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 can be made generally available to the scientific community.
1. Method of measuring a localized IR spectra of a sample comprising:
interacting an AFM probe with a region of a sample;
illuminating the sample with pulsed, variable wavelength IR radiation at a pulse frequency at or near a resonant frequency of the AFM probe with at least one of an optical parametric oscillator or a quantum cascade laser as an IR source;
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; 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 2 wherein a pulse frequency of the IR source is chosen to be at or near a contact resonant frequency of the AFM probe.
4. System for measuring a localized IR spectrum on a sample surface comprising:
a pulsed, variable wavelength source including at least one of an optical parametric oscillator or a quantum cascade laser 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.
5. Method of measuring a localized IR spectra of a sample comprising
interacting an AFM probe with a region of a sample;
illuminating the sample with pulsed, variable wavelength IR radiation at a pulse frequency at or near a resonant frequency of the AFM probe with at least one of an optical parametric oscillator or a quantum cascade laser as an IR source; and,
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.
6. Method of claim 5 further comprising scanning the probe to various points on the sample surface and repeating the data collection step.