Download or read book First Principles Investigations of Electronic Structure and Transport Properties of Graphitic Structures and Single Molecular Junctions written by Jonathan R. Owens and published by . This book was released on 2014 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electronic Structure and Transport in Solids from First Principles written by Jamal Ibrahim Mustafa and published by . This book was released on 2016 with total page 125 pages. Available in PDF, EPUB and Kindle. Book excerpt: The focus of this dissertation is the determination of the electronic structure and trans- port properties of solids. We first review some of the theory and computational methodology used in the calculation of electronic structure and materials properties. Throughout the dis- sertation, we make extensive use of state-of-the-art software packages that implement den- sity functional theory, density functional perturbation theory, and the GW approximation, in addition to specialized methods for interpolating matrix elements for extremely accurate results. The first application of the computational framework introduced is the determi- nation of band offsets in semiconductor heterojunctions using a theory of quantum dipoles at the interface. This method is applied to the case of heterojunction formed between a new metastable phase of silicon, with a rhombohedral structure, and cubic silicon. Next, we introduce a novel method for the construction of localized Wannier functions, which we have named the optimized projection functions method (OPFM). We illustrate the method on a variety of systems and find that it can reliably construct localized Wannier functions with minimal user intervention. We further develop the OPFM to investigate a class of materials called topological insulators, which are insulating in the bulk but have conductive surface states. These properties are a result of a nontrivial topology in their band structure, which has interesting effects on the character of the Wannier functions. In the last sections of the main text, the noble metals are studied in great detail, including their electronic properties and carrier dynamics. In particular, we investigate, the Fermi surface properties of the no- ble metals, specifically electron-phonon scattering lifetimes, and subsequently the transport properties determined by carriers on the Fermi surface. To achieve this, a novel sampling technique is developed, with wide applicability to transport calculations. Additionally, the generation and transport of hot carriers is studied extensively. The distribution of hot carri- ers generated from the decay of plasmons is explored over a range of energy, and the transport properties, particularly the lifetimes and mean-free-paths, of the hot carriers are determined. Lastly, appendices detailing the implementation of the algorithms developed in the work is presented, along with a useful derivation of the electron-plasmon matrix elements.

Download or read book Molecular Electronics written by Juan Carlos Cuevas and published by World Scientific. This book was released on 2010 with total page 724 pages. Available in PDF, EPUB and Kindle. Book excerpt: 1. The birth of molecular electronics. 1.1. Why molecular electronics?. 1.2. A brief history of molecular electronics. 1.3. Scope and structure of the book -- 2. Fabrication of metallic atomic-size contacts. 2.1. Introduction. 2.2. Techniques involving the scanning electron microscope (STM). 2.3. Methods using atomic force microscopes (AFM). 2.4. Contacts between macroscopic wires. 2.5. Transmission electron microscope. 2.6. Mechanically controllable break-junctions (MCBJ). 2.7. Electromigration technique. 2.8. Electrochemical methods. 2.9. Recent developments. 2.10. Electronic transport measurements. 2.11. Exercises -- 3. Contacting single molecules: Experimental techniques. 3.1. Introduction. 3.2. Molecules for molecular electronics. 3.3. Deposition of molecules. 3.4. Contacting single molecules. 3.5. Contacting molecular ensembles. 3.6. Exercises -- 4. The scattering approach to phase-coherent transport in nanocontacts. 4.1. Introduction. 4.2. From mesoscopic conductors to atomic-scale junctions. 4.3. Conductance is transmission : heuristic derivation of the Landauer formula. 4.4. Penetration of a potential barrier : tunnel effect. 4.5. The scattering matrix. 4.6. Multichannel Landauer formula. 4.7. Shot noise. 4.8. Thermal transport and thermoelectric phenomena. 4.9. Limitations of the scattering approach. 4.10. Exercises -- 5. Introduction to Green's function techniques for systems in equilibrium. 5.1. The Schrodinger and Heisenberg pictures. 5.2. Green's functions of a noninteracting electron system. 5.3. Application to tight-binding Hamiltonians. 5.4. Green's functions in time domain. 5.5. Exercises -- 6. Green's functions and Feynman diagrams. 6.1. The interaction picture. 6.2. The time-evolution operator. 6.3. Perturbative expansion of causal Green's functions. 6.4. Wick's theorem. 6.5. Feynman diagrams. 6.6. Feynman diagrams in energy space. 6.7. Electronic self-energy and Dyson's equation. 6.8. Self-consistent diagrammatic theory : the Hartree-Fock approximation. 6.9. The Anderson model and the Kondo effect. 6.10. Final remarks. 6.11. Exercises -- 7. Nonequilibrium Green's functions formalism. 7.1. The Keldysh formalism. 7.2. Diagrammatic expansion in the Keldysh formalism. 7.3. Basic relations and equations in the Keldysh formalism. 7.4. Application of Keldysh formalism to simple transport problems. 7.5. Exercises -- 8. Formulas of the electrical current : exploiting the Keldysh formalism. 8.1. Elastic current : microscopic derivation of the Landauer formula. 8.2. Current through an interacting atomic-scale junction. 8.3. Time-dependent transport in nanoscale junctions. 8.4. Exercises -- 9. Electronic structure I: Tight-binding approach. 9.1. Basics of the tight-binding approach. 9.2. The extended Huckel method. 9.3. Matrix elements in solid state approaches. 9.4. Slater-Koster two-center approximation. 9.5. Some illustrative examples. 9.6. The NRL tight-binding method. 9.7. The tight-binding approach in molecular electronics. 9.8. Exercises -- 10. Electronic structure II : density functional theory. 10.1. Elementary quantum mechanics. 10.2. Early density functional theories. 10.3. The Hohenberg-Kohn theorems. 10.4. The Kohn-Sham approach. 10.5. The exchange-correlation functionals. 10.6. The basic machinery of DFT. 10.7. DFT performance. 10.8. DFT in molecular electronics. 10.9. Exercises -- 11. The conductance of a single atom. 11.1. Landauer approach to conductance: brief reminder. 11.2. Conductance of atomic-scale contacts. 11.3. Conductance histograms. 11.4. Determining the conduction channels. 11.5. The chemical nature of the conduction channels of oneatom contacts. 11.6. Some further issues. 11.7. Conductance fluctuations. 11.8. Atomic chains : parity oscillations in the conductance. 11.9. Concluding remarks. 11.10. Exercises -- 12. Spin-dependent transport in ferromagnetic atomic contacts. 12.1. Conductance of ferromagnetic atomic contacts. 12.2. Magnetoresistance of ferromagnetic atomic contacts. 12.3. Anisotropic magnetoresistance in atomic contacts. 12.4. Concluding remarks and open problems -- 13. Coherent transport through molecular junctions I : basic concepts. 13.1. Identifying the transport mechanism in single-molecule junctions. 13.2. Some lessons from the resonant tunneling model. 13.3. A two-level model. 13.4. Length dependence of the conductance. 13.5. Role of conjugation in [symbol]-electron systems. 13.6. Fano resonances. 13.7. Negative differential resistance. 13.8. Final remarks. 13.9. Exercises -- 14. Coherent transport through molecular junctions II : test-bed molecules. 14.1. Coherent transport through some test-bed molecules. 14.2. Metal-molecule contact : the role of anchoring groups. 14.3. Tuning chemically the conductance : the role of side-groups. 14.4. Controlled STM-based single-molecule experiments. 14.5. Conclusions and open problems -- 15. Single-molecule transistors : Coulomb blockade and Kondo physics. 15.1. Introduction. 15.2. Charging effects in transport through nanoscale devices. 15.3. Single-molecule three-terminal devices. 15.4. Coulomb blockade theory : constant interaction model. 15.5. Towards a theory of Coulomb blockade in molecular transistors. 15.6. Intermediate coupling : cotunneling and Kondo effect. 15.7. Single-molecule transistors : experimental results. 15.8. Exercises -- 16. Vibrationally-induced inelastic current I : experiment. 16.1. Introduction. 16.2. Inelastic electron tunneling spectroscopy (IETS). 16.3. Highly conductive junctions : point-contact spectroscopy (PCS). 16.4. Crossover between PCS and IETS. 16.5. Resonant inelastic electron tunneling spectroscopy (RIETS). 16.6. Summary of vibrational signatures -- 17. Vibrationally-induced inelastic current II : theory. 17.1. Weak electron-phonon coupling regime. 17.2. Intermediate electron-phonon coupling regime. 17.3. Strong electron-phonon coupling regime. 17.4. Concluding remarks and open problems. 17.5. Exercises -- 18. The hopping regime and transport through DNA molecules. 18.1. Signatures of the hopping regime. 18.2. Hopping transport in molecular junctions : experimental examples. 18.3. DNA-based molecular junctions. 18.4. Exercises -- 19. Beyond electrical conductance : shot noise and thermal transport. 19.1. Shot noise in atomic and molecular junctions. 19.2. Heating and heat conduction. 19.3. Thermoelectricity in molecular junctions -- 20. Optical properties of current-carrying molecular junctions. 20.1. Surface-enhanced Raman spectroscopy of molecular junctions. 20.2. Transport mechanisms in irradiated molecular junctions. 20.3. Theory of photon-assisted tunneling. 20.4. Experiments on radiation-induced transport in atomic and molecular junctions. 20.5. Resonant current amplification and other transport phenomena in ac driven molecular junctions. 20.6. Fluorescence from current-carrying molecular junctions. 20.7. Molecular optoelectronic devices. 20.8. Final remarks. 20.9. Exercises -- 21. What is missing in this book?

Download or read book Transport Properties of Molecular Junctions written by Natalya A. Zimbovskaya and published by Springer. This book was released on 2013-09-07 with total page 338 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive overview of the physical mechanisms that control electron transport and the characteristics of metal-molecule-metal (MMM) junctions. As far as possible, methods and formalisms presented elsewhere to analyze electron transport through molecules are avoided. This title introduces basic concepts--a description of the electron transport through molecular junctions—and briefly describes relevant experimental methods. Theoretical methods commonly used to analyze the electron transport through molecules are presented. Various effects that manifest in the electron transport through MMMs, as well as the basics of density-functional theory and its applications to electronic structure calculations in molecules are presented. Nanoelectronic applications of molecular junctions and similar systems are discussed as well. Molecular electronics is a diverse and rapidly growing field. Transport Properties of Molecular Junctions presents an up-to-date survey of the field suitable for researchers and professionals.

Download or read book Electrons in Molecules written by Jean-Pierre Launay and published by Oxford University Press, USA. This book was released on 2014 with total page 511 pages. Available in PDF, EPUB and Kindle. Book excerpt: The purpose of this book is to provide the reader with essential keys to a unified understanding of the rapidly expanding field of molecular materials and devices: electronic structures and bonding, magnetic, electrical and photo-physical properties, and the mastering of electrons in molecular electronics. Chemists will discover how basic quantum concepts allow us to understand the relations between structures, electronic structures, and properties of molecular entities and assemblies, and to design new molecules and materials. Physicists and engineers will realize how the molecular world fits in with their need for systems flexible enough to check theories or provide original solutions to exciting new scientific and technological challenges. The non-specialist will find out how molecules behave in electronics at the most minute, sub-nanosize level. The comprehensive overview provided in this book is unique and will benefit undergraduate and graduate students in chemistry, materials science, and engineering, as well as researchers wanting a simple introduction to the world of molecular materials.

Download or read book First Principles Electronic Structure and Transport Calculations in Materials with Defects and Impurities written by Manoj K. Srivastava and published by . This book was released on 2012 with total page 99 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present electronic structure and electron transport studies of materials with defects and impurities using density-functional theory. We develop a plane wave transport method based on density-functional theory for low symmetry nonorthogonal lattices. This is achieved by generalizing Choi and Ihm's algorithm for high symmetry lattices which requires the transport direction along a lattice vector that must be perpendicular to the basal plane formed by two other lattice vectors. This restriction is overcome in our method, allowing solutions to problems in which the transport direction is not along any lattice vectors. We apply our generalized transport method to calculate interface resistivity of grain boundaries in copper. Other than surface defects, we also study point defects such as single atom vacancy and impurities. Using electronic structure methods, we investigate adsorption of gold and iron clusters on perfect and defected graphene with a single vacancy. We focus on the size dependence of the electronic properties such as binding energy, charge transfer, magnetization, and density of states. Perfect graphene is found to be doped for Au clusters with an odd number of atoms and undoped with an even number of atoms. An odd-even oscillation in the magnetic moments is observed in Au-perfect as well as defected graphene system. While Fen clusters remain to be magnetic for all n, the spin of a single Fe atom on a defect site is very small due to a covalent bonding to C atoms.

Download or read book Electronic Structure written by and published by Elsevier. This book was released on 2000-07-19 with total page 1071 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is the second volume in the Handbook of Surface Science series and deals with aspects of the electronic structure of surfaces as investigated by means of the experimental and theoretical methods of physics. The importance of understanding surface phenomena stems from the fact that for many physical and chemical phenomena, the surface plays a key role: in electronic, magnetic, and optical devices, in heterogenous catalysis, in epitaxial growth, and the application of protective coatings, for example. Therefore a better understanding and, ultimately, a predictive description of surface and interface properties is vital for the progress of modern technology. An investigation of surface electronic structure is also central to our understanding of all aspects of surfaces from a fundamental point of view. The chapters presented here review the goals achieved in the field and map out the challenges ahead, both in experiment and theory.

Download or read book Handbook of Nanophysics written by Klaus D. Sattler and published by CRC Press. This book was released on 2010-09-17 with total page 770 pages. Available in PDF, EPUB and Kindle. Book excerpt: Intensive research on fullerenes, nanoparticles, and quantum dots in the 1990s led to interest in nanotubes and nanowires in subsequent years. Handbook of Nanophysics: Nanotubes and Nanowires focuses on the fundamental physics and latest applications of these important nanoscale materials and structures. Each peer-reviewed chapter contains a broad-

Download or read book Molecular Electronics An Introduction To Theory And Experiment 2nd Edition written by Elke Scheer and published by World Scientific. This book was released on 2017-05-19 with total page 846 pages. Available in PDF, EPUB and Kindle. Book excerpt: Molecular Electronics is self-contained and unified in its presentation. It can be used as a textbook on nanoelectronics by graduate students and advanced undergraduates studying physics and chemistry. In addition, included in this new edition are previously unpublished material that will help researchers gain a deeper understanding into the basic concepts involved in the field of molecular electronics.

Download or read book Electronic Structure And Chemical Bonding written by Dunod Editeur and published by World Scientific. This book was released on 1996-09-20 with total page 309 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book addresses the problem of teaching the Electronic Structure and Chemical Bonding of atoms and molecules to high school and university students. It presents the outcomes of thorough investigations of some teaching methods as well as an unconventional didactical approach which were developed during a seminar for further training organized by the University of Bordeaux I for teachers of the physical sciences.The text is the result of a collective effort by eleven scientists and teachers: physicists and chemists doing research at the university or at the CRNS, university professors, and science teachers at high-school or university level.While remaining wide open to the latest discoveries of science, the text also offers a large number of problems along with their solutions and is illustrated by several pedagogic suggestions. It is intended for the use of teachers and students of physics, chemistry, and of the physical sciences in general.

Download or read book Theoretical Investigations of Molecular Wires written by Julio Leopoldo Palma and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This molecule has two stable conformations (cis and trans) in its electronic ground state, with considerable differences in their conductance. The electron transport properties were calculated using first-principles methods combining non-equilibrium Green's function (NEGF) techniques with density functional theory (DFT). For the azobenzene studies, we included electron-donating groups and electron-withdrawing groups in meta- and ortho- positions with respect to the azo group. The results showed that the molecular structure is crucial in optimizing the electron transport properties of chemical structures, and that the transport properties in electronic devices at the molecular level can be manipulated, enhanced or suppressed by a careful consideration of the effects of chemical modification.

Download or read book Electronic Structure and Chemical Bonding written by J. R. Lalanne and published by World Scientific. This book was released on 1996 with total page 320 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book addresses the problem of teaching the Electronic Structure and Chemical Bonding of atoms and molecules to high school and university students. It presents the outcomes of thorough investigations of some teaching methods as well as an unconventional didactical approach which were developed during a seminar for further training organized by the University of Bordeaux I for teachers of the physical sciences.The text is the result of a collective effort by eleven scientists and teachers: physicists and chemists doing research at the university or at the CRNS, university professors, and science teachers at high-school or university level.While remaining wide open to the latest discoveries of science, the text also offers a large number of problems along with their solutions and is illustrated by several pedagogic suggestions. It is intended for the use of teachers and students of physics, chemistry, and of the physical sciences in general.

Download or read book Applications of Electronic Structure Theory written by Henry Schaefer and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 470 pages. Available in PDF, EPUB and Kindle. Book excerpt: These two volumes deal with the quantum theory of the electronic structure of ab initio is the notion that approximate solutions molecules. Implicit in the term of Schrodinger's equation are sought "from the beginning," i. e. , without recourse to experimental data. From a more pragmatic viewpoint, the distin guishing feature of ab initio theory is usually the fact that no approximations are involved in the evaluation of the required molecular integrals. Consistent with current activity in the field, the first of these two volumes contains chapters dealing with methods per se, while the second concerns the application of these methods to problems of chemical interest. In a sense, the motivation for these volumes has been the spectacular recent success of ab initio theory in resolving important chemical questions. However, these applications have only become possible through the less visible but equally important efforts of those developing new theoretical and computational methods and models. Henry F. Schaefer vii Contents Contents of Volume 3 xv Chapter 1. A Priori Geometry Predictions 1. A. Pople 1. Introduction . . . . . . . . . . . . . . . . . . . 1 2. Equilibrium Geometries by Hartree-Fock Theory 2 2. 1. Restricted and Unrestricted Hartree-Fock Theories 2 2. 2. Basis Sets for Hartree-Fock Studies . . . . . 4 2. 3. Hartree-Fock Structures for Small Molecules . 6 2. 4. Hartree-Fock Structures for Larger Molecules 12 3. Equilibrium Geometries with Correlation . . 18 4. Predictive Structures for Radicals and Cations 20 5. Conclusions 23 References 24 Chapter 2. Barriers to Rotation and Inversion Philip W. Payne and Leland C.

Download or read book First principles Studies of Carbon Nanostructures and Spin phonon and Electron phonon Coupling in Solids written by Kevin Timothy Chan and published by . This book was released on 2012 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work presents first-principles theoretical studies on two topics of condensed matter physics. The first topic is the adsorption of metal adatoms on graphene. Graphene, a two-dimensional material made of carbon atoms arranged in a honeycomb lattice, has many outstanding properties that can be enhanced or tailored by adsorbing adatoms on its surface. The second topic involves the coupling of spins or electrons to phonons in a solid. The interaction between different degrees of freedom of a material complicates the study of its properties but also leads to fascinating phenomena, such as superconductivity, and potential device applications. This dissertation is organized into six chapters: · In Chapter One, we give an overview of this work and review the first-principles theory and methods used in our studies. · Chapter Two focuses on structural, energetic, and electronic properties for a variety of adatom species adsorbed on the graphene surface. We classify different species as having mostly ionic or covalent character of bonding to graphene. For ionically bonded adatoms, charge transfer between the adatom and graphene is signficant. We find general trends relating the surface dipole moment, work function, and atomic ionization potential of the adatom species. · In Chapter Three, we study the electronic structure of adatoms on graphene when a gate voltage is applied to control the number of electrons in the system. Lithium on graphene, a prototype system, and cobalt on graphene, an experimentally relevant case, are studied. We find that localized states on the adatom can be charged or discharged by the application of gate voltage, and we study the changes in potential and charge density of the system as electrons are added or removed. · In Chapter Four, we extend the work in Chapter Three to consider the possibility of transforming the electronic structure of one species of adatom on graphene into that of another by applying a gate voltage. We find that within our model, such transformations are possible for certain adatom species. · In Chapter Five, the zone-center phonons for the frustrated antiferromagnetic compound ZnCr2O4 are calculated. We find that the transition from nonmagnetic to antiferromagnetic ordering causes a splitting of certain degnerate phonon frequencies, in agreement with experimental results. · In Chapter Six, the pressure dependence of electron-phonon coupling and the superconducting transition temperature (Tc) in elemental arsenic is studied. We find that an experimentally observed peak in Tc as a function of pressure is related to a structural transition and can be explained mainly by changes in electronic structure and phonon frequencies with pressure.

Download or read book Introduction to Graphene Based Nanomaterials written by Luis E. F. Foa Torres and published by Cambridge University Press. This book was released on 2014-01-23 with total page 425 pages. Available in PDF, EPUB and Kindle. Book excerpt: A detailed primer describing the most effective theoretical and computational methods and tools for simulating graphene-based systems.

Download or read book Molecular Scale Electronics written by Xuefeng Guo and published by John Wiley & Sons. This book was released on 2020-07-02 with total page 408 pages. Available in PDF, EPUB and Kindle. Book excerpt: Provides in-depth knowledge on molecular electronics and emphasizes the techniques for designing molecular junctions with controlled functionalities This comprehensive book covers the major advances with the most general applicability in the field of molecular electronic devices. It emphasizes new insights into the development of efficient platform methodologies for building such reliable devices with desired functionalities through the combination of programmed bottom-up self-assembly and sophisticated top-down device fabrication. It also helps to develop an understanding of the device fabrication processes and the characteristics of the resulting electrode-molecule interface. Beginning with an introduction to the subject, Molecular-Scale Electronics: Concept, Fabrication and Applications offers full chapter coverage on topics such as: Metal Electrodes for Molecular Electronics; Carbon Electrodes for Molecular Electronics; Other Electrodes for Molecular Electronics; Novel Phenomena in Single-Molecule Junctions; and Supramolecular Interactions in Single-Molecule Junctions. Other chapters discuss Theoretical Aspects for Electron Transport through Molecular Junctions; Characterization Techniques for Molecular Electronics; and Integrating Molecular Functionalities into Electrical Circuits. The book finishes with a summary of the primary challenges facing the field and offers an outlook at its future. * Summarizes a number of different approaches for forming molecular-scale junctions and discusses various experimental techniques for examining these nanoscale circuits in detail * Gives overview of characterization techniques and theoretical simulations for molecular electronics * Highlights the major contributions and new concepts of integrating molecular functionalities into electrical circuits * Provides a critical discussion of limitations and main challenges that still exist for the development of molecular electronics * Suited for readers studying or doing research in the broad fields of Nano/molecular electronics and other device-related fields Molecular-Scale Electronics is an excellent book for materials scientists, electrochemists, electronics engineers, physical chemists, polymer chemists, and solid-state chemists. It will also benefit physicists, semiconductor physicists, engineering scientists, and surface chemists.

Download or read book First principles Calculations and Model Hamiltonian Approaches to Electronic and Optical Properties of Defects Interfaces and Nanostructures written by Sangkook Choi and published by . This book was released on 2013 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt: The dynamics of electrons governed by the Coulomb interaction determines a large portion of the observed phenomena of condensed matter. Thus, the understanding of electronic structure has played a key role in predicting the electronic and optical properties of materials. In this dissertation, I present some important applications of electronic structure theories for the theoretical calculation of these properties. In the first chapter, I review the basics necessary for two complementary electronic structure theories: model Hamiltonian approaches and first principles calculation. In the subsequent chapters, I further discuss the applications of these approaches to nanostructures (chapter II), interfaces (chapter III), and defects (chapter IV). The abstract of each section is as follows. Section II-1 The sensitive structural dependence of the optical properties of single-walled carbon nanotubes, which are dominated by excitons and tunable by changing diameter and chirality, makes them excellent candidates for optical devices. Because of strong many-electron interaction effects, the detailed dependence of the optical oscillator strength of excitons on nanotube diameter, chiral angle, and electronic subband index (the so-called family behavior) however has been unclear. In this study, based on results from an extended Hubbard Hamiltonian with parameters derived from ab initio GW-BSE calculations, we have obtained an explicit formula for the family behavior of the oscillator strengths of excitons in semiconducting single-walled carbon nanotubes (SWCNTs), incorporating environmental screening. The formula explains well recent measurements, and is expected to be useful in the understanding and design of possible SWCNT optical and optoelectronic devices. Section II-2 Wave supercollimation, in which a wavepacket is guided to move undistorted along a selected direction, is a highly desirable property that is difficult to achieve for photons and has yet to be experimentally seen for electrons. Disorder in a medium would inhibit supercollimation. Here, we report a counter-intuitive phenomenon of electron supercollimation by disorder in graphene, made possible by its Dirac fermion states. We show that one can use one-dimensional disorder potentials to control electron wavepacket transport along the potential fluctuation direction. This is distinct from all known systems where the wavepacket would be further spread by the disorder and hindered in the potential fluctuating direction. This phenomenon has significant implications in the understanding and applications of transport in graphene and other Dirac fermion materials. Section III-1 The origin of magnetic flux noise in superconducting quantum interference devices with a power spectrum scaling as 1 / f ( f is frequency) has been a puzzle for over 20 years. This noise limits the decoherence time of superconducting qubits. A consensus has emerged that the noise arises from fluctuating spins of localized electrons with an areal density of 5×1017 m−2. We show that the physical origin of the phenomenon are localized metal-induced gap states at the interface. In the presence of potential disorder at the metal-insulator interface, some of the metal-induced gap states become localized and produce local moments. A modest level of disorder yields the observed areal density. Section III-2 We present a microscopic theory of disorder-induced magnetic moment generation at nonmagnetic metal-insulator interfaces. Screened Hartree-Fock solution of a tight-binding Hamiltonian with electron-electron interaction, in which disorder is mimicked by the Anderson disorder model, shows that magnetic moments are originated from localized metal-induced gap states at the interface. Magnetic moment areal density becomes saturated at a maximum value of 4×1017 m−2 as the disorder magnitude increases, consistent with the observed universality of measured local magnetic moment areal density. Dielectric screening effect is found to be essential for understanding the relatively universal behavior of the observed value. Section IV-1 Optical initialization of the negatively charged nitrogen-vacancy (NV−) center in diamond makes it one of the best candidates for realization of addressable spins in the solid state for quantum computing and other studies. However, its exact mechanism was not clear. We show that exact diagonalization of a many-electron Hamiltonian with parameters derived from ab initio GW calculations puts strong constraints on the mechanism. The energy surfaces of the low-energy many-body states and the relaxation processes of photo-excitation responsible for the optical initialization are calculated. Intersystem crossings are shown to be essential Section IV-2 Graphene has been predicted to be a good test material for atomic collapse theory due to its linear band structure with a Fermi velocity 300 times slower than the speed of light. The Crommie group at UC Berkeley measured, using scanning tunneling microscopy, electrons bound to the positively charged calcium dimers on graphene, which corresponds to electrons collapsed to the super-heavy nucleus in artificial atoms. To compare measured bound states to atomic collapse theory in an artificial atom on graphene, the net charges associated with calcium dimers should be quantified. Here, we quantified the net charges associated with a calcium dimer using density function theory.