Heterodyne scanning probe microscopy method and scanning probe microscopy system

Patent metadata

Field	Value
Publication number	US-11635448-B2
Application number	US-202017612507-A
Country	US
Kind code	B2
Filing date	May 22, 2020
Priority date	May 21, 2019
Publication date	Apr 25, 2023
Grant date	Apr 25, 2023

Abstract

The present document relates to a heterodyne scanning probe microscopy (SPM) method for subsurface imaging, and includes: applying an acoustic input signal to a sample and sensing an acoustic output signal using a probe. The acoustic input signal comprises a plurality of signal components at unique frequencies, including a carrier frequency and at least two excitation frequencies. The carrier frequency and the excitation frequencies form a group of frequencies, which are distributed with an equal difference frequency between each two subsequent frequencies of the group. The difference frequency is below a sensitivity threshold frequency of the cantilever for enabling sensing of the acoustic output signal. The document also describes an SPM system.

First claim

The invention claimed is:

1. A heterodyne scanning probe microscopy method for imaging structures below a surface of a sample, the method including:
applying, using a transducer, an acoustic input signal to the sample;
sensing an acoustic output signal using a probe, the probe including a cantilever and a probe tip, wherein the probe tip is in contact with the surface, wherein the acoustic output signal is representative of an amount of indentation of the surface by the probe tip in response to the acoustic input signal applied to the sample;
wherein the acoustic input signal comprises a plurality of signal components that each have a unique frequency, wherein the plurality of signal components comprise:
a base signal component at a carrier frequency; and
a plurality of additional signal components having further excitation frequencies;
wherein the carrier frequency and the further excitation frequencies together form a group of frequencies, wherein frequencies of the group of frequencies are distributed with an equal difference frequency between each two subsequent frequencies of the group of frequencies;
wherein the equal difference frequency is a frequency below a sensitivity threshold frequency for enabling said sensing the acoustic output signal;
wherein the plurality of additional signal components are provided as sideband signal components such that in a frequency domain the further excitation frequencies of the sideband signal components are arranged at either side of the carrier frequency of the base signal component, and
wherein at least two sideband signal components are arranged at either side of the carrier frequency.

2. The heterodyne scanning probe microscopy method according to claim 1 , wherein the carrier frequency is a frequency of at least five times a contact resonance frequency of the cantilever.

3. The heterodyne scanning probe microscopy method according to claim 1 , further comprising:
preselecting, for at least one of the additional signal components or the base signal component, at least one of a signal component amplitude or a signal component phase associated with the respective at least one signal component; and
providing each signal component having the predetermined signal component amplitude or signal component phase associated therewith, so as to obtain the acoustic input signal having a desired envelope.

4. The heterodyne scanning probe microscopy method according to claim 3 , wherein the preselecting of the at least one of the signal component amplitude or phase is performed so as to improve at least one envelope parameter to obtain the acoustic input signal having the desired envelope,
wherein the at least one envelope parameter is a type taken from the group of parameter types consisting of: a pulse repetition frequency, a temporal distribution of amplitude within the envelope; a temporal distribution of power within the envelope; an overall peak amplitude; and a root means square amplitude.

5. The heterodyne scanning probe microscopy method according to claim 1 , wherein the base signal component has an amplitude A 0 ,
wherein each of the additional signal components has an amplitude A i =α i *A 0 , and
wherein 0≤α i ≤10.

6. The heterodyne scanning probe microscopy method according to claim 1 , wherein the sensitivity threshold frequency is smaller than or equal to a sixth contact resonant mode frequency of the cantilever.

7. The heterodyne scanning probe microscopy method according claim 1 , wherein an equal number of sideband signal components having their further excitation frequencies below and above the carrier frequency is provided.

8. The heterodyne scanning probe microscopy method according to claim 1 , wherein the signal components include:
two or more base signal components having different respective carrier frequencies; and
a plurality of additional signal components at further excitation frequencies, the plurality of additional signal components being associated with each base signal component;
wherein the carrier frequency and the further excitation frequencies of each base signal component and associated additional signal components of the base signal component, together form a group of frequencies associated with the respective base signal component, so as to form two or more groups of frequencies,
wherein the frequencies of each group of frequencies are distributed with an equal group difference frequency between each two subsequent frequencies of the group of frequencies, and wherein the group difference frequency is a frequency below the sensitivity threshold frequency.

9. The heterodyne scanning probe microscopy method according to claim 8 , wherein one or more conditions are met from the group consisting of:
the group difference frequencies of the two or more groups of frequencies are equal;
a difference between respective carrier frequencies of the two or more base signal components is a positive integer multiple times the group difference frequency of at least one of the groups of frequencies; and
wherein the group difference frequencies of the two or more groups of frequencies are different.

10. The heterodyne scanning probe microscopy method according to claim 1 , wherein the transducer is arranged for producing the acoustic input signal such that:
the carrier frequency is a frequency within a range of 5 MHz to 200 MHz.

11. A scanning probe microscopy system for imaging structures on or below the surface of a sample, comprising a probe for scanning the sample surface, wherein the probe comprises a probe tip mounted on a cantilever, and wherein the probe is mounted on a sensing head arranged for bringing the probe tip in contact with the sampling surface,
the system further comprising a motion actuator for enabling motion of the probe relative to the sample, a transducer for applying an acoustic input signal to the sample, and a probe deflection sensor for producing a sensor signal indicative of an acoustic output signal received via the probe tip, wherein the acoustic output signal is representative of an amount of indentation of the surface by the probe tip in response to the acoustic input signal when it is in use applied to the sample;
wherein the transducer is arranged for producing the acoustic input signal such as to comprise a plurality of signal components that each have a unique frequency, wherein the plurality of signal components comprise:
a base signal component at a carrier frequency; and
a plurality of additional signal components having further excitation frequencies;
wherein the carrier frequency and the further excitation frequencies together form a group of frequencies, wherein the frequencies of the group of frequencies are distributed with an equal difference frequency between each two subsequent frequencies of the group of frequencies; and
wherein the equal difference frequency is a frequency below a sensitivity threshold frequency for enabling said sensing of the acoustic output signal;
wherein the plurality of additional signal components are provided as sideband signal components such that in a frequency domain the further excitation frequencies of the sideband signal components are arranged at either side of the carrier frequency of the base signal component, and
wherein at least two sideband signal components are arranged at either side of the carrier frequency.

12. The scanning probe microscopy system according to claim 11 , wherein the transducer is arranged for producing the acoustic input signal such that:
the carrier frequency is a frequency of at least five times a contact resonance frequency of the cantilever.

13. The scann

Assignees

• TNO

Inventors

• Rajadurai Sri Ram Shankar
• Piras Daniele
• HATAKEYAMA Kodai
• Van Neer Paul Louis Maria Joseph
• Van Es Maarten Hubertus
• Sadeghian Marnani Hamed
• Van Der Lans Marcus Johannes

Classifications

• G01N29/343

  pulse waves, e.g. particular sequence of pulses, bursts · CPC title

• G01N29/4436

  with a reference signal (amplitude comparison G01N29/48) · CPC title

• G01Q20/02

  by optical means · CPC title

• G01N29/348

  with frequency characteristics, e.g. single frequency signals, chirp signals (measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00) · CPC title

• G01Q60/32 Primary

  AC mode · CPC title