Method of performing atomic force microscopy with an ultrasound transducer

Patent metadata

Field	Value
Publication number	US-11067597-B2
Application number	US-201816760687-A
Country	US
Kind code	B2
Filing date	Nov 2, 2018
Priority date	Nov 3, 2017
Publication date	Jul 20, 2021
Grant date	Jul 20, 2021

Abstract

A method of performing atomic force microscopy (AFM) measurements, uses an ultrasound transducer to transmit modulated ultrasound waves with a frequency above one GHz from the ultrasound transducer to a top surface of a sample through the sample from the bottom surface of the sample. Effects of ultrasound wave scattering are detected from vibrations of an AFM cantilever at the top surface of the sample. Before the start of the measurements, a drop of a liquid is placed on a top surface of the ultrasound transducer. The sample is placed on the top surface of the ultrasound transducer, whereby the sample presses the liquid in the drop into a layer of the liquid between the top surface of the ultrasound transducer and a bottom surface of the sample. The AFM measurements are started after a thickness of the layer of the liquid has stabilized.

First claim

The invention claimed is:

1. A method of performing atomic force microscopy (AFM) measurements, the method comprising
providing an ultrasound transducer;
placing a drop of a liquid on a top surface of the ultrasound transducer;
placing a sample on the top surface of the ultrasound transducer, whereby the sample presses the liquid in the drop into a layer of the liquid between the top surface of the ultrasound transducer and a bottom surface of the sample;
providing a basin for said liquid, the top surface of the ultrasound transducer being located within the basin, wherein the basin is empty or a surface level of the liquid in the basin is below the top surface of the ultrasound transducer during the steps of placing the drop of liquid and placing the sample on the top surface of the ultrasound transducer;
transmitting modulated ultrasound waves from the ultrasound transducer to a top surface of the sample through the sample from the bottom surface of the sample to the top surface of the sample;
filling the basin with the liquid after the thickness of the layer of the liquid has stabilized, thereby raising the surface level of the liquid in the basin above the top surface of ultrasound transducer; and
performing measurements of vibrations of a cantilever excited by the modulated ultrasound waves while a probe tip on the cantilever is in contact with the top surface of the sample, after a thickness of the layer of the liquid has stabilized.

2. The method according to claim 1 , wherein a volume of the drop that is placed on the top surface of the ultrasound transducer, divided by a contact area between the sample and the ultrasound transducer is less than half a micrometer.

3. The method according to claim 1 , wherein the surface level of the liquid is kept below the top surface of the sample and the bottom surface of the sample is below the surface level of the liquid after said filling.

4. The method according to claim 1 , the method further comprising replenishing the liquid in the basin between successive ones of the measurements.

5. The method according to claim 1 , wherein a volume of the drop that is placed on the top surface of the ultrasound transducer, divided by a contact area between the sample and the ultrasound transducer is less than two micrometer.

6. The method according to claim 1 , the method comprising clamping the bottom surface of the sample and the top surface of the ultrasound transducer against each other, thereby exerting a pressing force on the liquid in the layer of the liquid between the bottom surface of the sample and the top surface of the ultrasound transducer, at least until the thickness of the layer of the liquid has stabilized.

7. The method according to claim 6 , wherein the clamping is performed by at least one of exerting the pressing force onto the top surface of the sample using at least one spring, applying suction to the bottom surface of the sample, electrostatic clamping, magnetic clamping and electro-wetting.

8. The method according to claim 1 , further comprising:
performing ultrasound reflection measurements using the ultrasound transducer after the sample has been placed on the top surface of the ultrasound transducer;
monitoring changes in results of the reflection; and
starting the measurements of vibrations of the cantilever upon detection that results of the reflection measurements indicate that the thickness of the layer of the liquid has stabilized.

9. The method according to claim 1 , wherein the liquid is water, paraffin, alcohol, liquefied wax, mercury, a gallium-alloy, an adhesive, or solder tin.

10. The method according to claim 1 , further comprising lowering a temperature of the liquid below a solidification temperature of the liquid after the thickness of the layer of the liquid has stabilized.

11. An AFM measuring system, comprising:
an ultrasound transducer;
a basin for a liquid, a top surface of the ultrasound transducer being located within the basin, an upper edge of a wall of the basin lying so high that, when the basin is filled, a surface level of the liquid in the basin lies above the top surface of the ultrasound transducer;
an AFM cantilever located above the top surface of the ultrasound transducer, for contacting a top surface of a sample between the AFM cantilever and the top surface of the ultrasound transducer;
a detector configured to detect bending of the AFM cantilever; and
a first elastically deformable clamp configured to be placed in contact with the top surface of the sample and press the top surface of the sample elastically towards the top surface of the ultrasound transducer.

12. The system according to claim 11 , the wherein the first elastically deformable clamp is configured to be placed in contact with the top surface of the sample over the basin, and wherein the top surface of the sample is pressed elastically towards the top surface of the ultrasound transducer into the basin.

13. The system according to claim 11 , wherein the first elastically deformable clamp comprises a first leaf spring, the system further comprising a frame, to which the first elastically deformable leaf spring is connected, and at least a second elastically deformable clamp comprising a second leaf spring connected to the frame, the at least one second elastically deformable clamp also being configured to be placed in contact with the top surface of the sample and to press the top surface of the sample elastically towards the top surface of the ultrasound transducer.

14. The system according to claim 12 , wherein the first elastically deformable clamp and the at least second elastically deformable clamp are placed in contact with the top surface of the sample at equal distances to the cantilever, at contact points that lie mirror symmetrically with respect to the cantilever.

15. The system according to claim 12 , wherein the first elastically deformable clamp is configured to exert a force within a range of 0.01 to 0.1 Newton on the sample.

16. The system according to claim 11 , wherein the first elastically deformable clamp comprises a contact body, a lowest part of the contact body having a rounded shape for contact with the sample.

17. The system according to claim 11 , further comprising the sample, wherein the sample rests on, or is pressed against the top surface of the ultrasound transducer within the basin, with the top surface of the ultrasound transducer and a bottom surface of the sample within the basin and a top surface of the sample above the basin.

18. An AFM measuring system, comprising:
an ultrasound transducer;
a basin for a liquid, a top surface of the ultrasound transducer being located within the basin, an upper edge of a wall of the basin lying so high that, when the basin is filled, a surface level of the liquid in the basin lies above the top surface of the ultrasound transducer;
an AFM cantilever located above the top surface of the ultrasound transducer, for contacting a top surface of a sample between the AFM cantilever and the top surface of the ultrasound transducer;
a detector configured to detect bending of the AFM cantilever; and
a first elastically deformable clamp,
wherein the ultrasound transducer performs ultrasound reflection measurements after the sample has been placed on the top surface of the ultrasound transducer, wherein changes in results of the reflection measurements are monitored, and wherein, when the changes in results of the reflection measurements indicate that the thickness of the layer of the liquid has stabilized, measurement

Assignees

• TNO

Inventors

• Van Riel Martinus Cornelius Johannes Maria
• Van Neer Paul Louis Maria Joseph
• Sadeghian Marnani Hamed
• Van Es Maarten Hubertus

Classifications

• G01N29/0681 Primary

  by acoustic microscopy, e.g. scanning acoustic microscopy · CPC title

• G01Q30/14 Primary

  Liquid environment · CPC title

• G01N29/346

  with amplitude characteristics, e.g. modulated signal · CPC title

• G01N2291/2697

  Wafer or (micro)electronic parts · CPC title

• G01Q60/32 Primary

  AC mode · CPC title