JP2010067613A - Ion barrier membrane for use in vacuum tube using electron multiplying, electron multiplying structure for use in vacuum tube using electron multiplying, and vacuum tube using electron multiplying provided with such electron multiplying structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an improved electron multiplying structure for use in vacuum tube using electron multiplying, which has an improved performance in term of shielding capabilities against stray ions and reduced loss of emitted electrons. <P>SOLUTION: The invention comprises an input face (7) intended to be oriented in a facing relationship with an entrance window (2) of the vacuum tube, and an output face (8) intended to be oriented in a facing relationship with a detection surface (3) of the vacuum tube, as well as an ion barrier membrane (10) for shielding off stray ions. The ion barrier membrane (10) is composed of at least one atomic layer containing grapheme. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electron multiplication structure for a vacuum tube using electron multiplication. The electron multiplying structure includes an incident surface disposed in a relationship facing the light entrance window of the vacuum tube, an exit surface disposed in a relationship facing the detection surface of the vacuum tube, and ions that shield stray ions. And an ion barrier membrane.

  The invention also relates to a vacuum tube using electron multiplication. The vacuum tube has a photocathode (photocathode) capable of emitting electrons into the vacuum chamber when irradiated with light, and separates the emitted electrons from the photocathode with respect to the photocathode. And an electric field means for accelerating toward the anode (anode) arranged to have an opposing relationship, and the electron multiplication structure of the present invention arranged between the photocathode and the anode in the vacuum chamber. .

  The present invention also relates to an ion barrier membrane used in the vacuum tube and / or electron multiplier structure of the present invention.

In the present invention, a vacuum tube structure that uses or performs electron multiplication includes image intensifier tubes, open faced electron multipliers, channeltrons, microchannel plates, and also secondary electron emission as a gain mechanism. Including photomultipliers and image intensifiers such as image intensifiers, including members or parts such as microchannel plates and discrete dynodes using phenomena.
Such vacuum tubes are known in the industry.
They have a cathode that emits so-called photoelectrons under the influence of incident radiation such as light or X-rays, and the emitted photoelectrons move towards the anode under the influence of an electric field.
The electrons that collide with the anode constitute an information signal, which is processed by suitable processing means.

  In modern image intensifier tubes, an electron multiplying structure, often a microchannel plate or MCP, is placed between the cathode and anode to increase the image intensifying action. When the electron multiplier structure is configured as a channel plate, the channel plate is a hollow tube extending between the entrance surface and the exit surface, such as a bundle of hollow glass fibers or a group of such glass fibers. including. A (voltage) potential difference is applied between the entrance surface and the exit surface of the channel plate, and electrons entering the entrance surface move in the direction of the exit surface. In this movement, the number of electrons is reduced due to the secondary electron emission effect. To increase. After leaving the channel plate on the exit surface, these electrons (primary electrons and secondary electrons) are accelerated in the direction of the anode in the usual manner.

  In each of these devices, a phenomenon called ion feedback occurs. This phenomenon occurs when electrons (having a negative charge) that have acquired sufficient kinetic energy in the accelerating electric field collide, ionize atoms or molecules existing in the vacuum chamber, or adsorb on the surface subjected to the electron collision. Get up when you are.

  When an electron strikes an electron from the outer region of the atom's electron cloud due to an electron collision, which causes a neutral gas atom or molecule to be positively charged, the ion is affected by the same electric field, but is positively charged. Therefore, it moves in the opposite direction, acquires kinetic energy, and collides with the incident side surface of the device.

  Such ion return collisions are quite often quite significant and often disturb or reduce the signal emitted by the device as ion spots or so-called after pulses in the image of the device. Let In many conventional devices, special care is taken with regard to design, assembly, or operating voltage or operating pressure range limits to avoid or reduce the effects of ion feedback.

  In particular, in an image intensifier tube device having a member surface formed of or having a negative electron affinity of a single atom that is easily affected, such as GaAs having a Cs-based surface layer. In order to solve the problem, a so-called ion barrier membrane is arranged in the vacuum chamber in order to shield the member surface from floating ions. Such a membrane prevents such stray ions from being permanently damaged and reducing the emission quantum efficiency of the photocathode.

The basic disadvantage of such an ion barrier membrane is that it not only prevents the return of stray ions, but also reduces the amount of primary electrons that are expected to transmit signal or image information towards the anode in the device. is there. As a result of practical considerations regarding strength, desired transmission for electrons and desired non-transmission for ions, materials such as Al ₂ O ₃ or SiO ₂ or other compounds with low atomic mass are used. In most cases, the thickness of the barrier membrane is tens of nanometers.

  An object of the present invention is to provide an electron multiplying structure with improved performance in terms of shielding ability against stray ions and reduced loss to emitted electrons.

  For this purpose, in the electron multiplication structure of the present invention, the ion barrier membrane is composed of at least one atomic layer containing graphene.

  A graphene is a monoatomic flat sheet of carbon atoms having a hexagonal crystal lattice, and can be configured as a membrane that shields a fragile or susceptible member surface of a vacuum tube from floating ions. In particular, it has been found that the monoatomic thickness graphene layer is impermeable to suspended ions and can act as an efficient ion barrier membrane.

  Furthermore, since the carbon atom monoatomic membrane can be configured as a very thin membrane layer, the loss of electrons is extremely low. It therefore has the best detection quantum efficiency (DOE) in the device used to prevent “floating” ion feedback.

  By configuring an ion barrier membrane using a plurality of atomic layers containing graphene, the shielding ability of the ion barrier membrane of the present invention is further improved, or more greatly influenced or more effective. Can do.

  More specifically, the at least one atomic layer includes only graphene.

  In a specific embodiment of the present invention, the ion barrier membrane is disposed on the incident surface of the electron multiplying structure. In another embodiment, the ion barrier membrane is disposed on the exit surface of the electron multiplying structure.

  In still another embodiment, the electron multiplying structure is configured to support a light entrance window of a vacuum tube.

  In yet another embodiment, the electron multiplier structure is configured as a channel plate, particularly a microchannel plate. In another embodiment, the electron multiplier structure is configured as an array of secondary electron emission dynodes.

  In another aspect of the present invention, a vacuum tube using electron multiplication is used as an image intensifier tube. In another embodiment, the vacuum tube is configured as a photomultiplier tube.

  Furthermore, the embodiment in which the vacuum tube is configured as a channeltron or microchannel plate detector is superior to conventional devices.

  According to the present invention, it is possible to obtain an electron multiplying structure with improved performance with respect to the shielding ability against stray ions and the reduction of loss to emitted electrons.

It is a figure which shows the vacuum tube provided with the electron multiplication structure by a prior art. It is a figure which shows 1st Embodiment of the vacuum tube using an electron multiplication provided with the electron multiplication structure by this invention. It is a figure which shows 2nd Embodiment of the vacuum tube using an electron multiplication provided with the electron multiplication structure by this invention. It is a figure which shows 3rd Embodiment of the vacuum tube using an electron multiplication provided with the electron multiplication structure by this invention. It is a figure which shows 4th Embodiment of the vacuum tube using an electron multiplication provided with the electron multiplication structure by this invention.

  Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

  In the following detailed description, like parts are designated with the same reference numerals for the sake of clarity.

  FIG. 1 shows in cross-section an example of a vacuum tube, for example an image intensifier. The illustrated image intensifier has a tubular housing 1 having an entrance window or cathode window 2 and a detection window or anode window 3. The housing can be made of glass, for example, and the cathode window and the anode window are the same. However, the detection window 3 may be a fiber optic plate or may be composed of a scintillating screen or a pixelated array of elements (eg a semiconductor active pixel array). If the cathode and possibly the anode are arranged in the housing in an insulated manner, for example using a separate carrier, the housing can also be made of metal.

  If the image intensifier is configured to receive x-rays, the cathode window can be composed of a thin metal. However, the anode window is light transmitting. The cathode 4 may be provided or attached directly on the incident surface 7 of the channel plate 6. Such variants are known per se and are not shown in detail.

  In the illustrated example, the actual cathode 4 is inside the light entrance window 2 and emits electrons due to the influence of incident light or X-rays (shown as “hv” in FIGS. 1 to 5). . The emitted electrons are accelerated in the direction of the anode 5 arranged inside the detection window 3 in a known manner under the influence of an electric field (not shown).

  The photocathode 4 may be formed of one or two or more materials included in the III column (Group III) and / or the V column (Group V) of the periodic table of elements.

  The electron multiplication structure of the present embodiment is configured as a channel plate 6 extending substantially parallel to the cathode 4 and the anode 5, and is disposed between the cathode and the anode. For example, a large number of tubular channels having a diameter of 8 to 12 μm include an incident surface 7 of the channel plate (facing the light entrance window 2 (cathode 4)) and an output surface 8 of the channel plate (detection surface 3 (anode 5)). It extends between the two).

  As explained in the introductory part of this application, the signal emitted from the device is disturbed or reduced by ion spots or so-called afterpulses in the image of the device due to the phenomenon of “ion feedback”. In many conventional devices, special care is taken to avoid or reduce the effects of ion feedback with respect to design, assembly, operating pressure range limitations, or operating voltage.

  This phenomenon occurs when an electron (having a negative charge) that has acquired sufficient kinetic energy in an accelerating electric field collides with an atom or molecule that still exists in the vacuum chamber and ionizes, or an electron collides. Occurs when adsorbed on the surface, here the anode 5 and the detection window 3.

  According to the present invention, as disclosed in FIGS. 2 to 5, the electron multiplying structure 6 includes an ion barrier membrane 10. The ion barrier membrane 10 is composed of at least one atomic layer containing graphene.

  For ease of illustration, the atomic layer graphene ion barrier membrane is shown as a thick line.

  Graphene is a monoatomic flat sheet of carbon atoms with a hexagonal crystal lattice, and can be configured as a membrane that shields the vulnerable or susceptible member surfaces of vacuum tubes that use electron multiplication from floating ions. . In particular, the monoatomic thickness graphene layer is impermeable to stray ions moving from the detection window 3 (5) toward the electron multiplication structure 8 and the light entrance window 2 (4) by an applied electric field. It was confirmed. The graphene monoatomic layer can act as an efficient ion barrier membrane.

  Furthermore, since the carbon atom monoatomic membrane, for example, graphene, can be configured as a very thin membrane layer, the detection window 3 (5) from the light entrance window 2 (4) and the electron multiplying structure 8 by the applied electric field. The loss of electrons moving toward the Thus, the best detection quantum efficiency (DQE) is obtained in an apparatus used to prevent “floating” ion feedback.

  The shielding ability of the graphene ion barrier membrane 10 is further improved, greatly influenced, or has a greater effect by configuring the ion barrier membrane with a plurality of atomic layers including graphene.

  In one embodiment, the graphene ion barrier membrane 10 can be disposed between the anode 5 / detection window 3 and the exit surface 8 of the electron multiplier means 6 (FIG. 2).

  In another embodiment (FIG. 3), the graphene ion barrier membrane 10 is disposed on the emission surface 8 of the electron multiplying means 6 and attached or pasted, for example.

  In still another embodiment (FIG. 4), the graphene ion barrier membrane 10 is disposed on the incident surface 7 of the electron multiplying means 6, and is attached or pasted to the incident surface 7, for example. In the form (FIG. 5), the graphene ion barrier membrane 10 is disposed inside the light entrance window 2, particularly on the cathode 4, and is attached or affixed (or supported), for example.

  The vacuum tube of the present invention can be configured as an image intensifier tube, can be configured as, for example, a photomultiplier tube, and can also be configured as a channeltron or microchannel plate detector.

  DESCRIPTION OF SYMBOLS 1 Housing, 2 Incoming window, 3 Detection window, 4 Cathode, 5 Anode, 6 Channel plate (electron multiplication means), 7 Incident surface, 8 Outgoing surface, 10 Ion barrier membrane.

Claims (15)

An electron multiplier structure for a vacuum tube using electron multiplication,
An incident surface disposed to face the light entrance window of the vacuum tube;
An exit surface disposed so as to face the detection window of the vacuum tube;
With an ion barrier membrane that shields floating ions,
The ion multiplying structure, wherein the ion barrier membrane includes at least one atomic layer containing graphene.   The electron multiplying structure according to claim 1, wherein the ion barrier membrane includes a plurality of atomic layers including graphene.   The electron multiplication structure according to claim 1, wherein the at least one atomic layer includes only graphene.   4. The electron multiplying structure according to claim 1, wherein the ion barrier membrane is provided on the incident surface of the electron multiplying structure.   The electron multiplication structure according to claim 1, wherein the ion barrier membrane is provided on the emission surface of the electron multiplication structure.   The electron multiplying structure according to any one of claims 1 to 5, wherein the electron multiplying structure is provided so as to support the light entrance window of the vacuum tube.   7. The electron multiplying structure according to claim 1, wherein the electron multiplying structure is configured as a channel plate, particularly a micro channel plate.   7. The electron multiplication structure according to claim 1, wherein the electron multiplication structure is configured as an array of secondary electron emission dynodes. A vacuum tube with electron multiplication having a photocathode capable of emitting electrons into a vacuum chamber when irradiated with light,
An electric field means for accelerating the emitted electrons from the photocathode toward an anode spaced apart and opposed to the photocathode;
A vacuum tube having the electron multiplying structure according to one or more of claims 1 to 8, which is disposed between the photocathode and the anode in the vacuum tube.   10. The vacuum tube according to claim 9, wherein the photocathode is formed of one or more of materials included in group III and / or group V of the periodic table of elements.   The vacuum tube according to claim 9 or 10, wherein the vacuum tube is configured as an image intensifier tube.   The vacuum tube according to claim 9 or 10, wherein the vacuum tube is configured as a photomultiplier tube.   The vacuum tube according to claim 9 or 10, wherein the vacuum tube is configured as a channeltron.   The vacuum tube according to claim 9 or 10, wherein the vacuum tube is configured as a microchannel plate detector.   15. An ion barrier membrane according to one or more of claims 1-14.

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