Special Seminar: Infrared vibrational nanospectroscopy via molecular force detection
Tuesday, March 4, 2014
2:00 p.m.-3:30 p.m. IREAP Large Conference Room (ERF 1207)
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Title of Talk: Infrared vibrational nanospectroscopy via molecular force detection
I will discuss a technique for high-sensitivity nanoscale molecular vibrational spectroscopy in mid- and far-infrared developed in our laboratory. Molecular absorption is detected by observing atomic force microscope cantilever deflection due to mechanical forces exerted on the cantilever tip by molecules excited with laser pulses. Spectra are obtained by recording the cantilever deflection amplitude as a function of wavelength. Tip-enhancement of light intensity and mechanical cantilever resonance enhancement are used to achieve nanoscale spatial resolution and nearly single-molecule sensitivity. We demonstrate non-destructive mid-infrared spectroscopy and imaging of molecular monolayer islands with high signal-to-noise ratio and better than 30 nm spatial resolution in air. We estimate that approximately 300 molecules contribute to cantilever deflection in our current experiments and spectra of as few as 30 molecules would be detectable. With further improvements, single-molecule sensitivity is feasible, something which has not been achieved for mid-infrared vibrational spectroscopy in ambient conditions by any means so far. Preliminary results of nanoscale spectroscopy in aqueous environment will also be presented.