Nanoscale infrared spectroscopy with multi-frequency atomic force microscopy

Patent metadata

Field	Value
Publication number	US-10557789-B2
Application number	US-201313956156-A
Country	US
Kind code	B2
Filing date	Jul 31, 2013
Priority date	Jul 31, 2013
Publication date	Feb 11, 2020
Grant date	Feb 11, 2020

Abstract

Described are techniques for obtaining spectroscopic information from sub-micron regions of a sample using a probe microscope. The current invention uses the response of an AFM cantilever at a plurality of frequencies to substantially reduce the impact of background absorption away from the sub-micron region of interest. This innovation substantially improves the quality of spectra for top down illumination of samples that are not suitable for bottoms up illumination of the prior art.

First claim

We claim:

1. A method for obtaining spectroscopic information about a sub-micron region of a sample on a sample mount using an atomic force microscope, the method comprising:
a) Interacting a probe of the atomic force microscope (AFM) with the sub-micron region of the sample;
b) Illuminating the sample with a top down beam of radiation;
c) Measuring a response of the AFM probe due to absorption of incident radiation at a plurality of radiation wavelengths;
d) Determining the AFM probe response at a plurality of AFM probe oscillation frequencies;
e) Decomposing the AFM probe response at the plurality of AFM probe oscillation frequencies into sub-micron sample region components at about an apex of a tip of the probe, and background components, and use the sub-micron sample region components to calculate spectroscopic information about the sub-micron region of the sample, wherein the background components are caused by absorption of the radiation by at least one of a cantilever of the probe, part of the tip of the probe away from the tip apex, and a region of the sample away from the tip apex; and
f) Storing a representation of the spectroscopic information on a machine readable medium.

2. The method of claim 1 wherein the combining step comprises subtracting a scaled response at a frequency corresponding to a fundamental cantilever resonance mode from the probe response at a frequency corresponding to a higher order resonance mode.

3. The method of claim 1 wherein the combining step comprises decomposing the probe response at a plurality of frequencies and wavelengths into multiple component spectra.

4. The method of claim 3 wherein the component spectra comprise at least a background response and a response originating from the sub-micron region.

5. The method of claim 3 wherein decomposing the probe response comprises applying at least one of: multivariate curve resolution, self-modeling mixture analysis, band target entropy minimization, spectral demixing, and alternating least squares.

6. The method of claim 1 wherein the spectroscopic information comprises a spectrum indicative of wavelength dependent absorption of the sub-micron region.

7. The method of claim 1 wherein the plurality of frequencies correspond to cantilever resonance modes.

8. The method of claim 7 wherein the cantilever oscillation modes are comprised of at least one of: contact resonance modes, free resonance modes, and tapping resonance modes.

9. The method of claim 1 wherein the probe response at the plurality of frequencies is decomposed into component spectra and component weighting factors.

10. The method of claim 1 wherein the illumination is top down illumination.

11. The method of claim 1 wherein the sample is substantially opaque to infrared light.

12. The method of claim 1 wherein the sample comprises an in-situ sample.

13. A method for obtaining spectroscopic information about a sub-micron region of a sample using an atomic force microscope, the method comprising:
a) Interacting a probe of the atomic force microscope (AFM) with the sub-micron region of the sample;
b) Illuminating the sample with a beam of radiation, at least a portion of the radiation incident on the sub-micron region of the sample;
c) Measuring a response of the probe due to absorption of incident radiation;
d) Determining the AFM probe response at or near a plurality of probe oscillation mode frequencies;
e) Applying at least one of multivariate curve resolution, self-modeling mixture analysis, spectral demixing, and alternating least squares to the AFM probe response at a plurality of AFM probe oscillation frequencies to decompose the AFM probe response into a background response component and a component from the response from the sub-micron region of the sample;
f) Producing a measurement of spectroscopic information of the sub-micron region of the sample resulting from the sub-micron sample region component; and
g) Storing a representation of the spectroscopic information on a machine readable medium.

14. The method of claim 13 wherein the spectroscopic information comprises an absorption spectrum.

15. The method of claim 13 wherein the beam of radiation comprises a radiation from a pulsed infrared source.

16. The method of claim 13 wherein the plurality of frequencies correspond to multiple resonance modes of the cantilever.

17. The method of claim 16 wherein the resonance modes comprise of at least one of: contact resonance modes, free resonance modes, and tapping resonance modes.

18. The method of claim 13 wherein the illumination is top down illumination.

19. The method of claim 13 wherein the sample is substantially opaque to infrared light.

20. The method of claim 13 wherein the sample is an in situ sample.

21. An apparatus for measuring spectroscopic information from a sub-micron region of a sample with a probe microscope (PM), the apparatus comprising:
a) a source of radiation that is directed towards a region of a sample in proximity to a probe of the probe microscope;
b) a PM probe response detection system that measures a signal indicative of a response of the probe of the probe microscope to radiation incident on the sample;
c) a demodulation system that decomposes the signal indicative of the probe response at a plurality of PM probe oscillation frequencies into a background component and probe proximity component;
d) a computation system that applies an algorithm to combine the probe proximity component response at the plurality of PM probe oscillation frequencies to calculate spectroscopic information about the sub-micron region of the sample.

22. The apparatus of claim 21 wherein the source of radiation emits infrared radiation including at least a portion emitted within a wavelength range between 2.5 to 15 μm.

23. The apparatus of claim 21 wherein the source of radiation comprises at least one of an optical parametric oscillator, and a quantum cascade laser.

24. The apparatus of claim 21 wherein the source of radiation comprises at least one of broadband laser, a super continuum laser, a femtosecond laser, a frequency comb laser, and a thermal source.

Assignees

• Bruker Nano Inc

Inventors

• Prater Craig
• Kjoller Kevin
• Gotthard Doug
• Hu Qichi

Classifications

• G01Q60/32

  AC mode · CPC title

• G01N21/35 Primary

  using infrared light (G01N21/39 takes precedence) · CPC title

• G01Q60/363

  Contact-mode AFM · CPC title

• G01Q30/02 Primary

  Non-SPM analysing devices, e.g. SEM [Scanning Electron Microscope], spectrometer or optical microscope · CPC title