JP3244021B2 - Scanning probe microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a scanning probe microscope, and more particularly, to a scanning probe microscope having a plurality of measurement modes.

[0002]

2. Description of the Related Art A scanning tunneling microscope (STM) using a tunnel current flowing between a probe and a sample surface, and an atomic force acting between a probe and a sample surface are measured as a device for analyzing a fine surface shape. A scanning probe microscope such as an atomic force microscope (AFM) is known.

[0003] A scanning tunneling microscope (STM) allows a probe or a sample to move in a three-dimensional direction by moving a probe close to a sample surface so that a tunnel current flowing between the probe and the sample surface is constant. By controlling the distance between the sample surface and the probe on the order of sub-nanometers, the three-dimensional shape is measured with atomic-level resolution, and the atomic arrangement on the material surface and the surface shape of the material surface are observed. It is. An atomic force microscope (AFM) includes a probe, a cantilever that supports the probe, and a displacement measurement system that detects the bending of the cantilever. An atomic force (attraction or attraction) between the probe and the sample is provided. (Repulsive force) is detected and controlled to keep this interatomic force constant, thereby observing the shape of the sample surface. It is possible to observe non-conductive substances such as organisms, organic molecules, and insulators. A microscope that can do it.

A scanning probe microscope has a plurality of measurement modes. For example, an atomic force microscope has various measurement modes such as a contact mode, a constant height mode, a non-contact mode (resonance mode), and a dynamic mode. . The contact mode is a mode in which the surface of the sample is scanned while performing feedback control so that the repulsive force acting between the cantilever and the sample becomes constant, and the height is measured from the feedback amount.The constant height mode is a mode in which the height of the cantilever is measured. This mode scans the sample surface while keeping it constant and measures the height from the amount of deflection of the cantilever.The non-contact mode ensures that the attractive force between the cantilever vibrating near the resonance point and the sample is constant. In this mode, the height is measured from the amount of feedback by scanning the sample surface while performing feedback control.Dynamic mode is used to maintain a constant repulsion between the cantilever vibrating near the resonance point and the sample. Scans the sample surface while performing feedback control, and measures the height from the amount of feedback. It is a mode for. The measurement mode is selected according to the characteristics of the measurement sample or the measurement purpose, and a detection signal having a signal characteristic corresponding to the measurement mode is output. In a conventional scanning probe microscope, after a detection signal output from a detector is amplified by a preamplifier for signal detection, signal processing is performed in a signal processing unit to perform data measurement and feedback control.

[0005]

The output of the detector of the scanning probe microscope has a signal characteristic corresponding to the measurement mode. For example, in an atomic force microscope, a detection signal detected in the contact mode has a relatively large signal intensity, and has a linear (linear) signal characteristic in which the ratio between the change in the detection signal and the unevenness of the sample surface is linear. The detection signal detected in the contact mode (resonance mode) has a small signal intensity, a change in the detection signal is large with respect to a change in unevenness on the sample surface, and has a signal characteristic with high sensitivity.

The conventional scanning probe microscope amplifies the detection signals detected in such different measurement modes by a single signal detection preamplifier, and extracts a signal area corresponding to each measurement mode at a subsequent stage. The processing is being performed.
However, the signal detection preamplifier has signal amplification characteristics unique to the circuit, and it is difficult to perform optimal signal amplification for the detection signals in all measurement modes. For this reason, the conventional scanning probe microscope has a problem that an optimum S / N ratio, a response, a dynamic range, and the like cannot be obtained in signal processing depending on a measurement mode, so that an optimum measurement cannot be expected.

FIG. 5 is a diagram for explaining an output example of a detector output of the scanning probe microscope. Signal a in FIG.
FIG. 5 shows an example of signal characteristics in which the signal intensity is small and the change in the detection signal is large with respect to the change in the unevenness of the sample surface, which corresponds to the detection signal in the non-contact mode (resonance mode).
The signal b in the middle is an example of signal characteristics in which the signal intensity is relatively large and the ratio between the change in the detection signal and the unevenness on the sample surface is linear, and corresponds to the contact mode.

FIGS. 6 and 7 are diagrams for explaining an example of signal amplification of a detection signal. The signal A in FIG. 6 is an output example in which the detection signal a in FIG. 5 is amplified by a proportional amplifier having a linear amplification characteristic, and the output amplitude increases. Therefore, if control is performed by setting a feedback constant using this amplified signal, overshoot and undershoot will be repeated. This overshoot or undershoot may cause damage to the tip of the cantilever or the sample or deteriorate the reproducibility of the measurement result.

A signal B in FIG. 7 is an example of an output obtained by amplifying the detection signal b in FIG. 5 by a logarithmic amplifier having a logarithmic amplification characteristic, and the amplitude of the output is small. Therefore, if control is performed using a feedback constant set using this amplified signal, the signal area is degraded, and the obtained image data becomes blurred.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the conventional scanning probe microscope and to provide a scanning probe microscope capable of performing optimum measurement regardless of the measurement mode.

[0011]

The scanning probe microscope of the present invention performs an optimum measurement irrespective of the measurement mode by amplifying the detection signal obtained from the detector in accordance with the measurement mode. . The scanning probe microscope of the present invention is a measuring probe microscope having a plurality of measurement modes, in order to amplify a detection signal according to a measurement mode, a detection signal amplification unit having a plurality of signal amplification characteristics, a detection process A signal processing unit for inputting an amplified signal of the amplifying unit is provided, and signal amplification by the detection signal amplifying unit is performed with signal amplification characteristics according to the measurement mode.

A plurality of signal amplification characteristics of the detection signal amplifier correspond to a plurality of measurement modes of the scanning probe microscope, and a signal amplification characteristic for optimally amplifying according to a detection signal characteristic obtained in the measurement mode. It is. The detection signal amplification unit includes a plurality of amplifiers having signal amplification characteristics corresponding to the measurement mode, and the configuration of the first embodiment in which these amplifiers are selected and switched according to the measurement mode, and the signal amplification characteristics can be changed. The configuration according to the second embodiment may include an amplifier and change the signal amplification characteristic of the amplifier according to the measurement mode.

In a third embodiment, a detection signal amplifying section having a plurality of amplifiers includes a proportional amplifier and a logarithmic amplifier, and switches between the proportional amplifier and the logarithmic amplifier according to a measurement mode to amplify the signal to a signal processing section. It sends a signal. Note that the proportional amplifier is an amplifier that amplifies a signal with a linear amplification characteristic with respect to an input signal, and the logarithmic amplifier is an amplifier that amplifies a signal with a logarithmic amplification characteristic with respect to an input signal.

According to a fourth embodiment, in a contact mode of an atomic force microscope, a detection signal amplifying section obtains clear image data by using a proportional amplifier. A fifth embodiment is directed to an atomic force microscope. In the non-contact mode (resonance mode) of the microscope, the detection signal amplifying section uses a logarithmic amplifier to obtain measurement data that is stable, has good reproducibility, and has a wide dynamic range.

According to the scanning probe microscope of the present invention,
The detection signal amplification unit sets the signal amplification characteristics of the amplifier according to the measurement mode of the scanning probe microscope. The setting of the signal amplification characteristic is performed by an operation of selecting and switching an amplifier having a signal amplification characteristic suitable for the measurement mode from among a plurality of amplifiers, or an operation of changing the signal amplification characteristic of the variable amplifier according to the measurement mode. Can be. The detection signal detected by the detector is amplified by a detection signal amplification unit with an optimal signal amplification characteristic corresponding to the measurement mode, and then processed by a signal processing unit to perform feedback control and measurement.

According to the scanning probe microscope of the present invention,
Since the signal amplification of the detection signal can be performed with the signal amplification characteristics corresponding to the measurement mode, damage to the tip of the cantilever and the sample due to overshoot and undershoot and deterioration of reproducibility can be prevented. Deterioration can be prevented and clear image data can be obtained.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. A configuration example of an embodiment of the present invention will be described with reference to a schematic block diagram illustrating an embodiment of the scanning probe microscope of the present invention in FIG. The configuration shown in FIG. 1 schematically shows a scanning probe microscope, and can be applied to a scanning tunnel microscope, an atomic force microscope, and a horizontal force friction microscope.

In FIG. 1, a scanning probe microscope 1
Performs various signal processing such as a detector 2 for measuring a sample surface, a detection signal amplifying unit 3 for amplifying a detection signal obtained from the detector 2, and a control signal for measurement data and feedback control. A signal processing unit 4, a scanning unit 5 for scanning by moving a sample or a probe unit, and a scanning unit 5
Control section 6 for performing feedback control on the display, a display section 7 for displaying measurement data and the like, a detection signal amplifying section 3, a signal processing section 4, a feedback control section 6, and a control section for controlling the display section 7 and the like. 10 is provided.

The scanning probe microscope 1 has a configuration capable of performing measurement in a plurality of measurement modes, and the control unit 10 sets parameters corresponding to the measurement mode selected from the plurality of measurement modes, and responds to the measurement mode. Outputs control commands. Since the configuration shown in FIG. 1 is almost the same as that of a normal scanning probe microscope, a configuration for setting a signal amplification characteristic according to a measurement mode will be described below. The description of the configuration and operation common to the scanning probe microscope is omitted.

The scanning probe microscope 1 shown in FIG. 1 shows a first configuration example of the detection signal amplification unit 3. The detection signal amplifying unit 3 of the first configuration example has a configuration including a plurality of amplifiers configured to be selectable and switchable. FIG. 1 shows a configuration in which two amplifiers having different signal amplification characteristics, that is, a proportional amplifier 31 and a logarithmic amplifier 32, are provided, and both amplifiers 31 and 32 are selected and switched by a switching unit 33. The switching unit 33 selects one of the proportional amplifier 31 and the logarithmic amplifier 32 according to a control command (switching signal) from the control unit 10 and switches the connection between the detector 2 and the signal processing unit 4. By this switching, the detection signal detected by the detector 2 is linearly amplified by the proportional amplifier 31 or logarithmically amplified by the logarithmic amplifier 32 and sent to the signal processing unit 4. Here, the control command (switching signal) sent from the control unit 4 to the detection signal amplification unit 4 is output according to the measurement mode. Thus, the signal amplification characteristics of the detection signal amplifier 3 can be switched according to the measurement mode of the scanning probe microscope.

FIGS. 2 and 3 are diagrams for explaining an example of signal amplification of a detection signal. Here, a description will be given using the output example of the detector output shown in FIG. The detection signal a in FIG. 5 is a signal characteristic example in which the signal intensity is small and the detection signal change is large with respect to the unevenness of the sample surface. The signal b in FIG. This is an example of signal characteristics in which the ratio between the change and the unevenness of the sample surface is linear, and corresponds to the detection signals in the non-contact mode (resonant mode) and the contact mode, respectively.

FIG. 2 shows a case where the detection signal a in FIG. 5 is logarithmically amplified. The amplified signal A 'can be obtained by performing logarithmic amplification on a detection signal having a small signal intensity and a large signal change. Thus, the problem of exceeding the range of signal processing as shown in FIG. 6 can be solved, and optimal signal amplification can be performed. In addition,
The amplification factor can be set by a measurement parameter.

FIG. 3 shows a case in which the detection signal b in FIG. 5 is proportionally amplified. The detection signal b has a large signal intensity and has a linear ratio between the detection signal change and the unevenness of the sample surface. By performing the proportional amplification, the deterioration of the signal area as shown in FIG. 7 can be eliminated, and the optimum signal amplification can be performed. At this time, the control unit 10
If the logarithmic amplifier 32 is selected for the non-contact mode (resonant mode) and the proportional amplifier 31 is selected for the contact mode, the detection signal is set corresponding to the measurement mode performed by the scanning probe microscope. The proportional amplifier 31 or the logarithmic amplifier 32 of the amplifying unit 3 is selected, thereby performing an optimal signal amplification.

Next, the scanning probe microscope 1 shown in FIG.
Shows a second configuration example of the detection signal amplification unit 3. The detection signal amplification section 3 of the second configuration example has a configuration including a variable amplifier that can change the signal amplification characteristics. FIG.
1 is different from the configuration example shown in FIG. 1 only in the configuration of the detection signal amplifying unit 3, and therefore, only the configuration of the detection signal amplifying unit 3 will be described here.

The detection signal amplifying unit 3 includes a variable amplifier 34 capable of changing the signal amplification characteristics, and changes the signal amplification characteristics in accordance with a control command (change signal) from the control unit 4. Due to the change in the signal amplification characteristic, the detection signal detected by the detector 2 is amplified by the variable amplifier 34 with a predetermined amplification characteristic, and sent to the signal processing unit 4. Here, the control command (change signal) sent from the control unit 4 to the detection signal amplification unit 4 is output according to the measurement mode. Thus, the signal amplification characteristics of the detection signal amplifier 3 can be switched according to the measurement mode of the scanning probe microscope.

In the above embodiment, the signal amplification characteristics include:
Although the case of proportional amplification and logarithmic amplification are shown, other characteristics may be used.

[0027]

As described above, according to the scanning probe microscope of the present invention, optimum measurement can be performed regardless of the measurement mode.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram illustrating a scanning probe microscope according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining an example of signal amplification of a detection signal by the scanning probe microscope of the present invention.

FIG. 3 is a diagram for explaining an example of signal amplification of a detection signal by the scanning probe microscope of the present invention.

FIG. 4 is a schematic block diagram illustrating a scanning probe microscope according to a second embodiment of the present invention.

FIG. 5 is a diagram for explaining an output example of a detector output of the scanning probe microscope.

FIG. 6 is a diagram for explaining an example of signal amplification of a detection signal by a conventional scanning probe microscope.

FIG. 7 is a diagram for explaining an example of signal amplification of a detection signal by a conventional scanning probe microscope.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Scanning probe microscope, 2 ... Detector, 3 ... Detection signal amplifying part, 4 ... Signal processing part, 5 ... Scanning part, 6 ... Feedback control part, 7 ... Display device, 10 ... Control part, 31 ... Proportional amplifier .. 32 logarithmic amplifier 33 switching unit 34
Variable amplifier.

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Claims (1)

(57) [Claims] 1. A scanning probe microscope having a plurality of measurement modes, comprising: a detection signal amplifying section; and a signal processing section for performing signal processing on an amplified signal of the detection signal amplifying section, wherein the detection signal amplifying section includes the plurality of detection signal amplifying sections. Depending on the measurement mode, the signal intensity is small, the signal change is logarithmically amplified for the detection signal that is large in response to the unevenness of the sample surface, the signal intensity is large, and the ratio between the signal change and the unevenness of the sample surface is linear A scanning probe microscope characterized by proportionally amplifying a signal.