Sorting Semiconducting Single‐Walled Carbon Nanotubes by Water‐Soluble Polyfluorene Assisted Electrophoresis and Its Application in Field‐effect Transistors

Abstract

We report a considerably promising method based on agarose gel electrophoresis (AGE) to separate singlewalled carbon nanotubes by adding a water-soluble polyfluorene (w-PFO) as surfactant into the agarose gel. In this effective method, the AGE/w-PFO gel network will trap more semiconducting single-walled carbon nanotubes (SWNTs) with the assistance of w-PFO, for the strong interaction between w-PFO and semiconducting species. The optical absorbance, photoluminescence emission and resonant Raman scattering characterization were used to verify the separation effect. The purity of separated semiconducting species is as high as (98±1)%. The demonstrated field effect transistors give the on/off ratio and mobility about 27000 and 10.2 cm 2 •V −1•s −1 , respectively.Keywords agarose gel electrophoresis, field effect transistors, semiconducting single-walled carbon nanotubes, water-soluble polyfluorene IntroductionSingle-walled carbon nanotubes (SWNTs) have attracted widespread attention in recent years due to the unique structure.[1] Their extraordinary mechanical, chemical and electronic properties make them potentially suitable for a wide range of applications such as the field effect transistors (FETs), chemical sensors, logic circuits and transparent electrodes and emitter of electrospray ionization mass spectrometry. [2][3][4][5][6] Particularly, the high charge-carrier mobility of semiconducting SWNTs has a promising prospect for FETs. [7] However, SWNTs are generally produced as a mixture of semiconducting SWNTs (s-SWNTs) and metallic SWNTs (m-SWNTs) which is a barrier for the application in electronic fields. Although some research has been done to directly synthesize chiral selective nanotubes, the purity and yield of s-SWNTs are not satisfied. [8,9] In order to gain pure and scalable s-SWNTs, separation of raw carbon nanotube materials is still an optimal choice until now.In the last decade, various techniques have been developed to separate semiconducting SWNTs, such as polymer wrapping, density gradient ultracentrifugation (DGU), sephacryl gel-based chromatography, agarose gel, two-phase separation, etc. [10][11][12][13][14][15][16][17][18][19][20][21] Each of these techniques is able to separate SWNTs into metallic and semiconducting species in different level of success. In spite of their promises, each method has its own limited capability to scale up or requires a complex process of removing the surfactants or polymers. For example, Tanaka et al. [22] showed that agarose gel electrophoresis (AGE) can be used to separate metallic from semiconducting nanotubes effectively using sodium dodecyl sulfate (SDS) as the dispersant. The article reported that under the effect of electrophoresis, SWNTs wrapped with SDS have different level of interaction with gel, in which m-SWNTs migrated toward the anode faster than s-SWNTs. SWNTs thereby can be separated into two parts, metallic fraction and semiconducting fraction. Mesgari et al. [23] have made an improvement of AGE method to increase the purity and yield of s-S...