AM/FM MEASUREMENTS USING MULTIPLE FREQUENCY ATOMIC FORCE MICROSCOPY

• US 20180292432A1
• Filed: 12/11/2017
• Published: 10/11/2018
• Est. Priority Date: 04/23/2014
• Status: Active Grant

• Current Assignee: Oxford Instruments Asylum Research Inc (Oxford Instruments PLC)
• Original Assignee: Oxford Instruments Asylum Research Inc (Oxford Instruments PLC)
• Inventors: Proksch, Roger, Bemis, Jason, Labuda, Aleksander
• Granted Patent: US 10,444,258 B2
• Time in Patent Office: Days
• CPC Class Codes: G01Q 10/04 Fine scanning or positioning
• CPC Class Codes: G01Q 20/00 Monitoring the movement or position of the probe
• CPC Class Codes: G01Q 40/00 Calibration, e.g. of probes
• CPC Class Codes: G01Q 60/24 AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
• CPC Class Codes: G01Q 60/32 AC mode

Abstract

Apparatus and techniques presented combine the features and benefits of amplitude modulated (AM) atomic force microscopy (AFM), sometimes called AC mode AFM, with frequency modulated (FM) AFM. In AM-FM imaging, the topographic feedback from the first resonant drive frequency operates in AM mode while the phase feedback from second resonant drive frequency operates in FM mode. In particular the first or second frequency may be used to measure the loss tangent, a dimensionless parameter which measures the ratio of energy dissipated to energy stored in a cycle of deformation.

Claims

1. An atomic force microscope system, comprising:

a cantilever having a tip at one end and a driving part at its other end;

a cantilever position detector which detects a position of the cantilever;

a positioning system for controlling a position of the cantilever relative to a sample, the positioning system having a controller receiving feedback from the position detector, and producing outputs that drive movement of the cantilever,

the positioning system driving the cantilever at or near two or more eigenmodes of the cantilever,

where the positioning system operating by;

first operating by exciting the probe tip at a first eigenmode frequency and a first amplitude, and using the feedback to controls the distance between the base of the cantilever and the sample surface to maintain said distance,

exciting a second eigenmode frequency of the cantilever at a second amplitude different than the first amplitude, where at the second amplitude the cantilever eigenmode is interacting with predominantly repulsive forces to the surface,

determining amplitude and phase of the first eigenmode and of the second eigenmode, and using said amplitude and phase of the first eigenmode and of the second eigenmode to characterize the surface.

2. The system as in claim 1, wherein said positioning system keeps phase constant at a substantially constant value at the second eigenmode.

3. The system as in claim 1, wherein the first eigenmode cause the tip and sample to interact in attractive mode, and the second eigenmode is in a state where the tip-sample interactions cause it to be in both the attractive and the repulsive modes as it is positioned relative to the surface.

4. The system as in claim 1, wherein the first eigenmode is in an attractive mode and the second eigenmode is in a repulsive mode.

5. The system as in claim 1, wherein the first eigenmode interacts with the surface in the attractive mode before the second eigenmode is excited, and after the second eigenmode is excited, the first eigenmode is in a repulsive mode.

6. The system as in claim 5, wherein the change from attractive to repulsive is induced by addition of the second eigenmode energy and where the second eigenmode is in a state where the tip-sample interactions cause it to be at least one of attractive and repulsive.

7. The system as in claim 1, wherein the first eigenmode is in a repulsive mode and the second mode is in a repulsive mode.

8. The system as in claim 1, wherein at least one of the first and/or second eigenmode sare a cantilever resonant frequency.

9. The system as in claim 1, wherein said Cantilever position detector includes a photodetector.

10. A method of operating an atomic force microscope system, comprising:

driving a cantilever to different movement positions, the cantilever having a tip at one end and a driving part at its other end;

detecting a position of the cantilever;

controlling said driving for controlling a position of the cantilever relative to a sample,

receiving feedback from the position detector, and producing outputs that drive movement of the cantilever,

said driving the cantilever comprising driving the cantilever at or near two or more eigenmodes of the cantilever,

first exciting the probe tip at a first eigenmode frequency and a first amplitude, and using the feedback to controls the distance between the base of the cantilever and the sample surface to maintain said distance,

second exciting a second eigenmode frequency of the cantilever at a second amplitude different than the first amplitude, where at the second amplitude the cantilever eigenmode is interacting with predominantly repulsive forces to the surface, and

determining amplitude and phase of the first eigenmode and of the second eigenmode, and using said amplitude and phase of the first eigenmode and of the second eigenmode to characterize the surface.

11. The method as in claim 10, wherein said positioning system keeps phase constant at a substantially constant value at the second eigenmode.

12. The method as in claim 10, wherein the first eigenmode causes the tip and sample to interact in attractive mode, and the second eigenmode is in a state where the tip-sample interactions cause it to be in both the attractive and the repulsive modes as it is positioned relative to the surface.

13. The method as in claim 10, wherein the first eigenmode interacts with the surface in the attractive mode before the second eigenmode is excited, and after the second eigenmode is excited, the first eigenmode is in a repulsive mode.

14. The method as in claim 10, wherein the first eigenmode is in a repulsive mode and the second mode is in a repulsive mode.