Sheng-Rui Jian

Cross-sectional transmission electron microscopy observations on the Berkovich indentation-induced deformation microstructures in GaN thin films

Nanoindentation-induced mechanical deformation in GaN thin films prepared by metal-organic chemical-vapour deposition was investigated using the Berkovich diamond tip in combination with the cross-sectional transmission electron microscopy (XTEM). By using focused ion beam milling to accurately position the cross-section of the indented region, the XTEM results demonstrate that the major plastic deformation was taking place through the propagation of dislocations. The present observations are in support of attributing the pop-ins that appeared in the load–displacement curves to the massive dislocation activities occurring underneath the indenter during the loading cycle. The absence of indentation-induced new phases might have been due to the stress relaxation via the substrate and is also consistent with the fact that no discontinuity was found upon unloading.

Nanomechanical properties of lead zirconate titanate thin films by nanoindentation

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 Youngs modulus and hardness increased as the rapid annealing temperature increased from 600 to 800 °C, with the best results being obtained at 800 °C.

The nanoindentation responses of nickel surfaces with different crystal orientations

Molecular dynamics (MD) simulations are applied to elucidate the anisotropic characteristics in the material responses for crystallographic nickel substrates with (100), (110) and (111) surface orientations during nanoindentation, compensating for the experimental limitation of nanoindentation—particularly for pure nickel substrates of three crystallographic orientations. This study examines several factors under indentation: three-dimensional phases of plastic deformation which correspond to atomic stress distributions, pile-up patterns at maximum indentation depth, and extracted material properties at different crystallographic orientations. The present results reveal that the strain energy of the substrate exerted by the tip is stored by the formation of the homogeneous nucleation, and is dissipated by the dislocation sliding of the {111} plane. The steep variations of the indentation curve from the local peak to the local minimums are affected by the numbers of slip angle of {111} sliding plane. The pile-up patterns of the three nickel substrates prove that the crystalline nickel materials demonstrate the pile-up phenomenon from nanoindentation on the nano-scale. The three crystallographic nickel substrates exhibit differing amounts of pile-up dislocation spreading at different crystallographic orientations. Finally, the effects of surface orientation in material properties of FCC nickel material on the nano-scale are observable through the slip angle numbers of {111} sliding planes which influence hardness values, as well as the cohesive energy of different crystallographic surfaces that indicate Youngs modulus.

Observation of Growth of Human Fibroblasts on Silver Nanoparticles

Silver nanoparticles have drawn extensive attention as biomaterial components. Human fibroblasts were grown on various concentrations of silver nanoparticles during the period observation. Normal viability (0% silver particles) was increased from 6 to 72 hours, increasing the amount of human fibroblasts (1.5 × 104 to 7 × 106 cells/well) normally. Nevertheless, at higher concentrations of silver nanoparticles (50%) 1.11 × 105 cells/well remained after 72 hours. Results indicated that the increase in the concentration of silver nanoparticles reduced the number of fibroblasts and affected their fission. Silver nanoparticles were found under the membranes of fibroblast following dry treatment. The number of tissues declined because the silver nanoparticles interrupted the fission mechanism during their development in vivo.

Nanotribology and fractal analysis of ZnO thin films using scanning probe microscopy

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.

Mechanisms of p-GaAs(100) surface by atomic force microscope nano-oxidation

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(100) 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 (∼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)×10 7 Vc m −1 . Auger electron spectroscopy measurements confirm that the modified structures take the form of anodized p-GaAs(100). 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. (Some figures in this article are in colour only in the electronic version)

Yielding and plastic slip in ZnO

The mechanical properties of ZnO were examined using nanoindentation and microcompression. The modulus, hardness, onset of yielding, and shear strength of the as-grown wafer measured by nanoindentation are 140, 7.1, 12, and 3.6u2009GPa. The onset of shearing (3.6u2009GPa) corresponds to the theoretical shear strength. Young’s modulus and yield strength measured from micropillar samples were 123 and 3u2009GPa. The primary slip plane forms an acute angle of 62° with respect to the basal planes, indicting it is pyramidal. Thermal annealing does not affect the residual stresses but can reduce the defect concentration, thus improves the ZnO luminescent properties.

Molecular Dynamics Analysis of Effects of Velocity and Loading on the Nanoindentation.

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 Youngs 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.

Localized electrochemical oxidation of p-GaAs(100) using atomic force microscopy with a carbon nanotube probe

Th en anometre-scale oxidation characteristics of a p-GaAs(100) surface are investigated by atomic force microscope (AFM) electrochemical nanolithography with a multiwalled carbon nanotube (MWCNT) probe. The electrochemical parameters, such as anodizing voltages, scanning rate and modulated voltages, and how they affect the creation and growth of the oxide nanostructures are explored. The present results reveal that the initial growth rate (∼600 nm s −1 for 10 V) decreases rapidly as the electric field strength is decreased. The oxide practically ceases to grow as the electric field is reduced to the order of ∼1.2 × 10 7 Vc m −1 .A lso,the oxide growth rate depends not only on the electric field strength but also on the applied anodizing voltage. The present results show that the height of the oxide structures can be significantly improved at an applied anodizing voltage of 10 V by using a CNT probe. In addition, Auger electron spectroscopy (AES) measurements performed in the present work confirm that modified structures replace the form of anodizing p-GaAs(100). (Some figures in this article are in colour only in the electronic version)

Effects of temperature on surface clusters by molecular dynamics simulation

Abstract 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.