AVS 59th Annual International Symposium and Exhibition
    Scanning Probe Microscopy Focus Topic Wednesday Sessions
       Session SP+AS+BI+ET+MI+TF-WeA

Invited Paper SP+AS+BI+ET+MI+TF-WeA9
Nanoscale Chemical Composition Mapping with AFM-based Infrared Spectroscopy

Wednesday, October 31, 2012, 4:40 pm, Room 16

Session: Emerging Instrument Formats
Presenter: E. Dillon, Anasys Instruments
Authors: C.B. Prater, Anasys Instruments
M. Lo, Anasys Instruments
Q. Hu, Anasys Instruments
C. Marcott, Light Light Solutions
B. Chase, University of Delaware
R. Shetty, Anasys Instruments
K. Kjoller, Anasys Instruments
E. Dillon, Anasys Instruments
Correspondent: Click to Email
The ability to identify material under an AFM tip has been identified as one of the "Holy Grails" of probe microscopy. While AFM can measure mechanical, electrical, magnetic and thermal properties of materials, until recently it has lacked the robust ability to chemically characterize unknown materials. Infrared spectroscopy can characterize and identify materials via vibrational resonances of chemical bonds and is a very widely used analytical technique. We have successfully integrated AFM with IR spectroscopy (AFM-IR) to obtain high quality infrared absorption spectra at arbitrary points in an AFM image, thus providing nanoscale chemical characterization on the sub-100 nm length scale. Employing the AFM-IR technique, we have mapped nanoscale chemical, structural and mechanical variations in multilayer thin films, nanocomposites, polymer blends, organic photovoltaics, and biological materials including hair, skin, and bacterial and mammalian cells. Light from a pulsed infrared laser is directed at a sample, causing rapid thermal expansion of the sample surface at absorbing wavelengths. The rapid thermal expansion creates an impulse force at the tip, resulting in resonant oscillations of the AFM cantilever. The amplitude of the cantilever oscillation is directly related to the infrared absorption properties of the samples, enabling measurements of IR absorption spectra far below the conventional diffraction limit. AFM-IR can be used both to obtain point spectra at arbitrary points and to spatially map IR absorption at selected wavelengths. Simultaneous measurement of the cantilever's contact resonance frequency as excited by the IR absorption provides a complimentary measurement of relative mechanical properties. We have used these techniques to chemically identify individual chemical components in polymer nanocomposites and multilayer films and performed subcellular spectroscopy and chemical imaging on biological cells. Using self-heating probes we have been able to locally modify the state of a semicrystalline polymer and observe the resulting change in absorption spectra on the nanoscale. Using polarization sensitive AFM-IR, we have mapped spatial variations in molecular orientation in electrospun fibers.