한승우 교수

The fabrication of controlled nanostructures such as quantum dots, nanotubes, nanowires, and nanopillars has progressed rapidly over the past 10 years. However, both bottom-up and top-down methods to integrate the nanostructures are met with several challenges. For practical applications with the high level of the integration, an approach that can fabricate the required structures locally is desirable. In addition, the electrical signal to construct and control the nanostructures can provide sig

As the scale of transistors and capacitors in electronics is reduced to less than a few nanometers, leakage currents pose a serious problem to the device’s reliability. To overcome this dilemma, high-κ materials that exhibit a larger permittivity and band gap are introduced as gate dielectrics to enhance both the capacitance and block leakage simultaneously. Currently, HfO2 is widely used as a high-κ dielectric; however, a higher-κ material remains desired for further enhancement. To find new hi

Message-passing graph neural network interatomic potentials (GNN-IPs), particularly those with equivariant representations such as NequIP, are attracting significant attention due to their data efficiency and high accuracy. However, parallelizing GNN-IPs poses challenges because multiple message-passing layers complicate data communication within the spatial decomposition method, which is preferred by many molecular dynamics (MD) packages. In this article, we propose an efficient parallelization

Transition metal dichalcogenides (TMDs) have attracted enormous attention in diverse research fields. Especially, gas sensors are considered in a promising application exploiting TMDs. However, the studies are confined to only major TMDs such as MoS₂ and WS₂. Particularly, the chemoresistive sensing properties of two-dimensional (2D) NbS₂ have never been explored. For the first time, we report room temperature NO₂ sensing characteristics of 2D NbS<sub>

We have performed $\mathrm{ab}$ $\mathrm{initio}$ pseudopotential electronic structure calculations for various edge geometries of the $(n,n)$ single-wall nanotube with or without applied fields. Among the systems studied, the one with a zigzag edge exposed by a slant cut is found to be the most favorable for emission due to the existence of unpaired dangling bond states around the Fermi level. The next most favorable geometry is the capped nanotube where $\ensuremath{\pi}$-bonding states locali

The catalytic activity for the hydrogen evolution reaction (HER) at the anion vacancy of 40 2D transition-metal dichalcogenides (TMDs) is investigated using the hydrogen adsorption free energy (Δ G_H) as the activity descriptor. While vacancy-free basal planes are mostly inactive, anion vacancy makes the hydrogen bonding stronger than clean basal planes, promoting the HER performance of many TMDs. We find that ZrSe₂ and ZrTe₂ have similar Δ G_H as Pt, th

We report an extensive ab initio study of self-interstitials in V and Mo. Contrary to the widely accepted picture, the $〈111〉$ dumbbell is found to be the most stable structure. The activated state for migration is the crowdion configuration, with an extremely low barrier $(\ensuremath{\sim}0.01\mathrm{eV}),$ suggesting $1d$ (one-dimensional) diffusion at low temperatures and $3d$ diffusion at high temperature. In the case of Mo, the energy landscape between the $〈111〉$ and $〈110〉$ dumbbells is

Semiconducting inorganic materials with band gaps ranging between 0 and 5 eV constitute major components in electronic, optoelectronic and photovoltaic devices. Since the band gap is a primary material property that affects the device performance, large band-gap databases are useful in selecting optimal materials in each application. While there exist several band-gap databases that are theoretically compiled by density-functional-theory calculations, they suffer from computational limitations s

The native point defects in Fe2O3 are theoretically investigated using ab initio methods based on the GGA + U formalism. We consider vacancies and interstitials of Fe and O atoms as well as the electron polaron as Fe(II) defects at the host Fe(III) site. The formation energies and charge transition levels are computed for each defect type with careful elimination of size effects of the supercell. It is found that the Fe interstitial and vacancy form donor and acceptor levels close to band edges,

Abstract The ultimate transparent electronic devices require complementary and symmetrical pairs of n-type and p-type transparent semiconductors. While several n-type transparent oxide semiconductors like InGaZnO and ZnO are available and being used in consumer electronics, there are practically no p-type oxides that are comparable to the n-type counterpart in spite of tremendous efforts to discover them. Recently, high-throughput screening with the density functional theory calculations attempt

The ability to predict the behavior of point defects in metals, particularly interstitial defects, is central to accurate modeling of the microstructural evolution in environments with high radiation fluxes. Existing interatomic potentials of embedded atom method type predict disparate stable interstitial defect configurations in vanadium. This is not surprising since accurate first-principles interstitial data were not available when these potentials were fitted. In order to provide the input i

Two-dimensional (2D) molybdenum disulfide (MoS₂) has been attracting rapidly increasing interest for application in chemoresistive gas sensors owing to its moderate band gap energy and high specific surface area.

Field emission properties of the (10,10) carbon nanotube are investigated with a first-principles approach. Emission currents are obtained through integrations of the time-dependent Schr\"odinger equation. We find that the emission current from the states localized at the tip end is more than ten times greater than direct contributions from extended metallic $(\ensuremath{\pi}$ and ${\ensuremath{\pi}}^{*})$ states. The spatial distribution of the electronic wave function as it tunnels through th