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김성엽(Sung Youb Kim) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
Graphene has a great potential in the applications of nanoscale sensing devices, due to its excellent electric, electronic, optic, and mechanical properties. In terms of mechanics, graphene shows outstanding oscillation character as well because it has light weight and strong stiffness. In this paper, we conduct classical molecular dynamics calculations to demonstrate the possibility of single-atom mass sensor using graphene based on its oscillation character. We analyze the resonance frequency change of graphene due to additional mass. Here, we employ the Tersoff-Brenner Ⅱ potential for graphene and a Lennard-Jones potential to describe the interaction between carbon and Au atom. The resonance frequency shift of graphene after adding Au atom(s) mainly depends on the system size and temperature. As temperature goes high (>30K), the diffusion of Au atom(s) deteriorates the sensitivity of graphene sensor, because the diffusion barrier of metal atom on graphene is small.
김성엽(Sung Youb Kim),이영민(Youngmin Lee),임세영(Seyoung Im) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Coalescence process of two carbon nanotubes is analyzed using action-derived molecular dynamics. The unit step of merging consists of only four sequential generalized Stone-Wales transformations which occur in four heptagon-hexagon pairs around jointed part. We show that additional single carbon atom may play a role of autocatalyst, which reduces the activation barrier of merging significantly. An atomistic pathway of the Tjunction formation of carbon nanotubes is presented and the energy barriers during the process are obtained as well. In this case, we employ the perfect nanotube-model with two additional carbon atoms. Our results confirm that the coalescence and junction formation of carbon nanotubes may happen more frequently than theoretical predictions at the moderate temperature in the presence of additional carbon atoms.
김성엽(Sung Youb Kim),박종연(Jong Youn Park),조영삼(Young-Sam Cho),전석기(Sukky Jun),임세영(Seyoung Im) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
We present a multiscale scheme which describes the dynamic pictures of atoms in the multiple length-scale systems. Large-scale atomic systems are reduced to coarse grained system by the quasicontinuum, of which the dynamic pathways are rendered by the action-derived molecular dynamics proved effective for multiple time-scale problems such as rare events. Adatom diffusions on the metal (001) surface are selected for our numerical examples. The energy barriers of the diffusions and the real dynamic trajectories of the adatoms are calculated.
김성엽(Sung Youb Kim),임세영(Seyoung Im) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
We examine the mobility of an edge dislocation pair in Si crystal using action-derived molecular dynamics. The various structural changes of dislocation cores with atomic resolution and their corresponding energy barriers, the so-called Peierls barriers, are evaluated during the dislocation motion. The dislocation movement is achieved by sequential bond-breaking and re-bonding processes of concerned atoms, which occur layer by layer in contrast with the assumption in Peierls-Nabarro model. The energy barrier for the movement of an edge dislocation pair on shuffle plane is higher than 0.20 eV, if bond-breakages occur first. However, it is significantly reduced to be about 0.08 eV, when five-fold bonds are formed before bond-breakages. When the dislocation moves via this mechanism, energy barrier for the dislocation movement does not depend on the length of dislocation line.
수소저장매체로서의 리튬보론 수소화합물에 대한 제일원리계산
김성엽(Sung Youb Kim),이영민(Youngmin Lee),박정순(Jeong Soon Park),임세영(Seyoung Im) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
The structural stabilities of lithium borohydrides, ones of the prominent candidates as noble hydrogen storage materials, are investigated using a density functional scheme with generalized gradient approximation. PW91 potential is used to describe the exchange-correlation between electrons. LiBH₄, LiBH₂ and Li₃BH?, which are majorly concerned materials during hydrogen release process, have their stable crystal structures in Pnma(#62), P2₁/c(#14), Pna2₁(#33) space groups, respectively. We examine the thermodynamical enthalpy changes during chemical reactions of lithium borohydrides as well. LiBH₄ can release 18wt% of hydrogen via two different chemical reactions consisting of sequential endothermic processes.
김성엽(Sung Youb Kim),엄윤용(Youn Young Earmme) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.3
We calculate the variation of the surface stresses according to uniaxial and biaxial strains in face-centered cubic (FCC) metals. In our study, three mainly observed free surfaces of seven representative FCC metals are considered. Employed method is molecular mechanics, in which the interaction of atoms is described by empirical interatomic potentials. As uniaxial strain increases to tensile direction, the surface stresses on {100} and {110} free surfaces decrease monotonously, while those on {111} surface increase. These tendencies are the same regardless of the species of metals and interatomic potentials employed. However, when the system is under biaxial strain, surface stresses change different according to the surface directions, the species of metals, and even interatomic potentials. On {100} and {111} surfaces, heavy metals (Pt, Au) show the opposite variation to light metals (Ni, Cu). In the cases of Pd and Ag, the surface stresses reveal the opposite tendency, depending on interatomic potentials used.
Quantum Corral과 Dip-Pen Nanolithography의 전산모사
김성엽(Sung Youb Kim),이영민(Youngmin Lee),전석기(Sukky Jun),임세영(Seyoung Im) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
Two nanoscale fabrications on the surface using a scanning probe microscopy (SPM) are numerically simulated. One is the quantum corral which reveals standing-wave patterns of electrons due to adatoms on the metallic surface. Quantum multiple scattering theory via Green function approach is imposed for the simulations. The other example is the process of dip-pen lithography. Random walk algorithm is applied for describing the diffusion patterns of deposited molecules.