Atomic Force Microscopy System and Method for Nanoscale Measurement

• US 20120030846A1
• Filed: 07/29/2011
• Published: 02/02/2012
• Est. Priority Date: 07/30/2010
• Status: Active Grant

• Current Assignee: US Department of The Air Force (U.S. Department Of Defense)
• Original Assignee: US Department of The Air Force (U.S. Department Of Defense)
• Inventors: Sathish, Shamachary, Jata, Kumar V., Nalladega, Vijayaraghava, Blodgett, Mark P.
• Granted Patent: US 8,726,410 B2
• Time in Patent Office: Days
• US Class Current: 850/1
• CPC Class Codes: G01Q 60/08 MFM [Magnetic Force Microscopy] combined with AFM [Atomic Force Microscopy

Abstract

An atomic force microscope (AFM) system capable of imaging multiple physical properties of a sample material at the nanoscale level. The system provides an apparatus and method for imaging physical properties using an electromagnetic coil placed under the sample. Excitation of the coil creates currents in the sample, which may be used to image a topography of the sample, a physical property of the sample, or both.

Claims

1. An atomic force microscope system for imaging a sample material, wherein the sample material comprises a sample upper surface and at least one sample property, the atomic force microscope system comprising:

a cantilever including a reflective surface, a first end, and a second end, wherein the first end has a pointed tip and the second end defines a length between the first end and the second end;

a scanner coupled to the second end of the cantilever, wherein the cantilever is positioned such that the pointed tip is adjacent to the sample upper surface and such that the pointed tip is able to move across at least a portion of the sample upper surface;

a laser positioned to emit a light, wherein the light is focused on a portion of the reflective surface;

a photodetector positioned such that a portion of the light reflected from the reflective surface is detected by the photodetector;

a generator to generate a signal having a predetermined frequency and a predetermined amplitude;

an electromagnetic coil coupled to the generator to receive the signal and to excite the electromagnetic coil to create a time-varying magnetic field, wherein the time-varying magnetic field creates a second magnetic field within the sample material; and

a phase sensitive detector to measure an output of the photodetector and an amplitude of the signal to generate a topography image or at least one sample property image or both.

2. The atomic force microscope system of claim 1 wherein the photodetector is a four-quadrant photodiode detector.

3. The atomic force microscope system of claim 1 wherein the signal is a radio frequency signal.

4. The atomic force microscope system of claim 1 wherein the electromagnetic coil is an air-core electromagnetic coil or a ferrite-core electromagnetic coil.

5. The atomic force microscope system of claim 1 wherein the pointed tip includes a magnetic material.

6. The atomic force microscope system of claim 5 wherein the magnetic material comprises a magnetic film coating.

7. The atomic force microscope system of claim 1 wherein the length of the cantilever is substantially parallel to the sample upper surface and the pointed tip is substantially perpendicular to the sample upper surface.

8. The atomic force microscope system of claim 1 wherein the length of the cantilever is substantially perpendicular to the sample upper surface and the pointed tip is substantially perpendicular to the sample upper surface.

9. The atomic force microscope system of claim 1 wherein the sample property comprises an electrical, dielectric, ferroelectric, magnetostrictive, magneto-acoustic, or magneto-elastic property.

10. A method of using an atomic force microscope system to generate an image of a sample material, the method comprising:

placing the sample material near an electromagnetic coil;

supplying a signal to the electromagnetic coil such that the signal creates a time-varying magnetic field, wherein the sample material intersects the time-varying magnetic field such that a second magnetic field is induced within the sample material;

varying the second magnetic field by altering at least one of an amplitude and a frequency of the signal;

focusing a laser on a reflective surface of a cantilever;

raster-scanning the sample material with a pointed tip of the cantilever such that the pointed tip is in contact with a sample upper surface;

detecting a portion of the laser that is reflected from the reflective surface using a photodetector;

collecting an output of the photodetector and an amplitude of the signal to the electromagnetic coil; and

generating a topography image of the sample upper surface and at least one sample property image by comparing the output of the photodetector and the amplitude of the signal.

11. The method of claim 10 wherein the pointed tip is non-magnetic.

12. The method of claim 11 wherein the sample material is conductive and the sample property includes magneto-acoustic.

13. The method of claim 11 wherein the sample material is magnetic and the sample property includes magnetostriction.

14. The method of claim 10 wherein the pointed tip is magnetic.

15. The method of claim 14 wherein the sample material is ferroelectric and the sample property includes electrostriction.

16. The method of claim 14 wherein the topography image and sample property image are obtained simultaneously.

17. The method of claim 10 further comprising

positioning the cantilever to a predetermined distance above the sample upper surface;

and

raster-scanning the sample material with the cantilever at the predetermined distance above the sample upper surface.

18. The method of claim 17 wherein the sample material is conductive and the sample property includes electrical conductivity or resistivity.

19. The method of claim 17 wherein the sample material is dielectric and the sample property includes dielectric polarization.