| AVS 60th International Symposium and Exhibition | |
| Nanometer-scale Science and Technology | Tuesday Sessions |
| Session NS-TuP |
| Session: | Nanometer-scale Science and Technology Poster Session |
| Presenter: | K. Sekiya, Kochi University of Technology, Japan |
| Authors: | K. Sekiya, Kochi University of Technology, Japan H. Koji, Kochi University of Technology, Japan H. Furuta, Kochi University of Technology, Japan A. Hatta, Kochi University of Technology, Japan |
| Correspondent: | Click to Email |
Carbon Nanotubes (CNTs) have attracted particular attention because of their unique properties in various application fields. Especially, CNTs are strong candidate for the anisotropic opt-material in the future optical devices. Some unique optical properties of CNTs have been reported, such as polarization dependent absorption of vertically aligned (VA) short length SWNTs[1], and black body behavior of VA long length SWNTs[2].
There are few reports for the optical properties of CNT forests with controlled structures. We focused on the early growth stage of the CNT forests whose heights are near the light wavelength. In this paper, we investigated optical properties of CNTs having various lengths with controlled structure parameters, such as vertical alignment.
Fe/Al or Fe/AlO multi-layered catalyst films were prepared on Si substrates by magnetron sputtering method. CNT forests were grown on the substrates with the catalyst films by thermal CVD method from C2H2 source gas at 730 °C. The CNT growth height was controlled precisely at the order of micro meter by adjusting synthesis period using electronic valves with electric circuits. Optical properties of CNTs were observed by a reflectance spectroscope (HITACHI U-3900).
Two different CNT forest samples were prepared by controlling CVD condition, one is highly oriented VA CNTs (Sample high-VA) with the average diameter of about 15 nm and the other is relatively low-oriented CNT forest (Sample low-VA) with the average diameter of about 13 nm. The average growth height of Sample high-VA and low-VA were controlled at about 1, 2, and 3 μm. Their growth densities of sample high-VA and low-VA were almost same at 1011/cm2, which were estimated from the cross-sectional SEM images. From the diffuse reflectance spectra, it was found that the CNT forests had low reflectivity with the diffusion reflectance below 5%. From specular reflectance, it was found that the specular reflectance was reduced with increase of forest height for both of sample high-VA and low-VA. It is noted that specular reflectance of sample high-VA was lower than sample low-VA at the same growth height. Absorption coefficients per 1μm calculated from the specular reflectance of sample low-VA were lower than that of sample high-VA.
In conclusion, those anisotropic optical properties of CNT forests were considered caused by their unique anisotropic structural parameters of vertical orientation and diameters.
This work was supported by Japan Society for the Science (JSPS) KAKENHI (No. 24560050, Grant-in-Aid for Scientific Research (C).
[1] Y. Murakami et al., Carbon. 43(13) (2005) 2664–2676.
[2] K. Mizuno et al., PNAS 106 (2009) 6044-6047.