Papers by Author: Ping Yang

Abstract: In this paper, gold (Au) surface mechanical behaviors in electro-thermo-mechanical coupled service are studied using atomic force microscopy. The experimental results indicate that some pile-ups of the metal, caused by indentation, are formed whether or not an external electric field is applied during indentation. Scanned topographical images reveal a bright area around the indentation hole, indicating the area where the material had been pushed out. It was determined that when a DC external field is applied to a sample, the hardness value of the tested sample presents an increase trend with the increment of electric current, but a decrease trend for the residue area and the elastic modulus.

Abstract: Thin DLC film is in need for higher magnetic storage density. Surface modification and materials removal of DLC films were carried out in order to estimate the reliability of the ultra thin DLC films. Atomic force microscope (AFM) was used to investigate the wear resistance, surface modification and mechanical reliability of the films. Wear test by contact AFM indicated that wear depth under the same load was varied at different thick films. The local modification is studied using conductive atomic force microscope (C-AFM). Especially, topography change is observed when DC bias voltage applied. Experimental results show that the DLC surface is not modified after direct current applied on the tip. While positive voltage is applied on the DLC film surface, the nanoscale pit on the surface is formed clearly. According to the interaction force between CoCr coating MESP tip and the DLC film surface, as well as the Sondheimer oscillation theory, the “scale wing effect” of the pit is explained. Electromechanical coupling on the DLC film indicates that the depth of pit increases with the augment of force applied on surface when normal force is less than a certain threshold pressure.

Abstract: Micro-flowing technique gained popular applications in microdevices of microelectromechanical systems (MEMS), and the performance of micro-devices is greatly determined by the properties of micro-flow. This paper studied the characteristics of different viscosity fluid flowing over microchannels with different diameters and lengths under low pressure driving, and the influence of scale effects on the flowing characteristics of low viscosity fluids was also examined. The experiments studied the flow rate–pressure characteristics of distilled water flowing over microchannels with diameter of 13 μm, 20 μm, and silicon oil flowing over microchannels with diameters of 50 μm, 100 μm. The results indicate that, when the diameter of micro-channel is more than 20 μm, the flowing characteristics of distilled water and silicon oil agrees well with conventional flow theory, and when the diameter of microchannels is 13μm, the flowing characteristics are related to the length of micro-channel. When the length is relatively shorter, the flowing characteristics are almost in agreement with the conventional flow theory. When the length reaches 100 mm, the flow rate is much higher than the values predicted by theoretical calculation when the length reaches 100 mm. It is obvious that scale effect arises when the length arrives to 100 mm and the velocity slippage results in the great increase of flow rate.