Abstract
We demonstrate surface-enhanced ultrafast vibrational spectroscopy employing periodic arrays of infrared-resonant gold nanoantennas. The antenna-enhancements of molecular vibrational responses are analytically formulated with a simple coupled-dipole model, and the linear/nonlinear local signal enhancements are evaluated to be ~104and 107, respectively.
Highlights
Ultrafast infrared (IR) spectroscopy, including pump-probe and two-dimensional methods, is a powerful, label-free tool to resolve molecular conformational structures, structural dynamics, vibrational relaxations, etc. [1]
We demonstrate surface-enhanced ultrafast vibrational spectroscopy by using periodically-arranged IR-resonant nanoantennas, which satisfy the condition near the collective resonance [5, 6]
We analytically formulate the antennaenhancements of molecular vibrational responses with a simple coupled-dipole model (Fig. 1(a)), and evaluate the linear/nonlinear local signal enhancement factors by analyzing the experimental data with the analytic formulae
Summary
Ultrafast infrared (IR) spectroscopy, including pump-probe and two-dimensional methods, is a powerful, label-free tool to resolve molecular conformational structures, structural dynamics, vibrational relaxations, etc. [1]. A promising approach for increasing the sensitivity is to amplify the interaction of molecular vibrations with IR ultrashort pulses by employing IR-resonant nanoantennas [2]. It has been demonstrated that nonlinear vibrational signals are amplified with colloidal gold nanoparticles [3] and randomly-arranged resonant nanoantennas [4]. Further study is necessary to increase the sensitivity and to add new functionalities for wide use in materials science and life science. In this contribution, we demonstrate surface-enhanced ultrafast vibrational spectroscopy by using periodically-arranged IR-resonant nanoantennas, which satisfy the condition near the collective resonance [5, 6]. We analytically formulate the antennaenhancements of molecular vibrational responses with a simple coupled-dipole model (Fig. 1(a)), and evaluate the linear/nonlinear local signal enhancement factors by analyzing the experimental data with the analytic formulae
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