Surface Sensitive Atomic Force Microscope Based Infrared Spectroscopy

Patent metadata

Field	Value
Publication number	US-2020217874-A1
Application number	US-201816628908-A
Country	US
Kind code	A1
Filing date	Jul 9, 2018
Priority date	Jul 6, 2017
Publication date	Jul 9, 2020
Grant date	—

Abstract

System and Methods may be provided for performing chemical spectroscopy on samples from the scale of nanometers with surface sensitivity even on very thick sample. In the method, a signal indicative of infrared absorption of the surface layer is constructed by illuminating the surface layer with a beam of infrared radiation and measuring a probe response comprising at least one of a resonance frequency shift and a phase shift of a resonance of a probe in response to infrared radiation absorbed by the surface layer.

First claim

1 . A method of obtaining a signal indicative of an infrared absorption spectrum of a thin surface layer of a sample with a probe of a scanning probe microscope, comprising the steps of:
a. Interacting the probe with a surface layer of the sample; b. Illuminating the surface layer with a beam of infrared radiation; c. Measuring a probe response comprising at least one of a resonance frequency shift and a phase shift of a resonance of the probe in response to infrared radiation absorbed by the surface layer; d. Measuring the probe response at a plurality of wavelengths of the infrared radiation; e. Constructing a signal indicative of infrared absorption of the surface layer.

2 . The method of claim 1 wherein the surface layer is disposed on a substrate that also absorbs IR radiation over the plurality of wavelengths.

3 . The method of claim 2 wherein the substrate is at least 10× thicker than the surface layer.

4 . The method of claim 2 wherein the substrate is at least 100× thicker than the surface layer.

5 . The method of claim 2 wherein the substrate is at least 800× thicker than the surface layer.

6 . The method of claim 2 wherein the signal indicative of the IR absorption of the surface layer is at least 5× stronger than residual absorption bands from the substrate.

7 . The method of claim 2 wherein residual absorption peaks from the substrate that appear in the signal indicative of the IR absorption of the surface layer are at least 8× smaller than absorption peaks measured on bare substrate without the surface layer.

8 . The method of claim 1 wherein the probe is oscillated at a frequency wherein there is a substantially maximum slope of probe oscillation phase with resonance frequency shift.

9 . The method of claim 1 wherein the measuring probe response step comprises oscillating the probe at or near a resonance of the probe with a piezoelectric actuator.

10 . The method of claim 1 wherein the measuring probe response step comprises modulating the probe at or near a resonance of the probe with an actuator comprising at least one of: an electrostatic drive, a magnetic drive, an acoustic drive, an ultrasonic drive, a photothermal drive, a bimetallic drive, and joule heating thermal drive.

11 . The method of claim 1 further comprising the step of linearizing the signal indicative of infrared absorption of the surface layer.

12 . The method of claim 12 wherein the linearizing step comprises compensating for at least one of: nonlinear dependence of sample elasticity with temperature, nonlinear dependence of probe resonant frequency with sample elasticity, and nonlinear dependence of probe oscillation phase with resonance frequency shift.

13 . The method of claim 12 wherein the linearizing step comprises measuring a probe response as a function of power of the beam of infrared radiation to create a linearization function.

14 . The method of claim 14 wherein measuring probe response as a function of IR beam power is used to infer a relationship between probe response and sample temperature rise.

15 . The method of claim 14 comprising the step of scaling the probe response at a plurality of wavelengths by the linearization function.

16 . The method of claim 1 wherein the measuring probe response step comprises modulating an intensity of the beam of infrared radiation to induce an oscillatory response of the probe at or near a resonance of the probe.

17 . A scanning probe microscope (SPM) for measuring an infrared absorption spectrum of a sample with a probe, the SPM comprising:
an oscillation drive to drive the probe to interact with a surface layer of the sample; an infrared radiation source to illuminate the surface layer with a beam of infrared radiation; a detector that measures a response of the surface layer to the beam of IR radiation with the probe, wherein the detector measures at least one of a resonance frequency shift and a phase shift of a resonance of the probe, and wherein the detector measures the response at a plurality of wavelengths of the infrared radiation; and a controller that constructs a signal indicative of infrared absorption of the surface layer.

18 . The SPM of claim 17 wherein the oscillation drive drives the probe at a frequency so that there is a substantially maximum slope of probe oscillation phase with resonance frequency shift.

19 . The SPM of claim 17 wherein the surface layer is disposed on a substrate that also absorbs IR radiation over the plurality of wavelengths.

20 . The SPM of claim 17 , wherein the signal indicative of the IR absorption of the surface layer is at least 5× stronger than residual absorption bands from the substrate.

Assignees

• Bruker Nano Inc

Inventors

• Kjoller Kevin
• Prater Craig

Classifications

• G01Q60/32 Primary

  AC mode · CPC title

• G01Q60/58

  SThM [Scanning Thermal Microscopy] or apparatus therefor, e.g. SThM probes · CPC title

• G01Q30/04

  Display or data processing devices · CPC title

• G01N21/359

  using near infrared light · CPC title

• G01N21/3563

  for analysing solids; Preparation of samples therefor · CPC title