Unraveling nanoscale conduction and work function in a poly(3,4-ethylenedioxypyrrole)/carbon nanotube composite by Kelvin probe force microscopy and conducting atomic force microscopy

摘要

Poly(3,4-ethylenedioxypyrrole) or PEDOP films doped with triflate ions, dodecyl sulfate ions and benzyl sulfonate functionalized multiwalled carbon nanotubes (MWCNTs) have been synthesized by oxidative electropolymerization. The dynamic variation of local work function at the nanoscale has been followed by Kelvin probe force microscopy (KPFM) and the measure of heterogeneity of dopant distribution was assessed from the distinctive disparities in the current maps, using conductive atomic force microscopy (C-AFM). The surface potential profiles revealed a smaller work function for PEDOP-(MWCNT)SO_3~- film, and the current images showed a remarkably larger current sustaining capacity for this film, in contrast to PEDOP-CF_3SO_3~- and PEDOP-C_(12)H_(25))OSO_3~- films which, is a consequence of widespread interconnects between localized conducting domains of the polymer coated with carbon nanotubes. Functionalized nanotubes offer the prospect of conducting both electrons and ions, and therefore an almost seamless charge transport across PEDOP and (MWCNT)SO_3~- species is realized. Such an unhindered movement of charge is not realized in PEDOP films doped by the insulating triflate or dodecyl sulfate ions. Averaged point contact nanoscale I-V profiles confirmed this claim, as the PEDOP-(MWCNT)SO_3~- film showed carrier conductivity greater by four orders of magnitude, as compared to the PEDOP-CF_3SO_3~- film. The enhanced electronic function and the reduced band gap of PEDOP-(MWCNT)SO_3~- film (0.19 eV) in comparison to 3.65 eV in PEDOP-CF_3SO_3~- impacts charge transport properties favorably. The experimentally observed increased electrochromic color contrast and improved charge storage capacity of the PEDOP-(MWCNT)SO_3~- film show how the macroscopic properties of a conducting polymer are controlled by local charge propagation behavior. The combination of two powerful tools namely, KPFM and C-AFM help in unraveling the complex structure-function relationships in conducting polymer films.