JP3390754B2 - Optical 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 an optical scanning tunneling microscope (PSTM) for detecting an array of atoms on a surface of a material, an electron wave or a light wave propagating through the array, and evaluating the characteristics at the atomic level. ) Is related to.

[0002]

2. Description of the Related Art In a conventional STM or optical STM, tunnel current or evanescent light has been measured and evaluated by another current detection unit or light detection unit via a chip at the tip of a probe.

For this reason, the electrical or optical characteristics of the chip body and the current and light propagating portion are important, and various restrictions have been imposed. For example, in the STM, a metal such as tungsten has been used because it is an electrically conductive material.

On the other hand, the optical STM is a system for focusing light leaking from the optical waveguide 2 of the sample 1 on the fiber tip 4a of the optical fiber 4 to form an image, as shown in FIG. The distance dependence of the intensity, that is, the intensity of the leaked light changes exponentially like the tunnel current of the STM. Note that FIG. 7 is an enlarged cross-sectional view of part A of FIG.
In FIG. 6, 3 is a piezoelectric body for finely moving the fiber tip 4a, 5 is an optical multiplier, 6 is a feedback control circuit, 7 is a computer and an image display device, 8 is an objective lens (20 times), 9 is a polarization rotation plate, 10 is a laser.

[0005]

SUMMARY OF THE INVENTION Such an optical STM
In the above, it was necessary to coat the root of the chip with gold or the like so as to prevent leakage of light, leaving only the tip of the chemically etched optical fiber.

In view of the above situation, the present invention adopts a quantum structure capable of emitting light from the tip of the chip and controlling the state from the outside. Provided is an optical scanning tunneling microscope with a quantum effect chip that can detect the evanescent wave that should be detected because it is converted into light with a wavelength different from the wavelength of the light propagating through the substance in the background. The purpose is to do.

[0007]

In order to achieve the above object, the present invention provides, in an optical scanning tunneling microscope, (1) a probe having a semiconductor quantum effect chip supported by a cantilever having an arbitrary vibration mode ; A fine movement mechanism of a probe, a quantum structure modulation mechanism of the semiconductor quantum effect chip, a sample measured by the probe, a sample moving mechanism for setting the sample, a light source mechanism for irradiating the sample with excitation light, The probe is provided with a light detecting means which is close to the sample and detects light emitted by being excited by an electron or light tunnel.

(2) In (1), the tip of the semiconductor quantum effect chip constituting the probe has a sub-nanometer structure such as a quantum well, a quantum wire, and a quantum dot.

(3) In (2), the tip of the semiconductor quantum effect chip is made of a direct transition type semiconductor material such as GaAs or InGaAs.

(4) In (2), the tip of the semiconductor quantum effect chip is made of a pure semiconductor material or a semiconductor material doped with impurities.

(5) In the above (2), the tip of the semiconductor quantum effect chip is made of a material capable of once absorbing a propagating electron wave and emitting it again as fluorescence or phosphorescence. Then, the distance between the semiconductor quantum effect chip and the sample, the intensity of the electron wave, and the characteristics of the sample are measured.

(6) In (2) above, a semiconductor material having a narrow band width such as InGaAs is used for the tip of the semiconductor quantum effect chip, and the absorption is small with respect to the substrate and the sample. Emission at a wavelength can be obtained.

( 7 ) In the above (1), a voltage is applied between the substrate and the tip of the semiconductor quantum effect chip, or between the substrate and the sample, and the tip of the semiconductor quantum effect chip is charged. An optical scanning tunneling microscope capable of externally controlling the quantum effect possessed and varying the electrical or optical characteristics of the semiconductor quantum effect chip according to the characteristics of the detected quantum.

( 8 ) In the above (1), the photodetector means is a photodetector for detecting the light from the semiconductor quantum effect chip by spectroscopic analysis or color filter spectroscopy.

( 9 ) In the above (1), the light source mechanism is
It emits photons with higher energy than the quantization energy of the tip of the semiconductor quantum effect chip.

[0016]

According to the present invention, since it is configured as described above,
By making the tip of the semiconductor quantum effect chip a quantum structure that can emit light and control the state from the outside, it is not necessary to devise the tip of the chip described above, and the wavelength of the light propagating through the substance at the tip is Is converted into different light, so that the evanescent wave to be detected can be discriminated and detected from the background evanescent wave.

Therefore, the signal / noise ratio of the measurement is improved. Also, in order to detect light emitted at the tip of the semiconductor quantum effect chip, it is important only to arrange a detector having high sensitivity in the wavelength range at a high solid angle with respect to the tip of the chip. However, there is an advantage that it is not necessary to consider the signal propagation.

Further, like in consideration of the absorption properties of the sample, set in a range from the time quantization energy designs, the final fine adjustment, varied by controlling the voltage applied to the semiconductor quantum effect chip tip It becomes possible.

[0019]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an optical scanning tunneling microscope (PSTM) using a semiconductor quantum effect chip according to an embodiment of the present invention.
It is a figure which shows the whole structure of.

In the figure, the operation is shown in the optical STM mode as a reference. Light from the light source mechanism 15 (for example, Ar laser) controlled by the control device 20 irradiates the sample 21 (for example, biological sample or semiconductor sample) placed on the sample moving mechanism 16 controlled by the control device 20. .

The light component propagating inside or on the surface of the sample 21 is controlled by the control unit 20 by the control unit 20 by the quantum structure modulation mechanism 14 including the power source which is also controlled by the control unit 20. The controlled cantilever fine movement mechanism 13 picks up the chip portion 12 that can finely move in three dimensions. This is sample 2
It is shown that the propagating light of No. 1 has moved to the portion having the quantum effect at the tip of the tip portion 12 via the tunnel effect.

As a result, the optically excited tip portion having a quantum effect emits fluorescence due to recombination of electrons and holes. This fluorescence is detected by the detector 17 through the spectroscopic mechanism 18 via the condensing optical system 19 such as a lens or a concave mirror. The detected signal is processed by the controller 20 and taken out as information indicating the state of the sample 21. Based on this information, imaging or the like according to the characteristics of the sample 21 may be performed.

The photodetector 17 can detect the light from the semiconductor quantum effect chip 12 by spectroscope or color filter spectroscopy.

Further, as the light source 15 , one that emits photons having energy higher than the quantization energy of the tip of the semiconductor quantum effect chip 12 can be used.

The semiconductor quantum effect chip as a probe will be described below.

FIG. 2 is a diagram showing the structure of a semiconductor quantum effect chip as a probe of the first embodiment of the present invention.

As shown in this figure, a chip portion 12 is grown in a pyramid shape on a substrate 11 used as a cantilever. At the tip of the chip portion 12, a quantum fine structure portion 12a exhibiting a quantum effect is attached. This can be achieved using techniques such as semiconductor nanostructure growth techniques and chemical etching.

The size of the quantum fine structure portion 12a is
In FIG. 2, the root portion is shown at about 500 Å, but the tip portion is reduced to the level of a single atom. That is, it is configured as a fine quantum dot.

As described above, the semiconductor quantum effect chip forming the probe is provided at the end of the substrate such as a semiconductor, and the substrate is chemically controlled and polished to form a cantilever having an arbitrary vibration mode. It was done like this.

Further, in FIG. 2, the quantum fine structure portion 12a is drawn as an extension of the pyramid, but in reality, it is not necessarily this shape. Furthermore, in a semiconductor, such a shape is easier to grow, but in short, by attaching another material (such as a dye molecule) to the tip of the chip portion 12, its structure exhibits a quantum effect. While
It can be considered to operate as an optical STM chip.

The tip of the semiconductor quantum effect chip can be made of a pure semiconductor material or a semiconductor material doped with impurities.

With the above structure, the tip of the semiconductor quantum effect chip is made of a material capable of once absorbing a propagating electron wave and emitting it again as fluorescence or phosphorescence. The emitted light can be used to measure the distance between the semiconductor quantum effect chip and the sample, the intensity of the electron wave, and the property of the sample.

FIG. 3 is a diagram showing the structure of a semiconductor quantum effect chip as a probe of the second embodiment of the present invention.

As shown in this figure, GaAs and InGa
A quantum well structure made of a direct transition semiconductor material such as As is used by selective etching in chemical etching,
That is, the quantum well portion 33 grown on the substrate 31 used as a cantilever is exposed by utilizing the property that a specific material dissolves in a chemical solvent faster than other materials, and thus the quantum fine structure portion is exposed. It shows the case of using as the chip portion 32 having the quantum well tip portion 33a as.

At this time, the width of the quantum well 33 is set to, for example, 10
Although it is set to about 0Å, it may be larger or smaller. However, if it is larger than 200Å, the quantum effect becomes small and the spatial resolution of the device may become low.

As described above, the tip of the semiconductor quantum effect chip is formed as a quantum fine structure having a sub-nanometer structure such as a quantum well, a quantum wire, and a quantum dot.

Further, a semiconductor material having a narrow band width such as InGaAs is used for the tip of the semiconductor quantum effect chip, so that light emission at a wavelength with less absorption with respect to the substrate or the sample can be obtained.

FIG. 4 shows the spectral intensity distribution of fluorescence obtained from these chips. That is, the tip portion and the cantilever portion emit fluorescence by approaching the sample and being excited by a tunnel of electrons or photons. When this is observed spectroscopically by the photodetector of the present invention (corresponding to the detector 17 of FIG. 1), the fluorescence c (from the tip of the chip where the energy level is shifted to the higher energy side by the quantum effect is For example, the wavelength of 800 nm) is the excitation light a
The quantum effect at the tip can be controlled so as to be separated from (for example, a wavelength of 488 nm), fluorescence from the substrate, and background light b (for example, 877 nm).

Therefore, a high signal / noise ratio can be achieved by selectively detecting only the fluorescent component from this quantum chip. Of course, a higher signal / noise ratio can be achieved by using a lock-in amplifier other than spectral discrimination.

FIG. 5 is a block diagram showing an example of quantum effect modulation according to the third embodiment of the present invention.

In this figure, as shown in FIG. 3, by exposing the quantum well portion 33 at the tip of the chip portion 32, the quantum well tip portion 33a as a quantum fine structure portion is formed.
Are formed. The quantum confined Stark effect (here, the Stark effect is the vicinity in a gas, a liquid, or a solid) is obtained by attaching transparent electrodes 35 to both ends of the quantum well tip portion 33a and applying an arbitrary voltage from a power source 36 to the transparent electrodes 35. Influence of internal and external electric fields due to electrons and ions existing in
The absorption wavelength due to the quantum effect shifts to the longer wavelength side.

As a result, it becomes possible to select the quantized energy separated from the excitation light from the light source mechanism 15 (see FIG. 1) and the background, which makes it possible to optimize the signal / noise ratio and at the same time, The characteristics of different energy levels can be evaluated. That is, if the wavelength from a light source having an energy slightly higher than the quantum energy is changed for scanning and the quantum energy is also modulated correspondingly, the characteristics of the sample at each wavelength can be imaged.

The present invention is not limited to the above embodiments, and various modifications can be made within the spirit of the present invention, and these modifications are not excluded from the scope of the present invention.

[0045]

As described above in detail, according to the present invention, the following effects can be obtained.

(1) The structure of the optical scanning tunneling microscope is simplified, and the manufacture of the probe is simplified, so that the apparatus can be miniaturized and an inexpensive apparatus can be provided.
In manufacturing this probe, the semiconductor microfabrication technology already built up can be used as it is, and an optical scanning tunneling microscope with high reproducibility can be obtained.

(2) Since the tip portion of the semiconductor quantum effect chip has a quantum structure capable of emitting light and controlling the state from the outside, the tip portion of the chip is not required to be devised.
The evanescent wave to be detected is converted to light with a wavelength different from the wavelength of light propagating through the substance at the tip of the chip.
Discrimination can be detected from the background evanescent wave.

Therefore, the signal / noise ratio of the measurement is improved. Also, in order to detect light emitted at the tip of the semiconductor quantum effect chip, it is important only to arrange a detector having high sensitivity in the wavelength range at a high solid angle with respect to the tip of the chip. However, there is an advantage that it is not necessary to consider the signal propagation.

[0049] (3) in consideration of absorption properties of the sample, set in a range from the time quantization energy designs, the final fine-tuning, by controlling the voltage applied to the semiconductor quantum effect chip tip Can be changed.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of an optical scanning tunneling microscope using a semiconductor quantum effect chip showing an embodiment of the present invention.

FIG. 2 is a diagram showing the structure of a semiconductor quantum effect chip as a probe of the first embodiment of the present invention.

FIG. 3 is a diagram showing a structure of a semiconductor quantum effect chip as a probe of a second embodiment of the present invention.

FIG. 4 is a diagram showing a spectral intensity distribution of fluorescence from a chip portion of the present invention.

FIG. 5 is a configuration diagram showing an example of quantum effect modulation according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional optical scanning tunneling microscope.

FIG. 7 is an enlarged cross-sectional view of a portion A of FIG.

[Explanation of symbols]

11,31 substrate 12,32 chips 12a Quantum fine structure part 13 Cantilever fine movement mechanism 14 Quantum structure modulation mechanism including power supply 15 Light source mechanism 16 Sample moving mechanism 17 detector 18 Spectroscopic mechanism 19 Focusing optical system 20 Control device 21 samples 33 Quantum well section 33a Quantum well tip 35 Transparent electrode 36 power supply

Continuation of the front page (56) Reference JP-A-5-343023 (JP, A) JP-A-7-13082 (JP, A) JP-A-5-74401 (JP, A) JP-A-6-102457 (JP , A) JP-A-5-173076 (JP, A) JP-A-6-201998 (JP, A) JP-A-5-288995 (JP, A) European Patent Application Publication 581217 (EP, A 1) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 13/10-13/24 G12B 21/00-21/24 JISST file (JOIS)

Claims (9)

(57) [Claims] 1. A cantilever having an arbitrary vibration mode.
A probe having a semiconductor quantum effect chip supported by a bar , (b) a fine movement mechanism of the probe, (c) a quantum structure modulation mechanism of the semiconductor quantum effect chip, (d) a sample measured by the probe, (E) a sample moving mechanism for setting the sample, (f) a light source mechanism for irradiating the sample with excitation light, (g) the probe approaches the sample and is excited by an electron or light tunnel to emit light. An optical scanning tunneling microscope comprising: 2. The optical scanning tunneling microscope according to claim 1, wherein the tip of the semiconductor quantum effect chip constituting the probe has a sub-nanometer structure such as a quantum well, a quantum wire, and a quantum dot. 3. The optical scanning tunneling microscope according to claim 2, wherein the tip of the semiconductor quantum effect chip is made of a direct transition type semiconductor material such as GaAs or InGaAs. 4. The optical scanning tunneling microscope according to claim 2, wherein the tip of the semiconductor quantum effect tip is made of a pure semiconductor material or a semiconductor material doped with impurities. 5. The optical scanning tunneling microscope according to claim 2, wherein the tip of the semiconductor quantum effect chip is made of a material capable of once absorbing a propagating electron wave and emitting it again as fluorescence or phosphorescence. using the light, wherein the semi
An optical scanning tunneling microscope that measures the distance between the conductor quantum effect chip and the sample, the intensity of electron waves, and the characteristics of the sample. 6. The optical scanning tunneling microscope according to claim 2, wherein InGa is formed at the tip of the semiconductor quantum effect chip.
An optical scanning tunneling microscope capable of using a semiconductor material having a narrow band width such as As to obtain light emission at a wavelength with little absorption with respect to the substrate or sample. 7. The optical scanning tunneling microscope according to claim 1, wherein a voltage is applied between the substrate and the tip of the semiconductor quantum effect chip or between the substrate and the sample to obtain the semiconductor quantum effect. An optical scanning tunneling microscope capable of externally controlling the quantum effect possessed by the tip of the chip and varying the electrical or optical characteristics of the semiconductor quantum effect chip in accordance with the detected quantum characteristics. 8. The light scanning tunneling microscope according to claim 1, wherein the light detecting means is a light detector that detects light from the semiconductor quantum effect chip by spectrally separating the light with a spectroscope or a color filter. 9. The optical scanning tunneling microscope according to claim 1, wherein the light source mechanism emits photons having energy higher than the quantization energy of the tip of the semiconductor quantum effect chip.