A5084641887- 2D Materials and Applications
- Graphene research and applications
- Topological Materials and Phenomena
- Quantum Dots Synthesis And Properties
- Chalcogenide Semiconductor Thin Films
- MXene and MAX Phase Materials
- Quantum and electron transport phenomena
- Electrocatalysts for Energy Conversion
- Surface and Thin Film Phenomena
- Advanced Condensed Matter Physics
- Iron-based superconductors research
- Perovskite Materials and Applications
- Magnetic properties of thin films
- ZnO doping and properties
- Chemical and Physical Properties of Materials
- Semiconductor materials and interfaces
- Phase-change materials and chalcogenides
- Diamond and Carbon-based Materials Research
- Advanced Photocatalysis Techniques
- Organic and Molecular Conductors Research
- Quantum many-body systems
- Machine Learning in Materials Science
- Atomic and Subatomic Physics Research
- Electronic and Structural Properties of Oxides
- Mathematical Dynamics and Fractals
University of Hong Kong
2016-2024
State Key Laboratory of Synthetic Chemistry
2022
Princeton University
2009-2011
The recently discovered three dimensional or bulk topological insulators are expected to exhibit exotic quantum phenomena. It is believed that a trivial insulator can be twisted into state by modulating the spin-orbit interaction crystal lattice via odd number of band inversions, driving system through phase transition. By directly measuring invariants (for method measure Fu-Kane {$\nu_0$}, see Hsieh \textit{et.al.,} Science 323, 919 (2009) at...
A mechanistic understanding of interactions between atomically thin two-dimensional (2D) transition-metal dichalcogenides (TMDs) and their growth substrates is important for achieving the unidirectional alignment nuclei seamless stitching 2D TMD domains thus wafers. In this work, we conduct a cross-sectional scanning transmission electron microscopy (STEM) study to investigate atomic-scale nucleation early stage behaviors chemical vapor deposited monolayer (ML-) MoS2 molecular beam epitaxy...
Abstract Ultrathin two‐dimensional transition‐metal dichalcogenides (TMDs) have been pursued extensively in recent years for interesting physics and application potentials. For the latter, it is essential to synthesize crystalline TMD monolayers at wafer‐scale. Here, we report growth of single‐crystalline MSe 2 (M = Mo, W) wafer‐scale by molecular‐beam epitaxy low temperatures (200–400°C) on nominally flat Au(1 1 1) substrates. The epifilms intrinsic defect densities 10 12 cm −2 . grown...
Abstract Two-dimensional (2D) nanomaterials hold immense application potentials such as in high
performance nano-electronics, and asymmetric 2D structures with inherent electric dipoles will 
extends the promises. Yet synthesizing remains 
challenging. Herein, we report first synthesis of single-layer (SL) hexagonal (H-) phase polar 
Janus MoSeN via nitrogen-plasma-assisted molecular beam epitaxy (MBE). This is a significant 
achievement given...
Confining interacting particles in one-dimension (1D) changes the electronic behavior of system fundamentally, which has been studied extensively past. Examples 1D metallic systems include carbon nanotubes, quasi-1D organic conductors, metal chains, and domain boundary defects monolayer thick transition-metal dichalcogenides such as MoSe2. Here single bundles Mo6Se6 nanowires were fabricated through annealing a MoSe2 grown by molecular-beam epitaxy on graphene. Conversion from...
A mirror twin-domain boundary (MTB) in monolayer MoSe2 represents a (quasi) one-dimensional metallic system. Its electronic properties, particularly the low-energy excitations so-called 4|4P-type MTB, have drawn considerable research attention. Reports of quantum well states, charge density waves, and Tomonaga–Luttinger liquid (TLL) all been made. Here, by controlling lengths MTBs employing different substrates, we reveal low-temperature scanning tunneling microscopy/spectroscopy, Friedel...
Abstract Phosphorus (P) has been predicted to possess many two-dimensional (2D) allotropes, which have attracted intensive research attention due their excellent properties and application promises. While only 2D black P films successfully obtained by the exfoliation method, fabrication of other phosphorus structures epitaxial growth remains challenging. Recently, metal-phosphorus network (MPhoN), a superstructure consisted metal atoms realized, offers wider platform study related compounds....
Many transition-metal dichalcogenides, such as MoSe2, are direct-gap semiconductors at monolayer thickness, which hold potentials in nano-electronics, optoelectronics, and some new concept spin- valley-electronic applications. For device application, however, controllable doping of the materials is essential. Here we report hole epitaxial MoSe2 by nitrogen (N) plasma treatment with aim understanding defect structure its electronic characteristics. Examinations annular dark field scanning...
Abstract Tuning the conductivity and other electronic properties by doping in ultrathin layers of transition‐metal dichalcogenides is great scientific practical interest. As with traditional semiconductors, controllable essential for device applications materials. Here, hole epitaxial MoSe 2 phosphorus (P) are reported, where substitutional P at Se sites acts as a shallow acceptor. substituting identified annular dark field scanning transmission electron microscopy, Auger spectroscopy, X‐ray...
Abstract Single-layer (SL) transition-metal chalcogenides (TMCs) represent an important family of two-dimensional (2D) materials that have attracted intensive research attention recently. It has been established many TMCs are polymorphic can exist in different crystal structures and correspondingly exhibit diverse physical properties. Discovery new structural phases a is great scientific practical importance. In this work, we report polymorph SL-TMC, i.e. SL-Mo 5 Te 8 , attained by...
Abstract Interplay between defects like mirror twin boundaries (MTBs) and dopants may provide additional opportunities for furthering the research on two-dimensional monolayer (ML) transition metal dichalcogenides. In this work, we successfully dope rhenium (Re) into molecular beam epitaxy grown ML MoSe 2 confirm formation of a new type MTBs, named 4|4E-M (M represents metal, Mo/Re) according to configuration. Data from statistic atomic resolution scanning transmission electron microscopy...
We have extended our new materials class search for the experimental realization of Z2 topological insulators from binary [Bi2Se3-class, Xia et.al., Nature Phys. 5, 398 (2009)] and ternary [Half-Heusler class, Lin arXiv:1003.0155v1 (2010); arXiv:1003.2615v1 (2010)] series to non-Heusler Li-based intermetallic Li2M'X ($M'$=Cu, Ag, Au, $X$=Sb Bi) with CuHg2Ti-type structure. discovered that distorted-Li2AgSb is a lightweight compound harboring 3D insulator state Z2=-1 although groundstate lies...
Monolayer (ML) transition-metal dichalcogenides (TMDs) have attracted a lot of research interest in recent years due to their many interesting properties as well application promises. Depending on the specific combinations metals (e.g., Mo and W) with chalcogen elements S, Se, Te), binary TMDs exhibit wide spectrum physical characteristics, e.g., from metal semiconductor and/or superconductor. Extension ternary compounds alloys may offer even wider variations are thus both fundamental...
The Cu-doped topological insulator Bi$_2$Se$_3$ has recently been found to undergo a superconducting transition upon cooling, raising the possibilities that it is first known "topological superconductor" or realizes novel non-Abelian state. Its true nature depends critically on bulk and surface state band topology. We present photoemission spectroscopy results where by examining topology at many different copper doping values we discover topologically protected spin-helical states remain...
Abstract Band bending near mirror twin domain boundaries (MTBs) in a MoSe 2 monolayer grown on different substrates, i.e., highly oriented pyrolytic graphite (HOPG), graphene‐on‐SiC, and crystalline Au(110), is investigated by low temperature scanning tunneling microscopy/spectroscopy. Upshift of the valence band edge MTB observed both graphene HOPG whereas downshift found Au(110). For former, magnitudes are different. This explained based static charge model, where an accumulative exists at...
Topological insulators embody a newly discovered state of matter characterized by conducting spin-momentum locked surface states that span the bulk band gap. So far, most study on topological insulator surfaces has been limited to understanding their properties without strong Coulomb perturbation or breaking time reversal symmetry. We have used deposited iron, with large positive ionization and significant magnetic moment as probe modify electronic structure Bi2Se3 at gap energy scale....
There have been conflicting reports on the electronic properties of twin domain boundaries (DBs) in MoSe2 monolayer, including quantum well states, charge density wave, and Tomonaga-Luttinger liquid (TLL). Here we employ low-temperature scanning tunneling spectroscopy to reveal both confinement effect signatures TLL one-dimensional DBs. The data do not support CDW at temperatures down ~5 K.
Topological states of matter originate from distinct topological electronic structures materials. As for strong insulators (STIs), the surface (interface) is a direct consequence structure transition between materials categorized to different genus. Therefore, it fundamentally interesting if such character can be manipulated. Besides tuning crystal field and strength spin-orbital coupling (e.g., by external strain, or chemical doping), there currently rare report on state induced in ordinary...
Topological insulators (TIs) are novel materials that manifest spin-polarized Dirac states on their surfaces or at interfaces made with conventional matter. We have measured the electron kinetics of bulk doped TI Bi$_2$Se$_3$ angle resolved photoemission spectroscopy while depositing cathodic and anodic adatoms to add charge carriers opposite sign from dopants. These P-N overlayer create point transport regimes larger interface potentials than previous N-N type surface deposition studies,...