Chemical Nano-Imaging with Tip-Enhanced Vibrational Spectroscopy

Abstract

Many organic materials in electronic biological systems gain functionality through molecular structuring, heterogeneous morphologies, chemical interactions and coupling at functional interfaces. A major obstacle to understanding the fundamental nature of intra-inter-molecular interactions, however, is the combination of multi-length scale structural disorder ranging from nanometers to micrometers and multi-timescale dynamical interactions ranging from femtoseconds to minutes. To gain the desired nanometer spatial resolution with simultaneous spectroscopic specificity we combine scanning probe microscopy with vibrational spectroscopies using both tip-enhanced Raman (TER) and IR scattering scanning near-field optical microscopy (IR s-SNOM). We use TERS and IR s-SNOM to probe at the homogeneous sample size limit by virtue of the nanometer spatial near-field localization. Together with the associated enhanced near-field light-matter interaction based on improved mode matching provides domain-level structural information and even single-molecule sensitivity. We present several recent advances in near-field microscopy applied to nanoscale chemical identification, imaging nanoscale defects and the local chemical environment, and observations of dynamical fluctuations at the single molecule limit [1-5]. IR s-SNOM has become a powerful tool for nanoscale chemical identification of organic materials. Selected single wavelength IR s-SNOM tuned to the frequency of a characteristic vibrational mode has become a routine method for chemical mapping with nanoscale resolution, while broadband IR s-SNOM can offer greater chemical information through spectroscopic analysis of one or more vibrational modes (Fig. 1A). Using synchrotron infrared nano-spectroscopy (SINS) we extend the spectral range to ultra-broadband nanoscale spectroscopy spanning 300-5000 cm -1 to provide unambiguous nanoscale chemical identification through the vibrational fingerprint [2].