JP2003287522A - Near-field photoexcited squid microscope apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a near-field photoexcited SQUID microscope apparatus whose spatial resolution is on a nanometer scale. <P>SOLUTION: The near-field photoexcited SQUID microscope apparatus is provided with a near-field optical probe (30) which is arranged near a sample (2) and by which near-field light emitted from its tip by light from a light source is made to act on the sample, a SQUID (superconducting quantum interference device) (40) used to detect a change in a magnetic field in a sample region on which the near-field light acts, and a scanning means (13) used to relatively move a near-field light action point on the surface of the sample. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention excites a sample with near-field light and changes the state of the magnetic field of the sample to SQUID (SQUID: S
upperconducting Quantum In
The present invention relates to a near-field photoexcited SQUID microscope apparatus that measures and images with a terence device (superconducting quantum interference device).

[0002]

2. Description of the Related Art Conventionally, there has been known a scanning SQUID microscope apparatus capable of irradiating a sample with a laser beam, detecting a change in a magnetic field at an irradiation position with a SQUID, and obtaining an image from the signal (Japanese Patent Laid-Open No. 2000-242242). See 2001-50934).

In such a SQUID microscope apparatus, the sample 202 is irradiated with the laser beam 101 as excitation light, and the SQUID 103 detects the magnetic change of the irradiated portion of the sample 202, which is imaged.
And, in such a conventional device, the excitation light is
Sample 2 as it is by guiding laser light 101 with an optical fiber or the like
02 or the laser beam 101 is applied to the objective lens 104.
The sample 202 is focused and irradiated onto the sample 202.

[0004]

However, even when the laser light is condensed on the sample surface by the objective lens as described above, the condensed size of the light is limited to about the wavelength of the light. Therefore, it is desired to measure the magneto-optical distribution with high resolution at a resolution of nanometer scale space size.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a near-field photoexcitation SQUID microscope apparatus having a spatial resolution on the nanometer scale.

[0006]

In order to solve the above-mentioned problems, in the present invention, near-field light generated when a sharpened optical fiber is brought close to a sample rather than focusing the light on the sample by an objective lens or the like. To excite the sample. Near-field light is emitted from the tip of an optical fiber with an aperture diameter of several tens of nanometers, enabling optical excitation at a minute size that exceeds the conventional diffraction limit. As a result, the spatial resolution of the scanning SQUID microscope device can be significantly improved, and since the SQUID can be integrally formed near the tip of the optical fiber, there is no positional deviation between the optical axis and the magnetic axis, and stable operation is possible. . Also,
Since the sample and the SQUID and the sample and the tip of the optical fiber can be aligned at the same time, the operability is remarkably improved.

That is, the near-field light-excited SQUID microscope apparatus according to the present invention is arranged in the vicinity of a sample, and the near-field optical probe that causes the near-field light emitted from the tip by the light from the light source to act on the sample, A SQUID (superconducting quantum interference device: SQUID) for detecting a magnetic field change in the sample region on which the near-field light acts, and a scanning unit for relatively moving the near-field light action point on the sample surface. And

According to the near-field light-excited SQUID microscope apparatus according to the present invention, near-field light acts on a sample, but this near-field light is a minute region of the sample, that is, an extremely small portion exceeding the diffraction limit of light. Since it acts only on the microscopic region, the microscopic region of the sample can be used as the observation region, and since the change in the magnetic field of the sample is detected by the SQUID, it is possible to reliably observe extremely small changes in the magnetic field in the microscopic region. it can. Then, the state of this magnetic field change can be observed over the observation surface of the sample by the scanning means.

In the near-field light-excited SQUID microscope apparatus of the present invention, the near-field optical probe is an optical fiber type in which the near-field light is emitted from the tip by sharpening the tip of the core of the optical fiber. The coil is characterized in that it is integrally formed with the optical fiber on the end face of the optical fiber or on the side face near the end face.

According to the near-field light excitation SQUID microscope apparatus according to the present invention, the near-field light acts on the minute region of the sample from the tip of the near-field optical probe formed by sharpening the tip of the core of the optical fiber. Then, the magnetic field of the sample generated by the near-field light is detected by the SQUID from the pickup coil integrally provided on the end face of the optical fiber or on the side face near the end face. At this time, the pickup coil for detecting the magnetic field operates stably because there is no misalignment between the optical axis of the near-field optical probe irradiated with the near-field light and the magnetic detection axis. Further, since the sample and the pickup coil and the sample and the tip of the optical fiber type near-field optical probe can be aligned at the same time, the operability is remarkably improved.

In the near-field optical excitation SQUID microscope apparatus of the present invention, the near-field optical probe is an optical fiber type,
Squid is on the end face of the optical fiber or on the side face near the end face,
It is characterized by being integrally formed.

According to the near-field light excited SQUID microscope apparatus according to the present invention, the near-field light acts on the minute region of the sample from the tip of the near-field optical probe formed by sharpening the tip of the core of the optical fiber. The magnetic field of the sample generated by the near-field light is detected by the SQUID provided integrally with the optical fiber on the end face of the optical fiber or the side face near the end face. At this time, the SQUID for detecting the magnetic field operates stably because there is no positional deviation between the optical axis of the near-field optical probe irradiated with the near-field light and the magnetic detection axis. Further, since the sample and the SQUID and the sample and the tip of the optical fiber type near-field optical probe can be aligned at the same time, the operability is remarkably improved.

Further, the near-field optical excitation SQUID microscope apparatus according to the present invention makes the distance between the near-field optical probe and the sample constant, makes the output of the light source constant, and rearranges the strength of the detected magnetic field according to the scanning position. It is characterized in that it is imaged.

Further, the near-field light-excited SQUID microscope apparatus according to the present invention changes the near-field light probe-sample distance so as to make the output of the light source constant and the strength of the detected magnetic field constant. It is characterized in that the value of the distance between the optical probe and the sample is rearranged according to the scanning position for imaging.

Furthermore, the near-field optical excitation SQUID microscope apparatus according to the present invention makes the distance between the near-field optical probe and the sample constant, and adjusts the intensity of the light source so that the detected magnetic field has a constant intensity. It is characterized by rearranging the output of the light source of (1) and imaging.

Further, the distance between the near-field optical probe and the sample is
It is characterized by measuring by atomic force or shear force between the optical probe and the sample.

According to the near-field light excited SQUID microscope apparatus according to the present invention, the strength of the magnetic field detected by the SQUID,
The near-field optical probe-sample distance and the output value of the light source can be rearranged according to the scanning position to obtain a sample image, and an image according to the type of sample and the purpose of observation can be obtained. The near-field optical probe-sample distance can be selected by atomic force or shear force, and an image can be obtained according to the sample type and the purpose of observation.

The near-field light-excited SQUID microscope apparatus according to the present invention is characterized in that the light source has a variable wavelength of output light.

According to the near-field light-excited SQUID microscope apparatus according to the present invention, a microscope apparatus image of a sample can be obtained with light having a wavelength depending on the type of the sample and the purpose of observation.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing the basic configuration of a near-field light-excited SQUID microscope apparatus according to the first embodiment of the present invention, and FIG. 2 is an optical diagram of the near-field-light-excited SQUID microscope apparatus according to the embodiment of the present invention. FIG. 3 is a perspective view illustrating the structure of the fiber type probe tip, FIG. 3 is a side view of the optical fiber type probe tip of the near-field optical excitation SQUID microscope apparatus shown in FIG. 2, and FIG. 4 is a diagram of the optical fiber type probe tip shown in FIG. FIG. 5 is a bottom view, FIG. 5 is an illustration of an embodiment in which an optical fiber and a SQUID are separated, and FIG. 6 is an illustration of an embodiment in which a detection coil is provided in the optical fiber.

(First Embodiment) As shown in FIG. 1, a near-field light-excited SQUID microscope apparatus 1 according to this embodiment causes near-field light to act on a sample 2 from a near-field optical probe 30,
The near-field optical probe 30 includes a detection unit 10 that detects magnetism with a SQUID 40, and a control unit 60 that controls the detection unit 10 and performs imaging.

The detector 10 comprises a magnetic shield 11 for shutting off the magnetism from the outside, and a dewar 12 for keeping the inside temperature low. Inside the dewar 12, liquid helium 29 is stored, and the inside temperature of the liquid helium is ( Held at 4.2K).

Further, in the dewar 12, the sample 2 is driven by a piezo element as a scanning means to move the sample 2 in three directions of XYZ orthogonal to each other, and the near-field light action point on the surface of the sample 2 moves relatively to the sample 2. An XYZ piezo stage 13 is arranged. Further, the near-field optical probe 30 is provided with a micro-displacement means 20 for micro-displacement of the near-field optical probe 30 in the axial direction or micro-vibration in the direction perpendicular to the axis. It is measured by the utilized probe displacement amount measuring means (not shown).

In this example, the near-field optical probe 30 comprises a tip 21 of an optical fiber 14 composed of a core 21 and a clad 22.
It is formed by sharpening the core 21 of 4a.

In the present example, the near-field optical probe 3
Reference numeral 0 denotes a SQUID (superconducting quantum interference device: SQUID) 4 for detecting a change in the magnetic field in the sample region acted by the near-field light.
0 is integrally formed at the tip thereof. In FIG. 1, reference numeral 15 is a control line between the SQUID 40 and the control unit 60, and 16 is an X line.
A column that supports the YZ piezo stage 13 in the dewar 12, 17 is a holding portion that holds the optical fiber 14, and 18 is X.
A control line connecting the YZ piezo stage 13 and the control unit 60, and a control line 19 connecting the minute displacement means 20 and the control unit 60.

In this example, the XYZ piezo stage 13 is
In addition to moving the sample 2 in the horizontal direction (XY direction) to scan relatively to the near-field optical probe 30, the distance between the sample 2 and the near-field optical probe 30 (Z direction) can be changed. It is a thing. This XYZ piezo stage 13
Can realize a movable range of 10 μm or more and a position resolution of about 0.1 nm.

The control unit 60 has a system control unit 61 having an interface for connecting a computer to each control unit as a whole, a stage control unit 62 for controlling the position of the XYZ piezo stage 13, and a value for the SQUID 40. A SQUID control unit 63 for reading, a light control unit 64 for controlling the light amount of the light source including a light source to the optical fiber 14, and a displacement amount control unit 6 for controlling the displacement amount of the minute displacement means 20.
5 and an image display unit 66 that rearranges the amounts detected by the respective control units 62 to 65 to form an image. As the light source, a variable wavelength light source or a plurality of light sources whose wavelengths can be appropriately changed are selected and used.

The near-field optical probe 30 arranged directly above the sample 2 in the dewar 12 of the detector 10 is
As shown in FIG. 2, the SQUID 40 is integrally formed with the core 21 and the clad 22 located at the tip portion 14 a of the optical fiber 14. In this example, the optical fiber 14 is of a single mode, and the SQUID 40 is formed on the tip surface 24 of the clad 22. Squid 40 is a superconducting ring 4
Two Josephson junctions 42 are formed in the ring 1 and the ring. In FIG. 2, 15a indicates a current lead wire of the control line 15, and 15b indicates a voltage lead wire.

In this example, the core 21 of the optical fiber 14 is
A few μm to the outer side of the clad 22 in a conical shape
The core 21 is formed so as to protrude by .mu.m, and is formed as a taper portion 23 having an opening 25 at its tip. In this example, the core 21 of the optical fiber 14 has a diameter of about 10 μm, and the cladding 22 has an outer diameter of about 100 μm.

3 and 4 show specific examples of the configuration of the probe tip. In this example, a superconducting ring 41 is formed so as to surround the core 21, and a Josephson junction 42 by weak bridge coupling is provided. Further, the sharpened taper portion 23 of the core 21 is covered with a waveguide 26 of a metal thin film which also has a light shielding effect so as to prevent useless light from leaking. The thin metal film is removed from the tip of the tapered portion 23, and an opening 25 having a diameter of 50 nm or less is provided. In this example, near-field light is emitted from the opening 25.

Here, a method of manufacturing the near-field optical probe 30 will be described. First, the optical fiber 14 is a silica-based single-core single-mode fiber, and the core 21 is made of Ge.
O ₂ doped with about 10 mol% is used. The end surface of the optical fiber 14 is polished to form a flat surface. Then, when wet etching is performed with a hydrofluoric acid-based etching solution, the etching rate of GeO ₂ contained in the core 21 is slower than that of SiO ₂ , so that the tapered portion 23 in which the core 21 is sharpened conically can be formed. Specifically, HF (47
%): NH ₄ F (75%): H ₂ O = 0.4: 1: 1,
An optical fiber probe having a core temperature of 50 nm and a radius of curvature of 50 nm was manufactured at a liquid temperature of 35 degrees.

Next, Nb was deposited on the tip of the optical fiber by sputtering. At this time, it is advisable to rotate the optical fiber so that the film thickness becomes uniform or to revolve the position of the sputtering target. Next, the end face of the optical fiber is processed by a focused ion beam device (FIB). FI
B has a function of converging gallium ions to about 10 nm and scanning the gallium ions to perform ion milling in an arbitrary pattern. As shown in FIG. 4, the Nb film other than the SQUID and the waveguide is removed. In order to pull out the electrode from the SQUID manufactured on the end face, the electrode portion leading to the side face of the optical fiber is also processed. If the Josephson junction is of the bridge type, the film deposition and the ion milling only have to be done once, so it is easy to fabricate. DC with two Josephson junctions in this example
I showed the type SQUID, but if you use AC type SQUID,
Since only one joint is required and the labor for balancing the two joints can be saved, it is easier to manufacture.

Next, the optical fiber is tilted by 90 degrees, and the SQUID lead-out electrode portion and the core tip portion are milled from the side surface direction. As a result, the Nb film covering the tip portion is removed, and the opening 25 is exposed. The smaller the diameter of the opening 25 is, the more the spatial resolution can be improved, but the amount of light is small, so about 50 nm is appropriate.

After that, a thin wire cable is connected to the SQUID 40 as the shielded control line 15 so that a signal can be transmitted to the SQUID control unit 63.

The near-field optical probe 30 prepared in this way
Are arranged as shown in FIG. In this example, the temperature in the cryostat is the liquid helium temperature (4.2K) at which Nb becomes a superconducting state. The cooling may be performed by immersing it in the liquid helium in the present apparatus as shown in FIG. 1, but conduction cooling from a refrigerator or the like may be used.

Here, when the sample is a semiconductor, electrons and holes are generated in the sample when irradiated with light having a photon energy larger than the band gap. Generation and movement of these are weak, but electromagnetic waves are generated. Squid is highly sensitive and responds up to high frequencies. There are two cases for controlling the SQUID.

One is the flux lock loop (F
LL) circuit (closed loop). In this case, a dynamic range of about 6 digits can be realized.
However, the practical limit of the frequency response speed is 1 MHz.

The other method is to use it as it is in an open loop. When a Josephson junction is irradiated with an electromagnetic wave in the microwave band, a DC voltage proportional to the frequency is generated in the Josephson junction.

In the near-field light-excited SQUID microscope apparatus configured as described above, the following three steps are required to obtain an image of a sample.
There is a street way. These methods may be appropriately selected depending on the type of sample and the purpose of measurement.

That is, the distance between the near-field optical probe and the sample is made constant, the output of the light source is made constant, and the intensity of the detected magnetic field is rearranged in accordance with the scanning position for imaging. The near-field optical probe-sample distance is changed so that the output of the light source is constant and the strength of the detected magnetic field is constant, and the value of the optical probe-sample distance is rearranged according to the scanning position. To image. Near-field optical probe-the distance between the sample is constant, the intensity of the light source is adjusted so that the detected magnetic field has a constant intensity,
The output of the light source at that time is rearranged and imaged.

In the above cases, the near-field optical probe-
The sample-to-sample distance can be measured by the atomic force or shear force between the optical probe and the sample. These measurements are performed by drivingly controlling the minute displacement means 20 while monitoring the drive amount in the displacement amount control section 65 by the probe displacement amount measuring means. That is, when measuring the interatomic force, the near-field optical probe 30 is slightly moved in the axial direction, while when using shear force, the near-field optical probe 30 is vibrated and its amplitude is measured. -Measure the distance between the samples.

(Second Embodiment) FIG. 5 shows a second embodiment of the near-field light-excited SQUID microscope apparatus according to the present invention. In this example, the optical fiber 14 and the SQUID 70 are separated. The SQUID 70 is formed on the flat substrate 72, and the sample 2 is arranged in the center of the SQUID 70. In this case SQUID 70
In order to prevent a chemical reaction between the sample 2 and the sample 2 and physical damage, a protective film 71 may be provided on the SQUID 70. The shape of the tip portion 14a of the optical fiber 14 is the same as that of the first embodiment except that no SQUID is formed. Further, the image formation is performed in the same manner as in the first embodiment.

Since the SQUID 70 is not integrated with the optical fiber in the near-field light-excited SQUID microscope apparatus according to this example, it can be manufactured at low cost. On the other hand, when the sample is moved for scanning, the SQUID also moves, which causes noise due to movement in the earth's magnetism. Therefore, it is advisable to move the optical fiber side for scanning. However, if the scanning range is made too large, the deviation from the center of the SQUID becomes large and the magnetic efficiency deteriorates.

(Third Embodiment) FIG. 6 shows a third embodiment of the near-field light excitation SQUID microscope apparatus according to the present invention. In this example, N formed on the tip portion 14a of the optical fiber 14 by the method described in the first embodiment.
Only the pickup coil 81 made of b is provided. The SQUID (not shown) is magnetically shielded at a position away from the tip of the optical fiber. Incidentally, reference numeral 8 in FIG.
2,83 are made at the same time as the pickup coil 81,
A signal line connecting the pickup coil 81 and the SQUID, and 84 a shield material. The shape of the tip portion 14a of the optical fiber 14 is the same as that of the first embodiment except that no SQUID is formed. Further, the image formation is performed in the same manner as in the first embodiment.

In this example, since it is not necessary to make a Josephson junction at the tip of the optical fiber, processing becomes easy. one side,
If the distance between the pick-up coil and the SQUID is too long, noise from the wiring connecting the pick-up coil and the SQUID cannot be ignored and the S / N ratio may deteriorate. Therefore, it is necessary to sufficiently shield the shield.

[0046]

As described above, according to the near-field light-excited SQUID microscope apparatus according to the present invention, the near-field light is made to act on the sample from the near-field optical probe, and the near-field light is acted on by the SQUID. Since the change in the magnetic field is detected, the spatial resolution is about several nanometers, which is 100 times more improved than the conventional one.

Further, in the present invention in which the pickup coil is integrated with the near-field optical probe, the pickup coil can be arranged at a distance of several microns from the sample, so that the magnetic sensitivity is greatly improved. Furthermore, since the pickup coil and the optical fiber are integrated, the positional relationship between the optical axis and the magnetic axis becomes constant, improving accuracy and stability.

Further, in the present invention in which the SQUID is integrally formed with the near-field optical probe, the SQUID can be arranged at a distance of several microns from the sample, so that the magnetic sensitivity is significantly improved. Furthermore, since the SQUID and the optical fiber are integrated, the positional relationship between the optical axis and the magnetic axis becomes constant, improving accuracy and stability.

Furthermore, in the present invention, the intensity of the magnetic field detected by the SQUID, the near-field optical probe-sample distance, and the output value of the light source are rearranged according to the scanning position to obtain a sample image. Images can be obtained according to the type and purpose of observation. The near-field optical probe-sample distance can be selected by atomic force or shear force, and an image can be obtained according to the sample type and the purpose of observation.

Further, according to the present invention in which the wavelength of output light can be changed, it is possible to obtain a microscope image of a sample with light having a wavelength according to the type of sample and the purpose of observation.

As described above, the near-field photoexcitation SQUID microscope apparatus according to the present invention enables analysis in a minute area of a semiconductor, and can be an important evaluation apparatus in material development and quantum device development.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of a near-field light excitation SQUID microscope apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating a structure of a tip of an optical fiber type probe of a near-field light excitation SQUID microscope apparatus according to an embodiment of the present invention.

FIG. 3 is a side view of the tip of an optical fiber type probe of the near-field light excitation SQUID microscope apparatus according to the embodiment of the present invention.

FIG. 4 is a bottom view of the tip of the optical fiber type probe of the near-field light excitation SQUID microscope apparatus according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram of a type in which an optical fiber and a SQUID are separated in a near-field light excitation SQUID microscope apparatus according to an embodiment of the present invention.

FIG. 6 is an explanatory diagram of a type in which a detection coil is provided in an optical fiber of a near-field light excitation SQUID microscope apparatus according to another embodiment of the present invention.

FIG. 7 is an explanatory diagram showing an example of a conventional scanning SQUID microscope apparatus.

[Explanation of symbols]

1 Near-field excitation SQUID microscope device 2 samples 10 Detector 11 Magnetic shield 12 Dewar 13 XYZ piezo stage (scanning means) 14 optical fiber 14a tip 15 control lines 20 Micro displacement means 21 core 22 Clad 23 Tapered part 24 Tip surface 25 openings 26 Waveguide 30 Near-field optical probe 40 Squid 41 Superconducting ring 42 Josephson junction 60 control 61 System control unit 62 Stage control unit 63 SQUID control unit 64 Light control unit 65 Displacement control unit 66 Image display section 70 Squid 71 Protective film 72 flat board 81 pickup coil

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masato Yoshizawa             4-17-19 Takamatsu, Morioka-shi, Iwate Iwadai Takamatsujuku             Sha 2-405 F-term (reference) 2G017 AA01 AD32                 2G053 AA30 AB01 AB13 CA10 CA18                       CA20 DB11 DB19                 4M113 AC07 AC08 AC22 BA04 CA13                       CA42

Claims (8)

[Claims] 1. A near-field optical probe which is arranged close to a sample and applies near-field light emitted from a tip by light from a light source to the sample, and a magnetic field change in a sample region acted by the near-field light. A near-field light-excited SQUID microscope apparatus, comprising: a SQUID for detecting the above, and a scanning means for relatively moving the near-field light action point on the sample surface. 2. The near-field optical probe is an optical fiber type in which the tip of the core of the optical fiber is sharpened and near-field light is emitted from the tip, and the pickup coil of the SQUID is an end face of the optical fiber or a side face near the end face. The near-field light-excited SQUID microscope apparatus according to claim 1, wherein the near-field light-excited SQUID microscope apparatus is integrally formed with the optical fiber. 3. The near-field optical excitation SQUID microscope according to claim 1, wherein the near-field optical probe is an optical fiber type, and the SQUID is integrally formed on an end face of the optical fiber or a side face near the end face. apparatus. 4. The near-field optical probe-sample distance is kept constant, the output of the light source is kept constant, and the detected magnetic field strength is rearranged in accordance with the scanning position for imaging. 1. The near-field light excited SQUID microscope apparatus according to claim 2 or claim 3. 5. The near-field optical probe-sample distance is changed so that the output of the light source is constant and the strength of the detected magnetic field is constant, and the value of the optical probe-sample distance is set to the scanning position. The near-field photo-excited SQUID microscope apparatus according to claim 1, wherein the image is relocated and imaged. 6. The near-field optical probe-sample distance is kept constant, the intensity of the light source is adjusted so that the detected magnetic field has a constant intensity, and the output of the light source at that time is rearranged for imaging. The near-field light-excited SQUID microscope apparatus according to claim 1, claim 2, or claim 3. 7. The near-field optical probe-sample distance is measured by an atomic force or shear force between the optical probe and the sample.
The near-field light-excited SQUID microscope apparatus described. 8. The light source according to claim 1, wherein the wavelength of the output light is variable, claim 1, claim 2, claim 3, claim 4, claim 5, claim 6 or claim 7. Near-field optically excited SQUID microscope system.