the layers studied for the fabrication of organic solar cells in which the processes of creation, the lifetime and the diffusion paths of the current carriers depend significantly on the film composition and the defects formed at the time of deposition of the active dye layers. © Published under licence by IOP Publishing Ltd.