JP3022648B2 - Scanning probe microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for scanning a sample surface using a probe, based on tunnel current, atomic force and magnetic force measured at each point on the surface, and positional information of each point. A scanning probe microscope for constructing an image of a sample surface by scanning.

[0002]

2. Description of the Related Art Such scanning probe microscopes include a scanning tunneling microscope (STM), an atomic force microscope (AFM) and a magnetic force microscope (MFM).

[0003] Unlike a conventional microscope, the STM is capable of detecting electrons bound in a sample, and is recently attracting attention as a very characteristic surface observation device capable of observing an atomic arrangement in real space. . In the STM, a voltage (tunnel voltage) is applied between the probe and the sample, and Z is adjusted so that the electron cloud of atoms at the tip of the probe and atoms on the surface of the sample slightly overlap.
The probe is brought close to the sample surface using a directional actuator, and a tunnel current is caused to flow between them. Then, while the height (Z direction) of the probe is servo-controlled using a Z-direction actuator so as to keep the tunnel current constant, the probe and the sample are relatively moved in the plane direction (XY direction) using the XY-direction actuator. (XY directions) to perform two-dimensional scanning. At this time, the servo voltage of the Z-direction actuator is read in synchronization with the position information on the surface, and the surface of the sample is observed by displaying an image.

The tunnel current J _T is represented by the following equation, where φ is the average of the work functions of the probe and the sample, and S is the distance between the probe and the sample.

J _T = k · exp (−A · φ ^1/2 · S) where k and A are certain constants. Therefore, tunnel J _T
Reacts sensitively to changes in S, and changes by about an order of magnitude for changes in S of 0.1 nm. Therefore, the STM can obtain a surface image with extremely high resolution (atomic scale resolution). Also, unlike the conventional reciprocal lattice spatial images obtained by methods such as X-ray diffraction, electron beam diffraction, and ion scattering, it has the feature that the atomic arrangement can be observed in real space. Further, since the voltage applied between the probe and the sample is equal to or lower than the work function of the sample, the magnitude of the flowing tunnel current is as small as the order of nA, the power consumption is low, and the sample is hardly damaged. Therefore, the STM is suitable for observation of a biological sample or the like, unlike an electron microscope or the like. Microscopic observation samples related to the living body / bio field are generally transparent. Based on this viewpoint, in order to use the STM for specimen observation in the biological and biotechnology fields, the one integrated with an optical microscope that observes the specimen surface by the reflected light from the specimen is Max.
Proposed by the Prang Institute. By the way, STM
Then, a piezoelectric element is generally used as an actuator for moving a probe or the like.

Particularly recently, a cylindrical piezoelectric actuator has become a mainstream actuator. This cylindrical actuator is provided with four electrodes extending in the axial direction outside a cylindrical piezoelectric body, and the inside is covered with one electrode. Such an actuator moves a probe fixed at one end and attached to a free end, which is the other end, in a three-dimensional direction. In other words, by applying a voltage of opposite polarity to the two outer electrodes facing each other and bending the piezoelectric body in that direction, the same voltage is applied to the four electrodes in the X and Y directions, or the voltage of the inner electrode is applied. Is changed to expand and contract the entire piezoelectric body, thereby moving the probe in the Z direction.

[0007]

Since the STM has an atomic scale resolution as described above, when observing a sample, it is necessary to previously find a portion to be observed using a high-magnification optical microscope. It is essential. However,
In the STM integrated with the optical microscope described above, since the optical system observes the sample using reflected light, when the sample is transparent and very thin, most of the light is transmitted through the sample and the contrast is good. I can't get an image. For this reason,
A transparent and very thin sample cannot be optically observed at a high magnification, and there is a disadvantage that a portion to be observed cannot be specified by STM. In other words, conventional scanning probe microscopes have only specific illumination means,
Illumination according to the observation purpose could not be performed, and a desired optical image could not be obtained.

An object of the present invention is to provide a scanning probe microscope capable of performing illumination according to the observation purpose.

[0009]

A scanning probe microscope according to the present invention is a scanning probe microscope for observing a sample using a probe, and comprises an illumination optical system capable of illuminating the sample by a plurality of illumination methods. An observation optical system for observing an optical image of the sample illuminated by the illumination optical system; and an actuator for relatively three-dimensionally driving the sample and the probe.

[0010]

The scanning probe microscope of the present invention can illuminate a sample by a plurality of illumination methods.

[0011]

FIG. 1 shows a scanning tunnel microscope according to a first embodiment of the present invention. A light source 12 for illuminating the sample is attached to an upper end of a cylindrical lamp house 14. At the lower end of the lamp house 14, a condenser lens 16 for converting light from a light source into a parallel light beam and a condenser lens 18 for condensing the parallel light beam are provided. Each of the condenser lenses 16 and 18 has an opening in the center thereof. A mounting base 19 is provided in the opening of the condenser lens 16, and a fixed end of a cylindrical piezoelectric actuator 20 extending downward on the mounting base 19. Is fixed. A free end of the cylindrical piezoelectric actuator 20 extends from an opening of the condenser lens 18, and a probe 22 for detecting a tunnel current is attached to a bottom surface thereof. The opening of the condenser lens 18 is
The aperture is formed so as not to interfere with the movement of the cylindrical piezoelectric actuator 20 when the probe 22 performs two-dimensional scanning.

The light emitted from the light source 12 is converted into a parallel light beam by the condenser lens 16 and then condensed by the condenser lens 18 on a transparent sample 24 placed on a transparent sample stage 26. The light incident on the sample 24 is scattered or refracted there, and a part of the scattered light or refracted light is incident on the objective lens 28. The light that has entered the lens 28 becomes a parallel light beam, enters the imaging lens 34 via the two reflecting mirrors 30 and 32, and forms an image. The image (input image) is enlarged by the eyepiece 36 and confirmed by the observer's eyes 40.

When performing the STM observation, the observer first moves the sample stage 26 while viewing the input image, and arranges the observation point of the sample 24 at the center of the field of view, thereby adjusting the probe 22 to the observation point. Next, a predetermined voltage (tunnel voltage) is applied between the probe 22 and the sample 24, and the probe 22 is brought closer to the sample 24 using the cylindrical actuator 20. During this time, the current flowing between the probe 22 and the sample 24 is monitored, and the approach of the probe 22 is stopped when a predetermined value of the tunnel current is detected. Subsequently, the cylindrical actuator 20
Probe 2 so that the value of the tunnel current is kept constant.
The probe 22 is moved in the XY directions (directions parallel to the sample surface) while servo-controlling the position of the sample 2 in the Z direction (direction perpendicular to the sample surface). At this time, the servo voltage of the actuator 20 is read, and the position information in the Z direction based on the servo voltage is displayed in synchronization with the position information in the XY directions, whereby an image of the surface of the sample 24 is obtained.

In this embodiment, dark-field illumination in which illumination light does not directly enter the objective lens allows an optical microscope image of the sample surface with good contrast to be obtained. Moreover, since the cylindrical actuator is provided inside the condenser lens, the STM can be made compact. In addition, since the sample is mounted on the upper surface of the sample stage, even a fluid sample can be observed in a stable state.

Next, a second embodiment of the present invention will be described with reference to FIG. In the drawing, members equivalent to those of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. In this embodiment,
An optical system for guiding light from a light source to a sample and an actuator mounting structure are different from those of the first embodiment.

The light source 12 is mounted on the upper part of the inside of the lamp house 14. The light source 12 is covered with a cylindrical support member 42. Have been. At the lower end of the lamp house 14, a transparent plate 50 for closing the lamp house is provided.
A convex mirror 46 for reflecting light from the light source is provided. Further, a concave mirror 48 for reflecting and converging light from the convex mirror 46 is provided inside the lamp house 14. Transparent plate 5
The fixed end of the cylindrical piezoelectric actuator 20 is attached to the lower side of the central portion of 0.

The light emitted from the light source 12 is transmitted to the collimator lens 4.
After being converted into a parallel light flux by 4, the light is reflected by the convex mirror 46 and becomes a divergent light flux. This divergent light beam is reflected by the concave mirror 48 to become a convergent light beam, and is condensed on the sample 24, where it is scattered or refracted. A part of the scattered light or refracted light is incident on the objective lens 28 to form an image as in the first embodiment, and is observed as an optical image of the sample surface.

In this embodiment, since the illumination light does not directly hit the actuator 20, the effect of the actuator 20 due to a temperature change is obtained in addition to the effects described in the first embodiment.
There is an advantage that the influence of the shape change is reduced.

Next, a third embodiment of the present invention will be described with reference to FIG. The light source 12 is a cylindrical piezoelectric actuator 2
0 and is attached to a support 58 that supports the fixed end of the actuator 20. Light source 1
Around the periphery of 2, a cylindrical support member 52 for supporting the two condenser lenses 16 and 18 is provided. A circular light-shielding plate 54 is provided between the condenser lens 16 and the condenser lens 18 via a shaft 56 so as to be rotatable. A transparent plate 60 is provided at the lower end (free end) of the actuator 20, and the probe 22 is attached to the lower part of the center of the transparent plate 60.

The light emitted from the light source 12 is converted into a parallel light beam by the condenser lens 16,
8 converges on the sample 24. At this time, the light shielding plate 54
By turning, the amount of light directly incident on the objective lens 28 can be adjusted. That is, if the angle of the surface of the light shielding plate 54 is made perpendicular to the optical axis, the light directly incident on the objective lens 28 disappears, resulting in dark-field illumination. Bright field illumination.

In the present embodiment, in addition to the advantages described in the second embodiment, bright-field / dark-field illumination can be adjusted by changing the direction of the light shielding plate 54. That is, an optimal optical image can be obtained by adjusting according to the sample. Further, the condenser lenses 16 and 18 are the same as those used in an ordinary optical microscope, and there is an advantage that parts of the ordinary optical microscope can be used as they are.

FIG. 4 shows a fourth embodiment of the present invention. This embodiment is different from the third embodiment in that the cylindrical piezoelectric actuator 20 is provided not on the illumination light source side but on the sample side. That is, the lower end (fixed end) of the actuator 20 is fixed to the base 64, and the upper end (free end) is provided with a transparent plate 60 in which the probe 22 is attached downward at the center. The base 64 has an opening in the center, and a cylindrical support 62 for supporting the sample table 26 is provided around the base 64. The objective lens 28 is accommodated inside the support 62. Other configurations are the same as those of the third embodiment.

In the present embodiment, similarly to the third embodiment, the bright-field and dark-field illumination can be adjusted by changing the direction of the light shielding plate 54, and an optimal optical image of the sample surface can be obtained. Further, similarly to the second embodiment, since the illumination light does not directly hit the actuator, there is no influence of the shape change of the actuator due to the temperature change. Furthermore, since the actuator is separated from the optical system, it can be realized only by attaching the actuator to an existing optical microscope.

[0024]

The scanning probe microscope of the present invention can illuminate a sample by a plurality of illumination methods, and can illuminate the sample according to the observation purpose. Therefore, a desired optical image of the sample can be obtained.

[Brief description of the drawings]

FIG. 1 shows a configuration of a scanning tunnel microscope according to a first embodiment of the present invention.

FIG. 2 shows a configuration of a scanning tunnel microscope according to a second embodiment of the present invention.

FIG. 3 shows a configuration of a third embodiment of the present invention.

FIG. 4 shows a configuration of a fourth embodiment of the present invention.

[Explanation of symbols]

12 ... light source, 16, 18 ... condenser lens, 20 ...
Cylindrical piezoelectric actuator, 28 ... objective lens, 34
… An imaging lens.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-18702 (JP, A) JP-A-3-199904 (JP, A) JP-A-3-205502 (JP, A) JP-A-2- 16403 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01B 21/00-21/32 G01B ^7/ 00-7/34

Claims (7)

(57) [Claims] 1. A scanning probe microscope for observing the surface of a sample using a probe, comprising: a light source for emitting illumination light; a means for condensing the illumination light; and an image of light transmitted through the sample. An observation optical system having means for performing, a probe held in parallel to an optical axis direction facing the sample, and an actuator for relatively three-dimensionally driving the sample and the probe. A scanning probe microscope characterized by the following. 2. A scanning probe microscope for observing the surface of a sample using a probe, comprising: a light source for emitting illumination light; dark-field illumination means for condensing the illumination light; An observation optical system having means for forming an image of light, a probe held in parallel to an optical axis direction facing the sample, and an actuator for relatively three-dimensionally driving the sample and the probe. A scanning probe microscope, comprising: 3. A light shielding plate for selectively blocking illumination light as required, whereby either one of bright field illumination and dark field illumination can be selectively performed. The scanning probe microscope according to claim 1. 4. The dark-field illuminating means further comprises a light-shielding plate for selectively blocking illumination light as required, and is capable of performing bright-field illumination in addition to dark-field illumination. The scanning probe microscope according to claim 2. 5. The scanning probe microscope according to claim 1, wherein the actuator is a cylindrical piezoelectric actuator, and an illumination optical system is disposed inside the actuator. . 6. The scanning device according to claim 1, wherein the actuator is a cylindrical piezoelectric actuator, and an objective lens of an observation optical system is disposed inside the actuator. Probe microscope. 7. The scanning probe microscope according to claim 1, further comprising a transparent sample stage for supporting said sample.