JPH10267950A - Lateral-excitation frictional-force microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a lateral-excitation frictional-force microscope in which the amplitude of a lateral vibration given across a sample and a probe is not affected by the weight of the sample. SOLUTION: A sample 102 is placed on a scanner 104 as a three-dimensional fine movement mechanism. A cantilever holder 300 supports a cantilever unit 108 so as to be capable of being vibrated to the Y-direction. The cantilever unit 108 is provided with a base 110, with a cantilever 112 which is fixed to the base and with a probe 114 which is formed at its tip. An objective lens 116 is coupled optically to a ZP sensor 200 via a beam splitter 118. A computing unit 120 which computes the displacement signal and the twist signal of the cantilever 112, a servo circuit 122 which computes the displacement in the Z- direction of the scanner, an X-Y scanning circuit 124 which drives the scanner for an X-Y scanning operation, an exciter 126 which outputs sine waves and an amplitude detector 128 which compares the twist signal with the sine waves are installed.

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 transversely excited friction microscope.

[0002]

2. Description of the Related Art A scanning probe microscope is a general term for a device for obtaining information on a sample surface using a probe, such as a scanning tunneling microscope and an atomic force microscope. There is a scanning force microscope that obtains information on a sample surface based on a force acting between the sample and the sample surface. Scanning force microscopes generally have a sharp pointed probe (probe) supported by the free end of a flexible cantilever, which is brought close to the sample surface and is generated between the probe tip and the atoms on the sample surface. While capturing the interaction force as deformation of the cantilever, the probe is scanned XY across the surface of the sample, and based on information on the position of the probe and information on the deformation of the cantilever at that time,
Obtain various information on the sample surface.

Further, as one of the scanning force microscopes, a lateral excitation friction force microscope (LMFFM: Lateral Modulation Friction) is used.
Force Microscope). This device is a further development of the atomic force microscope, in which the sample is vibrated in the Y direction during XY scanning, and the amplitude and phase of the torsion of the cantilever caused by this vibration are examined to obtain an uneven image of the sample surface. In addition, the frictional force acting between the sample and the probe, and the elastic modulus and viscosity of the sample can be measured.

[0004] As an example, FIG. 7 shows a transversely excited friction force microscope proposed by Mr. Yamanaka et al. Of the Institute of Mechanical Engineering, the Institute of Industrial Science and Technology. The sample 12 is placed on a scanner 14. Above the scanner 14, the cantilever unit 1
6 are arranged. The cantilever unit 16 includes the base 1
8, cantilever 20, and probe 22 formed at the tip
have. Further, an optical lever-type optical sensor for detecting displacement and torsion of the cantilever 20 is provided. This optical sensor includes a semiconductor laser 24, a condenser lens 26, and a four-division photodiode 28. Further, a calculator 3 for calculating a displacement signal and a torsion signal of the cantilever 20 from the output of the four-division photodiode 28.
0, a servo circuit 32 for controlling the position of the scanner 14 in the Z direction based on the displacement signal, a scanning circuit 34 for driving the scanner 14 for XY scanning, and applying a vibration in the Y direction between the probe 22 and the sample 12. Exciter 36 that outputs a sine wave for output, adder 38 that superimposes a sine wave output from exciter 36 on the Y signal output from scanning circuit 34, a torsional signal output from calculator 30 and an output from exciter 36 An amplitude detector 40 for comparing sine waves is provided.

The scanner 14 is supplied with an X signal for X scanning output from the scanning circuit 34 and a Y signal in which a sine wave of the exciter 36 is superimposed on a signal for Y scanning output from the scanning circuit. You. As a result, the scanner 14 vibrates at a predetermined amplitude in the Y direction, and the probe 22
Is raster-scanned. The arithmetic unit 30
The outputs a, b,
From c and d, a displacement signal AFM = a + b−c−d and a torsion signal LFM = a−b−c + d are output. Servo circuit 3
2 outputs a Z signal for controlling the scanner 14 so as to keep the displacement signal AFM at a constant value. This reflects the unevenness of the sample surface, which is processed as an unevenness signal. The amplitude detector 40 compares the sine wave output from the exciter 36 with the torsion signal LFM output from the arithmetic unit 30,
An amplitude signal that reflects the local elastic modulus, viscosity, and frictional force of the sample surface is output. By processing the concavo-convex signal and the amplitude signal in synchronization with the scanning signal output from the scanning circuit 34, information such as the concavity and convexity of the sample surface and the distribution of the elastic modulus can be obtained.

[0006]

In the above-described transversely excited friction force microscope, the sample is vibrated in the Y direction during the XY scanning, and the amplitude of the vibration depends on the frequency of the output of the exciter and the weight of the sample. Determined by For this reason, if the weight of the sample changes, the resonance frequency in the Y direction of the system consisting of the sample and the scanner changes accordingly, so that the amplitude of the vibration in the Y direction differs even when the same Y signal is applied. It will be. An object of the present invention is to provide a laterally-excited friction force microscope in which the amplitude of lateral vibration applied between a sample and a probe is not affected by the weight of the sample.

[0007]

SUMMARY OF THE INVENTION A transverse excitation friction force microscope according to the present invention comprises a cantilever having a probe at a free end, excitation means for vibrating the cantilever in parallel with the sample surface, and moving the sample to move the probe. Scanning means for scanning over the sample surface;
It has a detecting means for examining the displacement and torsion of the free end of the cantilever.

In the present invention, the probe is scanned by moving the sample, and the cantilever is vibrated to
A relative vibration parallel to the sample surface is applied between the probe and the sample. Therefore, the amplitude of the probe is not affected by the weight of the sample.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. Sample 102 is
It is placed on a scanner 104 which is a three-dimensional fine movement mechanism. Above the scanner 104, a cantilever unit 108 is supported by a cantilever holder 300. The cantilever holder 300 has a function of causing the cantilever unit 108 to vibrate in the Y direction. The specific structure of the cantilever holder 300 will be described later in detail. The cantilever unit 108 is the base 1
10, a strip-shaped cantilever 112 fixed to this,
The probe has a probe 114 formed at the tip of the cantilever 112. The base 110 has a length of 4 mm and a width of 2 m, for example.
m, made of glass or silicon wafer having a thickness of 0.5 mm. The cantilever 112 has a length of, for example, 200 μ.
m, a width of 20 μm, and a thickness of 1 μm. The probe 114 has a length of, for example, 10 μm by a silicon process or the like.
Formed. The cantilever unit 108 is the base 11
0 is elastically fixed to the cantilever holder 300 using an adhesive or a leaf spring.

An objective lens 116 is provided above the probe 114. The objective lens 116 is optically coupled to a ZP sensor 200 for detecting the displacement and twist of the cantilever 112 via a beam splitter 118 above the objective lens 116. ing. Although not shown, an observation optical system cooperating with the objective lens 116 is arranged above the beam splitter 118.

The cantilever holder 300 holds the probe 11
In order to adjust the position of No. 4, it is attached to an adjusting jig (not shown) fixed to the same structure as the ZP sensor 200. Further, the scanner 104 includes the probe 114 and the sample 10.
2 is mounted on a Z-direction coarse movement stage (not shown) to adjust the distance between the two.

Further, a calculator 120 for calculating a displacement signal and a torsion signal of the cantilever 112 from an output of the ZP sensor 200, a servo circuit 122 for controlling a displacement of the scanner in the Z direction based on the displacement signal, a scanner for XY scanning XY scanning circuit 124 for driving the probe, and an exciter 12 for outputting a sine wave for vibrating the probe 114 in the Y direction
6. The torsion signal output from the arithmetic unit 120 and the exciter 126
Is provided with an amplitude detector 128 for comparing the sine wave output from the.

As shown in FIG. 2, the ZP sensor 200 includes a semiconductor laser 202, a collimator lens 204 for converting the emitted light into parallel light,
6, a half mirror 208 for splitting the reflected light from the cantilever 112 into two different directions, and two critical angle prisms 400 and 2 for deflecting the light split by the half mirror 208.
10. Two split photodiodes 21 for receiving light reflected by the respective critical angle prisms 400 and 210
2 and 214. The light emitted from the semiconductor laser 202 becomes parallel light by the collimator lens 204, is reflected by the beam splitter 206, and is focused on the surface of the cantilever 112 by the objective lens 116.
The objective lens 116 is adjusted in advance so that the parallel light focuses on the surface of the cantilever 112 at the reference position, as shown in FIG. The light reflected by the cantilever 112 passes through the objective lens 116, passes through the beam splitter 206, is split into two directions by a half mirror 208, and the components reflected by the critical angle prisms 400 and 210 are split into two light receiving elements 212 and 214. Incident. The displacement of the cantilever 112 (that is, the probe 114) in the Z direction is obtained as a deviation from the focal position of the objective lens 116, and the outputs of the light receiving elements of the two-division photodiodes 212 and 214 are A and B as shown in the figure. , C, and D, the displacement signal AFM is obtained by the calculation of AFM = ABC-D. When the cantilever is twisted, the incident position of the beam on the two-part photodiodes 212 and 214 shifts as shown in FIG.
Is obtained by the calculation of LFM = AB + CD. In this embodiment, ZP is used to detect the displacement and torsion of the cantilever 112.
Although the sensor 200 is used, the optical lever type displacement sensor described in the conventional example (FIG. 7) may be used.

As shown in FIG. 3, the cantilever holder 300 has a mounting portion 302 for mounting the cantilever unit 108, a mounting portion 304 for mounting on the apparatus main body, and an elastic deformation portion 308 connecting the mounting portion 302 and the mounting portion 304. ing. The mounting portion 304 is provided with a fixed shaft 306 fixed to the apparatus main body. The elastically deforming portion 308 has two parallel side walls 310 constituting a parallel spring, and has a high rigidity in the X and Z directions and a structure that easily vibrates in the Y direction. Any material may be used as long as it is elastically deformed. A piezoelectric element 312 is attached inside each side wall 310, and constitutes a unimorph type actuator. The polarization directions of the two piezoelectric elements 312 are the same as shown in the drawing, and coincide with the Y direction. When the electrodes on the side walls of the two piezoelectric elements 312 are grounded and the same sine wave is applied to the inner electrodes, the two piezoelectric elements 312 expand and contract in opposite phases. In other words, when one expands, the other side contracts. Therefore, the mounting portion 302 vibrates in the Y direction. As a result, the cantilever unit 108 mounted thereon vibrates in the Y direction, and the probe 114 is excited in the Y direction.

Next, the operation will be described. As can be seen from FIG. 1, the scanner 104 includes the XY scanning circuit 12.
4 receives the XY signal supplied from
Move in the direction. At the same time, the cantilever holder 300 receives the sine wave signal supplied from the exciter 126 and vibrates the cantilever unit 108 at a predetermined frequency in the Y direction. As a result, the probe 114 vibrates in the Y direction at a predetermined amplitude, for example, 1 nm to 1 μm, and moves the area of, for example,
Raster scanning is performed so as to cover the line.

The displacement signal AFM indicating the displacement of the cantilever 112 in the Z direction is the output signal A of the ZP sensor 200,
For B, C, and D, AFM =
It is obtained by performing the operation of ABC + D. Also, the torsion signal LFM indicating the torsion of the cantilever is
It is obtained by performing an operation of LFM = AB + CD in arithmetic unit 120. Further, the calculation in the case of using the displacement sensor of the optical lever system is the same as that described with reference to FIG. 7, and thus the description is omitted here.

The servo circuit 122 supplies the scanner 104 with a Z signal for controlling the movement of the scanner 104 in the Z direction so as to keep the displacement signal AFM at a constant value. As a result, the cantilever 112 is always maintained in a posture displaced by a predetermined amount. Z output from the servo circuit 122
The signal reflects the unevenness of the sample surface, which is taken as an unevenness signal together with the XY signal into a processing device (not shown) for constructing an image.

The amplitude detector 128 performs amplitude detection or phase detection in synchronization with the output signal of the exciter 126.
As a result, the output signal Lout of the amplitude detector 128 reflects the local elastic modulus, viscosity, and friction characteristics of the portion of the sample surface where the probe 114 is in contact, and is processed in the same manner as the above-described uneven signal. It is taken into a device (not shown).

As described above, in this embodiment, the cantilever holder 300 has a function of vibrating the mounting portion 302 to which the cantilever unit 108 is attached in the lateral direction.
Is vibrated in the Y direction, thereby giving a lateral vibration between the probe 114 and the sample surface. Since the vibrating member is the cantilever unit 108, the resonance characteristic does not change even if the sample 102 is replaced. That is, the frequency of the vibration is not affected by the weight of the sample 102.

Further, since the cantilever unit 108 is smaller than the sample, there is an advantage that the vibration frequency can be set higher. Further, since the signal for giving the lateral vibration and the Y signal for the Y scanning are completely separated, there is an advantage that the accuracy of the detected signal is improved.

Hereinafter, several modified examples of the cantilever holder will be described with reference to FIGS. 4 to 7, the same members as those of the cantilever holder in FIG. 3 are denoted by the same reference numerals, and a detailed description of those members will be omitted here.

FIG. 4 shows the cantilever holder of the first modification.
Shown in This cantilever holder has a configuration in which the opening of the elastically deformable portion 308 of the cantilever holder in FIG. 3 is filled with a viscous material 314, for example, rubber or a gel material having vibration absorption. Such a viscous material 314
Reduces the Q value of the resonance in the Y-direction so that the Q value of the resonance in the Y-direction of the mounting portion becomes too high and the amplitude value fluctuates too much when vibrating near the excitation frequency. For example, the influence of the excitation frequency fluctuation can be reduced to 1/10 or less by making the Q value of 100 to be 10 or less.

FIG. 5 shows a cantilever holder according to a second modification.
Shown in This cantilever holder has a configuration in which two side walls constituting a parallel spring in the cantilever holder of FIG. 3 are changed to a single leaf spring 316, and piezoelectric elements 312 are provided on both surfaces thereof. That is, the elastic deformation portion 308 'of this modification is a bimorph-type actuator. In the cantilever holder of the present modification, there is an advantage that the drilling required for forming the elastically deformable portion in the form of a parallel spring when the cantilever holder of FIG. 3 is manufactured is unnecessary, and the manufacturing cost is reduced. .

FIG. 6 shows a cantilever holder according to a third modification.
Shown in This cantilever holder corresponds to a sample observation by liquid immersion, and has an L-shaped mounting portion 304 ', and is provided with a relief to a lateral wall of a water tank. The opening of the elastically deformable portion 308 is filled with a waterproofing filler 320 so as to prevent leakage current from flowing into the water, and also covered with a conductive wire 322 for supplying an excitation signal. By using the cantilever holder of this modification, sample observation by liquid immersion can be performed.

The specific examples of the present invention have been described with reference to the drawings. However, the present invention is not limited to the above-described embodiments, and various modifications and changes may be made without departing from the gist of the invention. Is possible.

The present invention can be expressed as follows. 1. A cantilever having a probe at its free end, excitation means for vibrating the cantilever parallel to the sample surface, scanning means for moving the sample and scanning the probe over the sample surface, and displacement and torsion of the free end of the cantilever. A laterally-excited friction force microscope having detection means for examining.

2. In the above item 1, the excitation means is a cantilever holder for supporting the cantilever, and a fixedly supported mounting portion, a mounting portion to which the cantilever is mounted, and a direction in which the mounting portion is parallel to the sample surface with respect to the mounting portion. A cantilever holder having a resiliently deformable elastically deformable portion for movably supporting the mounting portion, vibration generating means for vibrating the mounting portion, and an exciter for outputting a sine wave signal for driving the vibration generating means. , Horizontal excitation friction force microscope.

3. In the above item (2), the elastically deformable portion has two parallel leaf spring materials which are elastically deformed and whose normal line coincides with the vibration direction, and the vibration generating means is provided on one side of each leaf spring material. A transversely excited friction force microscope having two piezoelectric elements that expand and contract in opposite phases to each other.

4. In the above item (2), the elastically deforming portion has one elastically deformable leaf spring material whose normal line coincides with the vibration direction, and the vibration generating means is provided in opposite phases provided on both sides of the leaf spring material. Having two expanding and contracting piezoelectric elements,
Lateral excitation friction force microscope.

[0030]

According to the present invention, it is possible to obtain a transversely excited friction force microscope in which the transverse vibration applied between the sample and the probe is not affected by the weight of the sample.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a lateral excitation friction force microscope according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a ZP sensor shown in FIG.

FIG. 3 is a diagram showing a configuration of a cantilever holder of FIG. 1;

FIG. 4 is a view showing a first modification of the cantilever holder.

FIG. 5 is a view showing a second modified example of the cantilever holder.

FIG. 6 is a view showing a third modified example of the cantilever holder.

FIG. 7 is a view showing a conventional example of a transverse excitation friction force microscope.

[Explanation of symbols]

 Reference Signs List 102 sample 104 scanner 108 cantilever unit 112 cantilever 114 probe 120 computing unit 122 servo circuit 124 XY scanning circuit 126 exciter 128 amplitude detector 200 ZP sensor 300 cantilever holder 302 mounting part 304 mounting part 308 elastic deformation part 312 piezoelectric element

Claims (1)

[Claims] 1. A cantilever having a probe at a free end, excitation means for vibrating the cantilever in parallel with a sample surface, scanning means for moving a sample and scanning the probe over the sample surface, and a free end of the cantilever A transversely-excited friction force microscope having detection means for examining the displacement and torsion of a force.