Thermal transport, photoconduction and electrical switching in selected chalcogenide glasses exhibiting carrier type reversal

Department of Instrumentation, Cochin University of Science and Technology

Investigations on Photoconductivity and Electrical Switiching in Selected Chalcogenide Glasses

In this thesis, we present the results of our investigations on the photoconducting and electrical switching properties of selected chalcogenide glass systems. We have used XRD and X-ray photoelectron spectroscopy (XPS) analysis for confinuing the amorphous nature of these materials and for confirming their constituents respectively.Photoconductivity is the enhancement in electrical conductivity of materials brought about by the motion of charge carriers excited by absorbed radiation. The phenomenon involves absorption, photogeneration, recombination and transport processes and it gives good insight into the density of states in the energy gap of solids due to the presence of impurities and lattice defects. Photoconductivity measurements lead to the determination of such important parameters as quantum efficiency, photosensiti\'ity, spectral sensitivity and carrier lifetime. Extensive research work on photoconducting properties of amorphous semiconductors has resulted in the development of a variety of very sensitive photodetectors. Photoconductors are finding newer and newer uses eyery day. CdS, CdSe. Sb2S3, Se, ZnO etc, are typical photoconducting materials which are used in devices like vidicons, light amplifiers, xerography equipment etc.Electrical switching is another interesting and important property possessed by several Te based chalcogenides. Switching is the rapid and reversible transition between a highly resistive OFF state, driven by an external electric field and characterized by a threshold voltage, and a low resistivity ON state, Switching can be either threshold type or memory type. The phenomenon of switching could find applications in areas like infonnation storage, electrical power control etc. Investigations on electrical switching in chalcogenide glasses help in understanding the mechanism of switching which is necessary to select and modify materials for specific switching applications.Analysis of XRD pattern gives no further infonuation about amorphous materials than revealing their disordered structure whereas x-ray photoelectron spectroscopy,XPS) provides information about the different constituents present in the material. Also it gives binding energies (b.e.) of an element in different compounds and hence b.e. shift from the elemental form.Our investigations have been concentrated on the bulk glasses, Ge-In-Se, Ge-Bi-Se and As-Sb-Se for photoconductivity measurements and In-Te for electrical switching. The photoconducting properties of Ge-Sb-Se thin films prepared by sputtering technique have also been studied. The bulk glasses for the present investigations are prepared by the melt quenching technique and are annealed for half an hour at temperatures just below their respective glass transition temperatures. The dependence of photoconducting propenies on composition and temperature are investigated in each system. The electrical switching characteristics of In-Te system are also studied with different compositions and by varying the temperature.

Development of thermoplastic conducting polymer composites based on polyaniline and polythiophenes for microwave and electrical applications

The microwave and electrical applications of some important conducting polymers are analyzed in this investigation.One of the major drawbacks of conducting polymers is their poor processability,and a solution to overcome this is sought in this investigation.Conducting polymer thermoplastic composites were prepared by the insitu polymerization method to improve the extent of miscibility probably to a semi IPN level.The attractive features of the conducting composite developed are excellent processability,good microwave and electrical conductivity,good microwave absorption,load sensitivity and satisfactory mechanical properties.The composite shows typical frequency selective microwave absorption and refelection behaviors.

”Studies on Selected conducting polymers for Microwave and Electrical Applications

The electrical properties of polymers make up an inherently interdisciplinary topic, being closely associated, on the one hand, with the mechanical properties of polymers polarization and relaxation) and, on the other hand, with the semi conductive properties (conduction and break down). In addition, unlike conventional technologies, which use these properties in its various applications like antistatic coatings, rechargeable batteries, sensors, electrochromic devices, electrochemical devices etc, microwave technology extract the microwave absorbing ability of electrically conducting polymers. The conducting polymers are widely used in its potential applications like electro magnetic interference shielding, satellite communication links, beam steering radars, frequency selective surfaces etc. Considering the relevance of microwave applications of conducting polymers, the study of microwave properties of conducting polymers stands poised to become a compelling choice for synthetic chemists and condensed - matter physicists, physical chemists and material scientists, electrochemists and polymer scientists. The main aim of the present work is to study the microwave and low frequency properties of various conducting polymers, conducting semi-interpenetrating networks, conducting copolymers and to characterise it. Also this thesis collated the microwave properties of these conducting systems and exposes the various technologically important applications in the industrial, scientific, communication and defence applications.

Formation And Electrical Properties Of Polyacrylonitrile Thin Films Prepared By Plasma - Polymerisation

Due to the great versatility of the properties of polymer thin films, special interest has been taken in recent years on their preparation and electrical properties. The present thesis is entirely devoted to the study of the formation, structure and electrical properties of plasma» polymerised polyacrylonitrile (PAN) thin films. Eventhough the studies are confined to a single polymer film, the results in general are applicable to similar polar polymer films.

Investigation of structural, optical and electrical properties and valence band splitting in cu-ln-se compounds

Investigations on thin films that started decades back due to scientific curiosity in the properties of a two-dimensional solid, has developed into a leading research field in recent years due to the ever expanding applications of the thin films in the fann of a variety of active and passive microminiaturized components and devices, solar cells, radiation sowces and detectors, magnetic memory devices, interference filters, refection and antireflection coatings etc. [1]. The recent environment and energy resource concerns have aroused an enonnous interest in the study of materials in thin film form suitable for renewable energy sources such as photovoltaic devices. Recognition of the immense potential applications of the chalcopyrites that can fonn homojunctions or heterojunctions for solar cell fabrication has attracted many researchers to extensive and intense research on them. In this thesis, we have started with studies performed on CuInSe, thin films, a technologically well recognized compound belonging to the l•ill-VI family of semiconductors and have riveted on investigations on the preparation and characterization of compoWlds Culn3Se5. Culn5Seg and CuIn7Se12, an interesting group of compounds related to CuInSe2 called Ordered Vacancy Compounds, having promising applications in photovoltaic devices. A pioneering work attempted on preparing and characterizing the compound Culn7Sel2 is detailed in the chapters on OVC's. Investigation on valence band splitting in avc's have also been attempted for the first time and included as the last chapter in the thesis. Some of the salient features of the chalcopyrite c.ompounds are given in the next section .of this introductory chapter.

Structural, magnetic and electrical properties of the sol-gel prepared Li0.5Fe2.5O4 fine particles

Fine particles of lithium ferrite were synthesized by the sol-gel method. By subsequent heat treatment at different temperatures, lithium ferrites of different grain sizes were prepared. A structural characterization of all the samples was conducted by the x-ray diffraction technique. A grain size of around 12 nm was observed for Li0.5Fe2.5O4 obtained through the sol-gel method. Magnetic properties of lithium ferrite nanoparticles with grain size ranging from 12 to 32 nm were studied. Magnetization measurements showed that Li0.5Fe2.5O4 fine particles exhibit a deviation from the predicted magnetic behaviour. The as-prepared sample of lithium ferrite showed a maximum saturation magnetization of 75 emu g−1. Variation of coercivity is attributed to the transition from multi-domain to single domain nature. Dielectric permittivity and ac conductivity of all the samples were evaluated as a function of frequency, temperature and grain size. Variation of permittivity and ac conductivity with frequency reveals that the dispersion is due to the Maxwell–Wagner type interfacial polarization

On the optical and electrical properties of rf and a.c. plasma polymerized aniline thin films

Polyaniline is a widely studied conducting polymer and is a useful material in its bulk and thin film form for many applications, because of its excellent optical and electrical properties. Pristine and iodine doped polyaniline thin films were prepared by a.c. and rf plasma polymerization techniques separately for the comparison of their optical and electrical properties. Doping of iodine was effected in situ. The structural properties of these films were evaluated by FTIR spectroscopy and the optical band gap was estimated from UV-vis-NIR measurements. Comparative studies on the structural, optical and electrical properties of a.c. and rf polymerization are presented here. It has been found that the optical band gap of the polyaniline thin films prepared by rf and a.c. plasma polymerization techniques differ considerably and the band gap is further reduced by in situ doping of iodine. The electrical conductivity measurements on these films show a higher value of electrical conductivity in the case of rf plasma polymerized thin films when compared to the a.c. plasma polymerized films. Also, it is found that the iodine doping enhanced conductivity of the polymer thin films considerably. The results are compared and correlated and have been explained with respect to the different structures adopted under these two preparation techniques

Quality Governance based on Enterprise Engineering Method and Six Sigma Approach

Enterprise Modeling (EM) is currently in operation either as a technique to represent and understand the structure and behavior of the enterprise, or as a technique to analyze business processes, and in many cases as support technique for business process reengineering. However, EM architectures and methods for Enterprise Engineering can also used to support new management techniques like SIX SIGMA, because these new techniques need a clear, transparent and integrated definition and description of the business activities of the enterprise to be able to build up, optimize and operate an successful enterprise. The main goal of SIX SIGMA is to optimize the performance of processes. A still open question is: "What are the adequate Quality criteria and methods to ensure such performance? What must we do to get Quality governance?" This paper describes a method including an Enterprise Engineering method and SIX SIGMA strategy to reach Quality Governance

Short-term effects of human urine fertiliser and wood ash on soil pH and electrical conductivity

The fertiliser value of human urine has been examined on several crops, yet little is known about its effects on key soil properties of agronomic significance. This study investigated temporal soil salinization potential of human urine fertiliser (HUF). It further looked at combined effects of human urine and wood ash (WA) on soil pH, urine-NH_3 volatilisation, soil electrical conductivity (EC), and basic cation contents of two Acrisols (Adenta and Toje series) from the coastal savannah zone of Ghana. The experiment was a factorial design conducted in the laboratory for 12 weeks. The results indicated an increase in soil pH by 1.2 units for Adenta series and 1 unit for Toje series after one week of HUF application followed by a decline by about 2 pH units for both soil types after twelve weeks. This was attributed to nitrification of ammonium to nitrate leading to acidification. The EC otherwise increased with HUF application creating slightly saline conditions in Toje series and non-saline conditions in Adenta series. When WA was applied with HUF, both soil pH and EC increased. In contrast, the HUF alone slightly salinized Toje series, but both soils remained non-saline whenWA and HUF were applied together. The application ofWA resulted in two-fold increase in Ca, Mg, K, and Na content compared to HUF alone. Hence, WA is a promising amendment of acid soils and could reduce the effect of soluble salts in human urine fertilizer, which is likely to cause soil salinity.

Nano Electronics and Computer Science Research Group

This is the website for the Nano Research group based at the University of Southampton ECS department, and details current research topics and the people connected with these. It shows some of the current research topics undertaken at the center, and gives an outline of what can be done for post graduate courses.

Writing a Technical Report for Electronic and Electrical Engineers

Has a mixture of factual information (conventions on how a report should be structured) and motivational information on improving writing and communication skills

Artificial Intelligence

Pearon's resource from the Brookshear Chapter