JPH041988B2 - - Google Patents

Description

[Detailed description of the invention] "Technical field of invention" The present invention relates to improvements in proximity image tubes.

"Technical background of the invention and its problems" Image tubes are devices that convert infrared rays, X-rays, and other images that humans cannot directly see into visible light images, or that enhance weak light images. As one example, the proximity image tube shown in FIG. 1 will be explained. FIG. 1 shows a cross-sectional view thereof, in which a photocathode 1 formed on a glass face plate 2,
The fluorescent surfaces 3 formed on the other glass face plates 4 are vacuum-tightly sealed to an electrical insulator 5 serving as an envelope by means of supporting metal fittings 6 so as to face each other. The distance between the photocathode 1 and the fluorescent surface 3 is usually 1 to 2 mm, and a voltage of about 10 KV is applied to both when the image tube is operated, with the photocathode negative.

When the incident light image 7 is formed on the photocathode 1 in this manner, photons are emitted from the photocathode 1 in proportion to the intensity of each part of the incident light image. These photoelectrons are accelerated by the applied voltage and move towards the fluorescent surface 3. When reaching the fluorescent surface 3, the fluorescent surface 3 emits light due to the impact of these accelerated photoelectrons.
A light image that is several tens of times stronger than the incident light image is obtained on the fluorescent surface 3.

FIG. 2 shows a cross-sectional view of the fluorescent surface from which a visible light image is obtained in this manner. As shown in FIG. 2, a phosphor layer 8 is formed by depositing a phosphor on the surface of the glass face plate 4.
is formed, and a metal back layer 9 is formed on the surface of this phosphor layer 8. This metal back layer 9 is formed of a thin film of aluminum, and in addition to increasing the brightness, it also prevents light from the fluorescent surface from being fed back to the photocathode.

The photocathode absorbs light and emits photoelectrons, but some of the light passes through the photocathode and reaches the metal back layer on the fluorescent surface. The light beams that have reached the metal back layer are diffusely reflected here and irradiate the photocathode again. As a result, the optical image obtained on the fluorescent surface is fogged, resulting in a disadvantage that the contrast of the optical image on the fluorescent surface is significantly deteriorated.

In order to prevent such problems from occurring, it is sufficient to blacken the surface of the metal back layer, and for this purpose, an antireflection film 10 is formed on the metal back layer 9. The antireflection film 10 has conventionally been a soot-like black aluminum layer formed by vapor-depositing aluminum with good electron transparency in an inert gas atmosphere such as argon gas.

However, as the time spent using image tubes increased, the following problems began to occur. That is, as the operation continues, the soot-like aluminum layer is bombarded with photoelectrons from the photocathode and releases gas, degrading the degree of vacuum inside the tube. When the device stops operating and the electron bombardment stops, most of the emitted gas is absorbed by this black aluminum layer again. As such cycles are repeated, a certain type of gas that is not absorbed by the black aluminum layer or the photocathode gradually accumulates, and the gas pressure within the tube gradually increases.

If gas is absorbed by the photocathode, the photocathode sensitivity will deteriorate; on the other hand, if the gas pressure inside the tube increases, gas molecules will collide with photoelectrons during operation and become ions, which will hit the photocathode and electrons will be emitted. will be done. As a result, the signal-to-noise ratio is reduced and the resolution is also impaired.

``Object of the Invention'' The present invention has been made in consideration of these points, and an object of the present invention is to provide a close-up image tube with good characteristics that does not cause deterioration of the degree of vacuum inside the tube and provides a good fluorescent surface. It is.

"Summary of the Invention" Carbon, which has a low light reflectance and is more stable against gas than aluminum and has better electron transmission, is applied as a coating layer on the fluorescent surface of a proximity type image tube, eliminating various drawbacks of the conventional image tube. This was a significant improvement in performance as a compact image tube.

Embodiment of the Invention As shown in FIG. 3, a phosphor is deposited on a glass face plate 21, and a black carbon film 23 is formed on the phosphor surface on which a phosphor layer 22 is formed. One example of this method is as follows. That is, an argon atmosphere is used as the atmosphere in which the fluorescent plate is placed, and carbon is vapor-deposited. To evaporate the carbon,
The tip of a carbon rod is made thinner, this tip is pressed against the tip of another carbon rod, and a strong current is passed through this contact point to heat it and evaporate the carbon, resulting in soot-like or porous carbon consisting of an aggregate of fine particles. A layer is formed on the surface of the fluorescent surface to obtain a black coating. The thickness is several hundred angstroms in terms of a dense film. This alone does not provide sufficient adhesion strength, and therefore, during operation, carbon particles leave the substrate and fly to the photocathode, causing a problem in which electric field emission of electrons occurs. An effective means of increasing adhesive strength is to condense the particles of the layer by exposing it to a gas atmosphere of a volatile substance such as acetone or alcohol after vapor deposition, or by heating and evaporating it after depositing a thin layer of nitrocellulose. There are methods to solidify the fine particles. A thin carbon film evaporated in vacuum or by the discharge sputtering method becomes dark brown and the light reflectance is reduced, and the purpose is achieved to some extent, but in an argon atmosphere (for example, with an argon gas pressure of 10 mbar). When heated and vapor-deposited, a black carbon layer with even lower light reflectance is obtained, and even if the carbon layer is subjected to a treatment to increase the adhesion strength, the effect is not substantially impaired.

FIG. 4 shows the operating life characteristics of a proximity type image tube. For example, after about 500 hours,
The photoelectric sensitivity of the conventional one (indicated by 1 in the figure) on which a black aluminum film is formed decreases, but in the one of the present invention (indicated by 2 in the figure), there is little gas release from the black carbon layer, so the image Even if the tube is operated for a long period of time, there is no deterioration in the degree of vacuum inside the tube during operation, and the photoelectric sensitivity does not decrease and has been shown to be excellent in that it can always maintain a nearly constant value even after long periods of use. There is. Another reason for the small decrease in photoelectric sensitivity is that the black carbon layer well absorbs alkali metals such as cesium, which are the main components of the photocathode, and thus helps maintain the alkaline balance within the tube for a long time. It is also possible.

I have explained the proximity image tube above, but
Needless to say, the present invention can also be applied to the electrodes of electron tubes, for example, image pickup tubes having a close-up image section, which require measures to prevent reflection of light on the electrodes facing the photocathode.

"Effects of the Invention" When carbon is heated and evaporated in an argon atmosphere and deposited on the surface of the metal back layer of the fluorescent surface,
A soot-like or porous carbon layer with a black color with good electron transparency is formed thereon, which prevents fogging caused by diffuse reflection of light transmitted through the photocathode on the metal back layer. This carbon layer has excellent effects in that it does not cause a decrease in the vacuum inside the tube due to gas release from the tube, and furthermore, this carbon layer acts as an alkali replenishment source and prevents deterioration of photoelectric sensitivity. This significantly reduces the deterioration of the photoelectric sensitivity inside the tube, improves the life characteristics of a proximity image tube, and significantly improves performance.

[Brief explanation of drawings]

Figure 1 is a schematic explanatory diagram of a proximity image tube, Figure 2 is a schematic illustration of a proximity type image tube.
The figure is an enlarged cross-sectional view of a fluorescent surface portion of a conventional proximity image tube, and FIG. 3 is an enlarged cross-sectional view of a part of a fluorescent surface portion of a proximity image tube of the present invention.
FIG. 4 is a diagram showing the relationship between photoelectric sensitivity and operating time of a proximity image tube. 1... Photocathode, 3... Fluorescent surface, 2, 4... Glass face plate, 5... Electrical insulation ring, 8... Fluorescent layer,
9...Metal back layer, 10...Antireflection film, 2
1... Glass face piece, 22... Fluorescent layer, 23...
Black carbon film.

Claims (1)

[Claims] 1 A first face plate having a photocathode on the inner surface, and a second face plate having a fluorescent surface with a metal back on the inner face and disposed adjacent to the first face plate so as to face the first face plate. , a proximity type image tube formed by sealing the double-sided plates at predetermined intervals with an outer insulator, characterized in that a carbon layer with low light reflectance is adhered to the surface of the metal back on the fluorescent surface. Close-up image tube.