TY - JOUR
T1 - Model for quantitative tip-enhanced spectroscopy and the extraction of nanoscale-resolved optical constants
AU - McLeod, Alexander S.
AU - Kelly, P.
AU - Goldflam, M. D.
AU - Gainsforth, Z.
AU - Westphal, A. J.
AU - Dominguez, Gerardo
AU - Thiemens, Mark H.
AU - Fogler, Michael M.
AU - Basov, D. N.
PY - 2014/8/25
Y1 - 2014/8/25
N2 - Near-field infrared spectroscopy by elastic scattering of light from a probe tip resolves optical contrasts in materials at dramatically subwavelength scales across a broad energy range, with the demonstrated capacity for chemical identification at the nanoscale. However, current models of probe-sample near-field interactions still cannot provide a sufficiently quantitatively interpretation of measured near-field contrasts, especially in the case of materials supporting strong surface phonons. We present a model of near-field spectroscopy derived from basic principles and verified by finite-element simulations, demonstrating superb predictive agreement both with tunable quantum cascade laser near-field spectroscopy of SiO2 thin films and with newly presented nanoscale Fourier transform infrared (nanoFTIR) spectroscopy of crystalline SiC. We discuss the role of probe geometry, field retardation, and surface mode dispersion in shaping the measured near-field response. This treatment enables a route to quantitatively determine nanoresolved optical constants, as we demonstrate by inverting newly presented nanoFTIR spectra of an SiO2 thin film into the frequency dependent dielectric function of its mid-infrared optical phonon. Our formalism further enables tip-enhanced spectroscopy as a potent diagnostic tool for quantitative nanoscale spectroscopy.
AB - Near-field infrared spectroscopy by elastic scattering of light from a probe tip resolves optical contrasts in materials at dramatically subwavelength scales across a broad energy range, with the demonstrated capacity for chemical identification at the nanoscale. However, current models of probe-sample near-field interactions still cannot provide a sufficiently quantitatively interpretation of measured near-field contrasts, especially in the case of materials supporting strong surface phonons. We present a model of near-field spectroscopy derived from basic principles and verified by finite-element simulations, demonstrating superb predictive agreement both with tunable quantum cascade laser near-field spectroscopy of SiO2 thin films and with newly presented nanoscale Fourier transform infrared (nanoFTIR) spectroscopy of crystalline SiC. We discuss the role of probe geometry, field retardation, and surface mode dispersion in shaping the measured near-field response. This treatment enables a route to quantitatively determine nanoresolved optical constants, as we demonstrate by inverting newly presented nanoFTIR spectra of an SiO2 thin film into the frequency dependent dielectric function of its mid-infrared optical phonon. Our formalism further enables tip-enhanced spectroscopy as a potent diagnostic tool for quantitative nanoscale spectroscopy.
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U2 - 10.1103/PhysRevB.90.085136
DO - 10.1103/PhysRevB.90.085136
M3 - Article
AN - SCOPUS:84921052173
SN - 1098-0121
VL - 90
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
IS - 8
M1 - 085136
ER -