Surface Modification And Alignment Of Semiconducting Single-Walled Carbon Nanotubes

Semiconducting single-walled carbon nanotubes(s-SWCNTs)have shown promising applications in the field of micro-nano electronic devices due to their unique electrical,optical,mechanical and thermal properties.At present,due to its simple process,high-efficiency and high-selectivity,selective dispersion of conjugated polymers has become the main method for sorting high-purity s-SWCNTs.The implementation of high integrated circuit requires alignment of carbon tubes with high homogeneity in assembly density and inter-tube pitch.How to improve the entanglement and aggregation between electroneutral s-SWCNTs dispersed by the polymer and realize the preparation of SWCNT aligned films largely determines its potential applications in the electronic field.There are many research methods for the alignment of s-SWCNTs sorted by surfactants,however,the existing assembling methods were difficult to realize large-area alignment of electroneutral s-SWCNTs.This paper focuses on how to achieve large-area continuous alignment of high-purity s-SWCNTs separated by poly[9-(1-octylonoyl)-9H-carbazole-2,7-diyl](PCz),including the separation of high-purity s-SWCNTs by PCz in organic solvents,the modification of charge on the surface of electroneutral s-SWCNTs,the horizontal alignment of carbon tubes realized by"bi-phasic"dip-coating method,the fabrication of two-terminal resistor and thin-film transistors(TFTs)based on the aligned films of carbon nanotubes.The main results are as follows:1.Achieving modification of charges on the surface of PCz-sorted s-SWCNTs by charged polycyclic aromatic molecules.First screened out the charge modifier according to charged state and molecular configuration.It was found that positive-charged proflavine hemisulfate(PFS)was the best charge modifier,and chloroform is the best dispersing solvent.Then,combined with the changes of absorption spectroscopy and fluorescence spectroscopy,analyzed the interaction between PFS and s-SWCNTs.It was found that the fluorescent PFS could be adsorbed to the surface of s-SWCNTs to form positive-charged PFS-s-SWCNTs complex,and the obtained dispersion of PFS-s-SWCNTs after cleaning had good stability and monodispersity.Finally,according to the structural characteristics of s-SWCNTs,studied the adsorption distribution of PFS on the surface of carbon tubes.It was found that PFS tend to be adsorbed on the side-wall of carbon nanotubes,and the inter-tube electrostatic repulsion introduced by positive-charged PFS can offset intermolecular van der Waals force in the film-forming process of carbon nanotubes,effectively alleviating the entanglement and aggregation between carbon nanotubes.2.Developed a“bi-phasic”dip-coating method for realizing the horizontal alignment of positive-charged PFS-s-SWCNTs on the substrate surface,and PFS-s-SWCNTs in the aligned films aligned along the withdrawing direction of the substrate.Based on the evaluation of orientation structure by polarized Raman spectroscopy,it was found that the G band intensity of aligned PFS-s-SWCNTs array decreased monotonically with the increase of polarization angle,showing a better orientation degree with a deviation in the plus or minus 15.2°.Based on the experimental results,the mechanism of the formation of aligned films was analyzed.It was found that the introduced water seal was the key factor to realize the alignment of PFS-s-SWCNTs and the inter-tube electrostatic repulsion was the guarantee for uniform inter-tube pitch and better alignment of aligned PFS-s-SWCNTs arrays.3.Achieving the controlled preparation of wafer-scale continuous aligned PFS-s-SWCNTs arrays with controllable density and good alignment can be realized by adjusting the dip-coating process and the substrate size.The alignment coverage is greater than 95%and effective aligned area is up to wafer size(over 3 inches).Based on the optimized aligned films,prepared the two-terminal resistor and transistor devices.The resistance value of resistor in the direction parallel to the alignment was 1.74±0.02 M?,and perpendicular to the alignment was as high as 10~7 M?,showing a high degree of alignment and anisotropy.The transfer characteristics along the alignment direction in TFTs demonstrated the excellent semiconducting nature of the aligned s-SWCNTs,with the on-off ratios of 10~4-10~5.