A5063669156- 2D Materials and Applications
- Graphene research and applications
- Topological Materials and Phenomena
- Plasmonic and Surface Plasmon Research
- Perovskite Materials and Applications
- Quantum and electron transport phenomena
- Photonic and Optical Devices
- Metamaterials and Metasurfaces Applications
- Chalcogenide Semiconductor Thin Films
- Photonic Crystals and Applications
- MXene and MAX Phase Materials
- Terahertz technology and applications
- Quantum Dots Synthesis And Properties
- Molecular Junctions and Nanostructures
- Nanowire Synthesis and Applications
- Mechanical and Optical Resonators
- Semiconductor Quantum Structures and Devices
- Organic and Molecular Conductors Research
- Advanced Condensed Matter Physics
- Photorefractive and Nonlinear Optics
- Organic Electronics and Photovoltaics
- Advanced Fiber Laser Technologies
- Silicon Nanostructures and Photoluminescence
- Ga2O3 and related materials
- Diamond and Carbon-based Materials Research
Seoul National University
2002-2025
Yonsei University
2003-2019
Government of the Republic of Korea
2017
Seoul Institute
2017
Samsung (South Korea)
2015
Lawrence Berkeley National Laboratory
2009-2010
The effective synthesis of two-dimensional transition metal dichalcogenides alloy is essential for successful application in electronic and optical devices based on a tunable band gap. Here we show process Mo1-xWxS2 using sulfurization super-cycle atomic layer deposition Mo1-xWxOy. Various spectroscopic microscopic results indicate that the synthesized alloys have complete mixing Mo W atoms gap by systematically controlled composition number. Based this, synthesize vertically...
2D transition metal dichalcogenides (TMDCs) have emerged as promising candidates for post-silicon nanoelectronics owing to their unique and outstanding semiconducting properties. However, contact engineering these materials create high-performance devices while adapting large-area fabrication is still in its nascent stages. In this study, graphene/Ag contacts are introduced into MoS2 devices, which a graphene film synthesized by chemical vapor deposition (CVD) inserted between CVD-grown Ag...
Abstract 2D transition metal dichalcogenides (TMDs) have attracted much attention for their gas sensing applications due to superior responsivity at typical room temperature. However, low power consumption and reliable selectivity are the two main requirements sensors be applicable in future electronic devices. Herein, a p‐type (WSe 2 /WS ) n‐type (MoS /WSe photovoltaic self‐powered sensor is demonstrated using TMD heterostructures first time. The operated by effect of heterostructures,...
We report ultrafast pump-probe spectroscopy examining exciton dynamics in atomically thin MoS2. Spectrally- and temporally-resolved measurements are performed to investigate the interaction of two important direct-gap excitons (A B) their associated broadening kinetics. The show strongly correlated inter-excitonic dynamic, which transient blue-shifted excitonic absorption originates from internal A-B interaction. observed complex spectral response is determined by collision-induced linewidth...
We study the broadband optical conductivity and ultrafast carrier dynamics of epitaxial graphene in few-layer limit. Equilibrium spectra nominally buffer, monolayer, multilayer exhibit significant terahertz near-infrared absorption, consistent with a model intra- interband transitions dense Dirac electron plasma. Nonequilibrium transmission changes after photoexcitation are shown to be dominated by excess hole carriers, 1.2 ps monoexponential decay that reflects minority-carrier recombination time.
Two-dimensional stacks of dissimilar hexagonal monolayers exhibit unusual electronic, photonic and photovoltaic responses that arise from substantial interlayer excitations. Interband excitation phenomena in individual monolayer occur states at band edges (valleys) the momentum space; therefore, low-energy can be directed by two-dimensional rotational degree each crystal. However, this rotation-dependent is largely unknown, due to lack control over relative rotations, thereby leading...
We present terahertz spectroscopic measurements of Dirac fermion dynamics from a large-scale graphene that was grown by chemical vapor deposition and on which carrier density modulated electrostatic doping. The measured frequency-dependent optical sheet conductivity shows electron-density-dependence characteristics, can be understood simple Drude model. In low regime, the is constant regardless applied gate voltage, but in high it has nonlinear behavior with respect to voltage. Chemical...
Abstract Two-dimensional layered transition-metal dichalcogenides have attracted considerable interest for their unique layer-number-dependent properties. In particular, vertical integration of these two-dimensional crystals to form van der Waals heterostructures can open up a new dimension the design functional electronic and optoelectronic devices. Here we report photocurrent generation in graphene/MoS 2 /graphene by creating device with two distinct regions containing one-layer...
Solar-energy conversion by photoelectrochemical (PEC) devices is driven the separation and transfer of photogenerated charge carriers. Thus, understanding carrier dynamics in a PEC device essential to realizing efficient solar-energy conversion. Here, we investigate time-resolved emerging low-cost Sb2Se3 nanostructure photocathodes for water splitting. Using terahertz spectroscopy, observed an initial mobility loss within tens picoseconds due localization attributed origin rich surface...
While tremendous efforts have been made for developing thin perovskite films suitable a variety of potential photoelectric applications such as solar cells, field-effect transistors, and photodetectors, only few works focus on the micropatterning film which is one most critical issues large area uniform microarrays perovskite-based devices. Here we demonstrate simple but robust method with controlled crystalline structure guarantees to preserve its intrinsic properties. A micropatterns are...
Two-dimensional surface-scattering dynamics are central in the physics of topological insulators. Numerous electrical and optical measurements have evidenced that origins novel optoelectronic response can be traced back to Dirac surface-electron dynamics. Intrinsic surface dynamics, however, remain elusive because these experiments cannot access frequencies rate. Time-resolved terahertz spectroscopy is only apparatus for directly probing collective low-energy electronic transitions. Here, by...
Abstract The optical Stark effect is a coherent light–matter interaction describing the modification of quantum states by non-resonant light illumination in atoms, solids and nanostructures. Researchers have strived to utilize this control exciton states, aiming realize ultra-high-speed switches modulators. However, most studies focused on only lowest state due lack energy selectivity, resulting low degree-of-freedom devices. Here, applying linearly polarized laser pulse few-layer ReS 2 ,...
Broadband detection of mid-infrared (IR) photons extends to advanced optoelectronic applications such as imaging, sensing, and telecommunications. While graphene offers an attractive platform for broadband visible/IR photodetection, previous efforts improve its responsivity, example, by integrating light-absorbing colloids or waveguide antenna fabrication, were achieved at the cost reduced photon bandwidth. In this work, we demonstrate room-temperature operation a novel mid-IR photodetector...
Modulating light via coherent charge oscillations in solids is the subject of intense research topics opto-plasmonics. Although a variety methods are proposed to increase such modulation efficiency, one central challenge achieve high depth (defined by ratio extinction with/without light) under small photon-flux injection, which becomes fundamental trade-off issue both metals and semiconductors. Here, fabricating simple micro-ribbon arrays topological insulator Bi2Se3, we report an...
Abstract The 1 s exciton—the ground state of a bound electron-hole pair—is central to understanding the photoresponse monolayer transition metal dichalcogenides. Above exciton, recent visible and near-infrared investigations have revealed that excited excitons are much richer, exhibiting series Rydberg-like states. A natural question is then how internal excitonic transitions interrelated on photoexcitation. Accessing these intraexcitonic transitions, however, demands fundamentally different...
Abstract Electromagnetically induced transparency (EIT) analogs using metamaterials have diverse applications, including nonlinear optics, telecommunications, and biochemical sensors. These EIT can be actively controlled by embedding semiconducting materials into metamaterial structures, but most active require complex optical setups complicated fabrication processes. Graphene‐based are some of the promising systems because their simple controllability electrical bias, related researches so...
Controllable and reversible modulation of the electrical optical properties WS<sub>2</sub> was demonstrated <italic>via</italic> hydrazine doping sulfur annealing.
Abstract Carrier multiplication (CM) is a process in which high-energy free carriers relax by generation of additional electron-hole pairs rather than heat dissipation. CM promising disruptive improvements photovoltaic energy conversion and light detection technologies. Current state-of-the-art nanomaterials including quantum dots carbon nanotubes have demonstrated CM, but are not satisfactory owing to high-energy-loss inherent difficulties with carrier extraction. Here, we report van der...
Abstract Photolithography is the prevalent microfabrication technology. It needs to meet resolution and yield demands at a cost that makes it economically viable. However, conventional far-field photolithography has reached diffraction limit, which imposes complex optics short-wavelength beam source achieve high expense of efficiency. Here, we present cost-effective near-field optical printing approach uses metal patterns embedded in flexible elastomer photomask with mechanical robustness....
Higher-order topological insulators are recently discovered quantum materials exhibiting distinct phases with the generalized bulk-boundary correspondence. Td-WTe2 is a promising candidate to reveal hinge excitation in an atomically thin regime. However, initial theories and experiments focusing on localized one-dimensional conductance only, no experimental reports exist how spin orientations distributed over helical hinges-this critical, yet one missing puzzle. Here, we employ magneto-optic...
Modulation of the refractive index materials is elementary, yet it crucial for manipulation electromagnetic waves. Relying on inherent properties natural materials, has been a long-standing challenge in device engineering to increase index-modulation contrast. Here, we demonstrate significant amount ultrafast modulation by optically exciting non-equilibrium Dirac fermions graphene layer integrated onto high-index metamaterial. Furthermore, an extremely-large electrical up Δn ~ -3.4 (at 0.69...
Quantum beats, periodic oscillations arising from coherent superposition states, have enabled exploration of novel phenomena. Originating strong Coulomb interactions and reduced dielectric screening, two-dimensional transition metal dichalcogenides exhibit strongly bound excitons either in a single structure or hetero-counterpart; however, quantum coherence between is barely known to date. Here we observe exciton beats atomically thin ReS