Download or read book Structural and Charge Transporting Properties of Pure Liquid Crystalline Organic Semiconductors and Composites for Applications in Organic Electronics written by Kirill Kondratenko and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis is dedicated to various aspects of liquid crystalline (LC) organic semiconductors (OSCs) in regard to their applications in the field of organic electronics. The first part of this work deals with a well-known LC OSC based on phenyl-naphtalene. Two major ways of performance improvement are proposed and investigated : stabilization of LC structure by in situ photo-polymerization and introduction of electron acceptor doping impurity. In the first case, the influence of polymer network on mesophase order and charge transport is investigated by conventional experimental techniques and Time-Of-Flight (TOF) mobility measurements. Fot the doped materials, ab initio calculations are employed to predict their spectroscopic properties which is exhaustively compared with the experimental data obtained by optical and vibrational spectroscopy. The charge transport is studied by TOF method in the mesophase, while crystalline phase is investigated via conductive atomic force microscopy. A prototype of organic field effect transistor (OFET) is prepared to obtain an estimate of performance for a relevant real-world application. The second part of this work includes design and synthesis of a novel LC semiconductor based on anthracene, additional attention is made to obtain an easy-to-make and low production cost material. Noval molecule is fully characterized : molecular structure is confirmed by relevant techniques ; frontier molecular energy levels are studied by optical spectroscopy and cyclic voltammetry and confronted to values obtaines via ab initio calculations ; mesophase properties are investigated by optical microscopy and scanning calorimetry. charge transporting properties are characterized by means of an OFET device : it is found that new anthracene-molecule exhibits significant improvement of field-effect hole mobility over previously studied phenyl naphtalene derivative. Finally, photoconductive properties of the novel material are addressed in order to investigate its potential applications to organic phototransistors.

Download or read book Liquid Crystalline Semiconductors written by Richard J. Bushby and published by Springer Science & Business Media. This book was released on 2012-11-28 with total page 282 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is an exciting stage in the development of organic electronics. It is no longer an area of purely academic interest as increasingly real applications are being developed, some of which are beginning to come on-stream. Areas that have already been commercially developed or which are under intensive development include organic light emitting diodes (for flat panel displays and solid state lighting), organic photovoltaic cells, organic thin film transistors (for smart tags and flat panel displays) and sensors. Within the family of organic electronic materials, liquid crystals are relative newcomers. The first electronically conducting liquid crystals were reported in 1988 but already a substantial literature has developed. The advantage of liquid crystalline semiconductors is that they have the easy processability of amorphous and polymeric semiconductors but they usually have higher charge carrier mobilities. Their mobilities do not reach the levels seen in crystalline organics but they circumvent all of the difficult issues of controlling crystal growth and morphology. Liquid crystals self-organise, they can be aligned by fields and surface forces and, because of their fluid nature, defects in liquid crystal structures readily self-heal. With these matters in mind this is an opportune moment to bring together a volume on the subject of ‘Liquid Crystalline Semiconductors’. The field is already too large to cover in a comprehensive manner so the aim has been to bring together contributions from leading researchers which cover the main areas of the chemistry (synthesis and structure/function relationships), physics (charge transport mechanisms and optical properties) and potential applications in photovoltaics, organic light emitting diodes (OLEDs) and organic field-effect transistors (OFETs). This book will provide a useful introduction to the field for those in both industry and academia and it is hoped that it will help to stimulate future developments.

Download or read book Solution Processable Components for Organic Electronic Devices written by Beata Luszczynska and published by John Wiley & Sons. This book was released on 2019-06-11 with total page 688 pages. Available in PDF, EPUB and Kindle. Book excerpt: Provides first-hand insights into advanced fabrication techniques for solution processable organic electronics materials and devices The field of printable organic electronics has emerged as a technology which plays a major role in materials science research and development. Printable organic electronics soon compete with, and for specific applications can even outpace, conventional semiconductor devices in terms of performance, cost, and versatility. Printing techniques allow for large-scale fabrication of organic electronic components and functional devices for use as wearable electronics, health-care sensors, Internet of Things, monitoring of environment pollution and many others, yet-to-be-conceived applications. The first part of Solution-Processable Components for Organic Electronic Devices covers the synthesis of: soluble conjugated polymers; solution-processable nanoparticles of inorganic semiconductors; high-k nanoparticles by means of controlled radical polymerization; advanced blending techniques yielding novel materials with extraordinary properties. The book also discusses photogeneration of charge carriers in nanostructured bulk heterojunctions and charge carrier transport in multicomponent materials such as composites and nanocomposites as well as photovoltaic devices modelling. The second part of the book is devoted to organic electronic devices, such as field effect transistors, light emitting diodes, photovoltaics, photodiodes and electronic memory devices which can be produced by solution-based methods, including printing and roll-to-roll manufacturing. The book provides in-depth knowledge for experienced researchers and for those entering the field. It comprises 12 chapters focused on: ? novel organic electronics components synthesis and solution-based processing techniques ? advanced analysis of mechanisms governing charge carrier generation and transport in organic semiconductors and devices ? fabrication techniques and characterization methods of organic electronic devices Providing coverage of the state of the art of organic electronics, Solution-Processable Components for Organic Electronic Devices is an excellent book for materials scientists, applied physicists, engineering scientists, and those working in the electronics industry.

Download or read book Wspc Reference On Organic Electronics The Organic Semiconductors In 2 Volumes written by Seth R Marder and published by World Scientific. This book was released on 2016-06-24 with total page 896 pages. Available in PDF, EPUB and Kindle. Book excerpt: This 2-volume set provides the reader with a basic understanding of the foundational concepts pertaining to the design, synthesis, and applications of conjugated organic materials used as organic semiconductors, in areas including organic photovoltaic devices, light-emitting diodes, field-effect transistors, spintronics, actuation, bioelectronics, thermoelectrics, and nonlinear optics.While there are many monographs in these various areas, the emphasis here is both on the fundamental chemistry and physics concepts underlying the field of organic semiconductors and on how these concepts drive a broad range of applications. This makes the volumes ideal introductory textbooks in the subject. They will thus offer great value to both junior and senior scientists working in areas ranging from organic chemistry to condensed matter physics and materials science and engineering.Number of Illustrations and Tables: 168 b/w illus., 242 colour illus., 13 tables.

Download or read book Physical and Chemical Aspects of Organic Electronics written by Christof Wöll and published by John Wiley & Sons. This book was released on 2009-04-22 with total page 698 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic molecules are currently being investigated with regard to their application as active components in semiconductor devices. Whereas devices containing organic molecules for the generation of light - organic light emitting diodes (OLED) - have already reached the market (they e.g. display information on mobile phones), transistors where organic molecules are used to actively control currents and voltages are still in the development stage. In this book the principle problems related to using organic materials as semiconductors and to construct functioning devices will be addressed. A particular emphasis will be put on the difference between inorganic semiconductors such as Si, Ge and GaAs and organic semiconductors (OSC). The special properties of such soft matter require particular approaches for processing characterization and device implementation, which are quite different from the approach used for conventional semiconductors.

Download or read book The Non Local Density of States of Electronic Excitations in Organic Semiconductors written by Carl. R Poelking and published by Springer. This book was released on 2017-10-24 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book focuses on the microscopic understanding of the function of organic semiconductors. By tracing the link between their morphological structure and electronic properties across multiple scales, it represents an important advance in this direction. Organic semiconductors are materials at the interface between hard and soft matter: they combine structural variability, processibility and mechanical flexibility with the ability to efficiently transport charge and energy. This unique set of properties makes them a promising class of materials for electronic devices, including organic solar cells and light-emitting diodes. Understanding their function at the microscopic scale – the goal of this work – is a prerequisite for the rational design and optimization of the underlying materials. Based on new multiscale simulation protocols, the book studies the complex interplay between molecular architecture, supramolecular organization and electronic structure in order to reveal why some materials perform well – and why others do not. In particular, by examining the long-range effects that interrelate microscopic states and mesoscopic structure in these materials, the book provides qualitative and quantitative insights into e.g. the charge-generation process, which also serve as a basis for new optimization strategies.

Download or read book Charge Transport in Liquid Crystalline Smectic and Discotic Organic Semiconductors written by Sanjoy Paul and published by . This book was released on 2016 with total page 205 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic electronics offer the possibility of producing low cost, flexible, and large area electronics. Organic semiconductors (OSCs) (organic polymers and crystals), used in organic electronics, are promising materials for novel optical and electronic devices such as organic light emitting diodes, organic field effect transistors, organic sensors, and organic photovoltaics (OPVs). OSCs are composed of molecules weakly held together via van der Walls forces rather than covalent bonds as in the case of inorganic semiconductors such as Si. The combined effect of small wave function overlap, spatial and energetic disorder in organic semiconducting materials lead to localization of charge carriers and, in many cases, hopping conduction. OSCs also differ from conventional semiconductors in that charges photogeneration (e.g., in OPVs) proceeds via the production, diffusion, and dissociation of excitons. Liquid crystalline OSCs (LCOSCs) are semiconductors with phases intermediate between the highly ordered crystalline and completely disordered liquid phases. These materials offer many advantages including facile alignment and the opportunity to study the effects of differing intermolecular geometries on transfer integrals, disorder-induced trapping, charge mobilities, and photogeneration efficiency. In this dissertation work, we explored the photogeneration and charge transport mechanisms in a few model smectic and discotic LCs to better understand the governing principles of photogeneration and charge transport using conventional and novel methods based on the pulsed laser time-of-flight charge carrier transport technique. Four major interrelated topics were considered in this research. First, a sample of smectic LC was aligned in order to compare the resulting hole mobility to that of an unaligned sample, with the aim of understanding how the intermolecular alignment over large length scales affects the hopping probability. The role of the polarization of the photogenerating light was also explored in the context of these anisotropic systems. Next, the photogeneration and charge transport was investigated as a function of temperature, electric field, the wavelength and intensity of photogenerating light. Different exciton dissociation interfaces between the electrode and the LC to probe the details of the mechanism of excitonic dissociation (e.g., surface mediated generation vs. exciton-exciton fusion) were explored. Next, we have also developed a new method of spatially resolving the photogeneration and transport mechanisms in inhomogeneous OSCs called "scanning time of flight microscopy (STOFm)" which simultaneously obtains 2d images of transport coefficients and polarized transmittance. The STOFm was extensively used to study charge transport in various structured semiconductors: smectics, discotics, as well as in phase separated LC/polymer structures. Finally, this work involves characterization and analysis of transport in a number of new phenyl-naphthalene LC OSCs.

Download or read book Organic Electronics Volume 2 written by Thien-Phap Nguyen and published by John Wiley & Sons. This book was released on 2021-09-15 with total page 226 pages. Available in PDF, EPUB and Kindle. Book excerpt: Due to their special properties, organic semiconductors enable the development of large-area, low-cost devices, paving the way for flexible and nomadic applications that advantageously replace those made with traditional semiconductors. In this second volume, we study the main applications of organic semiconductors, such as organic light-emitting diodes (OLEDs), solar cells (OPVs) and organic field-effect transistors (OFETs). The commercialization of these new devices is then discussed within the Brabec triangle framework, in which yield, stability and production costs are the key factors. We also address the environmental impact of organic devices for their future development. This book presents the application side of organic electronics from a technological, economic and environmental perspective. It is intended for researchers and students in university programs or engineering schools specializing in electronics, energy and materials.

Download or read book Organic Electronics II written by Hagen Klauk and published by John Wiley & Sons. This book was released on 2012-03-26 with total page 443 pages. Available in PDF, EPUB and Kindle. Book excerpt: Like its predecessor this book is devoted to the materials, manufacturing and applications aspects of organic thin-film transistors. Once again authored by the most renowned experts from this fascinating and fast-moving area of research, it offers a joint perspective both broad and in-depth on the latest developments in the areas of materials chemistry, transport physics, materials characterization, manufacturing technology, and circuit integration of organic transistors. With its many figures and detailed index, this book once again also serves as a ready reference.

Download or read book Elucidation of Chemistry Structure Function Relationships in Molecular Semiconductors for Organic Electronic Applications written by Jeni Christine Sorli and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Molecular semiconductors are promising candidates for the active components of organic electronic devices as their optoelectronic properties can be tuned at the onset of synthesis, and they can be incorporated into lightweight, large-area, flexible devices at low costs. Yet, there are numerous challenges associated with molecular semiconductor systems and their commercial implementation, which largely stem from the structural heterogeneities present in polycrystalline thin films that strongly influence charge transport in devices. The microstructure of thin film active layers is dependent on both chemical structure and the processing conditions used. Thus, it is important to develop an understanding for the complex relationships that govern these systems. This thesis explores the development of chemistry-processing-structure-function relationships across multiple length scales in small molecule organic semiconductor systems. First, we explored the relationships between chemical structure and optoelectronic properties through targeted design of coronene derivatives for application in UV-absorbing, visibly transparent solar cells. We calculated the frontier orbital and excited state transition energies of over 350 candidate compounds and used the calculations to screen for promising molecules for synthesis and characterization. From our screening procedure, we selected and synthesized three coronene derivatives for use as donors in organic photovoltaic (OPV) active layers to produce visibly transparent OPVs, and in doing so demonstrated how integrated computational and experimental efforts can accelerate materials design. It is also important to understand how molecular semiconductors pack in the solid-state to elucidate the relationships between solid-state structure and device function. We explored the role of halogenated contorted hexabenzocoronene (cHBC) derivatives on the degradation of organic solar cells during stability testing and find that both fluorinated and chlorinated cHBCs, that start out amorphous as-deposited, crystallize during aging. The crystallization of cHBC derivatives produces gaps at the acceptor-buffer layer interface that hinder charge extraction, which results in the degradation of OPV device performance. We examined how atomistic substitution in the side group of triisopropylsilylethynylpentacene (TIPS-Pn) to produce triisopropylgermanylethynyl-pentacene (TIPGe-Pn), which maintains the size of the side group but increases its electron density, allows TIPGe-Pn to access a much broader structural phase space than TIPS-Pn. This work establishes that the solid-state packing of functionalized acenes depends on both the size of the side group and electron density, which may be tuned with simple atomistic substitutions. Finally, we explored the impact of grain boundaries on the kinetics of polymorphic transformations in a core-chlorinated naphthalene tetracarboxylic diimide. We determined that grain boundaries can lower the energy barrier by initiating polymorphic transformations. This work demonstrates the importance of grain boundaries, which are common in polycrystalline organic semiconductors, not only for their impact on charge transport but also in initiation of polymorphic transformations. Collectively, the work in this thesis highlights the importance of developing robust chemistry-processing-structure-function relationships that can guide material development. We demonstrate methodologies and illuminate concepts that will allow for further optimization and improvement to the performance and stability of organic electronics in the future.

Download or read book Organic Semiconductors for Optoelectronics written by Hiroyoshi Naito and published by John Wiley & Sons. This book was released on 2021-07-30 with total page 388 pages. Available in PDF, EPUB and Kindle. Book excerpt: Comprehensive coverage of organic electronics, including fundamental theory, basic properties, characterization methods, device physics, and future trends Organic semiconductor materials have vast commercial potential for a wide range of applications, from self-emitting OLED displays and solid-state lighting to plastic electronics and organic solar cells. As research in organic optoelectronic devices continues to expand at an unprecedented rate, organic semiconductors are being applied to flexible displays, biosensors, and other cost-effective green devices in ways not possible with conventional inorganic semiconductors. Organic Semiconductors for Optoelectronics is an up-to-date review of the both the fundamental theory and latest research and development advances in organic semiconductors. Featuring contributions from an international team of experts, this comprehensive volume covers basic properties of organic semiconductors, characterization techniques, device physics, and future trends in organic device development. Detailed chapters provide key information on the device physics of organic field-effect transistors, organic light-emitting diodes, organic solar cells, organic photosensors, and more. This authoritative resource: Provides a clear understanding of the optoelectronic properties of organic semiconductors and their influence to overall device performance Explains the theories behind relevant mechanisms in organic semiconducting materials and in organic devices Discusses current and future trends and challenges in the development of organic optoelectronic devices Reviews electronic properties, device mechanisms, and characterization techniques of organic semiconducting materials Covers theoretical concepts of optical properties of organic semiconductors including fluorescent, phosphorescent, and thermally-assisted delayed fluorescent emitters An important new addition to the Wiley Series in Materials for Electronic & Optoelectronic Applications, Organic Semiconductors for Optoelectronics bridges the gap between advanced books and undergraduate textbooks on semiconductor physics and solid-state physics. It is essential reading for academic researchers, graduate students, and industry professionals involved in organic electronics, materials science, thin film devices, and optoelectronics research and development.

Download or read book Organic Electronics written by Fabio Cicoira and published by John Wiley & Sons. This book was released on 2013-07-17 with total page 441 pages. Available in PDF, EPUB and Kindle. Book excerpt: An overview of the tremendous potential of organic electronics, concentrating on those emerging topics and technologies that will form the focus of research over the next five to ten years. The young and energetic team of editors with an excellent research track record has brought together internationally renowned authors to review up-and-coming topics, some for the first time, such as organic spintronics, iontronics, light emitting transistors, organic sensors and advanced structural analysis. As a result, this book serves the needs of experienced researchers in organic electronics, graduate students and post-doctoral researchers, as well as scientists active in closely related fields, including organic chemical synthesis, thin film growth and biomaterials. Cover Figure: With kind permission of Matitaccia.

Download or read book Charge Transport in Disordered Solids with Applications in Electronics written by Sergei Baranovski and published by John Wiley & Sons. This book was released on 2006-08-14 with total page 498 pages. Available in PDF, EPUB and Kindle. Book excerpt: The field of charge conduction in disordered materials is a rapidly evolving area owing to current and potential applications of these materials in various electronic devices This text aims to cover conduction in disordered solids from fundamental physical principles and theories, through practical material development with an emphasis on applications in all areas of electronic materials. International group of contributors Presents basic physical concepts developed in this field in recent years in a uniform manner Brings up-to-date, in a one-stop source, a key evolving area in the field of electronic materials

Download or read book MECHANICAL AND ELECTRO MECHANICAL PROPERTIES OF CRYSTALLINE ORGANIC SEMICONDUCTORS written by Marcos A. Reyes-Martinez and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The study of the physical properties of organic crystalline semiconductors has allowed the advent of a new generation of high-performance organic electronic devices. Exceptional charge-transport properties and recent developments in large-area patterning techniques make organic single crystals (OSCs) excellent candidates for their utilization in the next-generation of electronic technologies, including flexible and conformable organic thin-film devices. In spite of the profound knowledge of the structural and electrical properties of OSCs, knowledge of the mechanical properties and the effects of mechanical strain is almost non-existent. This dissertation aims to bring new understanding of the intrinsic mechanical properties and the effect of mechanical strains in charge transport phenomena in organic semiconductors. The wrinkling instability is chosen as the metrology tool for the effective in-plane elastic constants of OSCs. We demonstrate that the wrinkling instability can be used to obtain the elastic constants of single crystals of rubrene, tetracene, PDIF-CN$_2$ (N,N'-1H,1H-perfluorobutyldicyanoperylene-carboxydi-imide) and perylene. We demonstrate that wrinkling is a practical method to map the in-plane mechanical anisotropy in OSCs. In addition, we utilize wrinkling to characterize how the elastic modulus of pBTTT (poly(2,5-bis(3-alkylthiophen- 2-yl)thieno[3,2-b]thiophene)) changes with increasing molecular weight, from the monomer to the pentamer and the high molecular weight polymer. To elucidate the effects of mechanical strain on charge transport, we first demonstrate and quantify the existence of a piezoresistive effect in rubrene crystals by the application of bending strains along its b [010] axis. A piezoresistive coefficient of approximately 11.26 is determined and confirmed through density functional theory (DFT) calculations. Second, we take advantage of wrinkling as a unique way to strain the conducting channel of field-effect transistors in a non-destructive, reversible, and predictable manner. We observe field-effect mobility modulation upon wrinkling and establish that it is controlled by the strain experienced by the insulator-semiconductor interface upon deformation. Finally, we propose a model based on plate bending to quantify the net strain at the insulator-semiconductor interface and predict the change in mobility. These contributions are the first to quantitatively correlate the crystal structure and the mechanical properties of OSCs, as well as the first to study electro-mechanical behavior in OSCs.

Download or read book Energy and Charge Transfer in Organic Semiconductors written by Kohzoh Masuda and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 187 pages. Available in PDF, EPUB and Kindle. Book excerpt: Great progress has been made in the field of ordinary semiconductor physics and associated technologies. For the time being, if we could use new materials such as organic semiconductors progress in electronics could be accelerated. Characteristics of organic semiconductors that are superior to others are: i) high photo-conductivity under irradiation along with low leakage current in the dark, ii) high sensitivity of the conductivity to various gases and to pressure. iii) possibility of using them in the amorphous state, iv) possibility of making devices of extremely small size, v) large variety of the materials, which makes suitable choice of material component easy. A possible future development is a highly conductive material which could be used for electric power transmission - and which might help solve some of the problems posed by transmission losses. The U.S.-Japan Seminar on Energy and Charge Transfer in Organic Semiconductors was held in Osaka Japan, 6-9 August, 1973. Completed results were summarized and the direction for the future was discussed. Information was exchanged quite freely and actively in a pleasant atmosphere. Many of the papers presented at the seminar are published here but unfortunately a few could not be included. It would give us great pleasure if this seminar could be one step in the further development of the research in this field.

Download or read book Electronic Processes in Organic Semiconductors written by Anna Köhler and published by John Wiley & Sons. This book was released on 2015-06-08 with total page 436 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first advanced textbook to provide a useful introduction in a brief, coherent and comprehensive way, with a focus on the fundamentals. After having read this book, students will be prepared to understand any of the many multi-authored books available in this field that discuss a particular aspect in more detail, and should also benefit from any of the textbooks in photochemistry or spectroscopy that concentrate on a particular mechanism. Based on a successful and well-proven lecture course given by one of the authors for many years, the book is clearly structured into four sections: electronic structure of organic semiconductors, charged and excited states in organic semiconductors, electronic and optical properties of organic semiconductors, and fundamentals of organic semiconductor devices.

Download or read book Studies of Electronic Transport in Novel Smectic and Discotic Liquid Crystalline Organic Semiconductors written by Naresh Man Shakya and published by . This book was released on 2010 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic semiconductors(OSs) have stirred huge commercial interest due to their potential applications in electronic and optoelectronic devices such as field effect transistors, photovoltaic cells, and organic light-emitting diodes. Major benefits of OSs over conventional semiconductors include mechanical flexibility, low temperature processing, very low cost, and ease of fabrication in large area electronic devices on plastic and paper substrates. Liquid crystals (LCs) are particularly interesting classes of OSs, both from the standpoints of fundamental physics and practical applications. Systems we studied include a thiophene-benzene-thiophene-based smectic (1,4-di-(5-n-tridecylthien-2-yl)-benzene). This material exhibited polaron band behavior with very impressive hole transport (> 0.1 cm^2/Vs with the smectic-F phase templating large domains of more ordered phases with very large mobilities. The mobilities are high enough to be of practical interest. Another project involved calamitic LCs with pyridine-thiophene-thiophene-pyridine cores (5, 5'-di-(alkyl-pyridin-yl)-2, 2' bithiophenes). We found both electron and hole mobilities to be strongly electric field dependent but very weakly dependent on temperature. Pyridine-based LCs often exhibit very high order smectic phases and are therefore of interest as OSs. However, the mobilities of these materials were found quite low, even in high-order phases. We were able to describe some part of our data using Basseler's theory of hopping conduction in disordered systems. We also studied charge transport in a triphenylene-based discotic LC (1-nitro-2, 3, 6, 7, 10, 11-hexakis (pentyloxy) triphenylene). This material showed strong temperature and field dependent hole mobilities described by disorder dominated one-dimensional hopping. Since the columnar phase exists over a wide range of temperatures, such photo-conducting materials may be very useful for applications in electronics. Finally, we developed a technique to measure charge carrier mobility in freely suspended films of LCs in high vacuum. Here, the external field can be coupled easily to the molecular order, no electrodes contact the sample, and extremely high voltages can be applied. Also, both hole and electron mobility (which depends on high purity and absence of oxygen), and samples with a very wide range of thickness may be studied.