JPH03122505A - Scanning tunneling microscope - Google Patents

Abstract

PURPOSE:To make it possible to shift a starting position of scanning to an arbitrary position after wide-range scanning without using a rough-motion mechanism, by using a digital addition output of an output of a bit shifter and reference position data, as a scanning signal. CONSTITUTION:A bit shift number of a bit shift circuit 52 is set by a shift number signal from a CPU controller 1. Besides, offset values of X-scanning and Y-scanning are written in latch circuits 53 and 54 respectively. In digital adders 55 and 56, an output of the circuit 52 and an output of the circuit 53, and an output of the circuit 52 and an output of the circuit 54, are subjected to digital addition respectively and outputted to an X-scanning D/A converter 21 and a Y-scanning D/A converter 25 respectively. Thereby an X impression voltage corresponding to an X-scanning count value is outputted from the converter 21, while a Y impression voltage corresponding to a Y-scanning count value is outputted from the converter 25, and these voltage are impressed as scanning signals on a tube scanner 15 respectively. As the result, a desired sphere of a sample 17 can be scanned by a probe 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a scanning tunneling microscope capable of observing, for example, the surface of a sample in units of atoms.

[Prior Art] Recently, a scanning tunneling microscope (STM) has been developed that can observe the surface of a sample as an object to be measured in units of atoms.

Generally a metal probe (or probe needle) with a sharp tip
It is known that when a probe is placed as close as 1 nIM to the surface of a conductive sample and a predetermined voltage is applied between the probe and the sample, a tunnel current will flow between the probes and the sample. This tunneling current sensitively responds to changes in the distance between the probe and the sample and changes significantly. The so-called STM uses this property of tunneling current to observe the surface of a sample. In other words, if the probe is attached to an actuator that can move in three dimensions and the probe is scanned so that the tunneling current remains constant, the probe will trace the irregularities on the sample surface while maintaining a constant interval. .

By outputting the position of the probe at this time as a three-dimensional image, changes in the shape of the sample surface in atomic units can be observed as an image.

STM is a microscope with ultra-high resolution, and can ultimately observe the surface shape and surface properties of a sample at atomic scale. Therefore, when observing a desired part of a sample, first, a wide range (several μm) including the desired part is observed.
) is required in advance to roughly observe the area and then observe the desired area.

Furthermore, while observing a wide-range scanned 37M image (three-dimensional image), there may arise a need to enlarge and display only a portion of the image for detailed observation.

To meet these demands, conventional methods have been to obtain images based on data with a predetermined resolution obtained through wide-range scanning, then switch to a narrow scanning range, and move the probe over the sample surface at intervals greater than the interval at which tunneling current can be obtained. lift it from Then, after aligning the scanning center position with the desired position using an X-Y coarse movement mechanism using a pulse motor, etc., the lifted probe is lowered to the tunnel current area, and scanning is performed again to display the image. method was used.

[Problems to be Solved by the Invention] As mentioned above, in conventional STM, in response to a request to observe only a desired part in detail, the user switches from wide-range scanning to narrow-range scanning and moves the probe up and down. In the case of a method in which the center position of the scan is aligned with the position where you want to obtain an enlarged image using a coarse movement mechanism, and the image is formed by scanning again, the accuracy of the coarse movement mechanism for moving the sample determines the reliability of the 37M image. do. In fact, the accuracy of the coarse movement mechanism is extremely worse than the resolution of STM. In this way, after scanning a wide range, the probe is moved away from the sample, the sample is moved using the coarse movement mechanism, and then the probe is brought close to the sample again to observe the 37M image. Position reproducibility cannot be guaranteed due to resolution and accuracy. For this reason, there is a drawback that an enlarged image cannot be obtained precisely at a desired position.

Therefore, the present invention makes it possible to move the scanning start position for a desired scanning range to any position after wide-range scanning without using a coarse movement mechanism associated with vertical movement of the probe, thereby improving position reproducibility. The purpose of the present invention is to provide a scanning tunneling microscope that can ensure the reliability of magnified images.

[Means for Solving the Problems] In order to achieve the above object, the scanning tunneling microscope of the present invention is capable of observing the surface of an object to be measured in units of atoms, and after wide-range scanning, a bit shifter to which range setting data for setting the size of a desired scanning range included in this wide range is input, and an output of this bit shifter and reference position data of the desired scanning range with respect to a reference position of the wide range scanning; and an addition means for digitally adding , and is configured to change the scanning range and the scanning start position by using the output from the addition means as a scanning signal.

[Operation] This invention uses the above-mentioned means to move the probe without separating it from the object to be measured, so it is not affected by errors caused by the accuracy of the coarse movement mechanism, and it is possible to perform a 37M scan over a wide range.
This makes it possible to rescan a range corresponding to a part of the image and display it in an enlarged manner.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

Figure 1 shows the STM (scanning tunneling microscope) of this invention.
This shows the configuration of

In FIG. 1, 1 is an 8-bit CPU (Central Processing Unit) controller that controls the entire STM. An interface controller 2 is connected to this 8-bit CPU controller 1.
A host computer 100 is connected via an interface (GPIB).

The 8-bit CPU controller 1 also includes pulse motors (P, M,) for the Y stage [1], drivers 3,
P, M, driver 4 for moving the stage, variable start position circuit (STM scanning circuit) 5 for switching the scanning range and varying the start position of scanning, P, M, for moving the Z stage,
driver 6, 1 for A/D (analog/digital) conversion of the Z electrode voltage signal or tunnel current signal;
A 2-bit A/D converter 7 and a 10-bit D/A converter 8 for applying bias voltage are connected to each other via a CPU data bus.

The P, M, and driver 3 for moving the Y stage receive drive signals (pulse data) from the 8-bit CPU controller 1.
Accordingly, the Y stage moving P, M, and 9 are driven to move the Y stage 10 in the Y direction (front to back direction in the figure).

The X stage moving P, M, driver 4 drives the X stage moving P0M, 11 in accordance with the drive signal from the 8-bit CPU controller 1, and moves the X stage 12 in the X direction (horizontal direction in the figure). It is something.

The Z stage moving P, M, driver 6 drives the Z stage moving P, M, 13 in response to the drive signal from the 8-bit CPU controller 1, and moves the Z stage 14 in the Z direction (vertical direction in the figure). It is something that moves.

A tube scanner (piezoelectric element) 15 that constitutes an actuator that can be driven in three dimensions is attached to the lower surface of the two stages 14. A sexual probe (probe needle) 16 is provided. And this probe 1
6, a bias voltage (V bias) is applied by the 10-bit D/A converter 8.

On the other hand, on the upper surface of the X stage 12 facing the two stages 14, a sample 17 as an object to be measured is placed. A tunnel current (J tunnel) flows through the sample 17 by applying a predetermined bias voltage to the surface of the sample 17 with the probe 16 brought close to the sample 17 to about 1 nm. The tunnel current generated in this sample 17 is transmitted to the servo circuit 19 and the above-mentioned 12-bit A/R via the tunnel current amplification preamplifier 18.
The signal is supplied to the D converter 7.

The servo circuit 19 generates a Z electrode voltage signal (2 applied voltages) such that the tunnel current signal supplied via the preamplifier 18 has a constant value, and applies this to the 12-bit A/D.
Converter 7 and high voltage amplifier for applying Z electrode (H, V,
Z) 20. This Z applied voltage is H
, V, 220, the tube scanner 15 is expanded and contracted so that the distance between the probe 15 and the surface of the sample 17 is constant.

The 12-bit A/D converter 7 A/D converts the tunnel current signal supplied via the preamplifier 18 and outputs it to the 8-bit CPU controller 1. In addition, the Z electrode voltage signal supplied from the servo circuit 19 is
The data is converted into D and output to the 8-bit CPU controller 1.

The STM scanning circuit 5 is mainly composed of a bit shifter and a digital adder. In other words, this STM scanning circuit 5 operates from the 8-bit CPU controller 1 to the CPU
A scan counter circuit that counts up and down in accordance with the scan start signal supplied via the data bus.
16-bit output counter for scanning) 51, and the output from this scanning counter circuit 51 is sent to the 8-bit CPU controller 1.
A bit shift circuit (scanning range switching bit shifter) that shifts an arbitrary number of bits to the LSB side according to a shift number signal (range setting data) supplied from a 52.8-bit scanning offset value supplied from the CPU controller 1. A latch circuit (scanning offset 16-bit day latch circuit) 53, 54 that holds (reference position data), the output of this latch circuit 53 and the output of the bit shift circuit 52 are added to generate, for example, a scanning signal in the X direction. and a digital adder (adding means) 56 that adds the output of the latch circuit 54 and the output of the bit shift circuit 52 to generate, for example, a Y-direction scanning signal. has been done.

The output of the digital adder 55 is an X-scan 16-bit) D/A
It is supplied to the converter 21. This X scanning 16 bit D/A
The converter 21 generates an analog voltage output (X applied voltage) corresponding to the input, and outputs the analog voltage output (X applied voltage) to the +Xis electrode via a high voltage amplifier (H, V, +X) 22 and an inversion circuit 23 for applying the −X electrode. It is output to the high voltage amplifier (H, V, -X) 24. And these +X applied voltages, =
X applied voltage is H, V, +X22. By applying voltages to the tube scanner 15 via H, V, -X24, the probe 16 scans a desired scanning range on the surface of the sample 17 according to the scanning start position corresponding to the reference position data. The tube scanner 15 is deformed by application of each voltage so that the needle tip scans in the direction.

The output of the digital adder 56 is a Y-scan 16-bit D/A
It is supplied to converter 25. This Y scanning 16 bit D/A
The converter 25 generates an analog voltage output (Y applied voltage) corresponding to the input, and converts this into a −
This signal is output to a high voltage amplification amplifier (H, V, -Y) 28 for applying voltage to the Y electrode. And these +Y applied voltages,
-Y applied voltage is H, V, 10Y26. H, V, -Y2g
The probe 16 scans a desired scanning range on the surface of the sample 17 in the Y direction in accordance with the scanning start position corresponding to the reference position data. The tube scanner 15 is deformed as each voltage is applied.

In this way, by using the digital addition output of the bit shifter output into which the range setting data is input and the reference position data as a scanning signal, the probe 16 can be moved away from the sample 17 or without using a coarse movement mechanism. , the scanning range and the scanning start position can be changed.

FIG. 2 shows the configuration of the STM scanning circuit 5 in more detail. For convenience, only the scanning system in the X direction will be illustrated and explained here.

The X scan counter circuit 51a performs rooooHJ according to the scan start signal from the 8-bit CPU controller 1.
From rFFFFHJ to rFFFFHJ, counting is repeated several times for each scanning line, and when r 0000 o J is reached, counting is stopped.

The X-scan count bit shift circuit 52a shifts the 16-bit count value supplied from the X-scan counter circuit 51a to the LSB side by the number of bits corresponding to the shift number signal from the 8-bit CPU controller 1.
Data (output count value) with "0" inserted into the empty bits on the B side is output to the X count value digital adder 55. That is, this X scan count bit shift circuit 52
In case a, for example, when the count value from the X-scanning counter circuit 51a is rFFFFHJ, r7FFFHJ is output when a 1-bit shift is set, and r3FFFnJ is output when a 2-bit shift is set. In this way, by switching the bit shift number setting,
The output count value from the X-scan count bit shift circuit 52a is 1/2.1/4.1/8 of the count value supplied from the X-scan counter circuit 51a. ...becomes... Therefore, when the bit shift is set, the X-scan count value at the output of the digital adder 55 is obtained by repeating the range from If)000HJ to r7FFFHJ several times for the scan line.

The X count value digital adder 55 is composed of an upper side digital adder 55a and a lower side digital adder 55b. The X-scan offset value and the output count value supplied from the X-scan count bit shift circuit 52a are added separately to the upper side and the lower side.

That is, the upper digital adder 55a uses the upper 8 bits of the offset value supplied from the upper latch circuit 53a of the latch circuit 53 and the upper 8 bits of the output count value supplied from the X-scan count bit shift circuit 52a.
Addition with bit is performed. Further, in the lower digital adder 55b, the lower 8 bits of the offset value supplied from the lower latch circuit 53b of the latch circuit 53,
The output count value supplied from the X-scan count bit shift circuit 52a is added to the lower 8 bits. Therefore, the X scan count bit shift circuit 52a
In a state where the bit shift number of is set to "1", for example, r4 is input to the latch circuit 53 as an offset value.
If 000HJ is latched, digital adder 5
The X-scan count, which is the output of r40. The scanning line from oooJ to BFFFHJ is repeated several times.

Note that the X-scanning 16-bit D/A converter 21 to which the output of the digital adder 55 is supplied has rO
JV, rFFFFFoJ(7) and sometimes rlOJV
It outputs the applied voltage.

The above is the configuration of the system for moving the probe 16 in the X direction, but the X direction scanning system for moving the probe 16 in the X direction also has a similar configuration. However, in the case of an X-direction scanning system, the Y-scanning color 2-taper circuit only counts up and down once from rooooooJ to rFFFFHJ in accordance with the scan start signal from the 8-bit CPU controller 1. ing. In other words, the X-scanning clock during count-up has a frequency obtained by dividing the X-scanning clock (number of scanning lines x 2), and is cut to the same frequency as the X-scanning clock when all lines of scanning in the X direction are completed. Instead, a countdown is started, and the count is stopped when it reaches "0000H".

Furthermore, the Y-scan count bit shift circuit shifts the 16-bit count value supplied from the Y-scan color two-tar circuit by n bits, thereby reducing the output count value by 1/1.
2n. In this case, since the scanning range is square, the value of n (number of bit shifts) is
The same value is set for both Y.

Next, the operation in the above configuration will be explained. Note that here, the maximum scanning range is 10 μm x 10 μm.
Taking TM as an example, a case will be described in which a wide range scan of 10 μm is first performed, the 87M image thereof is observed, and then a scanning range of, for example, 2.5 μm is rescanned based on a desired point.

For example, when the probe 16 is currently being servoed at the scan start position (reference position) on the sample 17, a scan start signal instructing a wide range scan of 10 μm is sent from the 8-bit CPU controller 1 via the CPU data bus. TeS
Assume that the signal is supplied to the TM scanning circuit 5. In this case, the bit shift circuit 52 is set in advance as the bit shift number "0" by the shift number signal from the 8-bit CPU controller 1, and the latch circuits 53 and 54 are set with the X-scan offset value and the Y-scan offset value, respectively. as r
It is assumed that ooooooJ is set.

Then, the STM scanning circuit 5 outputs the X-scan count value obtained by repeating the count-up/down from "0000H" to "FFFFH" several times, for example, 512 times, in accordance with the above-mentioned scan start signal. to the D/A converter 21, and from rooooJ to rFFF
The X-scan count values, which are counted up and down only once until FoJ, are output to the X-scan 16-bit D/A converter 25, respectively.

As a result, the X-scanning 16-bit D/A converter 21 outputs an X applied voltage (0 to 10 V) corresponding to the X-scanning count value supplied from the STM scanning circuit 5, and this is used as the X-direction scanning signal. The signal is applied to the tube scanner 15 as follows. Similarly, the Y-scan 16-bit D/A converter 25 outputs a Y applied voltage (0 to 10 V) corresponding to the X-scan count value supplied from the STM scan circuit 5, and this is applied to the X-direction scan. Tube scanner 1 as signal
5.

As a result, the tube scanner 15 can move from 0 μm to 0 μm in the X direction.
The needle tip is deformed to move within a range of 10 μm, and with this one movement, it sequentially moves from 0 μm to 1 μm in the X direction.
By moving within a range of 0 μm, the probe 16 scans a range A of the 10 μm opening of the sample 17, as shown in FIG.

The data in this scan is sampled at, for example, 512 points, which is the same as the number of scanning lines mentioned above, and the S7M image obtained thereby is displayed in top view on the host computer 100. The shape of can be observed. In this case, the S7M image is a two-dimensional (X, Y) display, and the Z direction is displayed by changing brightness (luminance).

By the way, when observing the S7M image above, 10 μm
The scan start position (OOO
Oo X0OCIO)I ), 400 in the X direction
0H (2.5μm) 5oooo (5μm) in the Y direction
Suppose that a case arises in which it is desired to enlarge and display an image within a range of 2.5 μm based on the position (desired point) of point (m) (desired point).

In this case, first, the 8-bit CPU controller 1 outputs a scan start signal to the STM scanning circuit 5 to set the scanning range to 2.5 μm×2.5 μm.

That is, the bit shift number of the bit shift circuit 52 is set to "2" by the shift number signal from the 8-bit CPU controller 1. At this time, r4000HJ is written to the latch circuit 53 as an offset value for the X scan, and r800HJ is written as an offset value for the Y scan.
0HJ is written into the latch circuit 54.

Then, in the STM scanning circuit 5, the scanning counter circuit 51
(To be precise, in the X scan counter circuit 51a), rFF is input from roooonJ according to the scan start signal.
The count up/down until FFHJ is repeated several times for scanning lines, for example, 512 times, and the count result, the X-scan count value, is output to the bit shift circuit 52 (more precisely, the X-scan count bit shift circuit 52a). be done.

In the bit shift circuit 52, the X-scan count value is bit-shifted according to the bit shift number "2" set by the shift number signal, and then output to the digital adder 55.

The output from the bit shift circuit 52, that is, the output count value in the X direction, is processed by the digital adder 55.
It is added to the X-scan offset value r4000uJ written in the latch circuit 53, and the X-scan 16-bit D/A
The converter 21 outputs.

On the other hand, the scan counter circuit 51 (more precisely, the Y scan counter circuit not shown) outputs a Y scan count value that has been counted up/down only once from ro000+J to rFFFFHJ in accordance with the scan start signal. , is output to the bit shift circuit 52 (more precisely, a Y-scan count bit shift circuit not shown).

In this bit shift circuit 52, the Y-scan count value is bit-shifted according to the above-described bit shift number "2" and then output to a digital adder 56.

This Y-direction output count value is added to the Y-scan offset value r8000HJ written in the latch circuit 54 in the digital adder 56 and output to the Y-scan 16-bit D/A converter 25.

As a result, the X-scan 16-bit D/A converter 21 outputs an X applied voltage (2.5 to 5.OV) corresponding to the X-scan count value supplied from the digital adder 55, and this Tube scanner 1 as direction scanning signal
5.

Similarly, the Y-scan 16-bit D/A converter 25 outputs a Y applied voltage (5.0 to 7.5 V) corresponding to the Y-scan count value supplied from the digital adder 56. Tube scanner 1 as a scanning signal in the Y direction
5.

As a result, the tube scanner 15 is 2.5μ in the X direction.
The needle tip is deformed so as to move in the range of m to 5.0 μm, and along with this one movement, it sequentially moves 5.0 m to 5.0 μm in the Y direction.
By moving in the range of 0um to 7.5μm, as shown in FIG.
The probe 16 scans the diagonally shaded area)B.

In this case, by sampling the data in the above scanning at 512 points, which is the same number of scanning lines as above, that is, the same number of samples as in a wide range scan of 10 μm aperture, a high resolution 37M
You can get the image.

As described above, the probe can be moved without separating from the sample, and a range corresponding to a portion of the 37M image in wide-range scanning can be rescanned and enlarged for display.

That is, a shift number signal that sets the size of the desired scanning range after wide-range scanning is input to the bit shifter, and the output of this bit shifter and the X-direction and Y-direction of the desired scanning range with respect to the reference position of the wide-range scanning are input. By using the added output obtained by digitally adding the offset value of I'm trying to do what I can. This makes it possible to rescan the range corresponding to a portion of the 37M image during wide-range scanning without damaging the surface of the sample with the probe during re-approach or being affected by errors caused by the accuracy of the coarse movement mechanism. Enlarged display becomes possible. Therefore, the obtained 37M image has a higher resolution than an image enlarged and displayed through image processing, and can reproduce true shape changes more faithfully, as well as reduce the effort and time required for rescanning. It is something that

It should be noted that the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various modifications can be made without departing from the gist of the invention.

[Effect of the Invention J As detailed above, according to the present invention, the output of the digital addition of the output of the bit shifter and the reference position data is used as a scanning signal. It is possible to provide a scanning tunneling microscope that can move the scanning start position for a desired scanning range to an arbitrary position after scanning, and that can ensure position reproducibility and reliability of enlarged images.

[Brief explanation of drawings]

The drawings show one embodiment of this invention, and FIG.
FIG. 2 is a block diagram schematically showing the configuration of the STM scanning circuit. FIG. 3 is a diagram showing the operation. 1...8-bit CPU controller, 5...STM
Scanning circuit, 15...Tube scan, 16... Probe, 17... Sample (object to be measured), 52... Bit shift circuit, 55.56... Digital adder (adding means). Figure 3

Claims (1)

[Claims] In a scanning tunneling microscope capable of observing the surface of an object to be measured in units of atoms, range setting data for setting the size of a desired scanning range included within this wide range after scanning a wide range. a bit shifter into which is input; and an adding means for digitally adding the output of the bit shifter and the reference position data of the desired scanning range with respect to the reference position of the wide range scanning, and the output from the adding means is used as a scanning signal. A scanning tunneling microscope characterized in that by using the scanning tunneling microscope, a scanning range and a scanning start position thereof can be changed.