Semiconducting-enriched single wall carbon nanotube networks applied to field effect transistors N. Izard, S. Kazaoui ∗ , K. Hata, T. Okazaki, T. Saito, S. Iijima, and N. Minami National Institute of Advanced Industrial Science and Technology (AIST) 1-1-1 Higashi, Tsukuba, Ibaraki, 305-8565 Japan Substantial progress are reported on field effect transistors (FET) consisting of semiconducting single wall carbon nanotubes (s-SWNTs) without detectable traces of metallic nanotubes and im- purities. This outstanding result was made possible in particular by ultracentrifugation (250,000g) of solutions composed of SWNT powders with polyfluorene as extracting agent in toluene. Such s-SWNTs processable solutions were applied to realize FET, embodying randomly or preferentially oriented nanotube networks prepared by spin coating or dielectrophoresis. Devices exhibit a stable p-type semiconductor behavior in air with very promising characteristics: the on-off current ratio is 10 $^{5}$, the on-current level is around 10 µ A and the estimated hole mobility is larger than 2 cm $^{2}$/vs. The present results are demonstrated by optical absorption, Raman and electrical measurements. PACS numbers: Novel semiconductors materials for field effect tran- sistor FET and thin-film transistors TFT are highly demanded. 1 In particular, semiconducting single wall carbon nanotubes (s-SWNTs) are very promising, because individual s-SWNTs are known to exhibit high on-off current ratio, high electron/hole mobil- ity, to carry high current density and to operate at high frequencies. 2–5 Several groups have demonstrated excellent transfer characteristics using individual s- SWNTs, 2–5 but generally poor ones using ensemble (net- work and thin film) of SWNTs due to traces of metal- lic nanotubes (m-SWNTs) and impurities (catalytic and amorphous particles). 6–8 Therefore, very efficient meth- ods to selectively synthesis s-SWNTs or to selectively extract s-SWNTs from as-grown nanotubes are still re- quired. In recent years, several approaches to extract s- SWNTs from nanotube powders were explored using for instance chemical functionalization, 9–11 DNA and polymers wrapping, 12,13 and density gradient ultra- centrifugation techniques. 6 The latter efficiently sepa- rates s-SWNTs and m-SWNTs, but traces of surfactant and density gradient materials limit the performances of the FET. Very recently, two groups have reported on the selective extraction of near-armchair s-SWNTs from nanotube powders using polyfluorene as extracting agent. 14,15 According to Nish et al. , 14 the sample shows no detectable traces of m-SWNTs based only on optical spectroscopy. However, neither the electrical properties nor the fabrication of FET devices were addressed. In this letter, we report on the electronic properties of FET consisting of semiconducting-enriched single wall carbon nanotubes, without detectable traces of metallic nanotubes and impurities , with in our detection limits. This unprecedented achievement is made possible by ul- tracentrifugation (250,000g), sonication and filtration of solutions composed of SWNT powders with polyfluorene as extracting agent in toluene. Evidences are gathered by optical absorption, Raman and electrical measure- ments (see Fig.1). We shall demonstrate that such s- SWNTs realize high-performances FET devices compare to networks/thin films of SWNTs and solution process- able polymers/organic materials. 1,6,16 S-SWNTs solutions were prepared as follow. First, SWNTs powders (as-prepared HiPco, Carbon Nanotech- nologies Inc.), PFO (Poly-9,9-di-n-octyl-fluorenyl-2,7- diyl, Sigma-Aldrich) and toluene were mixed in the fol- lowing ratio SWNT (5 mg): PFO (5 mg): toluene (30 ml) FIG. 1: (Color online): (a) shows the optical absorption spec- tra and (b) the Raman spectra at 514.5 nm of L, M and S samples . (c) displays the transfer characteristic, I D vs V G for V DS =-14V of FET devices made of sample M and S. arXiv:1001.0892v1 [cond-mat.mtrl-sci] 6 Jan 2010 600 800 1000 1200 1400 1600 Wavelength (nm) 0.00 0.05 0.10 0.15 0.20 Absorbance M$_{11}$ S$_{22}$ S$_{11}$ L M S 514.5 nm (a) 150 200 250 300 Wavenumber (cm GLYPH<a0> $^{1}$) 0.0 0.2 0.4 0.6 0.8 1.0 Normalized Intensity s-SWNT m-SWNT (b) L M S -30 -20 -10 0 10 20 30 V$_{G}$ (V) 10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 I D  (A) M S (c)