JP2000230933A - Probe microscope and surface property analyzing method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus or method for extremely reducing the data size in obtaining a focus curve and capable of obtaining even data incapable of being obtained heretofore. SOLUTION: The probe microscope detects the mutual action force acting across a probe and a sample while changing the distance between the probe and the sample, to obtain detection data showing the magnitude of the mutual action force to the distance between the probe and the sample to obtain the surface properties of the sample. In this case, the probe microscope has a fitting function lead-out means for leading out a fitting function of the distance between the probe and the sample and the magnitude of mutual action force obtained on the basis of detection data and at least partially approximate to the detection data, a calculation means for calculating the difference between the fitting function and detection data at every distance between the probe and the sample, and a memory part for storing the calculated fitting function and the difference calculated by the calculation means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a surface property of a sample by a force microscope using a probe microscope.

[0002]

2. Description of the Related Art In recent years, a scanning probe microscope (SPM), which is rapidly progressing,
It has attracted much attention as a microscope that can observe various physical properties of the surface at the atomic level. Scanning force microscope (Scanning Force Microscope)
Is the most basic scanning probe microscope that underlies the various scanning probe microscopes currently derived. One of the measuring techniques of the scanning probe microscope is a technique called force curve mapping using a force curve. In this method, a force curve is obtained by recording a change in the bending of the cantilever obtained when the cantilever provided with the probe is moved toward or away from the surface of the object to be measured. By analyzing the obtained force curve, it is possible to check how much interaction force is acting on the distance between the sample surface and the probe.

In particular, research has been conducted to determine the long-range interaction force between the probe and the sample using the force curve before and after the probe contacts the sample, that is, with the tip of the probe away from the sample. It is being actively conducted. Examples of these interaction forces include hydrophobic interaction in a liquid and forces such as electric double layer force, and these interactions have been actively studied as interactions between biomolecules. In addition, the bonding force between molecules can be measured.

[0004] As described above, the force curve contains various information on the sample surface, and by analyzing the force curve, it is possible to evaluate the physicochemical properties of various surfaces. In fact, while scanning the cantilever in parallel with the surface to be used, force curves are obtained one after another at 128 × 128 grid points, and all the obtained force curves are analyzed to obtain various force curves. By extracting information on the sample surface and mapping the information, distribution images of various physicochemical properties of the sample surface can be obtained.

[0005]

However, while the force curve mapping method has a large amount of information, it has a very large amount of data and its handling is complicated. In such a situation, if the SN ratio of the data is further improved, or the dynamic range of the force curve data is expanded or the number of samplings of the force curve is increased in order to improve the data quality, the data size becomes enormous. And the computer is overloaded.

[0006] In addition, there is a demand for a measurement method that can obtain more information than conventional measurement methods.
An object of the present invention is to provide an apparatus or a method for obtaining a force curve in which the data size is extremely small in order to solve such a problem. Still another object of the present invention is to provide an apparatus or a method capable of acquiring information that could not be acquired until now.

[0007]

In order to solve the above-mentioned problems, the present invention detects the interaction force acting between the probe and the sample while changing the distance between the probe and the sample, and detects the interaction force between the probe and the sample. Acquisition of detection data indicating the magnitude of the interaction force with respect to the distance, in a probe microscope that can obtain the surface properties of the sample, obtained based on the detection data,
A function at least partially approximated to the detection data,
Fitting function deriving means for deriving a fitting function that is a function of the distance between the probe and the sample and the magnitude of the interaction force, and calculation for calculating the difference between the fitting function and the detection data for each distance between each probe and the sample And a storage unit for storing the calculated fitting function and the difference calculated by the calculating unit.

[0008] By obtaining a fitting function from the detection data obtained by the measurement in this way and storing the fitting function and the difference between the fitting function and the detection data, the data amount can be made smaller than before.
Further, the fitting function deriving means according to the present invention, among the detection data, the detection data obtained when the probe is in contact with the sample and the detection data obtained when the probe is not in contact with the sample. The apparatus further includes data separation means for separation, and a fitting function is derived based on detection data in a state where the probe separated by the data separation means is not in contact with the sample. By separating the data obtained when the contact is made and the data obtained when the contact is not made, and obtaining a fitting function from the detection data obtained when the contact is not made, a long-range interaction force can be obtained. In addition, since the data at the time of contact and the data at the time of non-contact each contain different information, in order to extract the information, the data obtained at the time of contact and the data obtained at the time of non-contact are also extracted. Separation is necessary.

Further, the apparatus further comprises detecting means for detecting an interaction force between the probe and the sample from the fitting function obtained by the fitting function deriving means, and an interaction force between a certain probe and the sample based on the fitting function. Can be obtained. Further, the data separation means may be configured such that the detection data obtained when the probe is in contact with the sample and the detection data obtained when the probe is not in contact with the sample depend on the magnitude of the noise in the detection data. Separated from data.

Another data separation means is a differential function obtained by differentiating the function indicating the magnitude of the interaction force with respect to the distance between the probe and the sample obtained based on the detection data by the distance between the probe and the sample. And the detection data obtained when the probe is in contact with the sample, before and after the value of the distance between the probe and the sample where the peak value of the differential function appears, and when the probe is not in contact with the sample. It may be separated from the obtained detection data.

Further, the fitting function has terms having different orders, and electrical or magnetic information is obtained by using a coefficient given to a -2 order term among the terms. In addition, the electric double layer interaction force can be obtained from the value given to the exponential coefficient. In addition, a temperature data acquisition unit for acquiring the temperature data by averaging the differences calculated by the calculation means may be further provided to obtain the temperature data.

In order to solve the above-mentioned problems, the present invention detects the interaction force acting between the probe and the sample while changing the distance between the probe and the sample, and detects the interaction force with respect to the distance between the probe and the sample. In a surface texture analysis method capable of acquiring detection data indicating the magnitude of force and obtaining the surface texture of a sample, a function having a value at least approximated to the detection data, the distance between the probe and the sample and the interaction A fitting function, which is a function of the magnitude of the force, is derived, and the difference between the fitting function and the detection data is calculated for each distance between each probe and the sample, and the calculated fitting function and the difference calculated by the calculating means are calculated. Is stored, and the surface property of the sample is detected using at least one of the fitting function and the difference calculated by the calculation means. Further, in the present invention, while changing the distance between the probe and the sample, the interaction force acting between the probe and the sample is detected, and detection data indicating the magnitude of the interaction force with respect to the distance between the probe and the sample is obtained. Then, in the surface texture analysis method capable of obtaining the surface texture of the sample, the first detection data obtained in a state where the probe is in contact with the sample and the first detection data obtained in a state where the probe is not in contact with the sample are included in the detection data. The obtained second detection data was separated, a fitting function was derived based on the second detection data, and the interaction force between the probe and the sample was detected from the fitting function. Then, the difference between the fitting function and the detection data is further obtained, and the standard deviation of the difference is obtained to detect the temperature of the sample surface.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment to which the present invention is applied will be described. FIG. 1 shows a scanning probe microscope according to an embodiment of the present invention. In this scanning probe microscope, a sample moving unit 3 provided in a U-shaped casing 1 for moving a sample 2 and a sample 2 provided in the sample moving unit 3 are provided.
, A probe 5 for scanning the surface of the sample 2 and receiving an interaction force with the sample surface, a housing 1 and the probe 5
Probe moving means 6 which is provided between the first and second members to change the position of the probe 5 with respect to the sample surface when acquiring a force curve.
And a light source 7 for detecting an interaction force with the sample 2 received by the probe 5 by an optical lever method, and a spot position of light reflected from a probe similarly provided for detecting by an optical lever method. A detection unit 8 for detecting, a sample movement unit drive unit 9 for driving the sample movement unit 3, a probe movement unit drive unit 10 for driving the probe movement unit 6, and a signal from the detection unit 8 A / D conversion unit 11 for converting into a digital signal, central processing unit 12 for controlling the scanning probe microscope and for signal processing
And a display unit 13 for displaying information obtained by the scanning probe microscope.

The probe 5 has a cantilever structure, and has a probe 51 at one end and a support 52 fixed to the probe moving means 6 at the other end. The cantilever of the probe 5 is irradiated with light from the light source 7, and the light spot reflected by the cantilever is received by the detector 8.
The detector 8 outputs a signal about the position of the received light spot. Since this signal indicates the inclination of the cantilever, the interaction force between the probe 5 and the surface of the sample 2 can be detected based on the signal from the detection unit 8. Note that a position-sensitive diode or the like is used for the detection unit 8.

Since the signal obtained from the detecting section 8 is an analog signal, the signal from the detecting section 8 is input to an A / D converter 11 for converting the signal into a digital signal. Then, the digital signal is input to the central processing unit 12 converted to a digital signal. Further, the sample moving means 3 comprises a tube scanner constituted by a piezoelectric element having a cylindrical shape. The sample moving means 3 can move the sample 2 by the voltage obtained from the sample moving means driving unit 9. In addition, the sample moving means driving unit 9 can generate a voltage for driving the tube scanner according to the moving data output from the central processing unit 12. The probe moving means 6 is formed of a block-shaped piezoelectric element. The moving unit 6 is driven by a voltage supplied from the probe moving unit driving unit 10. The probe moving means driving unit 10
Can generate a voltage for driving the probe moving means 6 according to the movement data output from the central processing unit 12.

The display means 13 uses a monitor in the present embodiment. However, the present invention is not limited to this, and any printer or other device capable of displaying information to humans may be used. Next, a method of acquiring a force curve will be described. First, the sample moving means 3 is driven so that the probe part 51 of the probe 5 is located on a desired measurement point of the sample 2. At this time, the central processing unit 12 outputs the movement data to the sample moving means driving unit 9.

Then, when the probe 51 comes to a desired measurement point, the probe 5 is moved next to approach the sample 2. At this time, the central processing unit 12 controls the probe moving means driving unit 1
The movement data of the probe 5 is output to 0. At the same time as the probe 5 approaches, the signal from the A / D converter 11 is also input, and the distance between the probe 5 and the surface of the sample 2 and the interaction force received by the probe 5 at that time are determined. The data is sequentially stored in a memory provided in the central processing unit 12.

Next, when the probe 5 approaches the sample 2 to a desired position, the probe 5 is moved away from the surface of the sample 2. At this time, similarly to the above, the central processing unit 12 outputs data to the probe moving means driving unit, and simultaneously outputs the A /
A signal from the D converter 11 is input. And the probe 5-
The distance between the surfaces of the sample 2 and the interaction force received by the probe 5 at that time are sequentially stored.

The above operation is performed while sequentially changing the position of the surface of the sample 2 on which the probe 5 comes directly above, and the force curve mapping is performed. By the way, in the scanning probe microscope of the present invention, since the distance between the probe 5 and the sample surface and the interaction force received by the probe 5 are sequentially stored, a large storage capacity is required even in a single measurement. I do. Therefore, the data once stored is processed as follows.

Next, a processing method in the central processing unit 12 will be described with reference to FIG. FIG. 2 shows a central processing unit 1
6 is a flowchart showing a processing procedure of data obtained in step 2. The process of the flowchart shown in FIG. 2 is performed for each measurement at one location. First, the central processing unit 12 outputs a signal indicating a location to be measured to the sample moving means driving unit 9 in a step not shown, and moves the sample 2 so that the probe 5 comes to a desired position on the sample 2. Move.

Next, the central processing unit 12 measures the force curve shown in step S001.
In the measurement of the force curve, the following operation is performed.
First, the probe 5 is brought close to the surface of the sample 2. At this time, the central processing unit 12 outputs a driving signal to the probe moving unit driving unit 10. In the meantime, the central processing unit 12 inputs a signal relating to the displacement of the probe 5 output from the A / D converter 11 and stores the relationship between the distance between the sample 2 and the probe 5 and the interaction force. When the distance between the probe 5 and the sample 2 reaches a predetermined distance, the probe 5 is moved in a direction away from the surface of the sample 2. At this time, the central processing unit 12 also outputs a driving signal to the probe moving unit driving unit 10 in the same manner. In the meantime, the central processing unit 12 inputs a signal relating to the displacement of the probe 5 output from the A / D converter 11 and stores the relationship between the distance between the sample 2 and the probe 5 and the interaction force.

The force curve obtained in this way is a curve shown by a thick line in FIG. In this figure, the vertical axis indicates the displacement of the cantilever (cantilever) of the probe 5, and the horizontal axis indicates the distance between the probe 5 and the surface of the sample 2. The order of the curve changes is in alphabetical order. The data of the force curve has a signal waveform as shown in FIG. FIG. 4 shows each signal waveform. The vertical axis indicates the strength of the signal, and the horizontal axis indicates the time. Note that this time is described along with the timing at which the probe is moved to obtain the force curve. And the alphabet in the figure corresponds to the alphabet described in FIG.

Next, the process proceeds to step S002, and FIG.
A smoothing process is performed on the force curve indicated by the thick line in (a), and smoothed force curve data is created and stored. The signal waveform of the smoothed force curve is as shown in FIG. The portion where the irregularities are repeated in such a short cycle is smoothed. It should be noted that unevenness generated in a long cycle is not smoothed.

When the smoothed force curve data is created, in step S003, a difference between the smoothed force curve data and the original force curve data is obtained. When the difference is obtained, the data where the difference is large on average is recognized as the data of the non-contact area, and the data where the difference is small is recognized as the data of the contact area.

In this step, the central processing unit 12 actually performs the following operations. First, a difference between the smoothed force curve data and the original force curve data is obtained, and the difference is obtained as a noise signal. The waveform of the noise signal is shown in FIG. Then, the noise signal is squared to obtain a squared waveform of the noise signal. The waveform is obtained in FIG. Finally, FIG.
Is smoothed to obtain a squared smoothed signal of the noise signal (see FIG. 4E).

A certain threshold value is set for the signal, and a region having a signal higher than the threshold value is determined as a non-contact region, and a region having a signal lower than the threshold value is determined as a contact region. The contact region and the non-contact region will be described with reference to FIG. 3. In FIG. 3A, there is a region between the points A and B where the probe 5 approaches the surface of the sample 2. 51
Is an area not in contact with the sample 2. The probe 5 also extends from F to G away from the surface of the sample 2, and is actually a region where the probe 51 does not contact the sample 2. Then, from B to D, the probe 51
And the area where the entire probe 5 comes closer.

As can be seen from FIG. 3 (a), the non-contact area has very uneven original data itself. Focusing on this, the scanning probe microscope according to the embodiment of the present invention sets a portion where the difference data from the leveled force curve is large as a non-contact region, and sets a portion where the difference is small as a contact region. Next, in the scanning probe microscope according to the embodiment of the present invention, a fitting function is created based on the data of the region that has been identified as the non-contact region in step S005. The fitting function is a function having a plurality of different orders, and an appropriate function is selected for each order coefficient to create a fitting function.

Specifically, the coefficient of each order reflects the corresponding physicochemical property. Therefore, an appropriate order is selected from the estimated long-range interaction to create a polynomial having a different order. Then, a fitting function can be obtained by performing fitting using the least square method based on the polynomial. After the fitting function is obtained in this way, next, in step S00
In step 7, the difference between the fitting function and each force curve data is calculated.

In the embodiment of the present invention, since it is desired to further obtain information on the temperature of the surface of the sample 2, the standard deviation is calculated from all the differences between the force curve data and the fitting function. Then, in order to obtain temperature information, a temperature parameter is further determined from the standard deviation in step S.
008. Such an operation is not particularly necessary when the temperature parameter is not calculated.

Then, in step S009, the obtained fitting function and the amount of deviation from the fitting function are stored as a force curve, and the force curve measured in step S001 is stored in a region where no fitting function has been obtained. . As described above, the scanning probe microscope according to the present embodiment calculates the difference between the fitting function only in the non-contact region and the force curve data of the fitting function and the original, and stores each of them.

Then, by moving the sample 2 so that the probe 5 comes to another position of the sample 2 and acquiring force curves at a plurality of positions, force curve mapping can be obtained. In this way, by storing only the fitting function and the difference between the fitting function and the force curve data, it is possible to reduce the number of bits required until now when storing all data in a desired dynamic range. Was completed.

Incidentally, in the case of the force curve data as shown in the present embodiment, a 32-bit data area was required in the conventional scanning probe microscope, but in the scanning probe microscope in the embodiment of the present invention. Fits within 16 bits. Therefore, the data amount can be halved. Thus, the storage capacity of the scanning probe microscope according to the embodiment of the present invention was reduced.

In this embodiment, a force curve is obtained only in the non-contact area. This is because in the non-contact area, the probe 5 is not in contact with the sample, so that it is very susceptible to disturbance and easily vibrates. This is considered to be the cause of the noise. Thermal vibration is considered as one of the disturbances. In the present embodiment, a parameter relating to temperature is obtained by obtaining the influence of the thermal vibration.

In the scanning probe microscope according to the embodiment of the present invention, in order to detect a long-range interaction force, coefficients in respective orders are obtained from a fitting function obtained in a non-contact area. To detect the interaction of the long-range interaction force. The coefficients provided for the respective orders have the following meanings. First, the value of the exponential term can extract the electric double layer interaction force. Also,-
The second order coefficient can obtain the amount of electrostatic and magnetic interaction. It should be noted that the polynomial used in the embodiment of the present invention is represented by Expression (1).

[0035]

F = a ₁ e ^−kz + a ₂ z ^{−2 In} Equation (1), z is the distance between the probe and the sample, and a1
, K is a coefficient indicating a parameter of the electric double layer interaction, and particularly, k is a parameter called Debye length.
a2 is a coefficient indicating a parameter of the electric or magnetic interaction. Then, the coefficient shown in Expression (1) is obtained, and the long-range interaction force is calculated based on the value of the coefficient.

In the present embodiment, the noise signal is used to separate the contact area and the non-contact area. However, the present invention is not limited to this. For example, a differential signal of the obtained force curve is obtained. When the differential signal has a maximum value, it is possible to separate the contact region from the non-contact region. In FIG. 3B, the vertical axis indicates the force curve differential signal intensity, and the horizontal axis indicates the distance between the cantilever and the sample. As described above, since snap-in and snap-out occur at the boundary between the non-contact area and the contact area, it is preferable to determine the contact area and the non-contact area by using the snap-in and snap-out.

[0037]

As described above, when the probe microscope according to the present invention is used, the data amount is reduced without lowering the dynamic range and the SN ratio, so that the data can be easily stored. Further, a fitting function is further obtained from the force curve as a polynomial having a desired order, and the long-range interaction force can be detected from the value of the coefficient of the polynomial, and the fitting function and the data of the original force curve can be obtained. From the difference, the temperature parameter can be obtained. Various information can be obtained with such a small amount of data.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a scanning probe microscope according to the present invention.

FIG. 2 is a flowchart performed by a central processing unit of the scanning probe microscope according to the present invention.

FIG. 3: (a) is an example of a force curve showing displacement of the cantilever with respect to the distance between the cantilever and the sample, and (b) shows a waveform of a signal obtained by differentiating the force curve obtained in (a). It is a thing.

FIG. 4 is a graph showing a signal waveform obtained by a scanning probe microscope according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 housing 2 sample 3 sample moving means 4 sample table 5 probe 51 probe section 52 support section 6 probe driving means 7 light source 8 detecting section 9 sample moving means driving section 10 probe moving means driving section 11 A / D conversion Unit 12 central processing unit 13 display means

Claims (10)

[Claims] 1. A method for detecting an interaction force acting between the probe and the sample while changing a distance between the probe and the sample, and indicating a magnitude of the interaction force with respect to a distance between the probe and the sample. In a probe microscope capable of obtaining detection data and obtaining the surface properties of the sample, obtained based on the detection data, and is a function of the distance between the probe and the sample and the interaction force, at least the A fitting function deriving unit that derives a fitting function that is a function fitted to a part of the detection data; and calculates a difference between the fitting function and the detection data for each distance between each probe and the sample. Calculating means; and a storage unit for storing the calculated fitting function and the difference calculated by the calculating means. A characteristic probe microscope. 2. The method according to claim 1, further comprising, of the detection data, detection data obtained when the probe is in contact with the sample and detection data obtained when the probe is not in contact with the sample. And a data separation unit for separating, based on detection data obtained in a state where the probe is not in contact with the sample, among the detection data separated by the data separation unit, a fitting for deriving the fitting function. The probe microscope according to claim 1, further comprising function deriving means. 3. The method according to claim 2, wherein the data separating unit determines whether the probe is in contact with the sample and the detection data obtained in a state in which the probe is in contact with the sample, according to a magnitude of noise included in the detection data. The probe microscope according to claim 2, wherein the detection data is separated from detection data obtained in a state where no detection data is obtained. 4. The data separating means obtains a differential function obtained by differentiating the fitting function by a distance between the probe and the sample, and obtains a value of a distance between the probe and the sample at which a peak value of the differential function appears. Before and after separating the detection data obtained in a state where the probe is in contact with the sample and the detection data obtained in a state where the probe is not in contact with the sample, according to claim 2, Probe microscope. 5. The fitting function has terms having different orders, and acquires electrical or magnetic information by using a coefficient given to a −2 order term among the terms. The probe microscope according to claim 2, wherein 6. The fitting function has a term having an exponent, and according to a value given to an exponential coefficient of the term,
The probe microscope according to claim 2, wherein an electric double layer interaction force is obtained. 7. The apparatus according to claim 1, further comprising a temperature data acquisition unit that acquires a difference between the fitting function and the detection data, and acquires a temperature data by averaging the difference. Probe microscope. 8. While changing the distance between the probe and the sample,
Detecting the interaction force acting between the probe and the sample, obtaining detection data indicating the magnitude of the interaction force with respect to the distance between the probe and the sample, and obtaining the surface properties of the sample. In a surface texture analysis method that can be performed, a fitting function that is a function fitted to at least a part of the detection data and is a function of a distance between the probe and the sample and a magnitude of the interaction force. Calculating a difference between the fitting function and the detection data for each distance between each of the probes and the sample; storing the calculated fitting function and a difference calculated by the calculating unit; Detecting a surface property of the sample by using at least one of a fitting function and a difference calculated by the calculation unit. Surface texture analysis method. 9. While changing the distance between the probe and the sample,
Detecting the interaction force acting between the probe and the sample, obtaining detection data indicating the magnitude of the interaction force with respect to the distance between the probe and the sample, and obtaining the surface properties of the sample. In the surface texture analysis method which can be performed, among the detection data, first detection data obtained in a state where the probe is in contact with the sample and second detection data obtained in a state where the probe is not in contact with the sample Separating the data from the data, deriving a fitting function based on the separated second detection data, and detecting an interaction force between the probe and the sample from the fitting function. . 10. The surface texture analysis method according to claim 9, further comprising obtaining a difference between the fitting function and the detection data, obtaining a standard deviation of the difference, and detecting a temperature of the sample surface. Characteristic surface texture analysis method.