JPH06221845A - Device for detecting deformation of cantilever of microscope, etc., of force between atoms - Google Patents

Abstract

PURPOSE:To detect the amount of deformation such as displacement and twisting at atom level of a cantilever in ultra-high-vacuum AFM, etc., using the reflection high-speed electron analysis method with a high accuracy and sensitivity. CONSTITUTION:The title device such as AFM detects force, etc., which is operated between the surface of a sample 3 and the needle at the tip of a cantilever 2 by three-dimensionally driving the relative position between them. It is provided with an electron gun 11 for generation electron rays, an electron lens 6 for converging electron rays 9 on the rear surface of the cantilever 2, an electron ray polarizer 7 for applying electron rays onto the rear surface of the cantilever 2 accurately, and a fluorescent screen 8 for detecting the image position of reflection diffraction electron rays 10 which are reflected and refracted from the rear surface of the cantilever 2, thus detecting the deformation of the cantilever 2 from the position of the detected reflection diffraction electron ray image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting deformation of a cantilever such as an atomic force microscope, and in particular, for observing a high resolution surface image of an insulating sample such as ceramics or polymer material, atomic force Atomic force microscope, etc. that detects surface irregularities by moving the cantilever or the sample three-dimensionally by bringing the cantilever closer to detect the surface displacement signal generated by the cantilever and detecting the deformation of the cantilever on the nanometer scale. The present invention relates to the deformation detecting device.

[0002]

2. Description of the Related Art As a method for detecting irregularities on a sample surface, the tip of the probe is brought close to the sample surface up to the nanometer order where the atom at the tip of the sharply polished tip and the electron cloud of atoms on the sample surface overlap. When a voltage is applied between the probe and the sample in this state, a tunnel current flows between them. Since this tunnel current is particularly sensitive to the distance between the probe and the sample (height of the probe), the distance between the sample and the probe can be measured by measuring the magnitude of the tunnel current. It can be measured very precisely.

A scanning tunneling microscope (STM) uses a height locus of the probe when the probe is horizontally scanned while controlling the height of the probe so that the tunnel current is constant. It is a device that observes uneven shapes and has attracted attention in analyzing surface atomic arrangements. Also,
STM is becoming established as a means of surface analysis, and its application field is expanding not only to the microscope method for examining atomic positions on the surface but also to the field of spectroscopy for locally examining the electronic state of the surface. . Moreover, the STM has been popularized in various fields in a short period of time because of its principle, simple mechanism, and small device size.

However, as a fundamental defect of STM, the tunnel phenomenon due to the quantum effect is used in its principle. Therefore, it can be applied only to a conductive probe and a conductive sample. For this reason, there is a big limitation that it cannot be applied to an insulator. The principle devised to solve this problem is the atomic force microscope (AFM) technique. In this method, a sharply polished probe is attached to the tip of a cantilever, which has a small spring constant, and the atomic force generated when the probe is brought up to several angstroms is basically used. It is a modification of STM technology. However, since this method can be applied to many insulating materials including biopolymers, ST
The field of application of M has expanded significantly.

Conventionally, the problem with this AFM is related to the detection method and the detection sensitivity of the cantilever position. As the detection method, an optical lever method, an optical interference method, a capacitance method and the like have been devised.
The optical lever method applies semiconductor laser light to the back surface of a cantilever that detects atomic force, and detects the reflected light with a semiconductor detector. A slight displacement of the cantilever causes a light shift (change in intensity). Is detected as
It has been put to practical use in atmospheric pressure AFM. This optical lever method will be briefly described with reference to FIG. In the figure, 1 is a semiconductor laser that emits laser light, 2 is a cantilever that detects an atomic force, 3 is a sample, 4 is a three-dimensional piezoelectric drive element, and 5 is a semiconductor photodetector. In this method,
The laser light emitted from the semiconductor laser 1 is applied to the back surface of the cantilever 2, and the light a reflected by the back surface of the cantilever 2 is incident on the semiconductor photodetector 5 whose position has been adjusted in advance. The sample 3 fixed to the three-dimensional piezoelectric driving element 4 faces the cantilever 2, and the distance between them is scanned within a two-dimensional plane while adjusting the distance to several angstroms. The detection surface of the semiconductor photodetector 5 is divided into two or four parts. For example, when the cantilever 2 moves due to a change in atomic force (irregularities on the surface), the reflected light moves by a displacement angle θ and the reflected light b Then, the detection amount of the semiconductor photodetector 5 changes. By converting this change as a change in the z-axis, the uneven shape of the surface of the sample 3 can be observed.

In the optical interference method, incident light is vertically irradiated on the back surface of the cantilever, the reflected light and the incident light are interfered with each other, and the displacement of the cantilever is detected from the movement of the interference fringes. Further, the capacitance method detects displacement of the cantilever based on a change in capacitance between the cantilever and an electrode arranged behind it.

[0007]

However, in the optical lever method, the semiconductor photodetector can be used only at a temperature of 100 ° C. or lower, and its heat resistance is limited, so that the ultrahigh vacuum device like an ultrahigh vacuum device can be used. It cannot be applied to equipment that must be heated at high temperatures to obtain There is also a problem that the light from the semiconductor laser has to be applied to the back surface of the small cantilever, which is difficult to adjust and cannot be applied to a device with a lot of vibration. Further, it is difficult to detect the twist of the cantilever which is a problem in a lateral force microscope (LFM) which is a kind of AFM.

Various methods are currently being attempted for the optical interference method and the capacitance method, but due to problems such as stability, they have not yet reached the stage where they can be put to practical use.

The present invention has been made in view of the above problems, and its object is, for example, the displacement or twisting of the cantilever at the atomic level, which is a problem in an ultrahigh vacuum scanning atomic force microscope. It is an object of the present invention to provide a completely new method for detecting the amount of deformation of (1) with high precision and high sensitivity using the reflection high-energy electron diffraction (RHEED) method.

[0010]

A cantilever deformation detecting device for an atomic force microscope or the like according to the present invention that achieves the above object drives a relative position between a sample surface and a probe at the tip of the cantilever three-dimensionally. Then, in a deformation detecting device of a cantilever such as an atomic force microscope that detects a force acting between the two as deformation of the cantilever, an electron gun for generating an electron beam and a deformation of one of the cantilevers An electron lens for converging on a position, and an electron beam deflecting means for irradiating an electron beam on the deformed position with high accuracy, and a position of a reflection diffraction electron beam image reflected and diffracted from the deformed position. Is provided, and the deformation of the cantilever is detected from the detected position of the reflected diffraction electron beam image.

[0011]

According to the present invention, the electron gun for generating the electron beam, the electron lens for converging the electron beam on any one of the deformed positions of the cantilever, and the electron beam for irradiating the deformed position with high accuracy. And a means for detecting the position of the reflected diffraction electron beam image reflected and diffracted from the deformed position, and the cantilever is deformed from the detected position of the reflected diffraction electron beam image. Because it detects
Due to the high sensitivity of the reflected diffraction electron beam image at the atomic level, the deformation of the cantilever can be detected with high accuracy and high sensitivity. Further, it becomes possible to detect even in an ultra-high vacuum device that is heated to a high temperature, and the position of the incident electron beam can be easily adjusted. Further, since the electron beam can be incident from a position apart from the sample position and the detecting means can be installed at a remote position, the detection can be performed with higher sensitivity, and the degree of freedom in the arrangement of the device is increased.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a cantilever deformation detecting device of an atomic force microscope or the like according to the present invention will be described below with reference to the drawings. FIG. 4 is a graph showing the vibration of the detected intensity with respect to time obtained by the reflection high-energy electron diffraction (RHEED) method. One intensity of this vibration corresponds to one atomic layer when vapor deposition is performed on the sample surface. Thus, RHEE
It can be seen that in D and the backscattered electron microscope (REM) method, the sensitivity of electron beam reflection diffraction to changes in the surface layer is high at the atomic level. The present invention is intended to detect the deformation of a cantilever such as an AFM with high sensitivity and accuracy by utilizing the high sensitivity of the reflection diffraction of an electron beam.

FIG. 1 shows the configuration of an embodiment of the present invention. In the figure, 11 is an electron gun for emitting an electron beam, 6 is an electron lens for narrowing the electron beam, 7 is a deflection coil for irradiating the cantilever 2 with the electron beam with high precision, and 2 is a cantilever for detecting an atomic force. 3 is a sample, 4 is a three-dimensional piezoelectric drive element, 8 is an electron beam detector such as a fluorescent screen and a channel plate, 9 is an incident electron beam, and 10 is a reflected diffraction electron beam from the cantilever 2.

In such an arrangement, adjusting the deflection coil 7 causes the electron lens 11 to exit from the electron gun 11.
The electron beam 9 focused by is incident on the back surface of the cantilever 2 at a small angle, and the reflected diffraction electron beam 10 reflected and diffracted by the crystal on the back surface of the cantilever 2 shows a diffraction image reflecting the crystal structure on the fluorescent screen 8. To project. Therefore, when measuring the intensity of the spot of interest in this diffraction image,
As in the case of the optical lever method of FIG. 5, the cantilever 2
Reflects the displacement amount of. If the crystallinity of the back surface of the cantilever 2 is not good, the diffraction image will be Laue ring that spreads in a semicircular ring shape around the central spot. Therefore, as shown in FIG. Good to stick. In this case, if the crystal 12 is selected to be a specific one, the diffraction image also becomes unique, so the position of the cantilever 2 can be easily detected from the diffraction image and the position of the incident electron beam 9 can be easily adjusted. Cantilever 2
The distance between the electron gun 11 and the electron gun 11 can be increased, which is desirable in terms of the degree of freedom of arrangement and the like. FIG. 3 shows an example of a diffraction image on the fluorescent screen 8 when the back surface of the cantilever 2 has good crystallinity. As described above, when the back surface of the cantilever 2 has good crystallinity, the diffraction image becomes a regular diffraction spot. Therefore, the displacement amount of the cantilever 2 can be measured not only in the center direct spot but also in the higher-order diffraction spot. It is possible to measure by paying attention to the movement of. Also, the deviation of the diffraction spot is
It reflects not only the vertical direction of the cantilever but also the twisting motion. Therefore, it can be used also in a lateral force microscope (LFM) in which detection of a cantilever twist is important. In this case, for example, the twist of the cantilever can be detected by simultaneously monitoring the signals of the direct spot and the high-order spot and taking the intensity ratio thereof.

The intensity of the diffracted spot may be measured by measuring the brightness projected on the fluorescent screen 8 from outside the vacuum by means such as a TV, or by setting a channel plate or the like at the position of 8 in the vacuum. It is also possible to directly measure it.

Although the AFM is assumed as a microscope utilizing the deformation of the cantilever, the cantilever deformation detecting device of the present invention is not limited to this, and a magnetic force microscope (M
It can also be used in other microscopes that utilize the deformation of the cantilever, such as FM) and scanning thermal profiler (STP). Here, the MFM is for observing the magnetic force distribution by measuring the deformation of the cantilever due to the magnetic force between the probe and the sample surface, and the STP is made of bimetal or the like, and the probe is used according to the temperature of the sample surface. The temperature distribution is observed by controlling the distance between the sample and the sample surface.

Although the cantilever deformation detecting device for the atomic force microscope and the like according to the present invention has been described with reference to some embodiments, the present invention is not limited to these embodiments and various modifications can be made.

[0018]

As is apparent from the above description, according to the deformation detecting device for a cantilever such as the atomic force microscope of the present invention, in developing an ultra-high vacuum atomic force microscope in an atomic force microscope, for example, Highly sensitive and highly accurate displacement detection technology was developed. By measuring the position of the diffraction spot, not only the displacement in the height direction but also the torsion of the cantilever can be measured. Only by adjusting the position of the electron beam, it is possible to use the same electron gun as a monitor of the vapor deposition process on the sample and a detecting means of the atomic force microscope.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment in which a deformation detecting device for a cantilever of the present invention is applied to an atomic force microscope.

FIG. 2 is a view showing a cantilever tip shape of a modified example.

FIG. 3 is a diagram showing an example of a diffraction image on a fluorescent screen.

FIG. 4 is a diagram showing intensity modulation of RHEED using an electron beam.

FIG. 5 is a diagram for explaining a conventional optical lever system.

[Explanation of symbols]

2 ... Cantilever 3 ... Sample 4 ... Three-dimensional piezoelectric drive element 6 ... Electron lens 7 ... Deflection coil 8 ... Fluorescent screen or channel plate (electron beam detector) 9 ... Incident electron beam 10 ... Reflection diffraction electron beam 11 ... Electron gun 12 …crystal

Claims (1)

[Claims] 1. Deformation of a cantilever such as an atomic force microscope that three-dimensionally drives the relative position between the sample surface and the probe at the tip of the cantilever to detect the force acting between the two as the deformation of the cantilever. In the detection device, an electron gun for generating an electron beam, an electron lens for converging the electron beam on one of the deformed positions of the cantilever, and an electron beam for irradiating the electron beam onto the deformed position with high accuracy. Electron beam deflecting means, and means for detecting the position of the reflected diffraction electron beam image reflected and diffracted from the deformed position, and the cantilever is deformed from the detected position of the reflected diffraction electron beam image. A cantilever deformation detection device for an atomic force microscope or the like, which is characterized by detecting.