JP3242787B2 - Photon scanning tunneling microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photon scanning tunneling microscope for measuring the shape of an object by detecting evanescent light localized on the surface of the object, and more particularly, to using an optical fiber probe as an optical probe for detecting evanescent light. The present invention relates to a photon scanning tunneling microscope.

[0002]

2. Description of the Related Art Conventionally, as a microscope for measuring the surface shape of an object with high resolution, a photon scanning tunnel for detecting evanescent light localized in a region smaller than the wavelength of light on the surface of the object and measuring the shape of the object is known. Microscope (PSTM: Ph
Oton Scanning Tunneling Microscope) is known as an ultra-high resolution optical microscope having a resolution exceeding the diffraction limit of a conventional optical microscope.

Specifically, as shown in FIG. 4, for example, when the sample surface is irradiated from the back surface of the sample 30 under the condition of total reflection, an evanescent field is generated on the sample surface according to the surface shape. In the photon scanning tunneling microscope, the resolution exceeding the diffraction limit of the conventional optical microscope is detected by detecting the intensity of the evanescent field with the optical probe 32 having the detection end 31 having an opening smaller than the wavelength of the evanescent light. Can be obtained.

As shown in FIG. 5, a conventional photon scanning tunneling microscope uses an optical system 44 for irradiating a laser beam from a semiconductor laser 43 from the back surface of a sample 30 and an evanescent beam localized on the surface of the sample 30. An optical probe 32 for collecting and condensing light, a photodetector 45 for detecting light from the optical probe 32, and an actuator 4 for driving the optical probe 32 based on control of a Z scanner 47 and an XY scanner 48.
9 and so on.

[0005] The actuator 49 drives the optical probe 32 based on the control of the Z scanner 47 and the control of the XY scanner 48 so that the tip of the optical probe 32 scans the surface of the sample 30. The addition circuit 42 adds the current from the control power supply 40 based on the reference signal and the current from the DC current source 41, and supplies a driving current to the semiconductor laser 43 to drive it.

On the other hand, the photodetector 45 detects light from the optical probe 32 and supplies a light intensity signal representing the intensity of the detected light to the lock-in amplifier 46, which locks the reference signal. The frequency component of the reference signal is extracted from the light intensity signal based on the extracted signal and supplied to the image processing system 50 via the Z-scanner.

That is, in this photon scanning tunneling microscope, the frequency component of the reference signal is superimposed on the laser beam from the semiconductor laser 43 and the lock-in amplifier 46
The frequency component of the reference signal is extracted from the light intensity signal, so-called synchronous detection is performed to reduce the influence of noise included in the light intensity signal.

Further, the image processing system 50 is configured to form and display an image of the sample 30 from the coordinate information from the XY scanner 48 and the light intensity signal. Thus, in the conventional photon scanning tunneling microscope, the sample 30
Was being measured.

On the other hand, as another microscope for measuring the surface shape of an object with high resolution, an atomic force microscope (AFM) for measuring an atomic force and measuring a shape of a sample is used.
roscope) is known.

In this atomic force microscope, a cantilever having a needle-like sharp point at the tip is brought into contact with the sample surface, and the sample surface is scanned to detect the amount of deflection of the cantilever due to the atomic force. The shape of the sample was measured by measuring the atomic force.

Another method for measuring the atomic force is to scan the sample surface by vibrating the cantilever at its resonance frequency with an electric oscillating element such as a piezo element.
A method of measuring a change in resonance frequency due to an atomic force to measure an atomic force has been known.

[0012]

However, in the conventional photon scanning tunneling microscope, since the scanning in the XY direction is performed while the position of the optical probe 32 in the Z direction is constant, the scanning with the sample 30 is performed by the unevenness of the surface of the sample 30 or the like. When the distance of the optical probe 32 changes, there is a problem that the light intensity of the evanescent light decreases and the measurement error increases.

Further, in the optical fiber probe 32 used in the conventional photon scanning tunneling microscope, the cladding diameter D (about 90 μm) is set to the length L (2 to 6) of the detection end 31.
(approximately μm), so that when scanning the surface of the sample, the peripheral end portion 33 of the clad may collide with the sample 20 and damage the sample and / or the probe itself.

Further, since the output of the evanescent light is extremely small, it is necessary for the optical fiber probe for detecting the evanescent light to avoid the influence of the scattered light and to increase the detection efficiency.

On the other hand, in an atomic force microscope, it is difficult to accurately produce a cantilever, and it is difficult to improve the resolution. In order to obtain an optical image of evanescent light or the like at the same time with an atomic force microscope, for example, a method of connecting an optical fiber to the tip of the cantilever and observing it is conceivable. It was necessary, and there was a problem that production was difficult and expensive.

The present invention has been made in view of the above-described problems, and has as its object to provide a photon scanning tunneling microscope with high measurement accuracy.

It is another object of the present invention to provide a photon scanning tunneling microscope in which the peripheral end of the cladding does not collide with the surface of the sample and does not damage the sample and the optical fiber probe.

Another object of the present invention is to provide a photon scanning tunneling microscope capable of measuring an atomic force simultaneously with measuring an optical image.

[0019]

In order to solve the above-mentioned problems, a photon scanning tunneling microscope according to the present invention comprises: an illumination light source for generating illumination light; and an illumination light source for guiding the illumination light from the illumination light source to a sample surface. An optical fiber probe comprising an optical system for irradiating and an optical fiber having a sharpened tip, disposed to be inclined with respect to the sample, and scattering and condensing evanescent light localized on the sample surface; Light detection means for detecting light from the fiber probe and outputting a detection output,
Scanning means for changing the positional relationship between the sample and the optical fiber probe so that the tip of the optical fiber probe scans the sample surface, and outputting position information, and detection light emitted from the side of the optical fiber probe. Displacement detecting means for detecting the displacement of the optical fiber probe by measuring an interference pattern generated by being blocked by the optical fiber probe, and the optical fiber probe is moved from the sample surface based on the displacement detected by the displacement detecting means. Measuring means for measuring a force to be received, position information from the scanning means, a detection output from the light detecting means, and a shape measuring means for measuring the shape of the sample based on the force measured by the measuring means. It is characterized by having.

Further, in the photon scanning tunneling microscope according to the present invention, the optical fiber probe has a base end portion having a thin clad at one end of an optical fiber composed of a core and a clad, and the base end portion is provided at a tip end of the base end. It has a detection end portion in which a core is sharpened, a gold coating layer on a surface of the detection end portion, and an opening at a tip of the detection end portion.

Further, the photon scanning tunneling microscope according to the present invention has a distance control means for controlling the scanning means based on the force measured by the measuring means to keep the distance between the surface of the sample and the optical fiber probe constant. It is characterized by the following.

[0022]

[0023]

In the photon scanning tunneling microscope according to the present invention, the optical fiber probe is formed of an optical fiber having a sharpened tip, and is provided with an optical fiber probe which is disposed obliquely with respect to the sample.
The evanescent light localized on the sample surface is scattered and collected, and the light from the optical fiber probe is detected by the light detecting means. Then, position information output from scanning means for changing the positional relationship between the sample and the optical fiber probe so that the tip of the optical fiber probe scans the sample surface, and detection light emitted from the side surface of the optical fiber probe By measuring an interference pattern generated by being interrupted by the optical fiber probe, the optical fiber probe is moved from the sample surface based on the displacement of the optical fiber probe detected by the displacement detecting means for detecting the displacement of the optical fiber probe. The shape of the sample is measured by the shape measuring means based on the force measured by the measuring means for measuring the received force and the detection output by the light detecting means.

In the photon scanning tunneling microscope according to the present invention, the gold coating layer on the surface of the detection end functions as a light-shielding portion for blocking light, and takes in evanescent light from the opening at the tip of the detection end.

In the photon scanning tunneling microscope according to the present invention, the distance control means controls the scanning means based on the force measured by the measuring means to keep the distance between the surface of the sample and the optical fiber probe constant. .

In the photon scanning tunneling microscope according to the present invention, the light source irradiates the detection light from the side of the optical fiber probe, and the detection means is generated when the detection light from the light source is blocked by the optical fiber probe. The displacement of the optical fiber probe is detected by measuring the interference pattern.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the photon scanning tunneling microscope according to the present invention will be described below in detail with reference to the drawings.

In this embodiment, a photon scanning tunneling microscope (hereinafter referred to as PSTM: Photon S) for measuring the shape of an object by detecting evanescent light localized on the surface of the object is used in the present invention.
Canning Tunneling Microscope).

As shown in FIG. 1, for example, the PSTM includes a laser light source 1 for generating a laser beam, an optical system 10 for guiding the laser beam from the laser light source 1 and irradiating the laser beam from the back surface to the front surface of the sample 2. An optical fiber probe 3 that scatters and condenses evanescent light localized on the surface of the sample 2 in proximity to the surface of the sample 2 and a photodiode 4 that detects light from the optical fiber probe 3 and outputs a detection output. When,
A driving unit 5 for driving the sample 2 so that the tip of the optical fiber probe 3 scans the surface of the sample 2 and outputting position information; a displacement detecting unit 20 for detecting displacement of the optical fiber probe 3; Control unit 6 for measuring the force received by optical fiber probe 3 based on the displacement detected by unit 20
And an image display unit 7 for displaying an image.

The control unit 6 measures and measures the shape of the sample based on the position information from the driving unit 5, the detection output from the photodiode 4, and the measured force of the optical fiber probe 3. The image of the surface of the sample 2 is displayed on the image display unit 7
To be displayed.

The optical system 10 includes a lens 11 for converting the laser beam from the laser light source 1 into a parallel beam, a mirror 12 for reflecting the laser beam from the lens 11, and a mirror 12. And a prism 13 for refracting the laser light from the lens 2, and the laser light collimated by the lens 11 is guided to the back surface of the sample 2 via the mirror 12 and the prism 13.

In this example, the case where the front surface of the sample 2 is illuminated by irradiating illumination light from the back surface of the sample 2 is explained. The illumination light may be emitted from above.

The optical fiber probe 3 is made of, for example, an optical fiber having a core and a clad, and has a base end 3a having a reduced thickness of the clad at one end, and a sharpened core at the end of the base end 3a. And a detection end 3b.

The optical fiber probe 3 is formed by etching one end of an optical fiber composed of, for example, a quartz core doped with germanium oxide and a quartz clad with an etching solution composed of ammonium fluoride, hydrofluoric acid and water, to thereby obtain a thickness of the clad. Is thinned to form a base end 3a, and further, the core is sharpened by etching with an etchant comprising ammonium fluoride, hydrofluoric acid and water to form a detection end 3b. As a result, the base end 3a
Can have a diameter of about 14 to 18 μm, which is more flexible than before, and the base end 3 a
Deflection occurs.

Further, a coating layer made of, for example, gold or the like having excellent light shielding properties is formed on the detection end 3b.
The tip of b is an opening. The optical fiber probe 3 is disposed with an inclination angle δ of 85 degrees with respect to the sample 2, and the base end portion 3 a is bent by an atomic force or the like received from the sample 2. . That is,
In this PSTM, a force based on an atomic force or the like is measured as the amount of deflection of the optical fiber probe 3.

The drive unit 5 drives the sample 2 based on the control from the control unit 6 so that the tip of the detection end 3b scans the surface of the sample 2, and transmits the position information to the control unit 6.
To supply. The optical fiber probe 3 scatters evanescent light localized on the surface of the sample 2 and collects the light from the opening of the detection end 3 b, and supplies the collected light to the photodiode 4. The photodiode 4 detects light from the optical fiber probe 3 and supplies a PSTM signal (detection output) indicating the intensity of evanescent light on the surface of the sample 2 to the control unit 6.

On the other hand, the displacement detector 20 detects the displacement of the optical fiber probe 3 and supplies an AFM signal indicating the amount of deflection of the optical fiber probe 3 to the controller 6. Control unit 6
Measures the force that the optical fiber probe 3 receives from the surface of the sample 2 based on the AFM signal from the displacement detector 20.

The controller 6 forms an image of the surface of the sample 2 based on the position information from the driver 5, the PSTM signal, and the force measured based on the AFM signal, and converts the image signal into an image. The image is supplied to the display unit 7, and the image display unit 7 displays an image based on the supplied image signal. That is, this P
In the STM, an optical image (PSTM image) of the surface of the sample 2 is measured based on the position information and the PSTM signal, and at the same time,
The shape of the surface of the sample 2 can be measured based on the position information and the force measured based on the AFM signal.

In this PSTM, the control unit 6 controls the drive unit 5 based on the force of the optical fiber probe 3 measured from the surface of the sample 2 measured as described above, so that the surface of the sample 2 is 3 is kept constant.

As a result, since the distance between the surface of the sample 2 and the detection end 3b is kept constant, the measurement accuracy of the evanescent light can be improved.

In the above-described embodiment, the PSTM
In the above, a case was described in which a coating layer made of gold or the like was formed on the detection end 3b, and the optical fiber probe 3 having an opening at the tip of the detection end 3b was used. However, the coating layer is not necessarily required. Similarly, even if the optical fiber probe 3 having no coating layer on the end 3b is used, the evanescent light can be scattered and collected from the tip of the detection end 3b.

Here, the displacement detecting section 20 will be described in more detail. A laser light source 21 for irradiating the optical fiber probe 3 with a laser beam from a side surface;
A two-division photodiode 22 that receives an interference pattern generated when the laser light from the laser light source 21 is blocked by the optical fiber probe 3, and a differential that outputs a difference signal based on the output of the two-division photodiode 22 The amplifier 23 and the gain A of the difference signal from the differential amplifier 23 are adjusted to indicate the amount of deflection of the optical fiber probe 3.
And an amplifier 24 that outputs an FM signal.

More specifically, the laser light from the laser light source 21 is focused on, for example, the front side of the optical fiber probe 3. When the laser light is blocked by the optical fiber probe 3, The laser beams diffracted from the left, right, left and right ends of the probe 3 interfere with each other to generate an interference pattern.

Therefore, the detection sensitivity of the interference pattern is improved as compared with the case where the laser light converted into parallel rays is irradiated from the side surface of the optical fiber probe 3.

The two-division photodiode 22 is
The interference pattern generated as described above is received to output two detection outputs Pa and Pb, and the differential amplifier 23 amplifies the difference between the detection outputs Pa and Pb and outputs a difference signal. The amplifier 24 adjusts the level of the difference signal and supplies the AFM signal to the control unit 6.

Specifically, the two-division photodiode 22
Is composed of two photodiodes 22a and 22b, for example, as shown in FIG. 2, such that the photodiodes 22a and 22b are located on the side of the optical fiber probe 3 in a direction perpendicular to the center axis of the optical fiber probe 3. It is arranged in.

The operation for measuring the displacement of the optical fiber probe 3 will now be described. For example, if the surface of the sample 2 has irregularities or the like, the optical fiber probe 3 receives a vertical force such as an atomic force based on the displacement dH. Then, as shown by a broken line in FIG. 2, the base end 3a is bent, for example, the base end 3a
The position of the AA ′ section of FIG.

When the laser light from the laser light source 21 is blocked by the base end 3a, the light diffracted from the left and right ends of the base end 3a interferes with each other, and an interference pattern occurs due to an optical path difference from the left and right ends of the base end 3a. (Light intensity distribution).

More specifically, for example, as shown in FIG.
a, 22b are arranged at a position of a distance R from the base end 3a. The diameter of the base end 3b is D.

At this time, the photodiodes 22a, 22a
The interference pattern on the plane 2b is obtained by comparing the distance L from the centers of the photodiodes 22a and 22b and the light intensity I in FIG.
As shown by a solid line in FIG. 3, when the displacement of the base end portion 3a is 0, the light intensity I becomes maximum at a point where the distance L is 0, that is, the optical path difference is 0, and the distance L is λ /
4D, that is, at a point where the optical path difference is λ / 2, the light intensity I is minimum, and the distance L is n times λ / 2D (n = ± 1, ± 2, ± 2).
3,...), That is, at a point where the optical path difference is n times λ, the light intensity I has a peak.

Here, for example, as described above, the base end 3a
Becomes dL, the distribution of the light intensity I moves by dL,
For example, as shown by a broken line in FIG. 3, a point where the light intensity I is the maximum is a point where the distance L is dL.

The light intensities Ia and Ib received by the photodiodes 22a and 22b are the light intensities I at the points where the distance L is a and b, and as shown in FIG.
When the displacement of a is 0, the light intensity becomes Ia = Ib = I ₀ , and when the displacement of the base end 3a is dL, Ia = I ₁ ,
Ib = I ₂ (I ₁ > I ₂ ). That is, the base end 3
The ratio of the light intensities Ia and Ib changes in accordance with the displacement dL of a. Therefore, the displacement detection unit 20 measures the displacement dL of the base end 3a by calculating the ratio of the light intensities Ia and Ib.

Specifically, for example, as described above, the photodiodes 22a and 22b receive the received light intensities Ia and Ia.
b, the detection outputs Pa and Pb are output in proportion to the differential output signal B. The differential amplifier 23 amplifies the difference between the detection outputs Pa and Pb to output a difference signal.
The FM signal is supplied to the control unit 6.

Thus, the displacement detector 20 detects the displacement of the optical fiber probe 3 to detect the amount of deflection of the optical fiber probe, and supplies an AFM signal indicating the amount of deflection of the optical fiber probe 3 to the controller 6. .

[0055]

As is apparent from the above description, according to the present invention, the position outputted from the scanning means for changing the positional relationship between the sample and the optical fiber probe so that the tip of the optical fiber probe scans the surface of the sample. By measuring the information and the interference pattern generated by the detection light emitted from the side surface of the optical fiber probe being blocked by the optical fiber probe, the displacement detected by the displacement detecting means for detecting the displacement of the optical fiber probe is measured. The shape of the sample is measured by the shape measuring means based on the force measured by the measuring means for measuring the force received by the optical fiber probe from the sample surface based on the displacement of the optical fiber probe and the detection output by the light detecting means. Photon scanning ton can measure atomic force with high accuracy simultaneously with optical image measurement It is possible to provide a Le microscope.

Further, in the present invention, the gold coating layer on the surface of the detection end functions as a light-shielding portion for blocking light, and evanescent light is taken in from the opening at the tip of the detection end, so that the peripheral end of the clad is obtained. It is possible to provide a photon scanning tunneling microscope having high detection efficiency without causing the portion to collide with the sample surface, damaging the sample and the optical fiber probe.

According to the present invention, the distance control means controls the scanning means based on the force measured by the measuring means to keep the distance between the surface of the sample and the optical fiber probe constant, thereby improving the measurement accuracy. A high photon scanning tunneling microscope can be provided.

In the present invention, the light source irradiates the detection light from the side of the optical fiber probe, and the detecting means measures an interference pattern generated when the detection light from the light source is blocked by the optical fiber probe. By detecting the displacement of the optical fiber probe, the displacement of the optical fiber probe can be measured with high accuracy, and a photon scanning tunnel microscope with improved measurement accuracy of the surface shape of the sample can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the structure of a photon scanning tunneling microscope to which the present invention has been applied.

FIG. 2 is a side view showing a specific configuration of a displacement detection unit included in the photon scanning tunneling microscope.

FIG. 3 is a diagram for explaining the operation of the displacement detection unit.

FIG. 4 is a diagram schematically illustrating the principle of a photon scanning tunneling microscope.

FIG. 5 is a diagram showing a structure of a conventional photon scanning tunneling microscope.

[Explanation of symbols]

 Reference Signs List 1 laser light source 2 sample 3 optical fiber probe 3a base end 3b detection end 4 photodiode 5 drive unit 6 control unit 7 image display unit 10 optical system 11 lens 12 mirror 13 prism 20 displacement detection unit 21 laser light source 22 photodiode 23 Differential amplifier 24 Amplifier

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01N 13/10-13/24 G12B 21/00-21/24 G01B 5/20 G02B 6/00 JICST file ( JOIS)

Claims (3)

(57) [Claims] 1. An illumination light source for generating illumination light, an optical system for guiding illumination light from the illumination light source to irradiate the sample surface, and an optical fiber having a sharpened tip, which is inclined with respect to the sample. An optical fiber probe disposed to disperse and converge evanescent light localized on the sample surface; light detection means for detecting light from the optical fiber probe and outputting a detection output; Scanning means for changing the positional relationship between the sample and the optical fiber probe so that the tip of the optical fiber probe scans the sample surface, and outputting position information, and detecting light emitted from the side surface of the optical fiber probe by the optical fiber probe. Displacement detecting means for detecting the displacement of the optical fiber probe by measuring an interference pattern generated by the interruption, and detecting by the displacement detecting means. Measuring means for measuring a force received by the optical fiber probe from the surface of the sample based on the displacement, position information from the scanning means, a detection output from the light detecting means, and a force measured by the measuring means. And a shape measuring means for measuring the shape of the sample. 2. The optical fiber probe according to claim 1, further comprising: an optical fiber having a core and a clad, having at one end a base end having a reduced thickness of the clad, and a detection end having a sharpened core at the end of the base end. Having a gold coating layer on the surface of the detection end,
2. The photon scanning tunneling microscope according to claim 1, wherein an opening is provided at a tip of the detection end. 3. The apparatus according to claim 1, further comprising a distance control means for controlling the scanning means based on the force measured by said measuring means so as to keep the distance between the surface of the sample and the optical fiber probe constant. The photon scanning tunneling microscope according to claim 2.