Doping-Induced Conductivity Transitions in Molecular Layers of Polyaniline: Optical Studies of Electronic State Changes

Abstract

The doping-induced conductivity transitions in molecular layers of polyaniline have been studied by monitoring the correlated optical and spectroscopic changes using spectroscopic and single wavelength extinction ellipsometry, also in total internal reflection mode (TIRE), together with reflection spectrometry. The measurements were performed on deposited multilayers as well as on a Langmuir monolayer at the air-water interface, as a function of acidic doping. We found that the characteristic spectroscopic features of conducting and insulating polyaniline persisted down to the single layer, both in the solid state and at the air-water interface. We also investigated in real time the modulation of conductivity induced by the intercalation of Li ions in the polyaniline film, by a combination of time-resolved ellipsometry and reflectivity spectra measurements. In this case, the enhanced sensitivity provided by the TIRE geometry, combined with the relatively fast time scale accessible by the single wavelength ellipsometry, allowed us to follow in detail in real time the doping/dedoping process.

Switching plasmon coupling through the formation of dimers from polyaniline-coated gold nanospheres

“…S4a †). 40,41 Different proton-doping levels between the previous work 38 and this work of ours can cause changes in the dielectric function. 39 Through electrodynamic simulations, we found that the peak shift caused by the reversible proton doping of PANI is increased with increasing dent depths (Fig.…”

Plasmonic/Nonlinear Optical Material Core/Shell Nanorods as Nanoscale Plasmon Modulators and Optical Voltage Sensors

“…PA NI was treated as adielectric material with its dielectric function obtained from ar ecent report. [38] By adapting the varying dielectric constant into the COMSOL simulation package, our simulation shows that achange of the refractive index by 0.05 in NLO shell can induce aredshift as large as 20 nm in the scattering spectra for as ingle Au/PANI core/shell NR with the aspect ratio of 1.6 (Figure 5a). Ther edshift is also dependent on the thickness of the PA NI shell (Figure 5b).…”

(Gold Nanorod Core)/(Polyaniline Shell) Plasmonic Switches with Large Plasmon Shifts and Modulation Depths

“…The amplitude modulation depth is often calculated as the ratio or the dB value of the amplitude between the modulation and carrier waves. The dielectric functions measured in recent works [ 40 ] for the proton-doped and undoped states of PANI were employed for the simulations. [ 26,48 ] In our study, dB was employed.…”

“…The solution was sucked away with a piece of fi lter paper after a certain period of time. [ 40 ] During the proton-doping (switching-off) process, PANI chains become positively charged, which results in slight chain expansion owing to electrostatic repulsion. Figure 3 a shows the spectral evolution of one representative (Au nanorod core)/(PANI shell) nanostructure from the 39-nm-shelled sample when the nanostructure was switched on.…”

“…[ 39 ] The conversion of PANI between states with distinct conductivities gives rise to a remarkable change in its dielectric function, [ 40 ] which forms the basis for manipulating the plasmonic properties of metal nanostructures. [ 39 ] The conversion of PANI between states with distinct conductivities gives rise to a remarkable change in its dielectric function, [ 40 ] which forms the basis for manipulating the plasmonic properties of metal nanostructures.…”