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Scanning probe microscope

Foreign code F110004071
File No. N021-11WO
Posted date Jul 8, 2011
Country EPO
Application number 07790991
Gazette No. 2048487
Date of filing Jul 19, 2007
Gazette Date Apr 15, 2009
International application number JP2007064237
International publication number WO2008015916
Date of international filing Jul 19, 2007
Date of international publication Feb 7, 2008
Priority data
  • P2006-207297 (Jul 31, 2006) JP
  • 2007JP64237 (Jul 19, 2007) WO
Title Scanning probe microscope
Abstract There is provided a scanning probe microscope apparatus which has a high sensitivity for the interaction between the cantilever and the sample and comprises a cantilever that can oscillate stably in dynamic mode even when a mechanical Q value is low.A driving signal having a frequency close to the resonant frequency of the cantilever (4) is supplied from the signal generator (9) to the oscillation exciting means (10) to separately (forcibly) oscillate the cantilever (4).And the frequency of the driving signal or the resonant frequency of the cantilever is controlled (by adjusting the distance between the cantilever (4) and the sample (1)), such that the phase difference between the oscillation of the cantilever (4) detected by the oscillation detecting means (5) and the driving signal becomes zero, i.e. the frequency of the driving signal and the resonant frequency of the cantilever (4) match.
Outline of related art and contending technology BACKGROUND ART
One of the imaging modes of an atomic force microscope, which is a kind of scanning probe microscopes, is FM (Frequency Modulation) mode.In FM mode, a cantilever of the atomic force microscope apparatus is self-oscillated, and the interaction force between the cantilever and a sample is detected from the changes in the oscillation frequency.Then, the interaction force is imaged, or the surface shape of the sample is imaged by adjusting the distance between the cantilever and the sample such that the interaction force is kept constant.
FIG. 1(a) and FIG. 1(b) are graphs showing characteristics of a conventional scanning probe microscope.
FIG. 1(a) is a graph showing an example of a relationship between the interaction force and the distance between the cantilever and the sample.The cantilever has a particular mechanical resonant frequency which is determined by its own spring constant and a mass.When an external force as shown in FIG. 1(a) which varies with the distance between the cantilever and the sample is applied, an apparent spring constant is changed and therefore the resonant frequency is changed. FIG. 1(b) is a graph showing an example of a relationship between the resonant frequency and the distance between the cantilever and the sample.
FIG. 2 shows an example of a control system of a conventional FM mode atomic force microscope.
FIG. 2 shows a sample 101, a sample stage 102, an XYZ scanner 103, a cantilever 104 that measures characteristics of the sample 101, an oscillation detecting means 105 for detecting an oscillation of the cantilever 104, a detected signal waveform processing system 106 that receives a detected signal from the oscillation detecting means 105 to bandpass filter, stabilize amplitude and adjust phase, an FM detector 107 that is connected to the detected signal waveform processing system 106, a controller 108 that is connected to the FM detector 107 , an oscillation exciting means 109 that is connected to the detected signal waveform processing system 106, an XY scanning and imaging system 110.The sample 101 can be scanned in the XYZ directions by using a Z-axis control signal from the controller 108 and an XY scanning signal from the XY scanning and imaging system 110.
In other words, a detected signal of an oscillation of the cantilever 104 is amplified, stabilized in amplitude, and phase-adjusted if necessary by the detected signal waveform processing system 106.Then the signal is fed back to the oscillation exciting means 109, and the cantilever 104 is self-oscillated at the resonant frequency.The resonant frequency of the cantilever 104 and therefore the interaction force between the cantilever 104 and the sample 101 can be obtained by detecting the frequency of the self-excited oscillation by the FM detector 107.
An interaction force image can be obtained by XY scanning the sample 101 according to an XY scanning signal from the XY scanning and imaging system 110 while detecting the interaction force as described above, and imaging the interaction force at each XY coordinate point.Furthermore, an image of the surface shape of the sample 101 can also be obtained by XY scanning the sample 101 while controlling the distance between the cantilever 104 and the sample 101, which is the position of the Z-axis, according to the Z-axis control signal from the controller 108 such that the interaction force is kept constant.
The feedback loop (self-excitation loop) which generates a self-excited oscillation may include frequency conversion process.This system is called a super heterodyne system.The super heterodyne system can be combined with a PLL to stabilize the oscillation.
Phase feedback system used in sample imaging apparatus is described in Applied Surface Science 157 (2000), pp. 332-336.The phase feedback system will be hereinafter described in detail.
Oscillation of a cantilever is described in WO 02/103328.A probe and probe microscope apparatus are described in WO 2005/015570.
Scope of claims [claim1]
1. A scanning probe microscope apparatus for imaging a sample using an interaction between the sample and a mechanical oscillator, the scanning probe microscope apparatus comprising:
a first controller;
an XYZ scanner for the sample and an XY scanning and imaging system, each being connected to the first controller;
a signal generator;
an oscillation exciting means connected to the signal generator;
a mechanical oscillator forcibly oscillated by an output signal from the oscillation exciting means;
an oscillation detecting means for detecting an oscillation of the mechanical oscillator,
a phase difference detecting means connected to the oscillation detecting means; and
a second controller for receiving a phase difference signal from the phase difference detecting means and transmitting a frequency control signal to the first controller and the signal generator;
wherein the signal generator is configured to generate a driving signal with a frequency close to the resonant frequency of the mechanical oscillator and to transmit the driving signal to the oscillation exciting means to oscillate the mechanical oscillator forcibly, and phase difference detected by the phase difference detecting means is kept constant.
[claim2]
2. The scanning probe microscope apparatus according to claim 1, wherein the mechanical oscillator is a cantilever.
[claim3]
3. The scanning probe microscope apparatus according to claim 1, further comprising:
first connecting means for receiving the phase difference signal from the phase difference detecting means;
second connecting means for receiving the frequency control signal from the second controller;
first switching means for switching between the first connecting means and the second connecting means; and
second switching means for switching the frequency control signal from the second controller on and off;wherein the first controller is connected to the output side of the first switching means, and the signal generator is connected to the output side of the second switching means.
[claim4]
4. The scanning probe microscope apparatus according to claim 1, further comprising:
a device for mixing the phase difference signal and the frequency control signal at an arbitrary ratio and transmitting the mixed signal to the first controller; and
a device for adjusting the frequency control signal to an arbitrary intensity and transmitting the adjusted signal to the signal generator.
[claim5]
5. The scanning probe microscope apparatus according to any one of claims 1 to 4, wherein a resonant frequency of the mechanical oscillator is measured and an interaction force between the sample and the mechanical oscillator is imaged based on the resonant frequency.
[claim6]
6. The scanning probe microscope apparatus according to any one of claims 1 to 4, wherein a resonant frequency of the mechanical oscillator is measured and a surface shape of the sample is imaged based on the resonant frequency.
[claim7]
7. The scanning probe microscope apparatus according to any one of claims 1 to 4, wherein a resonant frequency of the mechanical oscillator is measured and a relationship between the resonant frequency and a distance between the mechanical oscillator and the sample is obtained based on the resonant frequency.
  • Applicant
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
  • Inventor
  • KOBAYASHI, Dai
  • NISHIDA, Shuhei
  • KAWAKATSU, Hideki
IPC(International Patent Classification)
Specified countries Contracting States: CH DE LI
Reference ( R and D project ) CREST Nano Factory and Process Monitoring for Advanced Information Processing and Communication AREA
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