A5017972338- 2D Materials and Applications
- Graphene research and applications
- Molecular Junctions and Nanostructures
- Advancements in Battery Materials
- Perovskite Materials and Applications
- Transition Metal Oxide Nanomaterials
- X-ray Spectroscopy and Fluorescence Analysis
- Quantum and electron transport phenomena
- Advanced Battery Materials and Technologies
- Fullerene Chemistry and Applications
- ZnO doping and properties
- Machine Learning in Materials Science
- Image Retrieval and Classification Techniques
- Gaze Tracking and Assistive Technology
- Carbon Nanotubes in Composites
- Advanced Condensed Matter Physics
- Ga2O3 and related materials
- Advanced Memory and Neural Computing
- Advanced Vision and Imaging
- Catalysis and Oxidation Reactions
- Embedded Systems and FPGA Design
- Topological Materials and Phenomena
- MXene and MAX Phase Materials
- Aerospace and Aviation Technology
- Graphene and Nanomaterials Applications
Lawrence Berkeley National Laboratory
2016-2025
Yantai University
2024
Northwestern Polytechnical University
2024
University of Electronic Science and Technology of China
2021-2023
Dalian Jiaotong University
2020-2021
Shandong University of Science and Technology
2021
Argonne National Laboratory
2019
Binghamton University
2019
Georgia Institute of Technology
2019
Diamond Light Source
2019
We report the quasiparticle band gap, excitons, and highly anisotropic optical responses of few-layer black phosphorous (phosphorene). It is shown that these new materials exhibit unique many-electron effects; electronic structures are dispersive essentially along one dimension, leading to particularly enhanced self-energy corrections excitonic effects. Additionally, within a wide energy range, including infrared light part visible light, absorbs polarized structure's armchair direction...
Lithium-rich layered transition metal oxide positive electrodes offer access to anion redox at high potentials, thereby promising energy densities for lithium-ion batteries. However, is also associated with several unfavorable electrochemical properties, such as open-circuit voltage hysteresis. Here we reveal that in Li
Despite much interest in engineering new topological surface (edge) states using structural defects, such have not been observed yet. We show that recently imaged tilt boundaries gated multilayer graphene should support topologically protected gapless edge states. approach the problem from two perspectives: microscopic perspective of a tight-binding model and an ab initio calculation on bilayer, symmetry-protected (SPT) state for general multilayer. Hence, we establish tilt-boundary as first...
We report the quasiparticle band-edge energy of monolayer molybdenum and tungsten dichalcogenides, MX2 (M = Mo, W; X S, Se, Te). Beyond calculating bandgaps, we have achieved converged absolute energies relative to vacuum level. Compared with results from other approaches, GW calculation reveals substantially larger bandgaps different because enhanced many-electron effects. Interestingly, our calculations ratify band-gap-center approximation, making it a convenient way estimate energy. The...
In reduced-dimensional semiconductors, doping-induced carrier plasmons can strongly couple with quasiparticle excitations, leading to a significant band gap renormalization. However, the physical origin of this generic effect remains obscure. We develop new plasmon-pole theory that efficiently and accurately captures coupling. Using monolayer MoS(2) MoSe(2) as prototype two-dimensional (2D) we reveal striking renormalization above 400 meV an unusual nonlinear evolution their gaps doping....
Abstract The rapid insertion and extraction of Li ions from a cathode material is imperative for the functioning Li-ion battery. In many materials such as LiCoO 2 , lithiation proceeds through solid-solution formation, whereas in other LiFePO 4 lithiation/delithiation accompanied by phase transition between Li-rich Li-poor phases. We demonstrate using scanning transmission X-ray microscopy (STXM) that individual nanowires layered V O 5 gradients observed on intercalation arise electron...
The scarce inventory of compounds that allow for diffusion multivalent cations at reasonable rates poses a major impediment to the development intercalation batteries. Here, we contrast thermodynamics and kinetics insertion Li, Na, Mg, Al ions in two synthetically accessible metastable phases V2O5, ζ- ε-V2O5, with relevant parameters thermodynamically stable α-phase V2O5 using density functional theory calculations. metastability frameworks results higher open circuit voltage ions, exceeding...
It is well-known that excitonic effects can dominate the optical properties of two-dimensional materials. These effects, however, be substantially modified by doping free carriers. We investigate these solving first-principles Bethe–Salpeter equation. Dynamical screening included via sum-rule preserving generalized plasmon-pole model, are found to important in doped system. Using monolayer MoS2 as an example, we find upon moderate doping, exciton binding energy tuned a few hundred...
Optoelectronic excitations in monolayer ${\mathrm{MoS}}_{2}$ manifest from a hierarchy of electrically tunable, Coulombic free-carrier and excitonic many-body phenomena. Investigating the fundamental interactions underpinning these phenomena---critical to both physics exploration device applications---presents challenges, however, due complex balance competing optoelectronic effects interdependent properties. Here, optical detection bound- photoexcitations is used directly quantify...
We report a systematic study of the optical conductivity twisted bilayer graphene (tBLG) across large energy range (1.2–5.6 eV) for various twist angles, combined with first-principles calculations. At previously unexplored high energies, our data show signatures multiple van Hove singularities (vHSs) in tBLG bands as well nonlinearity single layer and their electron–hole asymmetry. Our also suggest that excitonic effects play vital role spectra tBLG. Including interactions calculations is...
Constrained-occupancy self-consistent-field ($\Delta$SCF) methods and many-body perturbation theories (MBPT) are two strategies for obtaining electronic excitations from first-principles. Using the distinct approaches, we study O $1s$ core that have become increasingly important characterizing transition metal oxides developing theory of strong correlations. Interestingly, find $\Delta$SCF approach, in its current single-particle form, systematically underestimates pre-edge intensity chosen...
When two sheets of graphene stack in a twisted bilayer (tBLG) configuration, the resulting constrained overlap between interplanar 2p orbitals produce angle-tunable electronic absorption resonances. By applying novel combination multiphoton transient (TA) microscopy and TEM, we resolve structure ensuing relaxation by probing resonant excitations single tBLG domains. Strikingly, find that population resonantly excited domains is enhanced many fold, forming major bottleneck. Two-photon TA...
Recently, measured optical absorption and photoluminescence spectra reveal substantial frequency shifts of both exciton trion peaks as monolayer molybdenum disulfide, MoS2, is cooled from 363 K to 4 K. First-principles simulations using the GW-Bethe-Salpeter equation approach satisfactorily reproduce these by incorporating thermal expansion effect. Studying temperature effects in MoS2 crucial for rectifying results available experiments with previous predictions zero-temperature-limit...
Understanding the diffusion mechanisms of Li ions through host materials and resulting phase evolution intercalated phases is paramount importance for designing electrode rechargeable batteries. The formation lithiation gradients discrete domains during intercalation leads to development strain within material responsible observed capacities most cathode being well below theoretically predicted values. Such mesoscale heterogeneity has also been implicated in loss capacity upon cycling. Due...
The path to realizing low-cost, stable, and earth-abundant photoelectrodes can be enabled through a detailed understanding of the optoelectronic properties these materials by combining theory experimental techniques. Of limited set oxide photocathode currently available, CuFeO2 has emerged as promising candidate warranting attention. In this work, highly compact thin films rhombohedral (3R) were prepared via reactive co-sputtering. Despite its 1.43 eV indirect band gap, cathodic photocurrent...
Solid-state lithium metal batteries (LMBs) are considered as one of the promising contenders for next-generation energy storage systems because their high density and safety performance. Since all-solid-state electrolytes still hampered by low electrical conductivity interfacial incompatibility, gel polymer (GPEs) more preferable with ionic conductivities comparable to liquid at room temperature good contact electrodes. In this study, a high-performance composite GPE semi-interpenetrating...
Recent reports have identified new metaphases of ${\mathrm{VO}}_{2}$ with strain and/or doping, suggesting the structural phase transition and metal-to-insulator might be decoupled. Using epitaxially strained ${\mathrm{VO}}_{2}/\mathrm{Ti}{\mathrm{O}}_{2}$ (001) thin films, which display a bulklike abrupt rutile to monoclinic transition, we employ x-ray standing waves combined hard photoelectron spectroscopy simultaneously measure electronic transitions. This study elegantly demonstrates...
The energy spectra and wavefunctions of bound excitons in important two-dimensional (2D) graphene derivatives, i.e., graphyne graphane, are found to be strongly modified by quantum confinement, making them qualitatively different from the usual Rydberg series. However, their parity optical selection rules preserved. Thus a one-parameter hydrogenic model is applied quantitatively explain ab initio exciton spectra, allows one extrapolate electron-hole binding spectroscopies 2D semiconductors...
Superconductivity in infinite-layer nickelates has stirred much research interest, to which questions regarding the nature of superconductivity remain elusive. A critical leap forward address these intricate is through growth high-crystallinity nickelates, including "parent" phase. Here, we report synthesis a high-quality thin-film nickelate, NdNiO2. This achieved perovskite precursor phase (NdNiO3) superior crystallinity on NdGaO3 substrate by off-axis RF magnetron sputtering and...
The great progress that optoelectronic technologies have achieved in van der Waals crystals promises the development of next-generation two-dimensional (2D) integrated systems (IOSs). Here, relying on anomalous avoidance pump-light absorption, harvest extremely strong Raman scattering, and achievement polarization inheritance by designed optical geometry, we realized laser wavelength tuning with ultrahigh precision (0.01 nm/25 K) layered MoS2 WS2 adjusting temperature. Our results offer a...
The growing interest in using x-ray spectroscopy for refined materials characterization calls accurate electronic-structure theory to interpret near-edge fine structure. In this work, we propose an efficient and unified framework describe all the many-electron processes a Fermi liquid after sudden perturbation (such as core hole). This problem has been visited by Mahan-Nozi\'eres-De Dominicis (MND) theory, but it is intractable implement various Feynman diagrams within first-principles...
We combine high-energy resolution fluorescence detection (HERFD) X-ray absorption spectroscopy (XAS) measurements with first-principles density functional theory (DFT) calculations to provide a molecular-scale understanding of local structure, and its role in defining optoelectronic properties, CH3NH3Pb(I1–xBrx)3 perovskites. The spectra probe ligand field splitting the unoccupied d states material, which lie well above conduction band minimum display high sensitivity halide identity,...
Common wisdom asserts that bound excitons cannot form in high-dimensional ($d>1$) metallic structures because of their overwhelming screening and the unavoidable resonance with nearby continuous bands. Strikingly we illustrate this prevalent assumption is not quite true. A key ingredient has been overlooked: Destructive coherent effects are capable thwarting formation resonance. As an example general mechanism, focus on experimentally relevant material predict twisted bilayer graphene, which...