JPH08184600A - Scanning probe microscope - Google Patents

Abstract

PURPOSE: To obtain a scanning probe microscope in which the thermal drift between a sample and a probe is compensated and by which a stable and accurate measurement can be performed by locally heating or cooling a constituent member which couples the sample to the probe so as to control its thermal expansion. CONSTITUTION: Temperature control elements 5, 7 in a direction which agrees with the X-axis direction 13 as the scanning direction of a scanning element 3 are attached respectively to partial parts of expansion and contraction parts 9, 11 which function as expansion and contraction materials used to adjust the distance between the element 3 and a sample 1. Then, when a probe 2 for the element 3 is drifted in the X-axis direction to the positive side (16) relatively with reference to the sample 1, a voltage is applied, in a heat-absorbing (cooling) direction, to the element 5, and in a heat- generating direction, to the element 7. Then, the expansion and contraction part 9 is contracted, the expansion and contraction part 11 expanded, the probe 2 is moved in the X-axis direction to the negative side (17), and a thermal drift inside the X-axis direction 13 is offset. When the direction of the drift is opposite, it is sufficient to apply a voltage in the opposite sign to the elements 5, 7. In addition, a thermal drift in the Y-axis direction can be offset in the same method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning probe microscope, and more particularly, to a distance between a probe and a sample caused by expansion and contraction of a material due to the influence of heat in a scanning probe microscope operating in an environment where the temperature changes drastically such as extremely low temperature or high temperature. It is used to reduce the drift of.

[0002]

2. Description of the Related Art Currently, scanning probe microscopes include scanning tunneling microscopes, atomic force microscopes, magnetic force microscopes and the like. In all of these principles, a sharply pointed probe is brought close to a few nm from the sample surface, and in this state, a certain region on the sample surface is scanned with the probe to meet the probe type and the measurement purpose. Surface information is obtained, and image processing is performed based on the information to obtain an image of the sample surface.

[0003]

The scanning probe microscope can operate not only at room temperature but also at extremely low temperature or high temperature. However, when operating in an environment with a large temperature difference from the outside, that is, room temperature, due to the expansion and contraction of the structural material accompanying the inflow or outflow of heat from the outside, until the steady state is reached. It can be seen that the position of the probe with respect to the sample changes with time. This phenomenon becomes remarkable especially when only the sample is heated or cooled.

For example, when stainless steel having a length of 1 cm is used as a structural material, the temperature change of 1 ° C. is 160
A displacement of nm is produced. Moreover, the time required for the scanning probe microscope to obtain one image is usually several seconds to several minutes, and the scanning region is several nm to several thousand nm. Therefore, if a temperature change of 1 ° C. occurs in one minute, the scanning is performed. The displacement until the end is about several tens nm to several hundreds nm, and the image distortion due to this is not negligible.

As a means for preventing the temperature drift, it is conceivable to first select a material having a small coefficient of thermal expansion as a component of the scanning probe microscope, or a material and a structure so that the thermal expansions cancel each other. It is very difficult to consider the thermal expansion coefficient of the probe. Although a method of softly correcting the scanning itself in the drift direction has been proposed, there is a problem that the range that can follow the drift is limited to the scanning range.

It is an object of the present invention to provide a means of compensating for thermal drift in scanning probe microscopy.

[0007]

According to the present invention, in order to solve the above-mentioned problems, the sample material is locally heated or cooled to form a sample-
Means are provided to compensate for thermal drift between the probes.

[0008]

According to the present invention, the components of the scanning probe microscope that couple the sample and the probe are locally heated or cooled to control the thermal expansion, thereby canceling the thermal drift and compensating for the drift. It is possible. As a heating / cooling control method, there are a method of directly controlling a heat source or a cold heat source and a method of controlling heat conduction from the heat source or the cold heat source.

In the former case, there is a method of using a Peltier element, resistance heating or the like as a heating and cooling means, and it is possible to electrically control the amount of heat generation or the amount of heat absorption.

In the latter case, a structure in which a heat conducting material capable of conducting heat to a heat source or a cold heat source is mechanically brought into contact with the components of the scanning probe microscope for coupling between the sample and the probe is used. By changing the pressure, the true contact area is changed, and the heat conduction characteristics at the contact surface are controlled. By disposing a plurality of such structures, it becomes possible to compensate for the thermal drift in the scanning plane and in the direction perpendicular to the scanning plane.

[0011]

【Example】

Example 1 In this example, thermal drift compensation is performed by directly heating or cooling the constituent materials of the scanning probe microscope.

The scanning tunneling microscope shown in FIG. 1 comprises a base portion 100, a sample 1 arranged on the base portion 100, a probe 2, a scanning element 3, and a coarse movement mechanism 4 for holding the scanning element 3.
Upper base 200 holding scanning mechanism 4 and scanning element 3
-It consists of the support parts 9, 10, 11, 12 which connect between the samples 1. Supports 9 and 1 for connecting the scanning element 3 to the sample 1
Since 0, 11, and 12 function as expansion / contraction units for adjusting the distance between the scanning element 3 and the sample 1, they are hereinafter referred to as expansion / contraction units. The scanning element 3 is provided on a part of the expansion / contraction part 9, 10, 11, 12.
The temperature control elements 5, 6, 7, and 8 are attached in the directions that coincide with the X-axis direction 13 and the Y-axis direction 14 in the scanning.

FIG. 2 shows a side view of the internal structure as seen from the Y-axis direction 14. When the probe 2 is drifting in the X-axis positive direction 16 relative to the sample 1, when voltage is applied to the temperature control element 5 in the heat absorption direction and to the temperature control element 7 in the heat generation direction, expansion and contraction occur. When the part 9 contracts and the expansion / contraction part 11 expands, the probe 2 moves in the X-axis negative direction 17 and the drift in the X-axis direction 13 is offset. When the drift direction is opposite, a voltage having the opposite sign may be applied to the temperature control elements 5 and 7. Further, the drift in the Y-axis direction 14 is similarly controlled by using the temperature control elements 6 and 8. When there is a drift in the Z-axis direction 15, that is, in the Z-axis negative direction 18 perpendicular to the sample 1, when a voltage is applied to the temperature control elements 5, 6, 7, and 8 in the heat absorption direction,
The contraction of the expansion / contraction parts 9, 10, 11, 12 causes the probe 2 to move in the Z-axis positive direction 19 and offset the drift in the Z-axis direction 15. When the drift direction is opposite, a voltage may be applied to the temperature control elements 5, 6, 7, 8 in the direction of heat generation.

By applying a voltage obtained by adding the drift control voltage in the X-axis direction 13 or the Y-axis direction 14 and the drift control voltage in the Z-axis direction 15 to the temperature control elements 5, 6, 7, and 8, all the directions are controlled. It is possible to control the drift.

Using graphite as the sample 1, tungsten as the probe 2, Peltier elements as the temperature control elements 5, 6, 7, 8 and stainless steel plates as the expansion / contraction parts 9, 10, 11, 12 at room temperature and in the atmosphere. went. Initially, a thermal drift of 1 nm / s was observed both in the plane of the sample and in the vertical direction, but when the drift control was performed by the method described above, it was reduced to 0,01 nm / s or less.
Similar effects were obtained using other scanning probe microscopes such as an atomic force microscope and a magnetic force microscope. Similar effects were obtained in a gas, a vacuum, or a solution as an operating atmosphere, and in all temperature ranges in which the scanning probe microscope can operate at an operating temperature of about 1K to about 1500K. As the stretchable parts 9, 10, 11, and 12,
Any material may be used, such as metals such as stainless steel, copper and aluminum, ceramics such as silicon oxide and aluminum oxide, organic substances such as bakelite and polystyrene, as long as they can reversibly expand and contract by heat.

The structure of the expansion / contraction parts 9, 10, 11, 12 is shown in FIG.
The structure is not limited to the structure shown in 1 above, and may be located anywhere as long as it mechanically connects the sample 1 and the probe 2. FIG.
In the scanning tunneling microscope shown in FIG. 1, the expansion / contraction part 20 is located between the scanning element 3 and the coarse movement mechanism 4. FIG. 4 shows an example of the shape of the expandable portion 20 in this case.

FIG. 4A is a rectangular parallelepiped, and FIG. 4B is a cylindrical type, and the temperature control element 21 is provided at a position such that the moving direction of the expansion / contraction part 20 coincides with the scanning direction of the scanning element 3. There is. In these cases, the voltage applied to the temperature control element 21 has the opposite sign to that shown in FIG. The tripod type shown in FIG. 4C is composed of three rods 22 which are perpendicular to each other, and the displacement of the probe 2 is controlled by expanding and contracting the rods 22 using the temperature control elements 21 attached to the respective rods 22. . The same effect was obtained using any of these.

Example 2 In this example, a thermal drift compensating device using resistance heating as a temperature control element is shown.

The scanning tunneling microscope shown in FIG. 5 includes a base 100, a sample 1, a probe 2, a scanning element 3, a coarse movement mechanism 4, an upper base 200, and supporting portions 9 and 10 for connecting between the scanning element 3 and the sample 1. , 11 and 12. In the expansion / contraction portions 9, 10, 11, 12 connecting the scanning element 3 and the sample 1, the resistance heating elements 30, 31, 32 are aligned in the X-axis direction 13 and the Y-axis direction 14 of the scanning of the scanning element 3. , 33 are attached respectively, and the expansion / contraction part 35 is attached with the resistance heating element 34.

FIG. 6 shows a side view of the internal structure as seen from the Y-axis direction 14. When the probe 2 drifts in the X-axis negative direction 17 relative to the sample 1, when the resistance heating element 30 is used for heating, the expandable portion 9 expands, so that the probe 2 moves in the X-axis positive direction. The movement in the direction 16 is canceled out by the drift in the X-axis direction 13. When the drift direction is opposite, the stretchable portion 11 may be heated using the resistance heating element 32.
Further, the drift in the Y-axis direction 14 is similarly controlled using the resistance heating elements 31 and 33. Z-axis direction 15, that is, the Z-axis negative direction 18 perpendicular to the sample 1
When there is a drift of No. 2, the resistance heating element 34 is used to heat and expand the expansion / contraction portion 35, so that the probe 2 moves in the Z-axis positive direction 19 and the drift in the Z-axis direction 15 is offset. When the drift direction is opposite, the resistance heating elements 30, 31, 32, 33 are used to expand / contract the expansion / contraction parts 9, 1.
It is sufficient to heat 0, 11, and 12. However, in the resistance heating elements 30, 31, 32, 33, the X-axis direction 13 or Y
It is necessary to supply a current obtained by adding the drift control current in the axial direction 14 and the drift control current in the Z-axis direction 15.

Silicon is used as the sample 1, platinum-iridium is used as the probe 2, tungsten heaters are used as the resistance heating elements 30, 31, 32 and 33, and expandable portions 9, 10, 11 and 12 are used.
Was measured at room temperature in the atmosphere using a stainless steel plate. Initially, 1 nm / s both in the sample plane and in the vertical direction
Thermal drift was observed, but when drift control was performed by the method described above, it was reduced to 0.01 nm / s or less. Similar effects were obtained using other scanning probe microscopes such as an atomic force microscope and a magnetic force microscope. In gas, vacuum or solution as an operating atmosphere,
The same effect was obtained in all operating temperature ranges of the scanning probe microscope from 1K to 1500K. Resistance heating elements 30, 31,
The materials for the materials 32 and 33 are not limited as long as they can be electrically heated, such as tungsten, nichrome wire, and graphite. The stretchable parts 9, 10, 11, 12 include stainless steel, copper,
Any material may be used as long as it reversibly expands and contracts by heat, such as metals such as aluminum, ceramics such as silicon oxide and aluminum oxide, and organic substances such as bakelite and polystyrene.

Embodiment 3 This embodiment shows an apparatus for performing thermal drift compensation by controlling the heat conduction between the constituent material of the scanning probe microscope and the heat source.

FIG. 7 shows a sectional view of a cryogenic scanning tunneling microscope. The present scanning tunneling microscope comprises a sample 1, a probe 2, and a scanning element 3. The scanning tunneling microscope main body 40 is evacuated while being fixed in a vacuum container 41 by a support tube 48, and the vacuum container 41 is further filled with liquid nitrogen. Refrigerant 43 such as
The temperature of the scanning tunneling microscope body 40 can be adjusted by being introduced into the Dewar bottle 42 filled with. The scanning element 3 is fixed to a movable base 44, and the movable base 44 is sandwiched by four ball bearings 45 and two springs 46, and is movable in the vertical direction.

A stepping motor 47 is provided on the outside of the upper end of the vacuum container 41, whereby a rotary shaft 49 in a support tube 48 is provided.
Drive screw 50 through. Since the driving screw 50 is screwed into the female screw hole 51 provided at the upper end of the moving base 44, the moving base 44 moves in the vertical direction by the rotation of the driving screw 50, and the probe 2 attached to the lower end of the scanning element 3 is moved. The distance between the sample and the sample 1 is controlled.

Further, the heat conducting portions 54 and 55 protruding from the vacuum container 41 are in contact with the expanding and contracting portions 52 and 53 of the scanning tunneling microscope body 40, respectively. The heat conducting portion also exists in the direction perpendicular to the paper surface. By controlling the heat conduction of the heat conduction parts 54, 55, the refrigerant 43-the expansion / contraction part 52,
It becomes possible to control the heat exchange between 53.

FIG. 8 shows a detailed structural example of the heat conducting portions 54 and 55.

In the heat conducting portion shown in FIG. 8A, the fixing portion 57 and the contact portion 58 are arranged so as to sandwich the piezo element 56.
Exists, and the heat conductor 59 is coupled between them. The fixed portion 57 is fixed to the refrigerant 43, and the contact portion 58 is connected to the expandable portion 5
By bringing them into contact with 2, 53, it becomes possible to control the heat conduction according to the contact pressure change on the contact surface due to the expansion and contraction of the piezo element 56. As the fixing portion 57 and the contact portion 58, metals such as copper, aluminum and gold, ceramics such as silicon oxide and aluminum oxide, organic substances such as bakelite and Teflon can be used. The heat conductor 49 may be a flexible material such as copper wire, gold foil, spring, or viton rubber. If the piezo element 56 is used as a heat conductor, the heat conductor 59, the fixing portion 57, and the contact portion 58 can be omitted.

In FIG. 8B, the contact pressure is controlled by pushing the leaf springs 60 provided at both ends of the heat conductor 61 by using the piezo elements 56 located between them.
As the heat conductor 61, metals such as copper, aluminum and gold, ceramics such as silicon oxide and aluminum oxide, organic substances such as bakelite and Teflon can be used.
A metal such as stainless steel or titanium is suitable for the leaf spring 60.

In FIG. 7, the scanning tunneling microscope body 4 is shown.
The operation when 0 is cooled by using the refrigerant 43 will be described. The probe 2 is in the positive X-axis direction 1 relative to the sample 1.
When drifting to 6, the heat conducting portion 54 is extended to increase the heat conductivity, and the heat conducting portion 55 is contracted to reduce the heat conductivity. As a result, the expansion / contraction part 52 contracts as the temperature decreases, and the expansion / contraction part 53 expands as the temperature rises, so that the probe 2 moves in the X-axis negative direction 17 and the drift in the X-axis direction 13 is offset. It When the drift direction is opposite, the opposite operation may be performed. Further, similar control is performed for drift in the Y-axis direction. When there is a drift in the Z-axis direction 15, that is, in the direction perpendicular to the sample 1 in the Z-axis negative direction 18, the heat conducting portions 54 and 55 are used to expand and contract the stretchable portion 5.
By decreasing and contracting the temperatures of 2, 53 and performing the same operation in the Y-axis direction, the probe 2 moves in the Z-axis positive direction 19 and the drift in the Z-axis direction 15 is offset. If the drift direction is opposite, the reverse operation is performed.

Silicon as the sample 1, gold as the probe 2,
A stainless plate was used as the side walls 52 and 53, and liquid nitrogen was used as the coolant 43, while the sample 1 was cooled to −196 ° C., and measurement was performed in an ultrahigh vacuum. The heat conducting parts 54 and 55 shown in FIG. 8A were used, the fixing part 57 and the contact part 58 were made of copper, and the heat conductor 59 was made of copper wire. Initially, 10 both in the sample plane and in the vertical direction
Although a thermal drift of nm / s was observed, when drift control was performed by the method described above, it was 0,01 nm /
s or less. As the stretchable portions 52 and 53, materials such as metals such as stainless steel, copper, and aluminum, ceramics such as silicon oxide and aluminum oxide, organic substances such as bakelite, polystyrene, and the like that can reversibly expand and contract by heat are made of materials. It doesn't matter. The coolant 43 is liquid nitrogen, liquid helium, cold water, or the like, and has a temperature difference from the sample 1 of 10
It should be about K or more. The operating atmosphere is gas, vacuum, or solution. Similar effects were obtained using other scanning probe microscopes such as an atomic force microscope and a magnetic force microscope.

[0031]

According to the present invention, thermal drift, which is one of the factors causing instability of a scanning probe microscope, can be reduced, and more stable and precise measurement can be performed as compared with the conventional method. The effect is particularly great in low-temperature or high-temperature operation.

[Brief description of drawings]

FIG. 1 is a perspective view of a scanning probe microscope in which thermal drift compensation is performed by directly heating or cooling a supporting portion that connects a scanning element and a sample 1.

FIG. 2 is a side view of the scanning probe microscope of FIG.

FIG. 3 is a perspective view of a scanning probe microscope in which thermal drift compensation is performed by directly heating or cooling a supporting portion of the scanning element 3.

FIG. 4 is a perspective view showing an example of a structure for directly heating or cooling the support portion of FIG. 3, (a) is a rectangular parallelepiped expansion / contraction portion, and (b) is a perspective view.
Is a cylindrical expansion / contraction part, and (c) is a tripod expansion / contraction part.

FIG. 5 is a perspective view of another example of the scanning probe microscope in which the thermal drift compensation is performed by directly heating or cooling the supporting portion connecting the scanning element and the sample 1.

6 is a side view of the scanning probe microscope of FIG.

FIG. 7 is a perspective view of another example of a scanning probe microscope in which thermal drift compensation is performed by directly heating or cooling a support portion that connects the scanning element and the sample 1.

8A and 8B are side views showing examples of the heat conducting portion of FIG. 7, where FIG. 8A is a heat conducting portion using a flexible heat conductor, and FIG. 8B is a heat conducting portion using a leaf spring.

[Explanation of symbols]

1 ... sample, 2 ... probe, 3 ... scanning element, 4 ... coarse movement mechanism,
5, 6, 7, 8, 21 ... Temperature control element, 9, 10, 1
1, 12, 20, 35, 52, 53 ... Expandable portion, 13 ... X
Axial direction, 14 ... Y-axis direction, 15 ... Z-axis direction, 16 ... X-axis positive direction, 17 ... X-axis negative direction, 18 ... Z-axis negative direction, 19 ...
Z-axis positive direction, 22 ... Rod, 30, 31, 32, 33,
34 ... Resistance heating element, 40 ... Scanning tunneling microscope body,
41 ... Vacuum container, 42 ... Dewar bottle, 43 ... Refrigerant, 4
4 ... Moving base, 45 ... Ball bearing, 46 ... Spring, 4
7 ... Stepping motor, 48 ... Support tube, 49 ... Rotating shaft, 50 ... Drive screw, 51 ... Female screw hole, 54, 55 ... Heat conduction part, 56 ... Piezo element, 57 ... Fixed part, 58 ... Contact part, 59 ... Heat conductors 60, 61 ... Leaf springs.

Claims (7)

[Claims] 1. A scanning probe microscope that compensates for positional thermal drift between the probe and the probe by locally controlling the temperature of a structure that positions the probe and the probe in a predetermined relationship. 2. The scanning probe microscope according to claim 1, wherein the temperature control is heating or cooling by a heat source, and the temperature of the heat source is controlled. 3. The scanning probe microscope according to claim 2, wherein the heat source is a Peltier element. 4. The scanning probe microscope according to claim 2, wherein the heat source is resistance heating. 5. The scanning probe microscope according to claim 1, wherein heat conduction between the structure and a heat source is controlled. 6. The scanning probe microscope according to claim 5, wherein the heat conduction control is control of contact pressure at the mechanical contact surface. 7. The scanning probe microscope according to claim 6, wherein the control of the contact pressure is temperature control by a piezo element.