First observation of selective alignment of semiconducting single-walled carbon nanotubes on quartz single crystal surfaces

Shimoyama, Iwao   ; Li, X.*; Shimada, Takashi*

Alignment of single-walled carbon nanotubes (SWNTs) is significantly important for many applications of SWNTs. Recently, it was reported that SWNTs grown by chemical vapor deposition (CVD) align along step arrays or one-dimensional atomic arrangements on some single crystal surfaces. This method is interesting to achieve large-scale alignment of SWNTs, however, the detail of the alignment mechanism has not been clarified, yet. In order to investigate the alignment mechanism, we utilized polarization dependent Raman spectroscopy for SWNTs grown on quartz single crystal surfaces by CVD. G-band of our sample showed high-frequency G-band and low-frequency G-band. Though both bands exhibited qualitatively same polarization dependence, the magnitude of polarization dependence of G-band was larger than that of G-band. Spectral change for different polarization configurations clarified that vibration modes were not main reason of our result. Comparing Stokes and anti-Stokes spectra, results obtained from samples with different growth conditions, and spectra measured by different resonant excitation conditions, we concluded that different magnitude of polarization dependence between G-band and G-band originated from different orientations between semiconducting SWNTs and metallic SWNTs. This result indicates selective alignment of semiconducting SWNTs on quartz single crystal surfaces.