High frequency deflection measurement of IR absorption
An AFM based technique has been demonstrated for performing highly localized IR spectroscopy on a sample surface. Such a technique implemented in a commercially viable analytical instrument would be extremely useful. Various aspects of the experimental set-up have to be changed to create a commercial version. The invention addresses many of these issues thereby producing a version of the analytical technique that cab be made generally available to the scientific community.
1. Method of measuring a localized IR spectra of a sample comprising:
illuminating sample with pulsed variable wavelength IR radiation with an optical parametric oscillator as an IR source;
placing an AFM probe on the sample;
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 absorption of radiation from the IR source; and,
repeating the collecting step while varying IR radiation wavelength to create an IR absorption spectrum from the deflection data.
2. Method of claim 1 further comprising scanning the probe to various points on the sample surface and repeating the data collection and spectra creation steps.
3. Method of claim 1 wherein a pulse frequency of the IR source is chosen to be at or near a contact resonant frequency of the AFM probe.
4. Method of claim 1 further comprising the step of measuring a relative thermal expansion coefficient of the region of sample by varying the probe's temperature; and, observing at least one of the deflection due to thermal expansion or the temperature due to thermal diffusivity.
5. System for measuring a localized IR spectrum on a sample surface comprising:
a pulsed, variable wavelength optical parametric oscillator as an IR source disposed to illuminate the sample; and,
an AFM, including a scanner, provision for mounting of the sample, a cantilever probe with a probe tip, and a cantilever deflection measurement capability.
6. System according to claim 5 wherein at least a part of the cantilever probe is transparent to IR energy from the IR source.
7. System according to claim 5 wherein at least a part of the cantilever probe is reflective to IR energy from the IR source.
8. System according to claim 5 wherein at least at a part of the cantilever probe is at least one of coated with or constructed of metal.