Inkook Jang

Modification of carbon nanotube-polystyrene matrix composites through polyatomic-ion beam deposition: predictions from molecular dynamics simulations

Abstract Classical molecular dynamics simulations are used to study polyatomic-ion beam deposition on pristine polystyrene (PS) substrates and carbon nanotube-PS matrix composite substrates. The ion beam consists of 20 C 3 F 5 + ions and the forces are calculated with a many-body, reactive empirical bond-order potential for hydrocarbons and fluorocarbons. The simulations predict that the ion beam deposition process will lead to covalent bond formation between the nanotube and the PS matrix. In addition, the responses of the composites to the ion-beam deposition are significantly different from the response of the pristine PS substrate. The simulations detail the atomic-scale mechanisms that are responsible for these differences.

Sliding orientation effects on the tribological properties of polytetrafluoroethylene

The chemical inertness, high melting point, and intrinsic lubricity of polytetrafluoroethylene (PTFE) have been used to develop solid lubricating parts for operation in extreme environments, from frying pans to satellites. The atomic-level mechanisms associated with friction and wear at PTFE surfaces are elucidated here by systematic investigations of the frictional anisotropy measured with respect to chain orientation. In particular, a combination of atomic-scale simulations, nanometer-scale atomic force microscopy experiments, micrometer-scale microtribometers experiments, and macroscale pin-on-disk experiments are used. Data across these length scales, from both the computational and experimental approaches, provide a consistent view of the mechanisms by which the structural orientation of PTFE contributes to its unique tribological properties.

Effect of the sliding orientation on the tribological properties of polyethylene in molecular dynamics simulations

The role of sliding orientation on the tribological properties of polyethylene (PE) is investigated by using classical molecular dynamics simulations. Cross-linked PE surfaces slide against one another in two different directions: one that is perpendicular to and one that is parallel to the aligned direction of the polymer chains. The results indicate that sliding in the parallel direction occurs with a lower friction coefficient than sliding in the perpendicular direction. In both cases, gross level stick-slip motion is observed to be associated with the sliding of a restrained, corrugated molecular interface. In addition, the simulations demonstrate the way in which the system stores more shear strain energy during sliding in the perpendicular direction. The tribological behavior of these PE surfaces is compared to the behavior of similarly modeled polytetrafluoroethylene surfaces; the differences and similarities between the two systems are discussed.

Study of C3H5+ ion deposition on polystyrene and polyethylene surfaces using molecular dynamics simulations

Molecular dynamics simulations of ion deposition processes are used to study the deposition of C3H5+ ions on crystalline polystyrene (PS) and polyethylene (PE) surfaces at energies of 50 and 25 eV. For each system, 80 trajectories are carried out on pristine surfaces and the incident angle in every case is normal to the surface. The forces are determined using the reactive empirical bond order method developed by Tersoff and parametrized for hydrocarbons by Brenner, coupled to long-range Lennard–Jones potentials. The simulations predict that the ions deposited at 50 eV either dissociate and stick to the surface or remain on the surface intact in 98% of the trajectories on PS, and in 89% of the trajectories on PE. At 25 eV, the ions are deposited intact in 70% of the trajectories on PS and dissociate in only 3%. No dissociation of the incident ions is predicted to occur on PE at 25 eV. Rather, the ions scatter away in 90% of the trajectories. Consequently, ion deposition on PE at 25 eV is predicted to be v...

Study of angular influence of C3H5+ ion deposition on polystyrene surfaces using molecular dynamics simulations

The influence of incident angle on the interaction of polyatomic hydrocarbon ions (C3H5+) with polystyrene surfaces is examined using classical molecular dynamics simulations. The forces are determined using the reactive empirical bond order method developed by Tersoff and parametrized by Brenner. The total incident energy is 50 eV and the angles considered are 0° (normal to the surface), 15°, 45°, and 75°. At each angle, the outcomes of 80 trajectories are compiled and averaged. The results show that intact ions scatter from the surface in only 2% of the trajectories and that the ions dissociate in 61% of the trajectories at normal incidence. At 75°, intact ions scatter away in 56% and they dissociate in only 30% of the trajectories. The largest total amount of carbon is deposited at normal incident angles. However, more ions or ion fragments are predicted to remain near the surface (penetrate 3.5–5.5 A) at 45°. This is because ion fragments tend to penetrate more deeply (6–7 A) into the surface at small...

Dependence of plasma-induced modification of polymer surfaces on polyatomic ion chemistry

Fluorocarbon plasmas are widely used to chemically modify surfaces and deposit thin films. The deposition of mass selected fluorocarbon ions is useful for isolating the effects specific to polyatomic ions. In this study, the detailed chemical modifications that result from the deposition of beams of polyatomic fluorocarbon ions (C3F5+ and CF3+) on polystyrene surfaces at experimental fluxes are identified using classical molecular dynamics simulations. These simulations elucidate how and why more efficient fluorination of the surface is achieved by CF3+ ion beam deposition, but C3F5+ ions are more efficient at growing fluorocarbon thin films.

Chemical modification of the poly(vinylidene fluoride-trifluoroethylene) copolymer surface through fluorocarbon ion beam deposition

Classical molecular dynamics simulations are used to study the effects of continuous fluorocarbon ion beam deposition on a poly(vinylidene fluoride-trifluoroethylene) [P(VDF-trFE)] surface, a polymer with electromechanical properties. Fluorocarbon plasma processing is widely used to chemically modify surfaces and deposit thin films. It is well accepted that polyatomic ions and neutrals within low-energy plasmas have a significant effect on the surface chemistry induced by the plasma. The deposition of mass selected fluorocarbon ions is useful to isolate the effects specific to polyatomic ions. Here, the differences in the chemical interactions of C3F5+ and CF3+ ions with the P(VDF-trFE) surface are examined. The incident energy of the ions in both beams is 50eV. The CF3+ ions are predicted to be more effective at fluorinating the P(VDF-trFE) surface than C3F5+ ions. At the same time, the C3F5+ ions are predicted to be more effective at growing fluorocarbon thin films. The simulations also reveal how the d...

Compact process model of temperature dependent amorphization induced by ion implantation

A compact process model of the thickness of amorphous layer generated by high dose ion implantation was developed. The model takes into account implantation temperature that has strong effect on the damage accumulation and amorphization dynamics. The model is based on the results of Kinetic Monte Carlo simulation of implantation process and provides means for fast and precise calculation of amorphous layer thickness created by most common species used in semiconductor technology, with a wide range of implantation energies, doses and temperatures.

Atomistic simulation flow for source-drain epitaxy and contact formation processes of advanced logic devices

An atomistic simulation flow for contact formation process was developed and integrated into logic transistor frontend process simulation. Existing atomistic kinetic lattice Monte Carlo model of epitaxy process was extended to silicidation. Metal and silicon diffusion and silicide formation reactions were taken into account at atomic level which allowed accurate simulation of silicide shape including faceting effects. This approach enables device performance prediction depending on design rules and parameters thus providing a way for TCAD-based technology optimization. As an implementation example a contact resistance prediciton depending on contact opening and recess depth for a 10-nm class logic device is demonstrated.

NANO-TRIBOLOGY OF A POLYTETRAFLUOROETHYLENE TRANSFER FILMS USING MOLECULAR DYNAMICS SIMULATION AND MICROTRIBOMETRY

Polytetrafluoroethylene (PTFE) is a well known solid lubricant and polymer nanocomposites based on PTFE are considered to be promising materials for tribological applications in space. Like other polymer materials, many properties of PTFE depend on morphology. In this study, molecular dynamics (MD) simulations are performed to examine the effect of chain configuration on the frictional behavior of PTFE at the molecular level and compared to microtribological studies on aligned transfer films of PTFE.