A5037035710- 2D Materials and Applications
- Perovskite Materials and Applications
- Quantum Dots Synthesis And Properties
- Graphene research and applications
- Semiconductor materials and devices
- Semiconductor Quantum Structures and Devices
- Copper Interconnects and Reliability
- Surface and Thin Film Phenomena
- Electronic and Structural Properties of Oxides
- Molecular Junctions and Nanostructures
- Strong Light-Matter Interactions
- Machine Learning in Materials Science
- Chalcogenide Semiconductor Thin Films
- Multiferroics and related materials
- Ferroelectric and Piezoelectric Materials
- Electron and X-Ray Spectroscopy Techniques
- Acoustic Wave Resonator Technologies
- MXene and MAX Phase Materials
- Organic and Molecular Conductors Research
- Ga2O3 and related materials
- Advanced Electron Microscopy Techniques and Applications
- GaN-based semiconductor devices and materials
- Solid-state spectroscopy and crystallography
- Magnetic properties of thin films
- Photoreceptor and optogenetics research
Kavli Energy NanoScience Institute
2018-2025
University of California, Berkeley
2019-2025
Lawrence Berkeley National Laboratory
2019-2025
Government of the United States of America
2025
Karpagam Academy of Higher Education
2025
Sri Sivasubramaniya Nadar College of Engineering
2019
Berkeley College
2019
Stanford University
2017-2018
Columbia University
2015-2017
SLAC National Accelerator Laboratory
2017
Abstract The ability to control the size of electronic bandgap is an integral part solid-state technology. Atomically thin two-dimensional crystals offer a new approach for tuning energies states based on unusual strength Coulomb interaction in these materials and its environmental sensitivity. Here, we show that by engineering surrounding dielectric environment, one can tune exciton binding energy monolayers WS 2 WSe hundreds meV. We exploit this behaviour present in-plane heterostructure...
Atomically thin transition metal dichalcogenides (TMDs) are direct-gap semiconductors with strong light-matter and Coulomb interaction. The latter accounts for tightly bound excitons, which dominate the optical properties of these technologically promising materials. Besides optically accessible bright systems exhibit a variety dark excitonic states. They not visible in spectra, but can strongly influence coherence lifetime linewidth emission from exciton In recent study, an experimental...
We report efficient nonradiative energy transfer (NRET) from core-shell, semiconducting quantum dots to adjacent two-dimensional sheets of graphene and MoS2 single- few-layer thickness. observe quenching the photoluminescence (PL) individual enhanced PL decay rates in time-resolved PL, corresponding 1-10 ns(-1). Our measurements reveal contrasting trends NRET rate dot van der Waals material as a function The increases significantly with increasing layer thickness graphene, but decreases...
We have investigated the phase transformation of bulk MoS2 crystals from metastable metallic 1T/1T' to thermodynamically stable semiconducting 2H phase. The material was prepared by Li intercalation and deintercalation. thermally driven kinetics were studied with in situ Raman optical reflection spectroscopies yield an activation energy 400 ± 60 meV (38 6 kJ/mol). calculate expected minimum pathways for these transformations using DFT methods. experimental corresponds approximately...
Ferroelectric semiconductors are rare materials with both spontaneous polarizations and visible light absorptions that promising for designing functional photoferroelectrics, such as optical switches ferroelectric photovoltaics. The emerging halide perovskites remarkable semiconducting properties also have the potential of being ferroelectric, yet evidence robust ferroelectricity in typical three-dimensional hybrid has been elusive. Here, we report on investigation all-inorganic perovskites,...
Nonlinear optics reveal how the chirality of ferroelectric vortices can be deterministically controlled using an electric field.
We investigate the effects of environmental dielectric screening on electronic dispersion and band gap in atomically-thin, quasi two-dimensional (2D) semiconductor WS$_2$ using correlative angle-resolved photoemission optical spectroscopies, along with first-principles calculations. find main effect increased to be a reduction gap, little change structure. These essentially rigid shifts bands results from special spatial structure changes Coulomb potential induced by environment 2D limit....
Abstract Strong optical nonlinearities play a central role in realizing quantum photonic technologies. Exciton-polaritons, which result from the hybridization of material excitations and cavity photons, are an attractive candidate to realize such nonlinearities. While interaction between ground state excitons generates notable nonlinearity, strength interactions is generally not sufficient reach regime nonlinear optics. Excited states, however, feature enhanced therefore hold promise for...
Electronic and optical excitations in two-dimensional moir\'e systems are uniquely sensitive to local atomic registries, leading materials- twist-angle specific correlated electronic ground states with varied degree of localization. However, there has been no direct experimental correlation between the sub-nanometer structure emergent excitonic transitions, comprising tightly-bound pairs photoexcited electrons holes. Here, we use cryogenic transmission electron microscopy spectroscopy...
Lattice reconstruction and corresponding strain accumulation play a key role in defining the electronic structure of two-dimensional moir\'e superlattices, including those transition metal dichalcogenides (TMDs). Imaging TMD moir\'es has so far provided qualitative understanding this relaxation process terms interlayer stacking energy, while models underlying deformation mechanisms have relied on simulations. Here, we use interferometric four-dimensional scanning transmission electron...
Abstract Despite extensive studies on size effects in ferroelectrics, how structures and properties evolve antiferroelectrics with reduced dimensions still remains elusive. Given the enormous potential of utilizing for high‐energy‐density storage applications, understanding their will provide key information optimizing device performances at small scales. Here, fundamental intrinsic dependence antiferroelectricity lead‐free NaNbO 3 membranes is investigated. Via a wide range experimental...
Abstract Point defects in two-dimensional materials are of key interest for quantum information science. However, the parameter space possible is immense, making identification high-performance very challenging. Here, we perform high-throughput (HT) first-principles computational screening to search promising within WS 2 , which present localized levels band gap that can lead bright optical transitions visible or telecom regime. Our computed database spans more than 700 charged formed...
Stabilization of topological spin textures in layered magnets has the potential to drive development advanced low-dimensional spintronics devices. However, achieving reliable and flexible manipulation beyond skyrmion a two-dimensional magnet system remains challenging. Here, we demonstrate introduction magnetic iron atoms between van der Waals gap magnet, Fe3GaTe2, modify local anisotropic interactions. Consequently, present direct observations order-disorder lattices transition. In...
The reduced dielectric screening in atomically thin transition metal dichalcogenides allows to study the hydrogen-like series of higher exciton states optical spectra even at room temperature.
Layered transition metal dichalcogenides exhibit the emergence of a direct bandgap at monolayer limit along with pronounced excitonic effects. In these materials, interaction phonons is dominant mechanism that limits exciton coherence lifetime. Exciton-phonon also facilitates energy and momentum relaxation, influences diffusion under most experimental conditions. However, fundamental changes in exciton–phonon are not well understood as material undergoes from to an indirect semiconductor....
Stacking van der Waals crystals allows for the on-demand creation of a periodic potential landscape to tailor transport quasiparticle excitations. We investigate diffusion photoexcited electron–hole pairs, or excitons, at interface WS2/WSe2 heterostructure over wide range temperatures. observe appearance distinct interlayer excitons parallel and antiparallel stacking track their through spatially temporally resolved photoluminescence spectroscopy from 30 250 K. While measured exciton...
We have used optical spectroscopy to observe spectral broadening of ${\mathrm{WS}}_{2}$ exciton reflectance peaks in heterostructures monolayer capped with mono- few-layer graphene. The is found be similar for the A and B excitons on order 5--10 meV. No strong dependence number graphene layers was observed within experimental uncertainty. can attributed charge- energy-transfer processes between two materials, providing an lower bound corresponding time scales 65 fs.
Modulation of weak interlayer interactions between quasi-two-dimensional atomic planes in the transition metal dichalcogenides (TMDCs) provides avenues for tuning their functional properties. Here we show that above-gap optical excitation TMDCs leads to an unexpected large-amplitude, ultrafast compressive force two-dimensional layers, as probed by situ measurements layer spacing at femtosecond time resolution. We this response arises from a dynamic modulation van der Waals interaction and...
Abstract The high light‐output efficiencies of In x Ga 1‐ N quantum‐well (QW)‐based light‐emitting diodes (LEDs) even in presence a large number nonradiative recombination centers (such as dislocations) has been explained by localization carriers radiative potential traps, the origins which still remain unclear. To provide insights on highly efficient spectrally resolved photoluminescence (PL) microscopy performed green‐light‐emitting 0.22 0.78 QW LEDs, selectively generating alloy layers....
Abstract Individual atomic defects in 2D materials impact their macroscopic functionality. Correlating the interplay is challenging, however, intelligent hyperspectral scanning tunneling spectroscopy (STS) mapping provides a feasible solution to this technically difficult and time consuming problem. Here, dense spectroscopic volume collected autonomously via Gaussian process regression, where convolutional neural networks are used tandem for spectral identification. Acquired data enable...
The tetragonal ThMn12-type structure is stabilized in (Ce1-xZrx)2T16M (x = 0.2 – 0.3; T Fe or Fe/Co, M Mo W) arc-melted alloys. Approximately 5 at. % of W admixture sufficient to transform the hexagonal Th2Ni17-type (Ce1-xZrx)Fe17 into nearly single-phase (Ce1-xZrx)Fe16M and/or (Ce1-xZrx)Fe15CoM bulk X-ray Rietveld refinements reveal that Zr and (W) substitute different sites crystal structure. Zirconium preferentially replaces Ce, whereas substitutes Fe. At room temperature, phases exhibit...