JP2000146805A - Sample table driving device for atomic force microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sample table driving device for an atomic force microscope capable of measuring surface force of a sample to be measured with high accuracy and high resolution by controlling the movement of the sample table with high reliability and repeatability. SOLUTION: A surface of a sample placed on a sample table 15 of an atomic force microscope and a probe provided on an end of a cantilever are brought close to each other and surface data of the sample are obtained based on an elastic deformation of the cantilever caused by interatomic force produced between the two. The sample table 15 is made up of an electric motor 21 for rotatingly driving a Z-axis drive mechanism 7 by means of high-resolution drive pulses for controlling the movement of the sample table 15 in the Z-axis direction, a feed screw 23 driven by and rotating with the electric motor 21 for moving a meshing nut with a required lead, and a differential spring means comprising a first spring member 17 elastically deformed by being pressed by the moving nut and a second spring member 11 having a spring constant higher than that of the first spring member 17 and elastically deformed dependently on the spring constant in keeping with the elastic deformation of the first spring member 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for driving a sample stage of an atomic force microscope (AFM) suitable for measuring the surface force (attraction, repulsion and adhesion) of a sample.

[0002]

The AFM used to obtain the surface information distribution of a sample is necessary for analyzing the dispersion characteristics of fine particles, analyzing the biological functions of biological macromolecules, analyzing the surface and interface, and the like. It is also used for measuring the surface force (Vandenwaals force, electrostatic force, magnetic force) of a sample.

Conventionally, a sample is moved in a three-dimensional direction (XYZ axes).
Using a piezoelectric element having an electrostrictive effect that is deformed by an amount corresponding to the applied voltage value as a Z-axis driving mechanism of the sample stage driving device that moves to the sample stage driving device, the sample in the Z-axis direction is determined based on the applied voltage value. The amount of movement of the table is measured in nanometer units, and the surface force of the sample is measured based on the amount of deformation of the cantilever that elastically deforms close to the sample surface.

[0004] However, although the relationship between the voltage and the amount of deformation of the piezoelectric element itself is approximately linear, but not completely proportional, the amount of movement cannot be measured with high reliability based on the voltage value. In addition, since the piezoelectric element itself has hysteresis, an error occurs in the amount of movement between the case where the sample approaches the probe of the cantilever and the case where the sample is separated from the probe, and the measurement result is not reliable. Furthermore, in the measurement mode in which the moving speed of the sample in the Z-axis direction is changed or the measurement is temporarily stopped and the relaxation measurement is performed, the piezoelectric element itself includes:
Since there is a certain drift width, for example, even when the application of the voltage is interrupted, it is deformed and moved, so that the measurement result is not reliable.

For this reason, in a sample stage driving device using a piezoelectric element as the Z-axis driving mechanism, the surface force of the sample cannot be measured with high accuracy (high resolution) and with high reliability.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned conventional drawbacks. An object of the present invention is to control the movement of a sample table with high reliability and reproducibility to control the surface force of a sample. To provide a sample stage driving device of an atomic force microscope capable of measuring the sample with high precision and high resolution.

[0007]

SUMMARY OF THE INVENTION Therefore, the present invention is directed to a method in which the surface of a sample placed on a sample stage and a probe provided at the tip of the cantilever are brought close to each other, and the elasticity of the cantilever due to an atomic force between the two. In an atomic force microscope that obtains surface information of a sample based on deformation, Z is used to control the movement of the sample stage to the Z axis.
The shaft drive mechanism is driven by a high-resolution drive pulse, an electric motor is rotated, the nut is rotated by the drive of the electric motor, a feed screw is used to move a meshing nut with a required lead, and is pressed by the moving nut to be elastically deformed. A first spring member and a second spring that has a higher spring constant with respect to the first spring member and that elastically deforms in accordance with the spring constant with the elastic deformation of the first spring member.
And a differential spring means comprising a spring member.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a Z-axis driving mechanism in the sample stage driving device.

The sample stage driving device 3 of the AFM 1 comprises an X-axis and Y-axis driving mechanism 5 and a Z-axis driving mechanism 7, and the X-axis and Y-axis driving mechanisms 5 correspond to X and Y axes corresponding to applied voltage values. It comprises piezoelectric elements 5a and 5b having an electrostrictive characteristic of being deformed by a predetermined amount in the axial direction and the Y-axis direction, respectively. The sample stage driving device 3 is mounted on an anti-vibration member (not shown).

A Z-axis drive mechanism 7 is attached to the X-axis and Y-axis drive mechanisms 5. A fixed frame 11a of a second spring member 11 is provided in a case 9 of the Z-axis drive mechanism 7 in the vertical direction (Z-axis direction). ) Is fixed. The second spring member 11
Is made of, for example, an aluminum material processed so as to have uniform rigidity, and has a fixed frame 11a fixed in the case 9, a movable frame 11b opposed to the fixed frame 11a at a required interval, and fixed. It is formed in a rectangular frame shape including connecting frames 11c and 11d connecting the upper and lower ends of the frame 11a and the movable frame 11b, respectively. And the second spring member 11 is movable frame 11
The movable frame 11b moves in the vertical direction (Z-axis direction) by moving in a parallelogram with the pressing of the first spring member 17 abutting on the lower end of the movable frame 11b.
Move to

A sample table 15 on which the sample 13 is placed is mounted on the upper end surface of the movable frame 11b. Also, the movable frame 11
b on the lower end surface side of the pressing means 1 via a first spring member 17.
9 are provided. The first spring member 17 is constituted by a compression spring having a lower spring constant than the second spring member 11. The first and second spring members 11.1
7 constitute differential spring means.

The pressing means 19 includes an electric motor 21 which can be numerically controlled, a feed screw 23 connected to a rotating shaft of the electric motor 21 and meshes with the feed screw 23. And a nut 25 that is slidably supported and abuts against the lower portion of the first spring member 17.

The electric motor 21 is, for example, a stepping motor having a five-excitation phase structure and making one rotation at 500 pulses. The electric motor 21 is not limited in the number of excitation phases and the number of pulses per rotation, but preferably has at least the above structure in order to achieve high resolution.

The electric motor 21 is connected to the split driving device 2.
The driving is controlled by the divided pulse output from the reference numeral 9. The split driving device 29 generates a split pulse obtained by changing the drive pulse of the electric motor 21 in a stepwise manner by a preset number of divisions, and generates, for example, a product name “CSD5”.
807VN "or" CSD5814VN "(all manufactured by Oriental Motor Co., Ltd.). The divided driving device 29 outputs divided pulses obtained by dividing one driving pulse into 1 to 250 according to the required moving resolution of the sample table 15.

More specifically, when the electric motor 21 has a five-excitation phase structure and is 500 pulse / r, the step angle per drive pulse is 0.72 °.
When the division number of 9 is 250, the electric motor 21 is 1250
One rotation is made by the 00 division pulse. As a result, the division drive device 29 varies the step angle of the electric motor 21 within the range of 0.00288 to 0.72 ° per division pulse.

The sample stage 1 attached to the sample stage driving device 3
Above 5, the base end of a cantilever 41 of gold or metal foil having a substantially constant spring constant is fixed. A probe 41a of diamond or tungsten wire is attached to the lower surface of the tip of the cantilever 41 with its tip facing the surface of the sample 13 placed on the sample table 15.

Above the intermediate portion of the cantilever 41 in the extending direction, light such as laser light condensed to a predetermined diameter is applied to the cantilever 4.
A light source 43 for irradiating an upper surface of the cantilever 41 at a predetermined incident angle is provided on the upper surface of the cantilever 41, and on a light path reflected from the upper surface of the cantilever 41,
For example, a light receiving device 45 such as a three-division photodiode is arranged.

The Z-axis drive mechanism 7 moves the sample table 15 minutely in the Z-axis direction (up-down direction) by the following operation.

FIG. 2 is an explanatory diagram showing the measurement state of the surface force. When the electric motor 21 is rotationally driven by the divided pulse from the divided driving device 29 to rotate the feed screw 23 in a predetermined direction and move the nut 25 upward to elastically deform the first spring member 17, the first spring The member 17 elastically deforms the second spring member 11 by the elastic force to move the movable frame 11b upward.

Now, as described above, the electric motor 21 has a five-phase excitation phase structure, 500 pulse / r,
Is 250, the feed amount per rotation of the feed screw 23 is 1 mm / r, and the spring constant ratio between the first spring member 17 and the second spring member 11 is 1: 500. The feed amount of the movable frame 11 becomes 0.008 μm (80 angstroms), and the moving resolution of the movable frame 11b in the vertical direction becomes 0.16 angstroms per divided pulse.

The electric motor 21 has a five-phase excitation structure,
00 pulse / r, the number of divisions of the division driving device 29 is 20
0, the feed amount per rotation of the feed screw 23 is 1 mm / r,
When the ratio of the spring constant between the second spring member 17 and the first spring member 11 is 1: 1000, the feed screw 23 per divided pulse is used.
Is 0.001 μm (10 Å), and the resolution of the movable frame 11b in the vertical direction is 0.01 Å per divided pulse.

The movable frame 11b in the Z-axis direction, and thus the sample stage 15 in the Z-axis direction, is based on the number of divided pulses from the divided drive device 29 applied to the electric motor 21.
Is controlled in nanometer units.

Next, the action of measuring the surface force of the sample 13 by the AFM 1 using the sample stage driving device 3 will be described. FIG. 3 is a chart showing the relationship between the moving distance of the sample and the surface force. FIG. 4 is a chart showing the relationship between the number of divided pulses and the amount of deflection of the cantilever.

After the sample 13 is placed on the sample table 15 waiting at a predetermined interval (for example, 500 nm) from the tip of the probe 41a, the two-dimensional position data of the measurement position is stored in the piezoelectric elements 5a and 5b. Corresponding predetermined voltage values are applied to make the measurement position on the surface of the sample 13 relative to the probe 41a.

In the above state, a driving pulse is applied to the division driving device 29, and the electric motor 21 is rotationally driven by the division pulses divided by a predetermined division number to move the sample table 15 upward to move the sample 13 When the surface is brought close to the probe 41a, the cantilever 41 is elastically deformed downward by the attraction of the sample 13 as shown in FIG. 3, for example, and then elastically deformed upward by the repulsive force. Then, the cantilever 41 abutting on the surface of the sample 13 is elastically deformed in accordance with the amount of movement of the sample table 15 as the sample table 15 moves. It should be noted that some samples 13 do not generate an attractive force. In this case, unlike the case shown in FIG. 3, a chart in which the cantilever 41 is directly elastically deformed upward by the repulsive force of the sample 13 is obtained.

At this time, the amount of movement of the sample table 15 (sample 13) can be obtained from the number of divided pulses applied to the electric motor 21 and the resolution per divided pulse. Further, the amount of elastic deformation and the direction of elastic deformation of the cantilever 41 due to the attractive force and the repulsive force are obtained by a current value based on the amount of change in the amount of light emitted from the light source 43 and reflected from the upper surface of the cantilever 41 and incident on each cell in the light receiving device 45. be able to. Since the spring constant of the cantilever 41 has a predetermined value in advance, the displacement, the spring constant, the attractive force and the repulsive force of the cantilever 41 can be obtained.

Based on the measured surface force of the sample 13, the dispersion characteristics of colloidal fine particles, three-dimensional structure analysis of biopolymer, molecular recognition, biological function analysis, interaction evaluation between surfactant aggregates, surfactant Evaluation of adsorption phenomena on the surface, analysis of surface and interface phenomena, and the like can be performed.

In the above description, the second spring member 11 is constituted by the opposed fixed frame 11a and movable frame 11b and the connection frames 11c and 11d which are connected at the upper and lower portions to form a quadrilateral. In the member 11, a connection frame 11c located at a boundary between the fixed frame 11a and the movable frame 11b
Forming a thin portion at each end of the second spring member 1d;
The spring constant of 1 may be changeable.

[0029]

According to the present invention, the surface force of the sample can be measured with high precision and high resolution by controlling the movement of the sample table with high reliability and reproducibility.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a Z-axis driving mechanism in a sample stage driving device.

FIG. 2 is an explanatory diagram showing a measurement state of a surface force.

FIG. 3 is a chart showing a relationship between a moving distance of a sample and a surface force.

FIG. 4 is a chart showing the relationship between the number of divided pulses and the amount of deflection of a cantilever.

[Explanation of symbols]

1-AFM, 7-Z axis drive mechanism, 11-second spring member,
13-sample, 15-sample stage, 17-first spring member, 21
Electric motors, 23 feed screws, 29-split drives,
41-cantilever, 41a-tip

Claims (4)

[Claims] An atom for obtaining surface information of a sample based on the elastic deformation of the cantilever caused by an atomic force between the surface of the sample placed on the sample stage and a probe provided at the tip of the cantilever. In an atomic force microscope, a Z-axis drive mechanism that controls the movement of the sample stage to the Z-axis moves an electric motor that rotates and drives with a high-resolution drive pulse, and moves a nut that rotates and meshes with the drive of the electric motor with a required lead. A first spring member that is elastically deformed by being pressed by a moving screw and a moving nut, and has a high spring constant with respect to the first spring member, and is elastically deformed in accordance with the spring constant with the elastic deformation of the first spring member. And a differential spring means comprising a second spring member. 2. A driving device according to claim 1, wherein the driving pulse output to the electric motor is divided into a predetermined number of divided pulses corresponding to a desired resolution by a divided driving device, and the electric motor is driven based on the divided pulses. A sample stage drive device capable of controlling the amount of movement of the sample stage in the Z-axis direction based on the number of divided pulses. 3. The square frame of a fixed frame and a movable frame facing each other and a connecting frame connecting both ends of the fixed frame and the movable frame at predetermined intervals. A sample stage drive device in which a sample stage is provided on a part of the movable frame. 4. The sample stage driving device according to claim 3, wherein each connecting frame is provided with a thin portion at a boundary between the fixed frame and the movable frame so as to be elastically deformable.