Stability and wrinkling of defective graphene sheets under shear deformation

Te-Hua Fang,Win-Jin Chang,Kai-Peng Lin,Siu-Tsen Shen 한국물리학회 2014 Current Applied Physics Vol.14 No.4

The molecular dynamic simulation is performed to study the wrinkling behavior of a graphene sheet with a hole subjected to a shear loading at different temperatures. Wrinkling is inevitable under pure shear loading. Four different hole diameters of 0, 0.8, 1.6, and 3.2 nm are chosen in this simulation. The results show that the number of ridges increases with an increase of the width of the graphene sheet. The shear stress induced in the defective graphene sheet increases with increasing temperature. In addition, the shear modulus of the defective graphene sheet also increases with an increase of temperature.

Indentation deformation of mesoporous anodic aluminum oxide

Te-Hua Fang,Tong Hong Wang,Shao-Hui Kang,Cheng-Hsin Chuang 한국물리학회 2009 Current Applied Physics Vol.9 No.4

Mechanical properties of anodic aluminum oxides (AAO) were achieved by means of a scanning electron microscope (SEM), an atomic force microscope (AFM), and indentation measurements. A two-step anodized mesoporous anodic aluminum oxide was successfully fabricated vertically and hollowly. Both microindentation and nanoindentation were carried out. Localized pop-in can be found during nanoindentation due to the collapse of the beneath cylindrical structures. Over a certain load, microindentation may induce radial cracks from the indented edge to outward of the AAO. The underside of the indented AAO sample was milled to figure out the structural changes. Mechanical properties of anodic aluminum oxides (AAO) were achieved by means of a scanning electron microscope (SEM), an atomic force microscope (AFM), and indentation measurements. A two-step anodized mesoporous anodic aluminum oxide was successfully fabricated vertically and hollowly. Both microindentation and nanoindentation were carried out. Localized pop-in can be found during nanoindentation due to the collapse of the beneath cylindrical structures. Over a certain load, microindentation may induce radial cracks from the indented edge to outward of the AAO. The underside of the indented AAO sample was milled to figure out the structural changes.

Effect of nitrogen doping on nanomechanical and surface properties of silicon film

Te-Hua Fang,Win-Jin Chang,Shao-Hui Kang,Jia-Hung Liou 한국물리학회 2009 Current Applied Physics Vol.9 No.6

The effect of nitrogen ion implantation on the nanomechanical properties of single crystal Si was evaluated by means of a conventional Vickers indentation and nanoindentation tests. The images of Si surfaces before and after nitrogen implantation were observed and their average surface roughnesses were measured by an atomic force microscope (AFM), while the changes in the morphology and microstructure of the single crystal Si by N implantation were examined by field emission scanning electron microscope (SEM) and X-ray diffractometer (XRD). In addition, the hydrophilic/hydrophobic surface property of the N-doping Si film was determined from the measurement of water contact angle by the sessile drop technique. Furthermore, the effects of the doping energy on the surface contact angle and the surface roughness and the Vickers hardness of the film are also investigated. The effect of nitrogen ion implantation on the nanomechanical properties of single crystal Si was evaluated by means of a conventional Vickers indentation and nanoindentation tests. The images of Si surfaces before and after nitrogen implantation were observed and their average surface roughnesses were measured by an atomic force microscope (AFM), while the changes in the morphology and microstructure of the single crystal Si by N implantation were examined by field emission scanning electron microscope (SEM) and X-ray diffractometer (XRD). In addition, the hydrophilic/hydrophobic surface property of the N-doping Si film was determined from the measurement of water contact angle by the sessile drop technique. Furthermore, the effects of the doping energy on the surface contact angle and the surface roughness and the Vickers hardness of the film are also investigated.

Optical and physical characteristics of In-doped ZnO nanorods

Te-Hua Fang,Shao-Hui Kang 한국물리학회 2010 Current Applied Physics Vol.10 No.4

In this paper the effect of indium dopants on structure, optical, electrical and mechanical properties of ZnO nanorods are studied. The average surface potentials and the surface currents of ZnO:In nanorods were 0.25–0.84 mV and 2.2–200 MΩ-cm, respectively. The turn-on threshold field for the vertical ZnO nanorods was around 2–16 V ㎛-1. Emission current densities of 3.3–911.4 mA cm-2 were obtained for an electrical field of 60–160 V ㎛-1. The photoluminescence (PL) spectrum measured at 15–300 K showed that the intensity of the peak at 2.06 eV increased with decreasing temperature, while the peak at 2.06 eV further red shifted and the peak at 3.39 eV blue shifted.

MOLECULAR DYNAMICS ANALYSIS FOR FRACTURE BEHAVIOR OF GRAPHENE SHEETS WITH V-SHAPED NOTCHES UNDER TENSION

Te-Hua Fang,Win-Jin Chang,Kai-Peng Lin,CHENG-I WENG 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2014 NANO Vol.9 No.8

Molecular dynamics (MD) simulations are performed to study the fracture behavior of armchair and zigzag graphene sheets with V-shaped notches subjected to tensile loading. The effects of temperature and notches depth on the fracture characteristics of the graphene sheets are examined. The results show that the cracks propagate from the notch tip along the direction perpendicular to the loading axis for armchair sheets. This is different from the zigzag graphene propagating along the direction of 45˚ from the loading axis. In addition, the fracture energy of zigzag graphene sheets is larger than armchair one at the same temperature condition.

Molecular dynamics study of the shear strength and fracture behavior of nanoporous graphene membranes

Te-Hua Fang,Zhe-Wei Lee,Win-Jin Chang 한국물리학회 2017 Current Applied Physics Vol.17 No.10

We perform molecular dynamics (MD) simulations to study the structural response and fracture characteristics of nanoporous graphene (NPG) membranes subjected to shear loading. The effects of porosity, temperature, and shear velocity on the mechanical responses of NPG membranes are examined. The results show that the wrinkling of the membrane becomes more obvious with increasing strain. Fractures occur around holes on the long diagonal of the NPG parallelogram, and fracture stress in the NPG membrane decreases with increasing porosity. In addition, the effect of shear velocity on the shear modulus decreases with increasing porosity. The fracture strain of NPG membranes with different porosities obviously decreases with increasing temperature. The results enhance our understanding of the shear mechanical properties of NPG membranes and are helpful for the design and application of highperformance NPG membranes.

Frictional Characteristics of Graphene Layers Using Molecular Dynamics Simulation

Te-Hua Fang,Win-Jin Chang,Fu-Yung Tung 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.9

Molecular dynamics simulations of an atomic force microscope (AFM) probe scanning the surface of a five-layer graphene were conducted. The AFM-like scanning probe was modeled by a capped single-wall carbon nanotube. Note that interference with the graphene surface induced frictional behavior; moreover, the effects on the friction system of scanning velocity, probe direction and temperature were investigated. Wrinkling of the graphene surface became more apparent at higher temperatures, while stick-slip friction was more apparent at a lower temperature and a slower scanning velocity. The friction coefficient of the system was approximately 0.001.

Size effect on nanomechanical properties of ZnO cones using in situ transmission electron microscopy

Shao-Hui Kang,Te-Hua Fang,Tao-Hsing Chen,Ching-Hong Kuo 한국물리학회 2013 Current Applied Physics Vol.13 No.8

Nanoscale fracture and strain-induced structure variation of ZnO nanocones are determined using in situ transmission electron microscopy compression experiments. For the single-crystalline nanocones with diameters of 100-300 nm, the Young’s modulus is in the range of 7.7-48 GPa and the ultimate tensile strength is in the range of 2.4-4.3%. The Young’s modulus and tensile strength increase with decreasing diameter. Here, we report the nanogenerator of ZnO nanocones can be used mechanical energy to output 90 nW/mm2

The coupled effects of size, shape, and location of vacancy clusters on the structural deformation and mechanical strength of defective nanowires

Pei-Hsing Huang,Te-Hua Fang,Chuen-Shii Chou 한국물리학회 2011 Current Applied Physics Vol.11 No.3

We investigate the tensile stretching behaviors of copper (Cu) nanowires (NWs) containing various vacancy defects using the embedded-atom molecular dynamics modeling approach. The coupled effects in various shapes, sizes, and locations of vacancy clusters (VC) and wire cross-sectional area on the mechanical strength and structural deformation of NWs are presented. The formation energies of VC defects are also evaluated. As the location of cluster defects changed from the edges to the surface or inside of wires, the yield strength decreased. Moreover, as the cluster shape changed from octahedron to cuboctahedron, the yield strength also substantially decreased. The extraordinarily structural evolution of defective wires that precede wire fracture from 10/4 transient multi-shell (TMS) structures necking into 1/5-type pentagonal rings were also identified via the analyses of potential energy, local stress, and atomistic number density.

Nanotribological behavior of diamond surfaces using molecular dynamics with fractal theory and experiments

Jen-Fin Lin,Te-Hua Fang,Cheng-Da Wu,Ko-Han Houng 한국물리학회 2010 Current Applied Physics Vol.10 No.1

The frictional and indented behavior of a diamond asperity on a diamond plate was carried out using a molecular dynamics (MD) and experiments. The contact load, contact area, dynamic frictional force,and dynamic frictional coefficient increased as the contact interference increased at a constant loading velocity. The microcontact and frictional behavior can be evaluated between a rigid smooth hemisphere to a deformable rough flat plane by combined the deformed behavior of the asperity obtained from MD results with the fractal and statistic parameters. The comparison and the discrepancy of simulated results and nanoindentation and scratching experimental results will be discussed.