Achieving Scalable Near‐Zero‐Index Materials

Abstract

Near-zero-index (NZI) materials are becoming increasingly important for photonic designs because they enable new ways to control light-matter interactions at the nanoscale. Many device prototypes that utilize NZI layers are created under conditions that are tool and laboratory specific, making widespread utilization and scalability of NZI materials difficult. Herein, this limitation is circumvented by using transparent conducting oxides (TCOs) produced from scalable commercial sources. The optical response of 49 distinct TCOs with NZI behavior from 12 different suppliers is quantified, including indium tin oxide (ITO), aluminumdoped zinc oxide (AZO), and fluorine-doped tin oxide (FTO). The measurements reveal that the ITO samples have the strongest NZI resonances with many samples exhibiting |n| < 0.6 with resonances occurring between 1150 and 1350 nm. Conversely, the FTO and AZO films present higher values of |n| (ranging from 0.6 to 0.9) at 1500-1900 nm. The optical properties, resistivities, and roughness values for all thin films are reported, creating a useful database for device design. Finally, novel NZI phenomena, such as the strong suppression of non-normal incidence illumination using the data collected from these samples, are demonstrated, opening the door to new opportunities for both research-grade and mass-produced NZI devices.

Manufacturing-Enabled Tunability of Linear and Nonlinear Epsilon-Near-Zero Properties in Indium Tin Oxide Nanofilms

“…In previous research, TCOs from 12 scalable commercial suppliers were utilized to report their ENZ and NZI properties influenced by λ ENZ . 30 Thus, controlling λ ENZ in tunable spectral ranges by stable experiments turns out to be an important issue. It is found that the carrier concentration, plasma frequency, and surface plasmon resonance responses of sputtered ITO films can be engineered through different deposition parameters, 31−33 which gives a useful instruction to further study the ENZ tuning.…”

“…Even the advanced techniques introduced in ref require a series of different samples with subsequential λ ENZ . In previous research, TCOs from 12 scalable commercial suppliers were utilized to report their ENZ and NZI properties influenced by λ ENZ . Thus, controlling λ ENZ in tunable spectral ranges by stable experiments turns out to be an important issue.…”