Ki Ryang Byun

Twist of hypothetical silicon nanotubes

The responses of hypothetical silicon nanotubes (SiNTs) under torsion have been investigated using an atomistic simulation based on the Tersoff potential. A torque, proportional to the deformation within Hookes law, resulted in ribbon-like flattened shapes and eventually led to breaking of the hypothetical SiNTs. Each shape change of the hypothetical SiNTs corresponded to an abrupt energy change and a singularity in the strain energy curve as a function of the external tangential force, torque, or twist angle. The dynamics of SiNTs under torsion can be modelled in continuum elasticity theory.

Defects in ultrathin copper nanowires: Atomistic simulations

We have performed atomistic simulations for cylindrical multi-shell (CMS)-type Cu nanowires containing defects. Our investigation has revealed some physical properties that have not been detected in previous studies that have considered defect-free nanowires. Since the vacancy formation energy is lowest in the core of a CMS-type nanowire, a vacancy formed in the outer shell of a CMS-type nanowire naturally migrates toward the core. The maximum of the formation energy of an adhered atom on the surface of a CMS-type nanowire was modeled using a 16-11-6-1 nanowire. The formation energy of an adhered atom decreased when the diameter of the CMS-type nanowire was either above or below the diameter of the peak energy maximum. This investigation found three recombination mechanisms for the vacancy-adhered atom pairs: (i) by direct recombination, (ii) by a kick-in recombination, and (iii) by a ring recombination. Vacancy formation energy calculations show that an onion-like cluster with a hollow was formed, and molecular dynamics simulations for various CMS-type nanowires found that vacancies migrated towards the core. From these, we obtained basic information on the formation of hollow CMS-type metal nanowires (metal nanotubes) [Y. Oshima, et al., Phys. Rev. B 65, 121401 (2002)].

Cluster deposition study by molecular dynamics simulation: Al and Cu cluster

The ionized cluster beam deposition of Al and Cu clusters has been investigated with a classical molecular dynamics simulation and the Metropolis Monte–Carlo simulation. The spreading of the cluster has been studied as functions of cluster size and initial cluster energy. When the local area reached the local melting spot on the surface around the impact point of an energetic cluster, during a few ps, intermixing was easily achieved and a good epitaxial film with optimum bulk density was formed. For uniform film growth using a cluster impact, it is necessary to make the local area temperature higher than melting temperature on the surface around the impact point of an energetic cluster.

Gigahertz frequency tuner based on a telescoping double-walled carbon nanotube: molecular dynamics simulations

The schematics of a gigahertz-range tuner is addressed as an application of a telescoping multi-walled carbon nanotube (CNT) that can be used repeatedly, and its dynamic operation is investigated via classical molecular dynamics simulations based on a (5,5)(10,10) double-walled CNT. Fine control of the telescoped length of the double-walled CNT enables its resonance frequency to be matched to one of the signal frequencies, and the telescoped nanotube can be tuned to its resonance frequency for use as a component of a bandpass filter.

Carbon-nanotube-based nanoelectromechanical switch

A nanoelectromechanical model based on atomistic simulations including charge transfer was investigated. Classical molecular dynamics method combined with continuum electric models could be applied to a carbon-nanotube nanoelectromechanical memory device that could be characterized by carbon-nanotube bending performance by atomistic capacitive and interatomic forces. The capacitance of the carbon atom was changed with the height of the carbon atom. We performed MD simulations for a suspended (5,5) carbon-nanotube-bridge with the length of 11.567 nm (LCNT) and the depth of the trench of 0.9 ~ 1.5 nm (H). After the carbon-nanotube collided on the gold surface, the carbon-nanotube-bridge oscillated on the gold surface with amplitude of ~1 Å, and the amplitude gradually decreased. When H ≤ 1.3 nm, the carbon-nanotube-bridge continually contacted with the gold surface after the first collision. When H ≥ 1.4 nm, the carbon-nanotube-bridge stably contacted with the gold surface after several rebounds. As H increased, the threshold voltage linearly increased. As the applied bias increased, the transition time exponentially decreased at each trench depth. When H / LCNT was below 0.13, the carbon-nanotube nanoelectromechanical memories were permanent nonvolatile memory devices, whereas the carbon-nanotube nanoelectromechanical memories were volatile memory or switching devices when H / LCNT was above 0.14. The turn-on voltages and tunneling resistances obtained from our simulations are compatible to those obtained from previous experimental and theoretical results.

Atomic Scale Simulations of Silicon Nanotubes under Axial Compression: AFM Application

This study showed the response of hypothetical silicon nanotubes under axial compression using an atomistic simulation based on the Tersoff potential. A pressure, proportional to the deformation within Hooke’s law, eventually led to a collapse of silicon nanotube and an abrupt change in structure. Using the sum of the cross sections of atoms on the cross section of silicon nanotube and the pressure on silicon nanotube, we determined Young’s modulus of silicon nanotubes that was constant irrespective of the diameter of silicon nanotubes. As the diameter of silicon nanotubes increased, the collapse pressure, that is to say the critical stress linearly decreased. However, net forces on silicon nanotubes at their collapses were almost constant irrespective of the diameter of silicon nanotubes. We calculated the variations of the volume of unit cell as a function of pressure that were not dealt within previous works that considered carbon nanotubes under compression. With properly chosen parameters of silicon ...