A5091754371- Surface and Thin Film Phenomena
- Perovskite Materials and Applications
- 2D Materials and Applications
- Semiconductor Quantum Structures and Devices
- Magnetic properties of thin films
- Chalcogenide Semiconductor Thin Films
- Electron and X-Ray Spectroscopy Techniques
- Quantum Dots Synthesis And Properties
- Advanced Chemical Physics Studies
- nanoparticles nucleation surface interactions
- Electronic and Structural Properties of Oxides
- Advanced Materials Characterization Techniques
- Graphene research and applications
- Topological Materials and Phenomena
- Photonic and Optical Devices
- Quantum and electron transport phenomena
- Theoretical and Computational Physics
- Terahertz technology and applications
- Molecular Junctions and Nanostructures
- Physics of Superconductivity and Magnetism
- Semiconductor materials and interfaces
- Advanced Semiconductor Detectors and Materials
- Advanced Electron Microscopy Techniques and Applications
- Copper Interconnects and Reliability
- Magnetic Properties and Applications
Okinawa Institute of Science and Technology Graduate University
2015-2023
Hong Kong University of Science and Technology
2004-2017
University of Hong Kong
2004-2017
University of Bradford
1984
The ability to synthesize high-quality samples over large areas and at low cost is one of the biggest challenges during developmental stage any novel material. While chemical vapor deposition (CVD) methods provide a promising low-cost route for CMOS compatible, large-scale growth materials, it often falls short demands in nanoelectronics optoelectronics. We present CVD synthesis single- few- layered MoS2 using direct vapor-phase sulfurization MoO2, which enables us obtain extremely...
Resolving the momentum degree of freedom excitons - electron-hole pairs bound by Coulomb attraction in a photoexcited semiconductor, has remained largely elusive goal for decades. In atomically thin semiconductors, such capability could probe forbidden dark excitons, which critically impact proposed opto-electronic technologies, but are not directly accessible via optical techniques. Here, we momentum-state WSe2 monolayer photoemitting their constituent electrons, and resolving them time,...
We visualize the distribution of electron around hole in an exciton and observe its elusive anomalous dispersion.
With rapidly growing photoconversion efficiencies, hybrid perovskite solar cells have emerged as promising contenders for next generation, low-cost photovoltaic technologies. Yet, the presence of nanoscale defect clusters, that form during fabrication process, remains critical to overall device operation, including efficiency and long-term stability. To successfully deploy perovskites, we must understand nature different types defects, assess their potentially varied roles in performance,...
Semiconducting 2D materials, like transition metal dichalcogenides (TMDs), have gained much attention for their potential in opto-electronic devices, valleytronic schemes, and semi-conducting to metallic phase engineering. However, graphene other atomically thin they lose key properties when placed on a substrate silicon, including quenching of photoluminescence, distorted crystalline structure, rough surface morphology. The ability protect these monolayer TMDs, such as molybdenum disulfide...
We present a terahertz spectroscopic study of polar ferrimagnet FeZnMo_{3}O_{8}. Our main finding is giant high-temperature optical diode effect, or nonreciprocal directional dichroism, where the transmitted light intensity in one direction over 100 times lower than opposite direction. The effect takes place paramagnetic phase with no long-range magnetic order crystal, which contrasts sharply all existing reports other magnetoelectric materials, ordering necessary prerequisite. In...
Low energy electron microscopy (LEEM) and photoemission (PEEM) are two powerful techniques for the investigation of surfaces, thin films surface supported nanostructures. In this review, we examine contributions these to our understanding graphene in recent years. These have been made studies on various metal SiC surfaces free-standing graphene. We discuss how real-time imaging capability LEEM facilitates a deeper mechanisms dynamic processes, such as growth intercalation. Numerous examples...
Abstract Van der Waals materials, existing in a range of thicknesses from monolayer to bulk, allow for interplay between surface and bulk nonlinearities, which otherwise dominate only at atomically-thin or extremes, respectively. Here, we observe an unexpected peak intensity the generated second harmonic signal versus thickness Indium Selenide crystals, contrast quadratic increase expected thin crystals. We explain this by interference effects offer new handle on engineering nonlinear...
We make a movie, on the nanometer and femtosecond scale, as we pull apart electrons with photoinduced surface field.
Recent years have seen the rapid discovery of solids whose low-energy electrons a massless, linear dispersion, such as Weyl, line-node, and Dirac semimetals. The remarkable optical properties predicted in these materials show their versatile potential for optoelectronic uses. However, little is known response picoseconds after absorbing photon. Here, we measure ultrafast dynamics four that share non-trivial band structure topology but differ chemically, structurally, structures: ZrSiS, which...
The temporal evolution of nonequilibrium coverage profiles in the Pb wetting layer on Si(111) surface is studied using low energy electron microscopy. initial step profile propagates rapidly at a constant velocity with an unperturbed shape. A model proposed that attributes this nonclassical equilibration behavior to diffusion thermally generated adatoms top layer. This can account for observed convectionlike mass transport, as well its dramatic dependence coverage. Such anomalous transport...
The temperature dependence of the step line tension on Si(111) $(1\ifmmode\times\else\texttimes\fi{}1)$ surface is determined from a capillary wave analysis two-dimensional island edge fluctuations and straight that are observed with low energy electron microscopy. decreases by nearly 20% linear coefficient $\ensuremath{-}0.14\phantom{\rule{0.3em}{0ex}}\mathrm{meV}∕\mathrm{\AA{}}\phantom{\rule{0.2em}{0ex}}\mathrm{K}$ between 1145 $1233\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Temporal...
Lattice rotations in graphene on Ru(0001) are investigated with low-energy electron microscopy and micro-low-energy diffraction. The measurements place an upper limit, 250 nm, the racemic length scale of recently reported chirality this system, arising from rotated features within unit cell. On a longer scale, small orientational coincidence substrate lattice found to be present vast majority layer. resulting proliferation small-angle grain boundaries may influence properties layer that is...
The structure and electronic properties of the $(\sqrt{13}\ifmmode\times\else\texttimes\fi{}\sqrt{13})R13.{9}^{\ensuremath{\circ}}$ $(2\sqrt{3}\ifmmode\times\else\texttimes\fi{}2\sqrt{3})R{30}^{\ensuremath{\circ}}$ ordered phases C${}_{60}$ on Pt(111) surface are investigated using combined dynamic low-energy electron diffraction density functional theory (DFT) calculations. two have same local adsorption structure, while they predicted by DFT calculations to exhibit very different...
Mass transport in the Pb wetting layer on Si(111) surface is investigated by observing nonequilibrium coverage profile evolution with low energy electron microscopy and microlow diffraction. Equilibration of an initial step occurs exchange mass between oppositely directed steep gradients that each move unperturbed shape. The bifurcation profile, shape two moving edges, time dependence equilibration are all at odds expectations for classical diffusion behavior. These observations signal a...
We report on the first terahertz (THz) emitter based femtosecond-laser-ablated gallium arsenide (GaAs), demonstrating a 65% enhancement in THz emission at high optical power compared to nonablated device. Counter-intuitively, ablated device shows significantly lower photocurrent and carrier mobility. understand this behavior terms of n-doping, shorter lifetime, enhanced photoabsorption arising from ablation process. Our results show that laser allows for efficient cost-effective...
Quantum well (QW) resonances are identified in Ag films on an Fe(100) surface and used low energy electron microscopy to monitor film morphology during annealing growth. We find that thermally decompose thicknesses stabilized by QW states at the Gamma point. Novel growth morphologies also observed highlight competition between kinetic limitations state energetics promote electronic These combined observations help explain unusual bifurcation mode of thermal decomposition was reported...
The adsorption and diffusion of CO molecules on a Pt(111) surface have been studied using low-energy electron microscopy (LEEM). explicit relationship between LEEM image intensity coverage that is determined during used to characterize nonequilibrium profiles are subsequently prepared by laser-induced thermal desorption. Real-time observations the temporal evolution these toward equilibrium uniform distributions analyzed predictive inverse solutions equation. These two methods determine...
A photocapacitive, dissipationless, optoelectronic terahertz response is observed in robust 3D van der Waals heterostructured flakes of hexagonal boron nitride and graphene. The fundamentally distinct from that the parent materials can be tuned insulating to photocapacitive semiconducting by varying composition. Such hybrid structures have broad implications for tunable potential devices. As a service our authors readers, this journal provides supporting information supplied authors. are...
Fe3S4 (greigite), a ferrimagnetic compound widely encountered in nature and of increasing technical interest, is prepared by vapor–solid interaction. This done laterally resolving ultrahigh vacuum multi-method instrument, which not only allows situ analysis the reaction product without influence environment but also follows its evolution during reaction. The physical method employed here avoids formation unwanted products that are produced usual wet chemical synthesis methods. resulting...
${\mathrm{SrMnSb}}_{2}$ is a candidate Dirac semimetal whose electrons near the $Y$ point have linear dispersion and low mass of cone. Here we demonstrate that ultrafast, 800-nm optical pulses can launch coherent phonon oscillations in ${\mathrm{Sr}}_{0.94}{\mathrm{Mn}}_{0.92}{\mathrm{Sb}}_{2}$, particularly an ${A}_{g}$ mode at 4.4 THz. Through first-principles calculations electronic phononic structure ${\mathrm{SrMnSb}}_{2}$, show high-amplitude this would displace atoms way transiently...
In the transition metal dichalcogenide ${\mathrm{IrTe}}_{2}$, low-temperature charge-ordered phase transitions involving Ir dimers lead to occurrence of stripe phases different periodicities, and nearly degenerate energies. Bulk-sensitive measurements have shown that, upon cooling, ${\mathrm{IrTe}}_{2}$ undergoes two such first-order $(5\ifmmode\times\else\texttimes\fi{}1\ifmmode\times\else\texttimes\fi{}5)$ $(8\ifmmode\times\else\texttimes\fi{}1\ifmmode\times\else\texttimes\fi{}8)$...