Boron nitride nanoresonators for phonon-enhanced molecular vibrational spectroscopy at the strong coupling limit

Abstract

Enhanced light-matter interactions are the basis of surface-enhanced infrared absorption (SEIRA) spectroscopy, and conventionally rely on plasmonic materials and their capability to focus light to nanoscale spot sizes. Phonon polariton nanoresonators made of polar crystals could represent an interesting alternative, since they exhibit large quality factors, which go far beyond those of their plasmonic counterparts. The recent emergence of van der Waals crystals enables the fabrication of high-quality nanophotonic resonators based on phonon polaritons, as reported for the prototypical infrared-phononic material hexagonal boron nitride (h-BN). In this work we use, for the first time, phonon-polariton-resonant h-BN ribbons for SEIRA spectroscopy of small amounts of organic molecules in Fourier transform infrared spectroscopy. Strikingly, the interaction between phonon polaritons and molecular vibrations reaches experimentally the onset of the strong coupling regime, while numerical simulations predict that vibrational strong coupling can be fully achieved. Phonon polariton nanoresonators thus could become a viable platform for sensing, local control of chemical reactivity and infrared quantum cavity optics experiments.

Nanoscale Guiding of Infrared Light with Hyperbolic Volume and Surface Polaritons in van der Waals Material Ribbons

“…h‐BN has a uniaxial permittivity and exhibits a hyperbolic isofrequency curve in two infrared Reststrahlen bands (regions between transversal and longitudinal optical phonon frequencies, ω TO and ω LO , respectively), where ε ⊥ > 0 and ε ∥ < 0 (lower band) and ε ⊥ < 0, ε ∥ > 0 (upper band), respectively. In the upper band, two types of HPs have been found: volume‐confined HPs in extended slabs, and in resonator structures, as well as surface‐confined HPs at the edges of slabs, linear antennas and cylindrical waveguides . However, a detailed study of HP modes in long ribbons with rectangular cross section, representing canonical linear waveguide structures, has not been reported yet.…”

Functional Mid‐Infrared Polaritonics in van der Waals Crystals

“…The confinement factor of α‐MoO 3 phonon polaritons is measured to be as high as n eff ≈ 60, and, surprisingly, the lifetime reaches up to 8 ps (γ −1 ≈ 200) which is about four times higher than that of the phonon polaritons in isotopically enriched h‐BN . The strong field confinement and ultralow loss of hyperbolic phonon polaritons in h‐BN and α‐MoO 3 provide a new and interesting physical platform with strong and directional light–matter interaction, enabling the realization of nanoscale photonic devices for a range of applications from deeply subdiffractional imaging to molecular spectroscopy …”

“…In addition to the high Q‐factor, a large confinement of λ 0 /86 was also realized, which results in a strong near‐field enhancement around the resonators . Figure a illustrates how the h‐BN nanoresonators were used for detecting the mid‐infrared spectral features of CH bond at 1450 cm −1 in 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl (CBP) . Exfoliated h‐BN flakes (40 nm thick) were transferred onto a CaF 2 substrate, h‐BN nanoribbons were patterned by the electron beam lithography followed by reactive ion etching.…”

2D Nitrogen‐Containing Carbon Material C5N as Potential Host Material for Lithium Polysulfides: A First‐Principles Study

“…[1][2][3][4] Among them, carbon-based 2D materials have always been the research focus. [1][2][3][4] Among them, carbon-based 2D materials have always been the research focus.…”