A5016780645- Graphene research and applications
- Surface and Thin Film Phenomena
- Chalcogenide Semiconductor Thin Films
- Electron and X-Ray Spectroscopy Techniques
- 2D Materials and Applications
- Semiconductor materials and devices
- Quantum and electron transport phenomena
- Semiconductor materials and interfaces
- Carbon Nanotubes in Composites
- Diamond and Carbon-based Materials Research
- Plasmonic and Surface Plasmon Research
- Quantum Dots Synthesis And Properties
- Silicon Carbide Semiconductor Technologies
- Boron and Carbon Nanomaterials Research
- Advancements in Battery Materials
- Electronic and Structural Properties of Oxides
- Chemical and Physical Properties of Materials
- Machine Learning in Materials Science
- Molecular Junctions and Nanostructures
- Ga2O3 and related materials
- Advanced Materials Characterization Techniques
- Metamaterials and Metasurfaces Applications
- ZnO doping and properties
- Advanced Memory and Neural Computing
- Topological Materials and Phenomena
Sandia National Laboratories
2016-2025
University of California, Riverside
2024
Los Alamos National Laboratory
2022
Purdue University West Lafayette
2022
Sandia National Laboratories California
2010-2021
Center for Integrated Nanotechnologies
2014-2019
National Technical Information Service
2011
Interface (United States)
2009-2011
Surface (Brazil)
2011
Nanomaterials Research (United States)
2011
We describe the synthesis of bilayer graphene thin films deposited on insulating silicon carbide and report characterization their electronic band structure using angle-resolved photoemission. By selectively adjusting carrier concentration in each layer, changes Coulomb potential led to control gap between valence conduction bands. This over suggests application switching functions atomic-scale devices.
The unusual transport properties of graphene are the direct consequence a peculiar band structure near Dirac point. We determine shape $\ensuremath{\pi}$ bands and their characteristic splitting, find transition from two-dimensional to bulk character for 1 4 layers by angle-resolved photoemission. By detailed measurements we derive stacking order, layer-dependent electron potential, screening length, strength interlayer interaction comparison with tight binding calculations, yielding...
We have investigated the effects of doping on a single layer graphene using angle-resolved photoemission spectroscopy. show that many-body interactions severely warp Fermi surface, leading to an extended van Hove singularity (EVHS) at $M$ point. The ground state properties with such EVHS are calculated, analyzing competition between magnetic instability and tendency towards superconductivity. find latter plays dominant role as it is enhanced by strong modulation interaction along line,...
The authors present a scanning tunneling spectroscopy (STS) study of the local electronic structure single and bilayer graphene grown epitaxially on SiC(0001) surface. Low voltage topographic images reveal fine, atomic-scale carbon networks, whereas higher bias are dominated by emergent spatially inhomogeneous large-scale similar to carbon-rich reconstruction SiC(0001). STS shows an ∼100meV gaplike feature around zero for both monolayer graphene/SiC, as well significant spatial inhomogeneity...
We report a study of the valence band dispersion twisted bilayer graphene using angle-resolved photoemission spectroscopy and ab initio calculations. observe two noninteracting cones near Dirac crossing energy emergence van Hove singularities where overlap for large twist angles (>5°). Besides expected interaction between cones, minigaps appeared at Brillouin zone boundaries moiré superlattice formed by misorientation layers. attribute these to periodic potential induced moiré. These...
Abstract Graphene, a two‐dimensional sheet of sp 2 ‐bonded carbon arranged in honeycomb lattice, is not only the building block fullerenes, nano tubes (CNTs) and graphite, it also has interesting properties, which have caused flood activities past few years. The possibility to grow graphitic films with thicknesses down single graphene layer epitaxially on SiC{0001} surfaces promising for future applications. nature epitaxial make them ideal objects surface science techniques such as...
Recently, it was demonstrated that the quasiparticle dynamics, layer-dependent charge and potential, c-axis screening coefficient could be extracted from measurements of spectral function few layer graphene films grown epitaxially on SiC using angle-resolved photoemission spectroscopy (ARPES). In this paper we review these findings, present detailed methodology for extracting such parameters ARPES. We also arguments against possibility an energy gap at Dirac crossing ED.
Epitaxial films of graphene on SiC(0001) are interesting from a basic physics as well an applications-oriented point view. Here, we study the emerging morphology in vacuo prepared using low-energy electron microscopy (LEEM) and angle-resolved photoemission spectroscopy (ARPES). We obtain identification single-layer bilayer by comparing characteristic features reflectivity spectra LEEM to π-band structure revealed ARPES. demonstrate that serves tool accurately determine local extent layers...
Heterogeneous engineering of two-dimensional layered materials, including metallic graphene and semiconducting transition metal dichalcogenides, presents an exciting opportunity to produce highly tunable electronic optoelectronic systems. In order engineer pristine layers their interfaces, epitaxial growth such heterostructures is required. We report the direct crystalline, monolayer tungsten diselenide (WSe2) on (EG) grown from silicon carbide. Raman spectroscopy, photoluminescence,...
Low-energy reflectivity of electrons from single- and multilayer graphene is examined both theoretically experimentally. A series minima in the over energy range 0--8 eV are found, with number depending on layers. Using first-principles computations, it demonstrated that a freestanding $n$-layer slab produces $n\ensuremath{-}1$ minima. This same result also found experimentally for supported SiO${}_{2}$. For bonded onto other substrates argued similar expected, although certain cases an...
Direct, tunable coupling between individually assembled graphene layers is a next step towards designer two-dimensional (2D) crystal systems, with relevance for fundamental studies and technological applications. Here we describe the fabrication characterization of large-area (> cm^2), coupled bilayer on SiO2/Si substrates. Stacking two films leads to direct electronic interactions layers, where resulting film properties are determined by local twist angle. Polycrystalline have...
We have observed the formation of graphene on SiC by Si sublimation in an Ar atmosphere using low-energy electron microscopy, scanning tunneling microcopy, and atomic force microscopy. This work reveals unanticipated growth mechanisms, which depend strongly initial surface morphology. Carbon diffusion governs spatial relationship between decomposition growth. Isolated bilayer steps generate narrow ribbons a distinctive cooperative process, whereas triple allow large sheets to grow step flow....
The values of the ionization energies transition metal dichalcogenides (TMDs) are needed to assess their potential usefulness in semiconductor heterojunctions for high-performance optoelectronics. Here, we report on systematic determination three prototypical TMD monolayers (MoSe2, WS2, and MoS2) SiO2 using photoemission electron microscopy with deep ultraviolet illumination. energy displays a progressive decrease from MoS2, MoSe2, agreement predictions density functional theory...
Oxidation of exfoliated gallium selenide (GaSe) is investigated through Raman, photoluminescence, Auger, and X-ray photoelectron spectroscopies. Photoluminescence Raman intensity reductions associated with spectral features GaSe are shown to coincide the emergence signatures emanating from by-products oxidation reaction, namely, Ga2Se3 amorphous Se. Photoinduced initiated over a portion flake highlighting potential for laser based patterning two-dimensional heterostructures via selective oxidation.
Chemical functionalization is required to adapt graphene's properties many applications. However, most covalent schemes are spontaneous or defect driven and not suitable for applications requiring directed assembly of molecules on graphene substrates. In this study, we demonstrate the electrochemically bonding trifluoromethylphenylene (CF3Ph) onto epitaxial graphene. Submonolayer full monolayer chemisorption was demonstrated by varying duration electrochemical driving potential. A 10×...
We report a striking coupling between strain and carrier concentration variations at micrometer scale in single-layer graphene grown on silicon carbide (SiC) (0001). The in-plane compressive (up to 0.4%) are probed using Raman spectroscopy. show that the large inhomogeneities initiate growth stage develop further by relaxation along mismatched symmetry axes of underlying substrate. is accompanied locally larger electron concentration, suggesting charge transfer reduces energy overall system....
Precise control of light–matter interactions at the nanoscale lies heart nanophotonics. However, experimental examination this length scale is challenging since corresponding electromagnetic near-field often confined within volumes below resolution conventional optical microscopy. In semiconductor nanophotonics, fields are further restricted confines individual subwavelength resonators, limiting access to critical in these structures. work, we demonstrate that photoelectron emission...
Dielectric metasurfaces, through volume‐type photonic resonances, enable precise control of light‐matter interactions for applications including imaging, holography, and sensing. The application space dielectric metasurfaces has extended from infrared to visible wavelengths by incorporating high refractive index materials, such as titanium dioxide (TiO 2 ). Understanding the fundamental fabrication limits these requires metrology with nanoscale resolution, sensitivity electromagnetic fields...
Conventional means of stacking two-dimensional (2D) crystals inevitably leads to imperfections. To examine the ramifications these imperfections, rotational disorder and strain are quantified in twisted bilayer graphene (TBG) using a combination Raman spectroscopic low-energy electron diffraction imaging. The twist angle between TBG layers varies on order 2° within large (50-100 μm) single-crystalline grains, resulting changes emergent response by over an magnitude. Rotational does not...