JP3029504B2 - Scanning tunnel microscope and information recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning tunneling microscope and an information recording / reproducing apparatus.

[0002]

2. Description of the Related Art A scanning tunneling microscope (STM) is a device capable of detecting mixed information of a surface shape and an electronic state of a sample at a resolution of an electronic order by utilizing electron tunneling. The scanning tunnel microscope can be applied to an information recording / reproducing device and the like in addition to the use as a microscope.

The scanning tunneling microscope has the following four modes for obtaining an image (STM image) showing the surface shape and electronic state of a sample.

(1) Constant current mode This is a mode for obtaining a topograph of the surface of a sample. In this state, a predetermined bias voltage V is applied between the probe having a sharp tip and the sample. detecting a tunnel current J _t which occurs when the distance z between the surface within several nm, the feedback amount when the feedback control of the distance z to the tunnel current J _t is constant (topo signal T) Obtain a topograph of the surface of the sample using (G. Binn
ig et al., Phys. Rev. Lett., 49, 57, 1982).

(2) Variable current mode This is a mode for obtaining a topography of an almost flat surface of a sample having only irregularities of a primitive scale or less, and a predetermined current between a probe having a sharp tip and the surface of the sample. while applying a bias voltage V, and the distance z between the probe and the sample surface less than several nm, by detecting the tunnel current J _t which occurs when scanning the probe at a high speed, the tunnel Current J
The change in _t is converted to a change in distance to obtain a topograph of the almost flat sample surface. Note that the tunnel current J _t is
Since it changes exponentially with distance z, in practice,
Logarithm of the tunnel current J _t (current signal) log
Using (J _t ), a topograph of the almost flat sample surface is obtained.

[0006] (3) a barrier height mode (current distance differential mode) of the tunnel barrier height is a mode to obtain a primitive measure the sample plane distribution of the (work function), the tunnel current J _t in the constant current mode described above the distance z is varied performed a plurality of times, by differentiating the tunnel current J _t at distance z, obtaining a height sample plane distribution of the tunneling barrier in the primitive scale. Incidentally, the tunnel current J _t in order to vary exponentially with the distance z, in fact, a tunnel current logarithm of J _t (current signal) log (J _t) value obtained by differentiating at a distance z (Tunnel Using the barrier height signal) log (J _t ) / dz, the in-plane distribution of the tunnel barrier height is obtained on a primitive scale.

[0007] (4) a mode of obtaining a sample plane distribution of the density of states of differential conductance mode electrons and phonons primitive scale, multiple times by changing the bias voltage V a tunnel current J _t in the constant current mode described above Then, using the value (differential conductance signal) dJ _t / dV obtained by differentiating the tunnel current J _t with the bias voltage V, the distribution of states of states of electrons and phonons in the sample plane is obtained on a primitive scale.

FIG. 13 is a block diagram showing a first conventional example of a scanning tunneling microscope.

The scanning tunneling microscope 100 has a table 1
The probe 101 is driven at a high frequency in the direction perpendicular to the surface (the Z-axis direction
The probe 101 is scanned along the surface of the sample 1 while slightly moving
Interaction between probe 101 and sample 1 surface
Tunnel current J caused by _t (1)
And the current signal shown in (2) above.
No. log (J_t) And the tunnel barrier shown in (3) above
Height signal log (J_t) / Dz
(IBM, J. Res. Develop., 30, 355, 1986, or P
hys. Rev. Leyy., 60 (12), 1166, 1988)
Probe 101, probe fine movement control mechanism 102, bias voltage
Generation circuit 103, current-voltage conversion circuit 104, logarithmic circuit 105
 , Servo signal generation circuit 106, and Z modulation signal generation circuit 1
07, adder 108, amplifier 109, lock-in
Tunnel barrier height signal generation circuit 110
And

Here, the current-voltage conversion circuit 104 and the logarithmic circuit
105 refers to the interaction between tip 101 and the surface of sample 1.
Resulting tunnel current J_t Detect and detect
Tunnel current J_t Current signal log according to
(J_t). The probe fine movement control mechanism 102 is
The probe 101 is moved in the Z-axis direction. Servo signal generation circuit
106 is the current signal log (J_t)
When a servo signal S for driving the control mechanism 102 is generated,
Generates a topo signal T corresponding to the generated servo signal S.
You. The Z-modulation signal generation circuit 107 searches in the Z-axis direction shown in FIG.
Z modulation signal M for finely moving needle 101 at high frequency_z Generate
Together with the Z-modulated signal M_z Reference signal R according to _z Occurs
I do. The tunnel barrier height signal generation circuit 110
Event signal log (J_t) And the reference signal R_z And from the tunnel bar
Rear height signal log (J_t) / Dz.

Next, using the scanning tunneling microscope 100, the topo signal T and the tunnel barrier height signal log (J _t ) /
The operation of obtaining the topography of the surface of the sample 1 by simultaneously obtaining dz and dz and obtaining the in-plane distribution of the height of the tunnel barrier on the sample plane will be described.

After a predetermined bias voltage V is applied between the probe 101 and the surface of the sample 1 from the bias voltage generating circuit 103, the distance z between the probe 101 and the sample 1 is less than several nm. The probe is adjusted by the probe fine movement control mechanism 102
101 is moved in the Z-axis direction shown in FIG. At this time, the probe
101 and the tunnel current J _t flowing between the sample 1 surface is input to the current-voltage conversion circuit 104, the tunnel voltage V _t
Is converted to Tunnel voltage V _t is input to a logarithmic circuit 105, by its logarithm is obtained, the current signal log (J _t) are generated. Current signal log
(J _t ) is input to the servo signal generation circuit 106, and the current signal log (J _t ) (that is, the tunnel current J _t )
And a servo signal S for performing feedback control of the distance z so that
Is generated. Servo signal S is input to the adder 108, after being added to the generated Z modulation signal M _Z by Z modulation signal generating circuit 107, the amplifier 10
9 is converted to a Z-axis control signal C _Z and input to the probe fine movement control mechanism 102. Thus, the distance z to the tunnel current J _t becomes constant is feedback controlled, the distance z is changed according to the Z modulation signal M _Z.

Thereafter, a predetermined bias voltage V is applied to the probe 101.
The probe 101 is scanned by the probe fine movement control mechanism 102 in the X-axis direction shown in FIG. At this time, at each measurement point, the reference signal R _Z output from the Z modulation signal generation circuit 107 and the current signal log (J _t ) are compared with the tunnel barrier height signal generation circuit.
110 are input to, by differentiating components on the distance z of the current signal log (J _t) is detected, the tunnel barrier height signal log (J _t) / dz is generated.

As a result, a topograph of the surface of the sample 1 can be obtained based on the topographic signal T generated by the servo signal generating circuit 106, and the tunnel barrier height signal log generated by the tunnel barrier height signal generating circuit 110 can be obtained. Based on (J _t ) / dz, the in-plane distribution of the height of the tunnel barrier can be obtained on a primitive scale.

Next, the current signal log (J _t ) and the tunnel barrier height signal log (J _t ) / dz are simultaneously obtained by using the scanning tunneling microscope 100, and an almost flat topography of the surface of the sample 1 is obtained. At the same time, the operation of obtaining the in-plane distribution of the height of the tunnel barrier on a primitive scale will be described.

After a predetermined bias voltage V is applied between the probe 101 and the surface of the sample 1 from the bias voltage generating circuit 103, the distance z between the probe 101 and the surface of the sample 1 becomes several n.
The probe 101 is moved by the probe fine movement control mechanism 102 in the Z-axis direction shown in FIG. At this time, a tunnel current J _t flowing between the probe 101 and the sample 1 is obtained.
Is input to the current-voltage conversion circuit 104, and the tunnel voltage V
Converted to _t . Tunnel voltage V _t is input to a logarithmic circuit 105, by its logarithm is obtained, the current signal log (J _t) are generated. Current signal lo
g (J _t ) is input to the servo signal generation circuit 106. In this case, since the distance z is not feedback-controlled,
The servo signal S output from the servo signal generation circuit 106 is kept at a predetermined value. Servo signal S is input to the adder 108, after being added to the generated Z modulation signal M _Z by Z modulation signal generating circuit 107, the amplifier 10
9 is converted to a Z-axis control signal C _Z and input to the probe fine movement control mechanism 102. This gives the distance z
Is changed only according to the Z modulation signal M _Z.

Thereafter, a predetermined bias voltage V is applied to the probe 101.
The probe 101 is scanned by the probe fine movement control mechanism 102 in the X-axis direction shown in FIG. At this time, at each measurement point, the reference signal R _Z output from the Z modulation signal generation circuit 107 and the current signal log (J _t ) are compared with the tunnel barrier height signal generation circuit.
110 are input to, by differentiating components on the distance z of the current signal log (J _t) is detected, the tunnel barrier height signal log (J _t) / dz is generated.

As a result, based on the current signal log (J _t ) generated by the logarithmic circuit 105, an almost flat topography of the surface of the sample 1 can be obtained, and the topography of the tunnel barrier height signal generating circuit 110 can be obtained. Based on the obtained tunnel barrier height signal log (J _t ) / dz, the distribution of the height of the tunnel barrier in the sample plane can be obtained on a primitive scale.

FIG. 14 is a block diagram showing a second conventional example of a scanning tunneling microscope.

The scanning tunneling microscope 200 has a tunneling current J caused by an interaction between the probe 201 and the surface of the sample 1 when the probe 201 is scanned along the surface of the sample 1.
_t is detected, and the topo signal T shown in the above (1), the current signal log (J _t ) shown in the above (2), and the differential conductance signal dJ _t / dV shown in the above (4) are obtained. (IBM, J. Res. Develop., 30,
355, 1986), a sharpened probe 201, a probe fine movement control mechanism 202, a bias voltage generation circuit 203, a current-voltage conversion circuit 204, a logarithmic circuit 205, and a servo signal generation circuit 206.
, An amplifier 207, a bias modulation signal generation circuit 208,
An adder 209 and a differential conductance signal generation circuit 210 including a lock-in amplifier and the like are included.

Here, the current-voltage conversion circuit 204 and the logarithmic circuit
205 and is configured to detect the tunnel current J _t caused by the interaction between the probe 201 and the sample 1 surface, the current signal log corresponding to the detected tunnel current J _t
(J _t ). The probe fine movement control mechanism 202 moves the probe 201 in a direction perpendicular to the surface of the sample 1 (the Z-axis direction in the figure). The servo signal generation circuit 206 outputs the current signal lo
A servo signal S for driving the probe fine movement control mechanism 202 is generated according to g (J _t ), and a top signal T corresponding to the generated servo signal S is generated. Bias voltage generation circuit 20
3 generates a bias voltage V applied between the probe 201 and the surface of the sample 1. Bias modulation signal generation circuit 208
Generates a bias modulation signal M _V that slightly changes the bias voltage V at a high frequency, and generates a bias modulation signal M _V
The reference signal R _V generated in accordance with the _V. The differential conductance signal generation circuit 210 calculates the tunnel current _Jt and the reference signal R
_A differential conductance signal dJ _t / dV is generated from _V and _V.

Next, the topological signal T and the differential conductance signal dJ _t / dV are simultaneously obtained by using the scanning tunneling microscope 200 to obtain the topograph of the surface of the sample 1 and the sample surface of the density of states of electrons and phonons. The operation when obtaining the inner distribution on a primitive scale will be described.

The predetermined bias voltage V output from the bias voltage generation circuit 203 is input to an adder 209 and added to the bias modulation signal M _V generated by the bias modulation signal generation circuit 208 to obtain a bias. It is converted into a control signal C _V. The bias control signal C _V is applied to the probe 201
Between the probe 20 and the surface of the sample 1,
The bias voltage applied between 1 and the surface of sample 1 is
It is changed in accordance with the bias modulation signal M _V. In this state, the probe 201 is moved by the probe fine movement control mechanism 202 in the Z-axis direction shown in the figure so that the distance z between the probe 201 and the surface of the sample 1 becomes a predetermined value of several nm or less. . At this time, the tunnel current J _t flowing between the probe 201 and the sample 1 is input to the current-voltage conversion circuit 204, is converted into the tunnel voltage V _t. Tunnel voltage V _t is input to a logarithmic circuit 205, by its logarithm is obtained, the current signal log (J _t) are generated. Current signal log
(J _t ) is input to the servo signal generation circuit 206 and the current signal log (J _t ) (that is, the tunnel current J _t )
And a servo signal S for performing feedback control of the distance z so that
Is generated. After the servo signal S is amplified by the amplifier 207, the probe fine movement control mechanism 202
Is input to Thus, the distance z is feedback-controlled so that the tunnel current _Jt is constant.

Thereafter, the bias control signal C _V is applied to the probe 201
In the state applied between the probe and the sample 1, the fine movement control mechanism
The probe 201 is scanned in the X-axis direction shown in FIG.
At this time, the reference signal R _V and the current signal log (J _t ) output from the bias modulation signal generation circuit 208 are input to the differential conductance signal generation circuit 210, respectively, and are related to the bias voltage V of the current signal log (J _t ). by differentiating component is detected, differential conductance signal dJ _t / dV is generated.

As a result, at each measurement point, a topograph of the surface of the sample 1 can be obtained based on the topographic signal T generated by the servo signal generating circuit 206, and the differential generated by the differential conductance signal generating circuit 210 can be obtained. samples plane distribution of the density of states of electrons and phonons can be obtained by primitive measure based on the conductance signal dJ _t / dV.

Next, using a scanning tunneling microscope 200, the current signal log (J _t ) and the differential conductance signal d
The operation when J _t / dV is obtained at the same time to obtain a topography of the almost flat surface of the sample 1 and the in-plane distribution of the state density of electrons and phonons on the sample plane will be described.

The predetermined bias voltage V output from the bias voltage generation circuit 203 is input to an adder 209, and is added to the bias modulation signal M _V generated by the bias modulation signal generation circuit 208, so that a bias is generated. It is converted into a control signal C _V. The bias control signal C _V is applied to the probe 201
Between the probe 20 and the surface of the sample 1,
The bias voltage applied between 1 and the surface of sample 1 is
It is changed in accordance with the bias modulation signal M _V. In this state, the probe 201 is moved by the probe fine movement control mechanism 202 in the Z-axis direction shown in the figure so that the distance z between the probe 201 and the surface of the sample 1 becomes a predetermined value of several nm or less. . At this time, a tunnel current J _t flowing between the probe 201 and the surface of the sample 1 is obtained.
Is input to the current-voltage conversion circuit 204, and the tunnel voltage V
Converted to _t . Tunnel voltage V _t is input to a logarithmic circuit 205, by its logarithm is obtained, the current signal log (J _t) are generated. Current signal lo
g (J _t ) is input to the servo signal generation circuit 206. In this case, since the distance z is not feedback-controlled,
The servo signal S output from the servo signal generation circuit 206 is kept at a predetermined value. After the servo signal S is amplified by the amplifier 207, the probe fine movement control mechanism 202
Is input to

Thereafter, the bias control signal C _V is applied to the probe 201
In the state applied between the probe and the sample 1, the fine movement control mechanism
The probe 201 is scanned in the illustrated X-axis direction by 202. At this time, at each measurement point, the reference signal R _V output from the bias modulation signal generation circuit 208 and the current signal l
og (J _t ) is input to the differential conductance signal generation circuit 210, and a differential component of the current signal log (J _t ) with respect to the bias voltage V is detected, thereby generating a differential conductance signal dJ _t / dV. .

As a result, based on the current signal log (J _t ) generated by the logarithmic circuit 105, an almost flat topograph of the surface of the sample 1 can be obtained, and the differential conductance signal generated by the differential conductance signal generating circuit 210 can be obtained. Based on the differential conductance signal dJ _t / dV, the distribution of states of states of electrons and phonons in a sample plane can be obtained on a primitive scale.

[0030]

However, the above-mentioned conventional scanning tunneling microscope has the following problems.

(1) Problems in the Scanning Tunneling Microscope 100 shown in FIG. 13 The tunnel current J _t is determined by the fact that the distance z between the probe 101 and the surface of the sample 1 changes, It changes even when there is a change in state, and the current signal log (J _t )
And the tunnel barrier height signal log (J _t ) / dz cannot be measured accurately, so that for a sample having an unequal electronic state, the topography of the almost uneven sample surface and the in-plane distribution of the height of the tunnel barrier There is a problem that cannot be obtained accurately.

In order to accurately obtain the in-plane distribution of the topography and the height of the tunnel barrier on the surface of an almost non-planar sample with respect to the sample having unequal electronic states, each measurement point on the surface of the sample is required. for the current signal log (J _t) and the tunnel barrier height signal log (J _t) / dz distance z dependence on whether the measurement respectively, or for a plurality of setting conditions for the distance z, the current signal log (J _t ) And the tunnel barrier height signal log (J _t ) / dz need to be measured.

However, in the scanning tunneling microscope 100,
To measure the dependence of the current signal log (J _t ) and the tunnel barrier height signal log (J _t ) / dz on the distance z, a plurality of surface scans of the probe 101 (scan in the X-axis direction shown in FIG. 13) (Scanning in the Y-axis direction in the figure), which requires a lot of time. on the other hand,
Current signal l for a plurality of setting conditions for distance z
og (J _t ) and the tunnel barrier height signal log
When each (J _t ) / dz is measured, a finite time difference determined by the scanning speed of the probe 101 occurs between the measurements under each set condition, so that the position shift of several atoms order or more due to drift and Due to changes in surface conditions, etc.
There is a problem that comparison in a strict sense is difficult.

Furthermore, the current signal log (J _t) and the tunnel barrier with respect to the height signal log (J _t) / dz distance dependence of the measurement of artificially current signal log (J _t) and the tunnel barrier at each measurement point height signal log (J _t) / scanning tunneling microscope 300 which continuously acquires distance dependence of dz has been proposed (Japanese Patent Laid-Open No. 3-43944). As shown in FIG. 15, the scanning tunneling microscope 300 includes a logarithmic circuit 105, a Z modulation signal generation circuit 107, and a tunnel barrier height signal generation circuit.
Instead of 110, an arithmetic circuit 305 and a Z displacement signal generation circuit
307 is different from the scanning tunneling microscope 100 shown in FIG.

Here, the Z displacement signal generation circuit 307 is the same as that shown in FIG.
(5) The probe 301 is moved in the Z-axis direction shown in the figure at a period much shorter than the scanning period in the X-axis direction shown in the figure, and the distance z between the probe 301 and the surface of the sample 1 is forcibly displaced. A Z displacement signal ΔZ is generated. The Z displacement signal ΔZ is calculated by adding the servo signal S generated by the servo signal generation circuit 306 and the adder
308 is added. The arithmetic circuit 305 is configured to generate a current signal log (J _T) by performing in real time a predetermined analog calculation using the tunnel voltage V _T sent from the current-voltage conversion circuit 304, a current signal l
The tunnel barrier height signal dlog (J _T ) / dz is generated by performing a predetermined analog operation in real time using og (J _T ) and the Z displacement signal ΔZ. Incidentally, the tunnel voltage V _T and Z displacement signal ΔZ is generally input to the arithmetic circuit 305 via a low-pass filter.

In such a scanning tunneling microscope 300, the distance z is displaced at a period much shorter than the scanning period of the probe 301 in the X-axis direction shown in the figure, and the current signal log (J _t ) and the tunnel barrier height signal log
By calculating (J _t ) / dz in real time, the current signal log at each measurement point is simulated.
(J _t ) and the tunnel barrier height signal log (J _t ) /
Although the distance dependency of dz can be continuously obtained, the circuit scale of the arithmetic circuit 305 must be increased.
Also, in such a direct current (DC) detection method, there is a limit to the removal of high-frequency noise existing near the signal band by the low-pass filter. There is a problem that cannot be avoided.

(2) Problems in Scanning Tunneling Microscope 200 shown in FIG. 14 In general, in a scanning tunneling microscope, a specific energy order is changed by changing a bias voltage applied between a probe and the surface of a sample. It is known that the electronic structure in can be detected selectively. For example,
Set the tunnel current J _T to 50mV bias voltage conditions fixed in 100 pA, when observing the sample with liquid crystal molecules aligned on a graphite substrate, an image that reflects the electronic structure of the graphite substrate was observed, also and by setting the bias voltage to 1V at the conditions of fixing the tunnel current J _T in 100pA to observe the sample, an image that reflects the arrangement of liquid crystal molecules is observed. Observations with such different bias voltages can be performed alternately,
Further, the arrangement of the liquid crystal molecules is not destroyed by the observation of the graphite substrate. Therefore, if the two images can be compared, the relative positional relationship between each liquid crystal molecule and the lattice of the graphite substrate can be known, and important information on the adsorption state can be obtained.

Further, the differential conductance signal dJ _t / d
It is known that V is reflected on the electronic density of states at the energy level determined by the bias voltage.
Therefore, by obtaining the differential conductance signal dJ _t / dV for a plurality of bias voltages, the energy spectrum structure of the electronic state density can be obtained.

However, in the scanning tunneling microscope 200 shown in FIG. 14, in order to measure the differential conductance signal dJ _t / dV for a plurality of bias voltages, a probe is required.
A plurality of surface scans 201 (scanning in the X-axis direction in the drawing and scanning in the Y-axis direction in the drawing) are required, and there is a problem that much time is required. When the differential conductance signal dJ _t / dV is measured for a plurality of bias voltages, a finite time difference determined by the scanning speed of the probe 201 occurs between measurements at each bias voltage. There is a problem that it is difficult to compare in a strict sense due to the occurrence of a positional shift of more than the atomic order and a change in the surface state.

In order to solve this problem, a scanning tunneling microscope capable of measuring a differential conductance signal dJ _t / dV by changing a bias voltage by one scanning of a probe is described below. Tunneling microscopes have been proposed.

[0041] (a) while changing the bias voltage at a much greater frequency than the scanning frequency of the probe by measuring the tunnel current J _t, respectively records the bias voltage and the tunnel current signal J _t at each measurement point , then tunneling current differential value relating to a bias voltage of J _t numerically computed by the computing circuit, pseudo scanning tunneling microscope for measuring the differential conductance signal dJ _t / dV for a plurality of bias voltages at each measurement point.

(B) The differential conductance signal dJ _t / dV is input to the arithmetic circuit by inputting the measured tunnel current _Jt and the bias voltage while changing the bias voltage at a frequency much higher than the scanning frequency of the probe. and analog operation in real time, quasi-scanning tunneling microscope for measuring the differential conductance signal dJ _t / dV for a plurality of bias voltages at each measurement point.

FIG. 16 is a block diagram showing a conventional example of the scanning tunnel microscope shown in FIG.

The scanning tunnel microscope 400 has a logarithmic circuit 20.
14 is different from the scanning tunneling microscope 200 shown in FIG. 14 in that an arithmetic circuit 405 and a bias change signal generating circuit 408 are included instead of 5, the bias modulation signal generating circuit 208, and the differential conductance signal generating circuit 210. Here, the bias change signal generation circuit 408 generates a bias voltage applied between the probe 401 and the surface of the sample 1 at a cycle much shorter than the scanning cycle of the probe 401 in the X-axis direction shown in the figure. A bias change signal ΔV that is forcibly changed is generated. In addition,
The bias change signal ΔV is added to a predetermined bias voltage V generated by the bias voltage generation circuit 403 by an adder 409, and converted into a bias control signal C _V. The arithmetic circuit 405 is configured to generate a current signal log (J _T) by performing in real time a predetermined analog calculation using the tunnel voltage V _T sent from the current-voltage conversion circuit 304, the tunnel voltage V _T and bias change signal ΔV
To perform a predetermined analog operation in real time to generate a differential conductance signal dJ _t / dV. Note that the tunnel voltage V _T and the bias change signal ΔV are
Generally, they are input to the arithmetic circuit 405 via a low-pass filter.

However, in each of the scanning tunneling microscopes shown in the above (a) and (b), the scale of the arithmetic circuit must be large, and such a direct current (D)
In the C-type detection method, there is a limit in removing high-frequency side noise existing in the vicinity of the signal band, and this residual noise cannot avoid serious influence on numerical and analog operations in an arithmetic circuit. There is.

An object of the present invention is to provide a scanning tunneling microscope and an information recording / reproducing apparatus which can easily obtain the distance dependence of the tunnel barrier height signal and the current signal or the bias voltage dependence of the differential conductance signal and the current signal. Is to do.

[0047]

SUMMARY OF THE INVENTION A scanning tunneling microscope according to the present invention detects a tunnel current caused by an interaction between a probe and the surface of a sample when the probe is scanned along the surface of the sample. The current signal , the topo signal and the tunnel
In a scanning tunneling microscope that respectively obtains a barrier height signal , a circuit that generates a reference clock and a frequency higher than a frequency that causes the probe to scan along the surface of the sample in synchronization with the reference clock, A probe moving means for forcibly moving the probe in the vertical direction, based on the reference clock, having a frequency higher than a frequency for scanning the probe along the surface of the sample, and having different phases from each other; A timing signal generating circuit for generating a plurality of timing signals; and a time-division sampling circuit for sampling the current signal by each of the timing signals, respectively.
Modulation signal generation that generates a modulation signal with a frequency higher than the number
A raw circuit, and perpendicular to the surface of the sample based on the modulation signal.
The probe perpendicular to the surface of the sample
Means for finely moving at a high frequency; and
The tunnel barrier height signal from the current signal
And a generating circuit .

[0048]

In the above case, the timing signal generation circuit
However, the other timing signals are synchronized with the reference clock.
Occur in synchronization with different phases,
The tunneling circuit by each other timing signal.
Be sure to sample each barrier height signal
You may .

Alternatively, the scanning tunneling microscope of the present invention applies a bias voltage between the sample and the probe,
When the probe is scanned along the surface of the sample, the tunnel current generated by the interaction between the probe and the surface of the sample is detected, and the current signal , the topo signal, and the differential conductor are detected .
In scanning tunneling microscope to obtain scan signals, respectively,
A circuit for generating a reference clock, bias voltage changing means for forcibly changing the bias voltage at a frequency higher than a frequency for scanning the probe along the surface of the sample in synchronization with the reference clock, and A timing signal generating circuit for generating a plurality of timing signals having a frequency higher than a frequency for scanning the probe along the surface of the sample based on a reference clock and having different phases from each other; A time-division sampling circuit for sampling each of the current signals ;
From the bias voltage change by the bias voltage changing means.
Signal generation circuit that generates a modulation signal with a large frequency
And a bias voltage changing means based on the modulation signal.
High-frequency bias voltage superimposed on changes in bias voltage
Means for minutely modulating the current with the
A current-to-voltage conversion circuit for converting the voltage to a voltage;
Differential conductance from the tunnel voltage as the illumination signal
And a circuit for generating a signal .

[0051]

In the above case, the timing signal generating circuit
However, the other timing signals are synchronized with the reference clock.
Occur in synchronization with different phases,
A differentiating timing signal by the other timing signals.
Sample each of the conductance signals
Is also good .

The information recording / reproducing apparatus according to the present invention detects a tunnel current generated by an interaction between the probe and the surface of the sample when the probe is scanned along the surface of the sample, and detects a current signal , In an information recording / reproducing apparatus that obtains a topo signal and a tunnel barrier height signal , respectively, and reads information recorded on the surface of the sample, a circuit that generates a reference clock; A probe moving means for forcibly moving the probe in a direction perpendicular to the surface of the sample at a frequency higher than the frequency at which the probe is scanned along the surface of the sample, and the probe based on the reference clock. A timing signal generating circuit having a frequency higher than the frequency to be scanned along the surface of the sample and having different phases from each other, generating a plurality of timing signals; Ri said division sampling circuit when each sample the current signal, the probe moving means
Modulation signal with a frequency higher than the probe's moving frequency
A modulation signal generating circuit that generates
Test the probe superimposed on the vertical movement with the surface of the sample.
Means for finely moving at a high frequency in a direction perpendicular to the surface of the material,
Tunneling from the current signal using the modulated signal as a reference signal
And a circuit for generating a barrier height signal .

[0054]

In the above case, the timing signal generation circuit
However, the other timing signals are synchronized with the reference clock.
Occur in synchronization with different phases,
The tunneling circuit by each other timing signal.
Be sure to sample each barrier height signal
You may .

Alternatively, the information recording / reproducing apparatus according to the present invention may be configured such that when a probe is scanned along a surface of a sample while applying a bias voltage between the sample and the probe, the probe and the surface of the sample can be moved. Detecting the tunnel current caused by the interaction between
A current signal , a topo signal, and a differential conductance signal , respectively, in an information recording and reproducing apparatus for reading information recorded on the surface of the sample, a circuit for generating a reference clock, and a circuit for synchronizing with the reference clock. Bias voltage changing means for forcibly changing the bias voltage at a frequency higher than the frequency at which the probe is scanned along the surface of the sample, and the probe is moved along the surface of the sample based on the reference clock. It has a frequency greater than the frequency of scanning Te, mutually different phases, a timing signal generating circuit for generating a plurality of timing signals, a dividing sampling circuit when the respectively sampling the current signal by the timing signal, the bias Voltage change
Means that the change in frequency is greater than the change in bias voltage.
A modulation signal generating circuit for generating a modulation signal;
Of bias voltage by bias voltage changing means
To modulate the bias voltage minutely with high frequency by superimposing
A stage and a current for converting said tunnel current to a tunnel voltage
A voltage conversion circuit, and using the modulation signal as a reference signal and
A circuit that generates a differential conductance signal from the channel voltage
And a road .

[0057]

In the above case, the timing signal generating circuit
However, the other timing signals are synchronized with the reference clock.
Occur in synchronization with different phases,
A differentiating timing signal by the other timing signals.
Sample each of the conductance signals
Is also good .

[0059]

The scanning tunnel microscope and the information recording / reproducing apparatus of the present invention operate as follows.

According to the present invention, the probe is moved by the probe moving means at a frequency higher than the frequency scanned along the surface of the sample.
At a high frequency and forcefully move it perpendicular to the sample surface.
Can be As a result, at each measurement point,
The distance to the surface of the material changes. At this time, the current
The signal is sampled by the time-division sampling
Has a higher frequency than the frequency that is scanned along the surface
And multiple timing signals with different phases.
Since each is sampled, each measurement point
Current signal sampled by each timing signal
Each correspond to a different distance between the tip and the surface of the sample.
Will do. Therefore, scan the tip once.
At each measurement point, the probe and the surface of the sample
Can obtain current signals for different distances between
You.

The probe movement is superimposed on the movement of the probe by the probe moving means.
When the probe is moved finely at high frequency,
At a fixed point, the distance between the tip and the surface of the sample is
Frequency that changes and is greater than the tip's travel frequency.
Number of modulated signals as reference signals and
To generate a barrier height signal.
, For different distances between the tip and the surface of the sample
Determines the dependence of the Nelbarrier height signal for each measurement point
Can be Therefore, the surface is scanned once with the probe
Just at each measurement point, the probe and the surface of the sample
Tunnel barrier height signal for different distances between
Obtainable.

According to the present invention, the bias voltage is
Use the bias voltage changing means to move the probe along the sample surface.
Forcibly changes at a frequency higher than the scanning frequency
Let me do. As a result, at each measurement point,
The bias voltage applied between the sample and the surface of the sample changes.
You. At this time, the current signal is
The frequency at which the step causes the tip to scan along the surface of the sample
Have different frequencies,
Number of timing signals each sampled
Sample at each timing signal at each measurement point.
The ringed current signals are the tip and sample
For different bias voltages applied to the surface
Becomes Therefore, each time the probe is scanned once,
Applied between the probe and the surface of the sample at the measurement point
Obtain current signals for different bias voltages
be able to.

Bias by the bias voltage changing means
Superimpose bias voltage at high frequency by superimposing on voltage change
In the case of modulation, the search is performed at each measurement point.
When the voltage applied between the needle and the surface of the sample changes
The modulation signal at a frequency greater than the bias voltage change
Differential signal from tunnel voltage using signal as reference signal
The probe and sample.
Small change in bias voltage applied to the surface
The dependence of the minute conductance signal is determined for each measurement point.
Can be Therefore, the surface is scanned once with the probe
Just at each measurement point, the probe and the surface of the sample
For different bias voltages applied during
A conductance signal can be obtained .

[0064]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a first embodiment of the scanning tunneling microscope of the present invention.

The scanning tunnel microscope 10 moves the probe 11 along the surface of the sample 1 along the surface of the sample 1 while finely moving the probe 11 at a high frequency in the direction perpendicular to the surface of the sample 1 (the Z-axis direction in the diagram). by detecting the tunnel current J _t caused by the interaction between the probe 11 and the sample 1 surface when brought into scanning in the axial direction, the current signal log (J _t), topo signals T and the tunnel barrier height signal log (J _t ) / dz is obtained, and differs from the conventional scanning tunneling microscope 100 shown in FIG. 13 in the following points.

(1) At a frequency higher than the frequency for scanning the probe 11 along the surface of the sample 1 in the X-axis direction shown in the figure and smaller than the frequency for finely moving the probe 11 in the Z-axis direction shown in the figure. A reference clock generating circuit 21 and a Z displacement signal generating circuit 22 are included as probe moving means for forcibly moving the probe 11 in the Z-axis direction shown in FIG.

(2) A frequency higher than the frequency at which the probe 11 is scanned along the surface of the sample 1 in the X-axis direction shown in FIG. A plurality of timing signals having different phases (first to third tunnel barrier height timing signals TB _{1 to} TB ₃ and a servo timing signal ST)
Includes a reference clock generation circuit 21 and a timing signal generation circuit 24.

[0069] The (3) as a split sampling means when the first to third tunnel barrier height timing signal TB ₁ ～TB ₃ samples the tunnel barrier height signal log (J _t) / dz respectively, time division sampling circuit 25 Including.

Here, the reference clock generation circuit 21 has a frequency higher than the frequency for scanning the probe 11 along the surface of the sample 1 in the X-axis direction shown in FIG. generating a reference clock RC having a frequency smaller than the frequency of the Z modulation signal M _Z. The Z displacement signal generation circuit 22 generates a Z displacement signal ΔZ in synchronization with the reference clock RC. The Z displacement signal ΔZ is added by the adder 23 to the servo signal S generated by the servo signal generation circuit 16 and the modulation signal M _Z generated by the Z modulation signal Z generation circuit 17. Timing signal generation circuit 2
4 generates first to third tunnel barrier height timing signals TB _{1 to} TB ₃ and a servo timing signal ST in synchronization with mutually different phases of the reference clock RC. The time-division sampling circuit 25 also samples the current signal log ( _Jt ) based on the servo timing signal ST.

Next, the operation of the scanning tunneling microscope 10 will be described with reference to the timing chart shown in FIG. 2 and the timing chart shown in FIG. 3, respectively.

[0072] In scanning tunneling microscope 10, topo signals T and current signal log (J _t) between the tunnel barrier height signal log (J _t) / dz and is 2 pixels shown in (A) S ₁ ~S ₈ By measuring in units, an image showing the topography of the surface of the sample 1 and an image showing the distribution of the height of the tunnel barrier in the sample plane on a primitive scale are obtained.
Accordingly, the distance between the pixels S _{1 to} S ₈ in the horizontal direction in FIG. 1A corresponds to the scanning time for the probe 11 to scan along the surface of the sample 1 in the X-axis direction in FIG.

[0073] When the measurement is started, Z modulation signal M _Z is Z
It is continuously generated by the modulation signal generation circuit 17. Here, the Z-modulated signal M _Z is perpendicular to the surface of the sample 1 (FIG. 1).
This is for finely moving the probe 11 at a high frequency (in the illustrated Z-axis direction), and its amplitude is set to 0.001 to 0.3 nm, and its waveform is a sine wave. The waveform of the Z modulation signal M _Z are step-wave, or a combination of the sawtooth or these waveforms.

When the measurement is started, the reference clock RC is continuously generated by the reference clock generation circuit 21. The reference clock RC is input to the Z displacement signal generation circuit 22, and the Z displacement signal ΔZ is generated by the Z displacement signal generation circuit 22 in synchronization with the reference clock RC. Here, the frequency of the reference clock RC is set higher than the frequency (reciprocal of the scanning time) for scanning the probe 11 along the surface of the sample 1 in the X-axis direction shown in FIG. At 22, a Z displacement signal ΔZ having a period equal to the scanning time can be generated. In addition,
The period of the Z displacement signal ΔZ is not necessarily required to be equal to the scanning time, but it is necessary to be equal to or shorter than the scanning time. The amplitude of the Z displacement signal ΔZ is not particularly limited, but is typically set to 0.1 to 3 nm. Further, the waveform of the Z displacement signal ΔZ is not particularly limited and is a sawtooth wave in the present embodiment, but may be a sine wave, a step wave, or a combination of these waveforms.

The reference clock RC generated by the reference clock generation circuit 21 is also input to the timing signal generation circuit 24, where the first to third tunnel barrier height timing signals TB _{1 to} TB ₃ and the servo timing signal ST are output. 2 (C) to 2 (F), the timing signals are generated by the timing signal generation circuit 24 in synchronization with mutually different phases of the reference clock RC.

When the measurement is started, after a predetermined bias voltage V is applied between the probe 11 and the surface of the sample 1 from the bias voltage generating circuit 13, the bias voltage V is applied between the probe 11 and the surface of the sample 1. The probe 11 is moved in the Z-axis direction shown in FIG. 1 by the probe fine movement control mechanism 12 so that the distance z becomes a predetermined value of several nm or less. At this time, the tunnel current J _t flowing between the probe 11 and the sample 1 surface is input to the current-voltage conversion circuit 14, is converted to the tunnel voltage V _t. Tunnel voltage V _t is input to a logarithmic circuit 15, by which the logarithm is determined, the current signal log (J _t) are generated. The current signal log (J _t ) is input to the time-division sampling circuit 25 and the servo timing signal S
By being sampled by T, it is converted into a first sampling current signal log (J _tm ). The first sampling current signal log (J _tm ) is input to the servo signal generation circuit 16, and the servo signal S for feedback controlling the distance z so that the first sampling current signal log (J _tm ) becomes constant. Is generated, and a top signal T corresponding to the servo signal S is generated. FIG. 2G shows an example of the servo signal S thus obtained.

[0077] The servo signal S is input to the adder 23, is added to the Z displacement signal ΔZ generated by Z modulation signal M _Z and Z displacement signal generating circuit 22 which is generated by the Z modulation signal generation circuit 17 Thereafter, the signal is amplified by the amplifier 19, converted into a Z-axis control signal C _Z , and input to the probe fine movement control mechanism 12. Thus, the distance z is feedback controlled so tunneling current J _t at the timing of the servo timing signal ST is constant, at the same time, the probe 11, a high frequency in Figure 1 the Z-axis direction by the Z modulation signal M _Z And the Z displacement signal ΔZ
Is forcibly moved in the Z-axis direction shown in FIG.

Thereafter, a predetermined bias voltage V is applied to the probe 11.
The probe 11 is scanned along the surface of the sample 1 in the X-axis direction shown in FIG. 1 by a probe scanning mechanism (not shown) with the voltage applied between the probe 1 and the surface of the sample 1. In this case, after the tunnel current J _t is converted by the current-voltage conversion circuit 14 to the tunnel voltage V _t, a logarithmic circuit 15 a current signal log (J _t)
Is converted to The current signal log (J _t ) is input to the time division sampling circuit 25 and the tunnel barrier height signal generation circuit 20. In the tunnel barrier height signal generation circuit 20, the current signal l ( _{Z t} ) and the reference signal R _Z (for example, a synchronization signal of the Z modulation signal M _Z ) sent from the Z modulation signal generation circuit 17 are used.
By detecting a differential component of distance og (J _t ) with respect to distance z, tunnel barrier height signal log (J _t ) / dz is detected.
Is generated. FIG. 3A shows an example of the tunnel barrier height signal log (J _t ) / dz generated by the tunnel barrier height signal generation circuit 20 in this manner.

Tunnel barrier height signal log (J _t ) /
dz is input to the time-division sampling circuit 25, and the first to third tunnel barrier height timing signals TB
_{1 to} TB ₃ , the first sampling tunnel barrier height signal lo
g ( _Jt1 ) / dz, the second sampling tunnel barrier height signal log ( _Jt2 ) / dz, and the third sampling tunnel barrier height signal log ( _Jt3 ) / dz, respectively (FIG. 3B). To (D)). as a result,
The first to third sampling tunnel barrier height signal _{log (J t1) / dz~log (} J t3) / dz than, 3
As shown in (E), the tunnel barrier height signal log (J _t ) with respect to the distance z between the probe 11 and the surface of the sample 1.
The dependency of / dz can be determined for each measurement point (corresponding to each pixel S _{1 to} S ₈ ).

Therefore, the scanning tunneling microscope 10 can measure the dependence of the tunnel barrier height signal log (J _t ) / dz on the distance z only by scanning the probe 11 only once.

In the above description, the first current signal lo
g (J _tm ) generates servo signal S, but logarithmic circuit 1
5, a signal obtained by averaging the current signal log (J _t ) output from the low-pass filter having a cut-off frequency much smaller than the frequency of the Z displacement signal ΔZ is input to the servo signal generation circuit 16. May occur. The frequency of the Z displacement signal ΔZ is set smaller than the mechanical resonance frequency of the probe fine movement control mechanism 12 and smaller than the cutoff frequency of the low-pass filter used in the current-voltage conversion circuit 14 and the logarithmic circuit 15. Is set.

Further, by forming the tunnel barrier height signal generation circuit 20 with a lock-in amplifier or the like, only the modulation component of the current signal log (J _t ) responsive to the Z modulation signal M _Z is synchronously detected in an AC manner. by, it may be obtained a signal proportional to the square root of the tunnel barrier height signal log (J _t) / dz as a differential component of the distance z of the current signal log (J _t) with a high S / N ratio.

Further, when the frequency of the scanning of the probe 11 in the X-axis direction shown in FIG. 1 is 1 Hz, when the frequency of the Z displacement signal ΔZ is set to 100 to 500 Hz, the measuring point becomes 100 to 500 per scanning line. Become. At this time, the frequency of the Z modulation signal M _Z is desirably set to about one to several 10 kHz. Note that the frequency of the Z modulation signal M _Z is set to be lower than the mechanical resonance frequency of the probe fine movement drive mechanism 12 and is lower than the cut-off frequency of the low-pass filter used in the current-voltage conversion circuit 14 and the logarithmic circuit 15. When the mechanical resonance frequency of the probe fine movement drive mechanism 12 is required to be several tens kHz or more, the bimorph type piezoelectric thin film structure formed on a silicon substrate or the like by the micromechanics technique is used for the fine movement control mechanism. A micro cantilever or the like can be used.

FIG. 4 is a schematic structural view showing a first reference example of the scanning tunneling microscope of the present invention.

The scanning tunnel microscope 30 scans the tunnel 31 along the surface of the sample 1 in the X-axis direction as shown in the figure, and generates a tunnel caused by the interaction between the probe 31 and the surface of the sample 1. The current _Jt is detected and the current signal log
(J _t ) and a topo signal T, respectively, which are different from the conventional scanning tunneling microscope 100 shown in FIG. 13 in the following points.

(1) The probe is scanned in the direction perpendicular to the surface of the sample 1 (Z-axis direction in the figure) at a frequency higher than the frequency at which the probe 31 is scanned along the surface of the sample 1 in the X-axis direction in the figure. The probe moving means for forcibly moving the needle 31 includes a reference clock generation circuit 41 and a Z displacement signal generation circuit 42.

(2) A plurality of timing signals (first and second signals) having a frequency higher than the frequency at which the probe 31 is scanned along the surface of the sample 1 in the X-axis direction shown in FIG. Tunnel current timing signal T
T ₁ , TT ₂ and a servo timing signal ST) are generated by a reference clock generating circuit 4 as a timing signal generating means.
1 and a timing signal generation circuit 44.

(3) The time-division sampling circuit 45 serves as time-division sampling means for sampling the current signal log (J _t ) using the first and second tunnel current timing signals TT ₁ and TT ₂ and the servo timing signal ST, respectively. including.

Here, the reference clock generation circuit 41 generates a reference clock RC having a frequency higher than the frequency at which the probe 31 is scanned along the surface of the sample 1 in the X-axis direction shown in FIG. The Z displacement signal generation circuit 42 generates a Z displacement signal ΔZ in synchronization with the reference clock RC. In addition,
The Z displacement signal ΔZ is added by the adder 43 to the servo signal S generated by the servo signal generation circuit 16. The timing signal generation circuit 44 synchronizes the first and second tunnel current timing signals TT ₁ and TT ₂ and the servo timing signal S
And T respectively.

Next, the operation of the scanning tunnel microscope 30 will be described with reference to the timing chart shown in FIG. 5 and the timing chart shown in FIG.

In the scanning tunneling microscope 30, the topo signal T and the current signal log (J _t ) are shown in FIG.
By measuring each pixel S _{1 to} S ₈ shown in (1), an image showing the topograph of the surface of the sample 1 is obtained. Therefore, the horizontal distance between the pixels S _{1 to} S ₈ in FIG. 4A corresponds to the scanning time for the probe 31 to scan along the surface of the sample 1 in the X-axis direction in FIG.

When the measurement is started, the reference clock RC is continuously generated by the reference clock generation circuit 41.
The reference clock RC is input to the Z displacement signal generation circuit 42, and the Z displacement signal ΔZ is generated by the Z displacement signal generation circuit 42 in synchronization with the reference clock RC. At this time, the frequency of the reference clock RC is set higher than the frequency for scanning the probe 31 along the surface of the sample 1 in the X-axis direction shown in FIG. In circuit 42, Z having a period equal to the scan time
A displacement signal ΔZ can be generated (see FIG. 5).
(B)). The period of the Z displacement signal ΔZ is not necessarily required to be equal to the scanning time, but it is necessary to be equal to or shorter than the scanning time. The amplitude of the Z displacement signal ΔZ is not particularly limited, but is typically set to 0.1 to 3 nm. Further, the waveform of the Z displacement signal ΔZ is not particularly limited, and may be a sine wave as shown in FIG. 5B, a step wave, a sawtooth wave, or a combination of these waveforms.

The reference clock RC is also input to the timing signal generating circuit 44, and the first and second tunnel current timing signals TT ₁ and TT ₂ and the servo timing signal ST
Is the reference clock R by the timing signal generation circuit 44.
C are generated in synchronization with different phases of C, respectively.
That is, the first tunnel current timing signal TT ₁ is generated at the timing of each point Z _h (black circle shown in FIG. 2B) of the Z displacement signal ΔZ (see FIG. 2C), and the second tunnel current The timing signal TT ₂ is generated at the timing of each point Z _l (black triangle shown in FIG. 3B) of the Z displacement signal ΔZ (see FIG. 3D), and the servo timing signal ST
It is generated at the timing of each point Z _m of the displacement signal ΔZ (white circle shown in FIG. 7B) (see FIG. 8E).

When the measurement is started, a predetermined bias voltage V is applied between the probe 31 and the surface of the sample 1 from the bias voltage generating circuit 33.
The probe 31 is moved by the probe fine movement control mechanism 32 so that the distance z between the probe and the surface of the probe becomes a predetermined value of several nm or less.
It is moved in the axial direction. At this time, the tunnel current J _t flowing between the probe 31 and the sample 1 surface is input to the current-voltage conversion circuit 34, is converted to the tunnel voltage V _t. Tunnel voltage V _t is input to a logarithmic circuit 35, by which the logarithm is determined, the current signal log
(J _t ) is generated. The current signal log (J _t ) is input to the time-division sampling circuit 45 and is sampled by the servo timing signal ST to be converted into a first sampling current signal log (J _tm ). The first sampling current signal log (J _tm ) is
The signal is input to the servo signal generation circuit 36. As a result, the first
Sampling current signal log (J _tm ) (that is,
A servo signal S for feedback-controlling the distance z such that the tunnel current J _t ) at the timing of each point Z _m of the Z displacement signal ΔZ is constant is generated by the servo signal generation circuit 36 and the servo signal S Is generated. FIG. 5F shows an example of the servo signal S obtained in this manner.

The servo signal S is input to the adder 43, added to the Z displacement signal ΔZ generated by the Z displacement signal generating circuit 42, and then amplified by the amplifier 39 to be converted into the Z axis control signal C _Z. Then, the probe fine movement control mechanism 32
Is input to Thus, each point Z _m of the Z displacement signal ΔZ
While the tunnel current J _t at the timing of the distance z to be constant is feedback controlled, at the same time, the probe 31 is forced to move in Figure 4 the Z-axis direction by the Z displacement signal [Delta] Z. FIG. 6A shows an example of the trajectory of the probe 31 that has been feedback-controlled in this manner.

Thereafter, a predetermined bias voltage V is applied to the probe 31.
The probe 31 is scanned in the X-axis direction shown in FIG. 4 along the surface of the sample 1 by a probe scanning mechanism (not shown) while the voltage is applied between the sample 1 and the sample 1. In this case, after the tunnel current J _t is converted by the current-voltage conversion circuit 34 to the tunnel voltage V _t, it is converted into a current signal log (J _t) in a logarithmic circuit 35. FIG. 6B shows an example of the current signal log (J _t ). The current signal log (J _t ) is input to the time-division sampling circuit 35 and the servo timing signal S
T and the first and second tunnel current timing signals TT
₁ and TT ₂ , so that the first sampling current signal log (J _tm ), the second sampling current signal log (J _th ), and the third sampling current signal
It is converted respectively to the sampling current signal log (J _tl) in (FIG. 6 (C), the reference (D)).

FIG. 6E shows the first sampling current signal log (J _tm ), second sampling current signal log (J _th ), and third sampling current signal log (J _th ) obtained as described above. An example of the measurement result of J _tl ) is shown. As shown in the figure, the first sampling current signal log (J _tm ) obtained by sampling with the servo timing signal ST is held at a constant value by the above-described feedback control. tunneling current timing signal TT _1, the second sampling current signal log obtained by sampling respectively TT ₂ (J _{t h)} and the third sampling current signal log (J _tl) is not necessarily a constant value , Probe 3
1 and the surface of the sample 1 independently change according to the distance z. That is, the second sampling current signal log (J _th ) and the third sampling current signal log (J _tl ) are respectively the probe 31 shown in FIG.
To become as indicating a current signal log (J _t) in the broken line A _h and dashed A _l trajectory, the probe 31 and the sample 1
Signal log for a distance z from the surface of
The dependency of (J _t ) can be obtained for each of the pixels S _{1 to} S ₈ . As a result, the second sampling current signal lo
g (J _th ) and the third sampling current signal log
(J _tl ) is necessarily clear in the observation of an organic substance or the like because the tunnel current J _t includes a physical quantity such as a tunnel via height which changes depending on the distance z between the probe 31 and the surface of the sample 1 as a parameter. It provides important information for clarifying the generating origin of the tunnel current J _t not.

Therefore, in the scanning tunneling microscope 30, the dependence of the current signal log (J _t ) on the distance z can be measured by scanning the probe 31 only once.

In the above description, the first current signal lo
Although the servo signal S is generated from g (J _tm ), the current signal log (J _t ) output from the logarithmic circuit 35 is averaged by a low-pass filter having a cutoff frequency much smaller than the frequency of the Z displacement signal ΔZ. The servo signal S may be generated by inputting the resulting signal to the servo signal generation circuit 36. The frequency of the Z displacement signal ΔZ is set to be lower than the mechanical resonance frequency of the probe fine movement control mechanism 32 and lower than the cutoff frequency of the low-pass filter used in the current-voltage conversion circuit 34 and the logarithmic circuit 35. Is set.

Next, the scanning tunneling microscope of the present invention will be described.
Example 2 will be described.

In the scanning tunneling microscope 10 shown in FIG. 1, the first to third tunnel barrier height timing signals TB _{1 to} TB ₃ and the servo timing signal ST are generated by the timing signal generation circuit 24 as described above. Then, the dependence of the tunnel barrier height signal log (J _t ) / dz on the distance z was measured. However, FIG.
The first and second tunnel current timing signals are shown in (D) TT _1, TT ₂ timing signal generating circuit 2
4 and the time-division sampling circuit 25
Similarly to the time-division sampling circuit 45 shown in FIG. 4, the first and second tunnel current timing signals TT
₁ and TT ₂ to sample the current signal log (J _t ) to obtain a second sampled current signal log
(J _th ) and the third sampling current signal log
By obtaining (J _tl ), the probe 11 is scanned only once, and the tunnel barrier height signal log (J _t ) / dz is obtained.
And the dependence of the current signal log (J _t ) on the distance z may be measured.

In the first and second embodiments described above, the current signal log for a plurality of discrete distances z is
(J _t ) or tunnel barrier height signal log (J _t )
Although the measurement of the dependence of / dz has been described, for example, a sawtooth signal is used as the Z displacement signal ΔZ, and a gate signal having the same frequency synchronized with the Z displacement signal ΔZ is used as the sampling timing signal. it is also possible to make measurements of the continuous distance dependence of the current signal log (J _t) or tunnel barrier height signal log (J _t) / dz for.

FIG. 7 is a schematic configuration diagram showing a third embodiment of the scanning tunneling microscope of the present invention.

The scanning tunneling microscope 50 moves the probe 51 along the surface of the sample 1 along the X-axis direction in the figure while slightly changing the bias voltage applied between the probe 51 and the surface of the sample 1 at a high frequency. by detecting the tunnel current J _t caused by the interaction between the probe 51 and the sample 1 surface when brought into scanned, the current signal log (J _t), topo signals T and differential conductance signal dJ _t / dV Are different from the conventional scanning tunnel microscope 200 shown in FIG. 14 in the following points.

(1) The bias voltage is forcibly applied at a frequency higher than the frequency at which the probe 51 is scanned along the surface of the sample 1 in the X-axis direction in FIG. As the bias voltage changing means for changing, a reference clock generating circuit 61 and a bias voltage changing signal generating circuit 62 are included.

(2) The probe 51 has a frequency higher than the frequency at which the probe 51 is scanned along the surface of the sample 1 in the X-axis direction as shown in the figure and smaller than the frequency at which the bias voltage is slightly changed. A plurality of timing signals (first to third differential conductance timing signals T
A timing signal generating circuit 64 is included as timing signal generating means for generating C _{1 to} TC ₃ and the servo timing signal ST).

(3) A time-division sampling circuit 65 is included as time-division sampling means for sampling the differential conductance signal dJ _t / dV with the first to third differential conductance timing signals TC _{1 to} TC ₃ , respectively.

Here, the reference clock generation circuit 61 is generated by the bias voltage modulation signal generation circuit 58 at a frequency higher than the frequency at which the probe 51 is scanned along the surface of the sample 1 in the X-axis direction shown in FIG. Bias voltage modulation signal M _V
Reference clock RC having a frequency lower than the frequency of
Occurs. The bias voltage change signal generation circuit 62 generates a bias voltage change signal ΔV in synchronization with the reference clock RC. The bias voltage change signal ΔV is converted by the adder 63 into the bias voltage V generated by the bias voltage generation circuit 53 and the bias voltage modulation signal generation circuit 58.
Is added to the bias voltage modulation signal M _V generated at
The timing signal generating circuit 64 generates the first to third differential conductance timing signals TC _{1 to} TC ₃ and the servo timing signal ST in synchronization with the mutually different phases of the reference clock RC. The time-division sampling circuit 65 also samples the current signal log ( _Jt ) based on the servo timing signal ST.

Next, the operation of the scanning tunneling microscope 50 will be described with reference to the timing chart shown in FIG. 8 and the timing chart shown in FIG.

In the scanning tunneling microscope 50, the topo signal T, the current signal log (J _t ), and the differential conductance signal dJ _t / dV are converted into the respective pixels S _{1 to} S ₈ shown in FIG.
By measuring in units, an image showing the topography of the surface of the sample 1 and an image showing the in-plane distribution of the state density of electrons and phonons on the sample plane are obtained. Therefore, the horizontal distance of each of the pixels S _{1 to} S _{8 in} the same figure (A) corresponds to the scanning time for the probe 51 to scan along the surface of the sample 1 in the X-axis direction in FIG.

When the measurement is started, the bias modulation signal M
_V is continuously generated by the bias modulation signal generation circuit 58. Here, the bias modulation signal M _V is for slightly changing the bias voltage applied between the probe 51 and the surface of the sample 1 at a high frequency, and has an amplitude of 1 to 5
It is set to 0 mV, and its waveform is a sine wave. The waveform of the bias modulation signal M _V, the step wave, or a combination of the sawtooth or these waveforms.

When the measurement is started, the reference clock RC is continuously generated by the reference clock generation circuit 61. The reference clock RC is input to the bias voltage change signal generation circuit 62, and the bias voltage change signal ΔV is generated by the bias voltage change signal generation circuit 62 in synchronization with the reference clock RC. Here, the frequency of the reference clock RC is set to be higher than the frequency for scanning the probe 11 along the surface of the sample 1 in the X-axis direction shown in FIG. In the generation circuit 62, a bias voltage change signal ΔV having a cycle equal to the scanning time can be generated. In addition,
It is not necessary to make the cycle of the bias voltage change signal ΔV equal to the scanning time, but it is necessary to make it equal to or shorter than the scanning time. The amplitude of the bias voltage change signal ΔV is not particularly limited, but is typically set to 0.1 to 3 V. Further, the waveform of the bias voltage change signal ΔV is not particularly limited, and is a sawtooth wave in the present embodiment, but may be a sine wave, a step wave, or a combination of these waveforms.

The bias voltage change signal ΔV is supplied to the adder 63
Then, the bias voltage V generated by the bias voltage generation circuit 53 and the bias modulation signal M _V generated by the bias modulation signal generation circuit 58 are added to generate a bias control signal C _V
Is converted to In FIG. 8 (B), shows a waveform obtained by adding the bias modulation signal M _V and the bias voltage change signal ΔV in the adder 63. When the bias control signal C _V is applied between the probe 51 and the surface of the sample 1, a predetermined bias voltage V is applied between the probe 51 and the surface of the sample 1. bias voltage between the needle 51 and the sample 1 surface, with is then slightly changed at a high frequency by the bias modulation signal M _V, and is forced to change the bias voltage change signal [Delta] V.

The reference clock RC generated by the reference clock generation circuit 61 is also input to the timing signal generation circuit 64, and the first to third differential conductance timing signals TC _{1 to} TC ₃ and the servo timing signal ST As shown in FIGS. 8C to 8F, the timing signals are generated by the timing signal generation circuit 64 in synchronization with mutually different phases of the reference clock RC.

When the measurement is started, the probe 51 is moved by the probe fine movement control mechanism 52 so that the distance z between the probe 51 and the sample 1 becomes a predetermined value of several nm or less, as shown in FIG. Z
It is moved in the axial direction. At this time, the tunnel current J _t flowing between the probe 51 and the sample 1 surface is input to the current-voltage conversion circuit 54, is converted to the tunnel voltage V _t. Tunnel voltage V _t is input to a logarithmic circuit 55, by which the logarithm is determined, the current signal log
(J _t ) is generated. The current signal log (J _t ) is input to the time-division sampling circuit 65 and is converted into a first sampling current signal log (J _tm ) by being sampled by the servo timing signal ST. The first sampling current signal log (J _tm ) is
The servo signal generation circuit 56 generates a servo signal S which is input to the servo signal generation circuit 56 and performs feedback control of the distance z so that the first sampling current signal log (J _tm ) becomes constant. , A top signal T corresponding to the servo signal S is generated. In FIG. 8 (G),
An example of the servo signal S obtained in this way is shown.

The servo signal S is input to the amplifier 57, amplified by the amplifier 57 and converted into a Z-axis control signal C _Z , and then input to the probe fine movement control mechanism 52. Thus, the distance z is feedback controlled so tunneling current J _t at the timing of the servo timing signal ST is constant.

After that, while the bias voltage V, the bias modulation signal M _V, and the bias voltage change signal ΔV are applied between the probe 51 and the surface of the sample 1, a probe scanning mechanism (not shown) is used. The needle 51 is scanned along the surface of the sample 1 in the X-axis direction shown in FIG. At this time, the tunnel current J _t
Is a logarithmic circuit 55 and a differential conductance signal generating circuit 6
0 and are respectively input. In differential conductance signal generating circuit 60, the bias modulation signal reference signal sent from the generating circuit 58 R _V (e.g., synchronization signal of the bias modulation signal M _V) and a tunnel current J _t, the bias voltage of the tunneling current J _t By detecting a differential component related to V, a differential conductance signal dJ _t / dV is generated. FIG. 9A shows an example of the differential conductance signal dJ _t / dV generated by the differential conductance signal generation circuit 60 in this manner.

The differential conductance signal dJ _t / dV is input to the time-division sampling circuit 65, and the first to third
By being sampled respectively by the differential conductance timing signal TC ₁ to Tc _3, first sampling differential conductance signal dJ _t1 / dV, the second sampling differential conductance signal dJ _t2 / dV and third sampling differential conductance signal dJ _t3 /
Each of them is converted to dV (see FIGS. 9B to 9D). As a result, from the first to third sampling differential conductance signal dJ _t1 / dV~dJ _t3 / dV, 9
As shown in (E), the dependence of the differential conductance signal dJ _t / dV on the bias voltage V can be obtained for each measurement point (corresponding to each of the pixels S _{1 to} S ₈ ).

Therefore, in the scanning tunneling microscope 50, the dependence of the differential conductance signal dJ _t / dV on the bias voltage V can be measured by scanning the probe 51 only once.

In the above description, the first current signal lo
g (J _tm ) generates servo signal S, but logarithmic circuit 5
5 is averaged by a low-pass filter having a cutoff frequency much smaller than the frequency of the bias voltage change signal ΔV, and a signal obtained by averaging the current signal log (J _t ) is input to the servo signal generation circuit 56. S may be generated. The frequency of the bias voltage change signal ΔV is set lower than the mechanical resonance frequency of the probe fine movement control mechanism 52, and is lower than the cutoff frequency of the low-pass filter used in the current-voltage conversion circuit 54 and the logarithmic circuit 55. Set smaller.

Further, the differential conductance signal generating circuit 6
By configuring the 0 like the lock-in amplifier, only the modulated component in response to the bias modulation signal M _V of the tunnel current J _t by AC to synchronous detection, as a differential component of the bias voltage V of the tunnel current J _t Alternatively, the differential conductance signal dJ _t / dV corresponding to the density of electromagnetic states at the energy level corresponding to the bias voltage value may be obtained at a high S / N ratio. Furthermore, when the frequency of the scanning of the probe 51 in the X-axis direction shown in FIG. 7 is 1 Hz, and the frequency of the bias voltage change signal ΔV is set to 100 to 500 Hz, the measurement point is 100 to 500 per scanning line.
become. At this time, it is desirable that the frequency of the bias voltage change signal ΔV be set to about 1 to several tens kHz. The frequency of the bias modulation signal M _V, along with is set smaller than the mechanical resonance frequency of the probe fine movement driving mechanism 52, than the cutoff frequency of the low pass filter used in the current-voltage conversion circuit 54 and the logarithmic circuit 55 When the mechanical resonance frequency of the probe fine movement drive mechanism 52 is required to be several tens kHz or more, a bimorph type piezoelectric thin film structure formed on a silicon substrate or the like by a micromechanics technique is used. A micro cantilever or the like can be used.

FIG. 10 is a schematic configuration diagram showing a second reference example of the scanning tunneling microscope of the present invention.

The scanning tunnel microscope 70 scans the probe 71 along the surface of the sample 1 in the X-axis direction shown in the figure, and generates a tunnel generated by the interaction between the probe 71 and the surface of the sample 1. The current _Jt is detected and the current signal log
(J _t ) and the topo signal T, respectively, and are different from the conventional scanning tunneling microscope 200 shown in FIG. 14 in the following points.

(1) A bias voltage applied between the probe 71 and the surface of the sample 1 at a frequency higher than the frequency at which the probe 71 is scanned along the surface of the sample 1 in the X-axis direction shown in FIG. Includes a reference clock generation circuit 81 and a bias voltage change signal generation circuit 82.

(2) A plurality of timing signals (first and second signals) having a frequency higher than the frequency for scanning the probe 71 along the surface of the sample 1 in the X-axis direction shown in FIG. Tunnel current timing signal T
A timing signal generating circuit 84 is included as timing signal generating means for generating T ₁ , TT ₂ and the servo timing signal ST).

(3) The time-division sampling circuit 85 serves as time-division sampling means for sampling the current signal log (J _t ) using the first and second tunnel current timing signals TT ₁ , TT ₂ and the servo timing signal ST, respectively. including.

Here, the reference clock generation circuit 81 generates a reference clock RC having a frequency higher than the frequency at which the probe 71 is scanned along the surface of the sample 1 in the X-axis direction in the figure. Bias voltage change signal generation circuit 82
Generates a bias voltage change signal ΔV in synchronization with the reference clock RC. Note that the bias voltage change signal ΔV is
The adder 83 adds the bias voltage V generated by the bias voltage generation circuit 73 to the bias voltage V. The timing signal generating circuit 84 generates the first and second tunnel current timing signals TT ₁ and TT ₂ and the servo timing signal ST in synchronization with mutually different phases of the reference clock RC.

Next, the operation of the scanning tunneling microscope 70 will be described with reference to the timing chart shown in FIG.
This will be described with reference to the timing charts shown in FIGS.

In the scanning tunneling microscope 70, the topo signal T and the current signal log (J _t ) are measured for each pixel S _{1 to} S ₈ shown in FIG.
An image showing the topograph of the surface of is obtained. Therefore, the horizontal distance of each of the pixels S _{1 to} S ₈ in FIG.
This corresponds to a scanning time in which the probe 71 scans along the surface of the sample 1 in the X-axis direction shown in FIG.

When the measurement is started, the reference clock RC is continuously generated by the reference clock generation circuit 81.
The reference clock RC is a bias voltage change signal generation circuit 82.
, And a bias voltage change signal ΔV is generated by the bias voltage change signal generation circuit 82 in synchronization with the reference clock RC. Here, the frequency of the reference clock RC is
The frequency for scanning the probe 71 along the surface of the sample 1 in the X-axis direction shown in FIG. 10 (the reciprocal of the scanning time) is equal to the scanning time in the bias voltage change signal generation circuit 82. A bias voltage change signal ΔV having a period can be generated (FIG. 11).
(B)). The cycle of the bias voltage change signal ΔV is not necessarily required to be equal to the scanning time, but it is necessary to make the cycle equal to or shorter than the scanning time. The amplitude of the bias voltage change signal ΔV is not particularly limited, but is typically set to 0.1 to 3 V.
Further, the waveform of the bias voltage change signal ΔV is not particularly limited, and is a sawtooth wave in the present embodiment, but may be a sine wave, a step wave, or a combination of these waveforms.

The bias voltage change signal ΔV is added to the adder 83
Is added to the bias voltage V generated by the bias voltage generation circuit 73 and converted into a bias control signal C _V. When the bias control signal C _V is applied between the probe 71 and the surface of the sample 1, a predetermined bias voltage V is applied between the probe 71 and the surface of the sample 1. The bias voltage between the needle 71 and the surface of the sample 1 is
Forcibly changed by the bias voltage change signal ΔV.

The reference clock RC is also input to the timing signal generation circuit 84, where the first and second tunnel current timing signals TT ₁ and TT ₂ and the servo timing signal ST
Is the reference clock R by the timing signal generation circuit 84.
C are generated in synchronization with different phases of C, respectively.
That is, the first tunnel current timing signal TT ₁ is generated at the timing of each point V _h (the black circle shown in FIG. 2B) of the bias voltage change signal ΔV (see FIG. 2C),
Each point V _l of the second tunnel current timing signal TT ₂ is the bias voltage change signal [Delta] V (black triangles shown in FIG. (B))
(See FIG. 3D), and the servo timing signal ST is generated at each point V of the bias voltage change signal ΔV.
_m (open circles shown in FIG. 7B) (see FIG. 7E).

Further, when the measurement is started, the probe fine movement control mechanism 72 moves the probe 71 so that the distance z between the probe 71 and the surface of the sample 1 becomes a predetermined value of several nm or less. 10
It is moved in the illustrated Z-axis direction. At this time, the tunnel current J _t flowing between the probe 71 and the sample 1 surface is input to the current-voltage conversion circuit 74, is converted to the tunnel voltage V _t. Tunnel voltage V _t is input to a logarithmic circuit 75,
By obtaining the logarithmic value, the current signal lo
g (J _t ) is generated. The current signal log (J _t ) is
By being input to the time-division sampling circuit 85 and being sampled by the servo timing signal ST,
It is converted into a first sampling current signal log (J _tm ). First sampling current signal log (J _tm )
Is input to the servo signal generation circuit 76 and the distance is set so that the first sampling current signal log (J _tm ) (that is, the tunnel current J _{t at} the timing of each point V _m of the bias voltage change signal ΔV) is constant. A servo signal S for feedback-controlling z is generated by a servo signal generation circuit 76, and a top signal T corresponding to the servo signal S is generated. FIG. 11F shows an example of the servo signal S thus obtained.

The servo signal S is amplified by the amplifier 77 and converted into a Z-axis control signal C _Z to control the fine movement control mechanism 7 of the probe.
2 is input. As a result, the bias voltage change signal Δ
As tunneling current J _t becomes constant at the timing of each point V _m and V, the distance z is feedback controlled. FIG. 12A shows an example of the trajectory of the probe 71 that has been feedback-controlled in this manner.

Thereafter, with the bias voltage control signal C _V applied between the probe 71 and the sample 1, the probe 71 is scanned in the X-axis direction shown in FIG. 10 by a probe scanning mechanism (not shown). You. In this case, after the tunnel current J _t is converted by the current-voltage conversion circuit 74 to the tunnel voltage V _t, it is converted into a current signal log (J _t) in a logarithmic circuit 75. FIG.
(B) shows an example of the current signal log (J _t ). The current signal log (J _t ) is supplied to the time-division sampling circuit 8.
5 and are respectively sampled by the servo timing signal ST and the first and second tunnel current timing signals TT ₁ and TT ₂ , so that the first sampling current signal log (J _tm ) and the second sampling current signal log (J _tm ) The signals are converted into a sampling current signal log (J _th ) and a third sampling current signal log (J _tl ), respectively (see FIGS. 12C and _12D ).

FIG. 12E shows the first sampling current signal log (J _tm ) and the second sampling current signal
An example of the measurement results of the sampling current signal log (J _th ) and the third sampling current signal log (J _tl ) of FIG. As shown in FIG. 12E, the first sampling current signal log (J _tm ) obtained by sampling with the servo timing signal ST is held at a constant value by the above-described feedback control. And the second sampling current signal log (J _th ) and the third sampling current signal log (J _tl ) obtained by sampling with the second tunnel current timing signals TT ₁ and TT ₂ are not necessarily constant values. Instead, they change independently according to the bias voltage (bias voltage V and bias voltage change signal ΔV) applied between the probe 71 and the surface of the sample 1. This is because the second sampling current signal log (J _th ) and the third sampling current signal log (J _tl ) are parameters whose physical quantity at which the tunnel current J _t changes according to a bias voltage (energy level) such as an electronic state density. It is because it includes as.

Therefore, the second sampling current signal log (J _th ) and the third sampling current signal log (J _tl ) respectively correspond to the points V _h and V _{h of} the bias voltage change signal ΔV shown in FIG. Since the current signal log ( _Jt ) at each point _Vl is indicated, the dependence of the current signal log ( _Jt ) on the bias voltage applied between the probe 71 and the surface of the sample 1 is determined for each pixel. S
It can be found for each ₁ to S _8. As a result, the scanning tunneling microscope 70 can measure the dependence of the current signal log (J _t ) on the bias voltage by scanning the probe 71 only once.

In the above description, the first current signal lo
Although the servo signal S is generated from g (J _tm ), the current signal log (J _t ) output from the logarithmic circuit 75 is averaged by a low-pass filter having a cutoff frequency much smaller than the frequency of the bias voltage change signal ΔV. The servo signal S may be generated by inputting the converted signal to the servo signal generation circuit 76. The frequency of the bias voltage change signal ΔV is set lower than the mechanical resonance frequency of the probe fine movement control mechanism 72 and is lower than the cutoff frequency of the low-pass filter used in the current-voltage conversion circuit 74 and the logarithmic circuit 75. Set smaller.

Next, the scanning tunneling microscope of the present invention will be described.
Example 4 will be described.

In the scanning tunneling microscope 50 shown in FIG. 7, the first to third differential conductance timing signals TC _{1 to} TC ₃ and the servo timing signal ST are generated by the timing signal generation circuit 64 as described above. Thus, the dependence of the differential conductance signal dJ _t / dV on the bias voltage was measured. However, FIG.
The first and second tunnel current timing signals TT ₁ and TT _{2 shown} in FIG.
4 and the time-division sampling circuit 65
Similarly to the time division sampling circuit 85 shown in FIG. 10, the first and second tunnel current timing signals TT
₁ and TT ₂ to sample the current signal log (J _t ) to obtain a second sampled current signal log
(J _th ) and the third sampling current signal log
By obtaining (J _tl ), the dependence of the differential conductance signal dJ _t / dV and the current signal log (J _t ) on the bias voltage can be measured by scanning the probe 51 only once. It may be.

In the third and fourth embodiments described above, the current signal log (J _t ) or the differential conductance signal dJ _t / d for a plurality of discrete bias voltages
Although the measurement of the dependence of V has been described, for example, a sawtooth signal is used as the bias voltage change signal ΔV, and a gate signal having the same frequency synchronized with the bias voltage change signal ΔV is used as the sampling timing signal. The current signal log for the point
A continuous bias voltage measurement of (J _t ) or the differential conductance signal dJ _t / dV can also be made.

Next, an information recording / reproducing apparatus according to the present invention will be described.

In recent years, there has been proposed an information recording / reproducing apparatus for performing high-density recording / reproducing in the atomic order (sub-nanometer) by applying the principle of the scanning tunneling microscope (for example, Japanese Patent Application Laid-Open No. 63-16552). Gazettes). Therefore, in such an information recording / reproducing apparatus, for example, at the time of recording, a physical quantity such as a tunnel via height is changed for a plurality of distances z, or a bias voltage corresponding to a specific energy level is changed. By simultaneously changing a plurality of physical quantities such as the electronic state density in a single scan, information is multiplex-recorded on the sample, and at the time of reproduction, the scanning tunnel according to the present invention shown in FIGS. 1, 4, 7 and 10 is used. First to third sampling current signals log (J _tm ) and log obtained respectively in each embodiment of the microscope.
(J _th ), log (J _tl ) or first to third sampling tunnel barrier height signals dlog (J _t1 ) / dz, d
log (J _t2 ) / dz, dlog (J _t3 ) or the first to third sampling differential conductance signals dJ _t1 / d
By reproducing information recorded on a sample using V, dJ _t2 / dV and dJ _t3 / dV, the storage density can be drastically increased and the recording / reproducing time can be greatly reduced. .

[0144]

As described above, according to the present invention,
Just scan the probe once on the surface, and at each measurement point
For different distances between the tip and the surface of the sample.
The distance of the current signal.
The effect is that dependency can be easily obtained.

In addition, each time the probe is scanned once, the
At the measurement point, the difference between the tip and the surface of the sample
To obtain the tunnel barrier height signal for different distances
The distance dependence of the tunnel barrier height signal.
There is also an effect that it can be easily obtained .

Further , according to the present invention, the probe is scanned once by plane scanning.
At each measurement point.
For different bias voltages applied between
The current signal can be obtained by
The effect that ass voltage dependency can be easily obtained
There is .

In addition, each time the probe is scanned once, the
Applied between the probe and the surface of the sample at the measurement point
Differential conductance for different bias voltages
Signal to obtain the differential conductance signal
Voltage dependency can be easily obtained.
There is also an effect .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of a scanning tunneling microscope of the present invention.

FIG. 2 is a timing chart for explaining the operation of the scanning tunneling microscope shown in FIG.

FIG. 3 is a timing chart for explaining the operation of the scanning tunneling microscope shown in FIG.

FIG. 4 is a schematic configuration diagram showing a first reference example of the scanning tunneling microscope of the present invention.

FIG. 5 is a timing chart for explaining the operation of the scanning tunneling microscope shown in FIG.

FIG. 6 is a timing chart for explaining the operation of the scanning tunneling microscope shown in FIG.

FIG. 7 is a schematic configuration diagram showing a third embodiment of the scanning tunneling microscope of the present invention.

FIG. 8 is a timing chart for explaining the operation of the scanning tunneling microscope shown in FIG.

FIG. 9 is a timing chart for explaining the operation of the scanning tunnel microscope shown in FIG. 7;

FIG. 10 is a schematic configuration diagram showing a second reference example of the scanning tunneling microscope of the present invention.

FIG. 11 is a timing chart for explaining the operation of the scanning tunneling microscope shown in FIG.

12 is a timing chart for explaining the operation of the scanning tunneling microscope shown in FIG.

FIG. 13 is a block diagram showing a first conventional example of a scanning tunneling microscope.

FIG. 14 is a block diagram showing a second conventional example of a scanning tunneling microscope.

FIG. 15 is a block diagram showing a conventional example of a scanning tunnel microscope capable of solving the problem in the scanning tunnel microscope shown in FIG.

FIG. 16 is a block diagram showing a conventional example of a scanning tunnel microscope that can solve the problem in the scanning tunnel microscope shown in FIG.

[Explanation of symbols]

1 Sample 10, 30, 50, 70 Scanning tunnel microscope 11, 31, 51, 71 Probe 12, 32, 52, 72 Probe fine movement control mechanism 13, 33, 53, 73 Bias voltage generation circuit 14, 34, 54 , 74 Current-voltage conversion circuit 15, 35, 55, 75 Logarithmic circuit 16, 36, 56, 76 Servo signal generation circuit 17 Z modulation signal generation circuit 19, 39, 57, 77 Amplifier 20 Tunnel barrier height signal generation circuit 21, 41 , 61, 81 Reference clock generation circuit 22, 42 Z displacement signal generation circuit 23, 43, 63, 83 Adder 24, 44, 64, 84 Timing signal generation circuit 25, 45, 65, 85 Time division sampling circuit 58 Bias voltage Modulation signal generation circuit 60 Differential conductance signal generation circuit 62, 82 Bias voltage change signal generation circuit V Bias voltage J _t tunneling current V _t tunnel voltage T topo signal log (J _t) current signal log (J _tm) first sampling the current signal log (J _th) second sampling current signal log (J _tl) of the third sampling current signal dlog (J _t) / dz tunnel barrier height signal dlog (J _t1) / dz first sampling tunnel barrier height signal dlog (J _t2) / dz second sampling tunnel barrier height signal dlog (J _t3) / dz third sampling tunnel barrier height signal dJ _t / dV differential conductance signal dJ _t1 / dV first sampling differential conductance signal dJ _t2 / dV second sampling differential conductance signal dJ _t3 / dV third sampling differential conductance signal TB ₁ first tunnel Bali Height timing signal TB ₂ second tunnel barrier height timing signal TB ₃ third tunnel barrier height timing signal TT ₁ first tunnel current timing signal TT ₂ second tunnel current timing signal TC ₁ first differential conductance timing signal TC ₂ Second differential conductance timing signal TC ₃ Third differential conductance timing signal ST Servo timing signal S Servo signal M _Z Z modulation signal M _V bias voltage modulation signal R _Z , R _V reference signal C _Z Z axis control signal C _V bias control signal RC reference clock ΔZ Z displacement signal ΔV bias change signal X, Y, Z axis

Continuation of the front page (56) References JP-A-3-43944 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01B ^7/ 00-7/34 G11B 9/00

Claims (8)

(57) [Claims] The present invention detects a tunnel current generated by an interaction between a probe and a surface of a sample when the probe is scanned along the surface of the sample, and detects a current signal , a topo signal and a tunnel signal .
In a scanning tunneling microscope for obtaining a tunnel barrier height signal , a circuit for generating a reference clock and a frequency higher than a frequency for scanning the probe along the surface of the sample in synchronization with the reference clock. A probe moving means for forcibly moving the probe in a direction perpendicular to the surface, and a frequency higher than a frequency for scanning the probe along the surface of the sample based on the reference clock, and having a phase mutually. A timing signal generating circuit for generating a plurality of different timing signals, and a time-division sampling circuit for sampling the current signal with each of the timing signals
Is larger than the moving frequency of the probe by the probe moving means.
A modulation signal generating circuit for generating a modulation signal having a threshold frequency;
Movement in a direction perpendicular to the surface of the sample based on the modulation signal
The probe at a high frequency in the direction perpendicular to the surface of the sample.
Means for operating the modulated signal as a reference signal.
Generate tunnel barrier height signal from rent signal
Scanning tunneling microscope, characterized in that a circuit. 2. The timing signal generating circuit according to claim 1, further comprising :
Different timing signals from the reference clock
Generated in synchronization with the phase, the time-division sampling circuit
Can be controlled by the other timing signals.
2. The scanning tunneling microscope according to claim 1 , wherein each of the light source signals is sampled . 3. A bias voltage is applied between the sample and the probe.
While scanning the probe along the surface of the sample
Tunnel created by interaction between needle and sample surface
Detects the current and outputs the current signal,
Scanning tunneling microscope that obtains each of the conductance signals
And a circuit for generating a reference clock and synchronizing with the reference clock
A frequency at which the probe is scanned along the surface of the sample.
The bias voltage is forcibly changed at a frequency higher than
Bias voltage changing means for controlling the
The frequency at which the probe is scanned along the surface of the sample.
It has a frequency greater than the number, position phase are different from each other, double
Signal generation circuit for generating a number of timing signals
And the current signal by the respective timing signals.
A time-division sampling circuit that samples each
From the bias voltage change by the bias voltage changing means.
Signal generation circuit that generates a modulation signal with a large frequency
And a bias voltage changing means based on the modulation signal.
High-frequency bias voltage superimposed on changes in bias voltage
Means for minutely modulating the current with the
A current-to-voltage conversion circuit for converting the voltage to a voltage;
Differential conductance from the tunnel voltage as the illumination signal
A scanning tunnel microscope comprising: a circuit for generating a signal . 4. The timing signal generating circuit according to claim 1, further comprising :
Different timing signals from the reference clock
Generated in synchronization with the phase, the time-division sampling circuit
Is the differential conductor by each other timing signal.
4. The scanning tunneling microscope according to claim 3, wherein the scanning tunneling microscope samples each of the scanning signals . 5. The method according to claim 1 , wherein the probe is scanned along the surface of the sample.
During the interaction between the tip and the surface of the sample
Current, topo signal and
Obtain the tunnel barrier height signal respectively, and
An information recording / reproducing device that reads information recorded on the surface
And a circuit for generating a reference clock, and synchronizing with the reference clock.
A frequency at which the probe is scanned along the surface of the sample.
Probe at a higher frequency than normal to the sample surface.
Probe moving means for forcibly moving, and the reference clock
Scanning the probe along the surface of the sample based on
Have frequencies greater than the frequency and are out of phase with each other
Timing signal generation to generate multiple timing signals
The raw signal and the current signal are generated by the timing signals.
-Division sampling circuit that samples each signal
Larger than the moving frequency of the probe by the probe moving means.
A modulation signal generating circuit for generating a modulation signal having a threshold frequency;
Movement in a direction perpendicular to the surface of the sample based on the modulation signal
The probe at a high frequency in the direction perpendicular to the surface of the sample.
Means for operating the modulated signal as a reference signal.
Generate tunnel barrier height signal from rent signal
An information recording / reproducing device, comprising: a circuit ; 6. The timing signal generating circuit according to claim 1, further comprising :
Different timing signals from the reference clock
Generated in synchronization with the phase, the time-division sampling circuit
Can be controlled by the other timing signals.
The information recording / reproducing apparatus according to claim 5, wherein each of the light source signals is sampled . 7. A bias voltage is applied between the sample and the probe.
While scanning the probe along the surface of the sample
Tunnel created by interaction between needle and sample surface
Detects the current and outputs the current signal,
Obtain the conductance signals and record them on the surface of the sample.
In an information recording / reproducing apparatus for reading recorded information, a circuit for generating a reference clock,
A frequency at which the probe is scanned along the surface of the sample.
The bias voltage is forcibly changed at a frequency higher than
Bias voltage changing means for controlling the
The frequency at which the probe is scanned along the surface of the sample.
Multiple frequencies with frequencies greater than
Signal generation circuit for generating a number of timing signals
And the current signal by the respective timing signals.
A time-division sampling circuit that samples each
From the bias voltage change by the bias voltage changing means.
Signal generation circuit that generates a modulation signal with a large frequency
And a bias voltage changing means based on the modulation signal.
High-frequency bias voltage superimposed on changes in bias voltage
Means for minutely modulating the current with the
A current-to-voltage conversion circuit for converting the voltage to a voltage;
Differential conductance from the tunnel voltage as the illumination signal
An information recording / reproducing apparatus, comprising: a circuit for generating a signal . 8. The timing signal generating circuit according to claim 1, further comprising :
Different timing signals from the reference clock
Generated in synchronization with the phase, the time-division sampling circuit
Is the differential conductor by each other timing signal.
The information recording / reproducing apparatus according to claim 7, wherein each of the information recording / reproducing apparatuses samples the signal .