Current-Sensing Atomic Force Microscopic Study of Doping Level Distribution in Doped Poly[2,2’-Bithiophene]

Direct Imaging of Charge/Dopant Distribution in PANI/PSS Thin Films Using Advanced Frequency Modulation Electrostatic Force Microscopy

This paper presents a detailed study that maps the surface charges and dopant distribution on the electropolymerized thin film of polyaniline-poly(styrenesulfonate) (PANI/PSS). The focus is on two distinct states of PANI/PSS: the fully doped emeraldine salt (ES/PSS) and the dedoped emeraldine base (EB/PSS). This investigation utilizes advanced frequency modulation electrostatic force microscopy (FM-EFM) and atomic force microscopy (AFM). The polymer film comprises polymer grains, and FM-EFM data suggest a non-uniform distribution of dopants on the grain surface, with a higher doped periphery than the core. Quantifying the charge at the periphery and core of ES/PSS and EB/PSS grains provides unique insight into the charge distribution within the polymer film. The charge density is estimated to be 10 times higher in the periphery region (∼120 μC/cm2) than in the core region (∼11 μC/cm2) and 100 times higher than EB/PSS (∼0.8 μC/cm2). We have directly observed the morphological changes of PANI/PSS from the ES/PSS state to the EB/PSS state using the AFM topographic profile. These findings provide a better understanding of the behavior of the charge/dopant distribution on the surface of the polymer films and pave the way for further research and development of PANI/PSS-based electronic devices.