Recent experiments identified Co3Sn2S2 as the first magnetic Weyl semimetal (MWSM). Using first-principles calculation with a global optimization approach, we explore the structural stabilities and topological electronic properties of... more
Recent experiments identified Co3Sn2S2 as the first magnetic Weyl semimetal (MWSM). Using first-principles calculation with a global optimization approach, we explore the structural stabilities and topological electronic properties of cobalt (Co)-based shandite and alloys, Co3MM’X2 (M/M’ = Ge, Sn, Pb, X = S, Se, Te), and identify stable structures with different Weyl phases. Using a tight-binding model, for the first time, we reveal that the physical origin of the nodal lines of a Co-based shandite structure is the interlayer coupling between Co atoms in different Kagome layers, while the number of Weyl points and their types are mainly governed by the interaction between Co and the metal atoms, Sn, Ge, and Pb. The Co3SnPbS2 alloy exhibits two distinguished topological phases, depending on the relative positions of the Sn and Pb atoms: a three-dimensional quantum anomalous Hall metal, and a MWSM phase with anomalous Hall conductivity (~1290 Ω−1 cm−1) that is larger than that of Co2S...
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We introduce a new class of electrides with nontrivial band topology by coupling materials database searches and first-principles-calculations-based analysis. Cs_{3}O and Ba_{3}N are for the first time identified as a new class of... more
We introduce a new class of electrides with nontrivial band topology by coupling materials database searches and first-principles-calculations-based analysis. Cs_{3}O and Ba_{3}N are for the first time identified as a new class of electrides, consisting of one-dimensional (1D) nanorod building blocks. Their crystal structures mimic β-TiCl_{3} with the position of anions and cations exchanged. Unlike the weakly coupled nanorods of β-TiCl_{3}, Cs_{3}O and Ba_{3}N retain 1D anionic electrons along the hollow interrod sites; additionally, a strong interrod interaction in C_{3}O and Ba_{3}N induces band inversion in a 2D superatomic triangular lattice, resulting in Dirac-node lines. The new class of electrides can serve as a prototype for new electrides with a large cavity space that can be utilized for various applications such as gas storage, ion transport, and metal intercalation.
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It is well understood that defect engineering can give rise to exotic electronic properties in transition-metal dichalcogenides, but to this date, there is no detailed study to illustrate how defects can be engineered to tailor their... more
It is well understood that defect engineering can give rise to exotic electronic properties in transition-metal dichalcogenides, but to this date, there is no detailed study to illustrate how defects can be engineered to tailor their thermal properties. Here, through combined experimental and theoretical approaches based on the first-principles density functional theory and Boltzmann transport equations, we have explored the effect of lattice vacancies and substitutional tungsten (W) doping on the thermal transport of the suspended molybdenum diselenide (MoSe2) monolayers grown by chemical vapor deposition (CVD). The results show that even though the isoelectronic substitution of the W atoms for Mo atoms in CVD-grown Mo0.82W018Se2 monolayers reduces the Se vacancy concentration by 50% compared to that found in the MoSe2 monolayers, the thermal conductivity remains intact in a wide temperature range. On the other hand, Se vacancies have a detrimental effect for both samples and more ...
Research Interests: Chemical Engineering, Evolutionary Biology, Marine Biology, Physiology, Biophysics, and 15 moreMaterials Science, Biotechnology, Ecology, Space Science, Medicine, Chemical Vapor Deposition, Thermal Conductivity, Phonon, Tungsten, Transition Metal Dichalcogenides, Vacancy Defect, Temperature Range, Monolayer, Mass Difference, and Defect engineering
We investigate the role of interfacial electronic properties on the phonon transport in two-dimensional MoS2 adsorbed on metal substrates (Au and Sc) using first-principles density functional theory and the atomistic Green's function... more
We investigate the role of interfacial electronic properties on the phonon transport in two-dimensional MoS2 adsorbed on metal substrates (Au and Sc) using first-principles density functional theory and the atomistic Green's function method. Our study reveals that the different degree of orbital hybridization and electronic charge distribution between MoS2 and metal substrates play a significant role in determining the overall phonon-phonon coupling and phonon transmission. The charge transfer caused by the adsorption of MoS2 on Sc substrate can significantly weaken the Mo-S bond strength and change the phonon properties of MoS2, which result in a significant change in thermal boundary conductance (TBC) from one lattice-stacking configuration to another for same metallic substrate. In a lattice-stacking configuration of MoS2/Sc, weakening of the Mo-S bond strength due to charge redistribution results in decrease in the force constant between Mo and S atoms and substantial redist...
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Hexagonal boron nitride (h-BN) is a promising substrate for graphene based nano-electronic devices. We investigate the ballistic phonon transport at the interface of vertically stacked graphene and h-BN heterostructures using first... more
Hexagonal boron nitride (h-BN) is a promising substrate for graphene based nano-electronic devices. We investigate the ballistic phonon transport at the interface of vertically stacked graphene and h-BN heterostructures using first principles density functional theory and atomistic Green's function simulations considering the influence of lattice stacking. We compute the frequency and wave-vector dependent transmission function and observe distinct stacking-dependent phonon transmission features for the h-BN/graphene/h-BN sandwiched systems. We find that the in-plane acoustic modes have the dominant contributions to the phonon transmission and thermal boundary conductance (TBC) for the interfaces with the carbon atom located directly on top of the boron atom (C-B matched) because of low interfacial spacing. The low interfacial spacing is a consequence of the differences in the effective atomic volume of N and B and the difference in the local electron density around N and B. For...
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Spin splitting of Rashba states in two-dimensional electron system provides a promising mechanism of spin manipulation for spintronics applications. However, Rashba states realized experimentally to date are often outnumbered by... more
Spin splitting of Rashba states in two-dimensional electron system provides a promising mechanism of spin manipulation for spintronics applications. However, Rashba states realized experimentally to date are often outnumbered by spin-degenerated substrate states at the same energy range, hindering their practical applications. Here, by density functional theory calculation, we show that Au one monolayer film deposition on a layered semiconductor surface β-InSe(0001) can possess "ideal" Rashba states with large spin splitting, which are completely situated inside the large band gap of the substrate. The position of the Rashba bands can be tuned over a wide range with respect to the substrate band edges by experimentally accessible strain. Furthermore, our nonequilibrium Green's function transport calculation shows that this system may give rise to the long-sought strong current modulation when made into a device of Datta-Das transistor. Similar systems may be identified...
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Bilayer graphene (BLG) with a tunable band gap appears interesting as an alternative to graphene for practical applications; thus, its transport properties are being actively pursued. Using density functional theory and perturbation... more
Bilayer graphene (BLG) with a tunable band gap appears interesting as an alternative to graphene for practical applications; thus, its transport properties are being actively pursued. Using density functional theory and perturbation analysis, we investigated, under an external electric field, the electronic properties of BLG in various stackings relevant to recently observed complex structures. We established the first phase diagram summarizing the stacking-dependent gap openings of BLG for a given field. We further identified high-density midgap states, localized on grain boundaries, even under a strong field, which can considerably reduce the overall transport gap.
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Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to transferring, direct epitaxy... more
Two-dimensional (2D) van der Waals (vdW) heterostructures are a family of artificially structured materials that promise tunable optoelectronic properties for devices with enhanced functionalities. Compared to transferring, direct epitaxy of vdW heterostructures is ideal for clean interlayer interfaces and scalable device fabrication. Here we report the synthesis and preferred orientations of 2D GaSe atomic layers on graphene (Gr) by vdW epitaxy. GaSe crystals are found to nucleate predominantly on random wrinkles or grain boundaries of graphene, share a preferred lattice orientation with underlying graphene, and grow into large (tens of micrometers) irregularly shaped, single-crystalline domains. The domains are found to propagate with triangular edges that merge into the large single crystals during growth. Electron diffraction reveals that approximately 50% of the GaSe domains are oriented with a 10.5 ± 0.3° interlayer rotation with respect to the underlying graphene. Theoretical...
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Research Interests: Materials Science, Hydrogen, Process Control, Hydrogen Storage, Pulsed Laser Deposition, and 15 moreHydrogen Storage Materials, Pore Size, High Temperature, High Speed, High Power, Surface Area, Particle Size, Room Temperature, Binding Energy, Neutron Scattering, Carbon Fibers, Electric Field, Particle Size Distribution, pore structure, and Vaporization
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Research Interests: Biochemistry, Chemistry, Inorganic Chemistry, Developmental Biology, Immunology, and 15 moreMolecular Biology, Biotechnology, Cancer, Ecology, Graphene, Crystallization, Cell Biology, Chemical Physics, Medicine, Graphite, Nucleation, CHEMICAL SCIENCES, Grain Size Effects, Epitaxy, and Organometallic Compounds
Research Interests: Materials Engineering, Physics, Condensed Matter Physics, Thermodynamics, Inorganic Chemistry, and 14 morePhysical Chemistry, Theoretical Chemistry, Hydrogen, Quantum Theory, Nanotechnology, Medicine, Copper, Nano Technology, Density Functional Theory, Theoretical Condensed Matter Physics, Hydrogen Bonding, Surface Properties, Physisorption, and Molecule
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We study the energetics, electronic structure and electron transport through neutral and charged oligo(phenylene ethylene) molecules within a self-assembled monolayer sandwiched between parallel gold electrodes. Our results indicate that... more
We study the energetics, electronic structure and electron transport through neutral and charged oligo(phenylene ethylene) molecules within a self-assembled monolayer sandwiched between parallel gold electrodes. Our results indicate that a net charge transfer to the molecules, induced by applying a bias voltage, may shift the balance between the pi-system conjugation and the Coulomb repulsion within the system, thus inducing a
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Driven by step-step (SS) attraction, a strained overlayer grown on a vicinal substrate is inherently unstable, as manifested by step bunching. The step-edge (or Ehrlich-Schwoebel) barrier effects may either accelerate, delay, or suppress... more
Driven by step-step (SS) attraction, a strained overlayer grown on a vicinal substrate is inherently unstable, as manifested by step bunching. The step-edge (or Ehrlich-Schwoebel) barrier effects may either accelerate, delay, or suppress step bunching, depending on the nature of the ES barriers for a given system. Using linear stability theory and numerical simulations, we analyze the morphological evolution in heteroepitaxial growth with explicit consideration of the competition between the SS and ES effects. We establish the ...
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Scanning tunneling microscopy (STM) is one of the indispensable tools to characterize surface structures, but the distinction between atomic geometry and electronic effects based on the measured tunneling current is not always... more
Scanning tunneling microscopy (STM) is one of the indispensable tools to characterize surface structures, but the distinction between atomic geometry and electronic effects based on the measured tunneling current is not always straightforward. In particular, for single-atomic-thick materials (graphene or boron nitride) on metallic substrates, counterintuitive phenomena such as a larger tunneling current for insulators than for metal and a topography opposite to the atomic geometry are reported. Using first-principles density functional theory calculations combined with analytical modeling, we reveal the critical role of penetrating states of metallic substrates that surpass 2D material states, hindering the measurement of intrinsic 2D materials states and leading to topography inversion. Our finding should be instrumental in the interpretation of STM topographies of atomic-thick materials and in the development of 2D material for (opto)electronic and various quantum applications.