Infrared Resonance Tailoring of Individual Split‐Ring Resonators with Phase‐Change Materials by Locally Changing the Dielectric Surrounding of the Antenna Hotspots

Abstract

For miniaturized active metasurfaces, resonance tuning of nanoantennas is a key ingredient. Phase‐change materials (PCMs) have been established as prime candidates for non‐volatile resonance tuning enabled by a change in the refractive index around nanoantennas. Conventionally, this tuning is induced by annealing the entire sample equally and does not allow changes on a meta‐atom level. Recently, it is demonstrated that individual rodantenna resonances can be adjusted by addressing each meta‐atom locally with precise laser pulses and switching the PCM there. However, simultaneously controlling several different modes remains elusive. In this work, PCM‐covered aluminum split‐ring resonators (SRRs) are switched locally to tune both the electric dipole resonances as well as the magnetic dipole resonances. By selectively switching the PCM at different hotspots of the SRRs, both resonances can be tuned individually. Finally, the field enhancement in the magnetic resonance allows continuous tuning of surface‐enhanced infrared absorption of native SiO2. This work serves as a proof of principle for sophisticated resonance tuning via changes in the refractive index at the hotspots of the selected antennas enabling fine‐tuning functionalities on a meta‐atom level and allows for post‐fabrication adjustments of metasurfaces.

Infrared Resonance Tuning of Nanoslit Antennas with Phase-Change Materials

“…Figure 1A): If the entire slit is covered by crystalline GST, only the crystallization depth influences the resonance position of the nanoantennas. This is drastically different from the resonance tuning mechanism previously observed for the conventional antenna structure of nanorods and split-ring resonators: 24,28 There, it was found that the resonance tuning is invariably influenced by both the spot size and the crystallization depth simultaneously because the fields of the antenna structures extend outward from the antenna ends (see Supplementary Note 1).…”

“…In particular, the crystallization depth plays a major role for the resonance shift. 24,28 In Figure 2B, four different slit antenna arrays locally addressed with crystallization pulses of varied pulse duration, and the corresponding measured reflectance spectra are visualized. At first, the slits were covered by amorphous GST.…”

“…The phenomenon that laser-induced crystallization often does not completely penetrate the PCM layer in the vertical direction has previously been demonstrated by locally addressing metallic nanorods and split-ring resonators. In particular, the crystallization depth plays a major role for the resonance shift. , …”

“…Nonvolatile tuning results in a persistent shift of the resonances even after all external stimuli are removed and can, e.g., be achieved with phase-change materials. − These materials exhibit (at least) two different (meta)­stable phases that are reversibly switchable upon heating. Both phases differ significantly in their optical and electrical properties due to a difference in atomic bonding.…”

Direct programming of confined surface phonon polariton resonators with the plasmonic phase-change material In3SbTe2

“…Remarkably, both phases show a large contrast in the refractive index, caused by a change in chemical bonding. In the amorphous phase, the atoms are covalently bonded, but in the crystalline phase a new bonding type occurs which is called metavalent 27 – 31 . The reversible phase change can be induced by locally heating the PCM with electrical or optical pulses.…”