Shao-Hui Kang

Surface and physical characteristics of ZnO:Al nanostructured films

Structural and surface characterizations of the ZnO:Al nanostructured films were achieved by means of x-ray diffraction, scanning electron microscope, atomic force microscope, and nanoindentation measurements. The films exhibited hydrophobic behavior with contact angles of about 133.2°–142.7°, and a decrease in the hardness and Young’s modulus with decreasing indentation depths. Buckling behavior took place during the indentation process, and the fracture strength of the films was also investigated. The results show that the phase transformation from zinc blende to wurtzite structure. Also, it should be correlated with belongs to chairtype Peierls distortion with up to 38° tilting (001) rock-salt structure along the (1¯21¯0) plane and followed tilting along the (101¯0) plane by about 32° for a fair match with (101¯0) Zn. A nanogenerator with ZnO nanorods was then fabricated to define its piezoelectric characteristics. The power density per unit substrate area is about 18.3 μW/mm2.

Effect of indium dopant on surface and mechanical characteristics of ZnO : In nanostructured films

Epitaxial ZnO:In nanorods films were grown on SiO2 substrates using a chemical solution method with a pre-coated ZnO sputtered seed layer. Structural and surface characterizations of the ZnO:In nanostructured films were achieved by means of x-ray diffraction, a scanning electron microscope, an atomic force microscope and contact angle measurements. The hardness and Young’s modulus of the nanostructured films were investigated by nanoindentation measurements. The results showed that when the indium dopant was increased, the hardness and Young’s modulus of the films also rose. The films exhibited hydrophobic behaviour with contact angles of about 128‐138 ◦ , and a decrease in the hardness and Young’s modulus with decreasing loads or indentation depths. Buckling behaviour took place during the indentation process, and the fracture strength of the films was also discussed. (Some figures in this article are in colour only in the electronic version)

Physical Behavior of Nanoporous Anodic Alumina Using Nanoindentation and Microhardness Tests

In this paper, the mechanical response and deformation behavior of anodic aluminum oxide (AAO) were investigated using experimental nanoindentation and Vickers hardness tests. The results showed the contact angle for the nanoporous AAO specimen was 105° and the specimen exhibited hydrophobic behavior. The hardness and the fracture strength of AAO were discussed and a three-dimensional finite element model (FEM) was also conducted to understand the nanoindentation-induced mechanism.

Elasticity and nanomechanical response of Aspergillus niger spores using atomic force microscopy

The elasticity and nanomechanical response of Aspergillus niger spores determined using atomic force microscopy (AFM) and nanoindentation are discussed. The force-displacement curve of the spore surfaces shows that the average surface roughness of spores was approximately 33 nm and that the adhesion force ranged from 9 to 28 nN. The Youngs modulus of the A. niger spores ranged from 0.1 to 21.4 GPa and the hardness ranged from 0.01 to 0.17 GPa. The critical buckling load of the spore membrane is 290 μN.

Nanoindentation characteristics of clamped freestanding Cu membranes

This research employed instrumented nanoindentation to address the issue of bending to stretching-induced deformation of clamped freestanding Cu membranes. The experimental results show that indentation-induced plastic deformation only comes into effect at the centre and the indented edge of the Cu membrane when the indenter is applied, while the other locations remain undamaged. A step-by-step evolution was presumed for the time histories of the bending to stretching-induced deformation and for the timing of the significant change in slope of the load-deflection curve. Deformation was deliberately introduced at the transition from the single-point bending indentation to the surface stretching indentation at the impact location touched with the indenter. Good elastic recovery was found at locations away from the indenter. A similar finding can be arrived at by means of finite element analysis.

Thermomechanical properties of polymer nanolithography using atomic force microscopy.

The temperature-dependent mechanical properties of polyethylene terephthalate (PET) polymers are investigated using force-distance curves, adhesion force, and atomic force microscope (AFM) nanolithography combined the heating techniques. The results show that the width of grooves on the polymers at 20-60 °C were in the range of 14-363 nm. The wear depth of the polymers increased with increasing heating temperature. A volume of 251.85-2422.66 μm(3) at a load of 30-50 nN with heating to 30-60 °C was removed, as compared to that of 26.60-70.30 μm(3) obtained at room temperature. The contact forces of PET started increasing at 9 nN, whereas the size of the holes was average at a pressure. The results may be of importance in explaining the heating relationship among adhesion force, volume removal rate, and pressure.

Creep Characteristics of Clamped Cu Membranes Subjected to Indentation

We present the creep characteristics of clamped Cu membranes subjected to instrumented indentation under different loads with an identical holding duration at their respective maximum loads. As-deposited Cu membranes were stored for 10 days at room temperature to release stress. During indentation, there were significant negative slopes with bouncing deflections at the holding stage because the stretched membranes relieved stress, indicating creep. Intact membranes observed under a microscope showed that such low loads are within the elastic indentation region. The critical load required to induce the presence of creep can further be classified using finite element analysis.

Mechanical Property Evaluation of ZnO Thin Films Using Nanoindentation and Scanning Probe Microscope

The characteristics of morphology, friction and nanotribological properties of ZnO thin films were achieved by means of x-ray diffraction, scanning probe microscopy (SPM), and nanoindentation. The ZnO thin films were deposited by a radio frequency magnetron sputtering system. Surface geometry and friction analysis were derived from atomic force microscopy/friction force microscopy (AFM/FFM). The hardness and Young’s modulus of the ZnO thin films were investigated by nanoindentation measurements with a Berkovich indenter. The films exhibited an increase in the hardness with decreasing load i.e. the indentation size effect (ISE) was found. In addition, the nanoscratched mechanical property of the films was discussed.

Molecular dynamics simulation of nanoscale mechanical behaviour of ZnO under nanoscratching and nanoindentation

Molecular dynamics is used to simulate the mechanical behaviour of zinc oxide under nanoscratching and nanoindentation. The effects of indenter speed and substrate temperature on the structure-phase formation, slip vector, radial distribution function, and residual stresses are investigated. Simulation results show that the dislocation loops nucleate and propagate, forming a body-centred tetragonal lattice structure along the slip direction due to high local stress. Furthermore, the dislocation loops nucleate and propagate due to the resolved shear stress along the 45° slip direction under nanoscratching. The average mean biaxial stress and the normal stress of the O layers are –9.35 and –4.36 GPa, respectively, and those of the Zn layers are –0.80 and –0.30 GPa, respectively. This may be attributed to the energetic O atoms, with which unstable atoms have high activation.

NANOMECHANICAL BEHAVIOR OF HUMAN MOLARS SOAKED IN SLIGHT ACID SOLUTIONS

This paper studied the mechanical and chemical properties of hydroxyl apatite (HA) crystal structure in the teeth when human molars were soaked in slight acid solution. First, we soaked the ground and polished molars respectively in the liquor of 30 wt.% H2CO3 and the liquor of 30 wt.% H2O2 for 10, 20, or 60 minutes. Next, we used a nanoindenter to measure the hardness and Youngs modulus. Finally, we used a scanning electron microscope (SEM) coupled with energy dispersive spectroscopy (EDS) to analyze the variation of Ca, P and Na in teeth, a high resolution transmitting electron microscope (HRTEM) to observe the arrangement of crystallization phase of HA, and X-ray diffraction (XRD) to analyze the crystallinity of the hexagonal phase of HA. The results showed that the demineralization phenomenon of the calcium–phosphorous compound in teeth made the teeth reduce sharply in hardness and Youngs modulus after they were soaked in the two slight acid solutions for 10 minutes, but the re-mineralization phenomenon made the hardness and Youngs modulus ascend gradually when the time lasted longer. With the same period of time, the teeth soaked in H2CO3 were lower in the hardness and Youngs modulus than that in H2O2.