Spectroscopic Nanoimaging of All-Semiconductor Plasmonic Gratings Using Photoinduced Force and Scattering Type Nanoscopy

Abstract

All-semiconductor plasmonic gratings are investigated by spectroscopic nanoimaging in the vicinity of the plasma frequency, where the material behaves as an epsilon near-zero (ENZ) material. Both phase-sensitive scattering type nanoscopy (s-SNOM) and photoinduced force microscopy (PiFM) are carried out on this structure. The obtained data and models reveal that PiFM, as for s-SNOM, can have a mostly dispersive line shape, in contrast with recent near-field spectra obtained with photothermal AFM nanoscopic imaging on ENZ material where absorption maxima are observed. On the obtained result, PiFM signal exhibited better sensitivity to the dielectric function variation while interferometric s-SNOM can provide additional phase information. Localized surface plasmon resonances (LSPR), highly confined on the structure edges were also observed with both techniques. A higher sensitivity was observed with PiFM for both dielectric contrast imaging and LSPR observation. In addition, for both microscopies, the near-field response is phenomenologically described using a similar formalism based on dipole-image dipole approach. In this model, the sensitivity difference between both techniques is mostly accounted for by probes having different polarizabilities.

Observation of nanoscale opto-mechanical molecular damping as the origin of spectroscopic contrast in photo induced force microscopy

“…Near-field electromagnetic field characterization [9][10][11][12][13][14] , nonlinear optical measurements such as Raman 15 spectroscopy and stimulated Raman spectroscopy 16,17 , time-resolved pump-probe microscopy 18 , organic solar cells studies 19 , optical phonon polariton imaging and nanoscale chemical 4 imaging in the mid-infrared 20 are but a few examples. While the dipole-dipole force model provides excellent agreement with the electromagnetic near field measurements in the visible 14 and with mid-infrared plasmonic resonance spectra 21 , extending this model to infrared vibrational resonances causes discrepancies between experiment and theory 20,22,23 . In particular, the dipole-dipole force model predicts a dispersive spectral response (or more accurately a combination of dispersive and dissipative responses), while the experimental results show a purely dissipative response.…”

“…While the dipole-dipole force model provides excellent agreement with the electromagnetic near-field measurements in the visible 14 and with mid-IR plasmonic resonance spectra 21 , extending this model to IR vibrational resonances causes discrepancies between experiment and theory 20,22,23 . In particular, the dipole-dipole force model predicts a dispersive spectral response, while the experimental results show a purely dissipative response.…”

Photo-Induced Force Microscopy by Using Quartz Tuning-Fork Sensor

“…In classical nearfield scattering theory, αs can be successfully explained with the help of an image dipole model, which yields α s = β α t , where β is the complex electrostatic reflection coefficient, given as β = ε − 1 / ε + 1, where ε is the dielectric constant of the sample. This short-range-induced dipole force typically shows the dispersive spectral line shape and strongly increases in the metal/plasmonic material where ε is negative, whereas the force is typically small under a few pN range in the organic and inorganic sample where ε is positive, even at its molecular resonance [14,15,16,17].…”

Nanoscale spectroscopic origins of photoinduced tip–sample force in the midinfrared

“…Compared to the PTIR and PFIR, the recently developed PiFM operates in the noncontact/tapping mode while monitoring the photoinduced force between the tip and the sample. Theoretically, when the light illuminates the tip–sample junction, the induced dipoles in the tip and in the sample generate a coulombic force whose spectral response follows a dispersive line shape (5, 18, 19). Meanwhile, near molecular resonances, there is a temperature rise of the sample due to light absorption, which results in the thermal expansion of the sample.…”