Download or read book EFFETS DES CORRELATIONS SUR LES PROPRIETES ELECTRONIQUES ET OPTIQUES DES SEMICONDUCTEURS ET ISOLANTS written by BRICE.. ARNAUD and published by . This book was released on 2000 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: CE TRAVAIL DE THESE PORTE SUR LE CALCUL AB-INITIO DES EXCITATIONS ELECTRONIQUES DANS LES SEMICONDUCTEURS ET LES ISOLANTS. DANS UN PREMIER TEMPS, UNE APPROCHE BASEE SUR LE FORMALISME D'UNE METHODE DE CALCUL DE STRUCTURE ELECTRONIQUE ALL-ELECTRON (PAW) A ETE DEVELOPPEE POUR CALCULER LES ENERGIES DES QUASIPARTICULES DANS L'APPROXIMATION GW INTRODUITE PAR HEDIN. DANS CETTE APPROXIMATION, LA SELF-ENERGIE S'ECRIT COMME LE PRODUIT DE LA FONCTION DE GREEN A UNE PARTICULE G ET DE L'INTERACTION DYNAMIQUEMENT ECRANTEE W CALCULEE DANS L'APPROXIMATION DE LA PHASE ALEATOIRE (RPA). PARTANT D'UN CALCUL DE L'ETAT FONDAMENTAL DANS L'APPROXIMATION DE LA DENSITE LOCALE (LDA), LES VALEURS PROPRES LDA SONT CORRIGEES EN TRAITANT LA DIFFERENCE ENTRE LA SELF-ENERGIE ET LE POTENTIEL D'ECHANGE-CORRELATION COMME UNE PERTURBATION. LES ENERGIES DES QUASIPARTICULES OBTENUES SONT GENERALEMENT EN BON ACCORD AVEC LES EXPERIENCES DE PHOTOEMISSION ET DEPENDENT PEU DU SCHEMA UTILISE POUR DECOUPLER LES ELECTRONS DE COEUR ET DE VALENCE OU ENCORE DU MODELE DE PLASMONS-POLES UTILISE POUR REPRODUIRE LA DEPENDANCE EN FREQUENCE DE L'INTERACTION DYNAMIQUEMENT ECRANTEE W. LES SPECTRES DE QUASIPARTICULES SONT ALORS UTILISES POUR CALCULER LA PARTIE IMAGINAIRE DE LA FONCTION DIELECTRIQUE MACROSCOPIQUE INCLUANT LES EFFETS DE CHAMPS LOCAUX ET LES EFFETS EXCITONIQUES (ATTRACTION ELECTRON-TROU). L'APPROCHE STANDARD POUR INCLURE LES EFFETS EXCITONIQUES DANS LE CALCUL DE LA FONCTION DIELECTRIQUE CONSISTE A RESOUDRE L'EQUATION DITE DE BETHE-SALPETER. CETTE APPROCHE A ETE APPLIQUEE A DIFFERENTS SEMICONDUCTEURS (SI, INP, GAAS, ALAS, MG 2SI ET MG 2GE) ET ISOLANTS (C, LIF, LICL, NACL ET KCL) ET IL A ETE MONTRE QU'IL ETAIT CRUCIAL D'INCLURE L'ATTRACTION ELECTRON-TROU AFIN D'OBTENIR DES SPECTRES CALCULES EN BONNE ADEQUATION AVEC LES SPECTRES OPTIQUES EXPERIMENTAUX.

Download or read book ABSORPTION OPTIQUE DES SEMI CONDUCTEURS ET ISOLANTS written by STEFAN ROBERT.. ALBRECHT and published by . This book was released on 1999 with total page 173 pages. Available in PDF, EPUB and Kindle. Book excerpt: NOUS PRESENTONS UNE METHODE POUR INCLURE DES EFFETS DE LA SELF-ENERGIE ET DES EFFETS EXCITONIQUES DANS DES CALCULS AB INITIO DES SPECTRES D'ABSORPTION. CES CALCULS SONT EFFECTUES EN UTILISANT L'ETAT DE L'ART EN MATIERE DE PSEUDOPOTENTIELS AVEC UNE BASE D'ONDES PLANES. NOUS CALCULONS D'ABORD L'ETAT FONDAMENTAL EN UTILISANT LA THEORIE DE LA FONCTIONNELLE DE DENSITE (DFT) ET L'APPROXIMATION DE LA DENSITE LOCALE (LDA). NOUS DETERMINONS ENSUITE LE SPECTRE DE QUASIPARTICULES PHYSIQUES EN CORRIGEANT LE POTENTIEL D'ECHANGE-CORRELATION DU CALCUL DFT-LDA AVEC LA SELF-ENERGIE, POUR LAQUELLE NOUS EMPLOYONS L'APPROXIMATION GW DE HEDIN. L'INTERACTION ELECTRON-TROU EST TRAITEE PAR UNE EQUATION EFFECTIVE DE SCHRODINGER A DEUX PARTICULES, QUE NOUS AVONS DERIVEE DES EQUATIONS COUPLEES INTEGRALES DE HEDIN EN PASSANT PAR L'EQUATION FONDAMENTALE DE BETHE-SALPETER. LE KERNEL D'INTERACTION COMPORTE UNE INTERACTION ECRANTEE COULOMBIENNE ET DES EFFETS D'ECHANGE ELECTRON-TROU, QUI REPRESENTENT LA STRUCTURE MICROSCOPIQUE DU SYSTEME ET QUI SONT AUSSI APPELES LES EFFETS DE CHAMP LOCAL. NOUS OBTENONS LES ETATS PROPRES EXCITONIQUES PAR DIAGONALISATION. CELA PERMET UNE ANALYSE DETAILLEE DES PROPRIETES OPTIQUES. EN APPLIQUANT DES PROPRIETES DE SYMETRIE NOUS REDUISONS LA DIMENSION DE LA MATRICE HAMILTONIENNE A DEUX PARTICULES ET NOUS POUVONS MINIMISER LE COUT DU CALCUL. NOUS APPLIQUONS CETTE APPROCHE AU SILICIUM, AU DIAMANT, A L'OXYDE DE LITHIUM ET AU TETRAMERE DE SODIUM. UN BON ACCORD AVEC L'EXPERIENCE EST OBTENU POUR LES SPECTRES D'ABSORPTION OPTIQUE DE SI ET DU DIAMANT, LA CONSTANTE DIELECTRIQUE STATIQUE DU DIAMANT ET POUR LE SEUIL D'ABSORPTION OPTIQUE DE LI#2O, QUI EST DETERMINE PAR UN ETAT EXCITONIQUE LIE. NOUS DISCUTONS PLUSIEURS APPROXIMATIONS DE LA METHODE ET NOUS MONTRONS LE MELANGE TRES FORT DES TRANSITIONS DE PARTICULES INDEPENDANTES DANS UN ETAT EXCITE DE L'AGREGAT NA#4.

Download or read book EFFET DE LA STRUCTURE SUR LES PROPRIETES ELECTRIQUES ET OPTIQUES D OLIGOMERES CONJUGUES SEMI CONDUCTEURS APPLICATION A LA REALISATION DE TRANSISTORS A EFFET DE CHAMP ET DE DIODE ELECTROLUMINESCENTES written by RIADH.. HAJLAOUI and published by . This book was released on 1995 with total page 139 pages. Available in PDF, EPUB and Kindle. Book excerpt: L'ETUDE STRUCTURALE DES POLYMERES CONJUGUES MONTRE QUE LEUR DESORDRE MOLECULAIRE ET STRUCTURAL LIMITE LA QUALITE DE LEUR PROPRIETES ELECTRONIQUES, ET RESTREINT DONC LEUR EVENTUELLE APPLICATION A DES COMPOSANTS ELECTRONIQUES. L'UTILISATION DE SYSTEMES MOLECULAIRES STRUCTURALEMENT BIEN DEFINIS DEVRAIT PAR CONTRE PERMETTRE DE S'AFFRANCHIR DE CES DEFAUTS CHIMIQUES ET PHYSIQUES, ET D'AMELIORER AINSI L'EFFICACITE DU TRANSPORT DE CHARGES DANS CES MATERIAUX SEMI-CONDUCTEURS. CETTE DEMARCHE EST ILLUSTREE ICI PAR L'ETUDE DU SEXITHIOPHENE (6T) ET DE SES DERIVES SUBSTITUES. LA PREMIERE PARTIE EST CONSACREE A LA DESCRIPTION DES TECHNIQUES EXPERIMENTALES DE PREPARATION DES FILMS MINCES, PUIS DES COMPOSANTS ELECTRONIQUES REALISES A PARTIR DE CES SEMI-CONDUCTEURS ORGANIQUES, TELS QUE TRANSISTORS A EFFET DE CHAMP EN COUCHE MINCE ET DIODES ELECTROLUMINESCENTES. L'ETUDE DES PROPRIETES STRUCTURALES ET OPTIQUES A MIS EN EVIDENCE QUE CES FILMS SONT POLYCRISTALLINS, ET QUE L'ORIENTATION DES CHAINES MOLECULAIRES SUR LE SUBSTRAT EST CONTROLEE PAR LA NATURE DU SUBSTRAT, PAR LA TEMPERATURE DE DEPOT ET PAR LA POSITION DE SUBSTITUTION DE GROUPES ALKYLES SUR CETTE MOLECULE (6T). LES MESURES DE CONDUCTIVITE ET DE MOBILITE D'EFFET DE CHAMP DU SEXITHIOPHENE ET DE SES DERIVES MONTRENT QUE POUR LE , -DIHEXYL-SEXITHIOPHENE, LA CONDUCTIVITE PRESENTE UNE ANISOTROPIE IMPORTANTE, ALORS QUE B,B'-DIHEXYL-SEXITHIOPHENE SE COMPORTE COMME UN ISOLANT. LA TEMPERATURE DU SUBSTRAT UTILISEE LORS DU DEPOT DU FILM INFLUE SUR LA CONDUCTIVITE ET SUR LA MOBILITE DU SEXITHIOPHENE. LA MOBILITE PLUS FAIBLE DE 6T A TEMPERATURE AMBIANTE EST ATTRIBUEE A UNE PLUS GRANDE CONCENTRATION DE DEFAUTS TELS QUE JOINTS DE GRAINS. LES CARACTERISTIQUES STATIQUES DES DIODES ELECTROLUMINESCENTES, DONT LES COUCHES ACTIVES SONT CONSTITUEES DE SEXITHIOPHENE OU DE L'UN DE SES DERIVES, MONTRENT UN EFFET REDRESSEUR (SEMI-CONDUCTEUR DE TYPE-P). LES CARACTERISTIQUES TRANSITOIRES MONTRENT UN COURANT CAPACITIF BREF, SUIVI D'UN COURANT PERMANENT DONNANT LIEU A EMISSION LUMINEUSE. DANS UNE STRUCTURE BICOUCHE, ON REMARQUE UNE AUGMENTATION DE L'EMISSION LUMINEUSE ET UNE AUGMENTATION DU RENDEMENT D'ELECTROLUMINESCENCE PAR RAPPORT A LA STRUCTURE MONOCOUCHE. L'INTENSITE DU SPECTRE D'ELECTROLUMINESCENCE ENREGISTRE POUR LA STRUCTURE BICOUCHE DANS LA GAMME 500-700 NM MONTRE QU'EN BAISSANT LA TEMPERATURE L'EMISSION AUGMENTE, CECI EST ATTRIBUE A UNE DIMINUTION DU RENDEMENT DES TRANSITIONS NON RADIATIVES

Download or read book ICREEC 2019 written by Ahmed Belasri and published by Springer Nature. This book was released on 2020-06-10 with total page 659 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book highlights peer reviewed articles from the 1st International Conference on Renewable Energy and Energy Conversion, ICREEC 2019, held at Oran in Algeria. It presents recent advances, brings together researchers and professionals in the area and presents a platform to exchange ideas and establish opportunities for a sustainable future. Topics covered in this proceedings, but not limited to, are photovoltaic systems, bioenergy, laser and plasma technology, fluid and flow for energy, software for energy and impact of energy on the environment.

Download or read book Graphene written by Wonbong Choi and published by CRC Press. This book was released on 2016-04-19 with total page 374 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since the late 20th century, graphene-a one-atom-thick planar sheet of sp2-bonded carbon atoms densely packed in a honeycomb crystal lattice-has garnered appreciable attention as a potential next-generation electronic material due to its exceptional properties. These properties include high current density, ballistic transport, chemical inertness,

Download or read book Innovate Bristol written by Sven Boermeester and published by . This book was released on 2019-12 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Innovate Bristol highlights and celebrates those companies and individuals that are actively working at building a better tomorrow for all. Innovation Ecosystems thrive through the involvement and support of companies and individuals from all industries, which is why the Innovate series not only focuses on the innovators but also those people whom the Innovation Ecosystem, would not be able to thrive without.

Download or read book Terahertz Techniques written by Erik Bründermann and published by Springer. This book was released on 2012-04-18 with total page 401 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research and development in the terahertz portion of the electromagnetic spectrum has expanded very rapidly during the past fifteen years due to major advances in sources, detectors and instrumentation. Many scientists and engineers are entering the field and this volume offers a comprehensive and integrated treatment of all aspects of terahertz technology. The three authors, who have been active researchers in this region over a number of years, have designed Terahertz Techniques to be both a general introduction to the subject and a definitive reference resource for all those involved in this exciting research area.

Download or read book Optical Properties Of Graphene written by Rolf Binder and published by World Scientific. This book was released on 2016-11-11 with total page 517 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive state-of-the-art overview of the optical properties of graphene. During the past decade, graphene, the most ideal and thinnest of all two-dimensional materials, has become one of the most widely studied materials. Its unique properties hold great promise to revolutionize many electronic, optical and opto-electronic devices. The book contains an introductory tutorial and 13 chapters written by experts in areas ranging from fundamental quantum mechanical properties to opto-electronic device applications of graphene.

Download or read book Handbook of Magnetic Materials written by K.H.J. Buschow and published by Gulf Professional Publishing. This book was released on 2001 with total page 606 pages. Available in PDF, EPUB and Kindle. Book excerpt: Volume 13 of the Handbook of Magnetic Materials, as the preceding volumes, has a dual purpose. As a textbook it is intended to be of assistance to those who wish to be introduced to a given topic in the field of magnetism without the need to read the vast amount of literature published. As a work of reference it is intended for scientists active in magnetism research. To this dual purpose, Volume 13 of the Handbook is composed of topical review articles written by leading authorities. In each of these articles an extensive description is given in graphical as well as in tabular form, much emphasis being placed on the discussion of the experimental material in the framework of physics, chemistry and material science. In Chapter 1 of this volume a general review of the experimental work on interlayer exchange coupling is presented along with a discussion of the current understanding of this field. There exists an extensive amount of scientific efforts devoted to 4f and 5f systems, including experimental and theoretical, as well as basic and applied research. Chapter 2 aims at reviewing a part of these efforts from the viewpoint of microscopic theory. Special attention is paid to the many new developments in the field. One of the intentions is to bring to the fore the darker areas of DFT theory applications. A review of novel experimental results and first-principle energy-band calculations of MOKE spectra will be presented in Chapter 3. Conventional co-operative phenomena, such as long-range order and elementary excitation, have realisations in nonmagnetic situations. This applies also to the phenomena of geometrical frustration. In Chapter 4 this topic is addressed by developing the basic principles underlying the magnetic phenomena.

Download or read book Acta electronica written by and published by . This book was released on 1983 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Physics of Magnetism and Magnetic Materials written by K.H.J Buschow and published by Springer Science & Business Media. This book was released on 2007-05-08 with total page 175 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this book, the fundamentals of magnetism are treated, starting at an introductory level. The origin of magnetic moments, the response to an applied magnetic field, and the various interactions giving rise to different types of magnetic ordering in solids are presented and many examples are given. Crystalline-electric-field effects are treated at a level that is sufficient to provide the basic knowledge necessary in understanding the properties of materials in which these effects play a role. Itinerant-electron magnetism is presented on a similar basis. Particular attention has been given to magnetocrystalline magnetic anisotropy and the magnetocaloric effect. Also, the usual techniques for magnetic measurements are presented. About half of the book is devoted to magnetic materials and the properties that make them suitable for numerous applications. The state of the art is presented of permanent magnets, high-density recording materials, soft-magnetic materials, Invar alloys and magnetostrictive materials. Many references are given.

Download or read book Iontronics written by Janelle Leger and published by CRC Press. This book was released on 2016-04-19 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt: With contributions from a community of experts, the book focuses on the use of ionic functions to define the principle of operation in polymer devices. It begins by reviewing the scientific understanding and important scientific discoveries made on the electrochemistry of conjugated polymers. It examines the known effects of ion incorporation, including the theory and modulation of electrochemistry in polymer films, and it explores the coupling of electronic and ionic transport in polymer films.

Download or read book Supra materials Nanoarchitectonics written by Katsuhiko Ariga and published by William Andrew. This book was released on 2016-10-07 with total page 348 pages. Available in PDF, EPUB and Kindle. Book excerpt: Supra-materials Nanoarchitectonics provides the latest information on design at the nanoscale, presenting a range of the new challenges that arise as the manipulation techniques that work at the macro- and micro-scale do not work at the nanoscale. The term nanoarchitectonics, coined by Japan's National Institute for Materials Science (NIMS), describes the organized interactions required at the nanoscale, replacing the traditional structure-building approach used in materials design. Nanoarchitectonics approaches material design via a profound understanding of the interactions between individual nanostructures and their organization. As the nanoarchitectonics paradigm fits well with the discipline of supramolecular chemistry, this book brings together these two approaches to demonstrate the potential of supramolecular nanoarchitectonics in the development of new materials, both at the nano- and macro-scale. - Written by the team that coined the term nanoarchitectonics, providing a detailed explanation of the approach and techniques of supramolecular nanoarchitectonics - Demystifies materials design via organized interactions at the nanoscale - Explains this new paradigm via practical scientific techniques

Download or read book III Nitride Semiconductors written by M.O. Manasreh and published by Elsevier. This book was released on 2000-12-06 with total page 463 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research advances in III-nitride semiconductor materials and device have led to an exponential increase in activity directed towards electronic and optoelectronic applications. There is also great scientific interest in this class of materials because they appear to form the first semiconductor system in which extended defects do not severely affect the optical properties of devices. The volume consists of chapters written by a number of leading researchers in nitride materials and device technology with the emphasis on the dopants incorporations, impurities identifications, defects engineering, defects characterization, ion implantation, irradiation-induced defects, residual stress, structural defects and phonon confinement. This unique volume provides a comprehensive review and introduction of defects and structural properties of GaN and related compounds for newcomers to the field and stimulus to further advances for experienced researchers. Given the current level of interest and research activity directed towards nitride materials and devices, the publication of the volume is particularly timely. Early pioneering work by Pankove and co-workers in the 1970s yielded a metal-insulator-semiconductor GaN light-emitting diode (LED), but the difficulty of producing p-type GaN precluded much further effort. The current level of activity in nitride semiconductors was inspired largely by the results of Akasaki and co-workers and of Nakamura and co-workers in the late 1980s and early 1990s in the development of p-type doping in GaN and the demonstration of nitride-based LEDs at visible wavelengths. These advances were followed by the successful fabrication and commercialization of nitride blue laser diodes by Nakamura et al at Nichia. The chapters contained in this volume constitutes a mere sampling of the broad range of research on nitride semiconductor materials and defect issues currently being pursued in academic, government, and industrial laboratories worldwide.

Download or read book Electronic transitions and correlation effects written by Johan Jönsson and published by Linköping University Electronic Press. This book was released on 2020-03-17 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt: Macroscopic properties of real materials, such as conductivity, magneticproperties, crystal structure parameters, etc. are closely related or evendetermined by the configuration of their electrons, characterized by electronicstructure. By changing the conditions, e.g, pressure, temperature, magnetic/electric field, chemical doping, etc. one can modify the electronic structure ofsolids and therefore induce a phase transition(s) between different electronic andmagnetic states. One famous example is a Mott metal-to-insulator phase transition,at which a material undergoes a significant, often many orders of magnitude, changeof conductivity caused by the interplay between itineracy and localization of thecarriers. Electronic topological transitions (ETT) involvechanges in the topology of a metal's Fermi surface. This thesis investigates theeffect of such electronic transitions in various materials, ranging from pureelements to complex compounds. To describe the interplay between electronic transitionsand properties of real materials,different state-of-the-art computational methods are used. The densityfunctional theory(DFT), as well as the DFT + U method, is used to calculatestructural properties. The validity of recently introduced exchange-correlationfunctionals, such as the strongly constrained and appropriately normed (SCAN)functional, is also assessed for magnetic elements. In order toinclude dynamical effects of electron interactions we use the DFT + dynamical meanfield theory (DFT + DMFT) method. Experiments in hcp-Os have reported peculiarities in the ratio betweenlattice parameters at high pressure. Previous calculations have suggested these transitions maybe related to ETTs and even crossings of core levels at ultra high pressure. Inthis thesis it is shownthat the crossing of core levels is a general feature of heavy transitionmetals. Experiments have therefore been performed to look for indications ofthis transition in Ir using X-ray absorption spectroscopy. In NiO, strongrepulsion between electrons leads to a Mott insulating state at ambientconditions. It has long been predicted that high pressure will lead to aninsulator-to-metal transition. This has been suggested to be accompanied by aloss of magnetic order, and a structural phase transition. In collaboration withexperimentalists we look for thistransition by investigating the X-ray absorption spectra as well as themagnetic hyperfine field. We find no evidence of a Mott transition up to 280GPa. In the Mott insulator TiPO4, application of external pressure has beensuggested to lead to a spin-Peierls transition at room temperature. Weinvestigate the dimerisation and the magnetic structure of TiPO4 at high pressure.As pressure is increased further, TiPO4 goes through a metal to insulatortransition before an eventual crystallographic phase transition. Remarkably, thenew high pressure phases are found to be insulators; the Mott insulating stateis restored. MAX phases are layered materials that combinemetallic and ceramic properties and feature layers of M-metal and X-C or N atomsinterconnected by A-group atoms. Magnetic MAX-phases with their low dimensionalmagnetism are promising candidates for applications in e.g., spintronics.The validity of various theoretical approaches are discussed in connection tothe magnetic MAX-phase Mn2GaC. Using DFT and DFT + DMFT we consider the hightemperature paramagnetic state, and whether the magnetic moments are formed bylocalized or itinerant electrons. Ett materials makroskopiska egenskaper, såsom ledningsförmåga, magnetiska egenskaper, kristallstrukturparametrar, etc. är relaterade till, eller till och med bestämda av elektronernas konfiguration, vilken karakteriseras av elektronstrukturen. Genom att ändra förhållandena, till exempel via tryck, temperatur, magnetiska och/eller elektriska fält, dopning, etc. är det möjligt att modifiera elektronstrukturen hos ett material, och därigenom inducera fasövergångar mellan olika magnetiska och elektron-tillstånd. Mott metall-till-isolator övergången är ett berömt exempel på en fasövergång, då ett material genomgår en omfattande, ofta flera tiopotenser, förändring i ledningsförmåga, orsakad av samspelet mellan ambulerande och lokaliserade laddningsbärare. Vid en elektronisk-topologisk övergång (eng. electronic topological transition, ETT) sker förändringar i elektronernas energifördelning vilket modifierar materialets Fermi-yta. I den här avhandlingen undersöks dylika övergångar i olika material, från rena grundämnen till komplicerade föreningar. Flera olika toppmoderna beräkningsmetoder används för att redogöra för samspelet mellan elektroniska fasövergångar och egenskaper hos riktiga material. Täthetsfunktionalterori (eng. density functional theory, DFT), samt DFT + U, har används för att beräkna strukturella egenskaper. Lämplighetsgraden i att använda nyligen publicerade exchangecorrelation- funktionaler, såsom SCAN (eng. strongly constrained and appropriately normed), för att beskriva magnetiska grundämnen undersöks även. För att inkludera dynamiska elektronkorrelationer använder vi metoden DFT + dynamisk medelfältteori (eng. dynamical mean field theory, DMFT). Experiment utförda på hcp-Os vid högt tryck visar underliga hopp i kvoten mellan gitterparametrar. Tidigare beräkningar har indikerat att dessa övergångar kan vara relaterade till elektronisk-topologiska övergångar och korsande av kärntillstånd. I den här avhandlingen visas också att korsning av kärntillstånden är en generell egenskap hos tunga övergångsmetaller. Därför utförs röntgenabsorptionsexperiment på Ir för att leta efter tecken på denna typ av övergång. Övergångsmetalloxiden NiO har sedan länge förutspåtts genomgå en isolator till metall Mott-övergång. Det har föreslagits att denna övergång sker vid höga tryck i samband med att materialets magnetiska ordning försvinner och en strukturell övergång sker. I samarbete med experimentalister letar vi efter denna övergång genom att studera röntgenabsorptionsspektra och det magnetiska hyperfina fältet. Vi ser inga indikationer på en Mott-övegång, upp till ett tryck på 280 GPa. Det har föreslagits att Mott-isolatorn TiPO4 genomgår en så kallad spin-Peierls-övergång, vid rumstemperatur, när tryck appliceras. Vi undersöker dimeriseringen och den magnetiska strukturen i TiPO4 som funktion av tryck. Vid höga tryck genomgår TiPO4 ytterligare övergångar, från en isolerande till en metallisk fas för att slutligen genomgå en strukturell övergång. De nya högtrycksfaserna visar sig anmärkningsvärt vara Mott-isolatorer. MAX-faser är en grupp material med specifik kristallstruktur, som kombinerar egenskaper från keramiska material och metaller. En MAX-fas består av lager av M –metall-atomer – och X – kol- eller kväveatomer – vilka sammanbinds av atomer från grupp A. Magnetiska MAX-faser som visar magnetiska egenskaper, liknande de för lågdimensionella material, är lovande kandidater för applikation inom exempelvis spinntronik. Den här avhandlingen undersöker lämplighetsgraden i att använda diverse teoretiska metoder för att beskriva magnetiska MAX-faser. Med hjälp av DFT och DFT + DMFT undersöker vi den paramagnetiska högtemperaturfasen och huruvida de magnetiska momenten bildas av lokaliserade eller ambulerande elektroner.

Download or read book III nitride Devices and Nanoengineering written by Zhe Chuan Feng and published by World Scientific. This book was released on 2008 with total page 477 pages. Available in PDF, EPUB and Kindle. Book excerpt: Devices, nanoscale science and technologies based on GaN and related materials, have achieved great developments in recent years. New GaN-based devices such as UV detectors, fast p-HEMT and microwave devices are developed far more superior than other semiconductor materials-based devices.Written by renowned experts, the review chapters in this book cover the most important topics and achievements in recent years, discuss progress made by different groups, and suggest future directions. Each chapter also describes the basis of theory and experiment.This book is an invaluable resource for device design and processing engineers, material growers and evaluators, postgraduates and scientists as well as newcomers in the GaN field.

Download or read book Handbook of Nanoscopy written by Gustaaf van Tendeloo and published by John Wiley & Sons. This book was released on 2012-12-21 with total page 1484 pages. Available in PDF, EPUB and Kindle. Book excerpt: This completely revised successor to the Handbook of Microscopy supplies in-depth coverage of all imaging technologies from the optical to the electron and scanning techniques. Adopting a twofold approach, the book firstly presents the various technologies as such, before going on to cover the materials class by class, analyzing how the different imaging methods can be successfully applied. It covers the latest developments in techniques, such as in-situ TEM, 3D imaging in TEM and SEM, as well as a broad range of material types, including metals, alloys, ceramics, polymers, semiconductors, minerals, quasicrystals, amorphous solids, among others. The volumes are divided between methods and applications, making this both a reliable reference and handbook for chemists, physicists, biologists, materials scientists and engineers, as well as graduate students and their lecturers.