Space and time characterization of laser-induced plasmas for applications in chemical analysis and thin film deposition

Après des décennies de développement, l'ablation laser est devenue une technique importante pour un grand nombre d'applications telles que le dépôt de couches minces, la synthèse de nanoparticules, le micro-usinage, l’analyse chimique, etc. Des études expérimentales ainsi que théoriques ont été menées pour comprendre les mécanismes physiques fondamentaux mis en jeu pendant l'ablation et pour déterminer l’effet de la longueur d'onde, de la durée d'impulsion, de la nature de gaz ambiant et du matériau de la cible. La présente thèse décrit et examine l'importance relative des mécanismes physiques qui influencent les caractéristiques des plasmas d’aluminium induits par laser. Le cadre général de cette recherche forme une étude approfondie de l'interaction entre la dynamique de la plume-plasma et l’atmosphère gazeuse dans laquelle elle se développe. Ceci a été réalisé par imagerie résolue temporellement et spatialement de la plume du plasma en termes d'intensité spectrale, de densité électronique et de température d'excitation dans différentes atmosphères de gaz inertes tel que l’Ar et l’He et réactifs tel que le N2 et ce à des pressions s’étendant de 10‾7 Torr (vide) jusqu’à 760 Torr (pression atmosphérique). Nos résultats montrent que l'intensité d'émission de plasma dépend généralement de la nature de gaz et qu’elle est fortement affectée par sa pression. En outre, pour un délai temporel donné par rapport à l'impulsion laser, la densité électronique ainsi que la température augmentent avec la pression de gaz, ce qui peut être attribué au confinement inertiel du plasma. De plus, on observe que la densité électronique est maximale à proximité de la surface de la cible où le laser est focalisé et qu’elle diminue en s’éloignant (axialement et radialement) de cette position. Malgré la variation axiale importante de la température le long du plasma, on trouve que sa variation radiale est négligeable. La densité électronique et la température ont été trouvées maximales lorsque le gaz est de l’argon et minimales pour l’hélium, tandis que les valeurs sont intermédiaires dans le cas de l’azote. Ceci tient surtout aux propriétés physiques et chimiques du gaz telles que la masse des espèces, leur énergie d'excitation et d'ionisation, la conductivité thermique et la réactivité chimique. L'expansion de la plume du plasma a été étudiée par imagerie résolue spatio-temporellement. Les résultats montrent que la nature de gaz n’affecte pas la dynamique de la plume pour des pressions inférieures à 20 Torr et pour un délai temporel inférieur à 200 ns. Cependant, pour des pressions supérieures à 20 Torr, l'effet de la nature du gaz devient important et la plume la plus courte est obtenue lorsque la masse des espèces du gaz est élevée et lorsque sa conductivité thermique est relativement faible. Ces résultats sont confirmés par la mesure de temps de vol de l’ion Al+ émettant à 281,6 nm. D’autre part, on trouve que la vitesse de propagation des ions d’aluminium est bien définie juste après l’ablation et près de la surface de la cible. Toutefois, pour un délai temporel important, les ions, en traversant la plume, se thermalisent grâce aux collisions avec les espèces du plasma et du gaz.

Plasma Polymerised Organic Thin Films-A Study on the Structural, Electrical and Nonlinear Optical Properties for Possible Applications

This proposed thesis is entitled “Plasma Polymerised Organic Thin Films: A study on the Structural, Electrical, and Nonlinear Optical Properties for Possible Applications. Polymers and polymer based materials find enormous applications in the realm of electronics and optoelectronics. They are employed as both active and passive components in making various devices. Enormous research activities are going on in this area for the last three decades or so, and many useful contributions are made quite accidentally. Conducting polymers is such a discovery, and eversince the discovery of conducting polyacetylene, a new branch of science itself has emerged in the form of synthetic metals. Conducting polymers are useful materials for many applications like polymer displays, high density data storage, polymer FETs, polymer LEDs, photo voltaic devices and electrochemical cells. With the emergence of molecular electronics and its potential in finding useful applications, organic thin films are receiving an unusual attention by scientists and engineers alike. This is evident from the vast literature pertaining to this field appearing in various journals. Recently, computer aided design of organic molecules have added further impetus to the ongoing research activities in this area. Polymers, especially, conducting polymers can be prepared both in the bulk and in the thinfilm form. However, many applications necessitate that they are grown in the thin film form either as free standing or on appropriate substrates. As far as their bulk counterparts are concerned, they can be prepared by various polymerisation techniques such as chemical routes and electrochemical means. A survey of the literature reveals that polymers like polyaniline, polypyrrole, polythiophene, have been investigated with a view to studying their structural electrical and optical properties. Among the various alternate techniques employed for the preparation of polymer thin films, the method of plasma polymerisation needs special attention in this context. The technique of plasma polymerisation is an inexpensive method and often requires very less infra structure. This method includes the employment of ac, rf, dc, microwave and pulsed sources. They produce pinhole free homogeneous films on appropriate substrates under controlled conditions. In conventional plasma polymerisation set up, the monomer is fed into an evacuated chamber and an ac/rf/dc/ w/pulsed discharge is created which enables the monomer species to dissociate, leading to the formation of polymer thin films. However, it has been found that the structure and hence the properties exhibited by plasma polymerized thin films are quite different from that of their counterparts produced by other thin film preparation techniques such as electrochemical deposition or spin coating. The properties of these thin films can be tuned only if the interrelationship between the structure and other properties are understood from a fundamental point of view. So very often, a through evaluation of the various properties is a pre-requisite for tailoring the properties of the thin films for applications. It has been found that conjugation is a necessary condition for enhancing the conductivity of polymer thin films. RF technique of plasma polymerisation is an excellent tool to induce conjugation and this modifies the electrical properties too. Both oxidative and reductive doping can be employed to modify the electrical properties of the polymer thin films for various applications. This is where organic thin films based on polymers scored over inorganic thin films, where in large area devices can be fabricated with organic semiconductors which is difficult to achieve by inorganic materials. For such applications, a variety of polymers have been synthesized such as polyaniline, polythiophene, polypyrrole etc. There are newer polymers added to this family every now and then. There are many virgin areas where plasma polymers are yet to make a foray namely low-k dielectrics or as potential nonlinear optical materials such as optical limiters. There are also many materials which are not been prepared by the method of plasma polymerisation. Some of the materials which are not been dealt with are phenyl hydrazine and tea tree oil. The advantage of employing organic extracts like tea tree oil monomers as precursors for making plasma polymers is that there can be value addition to the already existing uses and possibility exists in converting them to electronic grade materials, especially semiconductors and optically active materials for photonic applications. One of the major motivations of this study is to synthesize plasma polymer thin films based on aniline, phenyl hydrazine, pyrrole, tea tree oil and eucalyptus oil by employing both rf and ac plasma polymerisation techniques. This will be carried out with the objective of growing thin films on various substrates such as glass, quartz and indium tin oxide (ITO) coated glass. There are various properties namely structural, electrical, dielectric permittivity, nonlinear optical properties which are to be evaluated to establish the relationship with the structure and the other properties. Special emphasis will be laid in evaluating the optical parameters like refractive index (n), extinction coefficient (k), the real and imaginary components of dielectric constant and the optical transition energies of the polymer thin films from the spectroscopic ellipsometric studies. Apart from evaluating these physical constants, it is also possible to predict whether a material exhibit nonlinear optical properties by ellipsometric investigations. So further studies using open aperture z-scan technique in order to evaluate the nonlinear optical properties of a few selected samples which are potential nonlinear optical materials is another objective of the present study. It will be another endeavour to offer an appropriate explanation for the nonlinear optical properties displayed by these films. Doping of plasma polymers is found to modify both the electrical conductivity and optical properties. Iodine is found to modify the properties of the polymer thin films. However insitu iodine doping is tricky and the film often looses its stability because of the escape of iodine. An appropriate insitu technique of doping will be developed to dope iodine in to the plasma polymerized thin films. Doping of polymer thin films with iodine results in improved and modified optical and electrical properties. However it requires tools like FTIR and UV-Vis-NIR spectroscopy to elucidate the structural and optical modifications imparted to the polymer films. This will be attempted here to establish the role of iodine in the modification of the properties exhibited by the films

Electrical and Optical Properties of Znga2o4 Thin Films Deposited By Pulsed Laser Deposition

ZnGa2O4 spinel is a promising new UV transparent electronic conductor. Enhancing the electrical conductivity of this potential oxide phosphor can make it a promising transparent conducting oxide. In this paper, we have investigated the effects of processing and doping on the conductivity of semiconducting ZnGa2O4, particularly thin films. Crystalline zinc gallate thin films have been deposited on fused quartz substrates employing the pulsed laser deposition (PLD) technique at room temperature for an oxygen partial pressure of 0.1 Pa (0.001mbar). The films were found to be UV transparent, the band gap of which shifted to 4.75eV on hydrogen annealing. The band gap of the oxygen stoichiometric bulk powder samples (4.55eV) determined from diffuse reflection spectrum (DRS) shifted to 4.81eV on reduction in a hydrogen atmosphere. The electrical conductivity improved when Sn was incorporated into the ZnGa2O4 spinel. The conductivity of ZnGa2O4:Sn thin films was further improved on reduction.

Optical and Carrier Transport Properties of Cosputtered Zn–In–Sn–O Films and Their Applications to TFTs

The optical and carrier transport properties of amorphous transparent zinc indium tin oxide (ZITO)(a-ZITO) thin films and the characteristics of the thin-film transistors TFTs were examined as a function of chemical composition. The as-deposited films were very conductive and showed clear free carrier absorption FCA . The analysis of the FCA gave the effective mass value of 0.53 me and a momentum relaxation time of 3.9 fs for an a-ZITO film with Zn:In:Sn = 0.35:0.35:0.3. TFTs with the as-deposited channels did not show current modulation due to the high carrier density in the channels. Thermal annealing at 300°C decreased the carrier density and TFTs fabricated with the annealed channels operated with positive threshold voltages VT when Zn contents were 25 atom % or larger. VT shifted to larger negative values, and subthreshold voltage swing increased with decreasing the Zn content, while large on–off current ratios 107–108 were kept for all the Zn contents. The field effect mobilities ranged from 12.4 to 3.4 cm2 V−1 s−1 for the TFTs with Zn contents varying from 5 to 48 atom %. The role of Zn content is also discussed in relation to the carrier transport properties and amorphous structures.

Optical and electrical properties of co-sputtered amorphous transparent conducting zinc indium tin oxide thin films

Highly conductive and transparent thin films of amorphous zinc indium tin oxide are prepared at room temperature by co-sputtering of zinc 10 oxide and indium tin oxide. Cationic contents in the films are varied by adjusting the power to the sputtering targets. Optical transmission study of 11 films showed an average transmission greater than 85% across the visible region. Maximum conductivity of 6×102 S cm−1 is obtained for Zn/In/ 12 Sn atomic ratio 0.4/0.4/0.2 in the film. Hall mobility strongly depends on carrier concentration and maximum mobility obtained is 18 cm2 V−1 s−1 13 at a carrier concentration of 2.1×1020 cm−3. Optical band gap of films varied from 3.44 eV to 3 eV with the increase of zinc content in the film 14 while the refractive index of the films at 600 nm is about 2.0.

Characterization of Hydrothermally Annealed Low Temperature Bioactive Thin Film Coatings of Hydroxyapatite on TiAl6V4 Implant material

This thesis summarizes the results on the growth and characterisation of thin films of HA grown on TiAl6V4 (Ti) implant material at a lower substrate temperature by a combination of Pulsed laser deposition and a hydrothermal treatment to get sufficiently strong crystalline films suitable for orthopaedic applications. The comparison of the properties of the coated substrate has been made with other surface modification techniques like anodization and chemical etching. The in-vitro study has been conducted on the surface modified implants to assess its cell viability. A molecular level study has been conducted to analyze the adhesion mechanism of protein adhesion molecules on to HA coated implants.

Dielectric Properties of Electron Beam Evaporated Samarium Oxide Films

The dielectric properties of electron beam evaporated Sm2O3 films have been investigated in the frequency range from 1 kHz to 1 MHz at various temperatures (300 K-453 K). The dielectric constant is found to depend on film thickness and it attains a constant value beyond 1000 A. The present electron beam evaporated Sm2O3 films have a high dielectric constant of 43. The frequency dependence of and tan teeta at various temperatures is also studied.

Amorphous Oxide Transparent Thin Films: Growth, Characterisation and Application to Thin Film Transistors

This work mainly concentrate to understand the optical and electrical properties of amorphous zinc tin oxide and amorphous zinc indium tin oxide thin films for TFT applications. Amorphous materials are promising in achieving better device performance on temperature sensitive substrates compared to polycrystalline materials. Most of these amorphous oxides are multicomponent and as such there exists the need for an optimized chemical composition. For this we have to make individual targets with required chemical composition to use it in conventional thin film deposition techniques like PLD and sputtering. Instead, if we use separate targets for each of the cationic element and if separately control the power during the simultaneous sputtering process, then we can change the chemical composition by simply adjusting the sputtering power. This is what is done in co-sputtering technique. Eventhough there had some reports about thin film deposition using this technique, there was no reports about the use of this technique in TFT fabrication until very recent time. Hence in this work, co-sputtering has performed as a major technique for thin film deposition and TFT fabrication. PLD were also performed as it is a relatively new technique and allows the use high oxygen pressure during deposition. This helps to control the carrier density in the channel and also favours the smooth film surface. Both these properties are crucial in TFT.Zinc tin oxide material is interesting in the sense that it does not contain costly indium. Eventhough some works were already reported in ZTO based TFTs, there was no systematic study about ZTO thin film's various optoelectronic properties from a TFT manufacturing perspective. Attempts have made to analyse the ZTO films prepared by PLD and co-sputtering. As more type of cations present in the film, chances are high to form an amorphous phase. Zinc indium tin oxide is studied as a multicomponent oxide material suitable for TFT fabrication.

Optimization of Two Stage Process for the Growth of In2S3 , CuInSe2 and CuIn (Sel-xSx)2Thin Films for Solar Cell Application

Two stage processes consisting of precursor preparation by thermal evaporation followed by chalcogenisation in the required atmosphere is found to be a feasible technique for the PV materials such as n-Beta In2S3, p-CulnSe2, p-CulnS2 and p-CuIn(Sel_xSx)2. The growth parameters such as chalcogenisation temperature and duration of chalcogenisation etc have been optimised in the present study.Single phase Beta-In2S3 thin films can be obtained by sulfurising the indium films above 300°C for 45 minutes. Low sulfurisation temperatures required prolonged annealing after the sulfurisation to obtain single phase Beta-1n2S3, which resulted in high material loss. The maximum band gap of 2.58 eV was obtained for the nearly stoichiometric Beta-In2S3 film which was sulfurised at 350°C. This wider band gap, n type Beta-In2S3 can be used as an alternative to toxic CdS as window layer in photovoltaics .The systematic study on the structural optical and electrical properties of CuInSe2 films by varying the process parameters such as the duration of selenization and the selenization temperature led to the conclusion that for the growth of single-phase CuInSe2, the optimum selenization temperature is 350°C and duration is 3 hours. The presence of some binary phases in films for shorter selenization period and lower selenization temperature may be due to the incomplete reaction and indium loss. Optical band gap energy of 1.05 eV obtained for the films under the optimum condition.In order to obtain a closer match to the solar spectrum it is desirable to increase the band gap of the CulnSe2 by a few meV . Further research works were carried out to produce graded band gap CuIn(Se,S)2 absorber films by incorporation of sulfur into CuInSe2. It was observed that when the CulnSe2 prepared by two stage process were post annealed in sulfur atmosphere, the sulfur may be occupying the interstitial positions or forming a CuInS2 phase along with CuInSe2 phase. The sulfur treatment during the selenization process OfCu11 ln9 precursors resulted in Culn (Se,S)2 thin films. A band gap of 1.38 eV was obtained for the CuIn(Se,S)2.The optimised thin films n-beta 1n2S3, p-CulnSe2 and p-Culn(Sel-xSx)2 can be used for fabrication of polycrystalline solar cells.

Dielectric and optical properties of europium oxide films

The dielectric properties of vacuum-deposited europium oxide films have been investigated in the frequency range from 1 kHz to 1 MHz at various temperatures (300-543 K). The dielectric constant is found to depend on film thickness and it attains a constant value beyond 1000 Å. Films deposited at higher substrate temperatures (above 423 K) exhibit improved dielectric properties owing to the recovery of stoichiometry. The frequency variation of the loss factor exhibits a minimum which increases with rise in temperature. The breakdown field strength (about 106V cm-1) is found to be thickness dependent and it varies in accordance with the Forlani-Minnaja relation. The films exhibit ohmic conduction with an activation energy of 0.86 eV at low electric fields but at higher fields the conductivity becomes space charge limited. X-ray studies show that the films are amorphous in nature. The a.c. conductivity is proportional to ω at low frequency, whereas a square law dependence is observed at higher frequencies. The optical constants n, α and k and optical band gap are calculated from the UV-visible-near-IR spectra.

Highly conductive and transparent ZnO thin film using Chemical Spray Pyrolysis technique: Effect of doping and deposition parameters

In the present work we report the preparation details studies on ZnO thin films. ZnO thin films are prepared using cost effective deposition technique viz., Chemical Spray Pyrolysis (CSP). The method is very effective for large area preparation of the ZnO thin film. A new post-deposition process could also be developed to avoid the adsorption of oxygen that usually occurs after the spraying process i.e., while cooling. Studies were done by changing the various deposition parameters for optimizing the properties of ZnO thin film. Moreover, different methods of doping using various elements are also tried to enhance the conductivity and transparency of the film to make these suitable for various optoelectronic applications.

Investigations on Phaeocystis sp., A Harmful Bloom- Forming Alga Isolated from Cochin Estuary

Considering the importance of diversity of micro algae in our ecosystem and new invasion of many organisms, an attempt was made to monitor the Cochin estuary along the south west coast of India for the qualitative distribution of phytoplankton and to study the growth kinetics and allelopathic effect of the phaeocystis sp. Isolated from the cochin estuary. Phaeocystis blooms are common only in high latitude environments and they rarely occur in low latitude environments such as tropics and subtropics. As phaeocystis is grouped under harmful alga ,in the present study the factors causing the blooms formation in the ecosystem. The nutrient concentration of the water body along with other physiochemical parameters that includes temperature salinity and ph play an important role in triggering the bloom of phaeocystis .The phaeocystis harbor specific bacterial flora associated with it and they exert an important role in the growth ,haemolytic activity and the bloom phases of the alga. The harmful alga mainly depends on the production of alleopathic compounds for the establishment of bloom in the marine environments .These physiological properties of the phaecystis were considered for the study, along with the role of nutrients in the allelopathic and hemolytic activity

Spray Pyrolysed Tin Chalcogenide Thin Films: Optimization of optoelectronic properties of SnS for possible photovoltaic application as an absorber layer

In the early 19th century, industrial revolution was fuelled mainly by the development of machine based manufacturing and the increased use of coal. Later on, the focal point shifted to oil, thanks to the mass-production technology, ease of transport/storage and also the (less) environmental issues in comparison with the coal!! By the dawn of 21st century, due to the depletion of oil reserves and pollution resulting from heavy usage of oil the demand for clean energy was on the rising edge. This ever growing demand has propelled research on photovoltaics which has emerged successful and is currently being looked up to as the only solace for meeting our present day energy requirements. The proven PV technology on commercial scale is based on silicon but the recent boom in the demand for photovoltaic modules has in turn created a shortage in supply of silicon. Also the technology is still not accessible to common man. This has onset the research and development work on moderately efficient, eco-friendly and low cost photovoltaic devices (solar cells). Thin film photovoltaic modules have made a breakthrough entry in the PV market on these grounds. Thin films have the potential to revolutionize the present cost structure of solar cells by eliminating the use of the expensive silicon wafers that alone accounts for above 50% of total module manufacturing cost.Well developed thin film photovoltaic technologies are based on amorphous silicon, CdTe and CuInSe2. However the cell fabrication process using amorphous silicon requires handling of very toxic gases (like phosphene, silane and borane) and costly technologies for cell fabrication. In the case of other materials too, there are difficulties like maintaining stoichiometry (especially in large area films), alleged environmental hazards and high cost of indium. Hence there is an urgent need for the development of materials that are easy to prepare, eco-friendly and available in abundance. The work presented in this thesis is an attempt towards the development of a cost-effective, eco-friendly material for thin film solar cells using simple economically viable technique. Sn-based window and absorber layers deposited using Chemical Spray Pyrolysis (CSP) technique have been chosen for the purpose

Studies on prevulcanization of rubber latex with special reference to influence of storage and after treatments on properties of films

Systematic investigations on prevulcanization of NR latex with special reference to the influence of storage of latex and after-treatments of films, have been carried out. The other aspects studied include the effect of temperature on sulphur prevulcanization, the extent of crosslinking, tensile properties, stress relaxation characteristics, water absorption and leaching characteristics of prevulcanizcd latex films