JP7477211B2 - Atomic force microscope, control method, and program - Google Patents

Description

The present invention relates to an atomic force microscope, a control method thereof, and a program.

Conventionally, samples have been measured at atomic resolution using an atomic force microscope (hereinafter also referred to as AFM (Atomic Force Microscope)). For example, significant improvements in force detectors and force detection methods have made it possible to perform AFM observations at atomic resolution in liquid environments, where high-resolution observations were previously considered difficult (see, for example, Patent Document 1). This makes it possible to directly visualize solid-liquid interface phenomena with an AFM, which is expected to contribute to the development of a wide range of research fields.

Japanese Patent Application Laid-Open No. 8-129017

However, conventional AFMs have room for improvement in terms of their application to a variety of applications.

Therefore, the present invention aims to provide an AFM etc. that can be applied to a wider variety of applications.

In order to achieve the above object, an atomic force microscope according to one embodiment of the present invention includes a cantilever having a fixed end at one end in the longitudinal direction that is used to support the lever and a free end at the other end in the longitudinal direction, the cantilever having a probe protruding downward from the lever intersecting the longitudinal direction at the free end, a sample holder disposed below the cantilever and facing the cantilever to hold a sample, a drive unit that drives at least one of the cantilever and the sample holder to move the sample relative to the probe, and a drive unit that controls the drive unit to move the longitudinal line segment relative to the cantilever. and a control unit that causes the probe to scan the surface of the sample within a virtual plane, with a predetermined direction, which is a direction in which a projected image extends when projected onto a virtual plane that intersects with the direction in which the probe protrudes from the bar, as a main scanning direction, wherein the control unit causes the probe to scan the surface of the sample within the virtual plane, in a first direction scan in which the sample moves relatively from the one end side to the other end side, in a first mode in which the sample and the probe are brought close to each other by a first distance and move relatively at a first speed, and in a second direction scan in which the sample moves relatively from the other end side to the one end side, in a second mode in which the sample and the probe are moved away from each other by a second distance greater than the first distance and move relatively at a second speed faster than the first speed.

In addition, a control method according to one embodiment of the present invention includes a cantilever having a long lever, one end side in the longitudinal direction of which is a fixed end used to support the lever and the other end side in the longitudinal direction of which is a free end, the cantilever having a probe provided on the free end side that protrudes downward from the lever in a direction intersecting with the longitudinal direction, a sample holder that is disposed below the cantilever and faces the cantilever to hold a sample, a drive unit that drives the cantilever and the sample holder to move the sample relative to the probe, and a control method for controlling the drive unit to move the probe along a line segment in the longitudinal direction so that the probe protrudes from the cantilever. and a control unit that causes the probe to scan the surface of the sample within a virtual plane, with a predetermined direction as a main scanning direction being a direction in which a projected image extends when projected onto a virtual plane that intersects with the direction in which the sample is projected, the main scanning direction being a predetermined direction in which a projected image extends when projected onto the virtual plane that intersects with the direction in which the sample is projected, the control unit causing the probe to scan the surface of the sample within the virtual plane ...

Furthermore, one aspect of the present invention can also be realized as a program for causing a computer to execute the control method described above.

The present invention provides an atomic force microscope and the like that can be applied to a wider variety of applications.

FIG. 1 is a block diagram showing the configuration of an atomic force microscope according to an embodiment of the present invention. FIG. 2 is a schematic diagram for explaining the scanning direction of the probe of the atomic force microscope according to the embodiment. FIG. 3 is a flowchart showing the operation of the atomic force microscope according to the embodiment. FIG. 4 is a schematic diagram showing how the offset signal is handled in the atomic force microscope according to the embodiment. FIG. 5 is a graph showing an example of actual measurement values of various signals in the atomic force microscope according to the embodiment. FIG. 6 is a diagram for explaining the first direction scanning. FIG. 7 is a diagram for explaining the second direction scanning. FIG. 8 is a diagram showing the concept of increasing the scanning speed in the atomic force microscope 10 according to the embodiment. FIG. 9 is a first graph showing the displacement in the X-axis direction used for scanning with the atomic force microscope in the embodiment. FIG. 10 is a second graph showing the displacement in the X-axis direction used for scanning with the atomic force microscope in the embodiment. FIG. 11A is a first diagram showing the X-axis drive signal and the displacement of the X drive unit during scanning in the X-axis direction of the atomic force microscope according to the embodiment. FIG. 11B is a second diagram showing the X-axis drive signal and the displacement of the X drive unit during scanning in the X-axis direction of the atomic force microscope in the embodiment. FIG. 12A is a first diagram showing the measurement results of actin filaments in the example. FIG. 12B is a diagram showing the measurement results of actin filaments according to a comparative example. FIG. 12C is a graph showing the relationship between imaging speed and the survival rate of actin filaments in the embodiment. FIG. 13A is a second diagram showing the measurement results of actin filaments in the example. FIG. 13B is a diagram showing the measurement results of microtubules according to the embodiment. FIG. 14A is a graph showing the error signal, the feedback control output, and the cantilever deflection signal during forward scanning of the sample. FIG. 14B is a graph showing the error signal, the feedback control output, and the cantilever deflection signal during the return scan of the sample. FIG. 15 is a diagram for explaining the difference in force acting at different scanning positions of the cantilever. FIG. 16 is a graph showing the displacement in the X-axis direction used for scanning with an atomic force microscope in a modified example of the embodiment.

Before describing the embodiments of the present invention, we will explain in detail the problems in the conventional technology described in the background art above, and then we will explain in detail the atomic force microscope according to the present invention.

[Principle of Scanning Probe Microscope]
In a scanning probe microscope (SPM), a sharp probe is brought close to a sample, the interaction (tunnel current or interaction force, etc.) between the probe and the sample is detected, and the distance between the probe and the sample (z position of the probe) is feedback-controlled to keep this interaction constant. Furthermore, if the probe (or the sample) is scanned horizontally (x and y directions) while maintaining this feedback control, the probe (or the sample) will move up and down in response to the unevenness of the sample surface. If the trajectory of the up and down movement of the probe is recorded relative to the horizontal position, an image of the unevenness of the sample surface can be obtained.

[Atomic Force Microscope (AFM)]
An atomic force microscope (AFM) is a type of SPM that detects the interaction force acting between a probe and a sample, and controls the Z position of the probe to keep the distance between the probe and the sample constant. In an AFM, a cantilever with a sharp probe at its tip is used as a force detector. Usually, when the probe is brought close to a sample, an attractive interaction force caused by van der Waals force and electrostatic force acts first. Then, when the probe is brought even closer to the sample, a strong repulsive force caused by chemical interaction force overcomes these forces. In an AFM, when the probe is brought close to the sample surface, the Z position of the probe is feedback-controlled to keep the change in the attractive (or repulsive) force received by the probe constant. In this state, the probe is scanned horizontally to obtain a topographical image of the sample surface, as described above.

AFM uses a photodiode to detect the reflected light of a laser irradiated on the back of the cantilever, and measures the interaction force that the cantilever receives from the tip of the probe from the displacement (deflection) of the cantilever. This type of measurement method is also called the optical lever method.

Here, many examples of using biomaterials as the subject of AFM analysis have been reported. In particular, as an application example of AFM to such biomaterials, the possibility of directly observing the way in which the biomaterial exerts its function has been shown. On the other hand, since the exertion of the function of such biomaterials is realized by a fairly fast change, there are many subjects that are difficult to observe with the current time resolution (also called imaging speed) of AFM. In other words, after obtaining a topographical image at a first time point using AFM, the change in the target biomaterial may be completed by the time the next topographical image is obtained, making it difficult to capture the moment of change continuously over time.

Thus, in order to use current AFMs to observe biological materials, it is desirable to be able to improve the imaging speed. However, with current AFMs, the development of hardware technology that can improve the imaging speed has reached a plateau. Therefore, under the current circumstances, it is difficult to even improve the imaging speed by about two times. The present invention provides an AFM and a control method thereof that can improve the imaging speed of AFMs, which has thus reached a plateau, by 2.5 times or more.

(Embodiment)
Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. Note that each of the embodiments described below shows a specific example of the present invention. The numerical values, shapes, materials, components, the arrangement and connection forms of the components, steps, and the order of steps shown in the following embodiments are merely examples and are not intended to limit the present invention. Furthermore, among the components in the following embodiments, components that are not described in the independent claims showing the highest concept of the present invention will be described as optional components.

[Configuration of atomic force microscope]
FIG. 1 is a block diagram showing the configuration of an atomic force microscope according to an embodiment of the present invention.

The atomic force microscope 10 is an atomic force microscope for observing a sample 99, and includes a cantilever 11 having a probe 12, a displacement measuring unit 13, a feedback control unit 14, a PC (personal computer) 15, an XY drive control unit 16, a drive unit 17, and a sample holder 18. As shown in the lower left of the figure, the vertical direction is the Z axis, and two orthogonal axes that are perpendicular to the Z axis and perpendicular to each other are the X axis and Y axis, and the respective axial directions may be used in the description as the Z axis direction, the X axis direction, and the Y axis direction. In particular, the Z axis direction may be expressed as the up-down direction along the Z axis direction, with the Z axis positive side being the up direction and the Z axis negative side being the down direction. In addition, the XY plane may be simply expressed as the horizontal plane. These expressions of directions and surfaces are defined simply for the purpose of explanation, and are not intended to limit the directions, postures, etc., when the atomic force microscope 10 is used from words such as vertical and horizontal.

The cantilever 11 is a cantilever with a probe 12 at the tip of the lever 21, and functions as a force detector that detects the interaction force between the sample 99 and the tip of the probe 12. In this embodiment, the cantilever 11 is arranged so that the long lever 21 extends in the direction of the double arrow of the dashed line in the XZ plane. One end of the lever 21 on the positive side of the X-axis in the longitudinal direction is connected to a support part (not shown) that supports the lever 21, and is a fixed end. On the other hand, the other end of the lever 21 on the negative side of the X-axis in the longitudinal direction is a free end. The probe 12 is connected to the end of the lever 21 on the free end side by adhesive or the like.

The displacement measurement unit 13 is a circuit that measures the displacement of the cantilever 11 due to the interaction force between the sample 99 and the tip of the probe 12, and has an LD (Laser Diode) 13a, a PD (Photodiode) 13b, and a preamplifier 13c for detecting the displacement of the cantilever 11 in the Z-axis direction using the principle described above. In other words, the laser emitted from the LD 13a is reflected by the back surface of the cantilever 11 on the positive side of the Z axis, becomes reflected light, and enters the PD 13b, where it becomes an electrical signal indicating the displacement of the cantilever 11 in the Z-axis direction, and the electrical signal is amplified by the preamplifier 13c and output to the feedback control unit 14.

The feedback control unit 14 is a circuit that performs control to maintain a constant distance between the sample 99 and the tip of the probe 12 based on the displacement of the cantilever 11 measured by the displacement measurement unit 13, and generates a signal (Z-axis drive signal) that drives the drive unit 17 in the Z-axis direction to maintain constant the displacement of the cantilever 11 in the Z-axis direction indicated by the electrical signal sent from the preamplifier 13c, and outputs the signal to the drive unit 17 and the PC 15.

The PC 15 is equipped with a processor and memory, and by executing a predetermined program using the processor and memory, outputs an XY drive signal to the XY drive control unit 16 for controlling the drive unit 17 to scan the sample 99 in the X-axis and Y-axis directions, and also receives a Z-axis drive signal sent from the feedback control unit 14, and generates and displays a two-dimensional image showing the unevenness of the surface of the sample 99 based on the XY drive signal and the Z-axis drive signal.

The PC 15 also executes a predetermined program to add an offset signal to the electrical signal input to the feedback control unit 14 at a predetermined timing when the XY drive signal is being output. This offset signal will be described later, but when the electrical signal to which the offset signal has been added is input, the feedback control unit 14 drives at least one of the cantilever 11 and the sample holder 18 to move the sample 99 away from the probe 12. This PC 15 is, in other words, an example of a control unit.

The XY drive control unit 16 drives the drive unit 17 in the X-axis and Y-axis directions by outputting an X-axis drive signal and a Y-axis drive signal to the drive unit 17 in accordance with the XY drive signal sent from the PC 15, thereby scanning the sample 99 in the X-axis and Y-axis directions.

The driving unit 17 is a power part that drives at least one of the cantilever 11 and the sample holder 18 to move the sample 99 relative to the probe 12. Note that in this embodiment, an example in which the driving unit 17 drives only the sample holder 18 is described, but the driving unit 17 may drive the cantilever 11, or may drive both the cantilever 11 and the sample holder 18. The driving unit 17 may be realized in any configuration as long as it is capable of moving the sample 99 relative to the probe 12.

The driving unit 17 moves the sample holder 18 placed on the top in the X-axis, Y-axis and Z-axis directions according to the Z-axis driving signal sent from the feedback control unit 14 and the X-axis driving signal and Y-axis driving signal sent from the XY driving control unit 16. The driving unit 17 has an X driving unit 17a, a Y driving unit 17b and a Z driving unit 17c that move the sample holder 18 in the X-axis, Y-axis and Z-axis directions, respectively. The driving unit 17 is a scanner consisting of a piezoelectric element or the like that moves the sample 99 in the X-axis, Y-axis and Z-axis directions relative to the tip of the probe 12. Each of the X driving unit 17a, the Y driving unit 17b and the Z driving unit 17c includes a piezoelectric element configured to expand and contract independently in the X-axis, Y-axis and Z-axis directions.

The driving unit 17 drives the sample holder 18, so that the probe 12 scans the surface of the sample 99 as shown in FIG. 2. FIG. 2 is a schematic diagram for explaining the scanning direction of the probe of the atomic force microscope according to the embodiment. In FIG. 2, as an example, when a rectangular sample 99 is viewed from the Z-axis direction, the passing trajectory of the tip of the probe 12 is shown by thin lines and thin dashed lines when the upper position of the sample 99 through which the tip of the probe 12 has passed is projected onto the surface of the sample 99 along the paper surface. Here, the number of scanning lines in the main scanning direction has been reduced for readability, and the passing trajectory extending in a diagonal direction to the X-axis direction is shown, but in reality, the main scanning direction is scanned so that it approximately coincides with the X-axis direction.

In the following, the main scanning direction will be described as coinciding with the X-axis direction, but strictly speaking, minute scans are also performed in the Y-axis direction, and on a microscale, a passing trajectory may be formed that extends diagonally relative to the X-axis direction, as shown in Figure 2. In other words, the X-axis direction being the main scanning direction will be described as including the case where a passing trajectory extending diagonally relative to the X-axis direction is formed by minute scans in the Y-axis direction.

For simplicity, a passing trajectory is shown here that scans the entire region from one end of the sample 99 in both the X-axis direction and the Y-axis direction to the other end. The scanning of the probe 12 may form a passing trajectory that differs depending on the sample 99 used. For example, the probe 12 may go beyond the end of the sample 99 and scan the upper surface of the sample holder 18. Also, for example, the probe 12 may scan only a portion of the region within the sample 99 without reaching the end of the sample 99.

First, the probe 12 starts scanning from the end of the sample 99 on the negative X-axis and negative Y-axis sides, and scans along the first thin line counting from the negative Y-axis side toward the positive X-axis side. Next, the probe 12 scans along the first thin dashed line counting from the negative Y-axis side toward the negative X-axis side. Next, the probe 12 scans along the second thin line counting from the negative Y-axis side toward the positive X-axis side. Next, the probe 12 scans along the second thin dashed line counting from the negative Y-axis side toward the negative X-axis side.

In this way, the probe 12 starts from the starting position, tracing the thin lines and thin dashed lines in order, scanning largely in the X-axis direction while scanning little by little in the Y-axis direction. In this embodiment, the probe 12 scans the surface of the sample 99 with the X-axis direction as the main scanning direction, and detects the displacement in the Z-axis direction to generate a topography image corresponding to the scanned surface.

Returning to Figure 1, this main scanning direction will be explained. Lever 21 of cantilever 11 is an elongated member whose longitudinal direction is a direction intersecting with the upper main surface of sample holder 18 on which sample 99 is placed. Typically, in an atomic force microscope, the main scanning direction is set to be the direction in which a projected image extends when a line segment along this longitudinal direction is projected onto the XY plane, which is the scanning surface.

This is to prevent the force applied from the sample 99 to the probe 12 during scanning from acting in a direction that twists the cantilever 11. The cantilever 11 is constructed to be robust against such twisting forces, and generates a strong reaction force against the sample 99, destroying the sample 99. Therefore, in order to prevent the destruction of the sample 99, the cantilever 11 is constructed so that the direction in which the projected image extends when a line segment along the longitudinal direction is projected onto the scanning surface becomes the main scanning direction. Returning to FIG. 1, in the present invention, when a line segment along the longitudinal direction is projected onto the scanning surface as shown by the dashed line extending downward from one end and the other end of the dashed line indicating the longitudinal direction of the lever 21 toward the scanning surface, the probe 12 scans the surface of the sample 99 with the X-axis direction, which is the direction in which the projected image extends, as the main scanning direction, as indicated by the hollow double arrow.

The sample holder 18 is a structure that holds the sample 99, and is configured, for example, by a plate-like member on which the sample 99 can be placed. The sample holder 18 may have any configuration as long as it can hold the surface of the sample 99 on the observed side in a fixed manner, and may be, for example, a clamp that holds a hard sample. Furthermore, when a biological material is used as the sample 99, the sample holder 18 may be configured as a container that holds a liquid such as a physiological buffer solution together with the sample 99.

The atomic force microscope 10 is not limited to a static mode AFM that detects the interaction force between the probe 12 and the sample 99 from the displacement of the cantilever 11 caused by the interaction force between the probe 12 and the sample 99, but may be a dynamic mode AFM that detects the interaction force between the probe 12 and the sample 99 from changes in vibration amplitude, frequency, or phase caused by the interaction force between the probe 12 and the sample 99 when the cantilever 11 is mechanically vibrated at a frequency near its resonance frequency and scanned horizontally across the sample 99. In addition, the present invention is applicable to any atomic force microscope, regardless of its operating configuration, particularly as an atomic force microscope 10 that measures the sample 99 at high speed.

[Operation of the atomic force microscope]
Next, the operation of the atomic force microscope 10 according to this embodiment will be described with reference to Fig. 3. Fig. 3 is a flow chart showing the operation of the atomic force microscope according to this embodiment.

3, when the atomic force microscope 10 starts to operate and the probe 12 starts to scan the sample 99, the PC 15 outputs an XY drive signal according to time. The XY drive control unit 16 outputs an X-axis drive signal and a Y-axis drive signal to the X drive unit 17a and the Y drive unit 17b in response to the XY drive signal. As a result, the sample 99 moves relative to the probe 12 in the first direction at a first distance and a first speed (i.e., first direction scanning) (step S101). In the first direction scanning, the sample 99 moves relative to the probe 12 from one end side to the other end side of the lever 21. In other words, the sample 99 moves relative to the probe 12 toward the negative side of the X axis, and the probe 12 moves relative to the sample 99 toward the positive side of the X axis. The first direction scanning is a scan corresponding to the thin line shown in FIG. 2.

The first distance here is the distance at which the surface of the sample 99 and the tip of the probe 12 are closest to each other. At this time, although a repulsive force or the like may be generated between the surface of the sample 99 and the tip of the probe 12, causing them to be separated by a very small distance, the first distance is set as the distance at which a displacement in the Z-axis direction of the cantilever 11 occurs and a topography image can be formed. The first speed is a speed at which the necessary measurements can be made on the sample 99. Specifically, it is set to the fastest possible speed within a speed range at which a topography image can be obtained with the necessary resolution.

The PC 15 continues to output an XY drive signal according to time. The XY drive control unit 16 outputs an X-axis drive signal and a Y-axis drive signal to the X drive unit 17a and the Y drive unit 17b according to the XY drive signal. As a result, the sample 99 moves relative to the probe 12 in the second direction at a second distance and a second speed (i.e., second direction scanning) (step S102). In the second direction scanning, the sample 99 moves relatively from the other end side to the one end side of the lever 21. In other words, the sample 99 moves relatively to the probe 12 toward the positive side of the X axis, and the probe 12 moves relatively to the sample 99 toward the negative side of the X axis. The second direction scanning is a scan corresponding to the thin dashed line shown in FIG. 2.

Here, the second distance is longer than the first distance, for example, a distance at which the surface of the sample 99 and the tip of the probe 12 do not come into contact. Since the probe 12 scans the surface of the sample 99 in the XY plane, the second distance is set as a distance sufficiently large relative to the expected size of unevenness on the surface of the sample 99. The second distance may be set at least larger than the first distance. The reason for this will be described later. The second speed is faster than the first speed. The faster the second speed, the more likely it is to improve the imaging speed, but due to the limitations of the drive speed of the drive unit 17 and the balance with problems such as vibration, which will be described later, a range in which the second speed can be selected may be determined by performing a simulation or a preliminary test, and the fastest value within that range may be adopted.

The switching between the first distance and the second distance when switching between the first direction scanning and the second direction scanning is performed by an offset signal output from the PC 15. FIG. 4 is a schematic diagram showing the handling of an offset signal in the atomic force microscope according to the embodiment. The magnitude of the electric signal in FIG. 4 is changed by, for example, increasing or decreasing the voltage value. Here, the electric signal A is a signal output from the displacement measurement unit. The electric signal A is used in the difference calculator on the right side in FIG. 4 to calculate the difference with the set point signal A _S. The set point signal A _S in the embodiment is a voltage value that is a preset reference, and based on the voltage value (hereinafter also referred to as an error value) of the difference with the electric signal A calculated by the difference calculator, the deviation of the displacement amount of the cantilever 11 in the Z-axis direction from the target value can be detected.

By using an error value corresponding to this deviation in feedback control, the sample holder 18 is driven to cancel the error value, and the sample 99 and the probe 12 are maintained at the first distance. The offset signal A _OS is a signal whose voltage value changes on the time axis. Specifically, as shown in the graph in the balloon, during scanning in the first direction (corresponding to 1st in the figure), the voltage value of the offset signal A _OS becomes 0. On the other hand, during scanning in the second direction (corresponding to 2nd in the figure), the voltage value of the offset signal A _OS becomes a negative value.

As a result, the apparent difference with the set point signal A _S becomes large. This is treated as if a fairly large convex portion exists on the surface of the sample 99. Since this apparent large difference is used for feedback control, the sample holder 18 is driven to cancel such an error value as well. As a result, in order to maintain the convex portion on the surface of the sample 99, which does not actually exist, at the first distance, the distance between the sample 99 and the probe 12 is moved farther than the first distance and maintained at the second distance. Note that a similar operation can also be performed by adding an offset signal to the Z-axis drive signal for feedback control.

Various voltage values obtained by such operations are shown in Figure 5. Figure 5 is a graph showing an example of actual measured values of various signals in an atomic force microscope according to an embodiment. The top part of Figure 5 shows the change in the X-axis drive signal over time, with a larger value indicating that the sample 99 has moved relatively to the negative X-axis side with respect to the probe 12 (i.e., an increase over time indicates first direction scanning, and a decrease over time indicates second direction scanning). The middle part of Figure 5 shows the change in the offset signal over time. The bottom part of Figure 5 shows the displacement amount of the Z drive unit 17c over time.

As shown in Figure 5, the X-axis drive signal is an asymmetric triangular wave (hereinafter also referred to as sawtooth wave-like) that is close to a sawtooth wave, and it can be seen that the time required for the first direction scan and the second direction scan on the time axis are different. In particular, the period is shorter in the second direction scan where the voltage value drops, and it can be seen that the second direction scan is performed at a second speed that is faster than the first speed in the first direction scan. The periods of the first direction scan and the second direction scan will be described in detail later.

The offset signal shows a steep drop corresponding to the period of the second direction scan. This offset signal coincides with the schematic graph in FIG. 4 described above. It can be seen that the Z drive unit 17c is suddenly displaced by adding the offset signal in the second direction scan. As a result, in this embodiment, the sample holder 18 moves downward and is pulled away from the cantilever 11, and the sample 99 and the probe 12 are at the second distance. Note that the second distance does not have to be a uniform distance on the time axis as long as it is a distance equal to or greater than a certain distance at which the sample 99 and the probe 12 do not come into contact with each other. The second distance may be different between the first second direction scan and the second second direction scan, or the second distance may change during the first second direction scan. Therefore, the term "maintained at the second distance" encompasses at least the concept of the sample 99 and the probe 12 being separated at a certain distance at which they do not come into contact with each other.

Returning to FIG. 3, the PC 15 then determines whether or not the scanning end position where the scanning in the XY plane is ended has been reached (step S103). If the PC 15 determines that the scanning end position has not been reached (No in step S103), the process returns to step S101, and the first direction scanning is performed again. On the other hand, if the PC 15 determines that the scanning end position has been reached (Yes in step S103), the scanning is ended. Note that the above operation is an explanation of the process for obtaining one unevenness image at a certain point in time. In reality, it is assumed that a second unevenness image will be obtained in succession, so after Yes in step S103, the process returns to the scanning start position and scanning is started again from step S101. In addition, there are cases where the scanning end position is set on the positive side of the X axis in FIG. 2 (i.e., the scanning ends after the first direction scanning). In this case, a determination process similar to step S103 is added between step S101 and step S102 in the flowchart of FIG. 3.

[Specific method of controlling scanning]
A specific method of controlling the above-described scanning of the probe 12 on the sample 99 will be described below with reference to Figs. 6 to 11B. Fig. 6 is a diagram for explaining the first direction scanning. Fig. 7 is a diagram for explaining the second direction scanning. Fig. 6(a) shows the state of the first direction scanning of the conventional atomic force microscope from the same viewpoint as Fig. 1. Here, the sample holder 18 is driven, and the sample 99 moves relatively to the probe 12 toward the negative side of the X-axis. Fig. 7(a) shows the state of the second direction scanning of the conventional atomic force microscope from the same viewpoint as Fig. 1. Here, the sample holder 18 is driven, and the sample 99 moves relatively to the probe 12 toward the positive side of the X-axis.

Figure 6(b) shows a topographical image obtained by scanning in the first direction only. In Figure 6(b), the closer to white the image, the larger the convexity. When obtaining the topographical image shown in Figure 6(b), the topographical information obtained by scanning in the second direction is used to obtain the topographical image shown in Figure 7(b) described below. Figure 7(b) shows a topographical image obtained by scanning in the second direction only. In Figure 7(b), the closer to white the image, the larger the convexity. When obtaining the topographical image shown in Figure 7(b), the topographical information obtained by scanning in the first direction is used to obtain the topographical image shown in Figure 6(b) above. In other words, here, the topographical image information obtained by one scan is decomposed into the topographical image obtained by scanning in the first direction (Figure 6(b)) and the topographical image obtained by scanning in the second direction.

Figure 6(c) shows an error image in which the error values used in feedback control when obtaining the topographical image of Figure 6(b) are mapped two-dimensionally. Figure 6(d) shows a plot of the error values on the two-dot chain line in Figure 6(c). Figure 7(c) shows an error image in which the error values used in feedback control when obtaining the topographical image of Figure 7(b) are mapped two-dimensionally. Figure 7(d) shows a plot of the error values on the two-dot chain line in Figure 7(c).

Comparing FIG. 6(d) and FIG. 7(d), slight differences were observed depending on the direction from which scanning was performed on the raised ridges in the white areas in FIG. 6(b) and FIG. 7(b). Specifically, in FIG. 6(d), the error values were not particularly large in any of the locations, and there was an overall deviation in the error values estimated to be errors within a range of about -0.2V to 0.2V. On the other hand, in FIG. 7(d), there was an overall deviation in the error values estimated to be errors within a range of about -0.2V to 0.2V. Furthermore, in FIG. 7(d), the error value was large at the position corresponding to the right end of the raised ridges on the paper, reaching about -0.6V. A similar tendency was also observed in all of the scanning lines in the main scanning direction from left to right on the paper.

It is presumed that the change in the error value with respect to the scanning direction is caused by the difference in the torque applied to the cantilever 11 shown in FIG. 6(a) and FIG. 7(a). As shown in FIG. 6(a), the direction of the lateral (X-axis) force acting on the probe 12 from the sample 99 at the positive step (the step rising from the top surface of the sample holder 18 to the top surface of the sample 99) is opposite between the first direction scan (also called forward scan) and the second direction scan (also called return scan). Therefore, in the forward scan, the direction of the torque (torque (x)) acting on the cantilever 11 by the force in the X-axis direction is the same as the direction of the torque (torque (z)) acting on the cantilever 11 by the force in the Z-axis direction acting on the probe 12 from the sample 99. On the other hand, as shown in FIG. 7(a), in the return scan, the directions of the two torques are opposite. 6(a) and 7(a), a torque acting in a clockwise direction bends the cantilever 11 upward, and conversely, a torque acting in a counterclockwise direction bends the cantilever 11 downward. The amplitude of the cantilever 11 is measured as a displacement by the optical lever method, but this measurement method does not measure the displacement in the Z-axis direction near the tip of the cantilever 11, but measures the angle change caused by the torque. Therefore, the angle change caused by a torque acting in a clockwise direction is interpreted as a decrease in the amplitude value, and conversely, the angle change caused by a torque acting in a counterclockwise direction is interpreted as an increase in the amplitude value.

Here, FIG. 14A is a graph showing the error signal, feedback control output, and cantilever deflection signal during forward scanning of the sample. In FIG. 14A, (a) shows the change over time of the error signal, (b) shows the change over time of the feedback control output, and (c) shows the change over time of the deflection signal of the cantilever 11. Also, FIG. 14B is a graph showing the error signal, feedback control output, and cantilever deflection signal during return scanning of the sample. In FIG. 14B, (a) shows the change over time of the error signal, (b) shows the change over time of the feedback control output, and (c) shows the change over time of the deflection signal of the cantilever 11. Also, FIG. 15 is a diagram explaining the difference in the force acting at the scanning position of the cantilever. In FIG. 15, the tip of the probe 12 and the sample 99 are each shown as a circle, and the direction and magnitude of the force acting at each contact position are shown by vectors (Fx and Fz) in the figure. 15, (a) to (c) show the displacement over time when the cantilever 11 rides over a step in the sample 99. The dashed line in FIG. 15 shows the path traveled by the tip of the probe 12.

14A and 14B, the drop in the feedback control output means that the sample holder 18 is moving away from the probe 12. In FIG. 14B (a), it can be seen that the error signal is large on the positive side at the location indicated by the downward arrow a1, and large on the negative side at the location indicated by the leftward arrow a2. The large error at the arrow a1 appears for a short time (about 1 to 2 times the vibration period of the cantilever 11), whereas the large error at the arrow a2 appears for a relatively long time (several times the vibration period). At the location of the arrow a1, the probe 12 first comes into contact with the sample 99 (FIG. 15 (a)), and as the cantilever 11 vibrates in the Z-axis direction, a force in the Z-axis direction from the sample holder 18 to the probe 12 (arrow pointing up on the page in FIG. 15 (a)) and a force Fx in the X-axis direction from the sample 99 to the probe 12 act on the probe 12. In particular, it can be understood that the measured amplitude value in Fig. 14B(a) becomes larger due to the force Fx in the X-axis direction acting on the probe 12 from the sample 99. Immediately after this, the feedback control output moves upward as shown in Fig. 14B(b).

In other words, the sample holder 18 is driven in a direction approaching the probe 12. As a result, the force Fz in the Z-axis direction acting on the probe 12 from the sample 99 increases, but the error signal returns to almost zero (or a slightly negative value). The error signal is almost zero because, although the force Fx in the X-axis direction and the force Fz in the Z-axis direction both increase (Figure 15(b)), the torques generated by their respective actions are almost offset. During this time, the slightly negative error signal causes the feedback control output to gradually decrease, as shown in Figure 14B(b). In other words, the sample holder 18 is gradually moving away from the probe 12.

The error signal at the location of arrow a2 becomes larger on the negative side because the positive step of sample 99 becomes smaller, so the force Fx in the X-axis direction becomes considerably weaker, and the deflection due to the force Fz in the Z-axis direction becomes more pronounced (Figure 15(c)). The large negative error signal that appears for a relatively long time at arrow a2 is thought to appear in the error image of Figure 7(c). The time difference between arrows a1 and a2 is approximately 45 μs, which corresponds to a distance of 5 nm with a scanning speed in the X-axis direction of 110 μm/s. At this time, due to the influence of the thickness of the tip of probe 12, probe 12 does not reach the apex of sample 99 (Figure 15(c)).

From the above, it is believed that during return scanning, even if the resultant force of the forces acting in the X-axis direction and the Z-axis direction becomes large at points where the positive step of the sample is large, the torque acting on the cantilever 11 for each force is in the opposite direction, so they cancel each other out, and the feedback control does not work to reduce the resultant force, but instead increases the contact force between the probe 12 and sample 99. This contact force should be avoided as it also causes significant damage to the sample 99.

From this result, in the atomic force microscope 10 of this embodiment, contact between the sample 99 and the probe 12 during the second direction scan is avoided and not used to generate a topography image, and further, the scanning speed of the sample 99 as a whole is increased by speeding up the second direction scan. FIG. 8 is a diagram showing the concept of speeding up scanning with the atomic force microscope 10 according to the embodiment. In FIG. 8, the upper part shows a schematic diagram of scanning with a conventional atomic force microscope, and the lower part shows a schematic diagram of scanning with the atomic force microscope 10 of this embodiment. In each diagram in FIG. 8, the horizontal axis shows time, and the vertical axis shows the scanning position in the X-axis direction (i.e., the relative position between the sample 99 and the probe 12).

In both schematic diagrams, the graph resembles a periodic function in which the scanning position in the X-axis direction is displaced by going back and forth between the positive and negative sides of the X-axis. It can be seen that, compared to conventional atomic force microscopes, the atomic force microscope 10 of this embodiment has a shorter period in which the value on the vertical axis decreases, and the overall speed is significantly increased. In this way, the atomic force microscope 10 of the embodiment achieves high-speed scanning by changing the displacement in the X-axis direction over time from a triangular wave to something closer to a sawtooth wave (by making it like a sawtooth wave).

In addition to this increased speed, the number of times that the probe 12 approaches the sample 99 is reduced, and the probe 12 and the sample 99 are prevented from coming into contact during the second direction scan, which causes greater damage to the sample 99, such as by pushing the sample 99 downward. In other words, the scan in this embodiment is gentle on the sample 99. Damage accumulates in the sample 99 as a result of the scan, and the faster the scan, the greater the accumulated damage. The accumulated damage can eventually destroy the sample 99 itself, so by achieving such gentle scanning, it is also possible to further increase the speed of the first direction scan itself by the amount of damage not accumulated by the second direction scan.

Here, the sawtooth function shown in the lower part of Figure 8 can be said to be an ideal function from the viewpoint of increasing scanning speed. However, this sawtooth function contains many high-frequency components at the turning point where the first direction scan and the second direction scan switch, and if it is used as is to control scanning, vibrations may occur depending on the device configuration.

Therefore, in this embodiment, the occurrence of vibration is suppressed by removing high-frequency components based on this sawtooth wave function.

In this sawtooth function, the relative position of the probe 12 and the sample 99 in the X-axis direction is the relative position in the target positional relationship where the first-direction scan starts (i.e., the positional relationship when high-frequency components are allowed) is taken as the first reference point, the relative position in the target positional relationship where the first-direction scan ends is taken as the second reference point, and the division ratio, which is the ratio of the time required for the first-direction scan to one period, is taken as α. The change in the relative position of the probe 12 and the sample 99 in the X-axis direction in the time domain relative to the first reference point is calculated by linearly connecting the m-th period's (time, change) = ((m-1)T, first reference point), (time, change) = ((m-1)T + αT, second reference point), and (time, change) = (mT, first reference point) of the (m+1)th period. The above sawtooth function can be expressed by the following equation (1).

Furthermore, if equation (1) is expressed as a Fourier series, it can be transformed into equation (2).

For example, if the Fourier series of the above formula (2) is approximated by leaving the first nine terms and regarding the higher-order terms from the tenth term onwards as 0, high-frequency components can be removed. As a result, a part of the periodic function obtained is shown in FIG. 9. FIG. 9 is a first graph showing the displacement in the X-axis direction used for scanning with an atomic force microscope in the embodiment. Note that FIG. 9 shows a graph of a part corresponding to one period of the sawtooth function. Also, FIG. 9(a) shows the result at α=0.8, FIG. 9(b) shows the result at α=0.9, and FIG. 9(c) shows the result at α=0.95. As shown in FIG. 9(a) and FIG. 9(b), in the range up to α=0.9, a good approximation function close to the sawtooth function was obtained. On the other hand, the result of α=0.95 is not appropriate because vibration occurs in the X-axis direction. Although this can be improved by including higher-order terms in the Fourier series, in this case, some measure must be taken to suppress vibrations due to high-frequency components in the device configuration of the atomic force microscope 10.

The following explanation will be given using the approximation function obtained when α = 0.8 using the first nine terms of the Fourier series shown in Figure 9(a). Looking more closely at Figure 9(a), it can be seen that the apex positions of the maximum and minimum values are slightly shifted. To correct this, the atomic force microscope 10 in this embodiment further expands the function obtained as a result of the above-mentioned high-frequency component removal process in the change axis direction and time axis direction.

Specifically, the ascending gradient region (0≦t<αT) of the function X _a (t) obtained as a result of the processing for removing high frequency components is converted into X ₁ (t) by the following equation (3).

In addition, H(x) in the above formula (3) represents a Heaviside step function, and u ₁ (t) in the above formula (3) is as shown in the following formula (4).

Furthermore, the downward gradient region (αT≦t<T) of the function X _a (t) obtained as a result of the high frequency component removal process is converted into X ₂ (t) by the following equation (5).

In addition, u ₂ (t) in the above formula (5) is as shown in the following formula (6).

As a result of this processing, in the calculated approximation function, the point at which the amount of change in the mth period in the function before processing is maximum is made to coincide with ((m-1)T+αT, second reference point), and the point at which the amount of change in the mth period in the function before processing is minimum is made to coincide with ((m-1)T, first reference point). The approximation function obtained by the above processing is shown in Figure 10. Figure 10 is a second graph showing the displacement in the X-axis direction used for scanning with an atomic force microscope in an embodiment. As shown in Figure 10, the shift in the apex positions of the maximum and minimum values seen in Figure 9(a) has disappeared.

An example of a case where the atomic force microscope 10 is controlled as shown in the graph in Figure 10 is shown in Figures 11A and 11B. Figure 11A is a first diagram showing the X-axis drive signal and the displacement of the X drive unit during scanning in the X-axis direction of an atomic force microscope in an embodiment. In Figure 11A, the upper part shows the X-axis drive signal output for scanning in the X-axis direction. Also, in Figure 11A, the lower part shows the amount of displacement corresponding to the drive amount of the X drive unit 17a.

As shown in FIG. 11A, scanning in the X-axis direction is performed at about 10 kHz. For example, if scanning in the X-axis direction is performed at about 1 kHz, good results can be obtained by the above process alone (not shown). However, as shown in FIG. 11A, when scanning in the X-axis direction is performed at a frequency of 10 kHz, unnecessary vibrations may be generated by the above process alone. This is presumed to be due to excitation of mechanical resonance of the X drive unit. Therefore, in the atomic force microscope in this embodiment, the function is adjusted so as to suppress such vibrations as well. The transition (frequency characteristic) when the X drive unit 17a is driven at various frequencies can be expressed as a transfer function. In this embodiment, the inverse transfer function is automatically generated for any transfer function, and the X-axis drive signal output is adjusted by applying the "inverse transfer compensation method" which inversely calculates the signal to be output in order to obtain the original displacement of the X drive unit 17a.

Figure 11B is a second diagram showing the X-axis drive signal and the displacement of the X drive unit during scanning in the X-axis direction of an atomic force microscope in an embodiment. In Figure 11B, the upper part shows the X-axis drive signal output by applying the "inverse transfer compensation method" for scanning in the X-axis direction. In addition, in Figure 11B, the lower part shows the amount of displacement corresponding to the drive amount of the X drive unit 17a when the "inverse transfer compensation method" is applied. As shown in Figure 11B, by applying the "inverse transfer compensation method", the drive of the X drive unit 17a approaches the graph of the desired vibration, while the X-axis drive signal output for this drive has changed compared to Figure 11A.

In this way, the atomic force microscope 10 in this embodiment can apply various techniques to measure samples 99 for a wide range of applications, including biological materials.

[Modification]
In the above embodiment, a linear function is assumed in the return scanning portion of the sawtooth function, but the waveform of the return scanning portion may have various other functions. That is, the line connecting the forward scanning end point and the forward scanning start point does not have to be a straight line. For example, a 1/2 waveform of a cosine wave may be applied to such a section to connect the forward scanning end point and the forward scanning start point. The scanning waveform in this case is expressed by the following formula (7).

Furthermore, if equation (7) is expressed as a Fourier series, it can be transformed into equation (8).

In addition, A _n and B _n in the above formula (8) are as shown in the following formulas (9) and (10), respectively.

As a result, a part of the periodic function obtained is shown in FIG. 16. FIG. 16 is a graph showing the displacement in the X-axis direction used for scanning with an atomic force microscope in a modified embodiment of the embodiment. Note that FIG. 16 shows a graph of a portion corresponding to one period of the sawtooth function. FIG. 16(a) shows the result at α=0.8, and FIG. 16(b) shows the result at α=0.87. As shown in FIG. 16(a) and FIG. 16(b), a good approximation function close to the sawtooth function was obtained in the range up to α=0.87. As shown in the figure, if a sawtooth function to which a 1/2 waveform of a cosine wave is applied is used, no shift in the apex position occurs, and there is no need to perform calculations for this correction. In addition, any function that smoothly connects the end point of forward scanning and the start point of forward scanning may be applied to configure the sawtooth function.

[Example]
An example of the measurement results using the atomic force microscope 10 configured as above will be described below with reference to Figures 12A to 13B. Figure 12A is a first diagram showing the measurement results of actin filaments in the example. Figure 12B is a diagram showing the measurement results of actin filaments in the comparative example. Figure 12C is a graph showing the relationship between the imaging speed and the survival rate of actin filaments in the embodiment.

In the example shown in Figures 12A and 12B, the measurement is performed using an actin filament as sample 99. The actin filament is arranged (along the Y-axis direction) so as to cross the main scanning direction, which is more damaged by the measurement, because the step in the main scanning line direction becomes sharp. In Figure 12A, (a) shows an actin filament image at 0.00 seconds, (b) shows an actin filament image at 3.36 seconds, (c) shows an actin filament image at 6.72 seconds, and (d) shows an actin filament image at 10.08 seconds. In addition, in Figure 12B, (a) shows an actin filament image at 0.00 seconds, (b) shows an actin filament image at 0.64 seconds, (c) shows an actin filament image at 0.96 seconds, and (d) shows an actin filament image at 1.60 seconds.

As shown in Figure 12A, the measurement results for the Example showed that the filament structure was well maintained even after 10.08 seconds had elapsed. On the other hand, as shown in Figure 12B, the measurement results for the Comparative Example showed that the filament structure was largely destroyed after less than 1 second, and that almost no structure remained after 1.60 seconds.

In addition, in Fig. 12C, the ratio of unbroken actin filaments among 30 measurements of the embodiment was performed multiple times with different imaging speeds, and the results are shown as a circle plot. In addition, in Fig. 12C, the ratio of unbroken actin filaments among 30 measurements of the comparative example was performed multiple times with different imaging speeds, and the results are shown as a triangle plot.

Measurements in the embodiment showed that the survival rate of actin filaments was maintained even at high imaging speeds.

These results demonstrate the usefulness of the atomic force microscope 10 in the above embodiment.

Figure 13A is the second figure showing the measurement results of actin filaments in the embodiment. As with Figure 12A above, Figure 13A shows the results of measurements performed by changing only the direction of the actin filaments to be along the X-axis direction, which causes less damage. Figure 13A shows (a) an actin filament image at 0.00 seconds, (b) an actin filament image at 0.03 seconds, (c) an actin filament image at 0.07 seconds, and (d) an actin filament image at 10.03 seconds.

The measurement example shown in Figure 13A demonstrates that actin filaments can be measured at high speed without being destroyed. Here, it was shown that actin filaments can be measured at 25 fps.

Figure 13B shows the results of measuring microtubules in the embodiment. As with Figure 13A above, Figure 13B shows the results of measurements performed with microtubules arranged along the X-axis direction. Figure 13B shows (a) an image of a microtubule at 0.00 seconds, (b) an image of a microtubule at 0.04 seconds, (c) an image of a microtubule at 0.08 seconds, and (d) an image of a microtubule at 10.00 seconds.

In the measurement example shown in Figure 13B, it was shown that high-speed measurement is possible without destroying microtubules. Here, it was shown that microtubule measurement can be performed at 30 fps.

By adopting a sawtooth-like function in the X-axis direction with a shorter scan time in the second direction scan, a speed increase of 1.6 times was achieved compared to the conventional method. Furthermore, the above-mentioned scan can significantly reduce the effect of contact between the probe 12 and the sample 99 on the sample 99, and as a whole, a speed increase of about 2.5 times was achieved for fragile samples compared to the conventional method. In a situation where it is difficult to increase the speed of the atomic force microscope hardware, the usefulness of the present invention can be confirmed by the fact that a speed increase of 2.5 times can be achieved with only a slight modification of the control by the PC 15. Note that the present invention can be applied to all atomic force microscopes, including the Amplitude Modulation (AM) mode, Frequency Modulation (FM) mode, Phase Modulation (PM) mode, and Force-distance (FD)-based mode, as well as the DC (contact) mode, which does not vibrate the cantilever.

[Effects, etc.]
As described above, the atomic force microscope 10 in this embodiment includes a cantilever 11 having a long lever 21 with one end in the longitudinal direction that is a fixed end used to support the lever 21 and the other end in the longitudinal direction that is a free end, the cantilever 11 having a probe 12 provided on the free end side that protrudes downwardly from the lever 21 intersecting the longitudinal direction, a sample holder 18 that is disposed below the cantilever 11 and faces the cantilever 11 to hold a sample 99, a drive unit 17 that drives at least one of the cantilever 11 and the sample holder 18 to move the sample 99 relative to the probe 12, and a control unit 17 that controls the drive unit 17 to move a line segment in the longitudinal direction of the cantilever 11. and a control unit (e.g., PC 15) that causes the probe 12 to scan the surface of the sample 99 within the virtual plane, with a predetermined direction (X-axis direction) being the main scanning direction, which is the direction in which a projected image extends when projected onto a virtual plane that intersects the direction in which the probe 12 protrudes from the bar 11.The control unit causes the probe 12 to scan the surface of the sample 99 within the virtual plane, with a predetermined direction (X-axis direction) being the direction in which a projected image extends when projected onto a virtual plane that intersects the direction in which the probe 12 protrudes from the bar 11, and in a first direction scan in which the sample 99 moves relatively from one end side to the other end side, the control unit causes the probe 12 to scan in a first mode in which the sample 99 and the probe 12 are brought close to each other at a first distance and move relatively at a first speed, and in a second direction scan in which the sample 99 moves relatively from the other end side to the one end side, the control unit causes the probe 12 to scan in a second mode in which the sample 99 and the probe 12 are moved away from each other to a second distance farther than the first distance and move relatively at a second speed faster than the first speed.

In the second direction scanning, which relatively causes more damage to the sample 99, such an atomic force microscope 10 can suppress contact between the probe 12 and the sample 99 by separating them at a second distance, thereby reducing damage to the sample. As a result, the allowable value of damage to the sample 99 in the first direction scanning can be increased by an amount equivalent to the damage that is no longer caused by the second direction scanning. In other words, even if the relative movement speed is increased in the first direction scanning, it is possible to keep the damage to a range that the sample 99 can withstand for measurement. In other words, this control configuration makes it possible to increase the relative movement speed in the first direction scanning. On the other hand, it is also possible to perform measurements on a type of sample 99 that was not measurable in conventional measurements due to the large damage.

In addition, since the probe 12 does not contact the sample 99 in the second direction scan, it is possible to increase the relative movement speed in the second direction scan. In other words, since the probe 12 does not contact the sample 99, even if the relative movement speed is increased to the device limit of the atomic force microscope 10, there is no damage to the sample 99 due to contact with the probe 12. As described above, by improving the relative movement speed between the sample 99 and the probe 12, it is possible to measure the sample 99 at a speed that could not be captured by conventional measurements. In addition, by reducing the damage caused to the sample 99, it is possible to measure the sample 99 that could not be measured by conventional measurements because it could not withstand the damage caused. Therefore, an atomic force microscope that can be applied to measurements for a wider variety of applications is realized.

In addition, for example, the control unit may acquire an electrical signal corresponding to the displacement of the probe 12 in a direction intersecting the virtual plane (Z-axis direction) during scanning in the first direction, and maintain the distance between the probe 12 and the surface of the sample 99 at a first distance based on the difference between the acquired electrical signal and a predetermined reference signal, and during scanning in the second direction, add an offset signal to the acquired electrical signal to change the numerical value of the difference from the predetermined reference signal, thereby maintaining the distance between the probe 12 and the surface of the sample 99 at a second distance.

Accordingly, by simply adding an offset signal during scanning in the second direction, an atomic force microscope that can be applied to measurements for a wider variety of applications can be realized. In some cases, an atomic force microscope 10 that can achieve the above effects can be realized by simply adjusting the output values in the control system, without making any hardware modifications to a conventional atomic force microscope. Thus, the atomic force microscope 10 can be easily configured.

Also, for example, the control unit may move the sample 99 relative to the probe 12 along a trajectory for suppressing the occurrence of vibrations in the relative positions of the probe 12 and the sample 99 at the turning point where the first direction scan and the second direction scan switch.

This makes it possible to suppress the occurrence of vibrations in the relative positions of the probe 12 and the sample 99 at the turning point, which may occur in some cases. Since it is possible to suppress problems with measurement caused by vibrations, an atomic force microscope that can be applied to measurements for a wider variety of applications is realized.

For example, the control unit may determine the relative position of the probe 12 and the sample 99 in a predetermined direction in a target positional relationship where the first direction scanning is started as a first reference point, the relative position of the probe 12 and the sample 99 in a predetermined direction in a target positional relationship where the first direction scanning is ended as a second reference point, and a division ratio that is the ratio of the time required for the first direction scanning to one period is α, where α is the division ratio of the time required for the first direction scanning to one period, The amount of change may be determined by moving the sample 99 relative to the probe 12 along a trajectory represented by an approximation function calculated by regarding, as 0, higher-order terms greater than a predetermined order when a sawtooth function is expanded into a Fourier series, based on a sawtooth function having a period of T that linearly connects (time, amount of change)=((m-1)T, first reference point), (time, amount of change)=((m-1)T+αT, second reference point) of the mth period, and (time, amount of change)=(mT, first reference point) of the (m+1)th period.

According to this, by regarding higher-order terms greater than a predetermined order as 0 when the sawtooth function is expanded into a Fourier series when the occurrence of vibration is ignored, it is possible to remove high-frequency components contained in the sawtooth function and suppress the occurrence of vibration in the relative positions of the probe 12 and the sample 99 at the turn-around position. Since it is possible to suppress problems with measurement caused by vibration, an atomic force microscope that can be applied to measurements for a wider variety of applications is realized.

In addition, for example, the control unit may set the relative position of the probe 12 and the sample 99 in a predetermined direction in a target positional relationship where the first direction scanning is started as a first reference point, set the relative position of the probe 12 and the sample 99 in a predetermined direction in a target positional relationship where the first direction scanning is ended as a second reference point, and set a division ratio that is the ratio of the time required for the first direction scanning to one period to α, and calculate the amount of change in the relative positions of the probe 12 and the sample 99 in a predetermined direction in the time domain relative to the first reference point as (time, amount of change) of the mth period = ((m-1) The sample 99 may be moved relative to the probe 12 along a trajectory represented by an approximation function calculated by regarding higher-order terms greater than a predetermined order as 0 when the sawtooth function is expanded into a Fourier series based on a sawtooth function having a period of T, which successively connects the mth period (time, amount of change)=((m-1)T, first reference point) and (time, amount of change)=((m-1)T+αT, second reference point) linearly and the (m+1)th period (time, amount of change)=(mT, first reference point) by a 1/2 waveform of a cosine wave.

According to this, by regarding the higher-order terms greater than a predetermined order when the sawtooth function is expanded into a Fourier series when the occurrence of vibration is ignored as 0, it is possible to remove the high-frequency components contained in the sawtooth function and suppress the occurrence of vibration in the relative positions of the probe 12 and the sample 99 at the turn-around position. Since it is possible to suppress the occurrence of measurement problems due to vibration, an atomic force microscope applicable to measurements for a wider variety of applications is realized. In particular, with this sawtooth function, there is no shift in the change amount axis and time axis in the X-axis direction at the turn-around position, so that more appropriate scanning of the probe 12 is possible without additional processing such as adjusting such shifts, and therefore an atomic force microscope applicable to measurements for a wider variety of applications is realized with a simple system configuration.

In addition, for example, the control unit may calculate a function in which higher-order terms greater than a predetermined order when the sawtooth wave-like function is expanded into a Fourier series are regarded as 0, and the sample 99 may be moved relative to the probe 12 along a path represented by an approximation function calculated by expanding the function in the change axis direction and the time axis direction so that the point at which the change in the mth period in the calculated function is maximum coincides with ((m-1)T+αT, second reference point) and the point at which the change in the mth period in the calculated function is minimum coincides with ((m-1)T, first reference point).

This allows the deviations in the change amount axis and time axis in the X-axis direction of the turn-around position to be adjusted in a function calculated by regarding higher-order terms greater than a predetermined order in the Fourier series expansion as 0. This makes it possible to realize an atomic force microscope that can be applied to measurements for a wider variety of purposes.

Also, for example, the predetermined order may be 9 and the division ratio may be α = 0.8.

According to this, the atomic force microscope 10 can be constructed using 9 as the predetermined order and α = 0.8 as the division ratio. Since the relative movement between the sample 99 and the probe 12 during scanning can be increased in speed while suppressing the generation of vibration, an atomic force microscope that can be applied to measurements for a wider variety of purposes is realized.

In addition, the control method in this embodiment includes a cantilever 11 having a long lever 21, one end side in the longitudinal direction of which is a fixed end used to support the lever 21 and the other end side in the longitudinal direction of which is a free end, the cantilever 11 having a probe 12 provided on the free end side that protrudes downward from the lever 21 in a direction intersecting with the longitudinal direction, a sample holder 18 that is disposed below the cantilever 11 and faces the cantilever 11 to hold a sample 99, a drive unit 17 that drives the cantilever 11 and the sample holder 18 to move the sample 99 relative to the probe 12, and a drive unit 17 that controls the drive unit 17 to move the probe 12 along a line segment in the longitudinal direction from the cantilever 11. The control method for an atomic force microscope 10 has a control unit (e.g., PC 15) that causes the probe 12 to scan the surface of a sample 99 within a virtual plane with a predetermined direction (X-axis direction) as the main scanning direction, which is a direction in which a projected image extends when projected onto a virtual plane that intersects the direction in which the sample 99 is projected, and in a first direction scan in which the sample 99 moves relatively from one end side to the other end side, the sample 99 and the probe 12 are brought close to each other at a first distance and scanned by relative movement at a first speed, and in a second direction scan in which the sample 99 moves relatively from the other end side to the one end side, the sample 99 and the probe 12 are moved away from each other to a second distance farther than the first distance and scanned by relative movement at a second speed faster than the first speed.

This can achieve the same effect as the atomic force microscope 10 described above.

In addition, the program in this embodiment is a program for causing a computer to execute the control method described above.

This allows the effects of the above control method to be achieved using a computer.

(Other embodiments)
Although the present invention has been described based on the embodiment, the present invention is not limited to the above embodiment.

For example, the atomic force microscope according to the above embodiments may be realized as a dedicated device or as multiple devices.

In addition, communication between the components in the above-described embodiments may be performed either wired or wirelessly, and there are no particular limitations on the communication method, and any communication method may be used.

In addition, the control unit and the like according to the above embodiments are typically realized as an LSI, which is an integrated circuit. These LSIs may be integrated into a single chip, or may be integrated into a single chip to include some or all of the LSIs.

In addition, the integrated circuit is not limited to an LSI, but may be realized by a dedicated circuit or a general-purpose processor. A field programmable gate array (FPGA) that can be programmed after the LSI is manufactured, or a reconfigurable processor that can reconfigure the connections and settings of the circuit cells inside the LSI may be used.

In the above embodiment, each component may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

In addition, all numerical values used above are merely examples to specifically explain the present invention, and the embodiment of the present invention is not limited to the numerical values exemplified.

In addition, the division of functional blocks in the block diagram is one example, and multiple functions may be realized as one functional block, one function may be divided into multiple functional blocks, or some functions may be moved to other functional blocks. Furthermore, the functions of multiple functional blocks having similar functions may be processed in parallel or in a time-sharing manner by a single piece of hardware or software.

In addition, the order in which the steps are executed in the flowchart is merely for illustrative purposes in order to specifically explain the present invention, and the steps may be executed in an order other than the above. In addition, some of the steps may be executed simultaneously (in parallel) with other steps.

In addition, the present invention also includes forms obtained by applying various modifications to the above-described embodiments that may occur to those skilled in the art, and forms realized by arbitrarily combining the components and functions of the above-described embodiments without departing from the spirit of the present invention.

The present invention can be used for atomic force microscopes for a wider variety of applications.

10 Atomic force microscope 11 Cantilever 12 Probe 13 Displacement measuring unit 13a LD
13b PD
13c Preamplifier 14 Feedback control section 15 PC
16 XY drive control section 17 Drive section 17a X drive section 17b Y drive section 17c Z drive section 18 Sample holder 21 Lever 99 Sample

Claims (8)

a cantilever including a long lever, one end side in a longitudinal direction being a fixed end used for supporting the lever, and the other end side in the longitudinal direction being a free end, the cantilever being provided with a probe on the free end side protruding downward from the lever in a direction intersecting with the longitudinal direction;
a sample holder arranged below the cantilever and facing the cantilever to hold a sample;
a drive unit that drives at least one of the cantilever and the sample holder to move the sample relative to the probe;
a control unit that controls the drive unit to cause the probe to scan the surface of the sample within the imaginary plane with a main scanning direction being a predetermined direction along which a projected image extends when the line segment in the longitudinal direction is projected onto the imaginary plane that intersects with a direction in which the probe protrudes from the cantilever,
The control unit is
In a first direction scan in which the sample moves relatively from the one end side to the other end side, the sample and the probe are brought close to each other at a first distance and scanned in a first mode in which the sample and the probe move relatively at a first speed;
In a second direction scan in which the sample moves relatively from the other end side to the one end side, the sample and the probe are moved to a second distance greater than the first distance, and the sample is scanned in a second mode in which the sample and the probe move relatively at a second speed greater than the first speed ;
The control unit moves the sample relative to the probe along a trajectory in which a high frequency component of the amount of change in the time domain of the relative position of the probe and the sample in the predetermined direction is removed at a turning point where the first direction scan and the second direction scan are switched, compared to a trajectory in which an amount of change in the time domain of the relative position of the probe and the sample in the predetermined direction is uniform in each of the first direction scan and the second direction scan.
Atomic force microscope. The control unit is
during the first direction scanning, acquiring an electrical signal corresponding to a displacement of the probe in a direction intersecting the imaginary plane, and maintaining a distance between the probe and the surface of the sample at the first distance based on a difference between the acquired electrical signal and a predetermined reference signal;
2. The atomic force microscope according to claim 1, wherein during scanning in the second direction, an offset signal is added to the acquired electrical signal to change the numerical value of the difference from the predetermined reference signal, thereby maintaining the distance between the probe and the surface of the sample at the second distance. The control unit is
a relative position of the probe and the sample in the predetermined direction in a target positional relationship at which the first direction scan is started is set as a first reference point;
a second reference point is a relative position of the probe and the sample in the predetermined direction, the second reference point being a relative position in a target positional relationship at which the first direction scanning ends;
When a division ratio, which is a ratio of the time required for the first direction scan to one period, is α,
2. The atomic force microscope according to claim 1, wherein the sample is moved relative to the probe along the trajectory represented by an approximation function calculated by regarding, as 0, higher-order terms greater than a predetermined order when a sawtooth wave-like function is expanded into a Fourier series, based on a sawtooth wave-like function with a period of T that linearly connects, in order, (time, amount of change)=((m-1)T, first reference point) of the mth period, (time, amount of change)=((m-1)T+αT, second reference point), and (time, amount of change)=(mT, first reference point) of the (m+ 1) th period. The control unit is
a relative position of the probe and the sample in the predetermined direction in a target positional relationship at which the first direction scan is started is set as a first reference point;
a second reference point is a relative position of the probe and the sample in the predetermined direction, the second reference point being a relative position in a target positional relationship at which the first direction scanning ends;
When a division ratio, which is a ratio of the time required for the first direction scan to one period, is α,
2. The atomic force microscope according to claim 1, wherein the sample is moved relative to the probe along the trajectory represented by an approximation function calculated by regarding, as 0, higher-order terms greater than a predetermined order when the sawtooth wave-like function is expanded into a Fourier series, based on a sawtooth wave-like function having a period of T, which successively connects (time, amount of change)=((m-1)T, first reference point) of the mth period and (time, amount of change)=((m-1)T+αT, second reference point) of the mth period by a linear waveform and (time, amount of change)=((m-1)T+αT, second reference point) of the mth period and (time, amount of change)=(mT, first reference point) of the (m+ 1) th period by a half cosine wave. The control unit is
A function is calculated in which higher-order terms than a predetermined order are regarded as 0 when the sawtooth wave-like function is expanded into a Fourier series;
The point at which the calculated change amount in the m-th period in the function is maximum is made to coincide with ((m-1)T+αT, second reference point);
5. The atomic force microscope according to claim 3, wherein the sample is moved relative to the probe along the trajectory represented by the approximation function calculated by expanding the function in a direction of a change amount axis and a direction of a time axis so that a point at which a change amount in the calculated function for the mth period is smallest coincides with ((m -1)T , first reference point). the predetermined order is 9,
6. The atomic force microscope according to claim 3 , wherein the division ratio is α=0.8. a cantilever including a long lever, one end side in a longitudinal direction being a fixed end used for supporting the lever, and the other end side in the longitudinal direction being a free end, the cantilever being provided with a probe on the free end side protruding downward from the lever in a direction intersecting with the longitudinal direction;
a sample holder arranged below the cantilever and facing the cantilever to hold a sample;
a drive unit that drives the cantilever and the sample holder to move the sample relative to the probe;
and a control unit that controls the drive unit to cause the probe to scan the surface of the sample within a virtual plane, with a main scanning direction being a predetermined direction along which a projected image extends when the line segment in the longitudinal direction is projected onto the virtual plane intersecting a direction in which the probe protrudes from the cantilever, the control unit comprising:
In a first direction scan in which the sample moves relatively from the one end side to the other end side, the sample and the probe are brought close to each other at a first distance and scanned by relative movement at a first speed;
In a second direction scan in which the sample moves relatively from the other end side to the one end side, the sample and the probe are moved away from each other to a second distance greater than the first distance, and the sample and the probe are scanned by the relative movement at a second speed greater than the first speed ;
In the control method, the sample is moved relative to the probe along a trajectory in which a high-frequency component of the amount of change in the time domain of the relative position of the probe and the sample in the predetermined direction is removed at a turning point where the first direction scan and the second direction scan are switched over, compared to a trajectory in which an amount of change in the time domain of the relative position of the probe and the sample in the predetermined direction is uniform in each of the first direction scan and the second direction scan.
Control methods. A program for causing a computer to execute the control method according to claim 7 .

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