High speed adaptive-multi-loop mode imaging atomic force microscopy

Patent metadata

Field	Value
Publication number	US-10041970-B2
Application number	US-201515326237-A
Country	US
Kind code	B2
Filing date	Jul 14, 2015
Priority date	Jul 14, 2014
Publication date	Aug 7, 2018
Grant date	Aug 7, 2018

Abstract

A method for imaging a sample using a high speed dynamic mode atomic force microscope may include scanning a tip of a cantilever probe over a surface of the sample, regulating a vibration amplitude of the tip to remain constant at a set point value (Aset), via a first signal generated in a first feedback controller, measuring a mean tapping deflection of the tip, regulating the mean tapping deflection via a second signal generated in a second feedback controller, tracking and measuring an adjustment to the measured mean tapping deflection during the regulating. The method may further include generating an image topography of the sample based on the first signal, the second signal, and the measured adjustment of the mean tapping deflection of the cantilever probe.

First claim

The invention claimed is:

1. A method of imaging a sample using a high speed dynamic mode atomic force microscope, wherein the method comprises:
scanning a tip of a cantilever probe over a surface of the sample;
regulating a vibration amplitude of the tip to remain constant at a set point value (A set ), via a first signal generated in a first feedback controller;
measuring a mean tapping deflection of the tip;
regulating the mean tapping deflection via a second signal generated in a second feedback controller;
tracking and measuring an adjustment to the measured mean tapping deflection during the regulating; and
generating an image topography of the sample based on the first signal, the second signal, and the measured adjustment of the mean tapping deflection of the cantilever probe.

2. The method of claim 1 , wherein the high-speed dynamic mode atomic force microscopy comprises one or more of the following: tapping mode, non-contact mode, and peak force tapping mode.

3. The method of claim 1 , wherein regulating the mean tapping deflection comprises:
determining a desired mean deflection using a ratio of A set and a free amplitude; and
adjusting the measured mean tapping deflection to the desired mean deflection.

4. The method of claim 3 , wherein the desired mean deflection is determined such that the ratio of A set and the free amplitude is from about 10%-30%.

5. The method of claim 1 , wherein the second feedback controller comprises an inner-outer feedback loop structure, wherein an outer feedback loop regulates the mean tapping deflection, and an inner loop nested within the outer loop performs the tracking and measuring of the adjustment to the measured mean tapping deflection during the regulating.

6. The method of claim 5 , wherein the outer feedback loop is a proportional integral derivative (PID)-type controller having PID parameters K P , K I , and K D .

7. The method of claim 6 , wherein the PID-type controller employs the following algorithm:
d TM-set ( j+ 1)= k I d TM-set ( j )+ k P e TM ( j )+ k D [e TM ( j− 1)− e TM ( j )]

for e TM ( j )= d TM-d −d TM ( j ), and j= 2 . . . N− 1,
where:
N is total number of sampling periods per image;
d TM-d is desired mean deflection;
d TM (j) is mean deflection of the current sampling point; and
K P , K I and K D are the PID parameters.

8. The method of claim 7 , wherein the PID parameters have the following values: K P =1, K I =1, and K D =ρ, and wherein ρ is a sample point-to-point gradient factor.

9. The method of claim 8 , wherein ρ<1.

10. The method of claim 6 , wherein the PID-type controller employs the following algorithm:
d set,0 =d set,org ,
d set,k+1 =d set,k −[min( {circumflex over (d)} k+1 ( t ))− D* min ], k≥ 1

with {circumflex over (d)} k+1 ( t ) d k ( t )+ρ[( d k ( t )− d k−1 ( t ))], for tϵ[ 0, T scan ],

where:
d set,0 is deflection set-point on the first scanline;
d set,k is deflection set-point on the k th scanline;
d k+1 (t) is minimum of the predicted detection at the k+1 th scanline;
D* min is minimum deflection/force needed to maintain the stable repulsive tip-sample interaction;
T scan is scanning period;
d set,org is original deflection set-point chosen a priori to the imaging process; and
ρϵ[0,1] is gradient factor which can be tuned to improve the imaging quality.

11. The method of claim 1 , further comprising optimizing A set online based on a real time relationship between the measured mean deflection and vibration amplitude ratio of the A set and a free amplitude.

12. The method of claim 11 , further comprising predicting a next-line sample topography and a next-line tracking error for tracking of the mean tapping deflection adjustment, via a third feedback controller.

13. The method of claim 12 , wherein the third feedback controller is a feedforward controller comprising a data-driven iterative learning controller.

14. The method of claim 13 , wherein the feedforward controller implements the following algorithm to obtain a control input:

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Assignees

• Univ Rutgers

Inventors

• Zou Qingze
• Ren Juan
• Liu Jiangbo

Classifications

• 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

• G01Q60/34

  Tapping mode · CPC title