Infrared (IR) spectroscopy is a valuable tool for assessing the chemical composition of materials but the long IR wavelengths (2-16 �m) result in a diffraction-limited spatial resolution of several micrometers; precluding characterization at the nanoscale which is crucial to many nanotechnology applications.    Photo Thermal Induced Resonance (PTIR), is a new technique that circumvents the diffraction limit by employing a tunable pulsed laser for sample illumination and an AFM tip as a spatial filter to measure the  instantaneous thermal expansion induced by light absorption in the sample. Samples are placed on optically transparent prisms and illuminated in ATR configuration. Infrared spectra are obtained by plotting the amplitude of the tip deflection with respect to the laser frequency. PTIR was previously used for nanoscale chemical characterization under the assumption that the PTIR signal is proportional to the energy absorbed but this assumption was not verified experimentally previously.   In this work, electron beam nano-patterned polymer samples were fabricated directly on ZnSe prisms using customized adaptor pieces to evaluate the PTIR lateral resolution, sensitivity and linearity. Results shows that PTIR lateral resolution for chemical imaging is comparable to the lateral resolution obtained in the AFM height images, up to the smallest feature measured (100 nm). Spectra and chemical maps were produced from the thinnest sample analyzed (40 nm). Additionally, we demonstrate, for the first time, that the intensity of the PTIR spectra of thin films (< 1 �m) depends linearly on the sample thickness suggesting that PTIR can be effectively used for quantitative analysis at the nanoscale. Finally, by analyzing samples with an extended range of thicknesses we demonstrate that the PTIR signal is proportional to the local energy absorbed, to the thermal expansion and to persistence time of the thermal excitation in the sample, as previously predicted theoretically.

Chemical imaging beyond the diffraction limit using photothermal induced resonance technique

246th National Meeting (2013)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.