High frequency deflection measurement of IR absorption
An AFM based technique has been demonstrated for performing highly localized IR spectroscopy on a sample surface. Significant issues as to size, cost of implementation, and repeatability/robustness of results exist in commercializing the technique. The invention addresses many of these issues thereby producing a version of the analytical technique that can be made generally available to the scientific community.
1. A method for measuring a localized IR spectra of a sample comprising:
interacting an AFM probe tip with a region of a sample;
illuminating the sample with pulsed variable wavelength IR radiation at a pulse frequency
collecting deflection data from the probe due to exciting a resonant oscillation of the probe in response to thermal expansion of the sample due to spectrally dependent absorption of radiation from the IR;
applying a modulation signal to modulate the tip-sample interaction; and,
using heterodyne techniques to measure the tip response due to IR absorption due to heterodyne mixing of the IR source pulse frequency and the tip modulation frequency, thereby reducing the effect of background forces not localized to the tip.
2. The method of claim 1 comprising operating the AFM in tapping mode.