Efficient excitation of acoustic graphene plasmons for sub-nanoscale infrared sensing

Acoustic graphene plasmons (AGPs) exhibit extremely spatial confinement and near-field enhancement, holding great potential for sub-nanoscale infrared sensing. However, the efficient excitation of AGPs is challenging due to the large momentum mismatch between AGPs and the incident light. Here, we numerically demonstrate an efficient AGP launcher consisting of a monolayer graphene (MG)/graphene nanoantenna (GNA) array/gold reflector hybrid structure. The resonant GNA array, which is in close proximity to MG, excites ultra-confined AGPs between the GNA array and MG, as well as confined GPs in MG. Moreover, the excitation efficiency of AGPs is significantly enhanced due to the constructive interference. Benefiting from the ultra-confined near fields and gate-tunable resonance frequency of AGPs, the characteristic vibrational signals of the sub-nanoscale (0.8 nm) polyethylene layer and A/G-IgG protein layer can be distinctly observed in the absorption spectra of hybrid structure. The efficient AGP launcher provides a highly compact platform for subwavelength optics and sub-nanoscale sensing.