RU2497134C2 - Method of leading probe to sample for scanning probe microscope - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method of leading a probe to a sample for a scanning probe microscope involves carrying out steps where there is alternation of the operating mode of the leading motor with a fully retracted scanner and a mode for advancing the scanner with an inactive leading motor until, during one of the steps of advancing the scanner, the tip of the probe is close to the sample. At the steps of advancing the scanner, the scanner is controlled by a feedback circuit; the operating point of the feedback circuit at each step of advancing the scanner gradually changes, starting with the value of the input signal of the feedback circuit at the beginning of that step, such that the feedback, while moving the scanner, starting with a completely retracted state, produces said changes until the scanner is completely advanced or the tip of the probe is near the sample. The probe used is a power probe with an optical recording system. During the leading process, vibrations are generated in the cantilever of the power probe, and the proximity of the tip of the probe to the sample is determined from an abrupt jump of the oscillation phase signal.

EFFECT: reducing the degree of destructive action on an analysed sample, high measurement accuracy.

10 cl, 7 dwg

Description

The invention relates to the field of scanning probe microscopy. It can be used to bring the probe of a scanning probe microscope into working position, especially in difficult acoustic and mechanical conditions, for example, for subsequent measurements of the sizes of nano-objects and the relief of surfaces with a height difference of nanoscale.

A known method of supply using continuous operation of the supply engine with a closed feedback circuit and a fully extended scanner [1]. The feed motors stop and the feed stops when the scanner, controlled by the feedback circuit, is about half retracted.

The disadvantage of this method is that after approaching the tip of the probe to the sample, the operation of the supply engines continues. In addition, the choice of the operating point of the feedback circuit is carried out empirically in advance. This leads to an increase in the degree of destructive effect on the sample and the tip of the probe, a decrease in the accuracy of subsequent measurements, and a deterioration in their reproducibility.

There is also known a method of supplying a probe to a sample for a scanning probe microscope (SPM), during which the alternating stages of the operation of the supply engine with a fully retracted scanner and the steps of extending the scanner with the engine idle until the tip of the scanner is at one point near the sample [2]. The extension of the scanner is controlled by a feedback circuit with a pre-selected operating point. This method is selected as a prototype of the proposed solution.

The disadvantage of this method is that the choice of the operating point of the feedback circuit is carried out in advance empirically, which leads to an increase in the degree of destructive effect on the sample and the tip of the probe, a decrease in the accuracy of subsequent measurements and a deterioration in their reproducibility.

The technical result of the invention is to reduce the degree of destructive effect on the sample and the tip of the probe, reducing the error of subsequent measurements and improving their reproducibility.

The specified technical result is achieved by the fact that in the method of supplying the probe to the sample for the scanning probe microscope, during which the alternating stages of the operation of the supply engine with the scanner fully engaged and the stages of the extension of the scanner with the engine idle, until at one of the stages of the extension of the scanner the tip the probe will not be near the sample, the feedback circuit controls the scanner at the stages of the scanner extension, the working point of the feedback circuit at each stage of the scanner extension gradually changes I, starting from the value of the input signal of the feedback circuit at the moment of the beginning of this stage, so that the feedback, extending the scanner, starting from the fully retracted state, fulfills these changes until the scanner is fully extended or the tip of the probe near the sample.

There is also an option in which the proximity of the tip of the probe to the sample is determined by a sharp decrease in the speed of the scanner.

There is also an option in which a power probe with an optical recording system is used as a probe, oscillations of the probe probe console are excited during the supply process, and the proximity of the probe tip to the sample is determined by a sharp jump in the oscillation phase signal.

There is also an option in which the first stage of the operation of the supply motors does not stop until the input signal of the feedback circuit changes by a predetermined value due to the interaction of the tip of the probe with the sample.

There is also an option in which the rate of change of the operating point of the feedback circuit at the stages of extension of the scanner is adjusted so that the rate of extension of the scanner is maximum and the error error signal does not exceed a predetermined value.

There is also an option in which, after the tip of the probe is near the sample, the operating point of the feedback circuit continues to be adjusted.

There is also an option in which, according to the speed of the scanner’s extension, at the last moment before the supply is stopped, the angle of the curve is automatically determined by the input feedback signal from the distance from the tip of the probe — the sample.

There is also an option in which, after the tip of the probe is near the sample, the working point of the feedback circuit continues to be adjusted, and while adjusting the working point of the feedback circuit, the sufficient proximity of the tip of the probe to the sample is determined by a sharp decrease in the extension speed of the scanner.

There is also an option in which, after the tip of the probe is near the sample, the working point of the feedback circuit continues to be adjusted, and a power probe with an optical recording system is used as a probe, oscillations of the console of the power probe are excited, and during tuning the working point of the feedback circuit, the sufficient proximity of the tip of the probe to the sample is determined by a sharp jump in the signal of the oscillation phase.

There is also an option in which, according to the speed of the scanner extension, at the last moment before the supply is stopped, the angle of the curve of the input feedback signal from the distance of the tip of the probe is automatically determined - the sample and the angle of the curve of the input feedback signal from the distance of the tip of the probe - the sample is automatic feedback input calibration.

Figure 1 shows a General view of a scanning probe microscope.

Figure 2 shows in General terms a device for implementing the proposed method for supplying a probe to a sample for a scanning probe microscope.

Figure 3 shows the process of moving the probe by the scanner.

Figure 4 shows a diagram of the algorithm for supplying a scanning probe microscope according to the proposed method.

Figure 5 shows the position of the measuring head, scanner and probe at different stages of the supply of the proposed method.

Figure 6 shows an example of a curve of the input signal of the feedback circuit from the distance of the tip of the probe - sample.

Figure 7 shows a diagram of the algorithm for adjusting the operating point of the feedback circuit after performing a preliminary approach.

The scanning probe microscope includes a stationary platform 1 with a sample 2 on it (see Figure 1), a probe 3, the tip of the probe 4, a scanner 5, a measuring head 6, a feedback circuit 7, a feed motor 8. A feedback circuit 7 forms the control signal 9, which controls the extensions of the scanner 5, the input signal 10, generated by the probe 3, is fed to the input of the feedback circuit 7. For more details, see the device for the SPM and its components in [3, 4]. Most often, probe 3 is either a current probe with a current meter or a power probe with an optical recording system. The current probe is usually made in the form of a conductive wire. The power probe is usually made in the form of a chip and a flexible console with a tip probe fixed at the end that is in direct contact with sample 2 during measurements, and the optical recording system allows you to monitor the bending of the probe probe console. (The possible device of probe 3 is not shown in the diagram; for more details, see [5, 6]).

A device for implementing the proposed method also includes an inlet control unit 11 (see FIG. 2), which controls the operation of the inlet motors 8 and sets the operating point 12 of the feedback circuit 7.

The scanner 5, changing its length, allows you to move the probe 3 in the range L of the permissible lengths of the scanner 5 (see Figure 3).

The algorithm for supplying a scanning probe microscope according to the proposed method is conveniently depicted in the form of a diagram of FIG. 4. In rectangles 13-18, 21, sequentially performed actions of the algorithm are briefly described; in rhombuses 19, 20, the branching conditions of the algorithm are described.

Figure 5 shows the position of the measuring head 6, scanner 5 and probe 3 at different stages of the supply of the proposed method. During the approach of the proposed method, the steps for extending the scanner and moving the measuring head occur alternately.

The dependence of the input signal 10 (Figure 2) of the feedback circuit 7 from the distance of the tip of the probe 4 - sample 2 at a large distance from the sample H> H1 (see Figure 6) has the form of a horizontal dependence. For the semi-contact method of the microscope, the input signal 10 of the feedback circuit 7 is most often the amplitude M. For the signal of amplitude M, like for many other signals used as input signal 10 of the feedback circuit 7, the dependence on height becomes steeper when approaching the sample - dH2 / dM2 <dH1 / dM1 (Fig.6).

The algorithm for adjusting the operating point 12 of the feedback circuit 7 for supply, where after the tip of the probe is near the sample, the working point continues to be adjusted, implemented as a continuous cycle of actions 22-24, 26, 27 and conditions 25, 28 (Fig. 7 )

The method of supplying the probe to the surface is implemented as follows. Sample 2 is mounted on a fixed platform 1 (Figure 2). The feedback circuit 7 is opened, and the scanner 5 is fully retracted 13 (Figure 4). After this, the operation of the 14 feed motors 8 moving the measuring head 6 towards the sample 2 occurs. The moving of the measuring head 6 occurs at a distance not exceeding the length of the scanner 5, so as not to knowingly bring the tip of the probe 4 into contact with the sample and not damage sample 2 and the tip of the probe 4. After that, 15 the working point 12 of the feedback circuit 7 is set, equal to the input signal 10 of the feedback circuit 7 at the moment. Thus, the mismatch error signal turns out to be zero. After this, the feedback circuit 7 is closed 16 and the execution of the extension step 17-20 of the scanner begins. The position of the measuring head 6 and the scanner 5 at this moment is depicted in Fig.5A. After closing 16 feedback 7, sequential changes 17 of the operating point 12 of the feedback circuit 7 by a small amount, and waiting 18, so that feedback 7 has time to work out the change 17, until the scanner 5 is advanced 19 to the maximum value L. The position of the scanner 4 in the middle of its extension cycle 17-20 is shown in Fig.5B. The exit from the cycle 17-20 in Figs. 5A-5C occurs according to condition 19 - the scanner is at some value of the operating point 12 of the feedback circuit 7, fully extended (Fig. 5C). After the next preparation 13 for the operation of the engine, operation of the engine 14 and preparation 15, 16 for the next cycle 17-20 extension of the scanner 5, the measuring head 6 and the scanner 5 are in the position shown in Fig.5D. In figure 5, the execution of the cycle 17-20 due to the proximity of the sample 2 is completed upon the occurrence of condition 20 of proximity of the tip of the probe to the sample. The entire approach algorithm ends 21, the position of the measuring head 6 and the scanner 5 ensure that the tip of the probe 4 touches the sample 2 of FIG. 5F. In the considered specific process 13-21 (Figure 4) of the occasion (Figure 5), two stages of the extension of the scanner 5 and 5A-C and 5D-F occurred, which ended in the full extension of the L scanner 5 and the tip of the probe 4 touching the sample 2, respectively. The number of steps carried out during the approach of the extension of the scanner 5 depends on the initial position of the measuring head 6, sample 2 and the range of lengths of the scanner L (Fig. 5A). The last approaching step, the extension step of the scanner 5 is always pumped out by touching, FIG. 5F, the tip of the probe 4 of sample 2. All other steps of the extension, FIGS. 5A-5C, of the scanner 5, if present, always end with the fully extended position 5C of the scanner 5.

In the variant where the proximity of the tip of the probe 4 to the sample 2 is determined by a sharp decrease in the speed of the scanner 5, the length of the scanner 5 is measured each time in condition 20 (Figure 5). Each time, for exit cycle 17-20, exit conditions 19 or 20, the length of the scanner 5 will increase. When the tip of the probe 4 is near sample 2, the rate of change in the length of the scanner 5 will drop sharply. The curve of the input signal 10 of the feedback circuit 7 from the height (for example, for the case when the signal of the amplitude M of the forced oscillations of the console of the probe sensor acts as the input signal 10 of the feedback 7) (Fig. 6), explains what was said. For the same change in the working point 12 of the feedback circuit 7 dM2 = dM1 near sample 2, a much smaller approach of the tip of the probe 4 to sample 2 dH2 <dH1 will occur (and, therefore, a smaller elongation of the scanner 5, due to the operation of feedback circuit 7), than away from him. Thus, when the elongation dH2 decreases below some chosen threshold value in condition 20, the proximity of the tip of the probe 4 to sample 2 is determined and the cycle 17-20 of extension of the scanner ends, the supply ends 21.

In the embodiment in which a power probe with an optical recording system is used as probe 3, oscillations of the console of the power probe are excited during the supply process, and the proximity of the tip of probe 4 to sample 2 is determined by a sharp jump in the oscillation phase signal, condition 20 works as follows way. When approaching the tip of the probe 4 to sample 2, the phase signal undergoes a jump (approximately H = H2, see FIG. 6). Thus, condition 20 is triggered, when the phase signal from the previous execution of cycle 17-20 changes more than some threshold value, the supply ends 21.

In a method characterized in that the first stage of operation of the supply motors 8 does not stop until the input signal 10 of the feedback circuit 7 has changed by a predetermined value due to the interaction of the tip of the probe 4 with the sample 2, operation 14 of the supply motors 8, at the first execution, stops only when the input signal 10 of the feedback circuit 7 begins to noticeably change as it approaches the sample (H <H1 Fig.6).

In the method where the change rate of the operating point 12 of the feedback circuit 7 at the stages of extension of the scanner 5 is adjusted so that the extension speed of the scanner 5 is maximum and the error signal of the error does not exceed a predetermined value, the wait 18 (Figure 5) is as follows. During standby 18, after changing the operating point 12 of the feedback circuit 7, the error signal is measured with a high frequency. When the error of the mismatch decreases below a threshold value, the wait 18 is completed.

In the method, where after the tip of the probe 4 is near the sample 2, the operating point 12 of the feedback circuit 7 continues to be adjusted, the approach process by action 21 (Figure 4) does not completely end. Step 21 ends only the preliminary supply of the probe 4 to sample 2. During the entire subsequent measurement period, with a certain time interval, additional supply steps take place that correct the operating point 12 of the feedback circuit 7 so that the tip of the probe 4 remains near sample 2. Otherwise, due to changing experimental conditions (for example, the state of the surface of sample 2, the tip of the probe 4, air humidity), the tip of the probe 4 at some point in the measurements may be in insufficient proximity to the sample ztsu 2. Therefore, it becomes necessary to perform a cyclic action 22-28 (Figure 7). The waiting time 22 is chosen so that, due to changing experimental conditions, the tip of the probe 4 still remains in the acceptable ranges of distances to sample 2. Each time after waiting 22, the operating point 12 of the feedback circuit 7 begins to gradually change in the cycle 23-25 to until the tip of the probe 4 moves away 25 from the sample 2. The waiting time 24 is chosen so that the feedback loop 7 has time to work out the changes 23 of the operating point 10 of the feedback loop 7. After that, the reverse process of approaching the tip NDA 4 to the specimen 2 in the cycle 26-28 (Figure 7), as long as the probe tip 28 would not 4 near the sample 2. After that, the whole cycle is repeated 22-28. Under normal operation of the device and relatively stable experimental conditions, the waiting time 22 is most of the time for the complete cycle 22-28 and during this time the distance of the tip of the probe 4 - sample 2 can be considered optimal.

In the method where, according to the extension speed of the scanner 5, at the last moment before the supply is stopped, the angle of the slope of the curve automatically determines the feedback signal 10 from the distance of the tip of the probe 4 - sample 2, at the end of the supply 21 the following occurs. The slope of the curve is calculated near the sample artg (dM2 / dH2) (Fig.6), where dM2 is the last change 17 of the operating point 12 and dH2 is the length of the last extension of the scanner 5 during the wait time 18 before the completion of the supply 21.

In the method, where after the tip of the probe 4 is near the sample 2, the operating point 12 of the feedback circuit 7 continues to be adjusted, and while adjusting the working point 12 of the feedback circuit 7, the sufficient proximity of the tip of the probe 4 to the sample 2 is determined by a sharp decrease in speed the extension of the scanner 5, conditions 21 and 24 work as follows. The tip of the probe 4 is considered near sample 2 if the ratio dM2 / dH2 (Fig.6) is greater than some threshold value, otherwise the tip of the probe 4 is considered to be located far from sample 2.

In the method, where after the tip of the probe 4 is near the sample 2, the operating point 12 of the feedback circuit 7 continues to be adjusted, and a power probe with an optical recording system is used as probe 3, oscillations of the console of the power probe are excited, and the adjustment time of the operating point 12 of the feedback circuit 7, the sufficient proximity of the tip of the probe 4 to the sample 2 is determined by a sharp jump in the signal of the oscillation phase, conditions 25 and 28 (Fig. 7) operate as follows. When approaching the tip of the probe 4 to sample 2, the phase signal undergoes a jump (approximately H = H2, see FIG. 6). Thus, conditions 25 and 28 are triggered when the phase signal from the previous execution of the cycle (23-25 for condition 25, 26-28 for condition 28, Fig. 7) changes more than a certain threshold value.

In the method where, according to the extension speed of the scanner 5, at the last moment before the supply is stopped, the angle of the curve of the input signal 10 feedback 7 from the distance of the tip of the probe 4 is automatically determined 4 - sample 2 and the angle of the curve of the input signal 10 feedback 7 from the distance of the tip of the probe 4 - sample 2 is an automatic calibration of the input signal 10 of the feedback circuit 7, step 21 is performed as follows. The tangent of the slope of the curve is calculated near the sample dM2 / dH2 (Fig.6), where dM2 is the last change 17 of the operating point and dH2 is the value of the last extension of the scanner during waiting time 18 before completion of the supply 21. After that, using the approximation in which the curve section near the sample 2 H <H2 (Fig.6) is considered linear, the input signal 10 of the feedback circuit 7 is calibrated. As a result, it becomes possible to measure the value of the input signal 10 of the feedback circuit 7 and the error signal of the error in units of length.

TECHNICAL EFFECTS

Controlling the scanner at the stages of extending the scanner by the feedback circuit and gradually changing the operating point of the feedback circuit at each stage of extending the scanner, starting from the value of the input signal of the feedback circuit at the beginning of this stage, so that the feedback, extending the scanner, starting completely retracted state, worked through these changes until the scanner is fully extended or the tip of the probe is near the sample, allow you to bring the tip of the probe to the surface of the sample at optimal m value of the operating point of the feedback circuit. This allows to reduce the degree of destructive effect on the sample and probe, to reduce the error of subsequent measurements, to improve their reproducibility.

Determining the proximity of the tip of the probe to the surface by a sharp decrease in the speed of extension of the scanner allows you to bring the tip of the probe to the surface of the sample with the optimal value of the working point of the feedback circuit. This allows you to reduce the degree of destructive effect on the sample and the tip of the probe, to reduce the errors of subsequent measurements, to improve their reproducibility.

Using a power probe sensor with an optical recording system and determining the proximity of the tip of the probe to the sample by a sharp jump in the signal of the oscillation phase allow you to bring the tip of the probe to the sample at the optimal value of the operating point of the feedback circuit. This allows you to reduce the degree of destructive effects on the surface and tip of the probe, to reduce the error of subsequent measurements, to improve their reproducibility.

The termination of the first stage of operation of the supply motors only when the input signal of the feedback circuit changes by a predetermined value, due to the interaction of the tip of the probe with the sample, allows you to save time at the initial stage of the supply, while the tip of the probe is still at a considerable distance from the sample. When performing the approach for a fixed time, this saving allows smaller steps to change the working point of the feedback circuit at the stages of extension of the scanner. Thus, the operating point of the feedback circuit is selected more precisely. This allows you to reduce the degree of destructive effects on the surface and tip of the probe, to reduce the error of subsequent measurements, to improve their reproducibility.

Adjusting the rate of change of the operating point of the feedback circuit at the stages of extension of the scanner so that the speed of extension of the scanner is maximum and the error signal of the error does not exceed a predetermined value, when approaching for a fixed time, allows you to change the working point of the feedback circuit in smaller steps. Thus, the operating point of the feedback circuit is selected more precisely. This allows you to reduce the degree of destructive effects on the surface and tip of the probe, to reduce the error of subsequent measurements, to improve their reproducibility.

By adjusting the operating point of the feedback circuit by varying it in a certain range after the tip of the probe is near the surface, it is possible to keep the tip of the probe near the surface for the entire measurement period. This allows you to reduce the degree of destructive effects on the surface and the probe, reduce measurement errors, improve the reproducibility of measurements.

Automatic determination of the angle of the curve of the input feedback signal from the distance of the tip of the probe — the sample by the speed of the scanner extension at the last moment before the supply ceases to allow for subsequent measurements from deviations from the zero value of the mismatch error signal to determine the probe – sample distance fluctuations. This allows you to reduce the degree of destructive effects on the surface and the probe, reduce measurement errors, improve the reproducibility of measurements.

Determining the sufficient proximity of the tip of the probe to the surface by drastically reducing the rate of change of the scanner length while adjusting the working point of the feedback circuit by varying it in a certain range after the tip of the probe is close to the surface, allows maintaining the optimal value of the working point of the feedback circuit throughout the entire measurement period. This allows you to reduce the degree of destructive effects on the surface and the probe, reduce measurement errors, improve the reproducibility of measurements.

Determining the sufficient proximity of the tip of the probe to the surface by a sharp jump in the signal of the oscillation phase, when a power probe is used as a probe and vibrations of the probe probe console are excited, it allows maintaining the optimal value of the operating point of the feedback circuit throughout the entire measurement period. This allows you to reduce the degree of destructive effects on the surface and the probe, reduce measurement errors, improve the reproducibility of measurements.

Automatic calibration of the feedback signal input by the slope of the curve, the input feedback signal from the distance of the tip of the probe - a sample determined by the speed of the scanner at the last moment before the supply is stopped, allows, for example, in the case of measurements when the power probe oscillations of the console of the probe sensor are excited, determine the real amplitude and amplitude of the free oscillations of the tip of the probe. This allows you to reduce the degree of destructive effects on the surface and the probe, reduce measurement errors, improve the reproducibility of measurements.

LITERATURE

1. Bykov V.A. etc. Scanning probe microscopy for science and industry. // "Electronics: science, technology, business", No. 5.

2. Mininni; Paul I, Osborne; Jason R., Young; James M., Meyer; Charles R. Method and apparatus for rapid automatic engagement of a probe // US Pat 7665349 February 23, 2010.

3. Bykov V.A. and other "Scanning probe microscope" // Patent RU 2159454 C from 11.20.2000.

4. Bykov V.A. "Scanning probe microscope" // Patent RU 2152063 C from 06.27.2000.

5. Abramovitch D., Andersson S., Pao L, Schitter G. "A tutorial on the Mechanisms, Dynamics, and Control of Atomic Force Microscopes" // Proceedings American Control Conference, New York, July 2007, pp.3488-3502 .

6. Sokolov D.Yu. "A probe based on a quartz resonator for a scanning probe microscope" // Patent RU 2297054 C of 04/10/2007.

Claims (10)

1. The method of supplying the probe to the sample for a scanning probe microscope, during which the alternating stages of the operation of the supply engine with the scanner fully retracted and the stages of the extension of the scanner with the inoperative supply engine until the probe tip is near the sample at one of the stages of the extension of the scanner characterized in that the feedback circuit controls the scanner at the stages of the scanner extension, the operating point of the feedback circuit at each stage of the scanner extension gradually changes, starting with the input one signal of the feedback circuit at the beginning of this stage, so that the feedback, extending the scanner, starting from the fully retracted state, processes these changes until the scanner is fully extended or the tip of the probe is near the sample. 2. The method according to claim 1, characterized in that the proximity of the tip of the probe to the sample is determined by a sharp decrease in the speed of the scanner. 3. The method according to claim 1, characterized in that the probe uses a power probe with an optical recording system, during the supply process, the cantilever of the power probe sensor is excited, and the proximity of the tip of the probe to the sample is determined by a sharp jump in the signal of the oscillation phase. 4. The method according to claim 1, characterized in that the first stage of the operation of the supply motors does not stop until the input signal of the feedback circuit changes by a predetermined value due to the interaction of the tip of the probe with the sample. 5. The method according to claim 1, characterized in that the rate of change of the working point of the feedback circuit at the stages of extension of the scanner is adjusted so that the extension speed of the scanner is maximum and the error signal of the error does not exceed a predetermined value. 6. The method according to claim 1, characterized in that after the tip of the probe is near the sample, the operating point of the feedback circuit continues to be adjusted. 7. The method according to claim 1, characterized in that according to the speed of extension of the scanner at the last moment before the supply is stopped, the angle of the slope of the curve automatically determines the feedback signal from the distance the tip of the probe is a sample. 8. The method according to claim 6, characterized in that during the adjustment of the operating point of the feedback circuit, the sufficient proximity of the tip of the probe to the sample is determined by a sharp decrease in the speed of the scanner. 9. The method according to claim 6, characterized in that the probe uses a power probe with an optical recording system, oscillations of the console of the power probe are excited, and while adjusting the operating point of the feedback circuit, the sufficient proximity of the probe tip to the sample is determined by a sharp a jump in the signal of the oscillation phase. 10. The method according to claim 7, characterized in that according to the angle of inclination of the curve, the input feedback signal from the distance from the tip of the probe — the sample automatically calibrates the input signal of the feedback circuit.

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