A5045377460- Graphene research and applications
- Advanced Chemical Physics Studies
- Quantum and electron transport phenomena
- 2D Materials and Applications
- Carbon Nanotubes in Composites
- Molecular Junctions and Nanostructures
- Boron and Carbon Nanomaterials Research
- Surface and Thin Film Phenomena
- Physics of Superconductivity and Magnetism
- Fullerene Chemistry and Applications
- Semiconductor Quantum Structures and Devices
- Topological Materials and Phenomena
- Diamond and Carbon-based Materials Research
- High-pressure geophysics and materials
- Semiconductor materials and devices
- Semiconductor materials and interfaces
- Perovskite Materials and Applications
- Electronic and Structural Properties of Oxides
- Spectroscopy and Quantum Chemical Studies
- Superconductivity in MgB2 and Alloys
- Electron and X-Ray Spectroscopy Techniques
- Force Microscopy Techniques and Applications
- Mechanical and Optical Resonators
- Advanced Physical and Chemical Molecular Interactions
- Chalcogenide Semiconductor Thin Films
Lawrence Berkeley National Laboratory
2016-2025
University of California, Berkeley
2016-2025
University of California System
1976-2025
Sandia National Laboratories
2009-2020
Hong Kong University of Science and Technology
2013-2019
University of Hong Kong
2013-2019
Indian Institute of Information Technology Design and Manufacturing Jabalpur
2017
Berkeley College
1999-2017
University of Calabria
2017
Material Sciences (United States)
1998-2017
Based on a first-principles approach, we present scaling rules for the band gaps of graphene nanoribbons (GNRs) as function their widths. The GNRs considered have either armchair or zigzag shaped edges both sides with hydrogen passivation. Both varieties ribbons are shown to gaps. This differs from results simple tight-binding calculations solutions Dirac's equation based them. Our ab initio show that origin energy arises quantum confinement and crucial effect edges. For edges, appear...
We present a first-principles theory of the quasiparticle energies in semiconductors and insulators described terms electron self-energy operator. The full dielectric matrix is used to evaluate operator GW approximation: first term an expansion dynamically screened Coulomb interaction (W) dressed Green's function (G). Quasiparticle are calculated for homopolar materials diamond, Si, Ge as well ionic compound LiCl. results excellent agreement with available experimental data. In particular,...
The successful synthesis of pure boron nitride (BN) nanotubes is reported here. Multi-walled tubes with inner diameters on the order 1 to 3 nanometers and lengths up 200 were produced in a carbon-free plasma discharge between BN-packed tungsten rod cooled copper electrode. Electron energy-loss spectroscopy individual yielded B:N ratios approximately 1, which consistent theoretical predictions stable BN tube structures.
The isolation of graphene in 2004 from graphite was a defining moment for the "birth" field: two-dimensional (2D) materials. In recent years, there has been rapidly increasing number papers focusing on non-graphene layered materials, including transition-metal dichalcogenides (TMDs), because new properties and applications that emerge upon 2D confinement. Here, we review significant advances important developments materials "beyond graphene". We provide insight into theoretical modeling...
A new method for generating and using first-principles pseudopotentials is developed to treat explicitly the nonlinear exchange correlation interaction between core valence charge densities. Compared existing potentials, scheme leads significant improvement in transferability of potential. In particular, spin-polarized configurations are well described with a single The need separate spin-up spin-down ionic pesudopotentials is, thus, eliminated. can easily be implemented minimal increase...
We present a recently developed approach to calculate electron-hole excitations and the optical spectra of condensed matter from first principles. The key concept is describe electronic system by corresponding one- two-particle Green's function. method combines three computational techniques. First, ground state treated within density-functional theory. Second, single-particle spectrum electrons holes obtained $\mathrm{GW}$ approximation electron self-energy operator. Finally, interaction...
Extensive LDA and quasi-particle calculations have been performed on boron nitride (BN) single-wall multi-wall nanotubes. Strain energies are found to be smaller for BN nanotubes than carbon of the same radius, owing a buckling effect which stabilizes tubular structure. For tubes larger 9.5 Å in diameter, lowest conduction band is predicted free-electron-like with electronic charge density localized inside tube. these tubes, this at constant energy above top valence band. Consequently,...
We present first-principles calculations of the optical response monolayer molybdenum disulfide employing GW-Bethe-Salpeter equation (GW-BSE) approach including self-energy, excitonic, and electron-phonon effects. show that MoS2 possesses a large diverse number strongly bound excitonic states with novel k-space characteristics were not previously seen experimentally or theoretically. The absorption spectrum is shown to be dominated by binding energy close 1 eV strong broadening in visible...
We present a first-principles theory for the quasiparticle energies of semiconductors and insulators. The full dielectric matrix is used to evaluate nonlocal, energy-dependent electron self-energy operator. Both local-field effects dynamical screening are found be essential understanding energies. Results band gaps, optical transitions, dispersions silicon diamond in excellent agreement with existing experimental data.
Although the physics of materials at surfaces and edges has been extensively studied, movement individual atoms an isolated edge not directly observed in real time. With a transmission electron aberration-corrected microscope capable simultaneous atomic spatial resolution 1-second temporal resolution, we produced movies dynamics carbon hole suspended, single layer graphene. The rearrangement bonds beam-induced ejection are recorded as grows. We investigated mechanism reconstruction...
We present calculations of the quasiparticle energies and band gaps graphene nanoribbons (GNRs) carried out using a first-principles many-electron Green's function approach within $GW$ approximation. Because quasi-one-dimensional nature GNR, electron-electron interaction effects due to enhanced screened Coulomb confinement geometry greatly influence gap. Compared with previous tight-binding density functional theory studies, our calculated show significant self-energy corrections for both...
Junctions consisting of two crossed single-walled carbon nanotubes were fabricated with electrical contacts at each end nanotube. The individual identified as metallic (M) or semiconducting (S), based on their two-terminal conductances; MM, MS, and SS four-terminal devices studied. MM junctions had high conductances, the order 0.1 e(2)/h (where e is electron charge h Planck's constant). For an MS junction, nanotube was depleted junction by nanotube, forming a rectifying Schottky barrier. We...
Hybridization of the ${\mathrm{\ensuremath{\sigma}}}^{\mathrm{*}}$ and ${\mathrm{\ensuremath{\pi}}}^{\mathrm{*}}$ states graphene network is shown to be as important band-folding effects in determining metallicity small radius carbon nanotubes. Using detailed plane-wave ab initio pseudopotential local density functional (LDA) calculations, we find that electronic properties tubes are significantly altered from those obtained previous tight-binding calculations. Strongly modified low-lying...
Many-electron effects often dramatically modify the properties of reduced dimensional systems. We report calculations, based on an ab initio many-electron Green's function approach, electron-hole interaction optical spectra small-diameter single-walled carbon nanotubes. Excitonic qualitatively alter both semiconducting and metallic tubes. Excitons are bound by approximately 1 eV in (8,0) tube 100 meV (3,3) tube. These large explain discrepancies between previous theories experiments.
Introduction of pentagon-heptagon pair defects into the hexagonal network a single carbon nanotube can change helicity tube and alter its electronic structure. Using tight-binding method to calculate structure such systems we show that they behave as nanoscale metal/semiconductor or semiconductor/semiconductor junctions. These junctions could be building blocks devices made entirely carbon.
We present a new ab initio approach to calculate the interaction between electrons and holes in periodic crystals evaluate resulting coupled electron-hole excitations. This involves novel interpolation scheme reciprocal space solving Bethe-Salpeter equation for two-particle Green's function. apply this calculation of entire optical absorption spectrum, as well energies wave functions bound exciton states GaAs LiF. Very good agreement with experiment is observed.
The electronic structure of benzene on graphite (0001) is computed using the GW approximation for electron self-energy. quasiparticle energy gap predicted to be 7.2 eV graphite, substantially reduced from its calculated gas-phase value 10.5 eV. This decrease caused by a change in correlation energy, an effect completely absent corresponding Kohn-Sham gap. For weakly coupled molecules, this can described as surface polarization effect. A classical image potential model illustrates impact...
We introduce a technique based on the spatial localization of electron and phonon Wannier functions to perform first-principles calculations electron-phonon interaction with an ultradense sampling Brillouin zone. After developing basic theory, we describe practical implementation within density-functional framework. The proposed method is illustrated by considering virtual crystal model boron-doped diamond. For this test case, first discuss matrix element in representation. Then, assess...