A5034560994- Thermal properties of materials
- Mechanical and Optical Resonators
- 2D Materials and Applications
- Thermal Radiation and Cooling Technologies
- Quantum and electron transport phenomena
- Electronic and Structural Properties of Oxides
- Perovskite Materials and Applications
- Plasmonic and Surface Plasmon Research
- Semiconductor materials and devices
- Advanced Thermoelectric Materials and Devices
- Terahertz technology and applications
- Advanced Electron Microscopy Techniques and Applications
- Strong Light-Matter Interactions
- Force Microscopy Techniques and Applications
- Physics of Superconductivity and Magnetism
- Semiconductor Quantum Structures and Devices
- Graphene research and applications
- Advancements in Semiconductor Devices and Circuit Design
- MXene and MAX Phase Materials
- Ferroelectric and Piezoelectric Materials
- Photonic and Optical Devices
- Machine Learning in Materials Science
- Iron-based superconductors research
- Quantum, superfluid, helium dynamics
- Superconductivity in MgB2 and Alloys
University of California, Berkeley
2021-2025
Lawrence Berkeley National Laboratory
2022-2025
University of California System
2025
Peking University
2019-2024
Advanced microelectronics in the future may require semiconducting channel materials beyond silicon. Two-dimensional (2D) semiconductors, with their atomically thin thickness, hold great promise for electronic devices. One challenge to achieving high-performance 2D semiconductor field effect transistors (FET) is high contact resistance at metal–semiconductor interface. In this study, we develop a charge-transfer doping strategy WSe2/α-RuCl3 heterostructures achieve low-resistance ohmic...
2D metal carbides and nitrides (MXene) are promising candidates for electromagnetic (EM) shielding, saturable absorption, thermal therapy, photocatalysis owing to their excellent EM absorption. The plasmon resonances in metallic MXene micro/nanostructures may play an important role enhancing the absorption; however, contribution has not been determined due lack of a precise understanding its behavior. Here, use high-spatial-resolution electron energy-loss spectroscopy measure dispersion...
Room-temperature polar skyrmions, which have been recently discovered in oxide superlattice, received considerable attention for their potential applications nanoelectronics owing to nanometer size, emergent chirality, and negative capacitance. For practical applications, manipulation using external stimuli is a prerequisite. Herein, we study the dynamics of individual skyrmions at nanoscale via situ scanning transmission electron microscopy. By monitoring electric-field-driven creation,...
Significance As high-power devices approach nanoscale, interface thermal conductance (ITC) becomes a bottleneck to govern the device performance, which is dominated by phonons. In order gain insights into engineering ITC, here we measure local phonons across AlN/Si and AlN/Al interfaces using atomically resolved vibrational electron energy-loss spectroscopy. We find that dominant types of for ITC are very different in these two systems demonstrate ability correlate measured with at atomic...
Abstract Moiré superlattices of van der Waals heterostructures provide a powerful way to engineer electronic structures two-dimensional materials. Many novel quantum phenomena have emerged in graphene and transition metal dichalcogenide moiré systems. Twisted phosphorene offers another attractive system explore physics because features an anisotropic rectangular lattice, different from isotropic hexagonal lattices previously reported. Here we report emerging optical transitions twisted...
Abstract In single unit-cell FeSe grown on SrTiO 3 , the superconductivity transition temperature features a significant enhancement. Local phonon modes at interface associated with electron-phonon coupling may play an important role in interface-induced However, such have eluded direct experimental observations. The complicated atomic structure of brings challenges to obtain accurate structure-phonon relation knowledge. Here, we achieve characterizations and FeSe/SrTiO atomically resolved...
Abstract Directly mapping local phonon dispersion in individual nanostructures can advance our understanding of their thermal, optical, and mechanical properties. However, this requires high detection sensitivity combined spatial, energy momentum resolutions, thus has been elusive. Here, we demonstrate a four-dimensional electron loss spectroscopy technique, present position-dependent measurements boron nitride nanotubes. By scanning the beam real space while monitoring both transfer, are...
Coupled two-dimensional electron-hole bilayers provide a unique platform to study strongly correlated Bose-Fermi mixtures in condensed matter. Electrons and holes spatially separated layers can bind form interlayer excitons, composite Bosons expected support high-temperature exciton condensates. The excitons also interact with excess charge carriers when electron hole densities are unequal. Here, we use optical spectroscopy quantitatively probe the local thermodynamic properties of fluids...
Ultrafast charge transfer processes provide a facile way to create interlayer excitons in directly contacted transition metal dichalcogenide (TMD) layers. More sophisticated heterostructures composed of TMD/hBN/TMD enable new ways control exciton properties and achieve novel phenomena, such as insulators condensates, where longer lifetimes are desired. In this work, we experimentally study the dynamics heterostructure 1 nm thick hBN spacer between MoSe2 WSe2 monolayers. We observe hole from...
Nanoscale defects like grain boundaries (GBs) would introduce local phonon modes and affect the bulk materials' thermal, electrical, optical, mechanical properties. It is highly desirable to correlate atomic arrangements for individual precisely understand structure–property relation. Here we investigated localized of Al2O3 GBs by combination vibrational electron energy loss spectroscopy (EELS) in scanning transmission microscope density functional perturbation theory (DFPT). The differences...
Hyperbolic phonon polaritons (HPhPs) in orthorhombic-phase molybdenum trioxide ($\alpha$-MoO3) show in-plane hyperbolicity, great wavelength compression and ultra-long lifetime, therefore holding potential nanophotonic applications. However, its polaritonic response the far-infrared (FIR) range has long remained unexplored due to challenges experimental characterization. Here, using monochromated electron energy loss spectroscopy (EELS) a scanning transmission microscope (STEM), we probe...
Phonons are the primary heat carriers in non-metallic solids. In compositionally heterogeneous materials, thermal properties believed to be mainly governed by disrupted phonon transport due mass disorder and strain fluctuations, while effects of compositional fluctuation induced local states usually ignored. Here, scanning transmission electron microscopy energy loss spectroscopy sophisticated calculations, we identify vibrational ingredient-dependent interface modes Al x Ga 1 – N quantify...
Natural materials usually consist of isotopic mixtures, for which different ratios can lead to distinct material properties such as thermal conductivity and nucleation process. However, the knowledge interface remains largely unexplored mainly due challenges in identification property measurement at an atomic scale. Here, by using monochromated electron energy-loss spectroscopy a scanning transmission microscope, we reveal momentum-transfer-dependent lattice vibration behavior artificial...
Optical neural networks (ONNs) are a promising computational alternative for deep learning due to their inherent massive parallelism linear operations. However, the development of energy-efficient and highly parallel optical nonlinearities, critical component in ONNs, remains an outstanding challenge. Here, we introduce nonlinear microdevice array (NOMA) compatible with incoherent illumination by integrating liquid crystal cell silicon photodiodes at single-pixel level. We fabricate NOMA...
Excitonic insulators represent a unique quantum phase of matter, providing rich ground for studying exotic bosonic states. Strongly coupled electron-hole bilayers, which host stable dipolar exciton fluids with an density that can be adjusted electrostatically, offer ideal platform to investigate correlated excitonic insulators. Based on bilayers made MoSe2/hBN/WSe2 heterostructures, here we study the behavior in perpendicular magnetic field. We report observation oscillations both Coulomb...
Strongly coupled electron-hole bilayers can host quantum states of interlayer excitons, such as high-temperature exciton condensates at zero magnetic field. This state is predicted to feature perfect Coulomb drag, where a current in one layer accompanied by an equal but opposite the other. We used optical technique probe electrical transport correlated based on MoSe 2 /hBN/WSe heterostructures. observed drag excitonic insulator phase low temperatures; counterflow resistance excitons remained...
Abstract Nanoscale defects such as dislocations, have a significant impact on the phonon thermal transport properties in non-metallic materials. To unravel these effects, understanding of defect modes is essential. Herein, at atomic scale, localized phonons individual dislocation Si/Ge interface are measured via monochromated electron energy loss spectroscopy scanning transmission microscope. These then correlated with local microstructure, further revealing effects properties. The causes...
Two-dimensional semiconductors and their moiré superlattices have emerged as important platforms for investigating correlated electrons. However, many key properties of these systems, such the frequency-dependent conductivity, remain experimentally inaccessible because mesoscopic sample size. Here we report a technique to directly measure complex conductivity electrostatically gated two-dimensional in terahertz frequency range. Applying this WSe2 monolayer encapsulated hBN, observe clear...
Strongly coupled two-dimensional electron-hole bilayers can give rise to novel quantum Bosonic states: electrons and holes in electrically isolated layers pair into interlayer excitons, which form a Bose-Einstein condensate below critical temperature at zero magnetic field. This state is predicted feature perfect Coulomb drag, where current one layer must be accompanied by an equal but opposite the other, counterflow superconductivity, excitons superfluid with viscosity. Electron-hole strong...