Papers by Author: C.H. Sow

Abstract: Micropipette aspiration is a widely used experiment technique for studying mechanical properties of living cells. Its data can be processed in many different ways. Among them, a mathematical model called hemispherical cap model has been developed to evaluate the elastic modulus of the cell membrane undergoing micropipette aspiration. It has been commonly used in cell studies due to its simplicity and convenience. However, this mechanical model has its own assumptions and limitations. In this article, the authors used finite element simulation to obtain the validity range of micropipette radius used in hemispherical cap model. The results provide reliable size instructions in the preparation and post-processing of micropipette experiments.

Abstract: The effects of oxygen (O2) reactive ion etching (RIE) on the field emission (FE) properties of aligned CuO nanowire films are investigated systematically. It is found that the FE performance of the films is largely enhanced after initial exposure to reactive oxygen ions but degrades after extended treatment. As comparison, Ar RIE is also used to treat CuO nanowires, which, however, results in the deterioration of FE properties. The enhanced FE after O2 RIE is attributed to the shaper morphology, cleaner surface and better conductivity. On the other hand, increased work function and non-crystallized surface structure cause the deterioration of FE of CuO nanowires after Ar RIE treatments.

Abstract: Flake-shaped hematite (α-Fe2O3) nanostructure has been successfully fabricated by using a hot-plate to directly heat Fe foil or Fe-coated substrates in air at 300oC. After heating, the surface of the samples was found to be populated with α-Fe2O3 nanoflakes. Such growth of α-Fe2O3 nanoflakes was very substrate-friendly. They can be formed on blank Si wafer, patterened Si, AFM tips, silica sphere, quartz, glass slide, Al foil and electrochemically etched W tip. The formation process and the final products were investigated by glancing angle x-ray diffraction (GAXRD), micro-Raman, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate the final products are single crystalline α-Fe2O3 nanoflakes vertically standing on the Fe3O4 film that acts as the precursor for growth of α-Fe2O3. The α-Fe2O3 nanoflakes formed by this method show very sharp tip with the tip radii as small as several nanometers and large surface to volume ratio. Such nanoflakes may be potentially useful as novel candidates for future electron field emission and gas senor devices. Furthermore, it is believed that this simple and substrates-friendly method is useful in extending the applications of α-Fe2O3 nanostructures.

Abstract: A simple technique to synthesis crystalline Tungsten Oxide nanowires is presented. Using a standard thermal hotplate, a pure 99.9% tungsten foil is annealed to 484 ± 5 oC under ambient condition to generate vapor deposition of the heated materials on a piece of 150μm thick glass cover slide pressing on the tungsten foil. Tungsten oxide nanowires are found to deposit on the cover slide facing the heated tungsten foil. These tungsten oxide nanowires were characterized with SEM, TEM, EDX, micro-Raman and XRD. The crystalline nanowires were found to be straight and clean with a diameter of 10-300nm and a length of a few tens of micrometers.