perature rise from spectral absorption through the use of AFM cantilevers integrated with conventional Fourier transform IR (FTIR) spec- trometers [4,5]. These approaches allow broader spectrum measurement than near- field approaches, but the spatial resolution is typically limited due to thermal diffusion to the scale of many micrometers. We have developed and implemented a novel lab-based instrument that combines atomic force microscopy and infrared spec- troscopy to enable chemical characterization of polymer and other samples at scales below the diffraction limit. The instrument employs photothermal induced resonance (PTIR) that uses an AFM probe to measure local thermal expansion from IR light incident upon a sam- ple. The PTIR technique was originally devel- oped by Dazzi et al. [6-9] using the CLIO free electron source facility at Université Paris-Sud. To make this capability more broadly avail- able, we have developed an instrument based on a lab-scale IR source. As shown in Figure 1, the sample is illumi- nated with the pulsed tunable IR laser light source. When IR radiation is absorbed by the BIOGRAPHY Dr Craig Prater received a BS from Texas A&M in 1987 and a PhD from the University of California Santa Barbara in 1992. Between 1992 and 2007 Craig served in many tech- nology development and management roles at Digital Instruments/Veeco. In 2007 he became the CTO at Anasys Instruments. Craig and his colleagues have been focused on advancing nanoscale measurements of material properties with atomic force microscopy. ABSTRACT The ability to identify material under the tip of an AFM has been identified as one of the ‘Holy Grails’ of scanning probe microscopy. While AFM can measure mechanical, electri- cal, magnetic and thermal properties of materials, it has lacked the robust ability to chemically characterize unknown materials. Infrared spectroscopy is a benchmark tech- nique used in a broad range of sciences and industry to characterize and identify materi- als via vibrational resonances of chemical bonds. We have successfully integrated AFM with IR spectroscopy to allow measurement of high quality IR spectra at arbitrary points in an AFM image, thus providing nanoscale chemical characterization. KEYWORDS atomic force microscopy, infrared spec- troscopy, polymer, photothermal induced resonance, contact resonance, nanothermal analysis ACKNOWLEDGEMENTS This work was supported in part by NIST-ATP 70NANB7H7025 and NSF-SBIR 0750512. AUTHOR DETAILS Dr Craig B. Prater 121 Gray Avenue Santa Barbara, CA 93101, USA craig@anasysinstruments.com Microscopy and Analysis 24(3):5-8 (SPM), 2010 N ANOSCALE S PECTROSCOPY INTRODUCTION Atomic force microscopy (AFM) has been enor- mously successful addressing problems in basic nanoscale research as well as applied problems in materials science and engineering. A clear gap in AFM capabilities, however is the ability to chemically characterize regions of the sam- ple. This is especially important in the study of heterogeneous materials like polymer blends, multilayer films, nanocomposites and many other areas. Several AFM probe-based techniques have been used to exceed the diffraction limit of conventional infrared (IR) measurements. Tra- ditional IR microscopy has a resolution limit roughly three times the incident wavelength [1], on the scale of several to tens of micro- meters. Various optical scattering methods attempt to relate spectral optical properties of materials to their chemical composition [2,3]. However, in general, nearfield approaches are single or narrow band and do not produce rich spectra that can be used to characterize a broad range of vibrational resonances associ- ated with different chemical species. Other IR techniques are based on measuring local tem- Nanoscale Infrared Spectroscopy of Materials by Atomic Force Microscopy Craig Prater, 1 Kevin Kjoller, 1 Debra Cook, 1 Roshan Shetty, 1 Gregory Meyers, 2 Carl Reinhardt, 2 Jonathan Felts, 3 William King, 3 Konstantin Vodopyanov 4 and Alexandre Dazzi. 5 1. Anasys Instruments, Santa Barbara, CA, USA. 2. The Dow Chemical Company, Midland, MI, USA. 3. University of Illinois, Urbana-Champaign, IL, USA. 4. Stanford University, Stanford, CA, USA. 5. Université Paris-Sud, Orsay, France. Figure 1: The instrument (a) uses a pulsed, tunable IR source to excite molecular resonances in the sample. Absorption of IR radiation by the sample leads to a rapid thermal expansion that excites resonant oscillations of the cantilever. These oscillations decay in a characteristic ring-down (b). The ring-downs can be analyzed by Fourier techniques (c) to extract the amplitude and frequency of oscillations. Measuring the amplitude of the cantilever oscillation as a function of the source wavelength creates local absorption spectra (d). The oscillation frequencies of the ring-down are also related to mechani- cal stiffness of the sample. MICROSCOPY AND ANALYSIS SPM ISSUE APRIL 2010 5 d a b c