Fig. 1: Configurations of devices, transmission and photocurrent measurements, and optical simulation.
a Schematic representation of the measured devices (not to scale) consisting of two main configurations depending on the experiment. The 1st configuration (left panel) corresponds to that used exclusively for transmission measurements in Fourier Transform Infrared spectroscopy (FTIR), with the top metallic nanorods and the 2D stack below. A mercury-cadmium-telluride (MCT) detector is required to perform mid-infrared (mid-IR) spectroscopy. Devices 1 and 4 have this configuration. The 2nd configuration (right panel) consists of two grating bottom gates with a top 2D stack. Devices 2, 3, and 5 comprise this 2nd configuration. Devices 2 and 3 are measured using electrical spectroscopy, whereas device 5 is measured using FTIR. b The signal-to-noise ratio (SNR) of the five devices was measured using the corresponding technique, either by FTIR or photocurrent measurements (electrical spectroscopy). The noise level dashed line corresponds to an SNR of 1. The inset shows a Scanning electron microscopy (SEM) image of the metallic nanorod array with a central gap for configuration 2, corresponding to devices 2, 3, and 5. c Extinction (1-T/TCNP) spectrum of device 1 measured using FTIR, where T and TCNP are the transmittances of the device at a certain gate voltage and at charge neutrality point (CNP), respectively. The curves correspond to several Fermi levels, as indicated in the legend. The inset shows the optical image of the device 1. The white scale bar corresponds to 30 μm. The three columns above the 2D stack are arrays of 100 nm wide metal nanorods with a 50 nm gap between them. A and B arrows indicate the polaritonic resonances described in the main text. d Finite-difference time-domain (FDTD) simulated extinction spectra of device 1 for several Fermi levels. e Optical image and device circuitry of configuration 2, which corresponds to device 3 used for photocurrent measurements. f Scanning photocurrent map (in absolute value) of device 3 at the incident wavelength (λ) of 6.6 μm. The gates are set to GG1 at 0.4 V and GG2 at − 0.25 V, thus creating a pn-junction.
