Fig. 3: Metal-insulator transition induced optical anisotropy of PEDOT and FDTD simulations.
From: Metal to insulator transition for conducting polymers in plasmonic nanogaps
a Schematic illustration of eNPoM structure, orientated along \({\boldsymbol{x}}{\boldsymbol{,}}{\boldsymbol{y}}{\boldsymbol{,}}{\boldsymbol{z}}\) axes. Right inset: metal-insulator transition in nanogap and simulated scattering spectra using Drude model for different field orientations, \({{\boldsymbol{E}}}_{{\boldsymbol{y}}{\boldsymbol{,}}{\boldsymbol{z}}}\). Below inset: birefringence of PEDOT crystallites, along local \({\boldsymbol{a}}{\boldsymbol{,}}{\boldsymbol{b}}{\boldsymbol{,}}{\boldsymbol{c}}\) axes. \({{\boldsymbol{\varepsilon }}}_{{\boldsymbol{a}}{\boldsymbol{,}}{\boldsymbol{b}}{\boldsymbol{,}}{\boldsymbol{c}}}\): complex permittivity of PEDOT along each axis in dielectric (PEDOT0, purple) and metallic (PEDOT2+, orange) states. (b,c) Possible PEDOT crystallite orientations close to gold interfaces for b \({\boldsymbol{d}}\)<5 nm and c >5 nm thick coatings. d, e FDTD simulations of optical scattering cross-section for redox states in thick and thin PEDOT eNPoMs with vertical (\({{\boldsymbol{E}}}_{{\boldsymbol{z}}}\)) field orientation (for model see text)
