Excited-State Properties of Electrostatically Doped Low-Dimensional Structures

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TECHNICAL SUMMARYThis award supports computational and theoretical research and education to study doping effects on excited-state properties of low-dimensional structures of broad interest, including silicon nanowires, graphene and electrically gated bilayer graphene. Because of the geometry of these structures and the associated divergence of the electronic density of states close to the band edge, electrostatically doped free carriers can dramatically change the electronic screening of many-electron interactions. As a result, an even small amount of doping may substantially change the excited-state properties, such as the quasiparticle band gap and optical properties, making doping an efficient tool to tune the intrinsic electronic structure of low-dimensional materials in addition to its usual role of providing free carriers. The variation of many-electron effects may also modify the spin singlet-triplet splitting which would change the luminescence properties with possible application to quantum information technology. The research involves using density functional theory based methods along with GW and the solution of the Bethe-Salpeter equation.This award also supports educational activities, including a new course, 'First-Principles Calculations and Their Applications to Nanostructures,' in Washington University. Additional activities include a series of seminars for interested researchers from institutes nearby to introduce cutting-edge first-principles approaches and their applications to the nanotechnology. NONTECHNICAL SUMMARYThis award supports computational and theoretical research and education to investigate the properties of very tiny wires that are little more than a few atoms wide and single-atom thick carbon sheets known as graphene. The PI will use advanced computational methods that aim to predict properties of structures of atoms and materials starting from knowledge of their constituent atoms. Of particular interest are properties that involve how well materials and structures of atoms absorb or emit light. An aim of the work is to determine how the addition and removal electrons from the quantum wires or graphene can be used to design the quantum mechanical states of quantum wires and graphene. This project contributes to the knowledge base including methods and software upon which future device technologies will be based. Specific aspects of the work contribute to the design of photovoltaic devices for the efficient conversion of light to electricity. This award also supports educational activities, including a new course, 'First-Principles Calculations and Their Applications to Nanostructures,' in Washington University. Additional activities include a series of seminars for interested researchers from institutes nearby to introduce cutting-edge first-principles approaches and their applications to the nanotechnology.