Far-field midinfrared superresolution imaging and spectroscopy of single high aspect ratio gold nanowires

Abstract

Limited approaches exist for imaging and recording spectra of individual nanostructures in the midinfrared region. Here we use infrared photothermal heterodyne imaging (IR-PHI) to interrogate single, high aspect ratio Au nanowires (NWs). Spectra recorded between 2,800 and 4,000 cm−1 for 2.5–3.9-μm-long NWs reveal a series of resonances due to the Fabry–Pérot modes of the NWs. Crucially, IR-PHI images show structure that reflects the spatial distribution of the NW absorption, and allow the resonances to be assigned to the m = 3 and m = 4 Fabry–Pérot modes. This far-field optical measurement has been used to image the mode structure of plasmon resonances in metal nanostructures, and is made possible by the superresolution capabilities of IR-PHI. The linewidths in the NW spectra range from 35 to 75 meV and, in several cases, are significantly below the limiting values predicted by the bulk Au Drude damping parameter. These linewidths imply long dephasing times, and are attributed to reduction in both radiation damping and resistive heating effects in the NWs. Compared to previous imaging studies of NW Fabry–Pérot modes using electron microscopy or near-field optical scanning techniques, IR-PHI experiments are performed under ambient conditions, enabling detailed studies of how the environment affects mid-IR plasmons.

Bond-selective imaging by optically sensing the mid-infrared photothermal effect

“…5B ). The authors did the finite element simulations and obtained good consistency with the experimental results ( 79 ). Local cation-related inhomogeneities in mixed cation perovskites film ( Fig.…”

“…β = d n /d T is the temperature dependence of refractive index, also termed as thermo-optic coefficient. Typically, α and β are on the level of 10 −6 to 10 −4 /K for biological samples, metals, and polymers ( 25 , 78 , 79 ). The scattered field E s from sample under the incident probe field E i is expressed as E s = ∣ s ( n , l )∣ e i ϕ s ( n , l ) E i , where ∣ s ( n , l )∣ is the scattering amplitude and ϕ s ( n , l ) is the scattering optical phase.…”

“…Reprinted with permission from ref. ( 79 ). ( C ) MIP image of mixed cation perovskites FA 0.1 MA 0.9 PbI 3 films and MA/FA ratio map; the MIP spectra are obtained at the points shown in the ratio map.…”

Nanosecond-Resolution Photothermal Dynamic Imaging via MHz Digitization and Match Filtering

“…Lock-in free PDI offers nanoseconds temporal resolution that is ultimately limited by the photon detector response. For example, it can be used to study the nonlinear photothermal phenomenon, including the nanobubble generation within a life span of hundreds of nanoseconds 48,49 , higher-order thermal wave modulation on heat capacity and conductivity 50,51 ; revealing resistive heating profile of nanostructure 14 and detecting photothermal induced pressure wave. Those photothermal processes have a relatively short lifetime due to the rapidly dissipated heat.…”

“…With the capability of submicron-resolution mapping of chemical bonds in an aqueous environment, the mid-infrared photothermal imaging field quickly expands with innovations, including wide-field detection 7 , optical phase detection [8][9][10] , photoacoustic detection 11,12 , synergistic integration with Raman spectroscopy 13 . Mid-infrared photothermal microscopy has found broad applications, including non-contact material characterization [14][15][16] , bio-molecular mapping 13,17 , protein dynamics and aggregation in neurons 18,19 , bacterial response to antibiotics 20 , single virus detection 21 and imaging of metabolism in living cells and other organisms 5,12,22 .…”