Suklyun Hong - Academia.edu (original) (raw)

Papers by Suklyun Hong

Applied Physics Letters, 2005

We carry out first-principles density-functional calculations to investigate the electronic struc... more We carry out first-principles density-functional calculations to investigate the electronic structure of the gold-carbon nanotube contact. It is found that a pressure applied on the gold-nanotube contact shifts the Fermi level from the valence edge to the conduction edge of the carbon nanotube. This can explain the n-type transport behavior frequently observed in the nanotube field-effect transistor using the gold as electrodes. An atomistic model is proposed for a possible origin of the pressure when the nanotube is embedded in the gold electrode.

Nanomaterials, 2021

Using density functional theory calculations, atomic and electronic structure of defects in monol... more Using density functional theory calculations, atomic and electronic structure of defects in monolayer GeS were investigated by focusing on the effects of vacancies and substitutional atoms. We chose group IV or chalcogen elements as substitutional ones, which substitute for Ge or S in GeS. It was found that the bandgap of GeS with substitutional atoms is close to that of pristine GeS, while the bandgap of GeS with Ge or S vacancies was smaller than that of pristine GeS. In terms of formation energy, monolayer GeS with Ge vacancies is more stable than that with S vacancies, and notably GeS with Ge substituted with Sn is most favorable within the range of chemical potential considered. Defects affect the piezoelectric properties depending on vacancies or substitutional atoms. Especially, GeS with substitutional atoms has almost the same piezoelectric stress coefficients eij as pristine GeS while having lower piezoelectric strain coefficients dij but still much higher than other 2D ma...

Nano letters, Jan 10, 2018

Electrochemical intercalation is a powerful method for tuning the electronic properties of layere... more Electrochemical intercalation is a powerful method for tuning the electronic properties of layered solids. In this work, we report an electrochemical strategy to controllably intercalate lithium ions into a series of van der Waals (vdW) heterostructures built by sandwiching graphene between hexagonal boron nitride (h-BN). We demonstrate that encapsulating graphene with h-BN eliminates parasitic surface side reactions while simultaneously creating a new heterointerface that permits intercalation between the atomically thin layers. To monitor the electrochemical process, we employ the Hall effect to precisely monitor the intercalation reaction. We also simultaneously probe the spectroscopic and electrical transport properties of the resulting intercalation compounds at different stages of intercalation. We achieve the highest carrier density >5 × 10 cm with mobility >10 cm/(V s) in the most heavily intercalated samples, where Shubnikov-de Haas quantum oscillations are observed a...

Physical Review B, 1997

The bare and hydrogen-covered diamond (100) surfaces were investigated through pseudopotential de... more The bare and hydrogen-covered diamond (100) surfaces were investigated through pseudopotential density-functional calculations within the local-density approximation. Di erent coverages, ranging from one to two, were considered. These corresponded to di erent structures including 1 1, 2 1, and 3 1, and di erent hydrogen-carbon arrangements including monohydride, dihydride, and con gurations in between. Assuming the system was in equilibrium with a hydrogen reservoir, the formation energy of each phase was expressed as a function of hydrogen chemical potential. As the chemical potential increased, the stable phase successively changed from bare 2 1 to (2 1):H, to (3 1):1.33H, and nally to the canted (1 1):2H. Setting the chemical potential at the energy per hydrogen in H2 and in a free atom gave the (3 1):1.33H and the canted (1 1):2H phase as the most stable one, respectively. However, after comparing with the formation energy of CH4, only the (2 1):H and (3 1):1.33H phases were stable against spontaneous formation of CH4. The former existed over a chemical potential range ten times larger than the latter, which may explain why the latter, despite of having a low energy, has not been observed so far. Finally, the vibrational energies of the C H stretch mode were calculated for the (2 1):H phase.

Nanoscale, 2015

The production of holes by electron beam irradiation in hexagonal boron nitride is monitored over... more The production of holes by electron beam irradiation in hexagonal boron nitride is monitored over time using atomic resolution transmission electron microscopy.

Physical Review B, 2005

The Schottky barrier at the metal-nanotube contact has been a prime issue in the nanoscale device... more The Schottky barrier at the metal-nanotube contact has been a prime issue in the nanoscale devices. Here we use ab initio density-functional calculations to investigate the electronic structure and the Fermi level alignment at the metal-nanotube contacts. Consistent with the common concept of the large ͑small͒ work function of gold ͑aluminum͒ surfaces, the Fermi level of the gold layer is found to be aligned at the valence band edge, while that of the aluminum sits at the conduction band edge of the semiconducting carbon nanotube. However, upon the oxidation, the work function of aluminum surface becomes as large as that of the clean gold surface, causing the Fermi level to be aligned at the valence band edge of the semiconducting nanotube. This suggests that the carrier type of the nanotube field effect transistor could transform from n-type to p-type upon oxygen adsorption on the electrode surface. The oxidation-induced increase of the tunneling barrier is also investigated.

Japanese Journal of Applied Physics, 2004

In the chemical vapor deposition process for carbon nanotube growth using catalytic particles, ma... more In the chemical vapor deposition process for carbon nanotube growth using catalytic particles, many carbon atoms as well as hydrogen atoms coexist on actual surfaces of catalysts and their mutual interaction may change the adsorption and diffusion properties of carbon atoms. To investigate the effect of hydrogen on carbon diffusion on the Ni(111) surface we have performed pseudopotential density-functional calculations. The diffusion barriers of CH x (x ¼ 1, 2, 3) on Ni(111) are obtained and compared with that of a single carbon atom. The diffusion barrier decreases with the presence of attached hydrogens, which implies that such adsorbates with more hydrogen are likely to diffuse more easily.

Japanese Journal of Applied Physics, 2002

In order to investigate the relevance of the equilibrium crystal shape of a nickel particle durin... more In order to investigate the relevance of the equilibrium crystal shape of a nickel particle during carbon nanotube growth, we have performed self-consistent pseudopotential density-functional calculations. The nickel particle's equilibrium shape is obtained from the Wulff construction using the calculated surface energies. To understand the role of facets of the nickel particle, we investigate the adsorption and diffusion of the carbon atom on the nickel surfaces. The desorption energy of the carbon atom and the activation energy for carbon diffusion are found to be very different on different low-index facets, thus diffusion behaviors will also differ. It is found that the {111} and {110} facets are likely to be more reactive compared to the {100} facet. Therefore, the facets of the nickel particle will play an important role in carbon nanotube growth.

Current Applied Physics, 2003

To investigate the surface energy anisotropy of carbon-adsorbed iron surfaces related to carbon n... more To investigate the surface energy anisotropy of carbon-adsorbed iron surfaces related to carbon nanotube growth we have performed self-consistent pseudopotential density-functional calculations. The iron particle's equilibrium shape is obtained from the Wulff construction using the calculated surface energies. We investigate the adsorption and diffusion of carbon atoms on the iron surfaces. It is found that the desorption energy of the carbon atoms and the activation energy for carbon diffusion are very different on different facets. Using the energetics of carbon-adsorbed iron surfaces, we evaluate the formation energies of the surfaces as a function of carbon chemical potential. Since the surface energies of the low-index iron facets are affected differently by the presence of carbon, the crystal shape is changed correspondingly.

Applied Physics Letters, 2009

Adsorption geometries and binding affinities of metal nanoparticles onto carbon nanotubes ͑CNTs͒ ... more Adsorption geometries and binding affinities of metal nanoparticles onto carbon nanotubes ͑CNTs͒ are investigated through density-functional-theory calculations. Clusters of 13 metal atoms are used as models for metal nanoparticles. Palladium, platinum, and titanium particles strongly chemisorb to the CNT surface. Unlike the cases of atomic adsorptions the aluminum particle has the weakest binding affinity with the CNT. Aluminum or gold nanoparticles accumulated on the CNT develop the triangular bonding network of the metal surfaces in which the metal-carbon bond is not favored. This suggests that the CNT-Al interface is likely to have many voids and thus susceptible to oxidation damages.

The Journal of Physical Chemistry B, 2004

We have performed ab initio pseudopotential calculations in order to investigate the atomic and e... more We have performed ab initio pseudopotential calculations in order to investigate the atomic and electronic structure of pyridine adsorbed on the Ge(100) surface. A large number of pyridine/Ge(100) adsorption configurations possibly resulting from cycloadditions and Lewis acid-base reactions are presented. The configuration having the Ge-N linkage formed by dative bonding with adsorbed pyridine molecules tilted is the most stable, which explains the experimental STM images well. The dative bonding character is investigated by comparing the charge densities for the clean and pyridine-adsorbed Ge(100) surfaces. Finally the difference between the Ge(100) and Si(100) surfaces is discussed.

The Journal of Physical Chemistry B, 2005

The adsorption and decomposition of water on Ge(100) have been investigated using real-time scann... more The adsorption and decomposition of water on Ge(100) have been investigated using real-time scanning tunneling microscopy (STM) and density-functional theory (DFT) calculations. The STM results revealed two distinct adsorption features of H 2 O on Ge(100) corresponding to molecular adsorption and H-OH dissociative adsorption. In the molecular adsorption geometry, H 2 O molecules are bound to the surface via Ge-O dative bonds between the O atom of H 2 O and the electrophillic down atom of the Ge dimer. In the dissociative adsorption geometry, the H 2 O molecule dissociates into H and OH, which bind covalently to a Ge-Ge dimer on Ge(100) in an H-Ge-Ge-OH configuration. The DFT calculations showed that the dissociative adsorption geometry is more stable than the molecular adsorption geometry. This finding is consistent with the STM results, which showed that the dissociative product becomes dominant as the H 2 O coverage is increased. The simulated STM images agreed very well with the experimental images. In the real-time STM experiments, we also observed a structural transformation of the H 2 O molecule from the molecular adsorption to the dissociative adsorption geometry.

Japanese Journal of Applied Physics, 2006

The adsorption structures of pyrrole on a Ge(100) surface at low coverage have been investigated ... more The adsorption structures of pyrrole on a Ge(100) surface at low coverage have been investigated using ab initio densityfunctional theory (DFT) calculations. The most stable configuration is that the adsorbed pyrrole molecule with H dissociated forms a bridge between two down-Ge atoms of neighboring dimer rows through N-Ge bonding and C-Ge interaction. The corresponding simulated images explain well the flower-like features with a dark side observed in the experiment. Also, C-H dissociative structures are found to contribute as a minority to the features. A similar configuration to the most stable one, but with a dissociated H out of the region of interest, can explain the flower-like feature without a dark side. Finally, a C-and Nend-on configuration may be a possible candidate for bright protrusions in the STM images.

Journal of Physics: Condensed Matter

Using density functional theory calculations, we have studied the edge-functionalization of armch... more Using density functional theory calculations, we have studied the edge-functionalization of armchair graphene nanoribbons (AGNRs) with pentagonal-hexagonal edge structures. While the AGNRs with pentagonal-hexagonal edge structures (labeled (5,6)-AGNRs) are metallic, the edgefunctionalized (5,6)-AGNRs with substitutional atoms opens a band gap. We find that the band structures of edge-functionalized (5,6)-N-AGNRs by substitution resemble those of defect-free (N-1)-AGNR at the Γ point, whereas those at the X point show the original ones of the defect-free N-AGNR. The overall electronic structures of edge-functionalized (5,6)-AGNRs depend on the number of electrons, supplied by substitutional atoms, at the edges of functionalized (5,6)-AGNRs.

Scientific Reports

the transfer process. The intercalated atoms are expected to bring about charge doping or to chan... more the transfer process. The intercalated atoms are expected to bring about charge doping or to change the magnetic properties of the system. Results and Discussion Van der Waals ZGNR/h-BN heterostructures. First, we obtain the optimized geometry of the vdW ZGNR/h-BN heterostructure with no intercalated atom, as shown in Fig. 1(a), where the grey, blue, and pink colours represent carbon, nitrogen, and boron atoms, respectively. The most stable configuration resembles the Bernal stacking of graphite. The carbon atoms of the ZGNR are located on top of the boron atoms and the centre of h-BN hexagons; that is, the centres of the ZGNR hexagons are on top of the nitrogen atoms of h-BN. Our results are in consistent with the previous reports 20,23-26. The equilibrium distance between the ZGNR and the h-BN sheet is 3.15 Å. We find that the localized states exist at the edges of the ZGNR on the h-BN sheet, represented by the almost flat band of the zigzag edge around the Fermi level (E F). The localized states 27 , however, rapidly decay into the bulk, as shown in Fig. 1(b). Figure 1(b) shows the projected densities of states (PDOSs) at the left and right edges and near the middle of the ZGNR, respectively. The red, green, and yellow lines of the PDOSs of the ZGNR correspond to the same colours of carbon atoms at the ZGNR in Fig. 1(a), respectively. The

Physical Review B, 1998

We have evaluated the surface free energies of hydrogen-covered ͑100͒, ͑111͒, and ͑110͒ surfaces ... more We have evaluated the surface free energies of hydrogen-covered ͑100͒, ͑111͒, and ͑110͒ surfaces of diamond and silicon as a function of the hydrogen chemical potential using first-principles methods. The change in surface-energy anisotropy and equilibrium crystal shape due to hydrogen adsorption is examined. The three low-index facets are affected differently by the presence of hydrogen and unexpected differences are found between diamond and silicon. Taking into account possible formation of local facets on the hydrogencovered ͑100͒ surfaces, we find that the dihydride phase is not stable on both C͑100͒ and Si͑100͒, nor is the 3ϫ1 phase on C͑100͒. ͓S0163-1829͑98͒07208-7͔

Aps March Meeting Abstracts, Mar 1, 1998

The Journal of Physical Chemistry C, 2012

We have performed ab initio calculations to study the atomic and electronic structure of glycine ... more We have performed ab initio calculations to study the atomic and electronic structure of glycine on the Ge(100) surface. Previously, adsorption configurations of glycine on Ge(100) was studied using scanning tunneling microscopy (STM), density functional theory (DFT) calculations, and high-resolution core-level photoemission spectroscopy (HRCLPES), where the most probable structure observed in experiment was assigned to an "intrarow O−H dissociated and N dative bonded structure". Using DFT calculations with van der Waals corrections, we find that the intrarow structure is less stable by about 0.23 eV than another structure called "interrow O−H dissociated and N dative bonded structure", different from the previous study. Furthermore, comparing the energetics and theoretical STM images with the experimental images for glycine on Ge(100), we conclude that the structure observed in the STM experiment is clearly identified as the interrow O−H dissociated and N dative bonded structure. Finally, these results for glycine on Ge(100) are compared with those on Si(100).