Resonant probe driving arrangement and a scanning probe microscope including such an arrangement

• US 20030137216A1
• Filed: 12/05/2002
• Published: 07/24/2003
• Est. Priority Date: 04/20/2000
• Status: Active Grant

• Current Assignee: The University of Bristol
• Original Assignee: The University of Bristol
• Inventors: Humphris, Andrew David Laver, Tamayo de Miguel, Javier, Miles, Mervyn John
• Granted Patent: US 6,906,450 B2
• Time in Patent Office: Days
• US Class Current: 310/311
• CPC Class Codes: G01Q 10/065 Feedback mechanisms, i.e. wherein the signal for driving the probe is modified by a signal coming from the probe itself
• CPC Class Codes: G01Q 20/02 by optical means
• CPC Class Codes: G01Q 20/04 Self-detecting probes, i.e. wherein the probe itself generates a signal representative of its position, e.g. piezoelectric gauge
• CPC Class Codes: G01Q 60/32 AC mode
• CPC Class Codes: Y10S 977/85 Scanning probe control process

Abstract

A drive system is provided for a resonating probe device, such as a scanning probe microscope, wherein the amplitude of the drive signal is controlled by feeding back a phase shifted and amplified component of the amplitude of oscillation of the resonating element. Means are provided for electronically enhancing the quality factor of a resonating probe device when operated in a liquid environment. Such enhancement of the quality factor improves the sensitivity of the probe device.

Claims

1. A control apparatus for controlling a driving signal used to stimulate a resonating sensing element (23), in which the control apparatus is responsive to a sensor (24) used to monitor the motion of the sensing element characterised in that the control apparatus (26, 28, 30) comprises a signal processor (70) for filtering signals from the sensor so as to remove harmonics above a predetermined order from the signal, and drive signal controller (37, 40) responsive to the output of the signal processor for adjusting the driving signal so as to maintain the sensing element in resonance.

2. A control apparatus as claimed in claim 1, characterised in that said signal processor (30) is further arranged to identify a phase shift between the motion of the sensing element (23) and the driving stimulus applied to the element and the drive signal controller (36, 38) adjusts the driving signal so as to maintain the phase shift at substantially a predetermined value.

5. A control apparatus as claimed in claim 1 or 2, characterised in that the sensing element (23) is driven via one of alternating magnetic fields, alternating electrostatic fields, pressure waves and pulsed heating.

6. A control apparatus as claimed in claim 2, in which the predetermined phase shift is substantially 90 degrees.

7. A control apparatus as claimed in claim 2 or 6, in which the phase shift is measured by a phase sensitive detector (36), and the output of the detector is provided to a controller (38) which controller causes a change to the frequency of the driving signal.

8. A control apparatus as claimed in any one of the preceding claims, further comprising at least one other feedback loop (37, 40, 34;

80, 82;

36, 38, 32) for controlling a property of the drive signal used to stimulate the sensing element.

9. A control apparatus as claimed in claim 8, characterised in that one further feedback loop is provided, and said one further feedback loop controls the magnitude of the drive signal.

10. A control apparatus as claimed in claim 8 or 9, characterised in that a signal from the sensor (23) is phase shifted and amplified, said amplification being a function of the amplitude of said signal from the sensor, and combined with the drive signal.

11. A control apparatus as claimed in claim 8 or 9, characterised in that an amplitude of the drive signal is modulated as a function of the amplitude of the sensor signal.

12. An apparatus as claims 8 to 11, characterised in that the or one of the further feedback loops forms a feedback loop synthesising an effective quality factor for the sensing element in excess of its actual quality factor.

13. A scanning probe microscope including a control apparatus as claimed in any one of the preceding claims.

14. A chemical or bio-chemical sensor (100) comprising a resonating sensing element having a receptor therein, where the receptor interacts with a substance under test, in combination with a control apparatus as claimed in any one of claims 1 to 12.

15. A sensor as claimed in claim 14, wherein one side of the sensor is coated with a substance sensitive to a target substance under test.

3. A control apparatus as claimed 1 or 2, characterised in that the sensing element (23) is coupled to a drive element (22) via a liquid coupling.

4. A control apparatus as claimed in claim 3, characterised in that the drive element (22) is a piezo-electric element.

16. An apparatus for controlling the amplitude of a drive signal applied to a resonating element (23), the controller being responsive to at least one sensor (24) for measuring the oscillation of the sensing element (23), and comprising a signal processor (30) for extracting a parameter of the oscillation, and for using the parameter to control a parameter of the drive signal supplied to drive the sensing element in accordance with a first transfer function.

17. An apparatus as claimed in claim 16, characterised in that at least one of the signal processor and a drive element used to drive the resonating element is unresponsive to other parameters of the oscillation.

18. An apparatus as claimed in claim 16 or 17, characterised in that the parameter used to control the oscillation is the magnitude of oscillation.

19. An apparatus as claimed in claim 16 or 17 characterised in that the parameter used to control the oscillation is the phase difference between the drive signal and the motion of the resonating element.

20. An apparatus as claimed in claim 16 or 17 characterised in that the parameter used to control the oscillation is the frequency of the motion of the resonating element (23).

21. An apparatus as claimed in claim 16 or 17, in which the parameter used to control the oscillation is the harmonics of the frequency of oscillation below a predetermined order.

22. A method of driving a resonating element, comprising the steps of monitoring the vibrating motion of the resonating element, comparing a phase difference between a signal used to excite the resonating element and the motion of the resonating element, and varying the frequency of the signal used to excite the resonating element so as to maintain the phase difference at a predetermined value.