JPH07120418A - Local photoelectron detecting device and method therefor - Google Patents

Abstract

PURPOSE:To locally detect photoelectrons of high space resolving power, by giving a probe itself both function of irradiation of a sample with light and catch of the photoelectrons from the sample. CONSTITUTION:Under the condition of no irradiation of a sample 2, while measuring d.c. current between a probe 1 and the sample 2 by a current measuring means 11, a moving table 6 is moved by controlling with computer 15, the table 6 is stopped at detecting field emission current between both, the sample 2 is made to approach the probe 1, and at detecting tunnel current, the sample 2 is stopped and a light 3 is made incident on the probe 1. Hereafter, a scanning territory is set by the computer 15, and the sample 2 is moved in X, Y directions so as to be scanned. During the scanning, a, c current due to photoelectrons 4 between the probe 1 and the sample 2 is measured by the means 11. In the computer 15, the position of the probe 1 and the measured result by the means 11 at this position are let respond to each other, data of the number of electrons 4 generated from the sample 2 is taken in, and displayed on a CRT 16 as the sample image.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to photoelectron analysis devices, and more particularly to devices and methods for detecting localized photoelectrons.

[0002]

2. Description of the Related Art It is known that when a surface of a material is irradiated with light having an energy larger than the work function of the material, photoelectrons jump out from the surface. It is known to use this phenomenon for surface analysis.
servation of local Photoemission using a scanning
tunneling microscope JKGimzewski and others Ultramicro
scopy 42-44 (1992) 366-370. That is, in the ultra-high vacuum, the light is focused on the spot and applied to the sample surface, and the photoelectrons that emerge are locally captured by the STM (scanning tunneling microscope) probe, resulting in a difference in the work function of the surface. It has been reported that they have obtained. In this report, a method of improving the spatial resolution by coating the periphery of the STM probe with an insulator excluding the tip is proposed.

[0003]

However, the above-mentioned local photoelectron analysis method has a problem in that the spatial resolution cannot be obtained as expected. The present invention has been made in view of such problems, and an object thereof is to provide a detection device capable of performing local photoelectron detection with high spatial resolution.

[0004]

To achieve the above object, in the present invention, light is irradiated to the sample from the inside of the probe that receives the photoelectrons from the sample, preferably from the central portion, and the probe itself is sampled. The structure has two functions of irradiating light to the sample and capturing photoelectrons from the sample. Specifically, the local photoelectron detection device according to the present invention comprises a probe for receiving photoelectrons from a sample, a light irradiation unit for irradiating the sample with light from the inside of the probe, and a probe for the sample. Moving means for relatively moving, voltage applying means for applying a voltage between the probe and the sample, and current detecting means for detecting a current flowing between the probe and the sample by the photoelectrons received by the probe. ,
And a display unit for displaying information on the current detected by the current detection unit.

Further, the local photoelectron detection method according to the present invention irradiates the sample with light from the inside of the probe, receives the photoelectrons generated from the sample by the probe, and supplies the amount of current flowing between the probe and the sample. Is detected and information on the amount of current is displayed.

[0006]

In the present invention as described above, the light irradiating the sample is supplied from the inside of the probe, more preferably from the central portion, so that the sample can be irradiated vertically with the light. Therefore, the generation of photoelectrons can be limited to a small area,
Substantial resolution can be improved. Then, let the probe approach the so-called near-field region with respect to the sample,
When a hole smaller than the wavelength of light is provided at the tip of the probe and the sample is irradiated with light through this hole, the sample can be irradiated with evanescent light. The irradiation area of the evanescent light is about the same size as the hole at the tip of the probe, and can be smaller than the high wavelength of irradiation. Therefore, when the photoelectrons from the sample are detected by the probe, the detected photoelectrons are generated only from the irradiation area of the evanescent light, and it is possible to obtain an extremely high spatial resolution about the size of the hole at the tip of the probe. It will be possible.

As described above, when the probe is brought close to the so-called near-field region with respect to the sample to detect photoelectrons, a tunnel current is generated in addition to the current due to the photoelectrons, but the irradiation light is modulated. By detecting the current between the probe and the sample in synchronization with this modulation, it is possible to detect only the current caused by photoelectrons. For this purpose, the light irradiating means irradiates the sample with the modulated light from the central portion of the probe through an opening smaller than the wavelength of light, and the current detecting means synchronizes the modulation of the irradiating light with the light between the probe and the sample. It is effective to adopt a configuration in which the alternating current flowing through the sensor is detected.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a schematic structure of a local photoelectron detection device of this embodiment. The apparatus is a probe 1 in which a glass tube 1a having a sharp tip is provided with an aluminum film 1b, a voltage applying unit 10 for applying a predetermined voltage V between the sample 2 and the probe 1, the probe 1 and the sample 2 Current measuring means 11 for measuring a current flowing between the probe 1 and the first drive control means 12 for driving and controlling the actuator 5 for scanning the sample 2 with respect to the probe 1, and the actuator 5 in the probe 1 direction. Second for driving and controlling the moving table 6 which is moved to
Drive control means 13 and third drive control means 1 for controlling the drive for moving the probe holder 7 in the X and Y directions.
4, a computer 15 for storing information on the number of photoelectrons protruding from the surface of the sample based on the position information of the probe 1 with respect to the sample 2 and the current value measured by the current measuring means 11 at the position; Display as CRT
Have 16.

The first drive control means 12, the second drive control means 13 and the third drive control means 14 are controlled by a computer 15 through a GPIB cable.
Then, the position of the probe 1 with respect to the sample 2 is calculated by the computer 15 based on the movement amounts of the actuator 5 and the movement table 6. In the present embodiment, the actuator 5 causes the sample 1 to scan the probe 1 in the XY directions while maintaining the space between the probe 1 and the sample 2 at a predetermined interval. The range can be appropriately set by issuing a command from the computer 15 to the first drive control means 12 and changing the frequency and amplitude of the scanning signal (triangular wave) sent from the first drive control means 12 to the actuator 5. The current measuring means 11 has a function of measuring the AC component and the DC component of the current, respectively, and sending the data to the computer 15 as two independent information.

The probe 1 has a structure in which an aluminum film is attached to a glass tube 1a having a sharp tip. The manufacturing process of the probe 1 will be described below. Heat a part of a thin glass tube (outer diameter 1 mm) and pull it on both sides until it breaks, forming a sharp tip. After this, the glass tube is cut to a predetermined length (20 mm).

Next, aluminum is vapor-deposited to a thickness of 50 nm on the pole tip portion on the sharp tip side. Furthermore, in order to prevent light from leaking from the side, make the aluminum on the side of the glass tube thicker than the tip (200 nm).
Vapor deposition. According to this procedure, a probe having a hole with a diameter of about 50 nm can be obtained. FIG. 2 is a conceptual diagram showing the configuration of the local photoelectron detection device of this embodiment. This device is composed of a glass tube 1a having a sharp tip and an aluminum film 1b, and a probe 1 having a minute hole at the tip, a probe holder 7 for holding the probe 1, and a probe holder 7 for XY directions. The drive unit 25 for adjusting the position, the base 20, the support base 20a formed on the base 20 for holding the probe holder 7, the sample 2, the sample holder 26, and the sample holder 26 are moved in the XYZ directions 3 Dimensional actuator 5, moving table 6 on which actuator 5 is installed, light source 21 and probe 3 for light 3 from light source 21
The optical fiber 22 for injecting into Sample 2 was prepared by depositing 200 nm of gold on a silicon substrate and further depositing 50 nm of cesium on the silicon substrate in a pattern of 0.2 μm periodic line / space. The sample 2 is connected to the ground and attached to the sample holder 26 by adhesion.

The actuator 5 is of a tube scanner type which uses a piezo element, and applies an appropriate voltage to the piezo element to move the sample 2 to the probe 1 in the XY direction.
Scan in the direction. The actuator 5 also functions as a fine movement mechanism when the sample is displaced in the Z direction. Further, the actuator 5 is installed on the moving table 6, and the moving table 6 moves the sample 2 together with the actuator 5 in the Z direction. The moving table 6 is supported by the screw portion 24a via the bearing 23 and the screw 24. The thread portion 24a has a thread pitch of 0.3 mm, and the base 2
Screw 20c to be provided on the support portion 20b formed in 0
It is screwed together. When the screw 24 is rotated by a drive mechanism (not shown), the moving table 6 moves in the Z direction. The moving table 6 functions as a coarse movement mechanism when the sample 2 approaches the probe 1.

The probe holder 7 is supported on the base 20 by a support 20a. The drive device 25 is attached in the X and Y directions, and can adjust the positions of the probe 1 and the probe holder 7 in the X and Y directions. Light source 21
Emits a light 3 of 633 nm (He-Ne laser) and injects this light 3 into the probe 1 through the optical fiber 22. Further, the light source 21 has means for modulating the light 3.

FIG. 3 is a conceptual perspective view of the tube scanner type actuator used in this experimental example. The actuator 5 includes electrodes 31a and 31b for the X-direction scanning thick-electric elements and electrodes 32a and 32b for the Y-direction scanning thick-electric elements on the outer peripheral surface of the cylindrical thick-electric ceramics 30.
Are provided so as to face each other in the X direction and in the Y direction, respectively. On the inner peripheral surface of the thick electric ceramics 30,
A common electrode 33 is provided for each of the electrodes 31a, 31b, 32a, 32b. When scanning in the XY direction,
Potentials of the same size but different signs are applied between the electrodes in each direction. Also, when moving in the Z direction,
Set either positive or negative voltage and set this voltage to X, Y
The element is expanded and contracted in the Z direction by applying the same voltage between each electrode on all the outer peripheral surfaces and the common electrode 33.

The local photoelectron detection method of this embodiment will be described below again with reference to FIG. First, the computer 15 controls the second drive control means 13 while measuring the current (direct current) flowing between the probe 1 and the sample 2 by the current measuring means 11 without irradiating the sample 2 with the light 3. Then, the moving table 6 is moved toward the probe 1. At this time, a bias voltage of +5 V is applied to the sample 2 by the voltage applying means 10 to the probe 1. Current measuring means 1
When a current (field emission) is detected between the probe 1 and the sample 2 by 1, the moving table 6 is stopped.

After that, the potential of the probe 1 is set to + with respect to the sample 2.
Setting to 1.0 V, the actuator 5 is driven through the first drive control means 12 to bring the sample 2 closer to the probe 1,
When the tunnel current is detected, the sample 2 is stopped. By the above operation, the distance between the probe 1 and the sample 2 is set, but since the tunnel current flows between the most protruding protrusion at the tip of the probe 1 and the sample, the hole at the tip of the probe 1 is set. The distance between the sample and the sample is about several nanometers.

When the distance between the probe 1 and the sample 2 is set, the light 3 is injected into the probe 1. Here, the light 3 is modulated at 10 kHz. This is the current measuring means 11
This is because the current value due to the photoelectrons is measured by separating the current due to the tunnel current (direct current) from the current due to the photoelectrons (AC 10 kHz). After this, the computer 15
The scanning area is set by, and the sample 2 is moved by the actuator 5 by moving the sample 2 in the XY directions.

When scanning the probe 1 in the XY directions,
The Z of the actuator 5 is adjusted so that the tunnel current (direct current) component of the current measured by the current measuring means 11 has a constant value.
Feedback control of displacement in the direction. Further, during scanning, the current (alternating current) flowing by the photoelectrons 4 between the probe 1 and the sample 2 is measured by the current measuring means 11. The computer 15 associates the position of the probe 1 on the sample 2 (position on the XY plane) with the measurement result by the current measuring means 11 at this position, and determines the number of photoelectrons 4 generated from the sample 2. Capture data. This data is sent to the CRT 16 and displayed as a sample image on the screen.

When the sample 2 was analyzed by the above process, a sample image with high spatial resolution was obtained. This is because the region where the light 3 is irradiated on the sample 2 is narrowed to the wavelength of the light or less. In addition, all the above-mentioned Examples were performed in ultra-high vacuum. Further, in the above-mentioned embodiment, the sample 2 is moved by the actuator 5 with respect to the probe 1, but the probe 1 can be moved by the actuator, conversely. Thereby, the sample 2 can be fixed and a large sample can be measured.

[0020]

As described above, according to the present invention, since light is irradiated onto a sample through a hole having a size equal to or smaller than the wavelength of light,
Photoelectrons are generated only from this region. Therefore, an image with high spatial resolution can be obtained by reducing the size of the hole.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a local photoelectron detection device according to an embodiment.

FIG. 2 is a schematic diagram showing a configuration of a local photoelectron detection device according to an embodiment.

FIG. 3 is a schematic perspective view showing an actuator used in the local photoelectron detection device according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Probe 1a ... Glass tube with sharp tip 1b ... Aluminum film 2 ... Sample 3 ... Light 4 ... Photoelectron 5 ... Actuator 6 ... Moving table 7 ... Probe holder 10 ... Voltage applying means 11 ... Current measuring means 12 ... First drive control means 13 ... Second drive control means 14 ... Third drive control means 15. ..Computer 16 ... CRT 21 ... Light source 22 ... Optical fiber 25 ... Drive device 26 ... Sample holder 30 ... Thick electric ceramics

Claims (3)

[Claims] 1. A probe for receiving photoelectrons from a sample, a light irradiation means for irradiating the sample with light from the inside of the probe, and a moving means for moving the probe relative to the sample. ,
Voltage applying means for applying a voltage between the probe and the sample; current detecting means for detecting a current flowing between the probe and the sample by the photoelectrons received by the probe; and the current detecting means. And a display unit for displaying information on the electric current detected by the unit. 2. A probe for receiving photoelectrons from the sample, a light irradiating means for irradiating the sample with modulated light through an opening smaller than the wavelength of light from the inside of the probe, and the probe for the sample. Moving means for relatively moving, voltage applying means for applying a voltage between the probe and the sample, and alternating current flowing between the probe and the sample by the photoelectrons received by the probe. A local photoelectron detection device comprising: a current detecting unit for detecting; and a displaying unit for displaying information on the current detected by the current detecting unit. 3. A sample is irradiated with light from the inside of the probe, the photoelectrons generated from the sample are received by the probe, and the amount of current flowing between the probe and the sample is detected. A method for detecting local photoelectrons, characterized by displaying information.