JP2967172B1 - Spin detection axis rotation type spin polarization scanning tunneling microscope - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To provide a spin-polarized scanning tunneling microscope capable of detecting a magnetization state in an arbitrary direction by freely controlling the direction of magnetization in a probe with external light. SOLUTION: This device has a C3v type and a C4v type,
Both components include an STM control unit, a probe, a laser light source, and a phase detection amplifier. The C3v type has a general elliptical modulator, and the C4v type has a beam splitter and a circular polarization modulator as constituent elements. The probe is made of a direct transition semiconductor such as GaAs having C3v and C4v symmetry in the axial direction, respectively. Irradiate the probe with laser. By modulating the polarization of the irradiation light in the C3v type and the incident direction in the C4v type, carriers having spins parallel and anti-parallel to the target spin detection direction are alternately generated in the probe,
A two-dimensional distribution of spin polarization in an arbitrary direction on the sample surface is measured by detecting a change in tunnel current to the sample with a phase detection amplifier while scanning the position of the probe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spin-polarized scanning tunneling microscope, and more particularly, to a spin-detecting axis-rotated spin-polarized scanning tunnel capable of detecting a magnetization state of a magnetic material surface on an atomic scale. For a microscope.

[0002]

2. Description of the Related Art A scanning tunneling microscope (STM) is an apparatus that enables observation of the arrangement of atoms on a surface with atomic resolution. In this apparatus, when a nonmagnetic metal probe such as W (tungsten) or Pt (platinum) is scanned on a sample surface, a tunnel current flowing between the sample and the probe is measured to obtain an atomic image. The basic principle.
However, in this method, information on the magnetic state of the sample cannot be obtained because the tunnel current is not directly related to the magnetic state of the sample.

On the other hand, recently, a ferromagnetic probe is attached to the tip of a cantilever to scan the surface of a sample and detect a magnetic force applied to the probe from the sample, thereby measuring a magnetic state of the sample. Force microscopes (MFM) have been put to practical use.
However, this method has a problem that the spatial resolution is poor because a magnetic force that is a long-distance force is used.

In order to overcome these problems, a technique of a spin-polarized tunnel microscope (SP-STM) for obtaining magnetic information by measuring a spin-polarized tunnel current has been developed. For example, Wiesendanger et al. Observed the magnetic state of the antiferromagnetic Cr surface using a ferromagnetic CrO ₂ (chromium oxide) probe (R. Wiesendanger, HJ Guentherodt, GG Guentherod).
t, RJGambino, andR.Ruf, ”Observation of vacuum t
unneling of spin-polarized electrons with the scann
ing tunneling microscope ", Physical Review Letter
s, volume 65, number 7 (1990) pages 247-250.). However, this method has a problem that the magnetic field of the sample is disturbed by the leakage magnetic field of the probe because the ferromagnetic probe is used.

[0005] Therefore, by irradiating the inside of a probe made of a non-magnetic material such as GaAs (gallium arsenide) with light from the outside,
There has been proposed a method of exciting a small amount of electron spins and measuring the tunnel current of the spins. For example, Suzuki et al. Measured the magnetic domain of a Co (cobalt) thin film using a GaAs probe (Y. Suzuki, W. Nabhan, and K. Tanaka, "Ma
gnetic domains of cobalt ultrathin films observed
with a scanning tunneling microscope using optical
ly pumped GaAs tips ", Applied Physics Letters, volum
e71, number 21 (1997) pages 3153-3155.). In the measurement of Suzuki et al., Since the sample surface was irradiated with light perpendicularly, the apparatus was sensitive only to the component of magnetization perpendicular to the sample surface.

[0006]

On the other hand, it is known that the magnetization of a sample is directed in various directions in a space around a domain wall or the like. Therefore, in a spin-polarized STM device, it is desirable that magnetization in an arbitrary direction can be measured.

However, as described above, in the conventional spin-polarized STM using a GaAs probe, it is necessary to change the direction of light irradiation in order to change the direction of measurable magnetization. There was a problem to be solved that involved great difficulty. In addition, in order to detect spin in the in-plane direction of the film, in the conventional spin-polarized STM using a direct transition type semiconductor, it is necessary to make light substantially horizontally incident on the film surface. Until now, there has been no successful case of observing a magnetic image.

Therefore, an object of the present invention is to solve such a difficulty and to detect the magnetization state in an arbitrary azimuth (direction) by freely controlling the magnetization direction in the probe with external light. It is another object of the present invention to provide a spin detection axis-rotating spin-polarized scanning tunneling microscope.

[0009]

In order to achieve the above object, the present invention is directed to a probe made of a direct transition semiconductor such as GaAs having C3v symmetry in the axial direction, A laser light source for irradiating the laser light in the axial direction, and oscillating the polarized light of the irradiated light between two types of polarized light determined corresponding to the target spin detection direction, thereby forming the target spin detection direction in the probe. A general elliptical polarization modulator that alternately generates carriers having parallel spins and antiparallel spins, a phase detection amplifier that detects a change in tunnel current to the sample of the carrier, and the tunneling current detected by the phase detection amplifier. And an STM controller for measuring a two-dimensional distribution of spin polarization in an arbitrary direction on the sample surface by scanning the probe while detecting a change in the spin polarization.

Preferably, when the (θ, φ) direction of the polar coordinates is detected as the direction of the spin polarization, the polarization modulation of the light by the general elliptical polarization modulator is

[0011]

(Equation 2)

Performed between the [0012], however, the angle of the main shaft with the x-axis of the λ is elliptically polarized light, tan omega is the ellipticity, also, P _y is appearing y- direction when irradiated with x- linearly polarized light The spin polarization degree, P _z, is the spin polarization degree in the z-direction that appears when irradiated with right circularly polarized light, and the modulation frequency is 10 kHz or more and 100 kHz or less.

Preferably, a GaAs probe sharpened in the (111) direction by anisotropic etching is used as the probe having C3v symmetry, and a semiconductor laser (1.4 eV to 1.4 eV) is used as the laser light source for irradiation. 1.8e
V) is used.

Preferably, a Ga1-xAlxAs layer (0.1 <x <1, thickness 0.02 to 0.2 mm) is provided as a window material on the back surface of the probe, and light is irradiated from the back surface of the probe. The length of the probe is not more than 5 μm and not less than 200 nm.

Preferably, the general elliptically polarized light modulator comprises a Babinet Soleil phase compensator and a photoelastic modulator.

In order to achieve the above object, a sixth aspect of the present invention provides a laser light source for generating a laser beam and
A probe made of a direct transition semiconductor such as GaAs having a symmetry of 4v, and a linear polarization (p) of the laser beam applied to the probe from the axial direction of the probe and an angle inclined about ± 45 degrees with respect to the axis.
A beam splitter that alternately generates carriers having spins in the direction of the film surface in the probe by irradiating the laser light alternately with the probe. Circularly polarized light modulator that alternately generates carriers having spin upward and downward in the direction perpendicular to the film surface in the probe, and phase detection that detects the difference in tunnel current to the sample of the carrier. An STM for measuring a two-dimensional distribution of spin polarization in a vertical direction and a plane direction of the sample surface by scanning the probe while detecting a difference in the tunnel current with the amplifier and the phase detection amplifier. And a control unit.

Here, the modulation frequency of the circular polarization modulator is preferably 10 kHz or more and 100 kHz or less.

Preferably, a GaAs probe sharpened in the (100) direction by anisotropic etching is used as the probe having C4v symmetry, and a semiconductor laser (1.4 eV to 1.4 eV) is used as the laser light source for irradiation. 1.8e
V) is used.

Preferably, a Ga1-xAlxAs layer (0.1 <x <1, thickness 0.02 to 0.2 mm) is provided as a window material on the back surface of the probe, and light is emitted from the back surface of the probe. Irradiation is performed, and the length of the probe is not more than 5 μm and not less than 200 nm.

Preferably, a hemispherical lens having a diameter of 3 mm or less is arranged on the back surface of the probe on the light emitting side of the beam splitter, and a change in the incident angle of the light beam is caused by changing the angle of incidence of the light beam. The change of the incident position on the lens is performed by changing the incident position on the lens, and the change of the incident position of the light beam on the hemispherical lens is performed by oscillating a mirror or a prism constituting the beam splitter.

Preferably, the STM control unit comprises:
By rotating the sample or the entire optical system with respect to the axis of the probe, the spin detection direction is rotated in the sample plane.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a basic configuration of an embodiment of the present invention will be described.

In the spin-polarized STM device of the present invention, Ga
After adjusting the crystallographic symmetry and the macroscopic symmetry of a direct transition type semiconductor probe such as As, a spin-polarized electron of an arbitrary direction is obtained by controlling the polarization of the irradiation light, By measuring a tunnel current of the spin-polarized electrons to the ferromagnetic sample, magnetization in an arbitrary direction is locally detected.

On the other hand, in the conventional spin-polarized STM using the above-mentioned GaAs probe, only the so-called Fano effect (Fano effect) relating to spin-dependent photoelectron excitation was used.
Therefore, the direction of the excited spin was parallel to the traveling direction of light.

On the other hand, in the present invention, by using the so-called Tamura-Fader effect relating to spin-dependent photoelectron excitation, it is possible to excite spins perpendicular to the light traveling direction or at an arbitrary angle. I have to. The existence of the Tamura-Fader effect is theoretically expected (E. Tamura, W. Piepke, and R. Feder, "New spin-polari
zation effect in photoemission from nonmagnetic su
rfaces ".Physical Review Letters, volume59, number
8, (1987), page 934-937), and further experimentally confirmed in photoemission from a Pt (platinum) surface (B. Schmiedeskamp, B. Vogt, and U. Heinzmann, "Expe").
rimental verification of a new spin-polarization e
ffect in photoemission: polarized photoelectrons f
rom Pt (111) with linearly polarized radiation in n
ormal incidence and normal emission ", Physical Revi
ew Letters, volume60, number 7, (1988) page 651-654.
reference).

In the present invention, the Tamura-Fader effect and Fano
By using the effects in combination, it is possible to freely control the magnetization direction of the probe and measure the magnetization in an arbitrary direction without changing the light incident direction.

In the spin-polarized STM of the present invention, a direct transition type semiconductor having a crystal structure of C3v (compound triangular pyramid) or C4v (compound square pyramid) is used as a probe. C
When a direct transition type semiconductor having 3v symmetry is used as a probe, a laser beam is irradiated in parallel to the axis of the probe,
On the other hand, when a direct transition type semiconductor having C4v symmetry is used as a probe, a laser beam having an angle of about ± 45 degrees with the axis of the probe and a laser beam parallel to the axis are irradiated.

In the case where a direct transition type semiconductor having C3v symmetry is used as a probe, the irradiation light is made into a right-handed circularly polarized light and a left-handed circularly polarized light, so that the carrier is spin-polarized parallel or antiparallel to the axis ( (Conduction electrons or holes). On the other hand, by irradiating linearly polarized light in this arrangement, carriers that are spin-polarized in the film plane can be excited. The in-plane direction of the spin rotates in the film plane by rotating the polarization plane of the light. Therefore, by combining circularly polarized light and linearly polarized light, it is possible to excite a spin-polarized carrier oriented in an arbitrary direction in space.

Now, the x and y axes are taken in two directions perpendicular to the film surface, the z-axis is a direction perpendicular to the film surface, and the electric field vector of the irradiated light is expressed in Jones notation.

[0030]

(Equation 3)

Write: The x-axis is in one mirror plane of C3v. At this time, the spin polarization vector of the electron (hole) generated in the probe is

[0032]

(Equation 4)

## EQU1 ## Here, P _y is x- linearly polarized light emerges when irradiated y- direction of the spin polarization, the P _z is extremely appearing z- direction of the spin polarization when illuminated with right-circularly polarized light. Spin polarization P and polar coordinates (θ,
The direction of the spin polarization expressed by φ) is

[0034]

(Equation 5)

## EQU1 ## Where (θ, φ) is (π /
2,0) was taken to match the x-axis. This device changes the polarization of irradiation light.

[0036]

(Equation 6)

By modulating between the above, electrons (holes) having spin polarization in the (θ, φ) direction and in the (π−θ, φ + π) direction are alternately generated in the probe. The two-dimensional distribution of the spin polarization in the (θ, φ) direction on the sample surface is measured by scanning the probe while detecting the difference in the tunnel current of these carriers to the sample with the phase detection amplifier. .

On the other hand, when a direct transition type semiconductor having C4v symmetry is used as a probe, the light irradiated in the z-axis direction is subjected to right and left circularly polarized light modulation, so that the probe is moved in the + z direction and the −z direction in the probe. Electrons (holes) having spin polarization are generated alternately. The two-dimensional distribution of spin polarization in the vertical direction (z direction) on the sample surface is measured by scanning the probe while detecting the difference in tunnel current between these carriers and the sample with the phase detection amplifier. .

On the other hand, the linearly polarized light beam is irradiated to the probe from a direction inclined at about 45 degrees in the + x direction and the -x direction from the axis of the probe. The plane of polarization is an xz plane. +
With light irradiation inclined to the x side, electrons (or holes) spin-polarized in the + y (-y) direction are excited in the probe. -X
With the light irradiation tilted to the side, electrons (or holes) spin-polarized in the -y (+ y) direction are excited in the probe. These light irradiations are performed alternately, and the probe is scanned while detecting the difference of the tunnel current of the carrier excited by the carrier to the sample by the phase detection amplifier, so that the in-plane direction (y direction) to the sample surface is obtained. ) Is measured. By rotating the sample or the entire optical system with respect to the z-axis, the spin detection direction can be rotated in the sample plane.

[0040]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

First, embodiments of the present invention will be described separately for the C3v type and the C4v type.

1. FIG. 1 shows a configuration example of a C3v type device using a direct transition type semiconductor having a C3v type C3v symmetry as a probe. Here, 11 is a semiconductor probe using a direct transition semiconductor having C3v symmetry as a probe, 12 is a state of modulating light polarization, 13 is a general elliptical polarization modulator that performs light polarization modulation, and 14 is The laser light source and 15 are a sample.

In the configuration shown in FIG. 1A, a laser light source 14, a general elliptically polarized light modulator 13, and a semiconductor probe 1 are viewed from above.
1, the sample 15 is arranged in this order, and in the configuration of FIG. 1B, the laser light source 14, the general elliptically polarized light modulator 13, the sample 15, and the semiconductor probe 11 are arranged in this order from the bottom of the figure. Although the sequence order is different, both are C3
Acts the same as a v-type device.

First, a tunnel current is obtained by vertically bringing the probe 11 close to the sample 15. The probe 11 is fixed to a well-known piezo scanner (52 in FIG. 5 described later) composed of a plurality of scanning piezo elements, similarly to a normal STM, and can be freely moved in each of x, y, and z directions. You can move it. Here, the axial direction of the probe 11 is defined as the z direction. Tip 1
1 is scanned in the xy plane, and at the time of the scanning, the height of the probe 11 is set to be the same as in a normal STM, and a feedback circuit (see FIG. ). The bandwidth of the STM control circuit (56 in FIG. 5 described later) that performs this control is set to be smaller than the light modulation frequency described later. For example, it is set to 0 to 15 kHz.

The sample 15 is fixed to a stand or a holding member (not shown) so as to face the probe 11 and perpendicular to the axis of the probe 11. As shown in FIG. 1A, the probe 11 is irradiated with laser light from the back side thereof in parallel with the axis of the probe 11. Of course, as shown in FIG.
The probe 11 may be irradiated with laser light from the back side of the probe 5.
However, in this case, only a sample that transmits light can be measured.

As the laser light source 14, a light source that generates light having an energy between the band gap energy of the probe 11 and the band gap energy of the window material on the back side of the probe 11 is used. At this time, the energy of the photons is
It is desirable that the energy be close to the band gap energy. For example, the probe 11 is made of GaAs, and the window material is Ga0.7A1.
In the case of 0.3 As, from 1.43 eV to 1.80 e
A semiconductor laser emitting light between V is used as a light source.
The light intensity is desirably about 10 mW.

A general elliptically polarized light modulator 13 is provided between the semiconductor laser light source 14 and the probe 11.
Changes the polarization of the laser beam into an arbitrary polarization (elliptical polarization) and modulates the polarization. This polarization modulator 13
For example, a Babinet Soleil phase compensator (13 in FIG. 5 described later)
a) and a photoelastic modulator (13c in FIG. 5 described later). The polarization plane of the semiconductor laser light is set at an angle of 45 degrees with the crystal axis of the Babinet Soleil phase compensator. Also,
The crystal axis of the Babinet Soleil phase compensator and the crystal axis of the photoelastic modulator are set to be parallel.

In the polarization modulator 13 configured as described above, when the direction of the spin to be detected is the (θ, φ) direction in polar coordinates, as described above,

[0049]

(Equation 7)

A modulation is applied between the two polarized lights. However,
It is assumed that the mirror surface of the probe 11 corresponding to the C3v symmetry is parallel to the direction of φ = 0. To apply this modulation,
First, the phase shift δ of the Babinet Soleil phase compensator is

[0051]

(Equation 8)

Adjust to In this state, the laser light source 1
4. The entirety of the Babinet Soleil phase compensator / photoelastic modulator 13 is simultaneously rotated to adjust the polarization plane of the laser light in the direction of -φ / 2. With a photoelastic modulator,

[0053]

(Equation 9)

By alternately generating the phase shift δ, the emitted light is modulated between the aforementioned polarized lights.
This modulation frequency corresponds to a tunnel current detector (5 in FIG. 5 described later).
It is desirable to set it near the upper limit of the bandwidth of 5). For example, a modulation frequency of 15 kHz to 40 kHz is used.

The light modulated in this way is, for example,
As shown in FIG. 1A, irradiation is performed from the back side of the probe 11. As a result, as shown by reference numeral 12, the probe 1
In 1, carriers that are spin-polarized in (θ, φ) and (π−θ, φ + π) directions are alternately formed. If there is such a spin polarization on the surface of the sample 15, the detected tunnel current fluctuates at this modulation frequency. Therefore, the modulation frequency component of the tunnel current is selectively measured by using a phase detection amplifier (51 in FIG. 5 described later) at the subsequent stage of the tunnel current detector.

The measurement signal is recorded on a recording medium together with the position of the probe 11 while the probe 11 is being scanned by a general well-known STM control device (56 in FIG. A two-dimensional image of the magnetic state of the 15 surfaces is obtained. Then, by changing the modulation of light as described above, the direction of the spin to be detected can be arbitrarily changed.

FIG. 2 is a process chart showing a process of preparing the C3v type and C4v type probes. Here, 23 is a GaAs substrate, 22 is a GaAlAs window layer, 21 is a GaAs probe forming layer, 24 is a resist, and 25 is a completed probe.

The probe 11 is made of, for example, GaAs (11
1) GaAlAs window layer 22 on -B (As plane) substrate 23
After growing the p-type GaAs probe layer 21 and forming it, anisotropic etching is performed. That is, as shown in FIG. 2A, GaAs (1) is formed by liquid layer epitaxy.
11) GaAlAs (Al composition 0.3) on -B substrate 23
22) is epitaxially grown to a thickness of about 0.1 mm, and then p-type GaAs (Zn-doped, carrier concentration of 10 ¹⁷ to 10 ¹⁹ cm ⁻³ ) 21 is epitaxially grown to a thickness of about 500 nm.

Next, as shown in FIG. 2B, after a resist 24 is applied to the surface of the crystal, GaAs is applied from the back surface.
The s substrate 23 is removed by selective etching. Subsequently, the resist 24 is exposed by electron beam lithography,
An equilateral triangle mask having a side of 500 nm is made. The sides of this equilateral triangle are (1-10), (01-1) of GaAs21.
And (10-1) direction.

Next, as shown in FIG. 2C, the crystals were subjected to room temperature H ₂ SO ₄ (sulfuric acid): H ₂ O ₂ (hydrogen peroxide): H ₂ O (water) 1: 8: 1 Apply the mask to the etchant until it can be removed naturally. As a result, anisotropic etching occurs and the probe 25 is formed spontaneously. The radius of curvature of the tip of the probe 25 is 50 nm or less.

[0061] 2. FIG. 3 shows a configuration example of a C4v type device using a direct transition type semiconductor having a C4v type C4v symmetry as a probe. The STM part is the same as the C3v type.
Here, reference numeral 30 denotes a sample, 31 denotes a semiconductor probe having C3v symmetry, 32 denotes a hemispherical lens, 33 denotes a state of light polarization modulation, 34 denotes a deflector (beam splitter), and 35 denotes circular polarization modulation. And 36 are laser light sources.

In the configuration shown in FIG. 3A, the laser light source 36, the circular polarization modulator 35, and the deflector 3
4, a hemispherical lens 32, a semiconductor probe 31, and a sample 30 are arranged in this order. In the configuration of FIG. 3B, a laser light source 36, a circular polarization modulator 35, a deflector 3
4, the hemispherical lens 32, the sample 30, and the semiconductor probe 31 are arranged in this order, and the arrangement order of the components is different.
Both have the same function as a C4v type device. Hereinafter, the configuration of FIG. 3A will be described.

The sample 30 is fixed to a table or a holding member (not shown) so as to face the probe 31 and perpendicular to the axis of the probe 31. The probe 31 is irradiated with three laser beams from the back side. The first light beam is parallel to the axis of the probe 31. This light is modulated into right and left circularly polarized light by, for example, a high elasticity modulator constituting the circularly polarized light modulator 35.
The modulation frequency and the wavelength and intensity of the laser are C3v
It is the same as the type. In this manner, carriers that are spin-polarized in the z direction and the −z direction are alternately formed in the probe 31. Note that the axial direction of the probe 31 is the z direction.

If there is spin polarization in the z-axis direction on the surface of the sample 30, the tunnel current fluctuates at this modulation frequency, and this fluctuation is selectively measured by a phase detection amplifier (51 in FIG. 6 described later). To obtain a two-dimensional image. In this case, the device detects a spin-polarized component perpendicular to the film surface.

On the other hand, the second and third light beams are incident on the probe 31 via the hemispherical lens 32 from right and left oblique directions of about 45 degrees. This polarized light is p-polarized light. The wavelength and intensity of these rays are the same as in the case of the C3v type.
Then, the intensity of these two light beams is adjusted to be equal.

Assuming that these two light rays are in the xz plane, a carrier that is spin-polarized in the y (-y) direction is excited in the probe. If the second ray excites a carrier polarized in the y direction, the third ray excites a carrier polarized in the -y direction. Therefore, by alternately irradiating the second and third light beams, if there is a spin-polarized component in the y-direction in the sample 30, the tunnel current fluctuates. This fluctuation is detected by a phase detection amplifier (5 in FIG. 6 described later).
A two-dimensional image is obtained by selectively measuring in 1). in this case,
The device detects a spin-polarized component in the film plane. The orientation in the film plane can be changed by rotating the entire optical system on an axis.

As a method of alternately irradiating the second and third light beams, as shown in FIG. 4, a mirror 42 driven by a piezo 43 and a hemispherical small lens having a probe 31 attached to the back surface thereof are used. 32 can be used. In this case, the light source 41
Is linearly polarized. By slightly rotating the mirror 42 with the piezo 43, the light beam strikes different locations of the hemispheric lens 32. The hemispherical lens 32 has a focal point on its bottom surface, and if the incident position of light on its spherical surface changes, the incident angle of light on the focal point changes. Thus, a change in the position of the light beam can be changed to a change in the incident angle.

The probe 31 is formed by anisotropic etching after growing a GaAlAs window layer and a p-type GaAs probe layer on a GaAs (100) substrate, for example. The process of forming the probe 31 is shown in FIG. 2, which is the same as the case of the C3v probe.

With reference to FIG. 2, the process of forming the C4v probe 31 will be described in detail. GaAs by liquid layer epitaxy
(100) GaAlAs (Al composition 0.3
22) is epitaxially grown to a thickness of about 0.1 mm, and then p-type GaAs (Zn (zinc) doped, carrier concentration of 10 ¹⁷ to 10 ¹⁹ cm ⁻³ ) 21 of about 500 nm
Epitaxial growth (see FIG. 2 (a)).

After a resist 24 is applied to the surface of the crystal, the GaAs substrate 23 is removed from the back by selective etching. Next, the resist 24 is exposed by electron beam lithography to form a square mask having a side of 500 nm. The sides of the square are (010) and (0) of GaAs21.
01) parallel to the direction (see (b) of FIG. 2).

The crystals were subjected to 5 ° C. H ₃ PO ₄ (phosphoric acid): H ₂ O ₂ (hydrogen peroxide): H ₂ O (water) 10:
Apply to the 1: 1 etching solution until the mask can be removed naturally. As a result, anisotropic etching occurs and the probe 2
5 are formed. The radius of curvature of the tip of the probe 25 is 50 nm
It is as follows (see (c) of FIG. 2). (K. Yamaguchi and
S.Tada, "Fabrication of GaAs Microtips for Scanning
Tunneling Microscopy be Wet Etching ", Journal of t
he Electrochemical Socicty, volume 143, number 8 (199
6) See pages 2616-2619).

Next, a configuration example of the entire measurement system of the present invention including the above-described phase detection amplifier, piezo scanner, tunnel current detector, STM control unit, etc.
The type and the C4v type will be described separately.

FIG. 5 shows a configuration example of the C3v type. Reference numeral 51 denotes a phase detection amplifier for detecting a change in the tunnel current of the carrier to the sample 15. Reference numeral 51a denotes a signal input of the phase detection amplifier.
b is its amplified output and 51c is its reference signal input.
A piezo scanner 52 scans the position of the GaAs-C3v probe 11. Reference numeral 55 denotes a tunnel current detecting unit for detecting a tunnel current to the sample 15 of the carrier from the probe 11.
1 as a signal input 51a and as a tunnel current signal input 56a of the STM controller 56.

The laser light source 14 is a semiconductor laser 14
b, a semiconductor laser control power supply 14c for supplying power to the semiconductor laser, and a lens 14a for condensing the laser light of the semiconductor laser into parallel rays, and
A laser beam is irradiated in the axial direction of the C3v probe 11.

The general elliptically polarized light modulator 13 comprises a Babinet Soleil compensator 13a having a phase shift adjusting knob 13b and a photoelastic modulator 13c, and furthermore, a photoelastic modulator for supplying power to the photoelastic modulator 13c. Control power supply 13d
And a polarizer 13e arranged in the incident optical path of the photoelastic modulator 13c to deflect the laser beam. Further, a phase detection amplifier 5 is supplied from the photoelastic modulator control power supply 13d.
1 to the reference signal input 51c. The general elliptically polarized light modulator 13 converts the polarized light of the irradiation light from the polarizer 13e between two kinds of polarized lights determined corresponding to the target spin detection azimuth by using a Vinesoleil compensator 13a and a photoelastic modulator 13c. By vibrating the probe 11, carriers having spins parallel to the target spin detection direction and spins antiparallel to the target spin detection direction are generated alternately.

The STM control unit 56 includes a phase detection amplifier 51
Is supplied as an auxiliary signal input 56b, the auxiliary signal input 56b and the tunnel current signal input 56a are input, and a piezo control signal output 56c is output to the piezo scanner 52 to thereby output the GaAs-C3v probe 11. Is scanned, the two-dimensional distribution of spin polarization in an arbitrary direction on the surface of the sample 15 is measured.

FIG. 6 shows a configuration example of the C4v type. here,
Reference numeral 60 denotes a half mirror, and 61 denotes a total reflection mirror. The phase detection amplifier 51, the piezo scanner 52, the tunnel current detection unit 55, and the STM control unit 56 have the same configurations as those in FIG.

The laser light source 36 is a semiconductor laser 36
c, a semiconductor laser control power supply 36d for supplying power to the semiconductor laser, a lens 36b for condensing the laser light of the semiconductor laser into parallel rays, and a polarizer 36a for polarizing the laser light. C4v probe 31
Is irradiated with a laser beam polarized in the axial direction.

The circular polarization modulator 35 is a photoelastic modulator 35a.
And a photoelastic modulator control power supply 35b for supplying power to the photoelastic modulator 35a. Also, the reference signal input 5 from the photoelastic modulator control power supply 35b to the phase detection amplifier 51.
1c. The circular polarization modulator 35 includes a polarizer 36
The laser light irradiated in the axial direction of the GaAs-C4v probe 31 is subjected to right and left circular polarization modulation by passing the polarization of the irradiation light by the a through the photoelastic modulator 35a. Alternately generate carriers with vertically upward and downward spins. At this time, the mirrors 60 and 34a are removed.

The beam splitter 34 includes a mirror 34a arranged in the optical path of the beam transmitted through the photoelastic modulator 35a,
It has a mirror 42 and a piezo 43 that constitute the deflector shown in FIG.

The laser light emitted from the semiconductor laser 36c passes through the lens 36b and the polarizer 36, changes its direction at the mirrors 60 and 61, reflects off the mirrors 42 and 34a of the deflector, and is collected by the hemispherical lens 32. Then, the light is transmitted through the sample 30 and irradiated on the probe 31. In this way, the beam splitter 34 moves the probe 3 from the axial direction of the probe 31 and from the angle inclined about ± 45 degrees with respect to this axis.
By alternately irradiating 1 with linearly polarized laser light (p-wave), carriers having spins in the film surface direction are alternately generated in the probe 31.

The STM control section 56 has a phase detection amplifier 51
Is supplied as an auxiliary signal input 56b, the auxiliary signal input 56b and the tunnel current signal input 56a are input, and a piezo control signal output 56c is output to the piezo scanner 52, whereby the GaAs-C4v probe 31 is output. Is scanned, the two-dimensional distribution of the spin polarization in the vertical direction and the surface direction of the surface of the sample 30 is measured.

[0083]

As described above, according to the present invention,
It is possible to measure the magnetization of the surface of the ferromagnetic sample in an arbitrary direction on an atomic scale with almost no magnetic influence on the sample. The sensitivity to perpendicular magnetization according to the present invention is the same as that obtained by using a normal direct-transition semiconductor and injecting circularly polarized light parallel to the axis of the probe. For example, in principle, 10% of the total tunnel current
The signal of the degree is obtained. On the other hand, in order to detect spin in the in-plane direction of the film, in a conventional spin-polarized STM using a direct transition type semiconductor without using the present invention, it is necessary to make light incident on the film surface almost horizontally. For this reason, the polarization of light is easily disturbed, and there has been no example of successful observation of a magnetic image to date. However, when the present invention is used, since the polarization of light is not disturbed, a signal equivalent in principle to the detection of vertical spin (about 10% of the total tunnel current) can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a C3v spin-polarized STM according to an embodiment of the present invention.

FIG. 2 shows C3v type and C4 in one embodiment of the present invention.
FIG. 4 is a process chart showing a process of creating a v-type probe.

FIG. 3 is an apparatus configuration diagram of a C4v spin-polarized STM according to an embodiment of the present invention.

FIG. 4 is a schematic diagram illustrating a method of incident light on a C4v type spin-polarized STM according to an embodiment of the present invention.

FIG. 5 is an apparatus configuration diagram of a C3v type measurement system including a phase detection amplifier, a piezo scanner, a tunnel current detector, an STM control unit, and the like in one embodiment of the present invention.

FIG. 6 is an apparatus configuration diagram of a C4v type measurement system including a phase detection amplifier, a piezo scanner, a tunnel current detector, an STM control unit, and the like according to an embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 11 Semiconductor probe having C3v symmetry 12 Modulation of light polarization 13 General elliptical polarization modulator 13a Babinet Soleil compensator 13b Phase shift adjustment knob 13c Photoelastic modulator 13d Photoelastic modulator control power supply 14 Laser light source 14a Lens 14c Semiconductor laser 14a Semiconductor laser control power supply 15 Sample 21 GaAs probe fabrication layer 22 GaAlAs window layer 23 GaAs substrate 24 Resist 25 Finished probe 30 Sample 31 Semiconductor probe having C4v symmetry 32 Hemispherical lens 33 Light State of polarization modulation 34 Deflector (beam splitter) 34a, 60, 61 mirror 35 Circular polarization modulator 35a Photoelastic modulator 35b Photoelastic modulator control power supply 36 Laser light source 36a Polarizer 36b Lens 36c Semiconductor laser 36d Semiconductor laser -Control power supply 41 Light source 42 Deflector (mirror) 43 Deflector (piezo) 51 Phase detection amplifier 51a Signal input 51b Amplification output 51c Reference signal input 52 Piezo scanner 55 Tunnel current detection unit 56 STM control unit 56a Tunnel current signal input 56b Auxiliary signal input 56c Piezo control signal output

──────────────────────────────────────────────────続 き Continuing from the front page (73) Patentee 598143077 Eiichi Tamura 1-4-1 Higashi, Tsukuba City, Ibaraki Prefecture Within the Research Institute of Industrial Technology Integration Area (74) The above three agents Yoshikazu Tani ( 72) Inventor Yoshishige Suzuki 1-1-4 Higashi, Tsukuba, Ibaraki Pref., Institute of Industrial Technology, Institute of Industrial Technology (72) Inventor Eiichi Tamura 1-4-1, Higashi, Tsukuba, Ibaraki, Japan Within the research institute (72) Inventor Walid Nabhan Inspector Hideo Ariya in the Research Institute of Industrial Technology, 1-4-1 Higashi, Tsukuba, Ibaraki Pref. (56) References JP-A-9-280810 (JP, A) JP-A-9-145724 (JP, A) JP-A-10-206434 (JP, A) JP-A-6-160501 (JP, A) JP-A-2-199757 (JP, A) ) Surveyed field (Int.Cl. ⁶ , DB name) G01N 37/00 G01R 33/02

Claims (11)

(57) [Claims] 1. GaAs having C3v symmetry in the axial direction
A laser light source for irradiating a laser beam in the axial direction of the probe, and two kinds of polarizations determined according to a target spin detection direction. A general elliptically polarized light modulator that alternately generates carriers having spins parallel to the target spin detection direction and spins antiparallel to the target by oscillating between the probe and a tunnel current to the sample of the carrier. A phase detection amplifier for detecting a change; a two-dimensional distribution of spin polarization in an arbitrary direction on the sample surface by scanning the probe while detecting the change in the tunnel current with the phase detection amplifier. S to measure
A spin detection axis rotation type spin polarization scanning tunneling microscope comprising a TM control unit. 2. The azimuth of spin polarization is represented by (θ,
φ) When detecting the azimuth, the polarization modulation of light by the general elliptical polarization modulator is expressed by the following equation. Performed between, however, lambda is the angle of the main shaft with the x-axis of the elliptically polarized light, tan omega is the ellipticity, also, P _y appear when illuminated with x- linearly polarized y- directions of spin polarization , P _z
Is the spin polarization in the z-direction that appears when the right circularly polarized light is radiated, and the modulation frequency is 10 kHz or more and 100 kHz.
The spin-detection-axis rotation type spin-polarized scanning tunneling microscope according to claim 1, wherein: 3. A probe pointed by anisotropic etching to a (111) direction as a probe having the C3v symmetry.
3. A spin-detection axis-rotating spin-polarized scanning tunneling microscope according to claim 1, wherein an aAs probe is used, and a semiconductor laser (1.4 eV to 1.8 eV) is used as the laser light source for irradiation. . 4. A Ga1-x as a window material on a back surface of the probe.
AlxAs layer (0.1 <x <1, thickness 0.02 to 0.
4. The spin-polarized scanning spin-polarized scanning tunneling microscope according to claim 3, wherein the probe has a length of not more than 5 μm and not less than 200 nm. . 5. The spin detection axis rotation type spin polarization device according to claim 1, wherein the general elliptical polarization modulator includes a Babinet Soleil phase compensator and a photoelastic modulator. Polar scanning tunnel microscope. 6. A laser light source for generating a laser beam; a probe made of a direct transition semiconductor such as GaAs having C4v symmetry in the axial direction; and ± 45 degrees with respect to the axial direction of the probe and the axis. By alternately irradiating the probe with linearly polarized light (p-wave) of the laser light from the slightly inclined angle, a beam component that alternately generates carriers having spins in the film surface direction in the probe is provided. A circular polarization modulator that alternately generates carriers having vertical and downward spins perpendicular to the film surface in the probe by modulating left and right circular polarization of the laser light irradiated in the axial direction. A phase detection amplifier for detecting a difference in tunnel current from the carrier to the sample, and scanning the probe while detecting the difference in tunnel current with the phase detection amplifier, so that a vertical direction of the sample surface is obtained. Spin detection axis rotation type, characterized by comprising a STM control unit for measuring the two-dimensional distribution of spin polarization and plane direction spin-polarized scanning tunneling microscope. 7. The modulation frequency of the circular polarization modulator is 1
The spin detection axis rotation type spin-polarized scanning tunneling microscope according to claim 6, wherein the frequency is 0 kHz or more and 100 kHz or less. 8. A G4 pointed by anisotropic etching to a (100) direction as a probe having the C4v symmetry.
8. The spin-detection axis-rotating spin-polarized scanning tunneling microscope according to claim 6, wherein an aAs probe is used, and a semiconductor laser (1.4 eV to 1.8 eV) is used as the laser light source for irradiation. . 9. A Ga1-x as a window material on the back surface of the probe.
AlxAs layer (0.1 <x <1, thickness 0.02 to 0.
9. The spin-detecting shaft-rotating spin-polarized scanning tunnel according to claim 8, wherein the probe has a length of not more than 5 μm and not less than 200 nm. microscope. 10. A hemispherical lens having a diameter of 3 mm or less is arranged on the back side of the probe on the light beam emitting side of the beam splitter,
The change of the incident angle of the light beam is performed by changing the incident position of the light beam on the hemispherical lens, and the change of the incident position of the light beam on the hemispherical lens is changed by the mirror constituting the beam splitter. 10. The spin-polarized scanning spin-polarized scanning tunneling microscope according to claim 6, wherein the spinning is performed by vibrating a prism. 11. The apparatus according to claim 6, wherein the STM control unit rotates the sample or the entire optical system with respect to the axis of the probe to thereby rotate the spin detection direction in the plane of the sample. 11. A spin-polarized scanning tunneling microscope according to any one of claims 1 to 10.