ORCID Profile
0000-0002-6273-9324
Current Organisations
Yonsei University
,
University of Sydney
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Publisher: Elsevier BV
Date: 05-2023
Publisher: American Chemical Society (ACS)
Date: 19-02-2021
Publisher: Elsevier BV
Date: 05-2017
Publisher: Elsevier BV
Date: 11-2007
Publisher: American Physical Society (APS)
Date: 28-04-2006
Publisher: American Chemical Society (ACS)
Date: 16-03-2018
Publisher: IOP Publishing
Date: 17-04-2008
Publisher: American Chemical Society (ACS)
Date: 24-09-2018
DOI: 10.1021/ACS.JPCLETT.8B02474
Abstract: Experimental verification of optical modulation with external stress has not been easily available in flexible systems. Here, we intentionally induced extra stress in wide band gap ZnO thin films by a unique prestress-driven deposition processing that utilizes a stretching mode. The stretching mode provides homogeneous but biaxial stresses in the hexagonal wurtzite structure, leading to the extension of the c-axis and the contraction of the a-axis. As a result, the reduction of the optical band gap by ∼150 meV was observed for the strain of ∼4.87%. The band gap narrowing was found to occur from the respective downward and upward shifts of the conduction band minimum and valence band maximum under the applied stress. The experimental evidence of optical modulations was supported by the theoretical calculations using density functional theory. The reduced strong interactions between Zn d and O p orbitals were assumed to be responsible for the band gap narrowing.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9NR06076F
Abstract: Bilayer VSe 2 shows polymorphic 1T′ structure which can transit to the dynamic state of lattice vibrations, triggered by tunneling current.
Publisher: American Chemical Society (ACS)
Date: 02-06-2021
Publisher: American Physical Society (APS)
Date: 22-10-2009
Publisher: Physical Society of Japan
Date: 15-03-2013
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3CP53334D
Abstract: It has been previously reported that the system of single Pt atoms embedded in N-vacancy (V(N)) sites on the TiN(100) surface (Pt-TiN) could be a promising catalyst for proton exchange membrane fuel cells (PEM FCs). The adsorption of molecules on Pt-TiN is an important step, when it is incorporated as the anode or cathode of PEM FCs. Utilizing first principles calculations based on density functional theory, systematic investigations are performed on the adsorption of several atomic and molecular species on the Pt-TiN system, as well as the co-adsorption of them. The favorable binding sites and adsorption energies of several molecular species, namely carbon dioxide (CO2), carbon monoxide (CO), oxygen (O2), hydrogen (H2), hydroxyl (OH), an oxygen atom (O), and a hydrogen atom (H), are explored. For each, the adsorption energy and preferred binding site are identified and the vibrational frequencies calculated. It is found that CO2, CO and H prefer the Pt top site while OH and O favorably adsorb on the Ti top site. When CO and OH are co-adsorbed on the Pt-TiN(100) surface, OH weakens the adsorption of CO. The weakening effect is enhanced by increasing the coverage of OH. A similar behavior occurs for H and OH co-adsorption on the Pt-TiN(100) surface. Because co-adsorption with OH and H species weakens the adsorption of CO on Pt-TiN, it is expected that the acid and base conditions in PEM FCs could mitigate CO poisoning on functionalized Pt-TiN surfaces.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5CP90064F
Abstract: Correction for ‘A rational computational study of surface defect-mediated stabilization of low-dimensional Pt nanostructures on TiN(100)’ by Young Joo Tak et al. , Phys. Chem. Chem. Phys. , 2015, 17 , 9680–9686.
Publisher: Wiley
Date: 16-07-2021
Abstract: The decomposition, electron transfer, and protonation of oxygen molecules are typically assumed to be the rate‐limiting steps of the oxygen reduction reactions (ORR), and the activation energy barriers of these reactions can be surmounted using catalysts. In this study, the physical rate‐limiting step of the ORR consists of the adsorption of gaseous oxygen molecules at the liquid–solid phase boundary, indicating that the formation of a gas–liquid–solid triple‐phase boundary (TPB) is important for accelerating the ORR kinetics. This is experimentally confirmed by analyzing the ORR in aluminum–air batteries. Moreover, the formation of a TPB using the hierarchical pores of sparked reduced graphene oxide is demonstrated, which serve as the cathode, and the remarkable electrochemical performance of the fabricated battery is presented. These findings can be used to accelerate the ORR kinetics by maximizing the TPB, particularly in aluminum–air batteries.
Publisher: AIP Publishing
Date: 09-02-2021
DOI: 10.1063/5.0040835
Abstract: Refractory transition metal nitrides exhibit a plethora of polymorphic expressions and chemical stoichiometries. To afford a better understanding of how defects may play a role in the structural and thermodynamics of these nitrides, using density-functional theory calculations, we investigate the influence of point and pair defects in bulk metastable γ-MoN and its (001) surface. We report favorable formation of Schottky defect pairs of neighboring Mo and N vacancies in bulk γ-MoN and apply this as a defect-mediated energy correction term to the surface energy of γ-MoN(001) within the ab initio atomistic thermodynamics approach. We also inspect the structural distortions in both bulk and surfaces of γ-MoN by using the partial radial distribution function, g(r), of Mo–N bond lengths. Large atomic displacements are found in both cases, leading to a broad spread of Mo–N bond length values when compared to their idealized bulk values. We propose that these structural and thermodynamic analyses may provide some insight into a better understanding of metastable materials and their surfaces.
Publisher: American Chemical Society (ACS)
Date: 15-09-2022
DOI: 10.1021/ACS.NANOLETT.2C02763
Abstract: Layered group IV monochalcogenides are two-dimensional (2D) semiconducting materials with unique crystal structures and novel physical properties. Here, we report the growth of single crystalline GeS microribbons using the chemical vapor transport process. By using conductive atomic force microscopy, we demonstrated that the conductive behavior in the vertical direction was mainly affected by the Schottky barriers between GeS and both electrodes. Furthermore, we found that the topographic and current heterogeneities were significantly different with and without illumination. The topographic deformation and current enhancement were also predicted by our density functional theory (DFT)-based calculations. Their local spatial correlation between the topographic height and current was established. By virtue of 2D fast Fourier transform power spectra, we constructed the holistic spatial correlation between the topographic and current heterogeneity that indicated the diminished correlation with illumination. These findings on layered GeS microribbons provide insights into the conductive and topographic behaviors in 2D materials.
Publisher: AIP Publishing
Date: 12-05-2009
DOI: 10.1063/1.3123534
Abstract: First-principles density functional theory and a periodic-slab model have been employed to explore the adsorption of a two-chlorophenol molecule on a Cu2O(110) surface containing surface Cu–O bonds, namely, the Cu2O(110):CuO surface. The two-chlorophenol molecule is found to interact very weakly with the Cu2O(110):CuO surface, forming several vertical and flat orientations. These weakly bound states tend to result from interaction between the phenolic hydrogen and an oxygen surface atom. The formation of a two-chlorophenoxy moiety and an isolated hydrogen on the Cu2O(110):CuO surface from a vacuum two-chlorophenol molecule is determined to have an endothermicity of 8.2 kcal/mol (0.37 eV). The energy required to form a two-chlorophenoxy radical in the gas phase is also found to be much smaller when assisted by the Cu2O(110):CuO surface than direct breaking of the hydroxyl bond of a free two-chlorophenol molecule. The calculated binding energy of a two-chlorophenoxy radical adsorbed directly onto the Cu2O(110):CuO surface is −12.5 kcal/mol (0.54 eV). The Cu2O(110):CuO and Cu(100) surfaces are found to have similar energy barriers for forming a surface-bound two-chlorophenoxy moiety from the adsorption of a two-chlorophenol molecule.
Publisher: American Physical Society (APS)
Date: 11-07-2016
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4TA04863F
Abstract: The stability of different shapes of cuprous oxides was tested in deionized water with or without light irradiation. The morphology was degraded by the formation of CuO at the surface differently with each shape. TiIrO x -coated Cu 2 O particles presented improved stability for overall water splitting producing hydrogen and oxygen.
Publisher: American Physical Society (APS)
Date: 24-03-2008
Publisher: American Physical Society (APS)
Date: 21-03-2007
Publisher: American Chemical Society (ACS)
Date: 30-04-2018
DOI: 10.1021/ACS.INORGCHEM.8B00578
Abstract: Oxides of tantalum (common ex les including TaO, TaO
Publisher: Elsevier BV
Date: 2013
Publisher: Elsevier BV
Date: 03-2023
Publisher: American Chemical Society (ACS)
Date: 02-02-2018
Publisher: American Chemical Society (ACS)
Date: 23-05-2013
DOI: 10.1021/JP306495K
Publisher: Elsevier BV
Date: 09-2019
Publisher: American Physical Society (APS)
Date: 15-09-2017
Publisher: Elsevier BV
Date: 05-2013
Publisher: Elsevier BV
Date: 10-2012
Publisher: American Physical Society (APS)
Date: 26-01-2009
Publisher: Springer Science and Business Media LLC
Date: 08-06-2022
DOI: 10.1038/S41467-022-30838-Y
Abstract: To date, the search for active, selective, and stable electrocatalysts for the oxygen evolution reaction (OER) has not ceased and a detailed atomic-level design of the OER catalyst remains an outstanding (if not, compelling) problem. Considerable studies on different surfaces and polymorphs of iridium oxides (with varying stoichiometries and dopants) have emerged over the years, showing much higher OER activity than the conventionally reported rutile-type IrO 2 . Here, we have considered different metastable nanoporous and amorphous iridium oxides of different chemical stoichiometries. Using first-principles electronic structure calculations, we investigate the (electro)chemical stability, intercalation properties, and electronic structure of these iridium oxides. Using an empirical regression model between the Ir-O bond characteristics and the measured OER overpotentials, we demonstrate how activated Ir-O bonds (and the presence of more electrophilic oxygens) in these less understood polymorphs of iridium oxides can explain their superior OER performance observed in experiments.
Publisher: American Physical Society (APS)
Date: 10-08-2016
Publisher: American Chemical Society (ACS)
Date: 19-12-2016
DOI: 10.1021/ACS.JPCLETT.6B02503
Abstract: Perovskite oxides have the capacity to efficiently catalyze the oxygen reduction reaction (ORR), which is of fundamental importance for electrochemical energy conversion. While the perovskite catalysts have been generally utilized with a support, the role of the supports, regarded as inert toward the ORR, has been emphasized mostly in terms of the thermal stability of the catalyst system and as an ancillary transport channel for oxygen ions during the ORR. We demonstrate a novel approach to improving the catalytic activity of perovskite oxides for solid oxide fuel cells by controlling the oxygen-ion conducting oxide supports. Catalytic activities of (La
Publisher: Springer Science and Business Media LLC
Date: 14-12-2015
DOI: 10.1038/SREP18196
Abstract: In the present study, we investigated the role of an aliovalent dopant upon stabilizing the amorphous oxide film. We added beryllium into the Zr 50 Cu 50 metallic glass system and found that the amorphous oxide layer of Be-rich phase can be stabilized even at elevated temperature above T g of the glass matrix. The thermal stability of the amorphous oxide layer is substantially enhanced due to Be addition. As confirmed by high-temperature cross-section HR-TEM, fully disordered Be-added amorphous layer is observed, while the rapid crystallization is observed without Be. To understand the role of Be, we employed ab-initio molecular dynamics to compare the mobility of ions with/without Be dopant and propose a disordered model where Be dopant occupies Zr vacancy and induces structural disorder to the amorphous phase. We find that the oxygen mobility is slightly suppressed due to Be dopant and Be mobility is unexpectedly lower than that of oxygen, which we attribute to the aliovalent nature of Be dopant whose diffusion always accompany multiple counter-diffusion of other ions. Here, we explain the origin of superior thermal stability of amorphous oxide film in terms of enhanced structural disorder and suppressed ionic mobility due to the aliovalent dopant.
Publisher: AIP Publishing
Date: 11-08-2014
DOI: 10.1063/1.4892844
Abstract: Cadmium telluride (CdTe) is a p-type semiconductor used in thin-film solar cells. To achieve high light-to-electricity conversion, annealing in the presence of CdCl2 is essential, but the underlying mechanism is still under debate. Recent evidence suggests that a reduction in the high density of stacking faults in the CdTe grains is a key process that occurs during the chemical treatment. A range of stacking faults, including intrinsic, extrinsic, and twin boundary, are computationally investigated to identify the extended defects that limit performance. The low-energy faults are found to be electrically benign, while a number of higher energy faults, consistent with atomic-resolution micrographs, are predicted to be hole traps with fluctuations in the local electrostatic potential. It is expected that stacking faults will also be important for other thin-film photovoltaic technologies.
Publisher: Elsevier BV
Date: 07-2022
Publisher: American Chemical Society (ACS)
Date: 17-03-2017
Publisher: Springer Science and Business Media LLC
Date: 24-08-2023
DOI: 10.1038/S41524-023-01110-8
Abstract: Group I niobates (KNbO 3 and NaNbO 3 ) are promising lead-free alternatives for high-performance energy storage applications. Despite their potential, their complex phase transitions arising from temperature-dependent phonon softening and anharmonic effects on dielectric properties remain poorly explored. In this study, we employ density-functional theory (DFT) and self-consistent phonon (SCP) calculations to investigate finite-temperature phonons in cubic niobate perovskites. To include explicit anharmonic vibrational effects, SCP frequencies are shifted by the bubble self-energy correction within the quasiparticle (QP) approximation, providing precise descriptions of phonon softening in these strongly anharmonic solids. We further calculate the static dielectric constant of KNbO 3 and NaNbO 3 as a function of temperature using the Lyddane-Sachs-Teller (LST) relation and QP-corrected phonon dispersions. Our theoretical results align with experimental data, offering reliable temperature-dependent phonon dispersions while considering anharmonic self-energies and thermal expansion effects, enhancing our understanding of the complex relations between lattice vibrations and phase transitions in these anharmonic oxides.
Publisher: American Chemical Society (ACS)
Date: 23-01-2017
Publisher: Elsevier BV
Date: 10-2013
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6NR04354B
Abstract: Many different forms of mechanical and structural deformations have been employed to alter the electronic structure of various modern two-dimensional (2D) nanomaterials. Given the recent interest in the new class of 2D nanomaterials - phosphorene, here we investigate how the rotational strain-dependent electronic properties of low-dimensional phosphorene may be exploited for technological gain. Here, using first-principles density-functional theory, we investigate the mechanical stability of twisted one-dimensional phosphorene nanoribbons (TPNR) by measuring their critical twist angle (θc) and shear modulus as a function of the applied mechanical torque. We find a strong anisotropic, chirality-dependent mechano-electronic response in the hydrogen-passivated TPNRs upon vortical deformation, resulting in a striking difference in the change in the carrier effective mass as a function of torque angle (and thus, the corresponding change in carrier mobility) between the zigzag and armchair directions in these TPNRs. The accompanied tunable band-gap energies for the hydrogen-passivated zigzag TPNRs may then be exploited for various key opto-electronic nanodevices.
Publisher: American Chemical Society (ACS)
Date: 15-10-2019
Abstract: Strain engineering has been extensively explored for tailoring the material properties and, in turn, improving the device performance of semiconducting thin films. In particular, the effects of strain on the optical properties of these films have attracted considerable research interest, but experimental demonstrations in flexible systems have rarely been reported. Here, we exploited the variable optical properties of flexible ZnS thin films by imposing a controllable external compressive stress during a stretching-driven deposition process. This stress induced crystal anisotropy with an increase in tetragonality, which differs from that of the unstrained cubic ZnS thin films. The refractive index of the films was estimated by means of an envelope method using interference fringes. As a result, the reductions in the refractive index and optical band gap were observed by applying the stretching-driven strains with the resultant compressive stress. The modulated refractive index and its dispersion behavior were further investigated by employing a single-oscillator model to drive subsequent correlative parameters such as dispersion energy, oscillating strength, and high-frequency permittivity. As a proof of concept, an optical lens of ZnS was designed to confirm the effect of in situ stress-mediated optical modulation by detecting the variable focal length with stress.
Publisher: American Chemical Society (ACS)
Date: 04-05-2017
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C3RA46558F
Publisher: Elsevier BV
Date: 12-2023
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8CY00583D
Abstract: Microkinetic modeling, ab initio thermodynamics and Wulff–Kaishew construction are used to predict catalyst structural changes under reaction conditions.
Publisher: Elsevier BV
Date: 08-2012
Publisher: Springer Science and Business Media LLC
Date: 04-01-2021
Publisher: American Chemical Society (ACS)
Date: 27-03-2017
Publisher: American Physical Society (APS)
Date: 23-02-2010
Publisher: Elsevier BV
Date: 07-2013
Publisher: AIP Publishing
Date: 08-09-2009
DOI: 10.1063/1.3191784
Abstract: We present density functional theory investigations of the bulk properties of cerium oxides (CeO2 and Ce2O3) and the three low index surfaces of CeO2, namely, (100), (110), and (111). For the surfaces, we consider various terminations including surface defects. Using the approach of “ab initio atomistic thermodynamics,” we find that the most stable surface structure considered is the stoichiometric (111) surface under “oxygen-rich” conditions, while for a more reducing environment, the same (111) surface, but with subsurface oxygen vacancies, is found to be the most stable one, and for a highly reducing environment, the (111) Ce-terminated surface becomes energetically favored. Interestingly, this latter surface exhibits a significant reconstruction in that it becomes oxygen terminated and the upper layers resemble the Ce2O3(0001) surface. This structure could represent a precursor to the phase transition of CeO2 to Ce2O3.
Publisher: Springer Science and Business Media LLC
Date: 08-04-2023
DOI: 10.1038/S41467-023-37740-1
Abstract: A variety of phase transitions have been found in two-dimensional layered materials, but some of their atomic-scale mechanisms are hard to clearly understand. Here, we report the discovery of a phase transition whose mechanism is identified as interlayer sliding in lead iodides, a layered material widely used to synthesize lead halide perovskites. The low-temperature crystal structure of lead iodides is found not 2H polytype as known before, but non-centrosymmetric 4H polytype. This undergoes the order-disorder phase transition characterized by the abrupt spectral broadening of valence bands, taken by angle-resolved photoemission, at the critical temperature of 120 K. It is accompanied by drastic changes in simultaneously taken photocurrent and photoluminescence. The transmission electron microscopy is used to reveal that lead iodide layers stacked in the form of 4H polytype at low temperatures irregularly slide over each other above 120 K, which can be explained by the low energy barrier of only 10.6 meV/atom estimated by first principles calculations. Our findings suggest that interlayer sliding is a key mechanism of the phase transitions in layered materials, which can significantly affect optoelectronic and optical characteristics.
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8CP00559A
Abstract: The structural, vibrational, and diffusion properties of different ceria-based systems (including oxygen vacancies and rare-earth dopants (Sm or Gd)) have been examined using both first-principles density-functional theory calculations and finite-temperature molecular dynamics simulations.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5CP06163F
Abstract: The origin of the enhanced band valley degeneracy for Mg 2 Si 1−x Sn x (MSS) are examined using a temperature-broadened, orbital-projected band structure as calculated by hybrid density-functional theory (DFTHSE06). For MSS alloys, varying x Sn modulates the orbital nature of the conduction bands, and couples with the sublattice strain which directly manipulates the degree of the effective degeneracy.
Publisher: Elsevier BV
Date: 09-2008
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6TA03659G
Abstract: Using first-principles density-functional theory calculations, we investigate the advantage of using h-WO 3 (and its surfaces) over the larger band gap γ-WO 3 phase for the anode in water splitting. We demonstrate that h-WO 3 is a good alternative anode material for optimal water splitting efficiencies.
Publisher: Elsevier BV
Date: 12-2007
Publisher: AIP Publishing
Date: 14-01-2010
DOI: 10.1063/1.3292686
Abstract: Low energy ion recoil spectroscopy is a powerful technique for the determination of adsorbate position on metal surfaces. In this study, this technique is employed to compare the adsorption sites of hydrogen and deuterium on Pd(100) by detection of either H or D recoil ions produced by Ne+ bombardment. Comparisons of experimental and Kalypso simulated azimuthal yield distributions show that, at room temperature, both hydrogen isotopes are adsorbed in the fourfold hollow site of Pd(100), however, at different heights above the surface (H—0.20 Å and D—0.25 Å). The adsorbates remain in the hollow site at all temperatures up to 383 K even though they move up to 0.40–0.45 Å above the surface. Density functional theory calculations show a similar coverage dependent adsorption height for both H and D and confirm a real difference between the H and D adsorption heights based on zero point energies.
Publisher: American Physical Society (APS)
Date: 14-09-2007
Publisher: AIP Publishing
Date: 21-01-2015
DOI: 10.1063/1.4905919
Abstract: The effect of a subsurface hetero layer (thin gold) on the activity and stability of Pt skin surface in Pt3M system (M = 3d transition metals) is investigated using the spin-polarized density functional theory calculation. First, we find that the heterometallic interaction between the Pt skin surface and the gold subsurface in Pt/Au/Pt3M system can significantly modify the electronic structure of the Pt skin surface. In particular, the local density of states projected onto the d states of Pt skin surface near the Fermi level is drastically decreased compared to the Pt/Pt/Pt3M case, leading to the reduction of the oxygen binding strength of the Pt skin surface. This modification is related to the increase of surface charge polarization of outmost Pt skin atoms by the electron transfer from the gold subsurface atoms. Furthermore, a subsurface gold layer is found to cast the energetic barrier to the segregation loss of metal atoms from the bulk (inside) region, which can enhance the durability of Pt3M based catalytic system in oxygen reduction condition at fuel cell devices. This study highlights that a gold subsurface hetero layer can provide an additional mean to tune the surface activity toward oxygen species and in turn the oxygen reduction reaction, where the utilization of geometric strain already reaches its practical limit.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9CP04325J
Abstract: Nickel aluminate, NiAl 2 O 4 , adopts the inverse tetragonal P 4 1 22 structure and remains largely inverse below 1000 K.
Publisher: AIP Publishing
Date: 25-06-2018
DOI: 10.1063/1.5030178
Abstract: Over the past few decades, significant progress has been made to manipulate thermal transport in solids. Most of the effort has focused on reducing the phonon mean free path through boundary scattering. Herein, we demonstrate that the phonon confinement effect can also be used as a tool for managing thermal transport in solids. We measured the thermal conductivities of 10–70-nm-thick In0.53Ga0.47As nanofilms and found that the thermal conductivities decrease as the film thickness decreases. However, the reasons for this reduction differ for films with different thicknesses. The thermal conductivity of the 30- and 70-nm-thick In0.53Ga0.47As nanofilms decreases because of severe phonon boundary scattering. Our analysis indicates that phonon confinement occurs in the 10- and 20-nm-thick In0.53Ga0.47As nanofilms, which modifies phonon dispersion leading to changes in the phonon group velocity and the Debye temperature. These experimental and theoretical results could help to elucidate the phonon confinement effect in nanomaterials as well as establish a platform for understanding nanoscale thermal physics.
Publisher: American Physical Society (APS)
Date: 04-04-2008
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4CP02384F
Abstract: We study the chemisorption of Br on the low and high Miller-index surfaces of Pd nanoparticles, and provide a quantitative atomic picture and physics of these brominated palladium for the systematic design of more selective and active Pd shape-sculptured nanocatalysts.
Publisher: Elsevier BV
Date: 09-2012
Publisher: American Vacuum Society
Date: 07-2005
DOI: 10.1116/1.1881637
Publisher: Elsevier BV
Date: 07-2023
Publisher: American Chemical Society (ACS)
Date: 06-10-2023
DOI: 10.1021/JACS.3C07768
Publisher: American Chemical Society (ACS)
Date: 23-01-2018
DOI: 10.1021/ACS.NANOLETT.7B03897
Abstract: Understanding the mutual interaction between electronic excitations and lattice vibrations is key for understanding electronic transport and optoelectronic phenomena. Dynamic manipulation of such interaction is elusive because it requires varying the material composition on the atomic level. In turn, recent studies on topological insulators (TIs) have revealed the coexistence of a strong phonon resonance and topologically protected Dirac plasmon, both in the terahertz (THz) frequency range. Here, using these intrinsic characteristics of TIs, we demonstrate a new methodology for controlling electron-phonon interaction by lithographically engineered Dirac surface plasmons in the Bi
Publisher: American Physical Society (APS)
Date: 17-02-2015
Publisher: Korean Physical Society
Date: 2014
DOI: 10.3938/JKPS.64.289
Publisher: American Chemical Society (ACS)
Date: 04-03-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2TC01817A
Abstract: By means of a first-principles-based Landau–Devonshire model, we predict and explain why newly discovered intermediates can rationalize the persistent lack of a double polarization–electric field hysteresis for NaNbO 3 under an applied field.
Publisher: American Chemical Society (ACS)
Date: 22-05-2019
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8NR10278C
Abstract: Ultrathin MoO3-like nanolayers on a surrogate Au(111) substrate are proposed as new low-dimensional nanomaterials via a unique charge transfer mechanism.
Publisher: American Chemical Society (ACS)
Date: 24-12-2018
Abstract: Wetting of the liquid metal on the solid electrolyte of a liquid metal battery controls the operating temperature and performance of the battery. Liquid sodium electrodes are particularly attractive because of their low cost, natural abundance, and geological distribution. However, they wet poorly on a solid electrolyte near its melting temperature, limiting their widespread suitability for low-temperature batteries to be used for large-scale energy storage systems. Herein, we develop an isolated metal-island strategy that can improve sodium wetting in sodium-beta alumina batteries that allows operation at lower temperatures. Our results suggest that in situ heat treatment of a solid electrolyte followed by bismuth deposition effectively eliminates oxygen and moisture from the surface of the solid electrolyte, preventing the formation of an oxide layer on the liquid sodium, leading to enhanced wetting. We also show that employing isolated bismuth islands significantly improves cell performance, with cells retaining 94% of their charge after the initial cycle, an improvement over cells without bismuth islands. These results suggest that coating isolated metal islands is a promising and straightforward strategy for the development of low-temperature sodium-β alumina batteries.
Publisher: Springer Science and Business Media LLC
Date: 13-05-2022
DOI: 10.1038/S41427-022-00390-8
Abstract: Layered group-IV monochalcogenides, including GeS, GeSe, SnS, and SnSe, garner attention because of their anisotropic structures and properties. Here, we report on the growth of GeS microribbons via chemical vapor transport (CVT), which affords each of them with a low-symmetry orthorhombic structure and anisotropic optical and electronic properties. The single-crystalline nature of the GeS microribbon, which has a typical thickness of ~30 nm, is confirmed. Polarized Raman spectra reveal angle-dependent intensities that are attributed to the anisotropic layered structure of GeS microribbons. The photoluminescence (PL) spectra reveal a peak at ~1.66 eV. The angle-dependent PL and anisotropic absorption spectroscopy results provide evidence for a distinct anisotropic optical transition near the energy band edges this phenomenon is also predicted by our density functional theory (DFT)-based calculations. Strong in-plane direct-current transport anisotropy is observed under dark and white illumination by using back-gate cross-shaped field effect transistors (CSFETs) fabricated with the GeS microribbon significant gate-tunable conductivity is also confirmed. The strong anisotropy is further confirmed by the DFT-calculated effective mass ratio. Our findings not only support the application of GeS microribbons in anisotropic photoelectronic transistors but also provide more possibilities for other functional device applications.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5NR05605E
Abstract: Systematic engineering of atomic-scale low-dimensional defects in two-dimensional nanomaterials is a promising method to modulate the electronic properties of these nanomaterials. Defects at interfaces such as grain boundaries and line defects can often be detrimental to technologically important nanodevice operations and thus a fundamental understanding of how such one-dimensional defects may have an influence on their physio-chemical properties is pivotal for optimizing their device performance. Of late, two-dimensional phosphorene has attracted much attention due to its high carrier mobility and good mechanical flexibility. In this study, using density-functional theory, we have investigated the temperature-dependent energetics and electronic structure of single-layered phosphorene with various fault line defects. We have generated different line defect models based on a fault method, rather than the conventional rotation method. This has allowed us to study and identify new low-energy line defects, and we show how these low-energy line defects could well modulate the electronic band gap energies of single-layered two-dimensional phosphorene - offering a range of metallic to semiconducting properties in these newly proposed low-energy line defects in phosphorene.
Publisher: American Chemical Society (ACS)
Date: 16-05-2017
DOI: 10.1021/ACS.INORGCHEM.7B00661
Abstract: Phase ordering in the mixed-valence oxide Sb
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3NA00363A
Publisher: Physical Society of Japan
Date: 15-05-2012
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5RA17768E
Abstract: A synthetic route to produce surfactant-free SnS nanoplates with the Pbnm crystal structure is suggested. The process is quick and environmentally-friendly, accomplished under mild aqueous conditions by chemical transformation.
Publisher: Elsevier BV
Date: 03-2022
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CP03249D
Abstract: Using van der Waals corrected density-functional theory calculations, we study the fundamental physico-chemical properties of the molecular fragments of pyromellitic dianhydride oxydianiline (PMDA–ODA) on pristine and oxidized Cu(111) to investigate the effect of mild oxidation of the metal substrate on PMDA–ODA adsorption.
Publisher: American Chemical Society (ACS)
Date: 15-12-2012
DOI: 10.1021/NL202963Z
Abstract: A design for a heteroepitaxial junction by the way of one-dimensional wurzite on a two-dimensional spinel structure in a low-temperature solution process was introduced, and it's capability was confirmed by successful fabrication of a diode consisting of p-type cobalt oxide (Co(3)O(4)) nanoplate/n-type zinc oxide (ZnO) nanorods, showing reasonable electrical performance. During thermal decomposition, the 30° rotated lattice orientation of Co(3)O(4) nanoplates from the orientation of β-Co(OH)(2) nanoplates was directly observed using high-resolution transmission electron microscopy. The epitaxial relations and the surface stress-induced ZnO nanowire growth on Co(3)O(4) were well supported using the first-principles calculations. Over the large area, (0001) preferred oriented ZnO nanorods epitaxially grown on the (111) plane of Co(3)O(4) nanoplates were experimentally obtained. Using this epitaxial p-n junction, a diode was fabricated. The ideality factor, turn-on voltage, and rectifying ratio of the diode were measured to be 2.38, 2.5 V and 10(4), respectively.
Publisher: American Chemical Society (ACS)
Date: 02-07-2020
Publisher: Elsevier BV
Date: 04-2005
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CP07932B
Abstract: Using first-principles density-functional theory calculations, we systematically examine and analyze the detailed atomic structure and surface energetics of various oxidic motifs of Cu on Au(111), in search of new non-conventional, non-hexagonal surface oxidic structures in this system.
Publisher: Wiley
Date: 24-04-2017
Abstract: Ultrathin transition metal dichalcogenides (TMDs) have exotic electronic properties. With success in easy synthesis of high quality TMD thin films, the potential applications will become more viable in electronics, optics, energy storage, and catalysis. Synthesis of TMD thin films has been mostly performed in vacuum or by thermolysis. So far, there is no solution phase synthesis to produce large-area thin films directly on target substrates. Here, this paper reports a one-step quick synthesis (within 45-90 s) of TMD thin films (MoS
Publisher: Elsevier BV
Date: 04-2020
Publisher: American Chemical Society (ACS)
Date: 02-05-2019
Publisher: American Chemical Society (ACS)
Date: 17-11-2017
Abstract: Despite the ubiquitous nature of the Peltier effect in low-dimensional thermoelectric devices, the influence of finite temperature on the electronic structure and transport in the Dirac heterointerfaces of the few-layer graphene and layered tetradymite, Sb
Publisher: Wiley
Date: 28-10-2021
Abstract: A defect engineering of inorganic solids garners great deal of research activities because of its high efficacy to optimize erse energy‐related functionalities of nanostructured materials. In this study, a novel in situ defect engineering route to maximize electrocatalytic redox activity of inorganic nanosheet is developed by using holey nanostructured substrate with strong interfacial electronic coupling. Density functional theory calculations and in situ spectroscopic analyses confirm that efficient interfacial charge transfer takes place between holey TiN and Ni−Fe‐layered double hydroxide (LDH), leading to the feedback formation of nitrogen vacancies and a maximization of cation redox activity. The holey TiN−LDH nanohybrid is found to exhibit a superior functionality as an oxygen electrocatalyst and electrode for Li−O 2 batteries compared to its non‐holey homologues. The great impact of hybridization‐driven vacancy introduction on the electrochemical performance originates from an efficient electrochemical activation of both Fe and Ni ions during electrocatalytic process, a reinforcement of interfacial electronic coupling, an increase in electrochemical active sites, and an improvement in electrocatalysis/charge‐transfer kinetics.
Publisher: American Chemical Society (ACS)
Date: 22-01-2009
DOI: 10.1021/ES802523A
Abstract: Adsorption of perchloroethene (PCE), trichloroethene (TCE), and cis-dichloroethene (cis-DCE) on zerovalent iron is investigated using density functional theory (DFT) to evaluate hypotheses concerning the relative reactivity of these compounds on zerovalent iron. Four different chloroethene adsorption modes on the Fe(110) surface were studied using periodic DFT and the generalized gradient approximation (GGA). Of the adsorption sites examined, the atop site, where the chloroethene C==C bond straddles a surface iron atom, was the most energetically favorable site for the adsorption of all three chloroethenes. Electronic structure and property analyses provide an indication of the extent of sp2-sp3 hybridization. The strong hybridization of the pi-bonding orbital between the chloroethene C==C bond and the iron surface suggests that adsorbed chloroethenes are strongly activated on Fe(110) and are likely precursors for subsequent chloroethene dissociation on the Fe surface. When the effect of solvation is indirectly taken into account in the DFT simulations by considering the hydration energies of chloroethenes in bulkwater,the ordering ofthe adsorption energies of chloroethenes from the aqueous phase onto Fe(110) is in agreement with experimental observation (PCE > TCE > cis-DCE). Electronic properties of the adsorbed configurations of chloroethenes are also presented.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1NR04793K
Abstract: Tuning the nanomorphology of group 5 tetradymite M 2 X 3 (where M = Bi and Sb, and X = Se and Te) by going beyond thermodynamic equilibrium.
Publisher: Elsevier BV
Date: 05-2010
Publisher: Elsevier BV
Date: 09-2015
Publisher: American Physical Society (APS)
Date: 31-07-2008
Publisher: American Chemical Society (ACS)
Date: 28-08-2018
Publisher: American Chemical Society (ACS)
Date: 10-09-2018
Publisher: American Chemical Society (ACS)
Date: 08-10-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CP23534J
Abstract: As a first step towards a microscopic understanding of supported ultrathin nanofilms of TiN, we present state-of-the-art density-functional theory (DFT) calculations to investigate the interfacial properties of the TiN/MgO system as a function of film thickness. Optimized atomic geometries, energetics, and analysis of the electronic structure of the TiN/MgO systems are reported. In particular, we find that the work function of 1 ML of TiN(100) on MgO(100) exhibits a significant decrease, rationalized by the large surface dipole moment formation due to the changes in charge densities at the interface of this system. This decrease in the work function of TiN/MgO systems (as compared to pristine MgO(100) surface) could well benefit their application in metal-oxide-semiconductor devices as an ideal gate-stack material.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2NR31266B
Abstract: In this work, we present density-functional theory calculations to investigate the surface properties of TiN as a function of surface orientation and termination, as well as the influence of surface defects for various surface defect concentrations. We calculate both the surface energies (including vacancy formation) as a function of the nitrogen chemical potential, and plot the first-principles derived equilibrium crystal shape (ECS) under different growth conditions. We find that surface defects can considerably change the derived ECS of TiN (especially under nitrogen-lean conditions), highlighting the importance of surface defect consideration in modeling nanoparticle morphology.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4CE02431A
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4CP05930A
Abstract: A rational computational platform to design surface defect-mediated low-dimensional Pt/TiN nanocatalysts for next generation high-performance fuel cell technology via strong electronic metal–support interaction.
Publisher: Elsevier BV
Date: 02-2018
Publisher: Wiley
Date: 06-03-2022
Abstract: To expand the unchartered materials space of lead‐free ferroelectrics for smart digital technologies, tuning their compositional complexity via multicomponent alloying allows access to enhanced polar properties. The role of isovalent A‐site in binary potassium niobate alloys, (K,A)NbO 3 using first‐principles calculations is investigated. Specifically, various alloy compositions of (K,A)NbO 3 are considered and their mixing thermodynamics and associated polar properties are examined. To establish structure‐property design rules for high‐performance ferroelectrics, the sure independence screening sparsifying operator (SISSO) method is employed to extract key features to explain the A‐site driven polarization in (K,A)NbO 3 . Using a new metric of agreement via feature‐assisted regression and classification, the SISSO model is further extended to predict A‐site driven polarization in multicomponent systems as a function of alloy composition, reducing the prediction errors to less than 1%. With the machine learning model outlined in this work, a polarity‐composition map is established to aid the development of new multicomponent lead‐free polar oxides which can offer up to 25% boosting in A‐site driven polarization and achieving more than 150% of the total polarization in pristine KNbO 3 . This study offers a design‐based rational route to develop lead‐free multicomponent ferroelectric oxides for niche information technologies.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CP41392B
Abstract: As a first step towards a microscopic understanding of single-Pt atom-dispersed catalysts on non-conventional TiN supports, we present density-functional theory (DFT) calculations to investigate the adsorption properties of Pt atoms on the pristine TiN(100) surface, as well as the dominant influence of surface defects on the thermodynamic stability of platinized TiN. Optimized atomic geometries, energetics, and analysis of the electronic structure of the Pt/TiN system are reported for various surface coverages of Pt. We find that atomic Pt does not bind preferably to the clean TiN surface, but under typical PEM fuel cell operating conditions, i.e. strongly oxidizing conditions, TiN surface vacancies play a crucial role in anchoring the Pt atom for its catalytic function. Whilst considering the energetic stability of the Pt/TiN structures under varying N conditions, embedding Pt at the surface N-vacancy site is found to be the most favorable under N-lean conditions. Thus, the system of embedding Pt at the surface N-vacancy sites on TiN(100) surfaces could be promising catalysts for PEM fuel cells.
Publisher: Wiley
Date: 28-12-2015
Abstract: As a catalyst, single-atom platinum may provide an ideal structure for platinum minimization. Herein, a single-atom catalyst of platinum supported on titanium nitride nanoparticles were successfully prepared with the aid of chlorine ligands. Unlike platinum nanoparticles, the single-atom active sites predominantly produced hydrogen peroxide in the electrochemical oxygen reduction with the highest mass activity reported so far. The electrocatalytic oxidation of small organic molecules, such as formic acid and methanol, also exhibited unique selectivity on the single-atom platinum catalyst. A lack of platinum ensemble sites changed the reaction pathway for the oxygen-reduction reaction toward a two-electron pathway and formic acid oxidation toward direct dehydrogenation, and also induced no activity for the methanol oxidation. This work demonstrates that single-atom platinum can be an efficient electrocatalyst with high mass activity and unique selectivity.
Publisher: American Chemical Society (ACS)
Date: 18-08-2014
DOI: 10.1021/AR500133W
Abstract: The ability to assemble nanoscale functional building blocks is a useful and modular way for scientists to design valuable materials with specific physical and chemical properties. Chemists expect multicomponent, heterostructured nanocrystals to show unique electrical, thermal, and optical properties not seen in homogeneous, single-phase nanocrystals. Although researchers have made remarkable advances in heterogeneous nucleation and growth, design of synthetic conditions for obtaining nanocrystals with a target composition and shape is still a big challenge. There are several outstanding issues that chemists need to address before they can successfully carry out the design-based synthesis of multicomponent nanocrystals. For instance, small changes in the reaction parameters, such as the precursor, solvent, surfactant, reducing agent, and the reaction temperature, often result in changes in the structure and chemical composition of the final product. Although scientists do not fully understand the mechanisms underlying the nucleation and growth processes involved in the synthesis of these multicomponent nanocrystals, recent progress in understanding of the thermodynamic and kinetic factors have improved our control over their final structure and chemical composition. In this Account, we summarize our recent advances in understanding of the nucleation and growth mechanisms involved in the solution-based synthesis of multicomponent nanocrystals. We also discuss the various challenges encountered in their synthesis, emphasizing what still needs special consideration. We first discuss the three different nucleation paths from a thermodynamics perspective: amorphous nucleation, crystalline nucleation, and two-step nucleation. Amorphous nucleation and two-step nucleation involve the generation of nonstoichiometric nuclei. We initiate this process mainly by introducing an imbalance in the concentrations of the reduced elements. When the nonstoichiometric nuclei grow, we can add secondary elements to the growing nonstoichiometric nuclei. This leads to either the physical deposition or atomic mixture formation through the diffusion and rearrangement of constituents. The processes of mixture formation and the physical deposition of the secondary constituent element also compete and determine the shape and chemical composition of the final product. If the free energy change by mixture formation is positive (ΔGAB ≥ 0), physical deposition takes place predominantly, and the spreading coefficient (S) determines the structure of the nanocrystals. However, when mixture formation is highly spontaneous (ΔGAB < -ξ), the chemical composition of the final product is usually stoichiometric, and its shape then depends on the size of the primary nanocrystals. When the mixture formation and physical deposition are in competition (-ξ ≤ ΔGAB < 0), as commonly seen for many nanoalloy systems, both the chemical composition and the structure are determined by the size of the primary nanocrystals as well as the degree of mixture formation at the interface of the constituent components. Finally, we discuss the challenges and caveats that one needs to take into account when synthesizing multicomponent nanocrystals.
Publisher: American Physical Society (APS)
Date: 29-08-2014
Publisher: American Physical Society (APS)
Date: 20-01-2016
Publisher: American Chemical Society (ACS)
Date: 23-06-2016
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7NR03377J
Abstract: To build upon the structural ersity in the polymorphic phases of 2D phosphorene, we propose different assembly methods that involve four commonly reported parent phases ( i.e. the α-, β-, γ-, and δ-phosphorene) in combination with the lately reported low-energy one-dimensional defects in α-phosphorene.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5TC02191J
Abstract: Using hybrid density-functional theory (DFT) and ab initio molecular dynamics, we calculate and characterize glassy amorphous antimony oxides in elevated oxygen environments, and provide information on how their atomic and electronic structures change as a function of their oxygen environment.
Publisher: Royal Society of Chemistry (RSC)
Date: 28-10-2014
DOI: 10.1039/C4CP04473H
Abstract: Surface oxidation processes are crucial for the functionality of Cu-based catalytic systems used for methanol synthesis, partial oxidation of methanol or the water-gas shift reaction. We assess the stability and population of the "8"-structure, a [formula, see text:] oxide phase, on the Cu(111) surface. This structure has been observed in X-ray photoelectron spectroscopy and low-energy electron diffraction experiments as a Cu(111) surface reconstruction that can be induced by a hyperthermal oxygen molecular beam. Using density-functional theory calculations in combination with ab initio atomistic thermodynamics and Boltzmann statistical mechanics, we find that the proposed oxide superstructure is indeed metastable and that the population of the "8"-structure is competitive with the known "29" and "44" oxide film structures on Cu(111). We show that the configuration of O and Cu atoms in the first and second layers of the "8"-structure closely resembles the arrangement of atoms in the first two layers of Cu2O(110), where the atoms in the "8"-structure are more constricted. Cu2O(110) has been suggested in the literature as the most active low index facet for reactions such as water splitting under light illumination. If the "8"-structure were to form during a catalytic process, it is therefore likely to be one of the reactive phases.
Publisher: American Chemical Society (ACS)
Date: 09-10-2019
Publisher: American Chemical Society (ACS)
Date: 18-01-2017
Publisher: Elsevier BV
Date: 06-2022
Publisher: American Physical Society (APS)
Date: 24-02-2017
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4TC00586D
Abstract: This article reviews recent advances in solution-phase synthesis of anisotropic metal chalcogenide nanomaterials (1-D & 2-D) and their practical applications with some challenges in the solution-based synthesis.
Publisher: Elsevier BV
Date: 04-2009
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1TC03191K
Abstract: We have performed density-functional theory calculations to understand how applied epitaxial strain influences the thermodynamic, electronic, and (anisotropic) polarization properties in polar KNbO 3 polymorphs for next-generation Pb-free piezoelectric applications.
No related grants have been discovered for Aloysius Soon.