JP2008089444A - Method of measuring surface shape of soft material by probe microscope, and probe microscope used for measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of measuring a surface shape of a soft material by a probe microscope allowing accurate measurement of the surface shape of the soft material including a droplet or a material that has high volatility, and is soft and easy to deform, and to provide a probe microscope used for the measuring method. <P>SOLUTION: In measuring the surface shape of a sample made of the soft material by the probe microscope, voltage is applied between the sample and a conductive probe, the bias dependence of a solid material part and liquid material part on the surface of the sample based on the correlation between resonance frequency component of the conductive probe and application bias is measured, a bias value at which electrostatic forces acting on the solid material part and liquid material part (refer to Fig. 3) are equal is determined, the sample surface is scanned while the distance between the sample and conductive probe is kept so that the magnitude of the electrostatic force is constant in an applied state using the determined bias value, and the surface shape of the sample is accurately measured. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a method for measuring the surface shape of a soft material using a probe microscope and a probe microscope used for the measurement.
In particular, the present invention relates to a method for measuring the surface shape of a soft material including droplets or a material that is highly volatile and soft and easily deformed, and a probe microscope used in the measurement method.

In recent years, to measure not only solid surfaces but also surface shapes of soft materials and meniscus shapes of micron-sized liquid materials with a high degree of accuracy, such as surface shapes of materials that are highly soft and easily deformed. The demand for is increasing.
For example, the measurement of the surface shape of such a soft material includes measurement of soft materials such as oil and fat adhering to the magnetic disk surface, the ink shape at the nozzle portion of an inkjet printer, and the like.

Conventionally, as a method of observing such a liquid surface, an environment-controlled scanning electron microscope or atomic force microscope that can be observed in an environment close to atmospheric pressure is used.
For example, Patent Document 1 discloses the following observation means.
In other words, in order to prevent the sample from shrinking due to water evaporation during observation and to provide an electron microscope that can be observed without pretreatment, the water-retaining substance is connected to a water storage tank in the atmosphere. Means are disclosed for supplying moisture and for the water retention substance to supply moisture to the sample.
Thus, it is possible to observe the environment-controlled scanning electron microscope while supplementing from the outside the moisture that volatilizes from the sample surface.

In Patent Document 2, in order to measure the surface shape of a soft object, at least the tip portion of the probe is set so that the surface energy of the tip of the probe is lower than the interface energy between the tip portion and the substance to be measured. A method for determining the surface material is disclosed.
In this method, in the atomic force microscope, a configuration is used in which the tip of the probe is covered with a fluorine-based coating film or the like to prevent adhesion of oil and fat to the probe and destruction of the shape.
Furthermore, Non-Patent Document 1 reports on observation of droplets and the like using an apparatus capable of controlling / measuring piconewton order force in the latest atomic force microscope.
In other words, this device can control / measure not a force at the nano-Newton level, but a weaker force of the picononton order, so that the force between the probe and the target sample is set to be weak so that droplets can be observed. It can be done.
JP-A-08-050875 JP 2000-155084 A http: // www. asylum research. com / Image Gallery / Mat / Mat. shml # M2

However, the above-described conventional method for measuring the surface shape of a soft material has the following problems.
For example, in Patent Document 1, since an environment-controlled scanning electron microscope or atomic force microscope is used, it is difficult to observe with a high function or to measure an accurate shape.
In addition, it is difficult to observe the shape without any influence of electron beam irradiation, and there are many problems such as inability to observe in a complete atmospheric pressure state. Further, Patent Document 2 has a problem that the shape of the soft material itself cannot be accurately measured although the soft material can be prevented from adhering to the probe.
Furthermore, in the case of an atomic force microscope capable of detecting the force of the latest piconewton order, it requires a large capital investment because it is a dedicated device.

  In view of the above-mentioned problems, the present invention provides a probe microscope that can accurately measure the surface shape of a soft material including liquid droplets or a material that is highly volatile and soft and easily deformed. An object is to provide a measurement method and a probe microscope used in the measurement method.

In order to achieve the above object, the present invention provides a method for measuring the surface shape of a soft material using a probe microscope configured as follows, and a probe microscope used in the measurement method.
The method for measuring the surface shape of a soft material with a probe microscope according to the present invention is a method for measuring the surface shape of a sample with a soft material containing droplets or a material that is highly volatile and soft and easily deformed with a probe microscope. ,
A voltage is applied between the sample and the conductive probe, and the bias dependence of the solid material portion and the liquid material portion on the surface of the sample is determined based on the correlation between the resonance frequency component of the conductive probe and the applied bias. Measuring, and
Determining a bias value at which electrostatic forces acting between the solid material portion and the liquid material portion are equal based on the measurement result of the bias dependency; and
The surface of the sample is scanned while maintaining the distance between the sample and the conductive probe so that the magnitude of the electrostatic force is constant while being applied using the determined bias value. Measuring the shape; and
It is characterized by having.
Moreover, the method for measuring the surface shape of a soft material using a probe microscope according to the present invention is a step of measuring the surface shape of the sample,
When maintaining the distance between the sample and the conductive probe, the distance between the sample and the conductive probe is controlled using a frequency displacement detection method.
Moreover, the method for measuring the surface shape of a soft material using a probe microscope according to the present invention is a step of measuring the surface shape of the sample,
When maintaining the distance between the sample and the conductive probe, the distance between the sample and the conductive probe is controlled using an amplitude displacement detection method.
Further, the probe microscope of the present invention is a probe microscope used for measuring the surface shape of a sample using a soft material including a droplet or a material that is highly volatile and soft and easily deformed.
A conductive probe;
Voltage applying means for applying a voltage between the conductive probe and the sample;
Bias dependence of the solid material portion and the liquid material portion on the surface of the sample based on the correlation between the resonance frequency component of the conductive probe and the applied bias in the voltage application state between the probe and the sample by the voltage application means Measuring means for measuring sex;
The probe is configured so that the electrostatic force becomes a constant force by applying a bias value that equalizes the electrostatic force acting on each of the solid material portion and the liquid material portion based on the measurement result by the measuring means. And means for controlling the distance between the sample and
It is characterized by having.
The probe microscope of the present invention is characterized in that the means for controlling the distance between the probe and the sample is constituted by a control system using a frequency displacement detection method.
The probe microscope of the present invention is characterized in that the means for controlling the distance between the probe and the sample is constituted by a control system using an amplitude displacement detection method.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to measure the surface shape of a soft material containing a droplet or a material which is highly volatile and soft and easily deforms with high accuracy.

Next, a method for measuring the surface shape of a soft material using a probe microscope and a probe microscope used in the measurement method according to an embodiment of the present invention will be described.
FIG. 1 shows a schematic diagram of a configuration example of a control circuit of a scanning probe microscope in the present embodiment.
In FIG. 1, 1 is a conductive cantilever, 2 is a sample, 3 is a semiconductor laser, 4 is an optical displacement detector, 5 is a piezoelectric vibrator, and 18 is a PZT scanner on which the sample 2 is mounted.
In the present embodiment, the conductive cantilever 1 can be selected from various hardnesses, but it is desirable to use one having a resonance frequency of about 60 to 350 kHz.
From the viewpoint of spatial resolution, the tip curvature radius of the tip of the cantilever tip is preferably 40 nm or less and 20 nm or more.
Furthermore, the conductive coating film on the surface of the cantilever and the probe can be selected from metals such as Au, Ag, Pt, Pd, Zn, Cr, W, In, and their intermetallic compounds, and oxide semiconductors. Therefore, Au and Pt are preferable.

The cantilever 1 is fixed to a piezoelectric vibrator 5 and connected to a preamplifier 6, a phase shifter 7, a waveform converter 8 and an attenuator 9 to constitute a self-excited transmission circuit using a positive feedback transmission loop.
Further, 10 is an oscillator, 11 is a DC power supply, and 12 is an accumulator, and these constitute a power supply system circuit.
In the present embodiment, the power supply system circuit is connected to the sample 2 and configured to be able to apply a voltage to the grounded cantilever 1.
Further, 13 is an FM demodulator, 14 is a lock-in amplifier, 15 is an error amplifier, 16 is a filter, and 17 is a Z piezo driver, and these constitute a feedback circuit.
In the present embodiment, this feedback circuit extracts the electrostatic force between the probe at the tip of the cantilever 1 and the sample 2 and drives the scanner 18 on which the sample 2 is mounted so that the magnitude thereof is constant.
If the output of the Z piezo driver 17 of the feedback circuit is displayed in synchronization with in-plane scanning, the shape of the surface can be observed.
Further, when the feedback circuit is configured using the circuit components 19 and 20 indicated by the dotted lines in FIG. Atomic force microscope observation by frequency displacement detection becomes possible.

Next, a difference in bias dependency due to a difference in material in the method for measuring the surface shape of a soft material according to the present embodiment will be described.
FIG. 2 is a diagram for explaining a difference in bias dependency due to a difference in material between the nozzle portion and the liquid portion. FIG. 2 schematically shows a state in which the liquid protrudes from the nozzle tip.
When the interaction force (electrostatic force) is measured while a voltage is applied between the probe and the sample, the dependency on the bias differs because the nozzle portion and the liquid portion are made of different materials.
This measuring method will be described in more detail. First, in the state where a voltage is applied between the cantilever 1 and the sample 2, an interaction force (electrostatic force) acting between them is measured.
The ac component V _AC sin (ωt) as the output of the oscillator 10 and the direct current component V _DC as the output of the DC power source 11 are added together by the accumulator 12 and applied to the sample 2. At this time, the output of the transmitter 10 has a frequency of about 1 kHz and an amplitude of about 2 Vp-p.
In FIG. 3, the component of the resonance frequency ω is extracted by the lock-in amplifier 14 from the output of the optical displacement detector 4 that has detected the vibration of the cantilever 1, and the output of the lock-in amplifier 14 is plotted along the vertical axis. An example of measurement of bias dependency with _sample = V _DC on the horizontal axis is shown.
The output of the lock-in amplifier 14 corresponds to the first-order differential value by the applied voltage V _sample of the force gradient dF / dz acting between the probe and the sample.
Since the nozzle portion and the liquid portion are made of different materials, the bias dependence due to the electrostatic force acting between the probe and the sample is different, and their inclinations are different as shown in FIG.
Here, the bias value Vx at which the electrostatic force between the nozzle and the liquid probe is equal is read from FIG.
In the case of a material other than a metal material, this graph is not necessarily a straight line, but what is important is to find a bias value Vx at which the electrostatic force becomes equal.

When measuring the surface shape of the soft material, the bias value Vx is set to the DC output value of the power source 11 (V _DC = Vx), and feedback is applied so as to keep the magnitude of the electrostatic force constant regardless of the material. Therefore, the surface shape of the soft material can be accurately measured.
In the present invention, the circuit configuration is not limited to that shown in FIG. For example, it may be configured as shown in FIG.

According to the configuration of the present embodiment described above, the surface shape of a soft object or a droplet can be accurately measured by feeding back the electrostatic force that can be measured in a non-contact manner.
In addition, since it is a scanning probe microscope, it does not require a vacuum environment unlike an environment-controlled scanning electron microscope, and can be observed in the atmosphere. According to this, it is possible to accurately measure the surface shape of a material that has a high possibility of volatilization and is very soft and easily deformed.

Examples of the present invention will be described below.
[Example 1]
In Example 1, the control circuit of the scanning probe microscope basically has the same configuration as that in FIG.
Various hardness can be selected for the conductive cantilever 1, but in this example, a metal-coated product with a commercially available cantilever for an atomic force microscope (PP-NCLPt manufactured by NanoWorld AG, resonance frequency 190 kHz, PtIr coating) was used. .
Further, as the laser light emitted from the semiconductor laser 3, a laser light having a wavelength of 670 nm is used.
A configuration is adopted in which the laser light is irradiated and reflected on the back surface of the cantilever 1 and detected by an optical displacement detector 4 (Position Sensitive Detector using a four-division photodiode) to detect the vibration state of the cantilever 1.

In the present embodiment, when observing a sample having the form shown in FIG. 2, first, an interaction force (electrostatic force) acting between the cantilever 1 and the sample 2 is measured while a voltage is applied between the cantilever 1 and the sample 2.
At that time, the AC component V _AC sin (ωt) as the output of the oscillator 10 and the DC component V _DC as the output of the DC power source 11 are added together by the accumulator 12 and applied to the sample 2. At this time, the output of the transmitter 10 has a frequency of 1 kHz and an amplitude of 2 Vp-p.
Thus, the component of the frequency ω is extracted by the lock-in amplifier 14 from the output of the optical displacement detector 4 that detects the vibration of the cantilever 1, and the applied bias V _sample = V is plotted on the vertical axis. A measurement result as shown in FIG. 3 with _DC as the horizontal axis is obtained.
From this measurement result, the bias value Vx at which the electrostatic forces of the nozzle and the liquid probe are equal is read.

Next, the output voltage V _DC of the DC power source 11 is set to the bias value Vx, and the shape is measured.
The output of the waveform converter 8 is input to the lock-in amplifier 14 via the FM demodulator 13 to extract the component of the frequency ω, and the output is set to 0 by comparing the arbitrarily set value X with the error amplifier 15. A drive signal is output from the Z piezo driver 17 to the PZT scanner 18 as described above.
The distance between the sample and the probe is controlled so that a constant (set value X) electrostatic force can be detected by this feedback circuit, and the output signal of the Z piezo driver 17 and the scanning signal in the sample surface are displayed in synchronization. The shape of the sample surface as shown in FIG. 4 can be observed.
In FIG. 4, the peripheral part is a metal nozzle surface, and the central circular part represents the liquid surface.
At the time of observation, if the set value X is set to a relatively large value, the distance between the sample probes is reduced, and the spatial resolution of the observed image is improved, but the possibility of contact between the probe and the sample is also increased. In actual measurement, it is necessary to appropriately adjust the set value X and the excitation amplitude of the cantilever 1.

In addition, although the circuit which earth | grounds the cantilever 1 was demonstrated in the present Example, this invention is not limited to these structures.
For example, the same measurement is possible even if the sample is grounded and the accumulator 12 is connected to the cantilever 1.
In the control circuit of FIG. 1, a feedback circuit that grounds the sample and returns the output of the FM demodulator 13 to the Z piezo driver 17 through the error amplifier 19 and the filter 20 may be used.
That is, by using the feedback circuit including the error amplifier 19 and the filter 20 shown by the dotted line in FIG. 1 in a state where the power supply system circuits 10, 11 and 12 are not used and the sample 2 is grounded, atoms by frequency displacement detection are used. Observation with an atomic force microscope is possible.

[Example 2]
In the second embodiment, a configuration example using a control circuit of a scanning probe microscope different from the first embodiment will be described.
FIG. 5 shows a schematic diagram of a configuration example of another control circuit of the scanning probe microscope used in this embodiment.
The difference from the first embodiment is that the cantilever 1 is oscillated by the oscillator 21 instead of the self-excited transmission circuit, and the RMS-DC converter 22 is incorporated instead of the FM demodulator 13, and other than that of the first embodiment. The same.
Also in this example, as in Example 1, as a result of observing the sample shown in FIG. 2, a shape image similar to that in FIG. 4 can be obtained.

In addition, although the circuit which earth | grounds the cantilever 1 was shown also in the present Example, this invention is not limited to this.
For example, the same measurement is possible even if the sample is grounded and the accumulator 12 is connected to the cantilever 1.
In the control circuit of FIG. 5, the sample is grounded and the output of the optical displacement detector 4 is connected to the RMS-DC converter 22.
If a feedback circuit for returning to the Z piezo driver 17 through the error amplifier 19 and the filter 20 is used, an atomic force microscope observation based on amplitude displacement detection becomes possible.

Schematic which shows the structural example of the control circuit of the scanning probe microscope in embodiment and Example 1 of this invention. The figure for demonstrating the difference in the bias dependence by the difference in the material in a nozzle part and a liquid part in the surface shape measuring method of the soft material by the probe microscope of embodiment of this invention. The figure for demonstrating the example of a measurement of bias dependence by the probe microscope of embodiment of this invention. The figure which shows the example of surface shape measurement of the soft material by the probe microscope in Example 1 of this invention. Schematic which shows the structural example of the control circuit of the scanning probe microscope in Example 2 of this invention.

Explanation of symbols

1: Conductive cantilever 2: Sample 3: Semiconductor laser 4: Optical displacement detector 5: Piezoelectric vibrator 6: Preamplifier 7: Phase shifter 8: Waveform converter 9: Attenuator 10: Oscillator 11: DC power supply 12: Cumulative Calculator 13: FM demodulator 14: Lock-in amplifier 15: Error amplifier 16: Filter 17: Z piezo driver 18: PZT scanner 19: Error amplifier 20: Filter 21: Oscillator 22: RMS-DC converter

Claims (6)

A method for measuring the surface shape of a sample by a probe or a soft material including a liquid or a material that is highly volatile and soft and easily deformed.
A voltage is applied between the sample and the conductive probe, and the bias dependence of the solid material portion and the liquid material portion on the surface of the sample is determined based on the correlation between the resonance frequency component of the conductive probe and the applied bias. Measuring, and
Determining a bias value at which electrostatic forces acting between the solid material portion and the liquid material portion are equal based on the measurement result of the bias dependency; and
The surface of the sample is scanned while maintaining the distance between the sample and the conductive probe so that the magnitude of the electrostatic force is constant while being applied using the determined bias value. Measuring the shape; and
A method for measuring the surface shape of a soft material using a probe microscope. In the step of measuring the surface shape of the sample,
2. The soft object by a probe microscope according to claim 1, wherein the distance between the sample and the conductive probe is controlled using a frequency displacement detection method when maintaining the distance between the sample and the conductive probe. Surface shape measurement method. In the step of measuring the surface shape of the sample,
3. The probe according to claim 1, wherein when the distance between the sample and the conductive probe is maintained, the distance between the sample and the conductive probe is controlled using an amplitude displacement detection method. A method for measuring the surface shape of a soft material using a microscope. A probe microscope used for measuring the surface shape of a sample with a droplet or a soft material containing a material that is highly volatile and soft and easily deformed.
A conductive probe;
Voltage applying means for applying a voltage between the conductive probe and the sample;
Bias dependence of the solid material portion and the liquid material portion on the surface of the sample based on the correlation between the resonance frequency component of the conductive probe and the applied bias in the voltage application state between the probe and the sample by the voltage application means Measuring means for measuring sex;
The probe is configured so that the electrostatic force becomes a constant force by applying a bias value that equalizes the electrostatic force acting on each of the solid material portion and the liquid material portion based on the measurement result by the measuring means. And means for controlling the distance between the sample and
A probe microscope characterized by comprising:   The probe microscope according to claim 4, wherein the means for controlling the distance between the probe and the sample is configured by a control system using a frequency displacement detection method.   The probe microscope according to claim 4 or 5, wherein the means for controlling the distance between the probe and the sample is configured by a control system using an amplitude displacement detection method.

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