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

Spray Pyrolysed Zinc Oxide Thin Films : Effects of Doping and Ion Beam Irradiation

In recent years scientists have made rapid and significant advances in the field of semiconductor physics. One of the most important fields of current interest in materials science is the fundamental aspects and applications of conducting transparent oxide thin films (TCO). The characteristic properties of such coatings are low electrical resistivity and high transparency in the visible region. The first semitransparent and electrically conducting CdO film was reported as early as in 1907 [1]. Though early work on these films was performed out of purely scientific interest, substantial technological advances in such films were made after 1940. The technological interest in the study of transparent semiconducting films was generated mainly due to the potential applications of these materials both in industry and research. Such films demonstrated their utility as transparent electrical heaters for windscreens in the aircraft industry. However, during the last decade, these conducting transparent films have been widely used in a variety of other applications such as gas sensors [2], solar cells [3], heat reflectors [4], light emitting devices [5] and laser damage resistant coatings in high power laser technology [6]. Just a few materials dominate the current TCO industry and the two dominant markets for TCO’s are in architectural applications and flat panel displays. The architectural use of TCO is for energy efficient windows. Fluorine doped tin oxide (FTO), deposited using a pyrolysis process is the TCO usually finds maximum application. SnO2 also finds application ad coatings for windows, which are efficient in preventing radiative heat loss, due to low emissivity (0.16). Pyrolitic tin oxide is used in PV modules, touch screens and plasma displays. However indium tin oxide (ITO) is mostly used in the majority of flat panel display (FPD) applications. In FPDs, the basic function of ITO is as transparent electrodes. The volume of FPD’s produced, and hence the volume of ITO coatings produced, continues to grow rapidly. But the current increase in the cost of indium and the scarcity of this material created the difficulty in obtaining low cost TCOs. Hence search for alternative TCO materials has been a topic of active research for the last few decades. This resulted in the development of binary materials like ZnO, SnO2, CdO and ternary materials like II Zn2SnO4, CdSb2O6:Y, ZnSO3, GaInO3 etc. The use of multicomponent oxide materials makes it possible to have TCO films suitable for specialized applications because by altering their chemical compositions, one can control the electrical, optical, chemical and physical properties. But the advantages of using binary materials are the easiness to control the chemical compositions and depositions conditions. Recently, there were reports claiming the deposition of CdO:In films with a resistivity of the order of 10-5 ohm cm for flat panel displays and solar cells. However they find limited use because of Cd-Toxicity. In this regard, ZnO films developed in 1980s, are very useful as these use Zn, an abundant, inexpensive and nontoxic material. Resistivity of this material is still not very low, but can be reduced through doping with group-III elements like In, Al or Ga or with F [6]. Hence there is a great interest in ZnO as an alternative of ITO. In the present study, we prepared and characterized transparent and conducting ZnO thin films, using a cost effective technique viz Chemical Spray Pyrolysis (CSP). This technique is also suitable for large area film deposition. It involves spraying a solution, (usually aqueous) containing soluble salts of the constituents of the desired compound, onto a heated substrate.

Modified Circular Patch Antenna

A circular miqrostrip antenna with a modified structure is presented. By adjusting the feed location along the circumference of the patch it is possible to match the antenna with a C microstrip line of any impedance. The impedance bandwidth and radiation characteristics are unaffected by this structural V modification.

Modified mesoporous MCM-41 as hosts for photochromic spirobenzopyrans

The influence of the chemical composition and silylation of mesoporous MCM-41 materials on the photochromic behaviour of adsorbed spiropyran (BIPS) and 6-nitrospiropyran was studied. Upon incorporation, the spiropyrans underwent ring opening to form either zwitterionic merocyanine or its corresponding O-protonated form. In all silica MCM-41 or in the MCM-41 containing aluminium, the O-protonated merocyanine was predominantly formed. In the case of MCM-41 modified by silylation of the OH groups, a mixture of zwitterionic merocyanine and spiropyran was present. The photochromic response was studied by means of steady-state irradiation and by laser flash photolysis. Steady-state irradiation (λ > 450 nm) of the solid samples gives rise in all cases to an intensity decrease of the absorption bands corresponding to either the protonated or the unprotonated merocyanine form (reverse photochromism). In contrast, laser flash photolysis at 308 nm of spiropyrans supported on silylated MCM-41 allows observation of the photochemical ring opening of residual spiropyran to the corresponding zwitterionic form (normal photochromism).

Optical and electrical properties of amorphous zinc tin oxide thin films examined for thin film transistor application

Structural, electronic, and optical properties of amorphous and transparent zinc tin oxide films deposited on glass substrates by pulsed laser deposition (PLD) were examined for two chemical compositions of Zn:Sn=1:1 and 2:1 as a function of oxygen partial pressure PO2 used for the film deposition and annealing temperature. Different from a previous report on sputter-deposited films Chiang et al., Appl. Phys. Lett. 86, 013503 2005 , the PLD-deposited films crystallized at a lower temperature 450 °C to give crystalline ZnO and SnO2 phases. The optical band gaps Tauc gaps were 2.80−2.85 eV and almost independent of oxygen PO2 , which are smaller than those of the corresponding crystals 3.35−3.89 eV . Films deposited at low PO2 showed significant subgap absorptions, which were reduced by postthermal annealing. Hall mobility showed steep increases when carrier concentration exceeded threshold values and the threshold value depended on the film chemical composition. The films deposited at low PO2 2 Pa had low carrier concentrations. It is thought that the low PO2 produced high-density oxygen deficiencies and generated electrons, but these electrons were trapped in localized states, which would be observed as the subgap absorptions. Similar effects were observed for 600 °C crystallized films and their resistivities were increased by formation of subgap states due to the reducing high-temperature condition. High carrier concentrations and large mobilities were obtained in an intermediate PO2 region for the as-deposited films.

Studies on Thermoplastic Elastomer Based on Linear Low-Density Polyethylene and Latex Product Waste Modified with Thiocarbanilide

Latex waste like glove waste was effectively modified using a new reclaiming agent, thiocarbanilide. This modified waste was blended with linear low-density polyethylene (LLDPE) to develop a novel thermoplastic elastomer. Both uncrosslinked and dynamically crosslinked blends were prepared and their properties were studied. The results were found to be comparable to those of conventional thermoplastic elastomers.

Studies on Modified Atmosphere Packaging of Pearl Spot (Etroplussuratensis) With Special Emphasis to Biochemical and Microbiological Parameters

A modified atmosphere may be defined as a packaging or storage of a perishable product in an atmosphere other than that of air. A modified atmosphere (MA) applies to food packaged products changes continuously throughout the storage period. The pearl spot (Etroplus suratensis) is an important brackish water fish belonging to the family Cichlidae. The present work was carried out to see the effect of modified atmosphere packaging on the shelf life fresh pearl spot stored in ice to extent the shelf life. The objectives of the present study are to study the suitability of Thermoformed Trays for modified atmosphere packaging, to standardize the most suitable gas mixture for modified atmosphere packaging pearl spot based on sensory evaluation, to find out the effect of modified atmosphere packaging in comparison to air packaging, to study the biochemical, microbiological, sensory and textural characteristics during storage, to study the safety concern regarding the Clostridium botulinum during modified atmosphere packaging, to find out the most suitable chemical quality indices for modified atmosphere stored pearl spot

Broadband Cylindrical Dielectric Resonator Antenna Excited by Modified Microstrip Line

The impedance bandwidth of a high permittivity cylindrical dielectric resonator antenna excited by a micro strip line was significantly improved by modifying the feed geometry. The 10 dB return loss bandwidth is enhanced from 12 to 26% without much affecting the gain and other radiation properties of the antenna. Good agreement has been observed between the predicted and measured results

Broadband Cylindrical Dielectric Resonator Antenna Excited by Modified Microstrip Line

The impedance bandwidth of a high permittivity cylindrical dielectric resonator antenna excited by a micro strip line was significantly improved by modifying the feed geometry. The 10 dB return loss bandwidth is enhanced from 12 to 26% without much affecting the gain and other radiation properties of the antenna. Good agreement has been observed between the predicted and measured results

Metglas thin film based magnetostrictive transducers for use in long period fibre grating sensors

Metallic glass alloy Metglas 2826 MB based amorphous magnetic thin films were fabricated by the thermal evaporation technique. Transmission electron micrographs and electron diffraction pattern showed the amorphous nature of the films. Composition of the films was analyzed employing x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy techniques. The film was integrated to a long period fibre grating. It was observed that the resonance wavelength of the fibre grating decreased with an increase in the magnetic field. Change in the resonance wavelength was minimal at higher magnetic fields. Field dependent magnetostriction values revealed the potential application of these films in magnetostrictive sensor devices

Laser emission from transversely pumped dye-doped free-standing polymer film

We present a compact solid-state laser based on leaky mode propagation from a dye-doped polymer free-standing film waveguide. The edge emitted spectrum clearly indicated the existence of periodic resonant modes. The reflections from the lateral faces of the free-standing film provided the optical feedback thus giving rise to a Fabry–Perot like optical cavity. This together with the guidance through the gain medium gave rise to intense narrow emission lines. For a pump energy of 1.82 mJ/pulse, an intense line with FWHM ∼0.4 nmwas observed at 576.5 nm.

Laser emission from transversely pumped dye-doped free-standing polymer film

We present a compact solid-state laser based on leaky mode propagation from a dye-doped polymer free-standing film waveguide. The edge emitted spectrum clearly indicated the existence of periodic resonant modes. The reflections from the lateral faces of the free-standing film provided the optical feedback thus giving rise to a Fabry–Perot like optical cavity. This together with the guidance through the gain medium gave rise to intense narrow emission lines. For a pump energy of 1.82 mJ/pulse, an intense line with FWHM ∼0.4 nmwas observed at 576.5 nm.