Whispering gallery mode ultrasonically coupled scanning probe microscopy

• US 20080092659A1
• Filed: 05/30/2007
• Published: 04/24/2008
• Est. Priority Date: 03/18/2005
• Status: Active Grant

• Current Assignee: State Of Oregon Acting By And Through The State Board Of Higher Education On Behalf Of Portland State University
• Original Assignee: Oregon State University (Oregon University System), Portland State University (Oregon University System)
• Inventors: Flores, Andres, Padigi, Sudhaprasanna, Nordstrom, Richard
• Granted Patent: US 8,037,762 B2
• Time in Patent Office: Days
• US Class Current: 73/618
• CPC Class Codes: G01N 2291/02827 Elastic parameters, strength or force
• CPC Class Codes: G01N 29/0618 synchronised with scanning, e.g. in real-time
• CPC Class Codes: G01N 29/0681 by acoustic microscopy, e.g. scanning acoustic microscopy
• CPC Class Codes: G01N 29/12 by measuring frequency or resonance of acoustic waves measuring frequency or resonant frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04, G01H13/00; acoustic resonators G10K11/04; vibration or shock testing of structures G01M7/00
• CPC Class Codes: G01N 29/265 by moving the sensor relative to a stationary material
• CPC Class Codes: G01Q 60/32 AC mode

Abstract

Scanning probe microscopes include a probe tip coupled to a tuning fork or other acoustic resonator so as to apply a shear force when contacted to a specimen surface based on an applied acoustic signal. A secondary ultrasonic transducer is in acoustic communication with the specimen and a resonant structure. Probe tip-specimen displacement can be detected based on whispering gallery mode ultrasonic waves in the resonant structure using the secondary transducer, and such displacements maintained using feedback control based on whispering gallery mode acoustic wave magnitude.

Claims

1. A scanning microscope, comprising:

a probe having a probe tip for contacting a specimen;

a stage configured to provide a selected probe tip-specimen displacement;

a first acoustic transducer coupled to the probe;

a resonant cavity acoustically coupled to the probe tip; and

a second acoustic transducer acoustically coupled to detect acoustic waves in the resonant cavity.

2. The scanning probe microscope of claim 1, further comprising a first transducer driver configured to produce an acoustic vibration of the probe tip with the first acoustic transducer at a probe tip frequency, wherein the resonant cavity dimensions are based on the probe tip frequency.

3. The scanning probe microscope of claim 2, further comprising:

a translation stage configured for scanning that the probe tip with respect to a specimen surface; and

an image processor configured to receive electrical signals from the second transducer associated with acoustic waves in the resonant cavity as the probe tip is scanned and to produce an image of a specimen surface based on the received electrical signals.

4. The scanning probe microscope of claim 3, further comprising a quartz tuning fork that includes the first acoustic transducer, wherein the probe tip is secured to a tine of the tuning fork.

5. The scanning probe microscope of claim 1, wherein the resonant cavity includes a cylindrical section having a diameter associated with a probe tip drive frequency.

6. The scanning probe microscope of claim 5, wherein the cylindrical section is metallic.

7. The scanning probe microscope of claim 10, wherein the second transducer is configured to detect probe tip vibration based on acoustic waves in the resonant cavity.

8. The scanning probe microscope of claim 1, further comprising a controller configured to adjust probe tip-specimen separation to maintain a predetermined acoustic wave magnitude in the resonant cavity.

9. The scanning probe microscope of claim 8, further comprising a memory configured to store the probe tip-specimen separation.

10. The scanning probe microscope of claim 8, further comprising a display configured to present a specimen image based on the adjusted probe tip-specimen separations.

11. The scanning probe microscope of claim 10, wherein the predetermined acoustic wave magnitude is a constant magnitude.

12. A method, comprising:

scanning an oscillating probe tip over a specimen surface;

coupling an acoustic vibration associated with oscillations of the probe tip to a resonant cavity so as to form a resonant acoustic wave; and

detecting probe tip-specimen separation based on the resonant acoustic wave.

13. The method of claim 12, further comprising scanning the probe tip with respect to the specimen surface and adjusting the probe tip-specimen surface separation so as to maintain a predetermined resonant acoustic wave characteristic.

14. The method of claim 13, wherein the resonant acoustic wave characteristic is an amplitude.

15. The method of claim 14, further comprising storing a plurality of probe tip-specimen displacement adjustments.

16. The method of claim 15, further comprising displaying a specimen image based on the stored displacement adjustments.

17. The method of claim 13, wherein the predetermined resonant acoustic wave characteristic is a substantially constant magnitude.

18. The method of claim 12, wherein the resonant cavity includes a conical portion associated with a range of acoustic resonant frequencies.