Stage 2 - P2
Phase no. 7
Responsible: Dr. Adrian PETRIS
Title: "The study of the linear refractive and absorptive optical constants dependence on wavelength and thickness of thin layers for applications in photonics"
Abstract: We have determined the dependence on wavelength of the linear refractive index (Sellmeier equation) and of the absorption coefficient of ZnSe thin layers as function of their sub-wavelength thickness by using the results of the transmittance measurements only. The influence of the optical constants of the substrate on computing the optical constants of thin layers is carefully considered. The method used in this report, based on Swanepoel formalism, can be used for the measurement of the optical constants of any thin layer in its transparency range. The chalcogenide semiconductor ZnSe is a material important for photonics due to its large transparency spectrum (visible, near and mid-infrared) and high refractive index. The linear optical constants of ZnSe and their dependence on wavelength (in visible and near infrared spectral regions) and thickness will be used in the study of the nonlinear optical response of the considered thin structures.
Phase no. 8
Responsible: Dr. Valentin CRACIUN, Dr. Lucica BOROICA
Title: "Design, modeling, obtaining and characterization of nanostructured thin film from doped boro-phosphate vitreous and ceramic materials by MS"
Abstract: The study made in this phase involved research and design of vitreous and ceramic oxide compositions comprising as network formers phosphorus oxide, P2O5 and boron oxide, B2O3. They were using various oxides as fondants and stabilizers and doping oxides of d or f elements that induce optical, optoelectronic and magneto-optical properties.
At this stage was realized a study to design and modeling of vitreous boro-phosphate nano-structures. They were selected and processed by high-temperature melting, at 1250-1300 °C, 3 oxide compositions. Homogenised melts were poured into graphite molds, and the obtained glasses were undergoing a specific annealing treatment for 2 hours at 450-500 °C.
The samples were morphologically and structurally characterized and were used as targets and substrates for the deposition of thin films by radiofrequency plasma sputtering process (magnetron sputtering, MS). The films were characterized by atomic force microscopy, AFM.
Bulk samples were obtained by the unconventional method, comprising the wet obtaining of the raw materials, which was then melted in a furnace with superkantal – MoSi2 elements in alumina crucibles at a temperature of 1250-1300 °C for 2-4 hours. An alumina stirrer was used to stir the melt at speed of 100-300 rev/min.
Vitreous boro-phosphate bulk materials were used as targets for obtaining thin films on various substrates. A RF magnetron sputtering apparatus assisted by an ion cannon was used: technological installation type ER VARIAN 3119, designed and adapted by Elettorava SpA-Italy and INFLPR -Romania. Projected deposition parameters are: constant quartz = 8.25; BP2 target density = 2.752 g / cm3; argon pressure = 6,5x10-4 torr; active power = 136 W; reactive power = 0 W; intensity = 0.2 A; boro- silicate glass, quartz glass or silicon substrate. For the boro-silicate glass substrate, it was realised a deposition rate of 0.7-1.1 Ǻ / s and a film thickness of 10220 Ǻ for a 2h 46 min long deposition. AFM analysis of thin films deposited on borosilicate and quartz glass revealed a very low surface roughness, the highest quality being for the deposition on quartz glass.
The research results were presented at the International Conference "Condensed Matter and Materials Science 8th Physics - MSCMP", 12 to 16 September 2016, Chisinau, Moldova Republic, in the works: 1. "Boron phosphate sol-gel thin-films doped with dysprosium and ions therbium" ; 2. "Fracture toughness and hardness at micro- and nanoindentation of phosphate glasses depending on their composition"; 3. "Prolonged cyclic loading and holding indentation of aluminophosphate glass: kinetics of deformation". And at the International Conference "Society of Glass Technology Centenary Conference & European Society of Glass Science and Technology 2016 Conference, Glass - Back to the Future ", Sheffield, UK, 4-8 September 2016, in the works: 4." Spin coating sol-gel depositions from rare-earth doped boron-phosphate systems " and 5. "Structural, magnetic and morphological properties of Ce3+ and Tb3+ - doped phosphate silicate sol-gel thin film.
Phase no. 9
Responsible: Dr. Ionut JEPU
Title: "Thin film Mn containing magnetic structures study, obtained by TVA, for various operating temperatures"
Abstract: Two magnetic structures were proposed for this study, containing Fe and Co as ferromagnetic materials and Mn and Cu respectively for the non-magnetic interlayers, separating the magnetic layers. Both of these structures were obtained using thermionic vacuum arc technology (TVA) and it was proposed a comparison study from the magnetic sensitivity point of view, for different operating temperatures, the main aim being to find an optimum coating capable of considerable variation of its electric resistance at different values of the magnetic field. The comparison study consisted also in the morphological and structural differences between the two studied structures and their electric resistance variation in a constant magnetic field. The operating temperatures chosen for this study were room temperature and ~65 °C in order to simulate the functioning environment of the magnetic sensors devices which which are based on these type of structures.
For the coating procedure, TVA method was used using three independent anode-cathode systems and a high vacuum chamber. The magnetic elements (Fe and Co) were coated by metallic plasma generation (TVA) while the non-magnetic ones (Mn and Cu) which are easily ignited were coated by slow thermal evaporation. Both thin films were multilayer based, having in their component 16 individual layers, the total thickness being of 160 nm.
Following the morphological analysis, differences were observed between the two structures as follows: the Cu based one was a granular type while the Mn based was more smooth and compact. Compositional analysis highlighted the ferromagnetic concentration majority for the Mn based multilayer, with ~37.5 at% iron and ~39 at% of cobalt. This majority in the ferromagnetic material has its main effect in the way the electric resistance for this Mn-based structure is sensitive to low variation of the magnetic field. For the Cu-based structure, it was observed a non-magnetic majority, of 54 at%, while the magnetic material portion was 23.8 at % cobalt and 22 at% iron. The depth profile analysis showed the efficiency of the coating technique and highlighted the optimization of the coating parameters in order to obtain the desired structures. The non-invasive magnetic measurements, performed by MOKE showed for both structures their sensitivity in low magnetic field variations. The differences between the two were based on the amount of magnetic material present in each one of them. The electric and magnetic measurements showed a strong variation of the electric resistance, namely between 28% and 31% in a constant magnetic field for both operating temperatures.
Phase no. 10
Responsible: Dr. Aurelian MARCU
Title: "Production, characterization and properties control for laser fabricated hetero-nanoparticles"
Abstract: In this faze, there were fabricated iron nanoparticles (hematite (α Fe2O3), maghemite (γ Fe2O3) şi magnetite (Fe3O4)) using two ablation techniques: laser pirolysis and laser ablation in liquids. Nanoparticles were analysed from morphological (SEM and TEM), structural (EDX, XRD and teraherts spectroscopy) and functional (zeta potential and DLS) points of view. Even if from the particle purity point of view the laser ablation gave far better results, laser pirolysis seem to produce nanoparticles with less aggregation tendencies. From the laser optimisation point of view, for reaching (and eventually overtaking) the present results of the laser pirolysis, increasing of the laser power (P > 1 W) and decreasing the laser pulse duration seem to lead to an increasing of the obtained parameters and enhance the present performances of this technique.
Phase no. 11
Responsible: Dr. Catalin TICOS
Title: "Experimental setup for studying the interaction of an electron beam with micro/nanoparticles levitated in plasma"
Abstract: During this phase an experimental set-up was designed and built for studying the interaction of electron beams with energy 10 to 15 keV with micro/nanoparticles levitated in the sheath of a radiofrequency plasma. The set-up consists of an electron source, a set of electromagnetic coils which focus the electron beam and an interaction chamber where argon plasma is produced between two plan-parallel electrodes. After plasma ignition, micro/nanoparticles are inserted in the interaction chamber with a dropper. Due to electrical charging by plasma the micro/nanoparticles stay suspended above the rf electrode. During the interaction with the electron beam a pressure difference of at least two orders of magnitude must be obtained and kept constant between the beam channel and the interaction chamber. Taking into account that the electron beam is introduced in the interaction chamber through a flange with an orifice of 0.5 mm, a dedicated vacuum system was conceived to ensure the necessary pressure conditions.
Phase no. 12
Responsible: Dr. Sorin VIZIREANU/ Dr. R. IONITA
Title: "New procedure approach for liquids treatment by plasmas generated in various configurations"
Abstract: At this stage, the aim of the experiments consisted in studying and developing experimental configurations usable for liquid treatment by plasma and to identify the favorable conditions to change them. We studied several plasma sources based on radiofrequency discharge in various experimental configurations, applied for liquid treatments. Our plasma sources that operate at atmospheric pressure (open atmosphere) can be used in contact with many liquids and some of them may work also under liquid, immersed in suspensions. These sources were tested in bacterial suspensions, chemical solution compounds, even with easily inflammable substances alcohol, acetonitrile, etc. The efficiency of these treatments for modification of liquids/suspension properties is dependent on: plasma source type, injected RF power, gases type and theirs flows, treatment time, etc. The discharges in contact with aqueous liquids generate reactive radicals (ozone, hydrogen peroxide, hydroxyl ions, charged particles, strong local electric field, UV radiation etc) that initiate reactions in the liquid phase. The temperature, pH, conductivity and absorbance of liquids are changed, but also the properties of the dispersed materials. These studies have resulted in the development of advanced plasma sources configurations operating in contact or immersed in different liquids, leading to environmentally-friendly methods for liquid modification and obtaining nanomaterials with new functionalities.
Phase no. 13
Responsible: Dr. Magda NISTOR
Title: "Study of advanced oxide materials obtained by plasma techniques for applications in energy"
Abstract: The objective of this stage was to study advanced oxide materials as thin films grown by plasma techniques, with optimal and tunable physical properties for energy applications. Thin films from advanced oxide materials were grown by pulsed electron beam deposition method (PED), which has common features with pulsed laser deposition. Amorphous and transparent semiconducting oxide thin films such as In-Ga-Zn-O were grown by PED in different deposition conditions. Thin film composition was determined by means of Rutherford backscattering spectroscopy and electrical and optical measurements were performed to characterize these films. The role of film stoichiometry on the physical properties relevant for energy applications was studied in detail as function of growth conditions, evidencing the role of cationic composition on electrical and optical properties of films.
Phase no. 14
Responsible: Dr. Emanuel AXENTE
Title: "Experimental studies devoted to processing conditions optimization in case of Silicon-Germanium thin films synthesis by C-PLD"
Abstract: During the last decade, great efforts have been focused to discover and develop new materials with improved optical, electronic and physical properties. Extraordinary progresses have been made in the synthesis of novel compounds with remarkable features. However, the conventional “step by step” investigations are time consuming and expensive due to the requirements and the complexity of the materials used for the prospective technologies. Recently, the combinatorial approach has offered a comprehensive manner to overcome this barrier. Combinatorial approach implies the rapid synthesis of a large number of different but structurally related compounds in a single-step procedure. A collection of these synthesized compounds is referred in the literature as a combinatorial library. In this project, amorphous Silicon-Germanium combinatorial thin films were deposited by Combinatorial – Pulsed Laser Deposition (C-PLD). This was achieved by simultaneous ablation of two targets (pure silicon and germanium) and the deposition on glass and Al2O3 substrates kept at room temperature. Morphological and topological profiles were determined by microscopy techniques (SEM) while the profile of composition were obtained by energy dispersive spectroscopy (EDS). Optical properties and thickness profiles of the deposited structures were characterized by spectroscopic ellipsometry. We measured the corresponding electrical properties along the longitudinal direction of the samples for different consecutive SixGe1-x (0<x<1) compositions.
Phase no. 15
Responsible: Dr. Petronela GAROI
Title: "Methods for the spectral characterisation of doped optical materials for solar cells"
Abstract: Photovoltaics research initiative in Romania is of great interest, in accordance with the fundamental research. Thus, efforts in developing non-polluting solar materials are done intensively in recent years in research centers from our country, through various deposition technologies and methods. It is well known that, thin film photovoltaic technologies are appealing because they are prone to high levels of automated production. Our team investigated the behavior of TCO and chalcogenide thin films in achieving solar cells. Addressing this research topic on the spectral characterization of TCO materials for solar cells is justified in Romania, especially by choosing a suitable TCO. Following some preliminary tests, transparent oxide thin films (doped active materials for solar cells) were obtained by radio frequency magnetron sputtering method (rfMS). In this study, we reported a comparative analysis of In2O3:SnO2 oxide thin films (an ideal contact electrode for the achievement of solar cells) deposited by rfMS, having different thicknesses, in order to follow the changes in structural and optical performance of these oxide films. Details on obtaining and characterization of transparent oxide films were given in this report. The structure and morphology of deposited films were studied by XRD and AFM measurements. Uniform and polycrystalline films were obtained, with roughness values less than 10 nm. The forbidden bandwidth of the deposited films was estimated from the optical transmission spectra. The Swanepoel and Drude methods were used to investigate and determine the optical properties. They showed the oxide thin films exhibit good results with increasing thickness of the deposited film.