Ping-Chi Tsai

Nanomeasurement and fractal analysis of PZT ferroelectric thin films by atomic force microscopy

In this study, the radio frequency (RF) magnetron sputtering process is used to generate a PZT ferroelectric thin film on a silicon substrate. The surface characteristics of this lead zirconate titanate film Pb(ZrxTi1-x)O3 is then investigated by means of an atomic force microscopy (AFM) method. The relationship between the temperature of the rapid thermal annealing (RTA) process and the characteristics of the resulting microstructure is also examined. Various aspects of the surface are investigated, including its roughness, its microstructure and its fractal characteristics. The results demonstrate that higher annealing temperatures reduce surface roughness and promote increased grain size due to the phase transformations which are induced within the microstructure. The fractal analysis reveals that the fractal dimension, Ds, increases for larger AFM scan images, and that the value of Ds falls within the range 2.10-2.50 depending upon the scanned length/area and is calculated by the structure function. Finally, it is determined that the phase transformations which occur at higher annealing temperatures result in higher fractal dimensions.

Experimental and numerical investigation into buckling instability of carbon nanotube probes under nanoindentation

This study employs a series of experimental nanoindentation tests and molecular dynamics simulations to investigate buckling instabilities of carbon nanotube probes. It is found that the buckling mechanism varies as a function of probe lengths and initial inclination angles. The experimental results show that longer nanotubes buckle in local-buckling mode, whereas shorter nanotubes undergo global buckling. This study also suggests that the inclination angle also plays a key role in determining buckling behaviors of nanotube probes.

Molecular dynamics studies of atomic-scale friction for roller-on-slab systems with different rolling–sliding conditions

This paper presents the use of molecular dynamics?(MD) simulations to investigate atomic-scale frictional behaviour between a roller and a slab under rolling?sliding conditions. The simulations consider both abrasive wear and non-abrasive wear during the rolling?sliding process. Different rolling?sliding conditions are simulated by implementing various separation distances between the roller and the slab and by changing the angular velocity of the roller. The frictional and normal forces acting at the interface between the roller and the slab, and the temperature of both operating components, are calculated during the rolling?sliding process. The relationships between the roller?slab friction phenomena and the rolling?sliding conditions are investigated. Finally, the rolling?sliding characteristics associated with a hard-on-soft rolling?sliding system are compared with those of a soft-on-soft rolling?sliding system.

Buckling characterizations of an individual multi-walled carbon nanotube: Insights from quantitative in situ transmission electron microscope nanoindentation and molecular dynamics

Nanomechanics and real-time buckling deformation of an individual multi-walled carbon nanotube (MWCNT) were investigated through in situ nanoindentation within a transmission electron microscope (TEM). These in situ observations reveal a significant shell-to-Euler phase transformation in the buckling response of the nanotube. Objective evidences that the MWCNT possesses time-dependent characteristic were first suggested by combining in situ TEM nanoindentation performed strain rate influences on an individual MWCNT with classical molecular dynamics simulations. Structural evolutions and buckling instabilities for thin-wall and thick-wall CNTs are theoretically studied, indicating the role of the tube thickness and interwall van der Waals interactions in governing buckling behavior.

Investigation into the mechanical contact behavior of single asperities using static atomistic simulations

This study employs an atomic-scale model to investigate mechanical contact behaviors of a single asperity, particularly those which take place beyond the elastic limit threshold. The results obtained from the current model are found to be in good agreement with the predictions yielded by continuum theory as the contact behavior of the asperity transits from fully elastic to elastoplastic contact interface. Furthermore, the result shows that adhesion within the single asperity has the negligible influence during the loading stage; however, the adhesion force leads to the sizable clusters of copper atoms on the rigid plate during the unloading stage.