JPH06258014A - Scanning probe microscope and recorder and/or reproducer employing it - Google Patents

Abstract

PURPOSE:To obtain a plurality of types of observed image signal substantially concurrently by detecting current flowing between a probe and the surface of a sample when different bias voltages are applied to a plurality of different phase points. CONSTITUTION:A voltage applying circuit 14 applies an AC bias voltage between a probe 11 and the surface of a sample 12, detects 13 a current flowing therebetween, and sustains the current at a constant level by subjecting the distance therebetween to feedback control. During that interval, an imaging unit 26 images the surface profile of the sample 12 based on an output from a Z-axis drive circuit 31 in synchronism with the motion of the probe 11 in XY direction. In this regard, a timing circuit 15 outputs a timing signal at a designated phase point in synchronism with an output from the circuit 14. Signals corresponding to the surface profile of the sample 12 at respective bias voltages are sampled 2 by the circuit 31. The unit 26 then obtains different types of scanning tunnel microscopic image under different bias voltages substantially concurrently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a scanning probe microscope,
And an information recording apparatus and / or reproducing apparatus using the same.

[0002]

2. Description of the Related Art Recently, scanning tunneling microscopes (hereinafter referred to as ST
(Abbreviated as M) was developed [G. Binnig et al., Phys. Rev.
Lett., 49, 57 (1982)], whether it is a single crystal or an amorphous material, it has become possible to observe real-space images of conductor surfaces with high resolution in atomic order. The STM utilizes the fact that a tunnel current flows when a voltage is applied between the metal probe and the conductor surface to bring the distance between them to about 1 nm. The tunnel current is extremely sensitive to the distance between the two. The probe is scanned on the surface of the conductor while controlling the distance between the two so as to keep this tunnel current constant, and the surface shape of the conductor is constructed from the distance control signal. At this time, the resolution in the in-plane direction reaches about 0.1 nm. Recently, it has been reported that it is possible to even observe the atomic or molecular image of rare gas atoms or organic molecules adsorbed on the conductor surface. These results are interpreted as the STM detecting information regarding the interaction between the electron cloud at the tip of the probe and the electron cloud at the sample surface.

The STM has an advantage that observation can be carried out at low power without damaging the sample by electric current. Furthermore, it can be operated in the atmosphere and can be used for various materials. Therefore, it is expected to be applied not only to surface observation but also in a wide range of fields. For example, application to surface fine processing and high density information recording has been proposed. Furthermore, S
Applying TM technology, microscopes have been developed for observing the surface condition by detecting various types of interactions between the sample surface and the probe tip.
It is also called scanning probe microscope.

[0004]

When observing the surface by STM, a bias voltage is applied between the sample and the probe in order to pass a tunnel current. This bias voltage should be set to the most appropriate voltage depending on the type of sample to be observed. However, the observed image may differ depending on the bias voltage depending on the sample. For example, in an STM image of a gallium arsenide crystal plane, an STM image of an arsenic atom and an ST image of a gallium atom depending on a bias voltage.
There is a report that the M image is observed separately. When observing an organic molecular layer (liquid crystal molecules such as alkylcyanobiphenyl, saturated fatty acid, etc.) formed on graphite, a molecular image of the upper organic molecule can be obtained under a high bias voltage, and under a low bias voltage. A crystal lattice image of the lower layer graphite is obtained. For example, a bias of 1.0 V gives a saturated fatty acid molecular image, while a bias of 0.1 V gives a graphite lattice image of the substrate. Moreover, reversible image changes are observed even when the bias voltage is repeatedly changed. Utilizing such a phenomenon, images adsorbed on the crystal lattice of the lower layer substrate of organic molecules have been discussed by comparing images observed at different bias voltages using the same sample.

However, conventionally, since the STM images at different bias voltages are individually observed, if the relative position of the probe to the sample surface changes due to drift or the like during the observation time, the lower substrate surface The relative position of the atomic position in the organic molecule on the surface of the substrate with respect to the atom was not obtained accurately.

Further, a method of calibrating the position of the probe on the surface of the sample by observing the crystal lattice on the surface of the lower substrate has been proposed.

Further, in a recording and / or reproducing apparatus to which the principle of the scanning probe microscope is applied, a method of using an observed crystal lattice for positioning the probe at the time of recording or reproducing has been proposed. However, also in this case, either the crystal lattice image on the surface of the lower substrate or the image on the surface of the recording medium is observed, and if there is a drift or the like, accurate positioning may not be performed.

[0008]

The present invention has been made in view of the above problems. That is, the present invention is characterized in that an AC voltage is applied as the bias voltage. The frequency of the AC voltage is set lower than the cutoff frequency of the feedback control in the STM. The STM operation is performed by feedback controlling the distance between the tip of the probe and the sample surface so that the current flowing between the probe and the sample is always kept constant during the application of the alternating voltage. Further, the feedback control signals are detected at different phase points of the AC voltage, and STM images at different bias voltages corresponding to the respective phase points are observed substantially at the same time.

[0009]

The bias voltage applied between the probe and the sample is an AC voltage, and the current flowing between the probe and the sample surface is detected when different bias voltages are applied at different phase points. , It is possible to obtain a plurality of types of observation image signals almost at the same time.

[0010]

1 is a block diagram of a scanning tunneling microscope of the present invention.

In FIG. 1, 11 is a probe (electrode),
12 is a sample to be observed, 13 is a current detection circuit for detecting a current flowing between the probe 11 and the surface of the sample 12,
Reference numeral 14 is a voltage application circuit for applying a bias voltage between the probe 11 and the sample 12, and uses an AC voltage as the bias voltage. 15 is a sample / hold circuit 24,
25 is a timing circuit for giving sampling timing to 25. Reference numeral 21 is a logarithmic conversion circuit for logarithmically converting the detection output of the current detection circuit 13, 22 is a comparator for outputting a difference signal between the logarithmically converted input and a reference current value, and 23 is a component having a cut-off frequency or lower. Low-pass filter, 24 and 25 are sample / hold circuits that sample and hold the output of the z-direction drive circuit 31 based on different timing signals, and 26 is an xy-direction control circuit 3.
3 is an image forming apparatus that displays the output signal of the sample / hold circuit as the shape of the sample surface in synchronization with the movement of the probe 11 in the xy-axis directions. Reference numeral 31 is a z-direction drive circuit that outputs the drive signal for driving the z-direction fine movement device 32 based on the output signal of the filter, and 32 is the sample 1
2 z direction fine movement device for changing the distance between the surface and the probe 11, 33 is an xy direction drive circuit 34 and an xy direction control circuit for outputting to the image forming apparatus, 34 is an xy direction control circuit 3
An xy-direction drive circuit that outputs to drive the xy-direction fine movement device 35 based on the output signal of 3, and 35 is an xy-direction fine movement device that finely moves the probe in the xy-axis directions within the surface of the sample 12.

Next, the operation of this embodiment will be described.
The probe 11 provided so as to face the sample 12 is controlled by the z-direction fine movement device 32 and the xy-direction fine movement device 35 so that
It can move a small amount in the y- and z-axis directions. A bias voltage is applied between the probe 11 and the sample 12 by the voltage application circuit 14, and a current flowing between the probe 11 and the sample 12 is detected by the current detection circuit 13, so that the current is kept constant. The direction fine movement device 32 feedback-controls the distance between the tip of the probe 11 and the surface of the sample 12. While performing such feedback control, the probe 11 is driven on the surface of the sample 12 by the xy direction fine movement device 35 in accordance with the output of the xy direction control circuit 33. The shape of the sample surface can be obtained by performing imaging using the image forming apparatus 26 in synchronization with the movement of the probe 11 in the xy-axis directions by the control signal of the z-direction fine movement device 32, that is, the output of the z-direction drive circuit 31. it can.

The voltage application circuit 14 outputs an alternating voltage and applies a bias voltage between the probe 11 and the sample 12 with this alternating voltage. At this time, the current flowing between the probe 11 and the sample 12 is detected by the current detection circuit 13. The detected current signal is logarithmically converted by the logarithmic conversion circuit 21, and then the difference from the reference current value is taken out by the comparator 22, and the component below the cutoff frequency designated by the low-pass filter 23 is extracted. The z-direction fine movement device 3 is controlled by the z-direction drive circuit 31 so as to compensate the extracted signal.
2 is driven, and the distance between the tip of the probe 11 and the surface of the sample 12 is feedback-controlled. At this time, the fluctuation component of the current due to the fluctuation of the bias voltage which is an alternating current is included in the control signal of the z direction fine movement device, the probe 11 vibrates in the z axis direction at the alternating frequency of the bias voltage, and the bias voltage at each time The feedback control of the distance between the tip of the probe 11 and the surface of the sample 12 is performed so that the set reference current value is always obtained.

At the same time, the output of the z-direction drive circuit 31 is used as a signal for imaging the surface shape of the sample. The timing circuit 15 outputs a timing signal at a fixed phase point designated in synchronization with the output of the voltage application circuit 14 (FIG. 2). According to this timing signal, the output of the z-direction drive circuit 31 at the phase points with different bias voltages,
That is, a signal corresponding to the sample surface shape at each bias voltage at each timing is sampled by the sample / hold circuits 24 and 25, and the STM images of different types under the different bias voltages by the image forming device 26. Is obtained.

The cutoff frequency of the low-pass filter 23 is
It is preferable to set so as to cover the scanning frequency of the probe 11 and the spatial frequency of the surface shape of the observation sample obtained from the necessary resolution. On the other hand, in order to cause the movement of the probe 11 to follow the AC frequency of the bias voltage, the frequency of the bias voltage needs to be set lower than the cutoff frequency of the low pass filter 23. Moreover, the frequency of the bias voltage needs to have at least the spatial frequency of the surface shape of the observation sample, and take different bias voltage values within the required resolution. Thus, for example, the probe is scanned at 10 Hz and 50
In order to obtain an observation image with 0 pixels, the frequency of the bias voltage may be set to about 5 kHz. Therefore, the cutoff frequency of the low-pass filter is set to, for example, about 10 kHz or more so as to cover 5 kHz. Is preferred.

The phase points of the bias voltage for sampling are not limited to two points, but may be three or more points. Further, as shown in FIG. 1, as many sample / hold circuits as the number of phase points to be sampled may be provided, or the sample / hold circuits may respectively provide a plurality of phase points of the bias voltage according to the timing signal of the timing circuit 15. The output signal of the z-direction drive circuit 31 may be sampled and output.

By observing the sample surface by STM by such a method, two or more kinds of STM images at different bias voltages of two or more can be obtained almost simultaneously for the same sample. Furthermore, when observing the underlying substrate surface and organic molecules on the substrate surface at different bias voltages, even if the relative position of the probe to the sample surface changes during the observation time due to drift, etc. Since it is possible to detect the signals that make up the observed image for each of the different bias voltages, the relative position deviation between the atoms on the lower substrate surface and the atoms in the organic molecules on the surface can be suppressed to about the resolution or less. To be

Even if the image is distorted due to drift or the like, if the crystal lattice on the surface of the lower substrate is known, the same operation as the operation of converting the observed crystal lattice on the surface of the lower substrate into the known lattice is performed on the lower substrate. It is possible to reconstruct an observation image without distortion by applying it to the observation image of the sample.

Further, in the recording and / or reproducing apparatus applying the principle of the scanning probe microscope, even when the crystal lattice of the lower substrate surface of the recording medium is used for positioning the probe at the time of recording or reproducing, Since the state of the recording medium can be detected and the recording or reproducing operation can be performed while observing both the crystal lattice and the image of the surface of the recording medium at the same time, accurate positioning can be performed even when there is a drift or the like. In addition to the crystal lattice, the lower layer substrate surface may be modified in advance so that it can be observed by STM, and the known modified shape may be observed for positioning.

[0020]

According to the present invention, when observing a sample surface by STM, it is possible to obtain two or more kinds of STM images at the same sample at different bias voltages of two or more. Further, even when the lower substrate surface and the sample on the substrate surface are observed with different bias voltages, the lower substrate surface of the lower substrate surface is irrespective of whether there is a change in the relative position of the probe with respect to the sample surface during the observation time. It has become possible to accurately obtain the relative positions of the atoms and the atoms in the sample on the surface.

Further, in the recording and / or reproducing apparatus applying the principle of the scanning probe microscope, even when the lower layer substrate of the recording medium is used for positioning the probe at the time of recording or reproducing, recording is performed while observing the surface of the lower layer substrate. Since the state of the medium can be detected, accurate positioning can be performed regardless of the presence or absence of drift or the like.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an STM according to a first embodiment of the present invention.

FIG. 2A is a diagram showing a bias voltage waveform during an STM operation in the first embodiment of the present invention. (B) (c): The figure which shows the timing signal of the output signal detection of a z direction drive circuit.

[Explanation of symbols]

 11 probe 12 sample 13 current detection circuit 14 voltage application circuit 15 timing circuit 21 logarithmic conversion circuit 22 comparator 23 low-pass filter 24, 25 sample / hold circuit 26 image forming device 31 z-direction drive circuit 32 z-direction fine movement device 33 xy-direction control Circuit 34 xy direction drive circuit 35 xy direction fine movement device

Front page continuation (72) Inventor Yoji Yano 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. A probe, a moving means for moving the probe along a sample surface, and a voltage applied between the probe and the sample to detect a current flowing between the probe and the sample surface. Then, in the scanning probe microscope having a control means for feedback-controlling the distance between the probe and the sample surface so as to keep the current constant, the control means is provided between the probe and the sample. It has a voltage applying means for applying an alternating voltage and a detecting means for detecting respective signals at a plurality of different phase points of the alternating voltage, and the alternating voltage is an alternating voltage with a frequency that the control means can follow. A scanning probe microscope characterized in that 2. The detection means controls a fine movement means for minutely changing the distance between the probe and the sample surface so as to keep the current flowing between the probe and the sample surface constant. The scanning probe microscope according to claim 1, wherein the scanning probe microscope is a detection unit that detects a control signal. 3. An apparatus for recording information on a recording medium and / or reproducing information from the recording medium via a probe, wherein a voltage is applied between the probe and the recording medium to provide the probe and the recording medium. Detecting a current flowing between the surface and the surface, and having a control means for controlling the distance between the probe and the recording medium surface so as to keep the current constant, the control means, the probe and the It has a voltage applying means for applying an alternating voltage to the medium, and a detecting means for detecting respective signals at a plurality of different phase points of the alternating voltage, and the alternating voltage can follow the control means. A recording device and / or a reproducing device characterized by being an alternating voltage of a frequency. 4. The fine movement means for changing the distance between the probe and the surface of the recording medium by a small amount so that the detection means maintains a constant current flowing between the probe and the surface of the recording medium. 4. The recording device and / or the reproducing device according to claim 3, wherein the recording device and / or the reproducing device are detection means for detecting a control signal for controlling.