Graphene-based room-temperature IR detector for phonon-enhanced near-field molecular sensing

Mid-infrared (mid-IR) spectroscopy is a powerful analytical tool for the label-free and non-destructive identification of materials through their unique vibrational fingerprints. However, conventional mid-IR spectroscopy faces challenges in detecting minute amounts of molecules due to small infrared extinction cross-sections. Surface-enhanced infrared absorption (SEIRA) spectroscopy has emerged as a solution, utilizing various substrates to enhance incident infrared fields. Recent advancements in two-dimensional materials and phonon polaritons have opened new avenues for improving SEIRA sensitivity.   In this seminar, we demonstrate an ultra-compact on-chip SEIRA platform using a graphene-based detector. This detector consists of an h-BN/graphene/h-BN heterostructure on a metal split gate, creating a p-n junction with a thin layer of organic molecules directly evaporated on top of the heterostructure. This design exploits the strong field confinement of hyperbolic phonon polaritons, enhancing both molecular vibrational absorption and photocurrent generation at the p-n junction. Our method shows improved sensitivity compared to far-field transmission experiments, particularly for thin molecular layers. Simulations suggest the potential for detecting subwavelength-scale areas with increased sensitivity over diffraction-limited techniques.   Our on-chip phononic SEIRA approach opens exciting possibilities for enhanced molecular sensing at the nanoscale, potentially paving the way for more sensitive and compact molecular vibration detection platforms in the IR frequency range.