Method and apparatus of operating a scanning probe microscope

Patent metadata

Field	Value
Publication number	US-9274139-B2
Application number	US-201414172710-A
Country	US
Kind code	B2
Filing date	Feb 4, 2014
Priority date	Nov 13, 2008
Publication date	Mar 1, 2016
Grant date	Mar 1, 2016

Abstract

Methods and apparatuses are provided for automatically controlling and stabilizing aspects of a scanning probe microscope (SPM), such as an atomic force microscope (AFM), using Peak Force Tapping (PFT) Mode. In an embodiment, a controller automatically controls periodic motion of a probe relative to a sample in response to a substantially instantaneous force determined, and automatically controls a gain in a feedback loop. A gain control circuit automatically tunes a gain based on separation distances between a probe and a sample to facilitate stability. Accordingly, instability onset is quickly and accurately determined during scanning, thereby eliminating the need of expert user tuning of gains during operation.

First claim

We claim:

1. A scanning probe microscope (SPM) comprising:
a probe for moving in a periodic motion relative to a sample;
a position detector for detecting a motion of the probe;
a PFT mode force detection block for determining a substantially instantaneous force between the probe and the sample from the detected motion of the probe;
a controller for automatically controlling the periodic motion of the probe relative to the sample, in response to the substantially instantaneous force, by maintaining a feedback setpoint; and
wherein the controller automatically controls a gain in a corresponding feedback loop.

2. The SPM of claim 1 , further including a block for automatically controlling Z-limit.

3. The SPM of claim 1 , wherein the controller provides relative scanning motion between the probe and the sample and automatically controls a scan rate.

4. The SPM of claim 1 , wherein the feedback setpoint is a preset instantaneous force, and the controller automatically optimizes the preset instantaneous force.

5. The SPM of claim 1 , wherein the periodic motion is a relative oscillatory motion between the probe and the sample, and wherein the instantaneous force is determined prior to the completion of one cycle of the oscillatory motion.

6. The SPM of claim 1 , wherein the instantaneous force is a repulsive force.

7. The SPM of claim 1 , wherein a minimum controllable force corresponding to the instantaneous force is less than about 1 nN.

8. The SPM of claim 7 , wherein the minimum controllable force is less than about 10 pN.

9. The SPM of claim 7 , wherein the detected motion of the probe is synchronously averaged to reduce the minimum controllable force.

10. A gain control circuit for stabilizing an (SPM) comprising:
a distance detector for sampling a separation distance between a probe and a sample, wherein sampling occurs at a position corresponding to a peak force during an oscillation period between the probe and the sample;
an oscillation detector for detecting an amount of instability oscillation between separation distances; and
a gain controller configured to adjust a gain value by an increment if the amount of instability oscillation between separation distances exceeds a predetermined threshold.

11. The gain control circuit of claim 10 , wherein the increment is at least 5% of the gain value.

12. The gain control circuit of claim 10 , wherein the predetermined threshold is less than 1 nm.

13. The gain control circuit of claim 10 , wherein the gain value corresponds to an Integral (I) gain and a Proportional (P) gain.

14. The gain control circuit of claim 10 , wherein the gain value is adjusted upon changing an imaging location.

15. The gain control circuit of claim 10 , wherein the gain value controls a Z piezo for controlling the separation distance.

16. A method for stabilizing an (SPM) comprising:
receiving a plurality of separation distances between a probe and a sample, wherein the separation distances reflect a position corresponding to a peak force during an oscillation period between the probe and the sample;
detecting an amount of instability oscillation between separation distances; and
adjusting a gain value by an increment if the amount of instability oscillation between separation distances exceeds a predetermined threshold.

17. The method of claim 16 , further comprising adjusting the predetermined threshold based on roughness of the sample.

18. The method of claim 16 , wherein the separation distances reflect peak force positions of at least three adjacent force curves.

19. The method of claim 16 , further comprising determining a moving average based on separation distances.

20. The method of claim 19 , further comprising comparing a separation distance to the moving average.

Assignees

• Bruker Nano Inc

Inventors

• Shi Jian
• Hu Yan
• Hu Shuiqing
• Ma Ji
• Su Chanmin

Classifications

• G01B21/20

  for measuring contours or curvatures, e.g. determining profile · CPC title

• G01Q60/34

  Tapping mode · CPC title

• G01Q60/00

  Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof · CPC title

• G01Q60/32

  AC mode · CPC title

• G01Q60/24 Primary

  AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes · CPC title