JP2006058016A - Scanning probe microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the stability of two-dimensional scanning, to reduce noise of a voltage signal applied to a scanner and to improve the quality of an observation image especially in a narrow-band scanning, by solving the problem that the quality of an observation image is deteriorated by noise or drift possessed by a scanner drive circuit in wide area scanning in the case of narrow area scanning using a scanning probe microscope. <P>SOLUTION: The scanning probe microscope is constituted so as to detect the physical quantity acting across a probe and a sample, and includes a scanner for relatively scanning the probe and the sample, at least two scanner drive circuits corresponding to the scanning region of the scanner, and a switching means for switching at least two scanner drive circuits. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a scanning probe microscope, which is a general term for a scanning tunnel microscope, an atomic force microscope, a magnetic force microscope, a friction force microscope, a micro viscoelastic microscope, a surface potential difference microscope, a scanning near field microscope, and similar devices. is there.

  In recent years, the atomic force acting between the probe and the sample can be achieved by scanning the surface of the sample with the probe by placing the cantilever with the probe and the sample facing each other, setting the distance between the probe and the sample to be a few nanometers or less. 2. Description of the Related Art Scanning probe microscopes that measure physical quantities such as magnetic force or electrostatic force and obtain a concavo-convex image, magnetic image, spectroscopic image, etc. of a sample surface based on the measurement have attracted attention.

  In general, scanners used in scanning probe microscopes are made of a piezoelectric material that can be driven stably in the order of nanometers to micrometers, thereby enabling a wide variable range from narrow to wide. Scanning is possible.

  Figure 3 shows the scanner drive circuit. Commercially available high-voltage operational amplifiers are often used for scanner drive circuits. This high-voltage operational amplifier is an IC that can supply a power supply voltage up to about ± 200V, and can output an output voltage up to about ± 200V. This is because it is necessary to apply a voltage of about 200 V to the piezoelectric body in order to drive the scanner (piezoelectric body) used in the scanning probe microscope at the maximum several tens of nanometers. As described above, in the scanning probe microscope, in order to drive a scanner made of a piezoelectric material in a wide range, the driving signal of the scanner is amplified by an amplifier circuit capable of outputting up to a high voltage and applied to the scanner.

  However, observation of an atomic image or the like requires two-dimensional scanning in a narrow region of nanometer order. At this time, the noise and stability of the scanner drive circuit become a problem. As described above, a high-voltage operational amplifier is used to drive the scanner at a maximum of about ± 200 V so that the scanner drive circuit can scan a wide area.

  If this high voltage operational amplifier outputs a low voltage of several hundred millivolts, it will greatly affect the output voltage with low noise and drift of the high voltage amplifier, which was not a concern when outputting high voltage. Therefore, it appears as wobbling or noise in the observed image, causing poor image quality.

  As a conventional technique, there is a piezoelectric element driving mechanism that switches the electrode of a scanner according to a scanning region (for example, Patent Document 1).

JP 2000-350478 A

  The problem to be solved by the present invention is that the noise and drift of the wide area scanning scanner driving circuit deteriorate the quality of the observed image when the scanning probe microscope performs narrow area scanning.

  The invention of claim 1 is a scanning probe microscope for detecting a physical quantity acting between a probe and a sample, a scanner that relatively scans the probe and the sample, and at least two corresponding to the scanning region of the scanner. A scanning probe microscope comprising: a plurality of scanner driving circuits; and switching means for selectively connecting the at least two scanner driving circuits to the scanner.

  According to a second aspect of the present invention, the scanner driving circuit includes a scanning signal generator, a narrow area driving circuit that amplifies the scanning signal from the scanning signal generator with a low amplification degree, and a wide area driving circuit that amplifies the scanning signal with a high degree of amplification. The scanning probe microscope according to claim 1, further comprising:

  According to a third aspect of the present invention, the scanner driving circuit includes a narrow area driving circuit that scans a nanometer order area and a wide area driving circuit that scans a micrometer order area. Scanning probe microscope.

  According to a fourth aspect of the present invention, there is provided a scanning probe microscope according to any one of the first to third aspects, further comprising scanner drive control means for controlling the scanner drive circuit, wherein the scanner drive control means controls the scanner drive circuit according to a signal from the scanner drive control means. This is a scanning probe microscope in which switching means is switched.

  A fifth aspect of the present invention is the scanning probe microscope according to the fourth aspect, wherein the scanner drive control means is a computer.

  According to the present invention, the driving circuit for driving the scanner can be switched to a driving circuit having a suitable output voltage range, the stability of two-dimensional scanning can be increased, and noise of the voltage signal applied to the scanner can be reduced. The image quality of the observed image was improved particularly in narrow area scanning.

  Hereinafter, the present invention will be described in detail according to the best mode for carrying out the invention.

The configuration of the present invention will be described with reference to FIGS. FIG. 4 shows a control circuit in a scanning probe microscope (STM). A sample 2 is placed on the upper surface of the scanner 5 in a replaceable manner, and a probe 1 is placed facing the sample 2. The cylindrical scanner 5 is composed of a piezoelectric element that is a piezoelectric ceramic such as PbZrTiO ₃ . Electrodes X, Y, and Z are coated on the surface of the scanner 5, and when a voltage is applied by a power source (not shown), the free end on which the sample is placed is displaced in the XYZ directions.

  A current-voltage converter 3 is connected to the probe 1. The current-voltage converter 3 is a circuit that detects a tunnel current flowing between the probe 1 and the sample 2, converts the voltage, and outputs it. The height direction control circuit 4 connected to the current / voltage converter 3 receives the output of the current / voltage converter 3 and compares the reference voltage with the output of the current / voltage converter 3. This is a circuit for controlling the height direction of the scanner 5 so that a constant current flows through the scanner 5.

  The scanner driving circuit Z6 connected to the height direction control circuit 4 is a piezoelectric body driving circuit for causing the scanner 5 to operate in the height direction. The scanning signal generators X9 and Y10 are circuits that can output a scanning signal by setting scanning signal data sent from the computer 11, and are circuits that can output a scanning signal waveform with an output of maximum ± 10V.

  The scanner drive circuits Xw7 and Yw8 are shown in FIG. The scanner drive circuits Xw7 and Yw8 are piezoelectric drive circuits for causing the scanner 5 to perform two-dimensional scanning, and the output of the scanning signal generator is amplified by a high voltage operational amplifier 20 having an amplification factor of 20 times to a voltage of maximum ± 200V. Can be used for wide-area scanning.

  FIG. 5 shows the scanner drive circuits Xn and Yn. The scanner drive circuits Xn and Yn are piezoelectric drive circuits for causing the scanner 5 to perform two-dimensional scanning. The output of the scanning signal generator is amplified by an operational amplifier having a single amplification factor and can be output up to a voltage of ± 10V. It is a circuit and is used for narrow area scanning.

  The scanner 5 has a structure as shown in FIG. The X and Y electrodes of the scanner 5 can be driven by 20 μm in the XY directions by applying a maximum of ± 200 V to the electrodes of each piezoelectric body.

  In FIG. 4, the switch A 23 connected to each scanner drive circuit is turned OFF when the narrow area observation control signal sent from the computer 11 is detected, and the switch B 24 receives the narrow area observation control signal sent from the computer 11. Turns on when detected.

  The configuration of each unit in the figure has been described above. Next, the operation will be described. In FIG. 4, first, when a bias voltage is applied to the sample 2 and the probe 1 is moved closer to the sample 2, a tunnel current starts to flow through the probe 1 when the distance between the probe 1 and the sample 2 reaches a certain distance. . It is converted into a voltage value by the current-voltage converter 3 and input to the height direction (Z) control circuit 4. A reference value of the tunnel current is given to the height direction control circuit 4 as a voltage, the reference value is compared with the tunnel current, and a signal for driving the Z electrode portion of the scanner 5 in the direction in which the difference is reduced is given in the height direction. The control circuit 4 outputs. By driving the output of this height direction control circuit through the piezoelectric drive amplifier and driving the Z scanner 5, two-dimensional scanning is performed while performing feedback control so that the tunnel current becomes a constant value, and the surface of the sample 2 Can be obtained. That is, the unevenness on the sample surface can be observed at the atomic level by imaging the unevenness information based on the distance-converted voltage applied to control the Z direction at this time.

  The two-dimensional scanning of the scanning probe microscope can be realized by the scanner 5 made of a piezoelectric material. As shown in FIG. 1, the scanner 5 is provided with three piezoelectric bodies, X, Y, and Z. By applying a voltage signal to each electrode, the scanner 5 is driven by the piezoelectric effect of the piezoelectric body. Is possible. Thus, the scanner 5 performs two-dimensional scanning by applying a scanning signal as a voltage signal to the electrodes of the X and Y piezoelectric bodies.

  In FIG. 4, a scanning signal for performing two-dimensional scanning is generated by scanning signal generators X9 and Y10. When the operator sets a scanning area in the computer 11, the computer 11 calculates a voltage value to be applied to the piezoelectric body from the piezoelectric constant of the scanner 5 (piezoelectric body), and the voltage value is calculated based on the amplification degree of the scanner driving circuit. The divided value is set in the scanning signal generator, and the scanning signal generator outputs the voltage signal. As a result, the scanner 5 (piezoelectric body) can two-dimensionally scan the scanning region set by the operator.

  Now, when performing sample observation in a wide area, the operator sets the wide area observation to the computer 11. Wide-area observation here refers to surface observation that scans a wide area on the order of micrometers and obtains an observation image.

  When the computer 11 is set to the wide area observation, the computer 11 does not output the narrow area observation control signal to the switch A23 and the switch B24. Each switch does not change as shown in the figure, the switch A23 is ON, and the switch B24 is OFF.

  Next, the operator sets the scanning area to be observed on the computer 11. The computer 11 calculates the voltage value applied to the X and Y electrodes of the scanner 5 to drive the scanner 5 from the characteristics of the scanning region and the piezoelectric body set by the operator. A value obtained by dividing the calculated value by the amplification factor of the scanner driving circuit is set in the scanning signal generators X9 and Y10. The scanning signal generator outputs a scanning signal having a set value as a voltage signal to the scanner driving circuits Xw7 and Yw8. The scanner driving circuit amplifies the input scanning signal with a high voltage amplifier and outputs it. The scanner drive circuit applies the output voltage signal to the X and Y electrodes of the scanner 5. The scanner 5 starts two-dimensional scanning in the scanning area set by the operator.

  In this case, the scanner 5 can be driven to a maximum of 20 μm, and a wide area scan up to 20 μm can be performed. However, when observation is performed in a narrow area, as described above, noise and drift of the scanner driving circuit are greatly affected, and it is difficult to obtain a high-quality image.

  When performing sample observation in a narrow area, the operator sets the narrow area observation in the computer 11. The narrow area observation here refers to surface observation in which an observation image can be obtained by scanning a narrow area such as atomic image observation generally in the order of nanometers.

  When narrow range observation is set in the computer 11, the computer 11 outputs a narrow range observation control signal to the switch A23 and the switch B24. When each switch senses the narrow area observation control signal, the switch A23 is turned off and the switch B24 is turned on.

Next, the operator sets the scanning area to be observed on the computer 11. The computer 11 calculates a voltage value to be applied to the piezoelectric bodies of the scanners 5X and Y in order to drive the scanner 5 from the scanning region set by the operator and the characteristics of the piezoelectric bodies, and calculates the calculated values to the scanning signal generators X9 and Y10. Set to. The scanning signal generator applies the scanning signal having the set value to the scanner 5X, Y as a voltage signal.
The scanner 5 starts two-dimensional scanning in the scanning area set by the operator.

  In this way, by setting narrow-area observation, surface observation in a narrow area such as atomic image observation is possible without being affected by electrical noise and drift caused by the high-voltage operational amplifier 20 of the scanner drive circuit. Thus, the operator can obtain a high-quality observation image. However, since the scanner drive circuits Xn and Yn (FIG. 5) can only output a maximum of ± 10 V, the scanner 5 cannot be driven at 1 μm or more.

  Although the operation has been described above, the effect of the present invention is that it is possible to eliminate the fluctuation of the observed image, which is a problem in the observation in a narrow region such as the atomic image observation in the scanning probe microscope. In other words, in order to scan the scanning area, the driving circuit for driving the scanner is switched to a driving circuit having an appropriate output voltage range, thereby improving the stability of the two-dimensional scanning and reducing the noise of the voltage signal applied to the scanner. It is characterized by the fact that it has been reduced, thereby improving the quality of the observed image.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in Example 1, an example of a tunneling microscope is shown, but in general scanning probe microscopes such as an atomic force microscope, a magnetic force microscope, a friction force microscope, a micro viscoelastic microscope, a surface potential difference microscope, and a scanning near-field microscope are used. Can adapt.

  Further, instead of scanning the sample side, the probe side may be scanned.

  Further, there may be three or more scanner driving circuits.

  The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The configuration of the present invention will be described with reference to the drawings. FIG. 6 shows a control circuit in the STM of the scanning probe microscope. The current-voltage converter 3 is a circuit that detects a tunnel current flowing between the probe 1 and the sample 2, converts the voltage, and outputs it. The height direction control circuit 4 receives the output of the current-voltage converter 3, compares the reference voltage and the output of the current-voltage conversion circuit, and the scanner 5 outputs a constant current between the probe 1 and the sample 2. This circuit controls the height direction. The scanner drive circuit Z6 is a piezoelectric drive circuit for causing the scanner 5 to operate in the height direction. The scanning signal generators X9 and Y10 are circuits that can output a scanning signal by setting scanning signal data sent from the computer 11, and are circuits that can output a scanning signal waveform with an output of maximum ± 10V. The scanner driving circuit X26 is shown in FIG. The scanner drive circuit is a piezoelectric drive circuit for causing the scanner 5 to perform two-dimensional scanning. The scanner drive circuit has a circuit that can switch the output of the scanning signal generator by 1 to 20 times with a switch such as a multiplexer and has a maximum of ± 200V. A circuit that can output up to a voltage. The scanner driving circuit Y27 has a similar structure.

  The scanner 5 has a structure as shown in FIG. 1, and X, Y, and Z electrodes are provided on a piezoelectric body. By applying a maximum of ± 200 V to the X and Y electrodes of the piezoelectric body of the scanner 5, each can be driven by 20 μm. The switch A23 is turned off when the narrow area observation control signal sent from the computer 11 is sensed, and the switch B24 is turned on when the narrow area observation control signal sent from the computer 11 is sensed.

  The configuration of each unit in the figure has been described above. Next, the operation will be described. First, the operator sets a scanning area to be observed on the computer 11. The computer 11 calculates the voltage value applied to the X and Y electrodes of the scanner 5 to drive the scanner 5 from the characteristics of the scanning region and the piezoelectric body set by the operator. Based on the calculated value, the computer 11 determines an appropriate scanner drive circuit for the set scan area from among the scanner drive circuits A29, B30, and C31 in the scanner drive circuits X26 and Y27, and scan control is performed by the switch circuit 28. Send a signal to change the switch.

  In FIG. 6, values obtained by dividing the calculated value by the amplification factor of the scanner driving circuit determined to be appropriate are set in the scanning signal generators X9 and Y10. The scanning signal generators X9 and Y10 output the scanning signal having a set value as a voltage signal to the scanner driving circuits X26 and Y27. The scanner driving circuits X26 and Y27 amplify and output the input scanning signals by the scanner driving circuits 29, 30, and 31 selected by the switch circuit 28 having the scanning signals therein. The scanner drive circuits X26 and Y27 apply the output voltage signal to the X and Y electrodes of the scanner 5. The scanner 5 starts two-dimensional scanning in the scanning area set by the operator.

It is a figure which shows the structure of a tube type scanner. It is a figure which shows the control circuit of the scanning tunnel microscope of a prior art. It is a figure which shows the scanner drive circuit (Xw, Yw) in FIG. It is a figure which shows the control circuit of the scanning tunnel microscope by the 1st Example of this invention. It is a figure which shows the scanner drive circuit (Xn, Yn) in FIG. It is a figure which shows the control circuit of the scanning tunnel microscope by the 2nd Example of this invention. It is a figure which shows the scanner drive circuit (X, Y) in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Probe 2 Sample 3 Voltage-current converter 4 Height direction control circuit 5 Scanner 6 Scanner drive circuit Z
7 Scanner drive circuit Xw
8 Scanner drive circuit Yw
9 Scanning signal generator X
10 Scanning signal generator Y
11 Computer 12 Operation 13 Bias Amplifier 20 High Voltage Operational Amplifier 21 Scanner Drive Circuit Xn
22 Scanner drive circuit Yn
23 Switch A
24 Switch B
25 High Voltage Operational Amplifier 26 Scanner Drive Circuit X
27 Scanner Drive Circuit Y
28 Switch circuit 29 Scanner drive circuit A
30 Scanner drive circuit B
31 Scanner drive circuit C

Claims (4)

In a scanning probe microscope that detects a physical quantity acting between a probe and a sample,
A scanner that relatively scans the probe and the sample;
At least two scanner driving circuits corresponding to the scanning area of the scanner;
A scanning probe microscope comprising: switching means for selectively switching the at least two scanner driving circuits to be connected to the scanner.   The scanner driving circuit includes a scanning signal generator, a narrow area driving circuit that amplifies the scanning signal from the scanning signal generator with a low amplification degree, and a wide area driving circuit that amplifies the scanning signal with a high amplification degree. The scanning probe microscope according to claim 1. The scanning probe microscope according to claim 1 or 2, further comprising scanner drive control means for controlling the scanner drive circuit.
A scanning probe microscope in which the switching means is switched by a signal from the scanner drive control means. 4. The scanning probe microscope according to claim 3, wherein the scanner drive control means is a computer.

Images