Chemistry Weekly Seminar - Dr. Scott Rosendahl

TITLE:

Synchrotron Mid-Infrared Spectromicroscopy – Chemical Imaging and Mapping

ABSTRACT:

Synchrotron infrared light when coupled with appropriate optics enables broadband, diffraction-limited spatial resolution with high-quality (signal-to-noise) spectra for material analysis in numerous fields. This is the primary advantage to using synchrotron infrared light compared to conventional sources found in benchtop infrared instruments. The Mid-Infrared Spectromicroscopy beamline facilities available to researchers at the Canadian Light Source have generated many collaborations with multiple partners in Agriculture, Bio/Life, Environment, Materials and Cultural Heritage sciences. A common theme to these projects is infrared chemical imaging, or quantitatively, chemical mapping.

Developing the tools, devices and techniques that exploit these advantages of synchrotron light for infrared chemical imaging/mapping has been a focus of my research and is an ongoing effort. Lately, these include the developing of data analysis tools, microfluidic devices and expanding the capabilities of in-situ, time-resolved and polarization modulation techniques. One such technique developed by the beamline is Polarization Modulation Infrared Linear Dichroism Microscopy (µPM‐IRLD) and a particular application studying metallic nanostructures will be discussed and future directions from there.

Metallic nanostructures that exhibit tailored optical resonances in the mid-infrared spectral range are of particular interest for spectroscopic applications ranging from biochemical mechanisms to catalytic surface processes. The strength, spectral and spatial location of these resonances depend on a variety of parameters, including, but not limited to: the materials used to fabricate the structures, the size and shape of the structures, the orientation of these structures with respect to each other and the polarization of the impinging light. Current and typical fabrication methods focus on tuning such plasmonic structures and devices to one spectral band of interest. A means for generating multiple resonances in the mid-infrared is a highly sought-after goal and can be realized through the use of dendritic fractal patterns. By increasing the number of generations in the fractal pattern, the number of resonant spectral bands in the mid-infrared also increases. The challenge with such structures is to rationally design the size of the fractal so as to have resonances in the spectral regions of interest, such as the fingerprint region (1800-1000 cm-1) and the C-H vibrational modes (3100 – 2800 cm-1).