Sorting out semiconducting single-walled carbon nanotube arrays by preferential destruction of metallic tubes using xenon-lamp irradiation

We report herein a simple and reliable approach to prepare densely packed, well-aligned individual semiconducting single-walled carbon nanotube (s-SWNT) arrays using long-arc xenon-lamp (Xe-lamp) irradiation. The densely packed, well-aligned individual SWNT arrays (the mean density was ∼20 tubes/μm) were first grown on a-plane sapphire using ethanol containing 3 wt % water as the carbon source. It is found that water plays a key role in the improvement of the density and the alignment of the SWNT arrays. The densely packed aligned SWNT arrays were then irradiated by a long-arc Xe lamp. Atomic force microscopy manipulation, Raman spectroscopy, and electrical transport measurement revealed that the SWNTs with small diameters (d < 1 nm) and the metallic SWNTs (m-SWNTs) in the arrays can be preferentially destroyed, thus leaving s-SWNT arrays on the surface. In general, for the SWNTs with diameters in the region of 1.15-1.55 nm, the percentage of s-SWNTs increased from ca. 50% to 95% after 60 min of irradiation. In situ I - V measurement indicated that, with longer irradiation time, the on/off ratios of the field effect transistors fabricated by the as-grown SWNT arrays increased from below 10 to well above 2000. This change clearly indicated that the m-SWNTs were destroyed faster than the s-SWNTs.