JPH09167589A - Transmission electron microscope and signal detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the breakage of an optical fiber by using the optical fiber in which a conductive film for preventing electrostatic breakage is formed in a scintillator containing a fluorescent material, arranged for taking a photograph of an image of an electron microscope with TV camera. SOLUTION: When electrons accelerated at high voltage, especially electrons having uniform energy entered a substance layer (a fluorescent material 12 or an optical fiber 13), the relation of effective range and energy of the electron in the substance is represented by the specified empirical formula. When the empirical formula applicable at 1-3MeV is referenced, and electrons accelerated at 1, 2, 3MeV enter the optical fiber 13 having a density of 4.6g/cm<3> , each range distance becomes 0.92, 2.07, and 3.23mm. By arranging a conductive film 15 in the position corresponding to these range distances of the optical fiber, almost all entered electrons are returned from the conductive film 15 to an electron gun.an accelerating tube through an earthing conductor 16, and dielectric breakdown of the optical fiber 13 caused by accumulation of electrons is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal detection apparatus for an apparatus such as an electron microscope and an accelerator for detecting and analyzing the intensity of an electron beam or an ion beam.

[0002]

2. Description of the Related Art A transmission electron microscope converts the sample information contained in an electron beam into a visible light image by a scintillator such as a fluorescent plate, and an operator directly visually observes the image. Some devices have an optical fiber between the scintillator and the TV camera so that a bright image can be observed, so that the optical image of the scintillator can be efficiently transmitted to the TV camera.

[0003]

In a scintillator using an optical fiber, if the current value of the electron beam with which the scintillator is irradiated per unit time becomes large, the optical fiber may be broken.

An object of the present invention is to provide a scintillator capable of preventing breakage of the optical fiber used here.

[0005]

The electron beam with which the scintillator is irradiated causes its energy to generate an optical signal on a fluorescent screen or the like. The remaining electrons that do not contribute to the generation of the optical signal pass through the fluorescent plate and enter the optical fiber. Electrons that have entered the optical fiber, which is an electrically insulating material, travel a distance corresponding to the kinetic energy at the time of injection, and are accumulated at that position except for some leakage current. It is considered that when the accumulated electrons reach a certain potential, electrostatic scatter occurs in the optical fiber at that portion, and the scintillator is damaged.

In order to improve the resolution of the electron microscope,
Since the electrons are accelerated by a very stable high voltage, the distance of the electrons entering the optical fiber is almost constant. For this reason, a conductive film for discharging the electrons that have entered the position corresponding to the acceleration voltage is formed in the optical fiber, and the structure is such that electrons are not accumulated at the position to prevent dielectric breakdown. Further, when changing the accelerating voltage, it is possible to use an optical fiber having a size that matches the accelerating voltage, that is, replace the optical fiber with a length that matches the range of the set accelerating voltage.

The conductive film can prevent the dielectric breakdown of the optical fiber and provide a detector such as an electron microscope having a highly reliable scintillator.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 shows the structure of a general electron microscope. The electron beam 2 from the electron gun / accelerator tube 1 is irradiated onto the sample 4 with a condenser lens 3 having a desired current value and spot size. Electronic beam 2 transmitted through sample 4
Is focused by the objective lens 5, enlarged by the intermediate lens 6 and the projection lens 7, and an electron microscope image 9 of the sample 5 is obtained on the fluorescent plate 8.

In the electron microscope, a camera room 10 for photographing a film of an electron microscope image under the fluorescent plate 8 and a TV for displaying the electron microscope image.
There is a scintillator 11 arranged for the purpose of photographing with a camera. The electron microscope image 9 is photographed and observed with a TV camera by opening and closing the fluorescent plate 8.

For photographing an electron microscope image with a TV camera, the phosphor 12 on the top of the scintillator converts the electron microscope image into visible light,
An image can be formed on the TV camera 18 by the optical fiber 13, and the image can be observed on the CRT monitor 19.

FIG. 4 shows an example of the structure of the scintillator 11. A thin aluminum film 14 is vapor-deposited on the phosphor 12 which is the main part of the scintillator 11 to protect the phosphor 12 and perform the function of making the generated light effective. A conductive film 15 is vapor-deposited on the entire surface of the optical fiber 13 and is grounded to the outside by a ground wire 16. This is a measure to reduce the electric resistance of the optical fiber 13 which is an insulator and prevent charge-up. Further, the optical fiber 13 is T
The electron beam 2 is connected to the image pickup tube of the V camera 18 and efficiently transmits the optical signal generated by the phosphor 12.

FIG. 5 is a diagram in which the behavior and locus of electrons inside the scintillator 11 are estimated when the electron beam 2 is applied to the scintillator 11 (the aluminum film 14 shown in FIG. 4 needs to be described here). I omitted it because it doesn't exist).
Since each electron of the electron beam 2 is accelerated by a high voltage, when the fluorescent substance 12 is irradiated, some of the electrons give energy to the particles of the fluorescent substance 12 and an optical signal 31 including image information of the electron microscope 31. Contribute to the occurrence of.

The optical signal 31 is transmitted through the optical fiber 13,
The image pickup surface of the TV camera 18 is irradiated and detected as a signal of an electron microscope image and displayed on the CRT monitor 19. (A device, such as an image intensifier, that amplifies the optical signal 31 is interposed between the optical fiber 13 and the TV camera 18, and the irradiated optical signal 31 can be detected efficiently. , A special structure is formed on the image pickup surface of the TV camera 18).

The remaining electrons 21, which have not been contributed to the generation of the optical signal 31 by irradiating the phosphor 12, pass through the phosphor 12 with almost no energy consumption and enter the inside of the optical fiber 13. . The incident electrons 22 stop at a position where they travel a certain distance L from the end face in the optical fiber 13, and remain there as accumulated electrons 23. However, the stored electrons 23 flow from the inside of the optical fiber 13 as leak electrons 24 to the conductive film 15, and further return to the electron gun / accelerator tube 1 via the ground wire 16 and the ground.

At this time, considering the relationship between the incident amount of the incident electrons 22 per unit time and the leakage amount of the leak electrons 24 per unit time, when the latter is larger than the former, the accumulated electrons 2
The potential of 3 continues to maintain a low value, and when the latter and the former are equal, there is no change in the potential, and when the latter is smaller than the former, the potential of the stored electrons 23 gradually increases over time. It's easy to imagine.

In the case as a result, that is, when the electron amount of the electron beam 2 with which the phosphor 12 is irradiated is larger than the electron 24 leaking from the inside of the optical fiber 13 to the ground, the static electricity at the position of the accumulated electron 23 is generated. It is considered that the electric potential rises with time, and when the dielectric breakdown voltage of the optical fiber 13 is exceeded, the accumulated electrons 23 are discharged at once and the optical fiber is destroyed. Therefore, if the structure of the optical fiber 13 that the incident electrons 22 do not accumulate can be formed, the destruction of the optical fiber 13 should be prevented.

FIG. 1 shows the optical fiber of the present invention. In the figure, the part showing the present invention is the invention itself in the dimension in the light traveling direction of the optical fiber. Here, respectively 1,
The dimensions and conditions of the optical fiber corresponding to the examples of a few MeV are shown.

When an electron accelerated by a high voltage or the like, particularly an electron having uniform energy is incident on the material layer (here, the phosphor 12 or the optical fiber 13), the practical range R and energy MeV of the electron in the material are obtained. It is well known that the empirical formula shown below applies to the relationship of. As an example of the accelerating voltage, an empirical formula applied between 1 MeV and 3 MeV is cited here.

R (mg / cm ² ) = 530E (MeV) -1
06, density ρ (mg / cm ³ ), and range L (c
m) R (mg / cm ² ) = ρ (mg / cm ³ ) L (cm)
From the relationship of ρ (mg / cm ³ ) L (cm) = (530E-106) (mg
/ Cm ² ) L (cm) = (530E-106) (mg / cm ² ) / ρ (mg
/ Cm ³ ), which is L (cm) = 424 / ρ in the case of electrons accelerated at 1 MeV, and density ρ = 424
It is shown that when an electron is injected into a substance of (mg / cm ³ ), it reaches a depth of 1 cm.

An optical fiber 1 now having a density of 4.6 (g / cm ³ ).
When electrons accelerated by 1, 2, 3 MeV are incident on 3, the range becomes 0.92, 2.07, 3.23 (mm). This means that the electrons incident on the optical fiber stop at positions of 0.92 mm, 2.07 mm, and 3.23 mm from the incident surface, respectively. That is, most electrons having uniform energy as in an electron microscope enter and accumulate at this position.

Therefore, the conductive film 1 is provided at this position of the optical fiber.
If 5 is arranged, most of the incident electrons 22 return from the conductive film 15 through the ground wire 16 to the electron gun / accelerator tube 1 in FIG.
3 will not cause dielectric breakdown.

Further, usually, in an electron microscope, various accelerating voltages are set and used, but it can be dealt with by exchanging with a scintillator in which the size of the optical fiber is changed for each accelerating voltage. Further, although the description has been made here in correspondence with three types of acceleration voltages, this can be similarly configured with two types or n types.

FIG. 2 shows that, like the conventional scintillator, the same structure can be used in the present invention. First,
(A) is an example in which the image intensifier 51 is connected to the scintillator 13 and the TV camera 18 is configured. Further, (b) is an image intensifier 41 and a TV.
This is an example in which the camera 18 is connected by the optical lens 42, and the same effect can be expected in terms of functionality except for the transmissibility of the optical image.

FIG. 2 does not show the detailed structure of the image pickup surface of the TV camera 18 because it has no relation to the explanation of the present invention. However, in reality, there are problems due to the transmission efficiency and reflection of the optical image. Exists. Therefore, it should be noted that the resolution or resolution as a TV camera cannot be obtained only by the theoretical configuration shown in this figure.

[0025]

According to the present invention, a highly reliable scintillator used for an electron microscope or the like can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a structure of a scintillator according to the present invention.

FIG. 2 is an explanatory diagram of an application example of the present invention.

FIG. 3 is an explanatory diagram of a configuration principle of an optical system and an observation system of a general electron microscope.

FIG. 4 is an explanatory diagram of configurations of a scintillator and a TV camera.

FIG. 5 is an explanatory diagram of the behavior of electrons in the optical fiber and the estimation of the trajectory.

[Explanation of symbols]

12 ... Phosphor, 13 ... Optical fiber, 15 ... Conductive film, 16
… Grounding wire, 18… TV camera.

Claims (3)

[Claims] 1. A transmission electron microscope including an electron optical system including an electron gun / accelerating tube, a condenser lens, a sample holder, an objective lens, an intermediate lens and a projection lens, and a transmission electron microscope including a camera room for taking a picture, showing an image of the electron microscope. A transmission electron microscope characterized in that a scintillator including a phosphor provided for shooting with a TV camera uses an optical fiber treated with a conductive film to prevent electrostatic breakdown. 2. The conductive film according to claim 1, wherein a conductive film is provided on the entire surface of the optical fiber at a distance calculated from the range of accelerated electrons in the optical fiber forming the scintillator, and the incident electrons are easily flown to the ground. A signal detection device configured to emit. 3. The transmission electron microscope according to claim 2, wherein the scintillator is held for each accelerating voltage and is compatible even when a plurality of accelerating voltages are used.