Kok Chung Chin

Patterning and fusion of CuO nanorods with a focused laser beam

We report a simple technique that facilitates the micropatterning of an aligned array of CuO nanorods on a substrate as well as the fusion of the nanorods into fused junctions. The technique utilizes a focused laser beam from a He–Ne laser with moderate power to melt away the pointed end of as-grown CuO nanorods resulting in the formation of microballs at the tips of the truncated nanorods. The size of the microballs and the length of the truncated CuO nanorods were found to be dependent on the laser power used during the process. The nature of the microballs formed was investigated by high-resolution transmission electron microscopy and Raman spectroscopy. Such a focused beam provides an effective means to modify the morphology of the as-grown nanorod array and to pattern the aligned CuO nanorod array into interesting and potentially useful configurations. In addition, the focused laser beam was utilized to fuse and join nanorods, which could potentially be useful in the fabrication of nanorod circuits and network repair.

Selective area growth of aligned carbon nanotubes by ion beam surface modification

Abstract O2+ ion beams are used to modify the surface of 50 nm thick Fe catalyst films deposited on Si(100) substrates to demonstrate selective area growth of aligned multiwall carbon nanotubes (MWNT). Aligned MWNTs were grown on the modified Fe/Si substrate using the hot filament plasma enhanced chemical vapor deposition (HF-PECVD) method. A higher growth rate and density of MWNTs was observed on the ion-modified areas, facilitating selective area growth of aligned MWNTs at temperatures as low as 560 °C. Deposition of graphitic sheets at the initial growth process on the unmodified areas inhibits the deposition of MWNTs.

OPTICAL LIMITING STUDIES OF NEW CARBON NANOCOMPOSITES AND AMORPHOUS SixNy OR AMORPHOUS SiC COATED MULTI-WALLED CARBON NANOTUBES

By using fluence-dependent transmission measurement with nanosecond laser pulses, we have studied optical limiting (OL) properties of new carbon nanocomposites as well as amorphous SixNy or amorphous SiC coated carbon nanotubes suspended in distilled water. The observed nonlinearity at 532 nm contributed to OL performance of the carbon nanocomposites or carbon nanoballs (CNBs) is suggested to have its origin in the optically induced heating or scattering effects. It is found that when the linear transmittance of the CNBs is less than or equal to 70%, the intensity-dependent transmission of the CNBs is comparable to that of C60. While at 80% linear transmittance, CNBs possess better OL behavior than that of C60. These findings strongly support a potential application of CNBs for all laser protection devices. We have also observed OL effects in the amorphous silicon nitride (a-SixNy) and amorphous silicon carbide (a-SiC) coated multi-walled carbon nanotubes (MWNTs) at wavelengths of 532 and 1064 nm, and found that their OL performances are slightly poorer than that of their parent MWNTs. The possible sources of thickness-dependent OL effects of a-SixNy and a-SiC coated MWNTs are discussed.