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Conventional IR microscopy is widely used in a range of research but is limited from applications where feature sizes are approximately 10 microns and lower. This is due to the diffraction limit of the mid IR illumination which limits the resolution to roughly three times the wavelength.1 Atomic force microscopy (AFM) has been very successful in visualizing the structure of samples at the nanoscale. Researchers have long recognized that combining the nanoscale resolution of the AFM with the chemical identification of IR spectroscopy would provide a powerful analytical technique to chemically characterize regions of the sample. Several AFM probe-based techniques have been developed in an attempt to surpass the diffraction limit of conventional IR measurements. They include both traditional near field scanning optical microscopy (NSOM) as well as aperatureless near field scanning microscopy (ANSOM). The ANSOM technique has demonstrated impressive lateral resolution 2 but has not produced rich spectra that can be used to characterize a broad range of vibrational resonances. Additionally the ANSOM technique suffers from a limited signal to noise restricting analysis to specific sample classes. Other techniques developed to extend the resolution of IR spectroscopy are based on measuring the local temperature rise from spectral absorption through the use of AFM cantilevers integrated with conventional Fourier Transform Infrared (FTIR) spectrometers.3 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 microns. We have developed and utilized a novel lab-based instrument that combines AFM and infrared spectroscopy to enable chemical characterization of samples at sub-micron scales. The instrument makes use of a technique called photothermal induced resonance (PTIR).4 PTIR is accomplished by using a traditional AFM probe to sense the rapid local expansion of a sample that absorbs light from a pulsed IR source. As shown in figure 1, the sample is illuminated with a pulsed, tunable IR light source in a configuration similar to the attenuated total reflection (ATR) technique used in conventional IR spectroscopy. When the IR illumination is at a wavenumber which is an absorption band of the sample, it creates a rapid thermal expansion wave that excites resonant oscillations of the AFM cantilever. By measuring the amplitude of the cantilever vibrations as a function of the IR source wavelength, a local IR absorption spectrum can be created. The IR source is continuously tunable from 3600 to 1200 cm -1 . This covers a major portion of the mid-IR including important CH, NH and CO bands, as well as carbonyl and amide I/II bands. We have used this novel technique to image and chemically identify a variety of polymer samples. Figure 2 shows measurements performed on a blend of polycarbonate (PC) and acrylonitrile butadiene styrene (ABS) typically used as an impact modified polymer. The two components could be i...

Spectroscopic characterization of interconnects and circuits in semiconductor devices has become increasingly complicated as dimensions for breakthroughs and failure analysis are continuously shrinking. To achieve high spatial resolution infrared (IR) spectroscopic information, a pulsed infrared laser can be coupled to an atomic force microscope in the atomic force microscopy IR (AFM-IR) technique. The combination of AFM-IR and Lorentz contact resonance AFM (LCR-AFM) has great potential for providing high spatial resolution chemical and mechanical analysis. To demonstrate the feasibility of the AFM-based techniques, AFM-IR spectrum and images were obtained from the interlayer dielectrics of a test structure at a length scale shorter than the IR wavelength. Using the LCR-AFM technique, the relative mechanical properties of the components could be mapped distinctively by observing the contact resonance of the AFM probe. Finally, preliminary data suggest there may be AFM-IR spectral differences between contamination and the bulk material on a liquid crystal display.

with high affinity and exhibit a robust open probability~0.4. Substituting dual alanines for the 'IQ' residues in the IQ element significantly weakens apocalmodulin binding, and markedly diminishes peak open probability (~0.1). Overexpressing apocalmodulin fully rescues open probability, demonstrating that the effects on opening reflect apocalmodulin binding per se. This extensive structural and functional similarity substantiates a striking conservation of calmodulin regulation across Nav and Cav channels, joint investigation of which now presents as a genuinely synergistic endeavor.