Method and apparatus for resolution and sensitivity enhanced atomic force microscope based infrared spectroscopy
Methods and apparatus for obtaining extremely high sensitivity chemical composition maps with spatial resolution down to a few nanometers. In some embodiments these chemical composition maps are created using a combination of three techniques: (1) Illuminating the sample with IR radiation than is tuned to an absorption band in the sample; and (2) Optimizing a mechanical coupling efficiency that is tuned to a specific target material; (3) Optimizing a resonant detection that is tuned to a specific target material. With the combination of these steps it is possible to obtain (1) Chemical composition maps based on unique IR absorption; (2) spatial resolution that is enhanced by extremely short-range tip-sample interactions; and (3) resonant amplification tuned to a specific target material. In other embodiments it is possible to take advantage of any two of these steps and still achieve a substantial improvement in spatial resolution and/or sensitivity.
1. A method of mapping a surface of a heterogeneous sample with a probe of a scanning probe microscope, comprising the steps of:
a. Oscillating the probe at a first frequency f 1 ;
b. Interacting the probe with a first region of the sample;
c. Illuminating the sample with a beam of infrared radiation;
d. Modulating the beam of infrared radiation at frequency f m such that a resulting sideband frequency f sb is substantially equal to a resonance of the probe while interacting with a sample material at the first region;
e. Measuring a probe response at the first region of the sample at the sideband frequency due to infrared radiation incident on the sample;
f. Moving the probe to interact with a second region of a sample resulting in a shift in a resonance of the probe;
g. Retuning the modulation frequency f m resulting in a shifted sideband frequency that is substantially equal to the shifted probe resonance;
h. Measuring a probe response at the shifted sideband frequency on the second region due to infrared radiation incident on the sample; and
i. Creating a compositional map of the sample based on the measured probe responses, wherein the compositional map has a spatial resolution of <10 nm.
2. The method of claim 1 further comprising the step of adjusting probe interaction parameters to substantially maximize a contrast between the probe responses on the first and second regions.
3. The method of claim 1 wherein the step of retuning the modulation frequency is performed automatically.
4. The method of claim 1 further comprising the step of measuring a phase of oscillation of the probe while the probe is in interaction with the sample region.
5. The method of claim 4 further comprising the step of using the phase measurement to adjust the radiation modulation frequency f m .
6. The method of claim 4 further comprising the step of adjusting a parameter of probe interaction to substantially maximize a contrast in the phase measurement between two or more material components in the sample.
7. The method of claim 1 wherein the frequency f 1 substantially corresponds to a probe resonance.
8. The method of claim 1 wherein the sample region is immersed in a liquid.
9. A method of mapping a surface of a heterogeneous sample, the method comprising the steps of:
a. Oscillating the probe at a first frequency f 1 ;
b. Interacting a probe of a probe microscope with a first region of the sample;
c. Illuminating the sample with a beam of infrared radiation;
d. Modulating the beam of infrared radiation at frequency f m such that a resulting sideband frequency f sb is substantially equal to a resonance of the probe while interacting with a sample material at the first region;
e. Measuring a probe response to infrared radiation incident on the first region of the sample at the sideband frequency;
f. Moving the probe to interacting with a second region of a sample;
g. Retuning the modulation frequency f m resulting in a shifted sideband frequency that is substantially equal to a resonance of the probe while interacting with a sample material at the second region of the sample;
h. Measuring a probe response to infrared radiation incident on the second region of the sample at the shifted sideband frequency; and
i. Creating a compositional map of the sample based on the measured probe responses, wherein the compositional map has a spatial resolution of <10 nm.
10. A method of mapping a surface of a heterogeneous sample with a probe of a scanning probe microscope, comprising the steps of:
a. Oscillating the probe at a first frequency f 1 ;
b. Interacting the probe with a first region of the sample;
c. Illuminating the sample with a beam of infrared radiation;
d. Modulating the beam of infrared radiation at frequency f m such that a resulting sideband frequency f sb is substantially equal to a resonance of the probe while interacting with a sample material at the first region;
e. Measuring a probe response at the first region of the sample at the sideband frequency due to infrared radiation incident on the sample;
f. Moving the probe to interact with a second region of a sample resulting in a shift in a resonance of the probe;
g. Retuning the modulation frequency f m resulting in a shifted sideband frequency that is substantially equal to the shifted probe resonance;
h. Measuring a probe response at the shifted sideband frequency on the second region due to infrared radiation incident on the sample;
i. Measuring a phase of oscillation of the probe while the probe is in interaction with the sample region; and
j. Adjusting a parameter of probe interaction to substantially maximize a contrast in the phase measurement between two or more material components in the sample.
11. The method of claim 10 further comprising the step of creating a compositional map of the sample based on the measured probe responses.
12. The method of claim 11 wherein the compositional map has a spatial resolution of <10 nm.
13. The method of claim 10 further comprising the step of adjusting probe interaction parameters to substantially maximize a contrast between the probe responses on the first and second regions.
14. The method of claim 10 wherein the step of retuning the modulation frequency is performed automatically.
15. The method of claim 10 further comprising the step of using the phase measurement to adjust the radiation modulation frequency f m .
16. The method of claim 10 wherein the frequency f 1 substantially corresponds to a probe resonance.
17. The method of claim 10 wherein the sample region is immersed in a liquid.