Force measurement with real-time baseline determination

Patent metadata

Field	Value
Publication number	US-9575090-B2
Application number	US-201414563826-A
Country	US
Kind code	B2
Filing date	Dec 8, 2014
Priority date	Dec 7, 2013
Publication date	Feb 21, 2017
Grant date	Feb 21, 2017

Abstract

An atomic force microscope (AFM) and corresponding method to provide low force (sub-20 pN) AFM control and mechanical property measurement is provided. The preferred embodiments employ real-time false deflection correction/discrimination by adaptively modifying the drive ramp to accommodate to deflection artifacts.

First claim

The invention claimed is:

1. A method of detecting a force between a sample and a probe of an AFM, the method comprising:
positioning at least one of the probe and the sample at a location of interest of the sample;
moving at least one of the probe and the sample to lessen a separation therebetween and cause the two to interact;
measuring a deflection of the probe based on the moving step;
discriminating a deflection artifact from a deflection due to probe-sample interaction from the measured deflection data by continuously identifying a baseline during the moving step to derive an artifact free deflection and compare it with a predefined trigger force;
retracting the probe from the sample if the artifact free deflection substantially corresponds to the trigger force; and
determining the force between the sample and the probe, wherein the force is less than 20 pN.

2. The method of claim 1 , further comprising using the force as a trigger to change a parameter associated with the moving step.

3. The method of claim 2 , wherein the parameter is at least one of a speed, a direction and a force gradient.

4. The method of claim 1 , wherein the discriminating step includes comparing a drive ramp to a fit line based on data corresponding to the deflection, and further comprising extrapolating the baseline based on the comparison.

5. The method of claim 4 , wherein the fit line is determined by performing a least squares fit.

6. The method of claim 5 , further comprising repeating the comparing and extrapolating steps so as to provide a rolling baseline until a threshold trigger is met.

7. A method of detecting a force between a sample and a probe of an AFM, the method comprising:
positioning at least one of the probe and the sample at a location of interest of the sample;
moving at least one of the probe and the sample to lessen a separation therebetween and cause the two to interact;
measuring a deflection of the probe based on the moving step; and
using the measured deflection, in real time during the moving step, to determine an instantaneous baseline.

8. A method of detecting an observable interaction between a sample and a probe of an AFM, the method comprising:
positioning at least one of the probe and the sample at a location of interest of the sample;
moving at least one of the probe and the sample to lessen a separation therebetween and cause the two to interact;
measuring an observable interaction based on the moving step;
determining an observable interaction artifact from an observable interaction due to actual probe-sample interaction during the measuring step to derive an artifact free observable interaction and compare with a trigger;
retracting the probe from the sample if the artifact free observable interaction substantially corresponds to the trigger.

9. The method of claim 8 , wherein the observable interaction includes at least one of a group including: force, deflection, electric interaction (e.g., force, current, voltage), magnetic interaction, thermal interaction and electromagnetic interaction (e.g., scattering near field optical signals).

Assignees

• Bruker Nano Inc

Inventors

• Liu Changchun
• Pittenger Bede
• Hu Shuiqing
• Su Chanmin

Classifications

• G01Q10/06

  Circuits or algorithms therefor · CPC title

• G01Q30/06 Primary

  for error compensation · CPC title

• G01Q10/065 Primary

  Feedback mechanisms, i.e. wherein the signal for driving the probe is modified by a signal coming from the probe itself · CPC title