Browsing by Author "Jian, SR"

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Analysis of physical properties of III-nitride thin films by nanoindentation
(2003-06-01)
Jian, SR
;
Fang, TH
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The thin films of undoped GaN, GaN:Si, and Al0.12Ga0.88N on sapphire (0001) substrate using nanoindentation are investigated. The Young's modulus, hardness, and plastic energy of the films were calculated from the loading-unloading curve. The true hardness, maximum shear stress, and degree of elastic recovery are then deduced from the preceding calculated data. In addition, the loading-unloading curve clearly shows the pop-in phenomena, which can be attributed to the dislocation nucleation. To better understand the factors affecting the quality of films produced, the stress-strain relationship, which is able to reflect the quality of the fabricated films, is also analyzed using nanoindentation.
Effects of temperature on surface clusters by molecular dynamics simulation
(2003-07-01)
Jian, SR
;
Fang, TH
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
This article discusses the physical mechanisms for the evaporation phenomena of argon clusters on surfaces under various temperatures with the aid of molecular dynamics analysis by means of the Stoddard-Ford potential. Our simulated results indicate that the evaporation rate of the argon clusters increased drastically when the temperature was increased but the contact angle decreased. Furthermore, the thermal stability of the argon clusters is also discussed here. The evaporation mechanisms of argon clusters are clearly shown with the aid of molecular dynamics. (C) 2003 Elsevier Science B.V. All rights reserved.
Mechanisms of p-GaAs(100) surface by atomic force microscope nano-oxidation
(2005-07-21)
Jian, SR
;
Fang, TH
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
Nanopattering using atomic force microscope (AFM) has become an important area of research, for both fundamental research and future nanodevice applications. Local oxidation of p-GaAs(l 00) surface by using a negatively biased conductive AFM tip is a universal method for this purpose. The dependences of the height, aspect ratio and volume on applied anodization times and voltages during which the anodization voltage is applied were studied. We explore the kinetics and mechanisms of the anodization process and how factors such as the electric field strength and the relative humidity influence its growth rate and the contribution of ionic diffusion. The results revealed that the protruding oxide dot's height, aspect ratio and volume increase during longer anodization time and at larger anodization voltage as well as in higher relative humidity conditions. The high initial growth rate (similar to 300 nm s(-1) for 10 V) decreases quickly with decreasing electric field strength and the oxide practically ceases to grow at an order of (2-3) x 107 V cm(-1). Auger electron spectroscopy measurements confirm that the modified structures take the form of anodized p-GaAs(I 00). Also, the contribution of ionic diffusion increases by about 80% at a higher relative humidity. In addition, the nanohardness of the oxide structures was measured with the aid of an AFM-based nanoindentation technique.
Molecular dynamics analysis of effects of velocity and loading on the nanoindentation
(2002-11-15)
Fang, TH
;
Jian, SR
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
Three-dimensional molecular dynamics (MD) simulation is used to investigate the atomistic mechanism of nanoindentation process under various indentation loads and velocities that occur when a diamond tip interacts with the copper thin film. In this study, the model utilizes the Morse potential function to simulate interatomic forces between the specimen and tip. The results show that both Young's modulus and hardness increase up to a critical value and decrease there after for the indentation velocities, but decrease as the indentation loads increase. In additional, the contact stress-strain relationship is shown to be important.
Molecular dynamics for elastic and plastic deformation of a single-walled carbon nanotube under nanoindentation
(2004-06-01)
Fang, TH
;
Jian, SR
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
Mechanical characteristics of a suspended (10, 10) single-walled carbon nanotube (SWCNT) during atomic force microscopy (AFM) nanoindentation are investigated at different temperatures by molecular dynamics simulations. The results indicate that the Young modulus of the (10, 10) SWCNT under temperatures of 300-600K is 1.2-1.3 TPa. As the temperature increases, the Young modulus of the SWCNT increases, but the axial strain of the SWCNT decreases. The strain-induced spontaneous formation of the Stone-Wales defects and the rippled behaviour under inhomogeneous stress are studied. The rippled behaviour of the SWCNT is enhanced with the increasing axial strain. The adhesive phenomenon between the probe and the nanotube and the elastic recovery of the nanotube during the retraction are also investigated.
Nanomechanical characterizations of InGaN thin films
(2006-02-15)
Jian, SR
;
Fang, TH
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
InxGa1-x thin films with In concentration ranging from 25 to 34 at.% were deposited on sapphire substrate by metal-organic chemical vapor deposition (MOCVD). Crystalline structure and surface morphology of the deposited films were studied by using X-ray diffraction (XRD) and atomic force microscopy (AFM). Hardness, Young's modulus and creep resistance were measured using a nanoindenter. Among the deposited films, In0.25Ga0.75N film exhibits a larger grain size and a higher surface roughness. Results indicate that hardness decreases slightly with increasing In concentration in the InxGa1-xN films ranged from 16.6 +/- 1.1 to 16.1 +/- 0.7 GPa and, Young's modulus for the In0.25Ga0.75N, In0.3Ga0.7N and In0.34Ga0.66N films are 375.8 +/- 23.1, 322.4 +/- 13.5 and 373.9 +/- 28.6 GPa, respectively. In addition, the time-dependent nanoindentation creep experiments are presented in this article. (c) 2005 Elsevier B.V. All rights reserved.
Nanomechanical properties of lead zirconate titanate thin films by nanoindentation
(2003-08-06)
Fang, TH
;
Jian, SR
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
The nanomechanical properties of lead zirconate titanate (PZT) thin films were subjected to nanoindentation evaluation. A PZT thin film was created on a silicon substrate by radio frequency magnetron sputtering. The structure and surface morphology were analysed by x-ray diffraction and atomic force microscopy. Results show that PZT thin films were well ordered with a high (110) orientation and presented a pure perovskite-type structure and that the average roughness was reduced as the annealing temperature was increased. The Young's modulus and hardness increased as the rapid annealing temperature increased from 600 to 800degreesC, with the best results being obtained at 800degreesC.
Nanomechanical properties of TiC, TiN and TiCN thin films using scanning probe microscopy and nanoindentation
(2004-04-30)
Fang, TH
;
Jian, SR
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
TiC, TiN and TiCN thin films deposited on silicon (1 0 0) substrates using plasma enhanced chemical vapor deposition (PECVD) was investigated by scanning probe microscopy (SPM) and nanoindentation techniques. Results showed that the TiC film exhibits lower surface roughness and friction coefficient than the TiN and the TiCN films. Young's modulus and hardness both decreased as the indentation depth increased for all the films and the TiC film exhibited a higher hardness and Young's modulus. Additionally. the contact stress-strain relationships and fractal dimension were also analyzed. (C) 2004 Elsevier B.V. All rights reserved.
Nanotribology and fractal analysis of ZnO thin films using scanning probe microscopy
(2003-04-07)
Fang, TH
;
Jian, SR
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
Characteristics of crystalline structure, roughness and nanotribology of ZnO thin films deposited under various power conditions were achieved by means of x-ray diffraction and scanning probe microscopy (SPM). The ZnO thin films were deposited on the silicon (100) substrates by a radio frequency magnetron sputtering system. Fractal analysis was derived from SPM images, to calculate the fractal dimension complexity of the surface geometry, via a substituting structure function. The results show that the roughness decreases and nanowear rate increases as the sputtering power increases. In addition, the fractal dimensions of the ZnO thin films are also presented.