A5052486246- 2D Materials and Applications
- Perovskite Materials and Applications
- Atmospheric Ozone and Climate
- Graphene research and applications
- Atmospheric chemistry and aerosols
- Spectroscopy and Laser Applications
- MXene and MAX Phase Materials
- Quantum Dots Synthesis And Properties
- Spectroscopy and Quantum Chemical Studies
- Advanced Fiber Laser Technologies
- Electronic and Structural Properties of Oxides
- Diamond and Carbon-based Materials Research
- Advanced Chemical Physics Studies
- Boron and Carbon Nanomaterials Research
- Electron and X-Ray Spectroscopy Techniques
- Laser-Matter Interactions and Applications
- Strong Light-Matter Interactions
- Inorganic Chemistry and Materials
- Photonic and Optical Devices
- Anodic Oxide Films and Nanostructures
- Inorganic Fluorides and Related Compounds
- Iron-based superconductors research
- Semiconductor Quantum Structures and Devices
- Spectroscopy Techniques in Biomedical and Chemical Research
- Ga2O3 and related materials
Stanford University
2021-2025
Columbia University
2019-2023
SLAC National Accelerator Laboratory
2021-2023
University of Pennsylvania
2014-2016
California University of Pennsylvania
2015
Philadelphia University
2015
Larger monolayers with gold tapes Although the exfoliation of materials such as transition metal dichalcogenides produces high-quality electronic low defect densities, size is limited to micrometer scale. Liu et al. modified this method by creating atomically flat layers on polymer supports. The strong van der Waals adhesion layer allowed be exfoliated centimeter Multilayers could reassembled artificial structures, a MoSe 2 /WSe single-crystal bilayer twist angle chosen quench intralayer...
Nonlinear optical response from a van der Waals interface is modulated and enhanced in twistable boron nitride homostructures.
In the atmosphere, a dominant loss process for carbonyl oxide intermediates produced from alkene ozonolysis is also an important source of hydroxyl radicals. The rate appearance OH radicals revealed through direct time-domain measurements following vibrational activation prototypical methyl-substituted Criegee under collision-free conditions. Complementary theoretical calculations predict unimolecular decay in vicinity barrier 1,4 hydrogen transfer that leads to products. Both experiment and...
Under strong electromagnetic excitation, electron–hole (e-h) pairs may be generated in solids, which are subsequently driven to high energy and momentum, producing harmonics (HH) of the driving field. The HH efficiency depends on degree coherence between electron hole created by laser Here, we disrupt this e-h an atomically thin semiconductor photodoping via incoherent pairs. We observe a strong, systematic harmonic order-dependent intensity reduction. This trend is explained exponential...
Nonlinear optical materials possess wide applications, ranging from terahertz and mid-infrared detection to energy harvesting. Recently, the correlations between nonlinear responses certain topological properties, such as Berry curvature quantum metric tensor, have attracted considerable interest. Here, we report giant room-temperature nonlinearities in non-centrosymmetric two-dimensional materials-the Janus transition metal dichalcogenides 1 T' phase, synthesized by an advanced atomic-layer...
Unimolecular decay of Criegee intermediates produced in alkene ozonolysis is known to be a significant source OH radicals the troposphere. In this work, unimolecular methyl-substituted intermediate, syn-CH3CHOO, products shown occur at energies significantly below transition state barrier for 1,4 hydrogen transfer that leads these [Y. Fang et al., J. Chem. Phys. 144, 061102 (2016)]. The rate appearance arising from tunneling through obtained direct time-domain measurements following...
Photoinduced charge separation in transition-metal dichalcogenide heterobilayers is being explored for moir\'e excitons, spin-valley polarization, and quantum phases of excitons/electrons. While different momentum points can be critically involved dynamics, little known directly from experiments. Here we determine momentum-resolved electron dynamics the $\mathrm{W}{\mathrm{S}}_{2}/\mathrm{Mo}{\mathrm{S}}_{2}$ heterobilayer using time- angle-resolved photoemission spectroscopy. Upon...
We present a systematic study of the crystal-orientation dependence high-harmonic generation in monolayer transition-metal dichalcogenides, WS 2 and MoSe , subjected to intense linearly polarized midinfrared laser fields. The measured spectra consist both odd- even-order harmonics, with high-energy cutoff extending beyond 15th order for laser-field strength around ~1 V/nm. In we find that polarization direction odd-order harmonics smoothly follows field irrespective crystal orientation,...
Anti-Stokes photoluminescence (PL) is light emission at a higher photon energy than the excitation, with applications in optical cooling, bioimaging, lasing, and quantum optics. Here, we show how plasmonic nano-cavities activate anti-Stokes PL WSe2 monolayers through resonant excitation of dark exciton room temperature. The near-fields cavities excite out-of-plane transition dipole exciton, leading to from bright energy. Through statistical measurements on hundreds cavities, that coupling...
The unimolecular decay of carbonyl oxide intermediates, known as Criegee produced in alkene ozonolysis is a significant source OH radicals the troposphere. Here, rate appearance radical products examined directly time-domain for prototypical alkyl-substituted intermediate, CH3CH2CHOO, following vibrational activation under collision-free conditions. Complementary statistical Rice–Ramsperger–Kassel–Marcus calculations microcanonical CH3CH2CHOO are also carried out at energies vicinity barrier...
Raman microscopy is a powerful analytical technique for materials and life sciences that enables mapping the spatial distribution of chemical composition sample. State-of-the-art microscopes, based on point-scanning frequency-domain detection, have long (∼1s) pixel dwell times, making it challenging to acquire images significant area (e.g., 100×100µm). Here we present compact wide-field microscope time-domain Fourier-transform approach, which parallel acquisition spectra all pixels 2D...
A doubly hydrogen-bonded interaction between the Criegee intermediate and a deuterated carboxylic acid facilitates efficient H/D transfer to yield partially vinyl hydroperoxide.
Vertically stacked van der Waals (vdW) heterostructures exhibit unique electronic, optical, and thermal properties that can be manipulated by twist-angle engineering. However, the weak phononic coupling at a bilayer interface imposes fundamental bottleneck for future two-dimensional devices. Using ultrafast electron diffraction, we directly investigated photoinduced nonequilibrium phonon dynamics in MoS 2 /WS 4° twist angle WSe /MoSe heterobilayers with angles of 7°, 16°, 25°. We identified...
Abstract We conducted low-temperature photoluminescence (PL) spectroscopy experiments on individual WS 2 and MoSe nanoribbons prepared by gold-assisted exfoliation from the slanted surface of bulk crystals with a vicinal stepwise pattern. The are predominantly monolayer have widths varying hundreds nanometers down to tens nanometers. Most NRs display an emission profile similar 2D excitons monolayers. In contrast, characterized sharp peaks that can be attributed localized or trions. Moreover...
Two-dimensional twisted bilayer moir\'e structures provide a versatile material platform for realizing rich variety of strongly correlated electronic quantum phases intricately coupled with the periodically modulated lattice structures. In this work, we use ultrafast electron diffraction to directly reveal photoinduced dynamic evolution superlattice in $2^\circ$ and $57^\circ$ WSe$_2$/MoSe$_2$ heterobilayers. Upon above-band-gap photoexcitation, features are enhanced within 1 ps subsequently...
Ozonolysis of alkenes, a principle non-photolytic source atmospheric OH radicals, proceeds through unimolecular decay energized carbonyl oxide intermediates, known as Criegee intermediates. In this work, cold dimethyl-substituted intermediates are vibrationally activated in the CH stretch overtone region to drive 1,4 hydrogen transfer reaction that leads radical products. IR excitation (CH3)2COO reveals vibrational states with sufficient oscillator strength, coupling coordinate, and energy...
As a 2D dielectric material, hexagonal boron nitride (hBN) is in high demand for applications photonic, nonlinear optic, and nanoelectronic devices as an atomically flat thin or encapsulation layer. Unfortunately, the high-throughput preparation of macroscopic-scale hBN flakes with selective thickness ongoing challenge, limiting device fabrication technological integration. Here, we use various metal films to prepare millimeter-scale dimension, near-unity yields, tunable flake distributions...
Monolayer 2D semiconductors, such as WS
Abstract Confinement of monolayers into quasi‐1D atomically thin nanoribbons could lead to novel quantum phenomena beyond those achieved in their bulk and monolayer counterparts. However, current experimental availability nanoribbon species graphene is limited bottom‐up synthesis or lithographic patterning. In this study, a versatile direct approach introduced exfoliate van der Waals crystals as nanoribbons. Akin the Scotch tape exfoliation method for producing monolayers, technique provides...
Alloying inorganic cations such as Cs+ or Rb+ into hybrid lead halide perovskites has been shown to provide long-term material stability critical the implementation in solar cells, but little is known about how cation alloying affects electronic properties. Here we study single crystals of mixed-cation bromide perovskite, Csx(CH3NH3)1–xPbBr3, a range mixing ratios, x = 0.05–0.3. In contrast continuous bandgap tunability for mixed-anion alloys, find that bandgaps Csx(CH3NH3)1–xPbBr3 adopt...