Multiple Frequency Atomic Force Microscopy

• US 20100043107A1
• Filed: 10/20/2009
• Published: 02/18/2010
• Est. Priority Date: 04/25/2006
• Status: Active Grant

• Current Assignee: Oxford Instruments Afm Inc
• Original Assignee: Asylum Research Corporation (Oxford Instruments PLC)
• Inventors: Proksch, Roger B.
• Granted Patent: US 8,448,501 B2
• Time in Patent Office: Days
• US Class Current: 850/40
• CPC Class Codes: B82Y 35/00 Methods or apparatus for measurement or analysis of nanostructures
• 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

An apparatus and technique for extracting information carried in higher eigenmodes or harmonics of an oscillating cantilever or other oscillating sensors in atomic force microscopy and related MEMs work is described.

Claims

1. A method of operating an atomic force microscope to determine voltage:

dependent properties of a sample, comprising;

exciting a probe tip of a cantilever at a first frequency, using a first frequency source driving a first actuator for the cantilever;

using a second frequency source at a second frequency to vary a potential of the cantilever relative to the sample;

detecting cantilever response information to the sample at both values related to said first frequency and said second frequency.

2. A method as in claim 1, wherein said second frequency varies a voltage on the cantilever relative to the sample.

3. A method as in claim 2, further comprising grounding said sample.

4. A method as in claim 1, wherein said cantilever is driven to avoid touching the sample.

5. A method as in claim 1, wherein said cantilever response information includes values at said first and/or second frequencies or harmonics thereof.

6. A method as in claim 1, wherein said detecting comprises measuring the amplitude and phase of the first and second eigenmodes of the cantilever as measured characteristics of the sample.

7. A method as in claim 1, wherein said exciting comprises exciting that cantilever at or near a flexural resonance thereof.

8. A method as in claim 1, wherein said detecting comprises measuring the an amplitude of the cantilever at the first frequency as an error signal, and measuring information at said second frequency or a harmonic thereof to represent voltage dependent properties of the sample.

9. A method of operating an atomic force microscope to determine magnetic dependent properties of a sample, comprising:

exciting a probe tip of a cantilever at a first frequency, using a first frequency source driving a first actuator for the cantilever;

using a second frequency source at a second frequency different than said first frequency to vary a magnetic field according to a frequency of said second frequency source, in an area of the sample; and

detecting cantilever response information to the sample at both values related to said first frequency and said second frequency.

10. A method as in claim 9, wherein said magnetic field is created on a sample holder that holds the sample.

11. A method as in claim 9, wherein said magnetic field is created near the sample.

12. A method as in claim 9, wherein said magnetic field is created by the sample.

13. A method as in claim 9, wherein said cantilever is driven to avoid touching the sample.

14. A method as in claim 9, wherein said cantilever response information includes values at said first and/or second frequencies or harmonics thereof.

15. A method as in claim 9, wherein said detecting comprises measuring a amplitude and phase of the first and second eigenmodes of the cantilever as measured characteristics of the sample.

16. A method as in claim 9, wherein said exciting comprises exciting that cantilever at or near a flexural resonance thereof.

17. A method as in claim 9, wherein said detecting comprises measuring the an amplitude of the cantilever at the first frequency as an error signal, and measuring information at said second frequency or a harmonic thereof to represent voltage dependent properties of the sample.

18. A method of determining both topographic and material dependent properties of a sample, comprising:

exciting a probe tip of a cantilever at a first frequency near a flexural resonance thereof, using a first frequency source driving a first actuator at the first frequency, to drive the cantilever at said first frequency;

using a second frequency source at a second frequency different than the first frequency, to vary a characteristic of the sample at said second frequency;

detecting cantilever response information to the sample at both values related to said first frequency and said second frequency; and

using said cantilever response information to determine both topographic information about a surface of the sample, and simultaneously to determine material characteristic about the sample.

19. A method as in claim 18, wherein said second frequency varies a voltage on the cantilever relative to the sample.

20. A method as in claim 19, further comprising grounding said sample.

21. A method as in claim 18, wherein said second frequency varies a magnetic field on the sample.

22. A method as in claim 18, wherein said cantilever is driven to avoid touching the sample.

23. A method as in claim 18, wherein said cantilever response information includes values at said first and/or second frequencies or harmonics thereof.

24. A method as in claim 18, wherein said detecting comprises measuring the amplitude and phase of the first and second eigenmodes of the cantilever as measured characteristics of the sample.

25. A method as in claim 18, wherein said second frequency varies an ultrasonic field on the sample.

26. A method as in claim 25, further comprising using said cantilever as a waveguide for an ultrasonic field.

27. An atomic force microscope, comprising:

a sample holder, with a surface that holds a sample;

a cantilever, having a probe tip that is located near said surface;

a first actuator, which drives the cantilever to move a location of the cantilever;

a first frequency source driving said first actuator, to drive the cantilever at said first frequency;

a potential device, located to vary a potential of the cantilever relative to the sample;

a second frequency source at a second frequency different than the first frequency, varying said potential according to said second frequency; and

an AFM detector, detecting cantilever response information to the sample at both values related to said first frequency and said second frequency, said AFM detector producing output information representing both surface topography of said sample, and also voltage dependent properties of said sample.

28. A microscope as in claim 27, further comprising a connection grounding said sample holder.

29. A microscope as in claim 27, wherein said actuator drives said cantilever to avoid touching the sample.

30. A microscope as in claim 27, wherein said cantilever response information includes values at said first and/or second frequencies or harmonics thereof.

31. A microscope as in claim 27, wherein said detecting comprises measuring the amplitude and phase of the first and second eigenmodes of the cantilever as measured characteristics of the sample.

32. A microscope as in claim 27, wherein said detecting comprises measuring an amplitude of the cantilever at said first frequency as an error signal, and measuring information at said second frequency

or a harmonic thereof to represent voltage dependent properties of the sample.

33. An atomic force microscope, comprising:

a sample holder, with a surface that holds a sample;

a cantilever, having a probe tip that is located near said surface;

a first actuator, which drives the cantilever to move a location of the cantilever;

a first frequency source driving said first actuator, to drive the cantilever at said first frequency;

a magnetic field creation device, located to vary a magnetic field exposed to the sample;

a second frequency source at a second frequency different than the first frequency, varying said magnetic field according to said second frequency; and

an AFM detector, detecting cantilever response information to the sample at both values related to said first frequency and said second frequency, said AFM detector producing output information representing both surface topography of said sample, and also magnetic field dependent properties of said sample.

34. A microscope as in claim 33, wherein said magnetic field is created on said sample holder.

35. A microscope as in claim 33, wherein said magnetic field is created near the sample.

36. A microscope as in claim 33, wherein said magnetic field is created by the sample.

37. A microscope as in claim 33, wherein said first actuator drives said cantilever to avoid touching the sample.

38. A microscope as in claim 33, wherein said cantilever response information includes values at said first and/or second frequencies or harmonics thereof.

39. A microscope as in claim 33, wherein said detecting comprises measuring an amplitude of the cantilever at the first frequency as an error signal, and measuring information at said second frequency or a harmonic thereof to represent voltage dependent properties of the sample.