JPH04162110A - Scan type tunnel microscope device - Google Patents

Abstract

PURPOSE:To shorten the time needed for measurement of information on the physical properties and also to prevent such accidents as the breakage of a probe, etc., by adding a function to an integration circuit forming an integration system of a Z axis servo drive circuit to keep the output of the integration circuit at the final output of a servo close loop state in a servo open state. CONSTITUTION:When a produced holding signal is inputted through an input terminal 13 during acquisition of the information on the physical properties, the supply of a clock is cut to a latch circuit 17 with operation of a gate circuit 16 end the drive voltage of a piezoelectric element 1 is fixed. At the same time, the supply of a clock is also cut to a latch circuit 22 with operation of a gate circuit 21. Thus the output of 8 D/A converter 23 is kept at the output value of an integration circuit 11 set right before the input of the holding signal. Then an analog switch 10 is actuated by the holding signal end the output of a differential amplifier 12 is connected to the input of the circuit 11. Thus a feedback loop is formed and therefore the output of the circuit 11 is kept at the value set right before the input of the holding signal as long as the holding signal is supplied.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a scanning tunneling microscope device capable of obtaining information on physical properties of a sample surface quickly and reliably.

[Conventional technology]

The two-axis servo circuit of the scanning tunneling microscope device, which can obtain information on the physical properties of the sample surface, converts the target error analog signal into a digital signal using an A/D converter with the required speed and resolution, and 6, which is supplied to the D/A converter through a latch circuit whose clock is the conversion end signal of the converter.
The signal converted into analog by the D/A converter is used to drive the Z-axis actuator. The Z-axis servo drive circuit and Z-axis actuator keep the distance between the sample and the probe constant, and the X-axis scanning translation circuit, X-axis actuator, Y-axis scanning drive circuit, and Y-axis actuator move the sample to the measurement point. Moving. After the movement is completed, the drive signal is fixed by stopping the clock of the latch circuit using a hold signal. In other words, the distance between the sample and the probe is kept constant in an open loop. After that, the conditions between the sample and the probe (applied voltage, etc.)
Measure the necessary items by changing the After the measurement is completed, the conditions between the sample and the probe are returned to their original state, the hold is released, the servo loop is closed, and the servo system is stabilized before moving to the next measurement point. Note that related devices of this type include, for example, Japanese Unexamined Patent Publication No. 1-15817.

[Problem to be solved by the invention]

In the above conventional technology, no consideration is given to the fact that the output of the integrator circuit that constitutes the integral system of the Z-axis servo loop changes depending on the input conditions during hold, that is, when the servo loop is open. There was a problem in that it took a long time (the time constant of the integrating circuit and the time constant of the servo loop with respect to the amount of change) for the entire servo system to reach the normal value when it was returned to the closed position. Also, if the output change of the integrating circuit according to the input condition during hold, that is, during servo open loop, is in the direction of increasing the distance between the sample and the probe, the above problem will be solved, but if Otherwise, there was a problem that the probe and sample would collide and damage each other. An object of the present invention is to shorten the time required to measure physical property information in a scanning tunneling microscope device capable of obtaining physical property information on the surface of a sample, and to eliminate accidents such as breakage of the probe.

[Means to solve the problem]

In order to achieve the above object, the present invention adds a function to the integrating circuit constituting the integrating system of the Z-axis servo drive circuit to maintain the output of the integrating circuit at the final output value during the servo open loop and at the final output value during the servo closed loop. It is. (Function) The above function operates so that the output of the integrating circuit is not affected even if the conditions between the probe and the sample change during the servo open loop.Thereby, the conditions between the probe and the sample during the servo open loop are maintained. After obtaining information on the physical properties of the surface of the sample by changing the conditions, there is no fluctuation in the output of the integrating circuit when the conditions are returned to their original state and the servo is set to a closed loop.It is possible to immediately move to the next measurement point, and the overall In addition, it is possible to reduce the time required for accurate measurement. Also, it is possible to eliminate accidents in which the probe collides with the sample when switching the servo from open loop to closed loop.

【Example】

A first embodiment of the present invention will be described below with reference to FIG. In this figure, the X-axis scanning drive circuit, the X-axis actuator, the Y-axis scanning drive circuit, and the Y-axis actuator for moving the measurement point are omitted to avoid complicating the drawing. The tunnel effect current that flows depending on the distance between the probe 2 fixed to the movable end of the piezo element 1 as a Z-axis actuator and the sample 3 and the voltage applied from the power source 4 is transmitted through the resistor 5.
The signal is converted into a voltage by the differential amplifier 6 and becomes an interval information signal. The error between the interval information signal and the interval command signal given from the power source 7 passes through an error calculation circuit 8, and is weighted.
Linear amplifier 9, differential circuit 24, and analog switch 10
The signal is supplied to the integrating circuit 11 via. The linear amplifier 9, the differential circuit 24. The respective outputs of the integrating circuit 11 are added by an adding amplifier 14 to obtain the required speed and
The signal is input to a resolution A/D converter 15. The signal digitized by the A/D converter 15 is input to a latch circuit 17. The latch circuit 17 uses the conversion completion signal of the A/D converter 15 via the gate circuit 16 as a clock, and updates the output every clock. The output of the latch circuit 17 is input to the D/A converter 18, converted back to an analog signal, and then passed through the driver circuit 19 to become a signal for expanding and contracting the piezo element 1. Normally, the circuit system is configured in a loop like this, and the power supply 7
A servo operation is performed to maintain the probe and sample amount interval commensurate with the interval command signal given by . During this time, the output of the integrating circuit 11 is also input to an A/D converter 20 having the necessary speed and resolution, and the signal digitized by the A/D converter 20 is input to a latch circuit 22. The launch circuit 22 uses the conversion completion signal of the A/D converter 20 via the gate circuit 21 as a clock, and updates the output every clock. The output of the latch circuit 22 is input to the D/A converter 23 and converted back to an analog signal, and then input to the differential amplifier 12 and the integration circuit 11.
Compare with the raw output signal of , which is output but not used. When a generated hold signal is input from the input terminal 13 while obtaining physical property information, the clock to the latch circuit 17 is cut off by the operation of the gate circuit 16, and the drive voltage of the piezo element 1 is fixed. In other words, the distance between the probe 2 and the sample 3 is fixed. Similarly, the clock to the latch circuit 22 is cut off due to the operation of the gate circuit 21 by the hold signal, and the output of the D/A converter 23 is the same as that of the integrating circuit 1 immediately before the hold signal is input.
Holds the output value of 1. In addition, the hold signal activates the analog switch 10, and the output of the differential amplifier 12 is connected to the input of the integrating circuit 11, forming a feedback loop. , holds the value immediately before the halt signal is input. Therefore, while the hold signal is input, even if the conditions between the probe 2 and the sample 3 are changed, such as by changing the value of the electric current g4, the output of the integrating circuit 11 will not change, and the condition will not be changed. Even when the halt signal is stopped after returning to the original state and the circuit system is made into a closed loop, the distance between the probe 2 and the sample 3 does not change, making it possible to immediately move to the next measurement point. A second embodiment of the present invention will be described below with reference to FIG. The X-axis scanning drive circuit, X-axis actuator, Y-axis scanning drive circuit, and actuator for moving the measurement point are omitted so as not to make the drawings complicated. The tunnel effect current that flows depending on the distance between the probe 2 fixed to the movable end of the piezo element 1 as a Z-axis actuator and the sample 3 and the voltage applied from the power source 4 is transmitted through the resistor 5.
The signal is converted into a voltage by the differential amplifier 6 and becomes an interval information signal. The interval information signal and electric Il! The error with respect to the interval command signal given from 7 is weighted through an error calculation circuit 8, and is supplied to an integration circuit 11 via a linear amplifier 9 and an analog switch 10. The respective outputs of the linear amplifier 9 and the integrating circuit 11 are added by an adding amplifier 14, and inputted to an A/D converter 15 having the required speed and resolution. The signal digitized by the A/D converter 15 is input to a launch circuit 17. The latch circuit 17 uses the conversion completion signal of the A/D converter 15 via the gate circuit 16 as a clock, and updates the output every clock. The output of the launch circuit 17 is input to a D/A converter 18 and converted back to an analog signal, and then passes through a driver circuit 19 to become a signal for expanding and contracting the piezo element 1. Normally, the circuit system is configured in a loop like this, and the voltage g7
A servo operation is performed to maintain the probe and sample amount interval commensurate with the interval command signal given by . During this time, the output of the D/A converter 18 and the raw output signal of the integrating circuit 11 are compared and output by the differential amplifier 12, but are not used. When a generated hold signal is input from the input terminal 13 while obtaining physical property information, the clock to the latch circuit 17 is cut off by the operation of the gate circuit 16, and the drive voltage of the piezo element 1 is fixed. In other words, the distance between the probe 2 and the sample 3 is fixed. Further, the hold signal activates the analog switch 1o, and the output of the differential amplifier 12 is connected to the input of the integrating circuit 11 to form a feedback loop, so that the output of the integrating circuit 11 is The output value of the D/A converter 18 immediately before the hold signal is input is held. Therefore, while the hold signal is on, even if the conditions between the probe 2 and the sample 3 are changed, such as by changing the value of the power source 4, the output of the integrating circuit 11 will not change, and the condition will not change. When the hold signal is stopped after returning to the original state and the circuit system is made into a closed loop, the variation in the distance between the probe 2 and the sample 3 is very small. You can immediately move to the next measurement point. The second embodiment is effective for a servo circuit that mainly uses an integral system, and compared to the first embodiment, the circuit is simplified by N and the same effect can be obtained. In addition, in the analog memory that is a combination of an A/D converter, a latch circuit, a gate circuit, and an A/D converter in the first and second embodiments above, a capacitor may be used if the measurement time is very short. Even if it is replaced with a track hold circuit, the same effect can be obtained. Also, in software servo using a microcomputer and digital signal processor, the same effect as in the first and second embodiments can be obtained by holding the integral calculation when the distance between the probe and the sample is held, that is, when the servo is open loop. [Effects of the Invention] According to the present invention, in order to obtain physical property information when the distance between the probe and the sample is servo open loop (when the actuator drive signal is held), Even if the input conditions of the interval servo loop are changed, such as by changing the voltage, it will no longer be reflected in the output of the integrating circuit that constitutes the integral system of the interval servo loop, and the output of the integrating circuit will be the value immediately before the above-mentioned halt. , it is possible to immediately move to the next measurement point when the hold is released after restoring the input conditions. Furthermore, the probe will not be damaged by hitting the sample when the hold is released.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are block diagrams each showing a circuit configuration of an embodiment of the present invention. Explanation of symbols 1...Piezo element, 2...Tip, 3...Sample, 4...
'power supply.

Claims (1)

[Claims] 1. Apply voltage between the probe with a sharp tip and the sample,
A spacing servo drive circuit having an integral system for keeping the distance between the probe and the sample constant using a non-contact tunneling current between the probe and the sample, a Z-axis actuator, a horizontal scanning drive circuit, and an X-axis drive circuit. It has an axis actuator, a vertical scanning drive circuit, and a Y-axis actuator, and when the X-axis and Y-axis scanning is stopped, the output of the Z-axis servo drive circuit is fixed, and the distance between the probe and the sample is adjusted. It has a Z-axis hold function to hold the sample, and by taking measures such as changing the voltage between the probe and the sample when the Z-axis hold function is activated, it is possible to obtain physical property information or electrical information on the sample surface. In a scanning tunneling microscope device, during the Z-axis hold (Z-axis servo open loop), the output of an integral circuit forming an integral system of the Z-axis servo drive circuit is held at the final value during the Z-axis servo closed loop. A scanning tunneling microscope device characterized by added functions.