Liquid cell and passivated probe for atomic force microscopy and chemical sensing

• US 20050199047A1
• Filed: 03/10/2004
• Published: 09/15/2005
• Est. Priority Date: 03/11/2003
• Status: Active Grant

• Current Assignee: Board of Regents Nevada System of Higher Education (State of Nevada)
• Original Assignee: Benjamin S. Rogers, Jesse D. Adams, Todd A. Sulchek
• Inventors: Adams, Jesse D., Sulchek, Todd A., Rogers, Benjamin S.
• Granted Patent: US 7,260,980 B2
• Time in Patent Office: Days
• US Class Current: 73/105
• CPC Class Codes: B82Y 35/00 Methods or apparatus for measurement or analysis of nanostructures
• CPC Class Codes: G01Q 30/14 Liquid environment
• CPC Class Codes: G01Q 60/42 Functionalisation

Abstract

The invention provides a liquid cell for an atomic force microscope. The liquid cell includes a liquid cell housing with an internal cavity to contain a fluid, a plurality of conductive feedthroughs traversing the liquid cell housing between the internal cavity and a dry side of the liquid cell, a cantilevered probe coupled to the liquid cell housing, and a piezoelectric drive element disposed on the cantilevered probe. The cantilevered probe is actuated when a drive voltage is applied to the piezoelectric drive element through at least one of the conductive feedthroughs. A method of imaging an object in a liquid medium and a method of sensing a target species with the liquid cell are also disclosed.

Claims

1. A liquid cell for an atomic force microscope, the liquid cell comprising:

a liquid cell housing, the liquid cell housing including an internal cavity to contain a fluid;

a plurality of conductive feedthroughs traversing the liquid cell housing between the internal cavity and a dry side of the liquid cell;

a cantilevered probe coupled to the liquid cell housing, wherein at least a portion of the cantilevered probe is located inside the internal cavity; and

a piezoelectric drive element disposed on the cantilevered probe;

wherein the cantilevered probe is actuated when a drive voltage is applied to the piezoelectric drive element through at least one of the conductive feedthroughs.

2. The liquid cell of claim 1 wherein the liquid cell housing comprises a material selected from the group consisting of an acrylic, polymethyl methacrylate, glass, quartz, a thermoplastic polymer, a thermoset polymer, an insulating material, and a transparent material.

3. The liquid cell of claim 1 wherein the cantilevered probe comprises a material selected from the group consisting of silicon, polysilicon, silicon nitride, a metal film, a metal sheet, a zinc oxide film, a lead zirconate titanate film, silicon dioxide, a polymeric layer, and a combination thereof.

4. The liquid cell of claim 1 wherein the piezoelectric drive element comprises a material selected from the group consisting of zinc oxide, lead zirconate titanate, polyvinylidene fluoride, and a piezoelectric film.

5. The liquid cell of claim 1 further comprising:

an optical window in the liquid cell housing, wherein a beam of light traverses the optical window to optically monitor the cantilevered probe.

6. The liquid cell of claim 1 further comprising:

an inlet port connected between the internal cavity and the dry side of the liquid cell, wherein the fluid is injected into the internal cavity of the liquid cell housing.

7. The liquid cell of claim 1 further comprising:

a passivation layer disposed onto the piezoelectric drive element, wherein the piezoelectric drive element is electrically isolated when a conductive fluid is placed in the internal cavity of the liquid cell housing.

8. The liquid cell of claim 7, wherein the passivation layer comprises a material selected from the group consisting of silicon nitride, silicon dioxide, parylene, Teflon, an insulating polymer, and an insulating material.

9. The liquid cell of claim 1 further comprising:

an atomic probe tip coupled to a free end of the cantilevered probe.

10. The liquid cell of claim 1 further comprising:

a piezoresistive sense element coupled to the cantilevered probe, wherein a bending of the cantilevered probe is sensed by the piezoresistive sense element.

11. The liquid cell of claim 1 further comprising:

a treated section coupled to the cantilevered probe, wherein the treated section causes one of a deflection of the cantilevered probe or a shift in a resonant frequency of the cantilevered probe when exposed to a target species.

12. The liquid cell of claim 1 further comprising:

a probe heater coupled to the cantilevered probe, wherein the probe heater is heated when a heater voltage is applied to at least one conductive feedthrough electrically connected to the probe heater.

13. A method of imaging an object in a liquid medium, comprising:

positioning a liquid cell adjacent to the object, the liquid cell comprising a liquid cell housing with an internal cavity and a plurality of conductive feedthroughs connected between the internal cavity and a dry side of the liquid cell;

measuring the position of an atomic probe tip coupled to a free end of a cantilevered probe when the atomic probe tip contacts the object, the cantilevered probe being coupled to the liquid cell housing and a portion of the cantilevered probe being located inside the internal cavity; and

generating an image of the object based on the measured position of the atomic probe tip when the atomic probe tip is scanned across the object.

14. The method of claim 13 wherein the position of the atomic probe tip is measured with a piezoelectric sense element disposed on the cantilevered probe, the piezoelectric sense element electrically connected to at least one of the conductive feedthroughs.

15. The method of claim 14 wherein the piezoelectric sense element comprises a material selected from the group consisting of zinc oxide, lead zirconate titanate, polyvinylidene fluoride, and a piezoelectric film.

16. The method of claim 14 wherein the piezoelectric sense element is passivated to electrically isolate the piezoelectric sense element when a conductive fluid is placed in the internal cavity of the liquid cell.

17. The method of claim 14 wherein the piezoelectric sense element is passivated with a material selected from the group consisting of silicon nitride, silicon dioxide, parylene, Teflon, an insulating polymer, and an insulating material.

18. The method of claim 13 wherein the position of the atomic probe tip is measured with a piezoresistive sense element coupled to the cantilevered probe, the piezoresistive sense element electrically connected to at least one of the conductive feedthroughs.

19. The method of claim 13 wherein the position of the atomic probe tip is measured with a magnetic sense element coupled to the cantilevered probe, the magnetic sense element electrically connected to at least one of the conductive feedthroughs.

20. The method of claim 13 further comprising:

applying an excitation voltage through at least one conductive feedthrough to a piezoelectric drive element disposed on the cantilevered probe, wherein the position of the atomic probe tip is adjusted based on the excitation voltage.

21. The method of claim 20 wherein the excitation voltage comprises a topographical component, wherein the topographical component is adjusted to maintain the cantilevered probe in one of a constant force mode or a constant amplitude mode.

22. The method of claim 20 wherein the excitation voltage is applied at a frequency near a resonant frequency of the cantilevered probe to tap the atomic probe tip against the object.

23. The method of claim 20 wherein the position of the atomic probe tip is measured with a beam of light striking a photodetector, the beam of light reflected from at least a portion of the cantilevered probe.

24. The method of claim 13 further comprising:

injecting a fluid onto the object through an inlet port connected between the internal cavity and the dry side of the liquid cell.

25. A method of sensing a target species with a liquid cell, comprising:

driving a cantilevered probe with an excitation voltage, the cantilevered probe coupled to an internal cavity of the liquid cell, wherein the excitation voltage is applied to a piezoelectric drive element disposed on the cantilevered probe through at least one conductive feedthrough connected between the internal cavity and a dry side of the liquid cell;

measuring a first deflection amplitude of the cantilevered probe with a sense element coupled to the cantilevered probe;

exposing a treated section of the cantilevered probe to a target species;

measuring a second deflection amplitude of the cantilevered probe; and

determining the target species based on the first deflection amplitude measurement and the second deflection amplitude measurement.

26. The method of claim 25 wherein the piezoelectric drive element comprises a material selected from the group consisting of zinc oxide, lead zirconate titanate, polyvinylidene fluoride, and a piezoelectric film.

27. The method of claim 25 wherein the piezoelectric drive element is passivated to electrically isolate the piezoelectric drive element when a conductive fluid is placed in the internal cavity of the liquid cell.

28. The method of claim 25 wherein the piezoelectric drive element is passivated with a material selected from the group consisting of silicon nitride, silicon dioxide, parylene, Teflon, an insulating polymer, and an insulating material.

29. The method of claim 25 wherein the cantilevered probe is driven at a frequency near a resonant frequency of the cantilevered probe.

30. The method of claim 25 wherein the sense element comprises a piezoelectric sense element disposed on the cantilevered probe.

31. The method of claim 25 wherein the sense element comprises a piezoresistive sense element coupled to the cantilevered probe.

32. The method of claim 25 wherein the deflection amplitude of the cantilevered probe is measured with a beam of light striking a photodetector, the beam of light reflected from at least a portion of the cantilevered probe.

33. The method of claim 25 further comprising:

measuring a first frequency of the cantilevered probe with the sense element coupled to the cantilevered probe;

exposing the treated section of the cantilevered probe to the target species;

measuring a second frequency of the cantilevered probe; and

determining the target species based on the first frequency measurement and the second frequency measurement.

34. The method of claim 25 further comprising:

injecting a fluid into the interior cavity of the liquid cell through an inlet port connected between the internal cavity and the dry side of the liquid cell, the fluid comprising the target species.

35. The method of claim 25 further comprising:

tapping an atomic probe tip coupled to a free end of the cantilevered probe against a mechanical stop, the mechanical stop coupled to a base end of the cantilevered probe.