JPH0225702A - Scanning type tunnel microscope and scanning type tunnel spectroscope - Google Patents

Abstract

PURPOSE:To measure a surface shape of a sample with high accuracy without being influenced by mechanical vibration and heat from the outside by measuring a fluctuation of a relative position of the sample and an auxiliary probe and correcting a variation of a distance between a main probe and the sample. CONSTITUTION:When a piezoelectric element 3 and 4 are driven by operating an X-Y raster scanner 15, a main probe 6 is fluctuated in the vertical Z axis direction by following up ruggedness of the surface of a conductive sample 1. In this case, in case a fluctuation of a relative position is generated between the surface of the conductive sample 1, and the main probe 6 and an auxiliary probe 8 due to mechanical vibration and heat from the outside, an output of an integrator 41 related to the main probe 6 is detected after the fluctuation has been added, but since the auxiliary probe 8 is not scanned by the X-Y raster scanner 15, an output of an integrator 42 related to the auxiliary probe 8 is fluctuated only. Accordingly, when the output of the integrator 42 is subtracted from the output of the integrator 41 by a differential circuit 25, the fluctuation is negated.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a scanning tunneling microscope and a scanning tunneling microscope that measure the surface shape or surface electronic state of a sample whose surface is conductive at least with atomic resolution. Regarding spectroscopes.

[Conventional technology]

Generally, when a voltage is applied between a conductive sample and a thin metal probe and the probe is brought close to a distance of about 1 m, an electron cloud A is created between the probe 6a and the conductive sample 1a, as shown in FIG. This causes a tunnel current to flow. This tunneling current is very sensitive to changes in the distance between them; for example, when the distance is 0.
When the distance changes by 1 mm, the tunnel current changes exponentially by one order of magnitude.

Therefore, as shown in FIG. 6, when the probe 6a is scanned along the surface of the conductive sample 1a in the direction of arrow B using the piezo element 5a while keeping this tunnel current constant, the piezo element expands and contracts. Since the applied voltage corresponds to the surface shape, if this voltage is extracted and imaged, the surface structure of the conductive sample can be observed and measured on an atomic scale.

Furthermore, since the voltage applied between the probe 6a and the conductive sample 13 depends on the energy of the electrons involved in the tunneling phenomenon, the surface electronic state of the conductive sample 1a can be observed on the atomic order by using this voltage. .

Scanning tunnel microscopes and scanning tunnel spectroscopes that have been developed in recent years are applications of this principle. A piezo element that is displaced in the vertical direction and a piezo element that is displaced in the up and down The tip of the probe is scanned along at least the surface of the sample whose surface is conductive while keeping the tunnel current generated by applying a voltage between the probe and the surface of the sample constant through each piezo element through a circuit. By detecting the voltage applied to a piezo element that is displaced in two axes (up and down), it is possible to measure the distance between the probe and the sample, measure the surface shape of the sample, or measure the distance between the probe and the surface of the sample at appropriate points during scanning. The surface electronic state of the sample is measured by detecting changes in tunneling current that occur when various different voltages are applied to the sample. (G, B1nn1g+
H, Rohrer etal; IBM J, Re5ea
rch and deuclopment 30(19
86) No. 4 & No. 5, Kajimura, Mizutani, Ono; S
Prospects for TM development Publication of Japan Society for Precision Engineering, 12 (1987) P.
1811) [Problems to be Solved by the Invention] However, in such conventional scanning tunnel microscopes and scanning tunnel spectroscopes,
It is easily affected by external mechanical vibrations and displacement of the relative position between the probe and sample due to heat, and unless a measurement environment equipped with expensive equipment that can sufficiently eliminate these effects is It is not possible to accurately measure the surface shape or surface electronic state of a sample.

[Means to solve the problem]

This invention was made as a result of various studies in view of the current situation, and includes piezo elements that are displaced in the left and right X-axis directions, piezo elements that are displaced in the front and rear Y-axis directions, and upper and lower piezo elements that are displaced in the Y-axis direction. A piezo element that can be displaced in the X-axis direction is fixed, and the piezo element that can be displaced in three dimensions can be used to attach the main probe so that it can move slightly in three dimensions, and the main probe can be displaced in two axial directions, up and down. A piezo element that can be displaced in the vertical X-axis direction is fixed to a piezo element support in parallel with the piezo element that is to be moved, and the auxiliary probe is attached to the piezo element so that it can be moved slightly in the vertical X-axis direction, and control electronics are attached as appropriate. Scanning the tip of the main probe along at least the surface of the sample whose surface is conductive while keeping the tunnel current generated by applying a voltage between the main probe and the surface of the sample constant through each piezo element through a circuit,
During scanning, the voltage applied to the piezo element that is displaced in the upper and lower X-axis directions can be detected to measure the distance between the main probe and the sample and the surface shape of the sample, or to measure the surface shape of the sample at appropriate points during scanning. When measuring the surface electronic state of a sample by detecting changes in tunneling current caused by applying various different voltages between the surfaces of the sample, a piezo element supporting the auxiliary tip simultaneously applies voltage between the auxiliary tip and the sample. The voltage applied to the piezo element that supports the auxiliary probe is detected by keeping the tunneling current generated by applying the auxiliary probe constant, and the relative positional change between the sample and the auxiliary probe is measured. By correcting changes in the distance or tunneling current, the surface shape and surface electronic state of the sample can be unaffected by external mechanical vibrations or displacement of the relative position between the probe and sample due to heat. , which can be measured at a high level of sensitivity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A scanning tunneling microscope according to the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram showing an embodiment of a scanning tunneling microscope according to the present invention, in which 1 is a conductive sample, 2 is a conductive sample, and 2 is a conductive sample.
is a piezo element support. The piezo element support 2 has piezo element fixing walls 2a, 2b, and 2c formed in a three-dimensional direction at the bottom thereof, and piezo elements 3 that are displaced in the left and right X-axis directions on these piezo element fixing walls and in the front and rear Y-axis directions. A piezo element 4 that is displaced in the vertical direction and a piezo element 5 that is displaced in the upper and lower X-axis directions are fixed.
It is supported so that it can move slightly in the dimensional direction.

Reference numeral 7 denotes a piezo element that is displaced in the vertical X-axis direction, and is fixed in parallel with the piezo element 5 on the piezo element fixing wall 2C of the piezo element support 2, with an auxiliary probe 8 fixed to the lower end and displaced in the vertical X-axis direction. It is supported so that it can be moved slightly.

The piezo elements 3 and 4 fixed to the piezo element fixing walls 2a and 2b of the piezo element support 2 in this way are
They are connected to high voltage amplifiers 11 and 12 via wires 9 and 10, respectively, and further connected to an X-Y last scanner 15 via wires 13 and 14. Also X-
Y last scanner 15 is connected to storage oscilloscope 18 via wires 16 and 17.

Furthermore, the piezo elements 5 and 7 fixed to the piezo element fixing wall 2c of the piezo element support 2 are connected to high voltage amplifiers 21 and 22 via wiring lines 19 and 20, respectively, and further connected to high voltage amplifiers 21 and 22 via wiring lines 23 and 24. The differential circuit 25 is further connected to the storage oscilloscope 18 via a wiring 26.

Further, the main probe 6 and the auxiliary probe 8 each have a wiring 2
It is connected to current-voltage converters 29 and 30 via lines 7 and 28, and further connected to logarithmic converters 33 and 34 via lines 31 and 32. Logarithmic converters 33 and 34 are connected to comparators 37 and 3 via wires 35 and 36, and are further connected to integrators 41 and 42 via wires 39 and 40. The integrators 41 and 42 are connected to the wiring 2 which connects the high voltage amplifiers 21 and 22 and the differential circuit 25 via wiring 43 and 44.
3 and 24. Also, the reference voltage generator 4 is connected to the comparator 37 and the 3rd via wiring 45 and 46.
7 is connected.

The control electronic circuit is configured in this way, and when a voltage is applied between the main probe 6 and the auxiliary probe 8 and the conductive sample 1, a tunnel current is generated. Since the distance Z between the needle 8 and the conductive sample 1 has a logarithmic relationship, when a tunnel current is detected by the current-voltage converters 29 and 30, the logarithmic converters 33 and 34 immediately
This is so that a voltage proportional to the distance Z can be obtained.

Further, the reference voltage generator 47 sets a reference voltage corresponding to a certain distance ZO for keeping the main probe 6 and the auxiliary probe 8 above the conductive sample 1 by a certain distance ZO. The devices 37 and 38 calculate the deviation e (Z.

-2> is output. and integrator 41
and 42, and the high voltage amplifiers 21 and 22 connected by wires 43, 23 and 4424 actuate the piezo elements 5 and 7 by a distance corresponding to this deviation e, until the deviation e becomes 0. The main probe 6 and the auxiliary probe 8 are always kept at a constant distance Zo from the surface of the conductive sample 1 regardless of the displacement of the surface of the conductive sample 1. It is meant to follow.

[Effect]

Therefore, when measuring the surface shape of the conductive sample 1 with the scanning tunneling microscope configured in this way, the piezo element 3 is and 4 to scan in the left and right X-axis directions and the front and rear Y-axis directions in the same manner as the electron beam scanning motion of a television cathode ray tube, it is controlled to always maintain a constant distance ZO from the surface of the conductive sample 1. The main probe 6 moves vertically in the Z-axis direction following the irregularities on the surface of the conductive sample 1. The amount of expansion and contraction of the piezo elements 5 and 7 at this time is proportional to the drive voltage, and the integrator 41
Since the output change of 42 and 42 becomes a voltage corresponding to the vertical displacement of the surface of the conductive sample 1 in the Z-axis direction, when this is taken out, a voltage measurement value related to the surface shape of the conductive sample 1 can be obtained.

At this time, if a relative positional variation δ occurs between the surface of the conductive sample 1 and the main probe 6 and the auxiliary probe 8 due to external mechanical vibrations or heat, The output of the integrator 41 is detected by adding the variation δ, but since the auxiliary probe 8 is not scanned by the X-Y raster scanner 15, the output of the integrator 42 with respect to the auxiliary probe 8 is detected by adding the variation δ. Only.

Therefore, in the operating circuit 25, the output of the integrator 41 is converted to the integrator 4.
When the output of 2 is subtracted, the fluctuation δ is canceled out, and an output is obtained that is equivalent to no displacement of the relative position between the surface of the conductive sample 1 and the main probe 6 due to external mechanical vibrations, heat, etc. If this output signal and the scanning signal from the X-Y raster scanner 15 are input to the storage oscilloscope on the same day, it is possible to draw a bird's-eye view of the surface shape.

The above has explained the case of the scanning tunneling microscope of the present invention, but in the case of the scanning tunneling spectroscope, the control electronic circuit is changed from the configuration diagram of FIG. 1, and each piezo element 3 and 4 is The tip of the probe 6 is scanned along the surface of the conductive sample 1, and various different voltages are applied between the main probe 6 and the surface of the conductive sample 1 at appropriate points during the scan to measure changes in the tunnel current. It is sufficient to simultaneously detect the output fluctuation δ using the auxiliary probe 8. If such a scanning tunnel spectroscope is used, it is possible to detect external mechanical It is possible to obtain an output equivalent to the absence of physical vibrations and displacement of the relative position 1 between the surface of the conductive sample 1 and the main probe 6 due to heat, and it is possible to measure the electronic state of the surface of the conductive sample 10 with high precision. can.

Note that a conductive sample only needs to have at least a conductive surface, and even a non-conductive sample can be coated with a conductive substance such as platinum to change its surface shape and surface electronic state to be conductive. It can be measured in the same way as a conductive sample made of a conductive material.

〔Example〕

Next, embodiments of the invention will be described.

Example 1 Using the scanning tunneling microscope shown in Fig. 1, the main probe 6 and the auxiliary probe 8 were finished by etching tungsten wire to have a spherical tip radius of 0.1 μm or less. The surface shape of the aluminum reflective mirror 1 was measured with a scanning width of 1100 nm while applying dummy vibration to the sample stage on which the aluminum reflective mirror 1 was placed as a sample. FIG. 2 is a bird's-eye view of the surface shape of the aluminum reflective mirror drawn by inputting the measurement results into the storage oscilloscope 18.

Comparative Example 1 An aluminum reflective mirror 1 was prepared in the same manner as in Example 1, except that the auxiliary probe 8 and its operation were omitted.
0 surface profile was measured. FIG. 3 is a detailed diagram of the surface shape of the aluminum reflective mirror drawn manually using the storage oscilloscope 18 based on the measurement results.

Comparative Example 2 In Comparative Example 1, we stopped applying dummy vibration to the sample stage on which the aluminum reflective mirror 1 was mounted, and changed the entire measurement system to a precision measurement system equipped with a high-performance vibration isolator, a soundproof wall, and temperature and humidity control equipment. The surface shape of the aluminum reflective mirror 10 was measured in the same manner as in Comparative Example 1 except that it was installed in a dedicated room.

Figure 4 shows the measurement results on the storage oscilloscope 1.
8 is a bird's-eye view of the surface shape of an aluminum reflective mirror drawn by inputting the information into the screen.

〔Effect of the invention〕

As is clear from the bird hoe diagrams shown in Figures 2 to 4,
When using a conventional scanning tunneling microscope (Fig. 3), it is not possible to accurately measure the surface condition of an aluminum reflective mirror due to the influence of dummy vibration.
When the scanning tunneling microscope of this invention is used (Figure 2), the surface condition of the aluminum reflecting mirror is the same as when it is installed in a precision measurement room without dummy vibration (Figure 4). has been accurately measured,
Therefore, according to the scanning tunneling microscope of the present invention, the surface condition of a sample whose surface is electrically conductive can be controlled by external mechanical vibrations or thermal displacement of the relative position between the main probe and the sample. It can be seen that measurements can be made with uniform precision without being affected. Similarly, the surface electronic state of at least a conductive sample can be measured with high precision without being affected by external mechanical vibrations or displacement of the relative position between the main probe and the sample due to heat. I understand.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the scanning tunneling microscope of the present invention, and FIG. 2 is a cross-sectional diagram of the surface shape of an aluminum reflective mirror drawn by inputting the measurement results obtained in Example 1 into a storage oscilloscope. Figure 3 shows the shape of the surface of an aluminum reflective mirror drawn by inputting the measurement results obtained in Comparative Example 1 into a storage oscilloscope, and Figure 4 shows the measurement results obtained in Comparative Example 2 being input into a storage oscilloscope. A bird's-eye view of the surface shape of the aluminum reflective mirror drawn by input, FIG. 5 is an explanatory diagram of tunnel current, and FIG. 6 is a schematic diagram showing the principle of a scanning tunneling microscope. 1... Conductive sample (sample), 2... Piezo element support, 3, 4, 5.7... Piezo element, 6... Main probe, 8... Auxiliary probe patent application Person Hitachi Maxell Ltd. Figure 2 Scanning 1II1. I (nm) Fig. 3 Travel pressure (nm) Fig. 4 Travel h width (mouth m) Fig.

Claims (1)

[Claims] 1. A piezo element that is displaceable in the left and right X-axis directions, and a piezo element that is displaced in the front and rear Y-axis directions, on a piezo element support;
The piezo elements that are displaced in the upper and lower Z-axis directions are fixed, and the main probe is attached so that it can be moved slightly in the three-dimensional direction using these piezo elements that are displaced in three-dimensional directions, and the main probe is moved in the upper and lower Z-axis directions. A piezo element that is displaced in the vertical Z-axis direction is fixed to the piezo element support in parallel with the piezo element that is displaced in Each piezo element is displaced in three dimensions via an electronic circuit, and while the tunnel current generated by applying voltage between the main probe and the surface of the sample is kept constant, the tip of the main probe is connected to a sample whose surface is conductive at least. When measuring the distance between the main probe and the sample by scanning along the surface of the piezo element and detecting the voltage applied to the piezo element which is displaced in the up and down Z-axis direction during scanning, the piezo element that supports the auxiliary probe at the same time By applying a voltage between the auxiliary tip and the sample, the tunneling current generated by the auxiliary tip is kept constant, the voltage applied to the piezo element that supports the auxiliary tip is detected, and changes in the relative position of the sample and the auxiliary tip are measured. A scanning tunneling microscope 2 is characterized in that the distance between the main probe and the sample is corrected to measure the surface shape of the sample. A piezo element that moves in the front and rear Y-axis direction,
The piezo elements that are displaced in the upper and lower Z-axis directions are fixed, and the main probe is attached so that it can be moved slightly in the three-dimensional direction using these piezo elements that are displaced in three-dimensional directions, and the main probe is moved in the upper and lower Z-axis directions. A piezo element that is displaced in the vertical Z-axis direction is fixed to the piezo element support in parallel with the piezo element that is displaced in Each piezo element is displaced in three dimensions via an electronic circuit, and while the tunnel current generated by applying voltage between the main probe and the surface of the sample is kept constant, the tip of the main probe is connected to a sample whose surface is conductive at least. When scanning along the surface of the sample and applying various different voltages between the main tip and the surface of the sample at appropriate points during the scan, changes in the tunneling current that occur are detected, and the surface electronic state of the sample is measured. The piezo element supporting the auxiliary probe applies a voltage between the auxiliary probe and the sample, keeping the tunnel current generated constant, detecting the voltage applied to the piezo element supporting the auxiliary probe, and detecting the relationship between the sample and the auxiliary probe. A scanning tunneling spectroscope characterized by measuring relative position fluctuations, correcting changes in tunneling current, and measuring the surface electronic state of a sample.