Nanoscale dynamic mechanical analysis via atomic force microscopy (AFM-nDMA)

Patent metadata

Field	Value
Publication number	US-11940461-B2
Application number	US-202318133054-A
Country	US
Kind code	B2
Filing date	Apr 11, 2023
Priority date	Aug 6, 2018
Publication date	Mar 26, 2024
Grant date	Mar 26, 2024

Abstract

An atomic-force-microscope-based apparatus and method including hardware and software, configured to collect, in a dynamic fashion, and analyze data representing mechanical properties of soft materials on a nanoscale, to map viscoelastic properties of a soft-material sample. The use of the apparatus as an addition to the existing atomic-force microscope device.

First claim

The invention claimed is:

1. An apparatus configured to determine a mechanical property of a viscoelastic sample with an atomic-force-microscope (AFM) hardware, the apparatus comprising:
an excitation electronic circuitry operably connected with the AFM and configured to generate an excitation force signal that includes a fundamental signal at a fundamental frequency and multiple harmonic signals at corresponding multiple harmonics of the fundamental frequency, wherein
(a) said fundamental signal and said multiple harmonic signals have no pre-determined phase shifts with respect to one another such that the excitation force signal has a maximum excitation force value only at a beginning of a pre-determined time period and a minimum excitation force value only at an end of said pre-determinedtime period, or
b) said fundamental signal and said multiple harmonic signals have pre-determined phase shifts with respect to one another such that the excitation force signal includes multiple amplitude peaks within said pre-determined time period;

a feedback electronic circuitry configured to monitor both a mean value of said excitation force signal and an oscillatory component of said excitation force signal and to generate a feedback output representing both the mean value of said excitation force signal and the oscillatory component of said excitation force signal;
an electro-mechanical sub-system cooperated with the excitation electronic circuitry and the feedback electronic circuitry and configured:
when the cantilever is deflected by a pre-determined amount from a nominal orientation thereof, as determined by a position-detecting system of the apparatus, to cause a mechanical oscillation between the sample and the probe in response to the excitation force signal transferred from the excitation electronic circuitry; and
upon receiving the feedback output, to maintain one of the sample and the probe in a position, with respect to the other of the sample and the probe, in which at least one of
i) an average sample-loading force, generated by the probe, and
ii) an area of contact between a tip of the probe and a surface of the sample

is kept substantially constant during said mechanical oscillation; and

a programmable processor in operable communication with at least the position-detecting system and programmed:
to transfer the excitation force signal from the excitation electronic circuitry to the electro-mechanical sub-system, and
to suspend an operation of the electro-mechanical sub-system for a relaxation period of time sufficient for relaxation of a creep of the surface of the sample that is caused by repositioning of said one of the sample and the probe with respect to the other of the sample and the probe.

2. An apparatus according to claim 1 , wherein the
position-detecting system is configured to detect a deflection of a cantilever of a cantilevers probe of the AFM and to generate data representing the deflection; and
wherein the programmable processor is configured to acquire said data from the position-detecting system to determine a viscoelastic parameter after the relaxation period of time has lapsed.

3. An apparatus according to claim 2 , further comprising a recording device in operable communication with the programmable processor and configured to produce an output that is perceivable by a user and that represents said viscoelastic parameter.

4. An apparatus according to claim 1 , wherein said excitation electronic circuitry is configured to generate the excitation force signal including multiple sinusoidal signals that have respectively-corresponding distinct frequencies covering at least one decade in a frequency space, wherein amplitudes of said multiple sinusoidal signals are varied between a pre-defined maximum value and a pre-defined minimum value each of which the same for all of said multiple sinusoidal signals.

5. An apparatus according to claim 4 , configured to determine said viscoelastic parameter at said distinct frequencies that cover at least one decade in the frequency space in absence of using either a lock-in detection or a Fast-Fourier Transform based analysis.

6. An apparatus according to claim 1 , wherein said electro-mechanical sub-system is further configured to reposition one of the sample and the cantilevered probe until a cantilever of the cantilevered probe is deflected by a pre-determined amount from a nominal orientation of the cantilever.

7. An apparatus according to claim 1 , wherein said feedback electronic circuitry is configured to compensate for the creep of the surface of the sample.

8. An apparatus according to claim 1 , wherein the programmable processor is configured to control the excitation electronic circuitry to adjust one or more of maximum and minimum values of an amplitude and a phase of the oscillatory component of the excitation force signal thereby modulating a sample-loading force generated by the probe.

9. A method for determining a mechanical property of a viscoelastic sample with an atomic-force-microscope (AFM) hardware, the method comprising:
with the use of the apparatus according to claim 1 :
monitoring, with electronic circuitry of the apparatus, an operation of the apparatus at a reference frequency to correct for a change in at least one of (i) an area of contact between a tip of a cantilevered probe of the AFM hardware of the apparatus and a surface of the viscoelastic sample and (ii) an average sample-loading force, generated by said cantilevered probe and
measuring, at a set of frequencies that cover at least one decade in a frequency space, a viscoelastic parameter of a surface of the viscoelastic sample.

10. A method according to claim 9 , wherein said measuring includes measuring, at a set of frequencies that are necessarily within a range from 0.001 Hz to 1,000 Hz, the viscoelastic parameter of the surface of said viscoelastic sample in absence of using either a lock-in detection or a Fast-Fourier-Transform based analysis.

11. A method according to claim 9 , wherein said measuring includes measuring the viscoelastic parameter of the surface of the viscoelastic sample while compensating for at least one of a creep of the surface and a spatial drift of the apparatus.

12. A method according to claim 9 , further comprising modulating a sample-loading force imposed by the cantilevered probe on the viscoelastic sample by generating, with an excitation electronic circuitry of the apparatus, an excitation force signal that includes multiple sinusoidal signals having respectively-corresponding distinct frequencies that cover said at least one decade in the frequency space, wherein amplitudes of said multiple sinusoidal signals are varied between a pre-determined maximum value and a pre-determined minimum value each of which remains the same for all of said multiple sinusoidal signals.

13. A method according to claim 12 , wherein said generating multiple sinusoidal signals includes generating a fundamental signal at a fundamental frequency and multiple harmonic signals at different harmonics of said fundamental frequency to produce an excitation force signal to deflect the cantilever of the cantilevered probe under such conditions that
( 14 a ) said excitation force signal has a maximum value only at a beginning of a pre-determined time period and a minimum value only at an end of said pre-determined time period, or
( 14 b ) said excitation force signal having multiple amplitude peaks within said pre-determined time period.

14. A method according to claim 9 , further comprising:
while maintaining the area of contact to remain substantially constant,

Assignees

• Bruker Nano Inc

Inventors

• Osechinskiy Sergey
• Ruiter Anthonius
• Pittenger Bede
• Syed-Amanulla Syed-Asif

Classifications

• G01Q60/38 Primary

  Probes, their manufacture, or their related instrumentation, e.g. holders · CPC title

• G01Q10/04

  Fine scanning or positioning · CPC title

• G01Q20/04

  Self-detecting probes, i.e. wherein the probe itself generates a signal representative of its position, e.g. piezoelectric gauge · CPC title

• G01Q30/04

  Display or data processing devices · CPC title

• B82Y35/00

  Methods or apparatus for measurement or analysis of nanostructures · CPC title