JP4116294B2 - Photocathode and photoelectric conversion tube - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photocathode and a photoelectric conversion tube provided with the photocathode.
[0002]
[Prior art]
As a transmissive photocathode sensitive to ultraviolet rays, one containing tellurium; Te and an alkali metal (cesium; Cs, potassium; K, rubidium; Rb, etc.) is known. Such a photocathode is constituted by depositing a base film made of chromium or Cr on a window material such as quartz and depositing a photoelectron emission film of Te and an alkali metal thereon.
[0003]
Conventionally, this type of transmission type photocathode has been required to have high sensitivity in a shorter wavelength region, for example, a wavelength region of 200 nm or less, and low sensitivity in the visible region. In order to meet such demands, Cr, nickel; Ni, aluminum; Al, etc. have been mainly used as the base film of the conventional photocathode.
[0004]
On the other hand, in a photoelectric conversion tube having this type of photocathode, such as an image intensifier, gate operation is rarely required.
[0005]
[Problems to be solved by the invention]
On the other hand, in recent years, various demands have been made for this type of transmissive photocathode. For example, a transmissive photocathode that has high sensitivity in a wavelength range of 250 nm to 320 nm and can perform a gate operation. Faces are now required. However, the above-mentioned conventional Cr, Ni, Al and the like have good sensitivity in a short wavelength region, and the sensitivity tends to decrease in a wavelength region of 250 nm to 320 nm.
[0006]
Further, in order to perform the gate operation satisfactorily, it is necessary to reduce the surface resistance of the base film. However, when the conventional base film such as Cr, Ni, Al or the like is used, If the sheet resistance is lowered, the transmittance is lowered. For this reason, even if the photocathode is formed on the base film made of these metals, there is a problem that the effective quantum efficiency is lowered.
[0007]
Accordingly, an object of the present invention is to provide a photocathode that exhibits good sensitivity to light in the wavelength range of 250 nm to 320 nm and that can perform a gate operation well, and a photoelectric conversion tube using this photocathode. There is to do.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention completed as a result of trial and error by the present inventors is an ultraviolet transmissive window material, a base film containing titanium formed on the window material, and a base film formed on the base film. It is a photocathode suitable for detecting light in the wavelength range of 250 nm to 320 nm, comprising a tellurium and a photoelectron emission film containing an alkali metal.
[0009]
Here, the alkali metal is preferably cesium, potassium, or rubidium.
[0010]
Moreover, it can be set as a photoelectric conversion tube provided with the vacuum vessel provided with said photoelectric surface, and it multiplyes the electron which was accommodated in the vacuum vessel provided with the photoelectric surface, and was discharge | released from the photoelectron emission film | membrane. An image intensifier including an electron multiplying unit and a fluorescent screen that receives electrons multiplied by the electron multiplying unit and converts the multiplied electrons into light may be provided. At this time, it is preferable that the image intensifier can perform a gate operation.
[0011]
Further, a vacuum vessel provided with a photocathode, an electron multiplying means for multiplying electrons emitted from the photoelectron emission film contained in the vacuum vessel, and an electron multiplying means contained in the vacuum vessel. It can also be a photomultiplier tube comprising an anode through which the multiplied electrons are incident.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, an image intensifier will be described as an example of the photoelectric conversion tube.
[0013]
FIG. 1 is a cross-sectional view of an image intensifier having a photocathode according to the present invention. As shown in FIG. 1, the proximity type image intensifier 1 includes a vacuum vessel 2, and a photocathode 3 is provided inside the vacuum vessel 2. The photocathode 3 has an incident window member 4 that transmits incident light. The incident window material 4 only needs to be UV transmissive, and for example, a quartz plate and magnesium fluoride; MgF ₂ can be used.
[0014]
On the inner surface of the window material 4, a thin film of titanium and Ti is formed as a base film 5 by vacuum deposition by EB deposition (electron beam deposition). A photoelectron emission film 6 containing Te and alkali metals K, Cs, and Rb is formed on the base film 5. Various combinations of Te and alkali metals are conceivable in addition to K-Te, Cs-Te, and K-Cs-Te.
[0015]
Further, a microchannel plate 7 serving as a multiplication unit for multiplying electrons is provided behind the photocathode 3 in the vacuum vessel 2, and a phosphor screen 8 is provided further behind the microchannel plate 7. ing. The electrons multiplied by the microchannel plate 7 enter the phosphor screen 8. On the phosphor screen 8, incident electrons are converted into light and emitted to the outside. Further, an emission window member 9 is provided behind the phosphor screen 8. The light emitted from the fluorescent screen 8 is emitted to the outside through the emission window material 9.
[0016]
In the present embodiment, a Ti thin film is used as the base film 5. Since the base film 5 made of a Ti thin film has a low surface resistance, as shown in a later embodiment, the gate operation can be easily performed. Ti has good sensitivity in a wavelength range of 250 nm to 320 nm. Therefore, it can be suitably used as the base film 5 of the photocathode 3 that requires good sensitivity in the wavelength range of 250 nm to 320 nm. In addition, since Ti has a lower surface resistance than, for example, Cr, using Ti as the base film 5 can make the film thickness thinner than when using Cr. As a result, the spectral transmittance can be increased. In forming the photoelectron emission film 6, since Rb is not sensitive in the vicinity of 280 nm, it is desirable to use K and Cs as the photoelectron emission film 6, but Rb can also be used.
[0017]
【Example】
The inventors of the present invention conducted the following experiment in search of a material having a low surface resistance and suitable as a base film exhibiting good sensitivity in a wavelength range of 250 nm to 320 nm.
[0018]
<Experiment 1>
First, a base film showing good sensitivity in a wavelength range of 250 nm to 320 nm was obtained, and various materials were used as base films, and the quantum efficiency was measured. In this experiment, Ni, tungsten; W, nickel monoxide; NiO, platinum; Pt, Al, Cr, and Ti were used as the base film. Further, K-Cs-Te was used as the photoelectron emission film. Further, the base film using each material was formed so that the sheet resistance when depositing the base film was constant (11 kΩ). The result is shown in FIG.
[0019]
As can be seen from FIG. 2, the other materials except Cr and Ti showed high quantum efficiency in the region where the wavelength was approximately 200 nm, and the tendency was found that the quantum efficiency decreased as the wavelength increased. In addition, Cr has a quantum efficiency that slightly increases as the wavelength increases for light in the wavelength range of 200 nm to 250 nm, and quantum efficiency increases as the wavelength increases for light in the wavelength range longer than 250 nm. Tended to decrease. In contrast, Ti has a quantum efficiency that increases as the wavelength increases for light in the wavelength range of 200 nm to 270 nm, and Ti increases as the wavelength increases for light in the wavelength range longer than 270 nm. There was a tendency for efficiency to decrease. Moreover, Ti showed high quantum efficiency compared with the other material used for experiment with respect to the light of a wavelength range of 250 nm to 320 nm.
[0020]
From the results of Experiment 1 above, it was found that the base film using Ti exhibits good quantum efficiency for light in the wavelength range of 250 nm to 320 nm.
[0021]
<Experiment 2>
Subsequently, changes due to heat in the surface resistance of each of the base film made of Ti and the base film made of Cr were measured. In this experiment, the surface resistance of the base film when using an image intensifier with a photocathode whose base film is Ti, and the surface resistance of the base film when using an image intensifier whose base film is Cr, respectively. Measured. In this experiment, the sheet resistance was measured at the time of setting (when Cr or Ti was deposited on the base film), at the end of degassing, at the end of HC, after cooling, and after leakage. The result is shown in FIG.
[0022]
As can be seen from FIG. 3, at the time of setting, the surface resistance of the base film using slightly Cr was small, but at other times, the surface resistance of the base film using Ti was smaller. . From this result, it was found that the surface resistance can be reduced in the base film using Ti.
[0023]
<Experiment 3>
Furthermore, in the case where Ti was used as the base film of the photocathode, an experiment was conducted to examine the spectral sensitivity characteristics when the sheet resistance is different. In this experiment, the quantum efficiency was measured when the resistance of the base film was 3.2 kΩ, 6.5 kΩ, 9.0 kΩ, 11 kΩ, 15 kΩ, and 29 kΩ. The result is shown in FIG.
[0024]
As can be seen from FIG. 4, even when the surface resistance of the underlayer is different, the use of Ti as the underlayer increases the quantum efficiency as the wavelength increases for light in the wavelength range of 200 nm to 270 nm. For light in the wavelength range longer than 270 nm, there was a tendency for the quantum efficiency to decrease as the wavelength increased. Moreover, when focusing on the relationship between the sheet resistance and the quantum efficiency, it was not possible to find a correlation between the two. From this result, it was found that by using Ti as the base film, high quantum efficiency can be obtained for light in the wavelength range of 250 nm to 320 nm even when the sheet resistance is different.
[0025]
As a result of the above experiment, by making the photocathode having a base film using Ti, the surface resistance of the base film can be reduced, so that a good gate operation can be performed, and 250 nm to 320 nm can be performed. It was found that good sensitivity can be exhibited with respect to light in the wavelength range.
[0026]
The preferred embodiments of the present invention have been described above, but the present invention can be variously modified. For example, in the above embodiment, the photocathode is provided in the image intensifier, but it can also be provided in a photoelectric conversion tube other than the image intensifier, for example, a photomultiplier tube. The photomultiplier tube at this time can be configured as follows, for example. The photocathode 3 (FIG. 1) shown in the above embodiment is provided inside the vacuum vessel, and a dynode or microchannel plate serving as a multiplication unit for multiplying electrons is provided behind the photocathode 3. On the rear side, the anode (anode) is provided in a state of being accommodated in the vacuum vessel. A predetermined bias is applied to the anode via the lead pin to the photocathode, the electron multiplier, and the anode. An output signal from the anode is output to the outside through a lead pin.
[0027]
In the above-described embodiment, the base film is described as Ti. However, Ti here is not limited to pure Ti but may contain some impurities. Further, it may be a base film on which a natural oxide film is formed during Ti deposition.
[0028]
【The invention's effect】
As described above, according to the present invention, there is provided a photocathode that exhibits good sensitivity to light in the wavelength range of 250 nm to 320 nm and enables gate operation, and a photoelectric conversion tube using this photocathode. can do.
[Brief description of the drawings]
FIG. 1 is a side sectional view of an image intensifier according to the present invention.
FIG. 2 is a graph showing the relationship between the wavelength of transmitted light and quantum efficiency when various materials are used as a base film of a photocathode.
FIG. 3 is a graph showing changes in sheet resistance of a base film using Ti and a base film using Cr.
FIG. 4 is a graph showing the relationship between the wavelength of light transmitted through a base film using Ti having different surface resistance and quantum efficiency.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image intensifier, 2 ... Vacuum container, 3 ... Photoelectric surface, 4 ... Incident window material, 5 ... Underlayer film, 6 ... Photoelectron emission film, 7 ... Microchannel plate (multiplier part).

Claims (6)

An ultraviolet transmissive window material, a base film containing titanium formed on the window material, and a photoelectron emission film containing tellurium and alkali metal formed on the base film , 250 nm to Photocathode suitable for detection of light in the wavelength region of 320 nm . The photocathode suitable for detecting light in a wavelength range of 250 nm to 320 nm according to claim 1, wherein the alkali metal is cesium, potassium, or rubidium.   A photoelectric conversion tube comprising a vacuum vessel provided with the photocathode according to claim 1. A vacuum vessel provided with the photocathode according to claim 1 or 2,
Electron multiplying means for multiplying electrons emitted from the photoelectron emitting film contained in the vacuum container;
A fluorescent screen on which electrons multiplied by the electron multiplying means are incident, and the multiplied electrons are converted into light;
An image intensifier with.   The image intensifier according to claim 4, wherein gate operation is possible. A vacuum vessel provided with the photocathode according to claim 1 or 2,
An electron multiplying means for multiplying electrons emitted from the photoelectron emission film housed in the vacuum container;
A photomultiplier tube comprising an anode which is accommodated in the vacuum vessel and into which electrons multiplied by the electron multiplier are incident.

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