Ping-Feng Yang

Surface Morphological and Nanomechanical Properties of PLD-Derived ZnO Thin Films

This study reports the surface roughness and nanomechanical characteristics of ZnO thin films deposited on the various substrates, obtained by means of atomic force microscopy (AFM), nanoindentation and nanoscratch techniques. ZnO thin films are deposited on (a- and c-axis) sapphires and (0001) 6H-SiC substrates by using the pulsed-laser depositions (PLD) system. Continuous stiffness measurements (CSM) technique is used in the nanoindentation tests to determine the hardness and Young’s modulus of ZnO thin films. The importance of the ratio (H/Efilm) of elastic to plastic deformation during nanoindentation of ZnO thin films on their behaviors in contact-induced damage during fabrication of ZnO-based devices is considered. In addition, the friction coefficient of ZnO thin films is also presented here.

Molecular Dynamics Simulation of Nanoindentation-induced Mechanical Deformation and Phase Transformation in Monocrystalline Silicon

This work presents the molecular dynamics approach toward mechanical deformation and phase transformation mechanisms of monocrystalline Si(100) subjected to nanoindentation. We demonstrate phase distributions during loading and unloading stages of both spherical and Berkovich nanoindentations. By searching the presence of the fifth neighboring atom within a non-bonding length, Si-III and Si-XII have been successfully distinguished from Si-I. Crystallinity of this mixed-phase was further identified by radial distribution functions.

Mechanical Properties of Cu 6 Sn 5 , Cu 3 Sn, and Ni 3 Sn 4 Intermetallic Compounds Measured by Nanoindentation

We report in tins paper Youngs moduli and hardness of Cu₆Sn₅, Cu₃Sn, and Ni₃Sn₄ intermetallic compounds (IMCs) measured by nanoindentation. The samples were prepared by annealing Sn-Cu and Sn-Ni diffusion couples. Indentations performed along the directions lateral and perpendicular to the IMC layers show statistically indistinguishable Youngs moduli and hardness for each of the three IMCs. implying that these polycrystalline IMC aggregates are rather isotropic. Nanomechanical responses of the IMCs were shown to depend greatly on the strain rate during loading while independent of the strain rate during unloading. Multiple pop-in events were observed for Cu₆Sn₅ during loading at a strain rate lower than about 0.1 s^-1 to 0.5 s^-1. Topographies of the residual impressions were quantitatively measured and the pile-up features were apparent for the three IMCs.

Evaluating nanotribological behavior of annealing Si0.8Ge0.2/Si films

Abstract In this study, the SiGe epilayers were created on silicon substrate by using ultra-high vacuum chemical vapor deposition (UHV/CVD) and followed by annealing procedures. The frictional behaviors of SiGe epilayers were subjected to nanoscratch techniques under a ramping load. Damage caused by scratching was examined by atomic force microscopy (AFM); the results showed that the pile-up phenomena were significant on both sides of the scratch in the case of SiGe epilayers, suggesting that the dynamic deformation behavior was dominated by cracking as ploughing occurred during scratching. In addition, the SiGe epilayers films with different annealed conditions exhibited the decrease in coefficient of friction (COF), indicating the higher shear resistance exist in annealed SiGe epilayers, which probably affect the film uniformity and device yield under IC process integration.

Nanoindentation-induced Phase Transformation of Silicon

In this study, the deformation behavior of single-crystal Si (100) was examined using nanoindentation, followed by analysis using cross-sectional transmission electron microscopy (XTEM), scanning electron microscopy (SEM), and Raman microspectroscopy. XTEM samples were prepared by focused ion beam (FIB) milling to accurately position the cross-section through the indentations. The deformation via phase transformation was clearly observed with micro-Raman and XTEM, showing the presence of high-pressure crystalline phases Si-III and Si-XII following pressure release. The indentation fracture toughness of Si is also discussed

Identification of mechanical properties of Cu 6 Sn 5 , Cu 3 Sn, and Ni 3 Sn 4 intermetallic compounds using nanoindentation

We report in this paper Youngs moduli and hardness of Cu₆Sn₅, Cu₃Sn, and Ni₃Sn₄ intermetallic compounds (IMCs) measured by nanoindentation. The samples were prepared by annealing Sn-Cu and Sn-Ni diffusion couples. Indentations performed along the directions lateral and perpendicular to the IMC layers show statistically indistinguishable Youngs moduli and hardness for each of the three IMCs, implying that these polycrystalline IMC aggregates are rather isotropic. Nanomechanical responses of the IMCs were shown to depend greatly on the strain rate during loading while independent of the strain rate during unloading. Multiple pop-in events were observed for Cu₆Sn₅ during loading at a strain rate lower than about 0.1 s-¹ to 0.5 s^-1.

Growth of semi-polar (101̄3) AlN films on the silicon

Highly semi-polar (101̄3) oriented and fine structural AlN films were successfully prepared on silicon substrate by rf magnetron sputtering in this research. The dependence of the nitrogen concentrations and the material characteristics of the films (crystalline structure and micro morphology) were investigated. The crystalline structure of the films was determined by X-ray diffraction (XRD) and the surface microstructure of films was quantitatively investigated using an atomic force microscope (AFM). Different nitrogen concentrations (50%, 58%, 67% and 75%) were used to deposit the films. As decreasing the nitrogen concentrations, the XRD intensity of the semi-polar (101̄3) oriented increases, the crystallite size of the films increases and the roughness of top surface decreases. The experimental results demonstrate that the highly semi-polar (101̄3) oriented AlN films appeared at the lower nitrogen concentration.

First-Principles Calculations of Elastic Properties of Cu

Elastic properties of a solid are closely related to many fundamental solid-state properties. Theoretical calculations on elastic constants are well motivated by the advance in computational technologies, especially when mechanical testing on submicron components is extremely difficult. Elastic constants of a number of anisotropic lattice systems have been calculated based on the density functional theory, and good agreements between computational and experimental results have been found. In this study, we report elastic properties of the Cu-Sn crystalline phases, the epsiv-Cu3Sn and eta-Cu6Sn5, using first-principles calculations. The polycrystalline moduli obtained using the Voigt-Reuss scheme are 134.16 GPa for Cu3Sn and 125.98 GPa for Cu6Sn5 . Calculation results show that these Cu-Sn crystalline phases have the greatest stiffness along the c -direction. In particular, the results reveal the unique anisotropic feature along a - and b -directions within the Cu3Sn superstructure, which can hardly be resolved from experiments. Our results also suggest that the most compliant stiffness in the long-period direction is associated with the lattice modulation within the Cu3Sn superstructure.

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Nanotribological characteristics, including coefficient of friction, wear coefficient, and wear resistance, of Cu6Sn5, Cu3Sn, and Ni3Sn4 intermetallic compounds developed by annealing Sn-Cu or Sn-Ni diffusion couples were investigated in this work. The scratch test conditions combine a constant normal load of 10, 20, or 30 mN and a scratch rate of 0.1 1, or 10 mum/s. Experimental results indicate that as the normal load increases, the pile-up heightens and the scratch deepens, leading to greater coefficient of friction and wear coefficient while smaller wear resistance. Moreover, the scratch rate does not have a significant effect on the nanotribological characteristics except for Cu6Sn5 and Cu3Sn under a normal load of 10 mN. Though hardness of Cu6Sn5, Cu3Sn, and Ni3Sn4 is similar, Ni3Sn4 appears to be more prone to wear damage.

Sn and Cu

We investigated in this study structural and nanomechanical properties of zinc oxide (ZnO) thin films deposited onto langasite substrates at 200degC through r.f. magnetron sputtering with an r.f. power at 200 W in an 02/Ar gas mixture for different deposition time at 1, 2, and 3 h. Surface morphologies and crystalline structural characteristics were examined using x-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The deposited film featured a polycrystalline nature, with (100), (002), and (101) peaks of hexagonal ZnO at 31.75deg, 34.35deg, and 36.31deg. As the deposition time increased, the ZnO film became predominantly oriented along the c-axis (002) and the surface roughness decreased. Through Berkovich nanoindentation following a continuous stiffness measurement (CSM) technique, the hardness and Youngs modulus of the ZnO thin films increased as the deposition time increased, with the best results being obtained for the deposition time of 3 h.