Fig. 1: Concept of doped PBTTT polymer nanoantennas.

a Doping mechanism of PBTTT films with the TAB-2TFSI dopant. b Absorption spectra of films made from 1.5 wt% PBTTT (thickness ≈ 60 nm) in the doped (blue) and undoped (red) states. c In-plane permittivity dispersion of PBTTT in its doped (blue curve, real part; red curve, imaginary part) and undoped (dashed blue curve, real part; dashed red curve, imaginary part) states. The spectral range between ≈ 2 and 7 μm is defined as a metallic regime where the real permittivity is below zero for the doped polymer. d Dimensions of doped and undoped PBTTT nanodisk arrays on glass substrates used to simulate the extinction and near field profiles in e and f. e Simulated extinction and f nearfield response for nanodisk arrays (diameter = 394 nm, thickness = 95 nm, period = 800 nm, mesh size = 2 × 2 × 2 nm³ around the nanodisks) at the resonance peak wavelength of ~2011 nm, based on doped (blue) and undoped (red) PBTTT nanodisks. In (f), top panels are top views while bottom panels are cross sections of the nanodisks along the direction of the incident polarization, which is along the x-axis. x–y in-plane direction is 2 nm above the nanodisk and x–z cross-section is through the center of the nanodisk. The color scale bars show the square of the electric field strength relative to the incident light (|E | ²/|E₀ | ²).