WO1996025758A1

WO1996025758A1 - Channel electron multiplier with glass/ceramic body

Info

Publication number: WO1996025758A1
Application number: PCT/US1996/002021
Authority: WO
Inventors: James L. Knak
Original assignee: K And M Electronics, Inc.
Priority date: 1995-02-14
Filing date: 1996-02-13
Publication date: 1996-08-22
Also published as: AU4924496A

Abstract

A gas impervious channel electron multiplier (10) having monolithic body (12) composed of a glass-ceramic composite, the body (12) defining an interior passageway (16) extending from an entrance port (19) to an exit port (18), the outer surface of the body (12) and the surface of the passageway having a gas impervious layer and the surface of the passageway having a secondary emissive coating.

Description

CHANNEL ELECTRON MULTIPLIER WITH GLASS/CERAMIC BODY

Background of the Invention

The present invention relates to channel electron multipliers and a method of making the same. More particularly, the invention relates to a channel electron multiplier made from a monolithic ceramic body having a gas impervious surface.

Channel electron multipliers are often employed in instruments such as mass spectrometers, in which ions from the instrument are directed to the multiplier input. In response to incident ions, electrons are emitted, and those electrons in turn produce emission of secondary ions in the multiplier, resulting in an amplified signal at the multiplier output. Channel electron multipliers are also used in multiplier phototubes where they serve as amplifiers of the current emitted from a photocathode when impinged upon by an incident light signal. In such instruments, the electron multiplier and other functional elements are enclosed in a vacuum envelope so that the mean free path of electrons is not limited by ambient molecules.

Ceramic channel electron multipliers are preferred for such applications because they provide a durable body and preferable electrical characteristics. U.S. Patent No. 4,757,229, entitled CHANNEL ELECTRON MULTIPLIER, assigned to the assignee of the present invention, which is hereby incorporated by reference, discloses one such channel electron multiplier made from a monolithic ceramic body having a two or three dimensional curved conduit. U.S. Patent Nos. 4,967,115 and 5.097, 173, each entitled CHANNEL ELECTRON MULTIPLIER PHOTOTUBE, which are hereby incorporated by reference, each assigned to the assignee of the present invention, disclose phototubes made with ceramic channel electron multipliers.

One problem with prior art ceramic channel electron multipliers is that the outer surfaces are easily marred or marked during handling, for example, by forceps used to move the devices in various stages of the manufacturing process. To minimize such problems a hard outer layer, such as glass, is often applied to the outer surfaces of the device, generally adding an extra step to the manufacturing process and adding to the cost of manufacture. Another problem is that the ceramic material tends to emit gasses for a period of time after firing in a phenomenon known as "outgassing". To minimiz the effect of such outgassing, a gas impervious layer, normally of non-conductive glass is applied to the outer surfaces of such ceramic channel electron multipliers. That outer coating prevents the outgassing from disturbing the vacuum in which t device is to be operated. In accordance with conventional practice, the gas impervious outer layer is applied subsequent to the manufacture of the ceramic b of the multiplier, usually by hand.

The necessity of coating the exterior surfaces of channel electron multiplie with a gas impervious layer adds an extra step to the process of manufacturing th device, and thus increases the cost of the device. There is therefore a need for a ceramic channel electron multiplier that is inherently gas impervious and which be manufactured in a cost-efficient manner .

It is therefore an object of the invention to provide an inherently gas impervious ceramic channel electron multiplier.

It is a further object of the invention to provide a method for making an inherently gas impervious ceramic channel electron multiplier.

Other objects and advantages of the present invention will become appare upon consideration of the appended drawings and description thereof. Another object of the invention is to use a lead glass, which after sinterin process, would coat the channel surface with said glass. This glass can then be reduced to form a semi-conductor which has sufficient resistivity to support the electron flow required in standard CEMs. This would eliminate a secondary proc for coating the channel.

Summary of the Invention

The present invention relates generally to the design and construction of a channel electron multiplier. More particularly, the invention relates to an inhere gas impervious channel electron multiplier. According to one preferred embodiment, the multiplier includes a monolithic electrically insulating body fabricated from a glass-ceramic composite material. The body has at least one entrance port, at least one exit port, and a hollow curved passageway extending from the entrance port to the exit port. The outer surface of the body, and the surface of the passageway have a gas impervious glass layer, and the walls of the passageway include a secondary-emissive dynode material.

In one preferred embodiment, the walls of the passageway are non-parallel with respect to the outer surface of the body. The passageway may define a two or three dimensional curve, and may define at least one turn within the body. In one preferred embodiment, the passageway defines a helix or a spiral. The dynode material may be a semiconducting glass.

In other preferred embodiments, the passageway is seamless, and the entrance port is funnel shaped.

In another embodiment, the invention provides a method for fabricating the channel electron multiplier. The method includes using a preform body having a relatively low melting temperature and having an outer surface in the shape of the desired contour of the passageway. The preform is then surrounded with a composite material composed of a ceramic powder and a glass powder, the glass powder having a melting temperature which is higher than the melting temperature of the preform body and lower than the sintering, temperature of the ceramic powder. The composite material is then compressed or poured to form a matrix disposed about the preform, and using conventional ceramic procedures, the composite material matrix is subsequently raised to a temperature above the ceramic powder sintering temperature. As the temperature increases, the preform body initially melts and flows out of the matrix, leaving a passageway of the same shape as the preform body prior to the application of heat. Next, the glass powder melts and diffuses by capillary action at least in part through the ceramic powder matrix to the outer surface of that matrix and to the surface of the passageway passing through the matrix. Finally the ceramic powder sinters and forms a fused matrix. The fused matrix is then cooled, with the ceramic material now bearing a glass coating on its exterior surface and on the channel surface. In subsequent processing steps, the channel surface may be made semi-conductive providing a dynode structure for the device.

The invention accordingly comprises the apparatus and the method exemplified in the following detailed disclosure, the scope of which is indicated in the claims.

Brief Description of the Drawings

For a fuller understanding of the nature and the objects of the invention, reference should be made to the following detailed description and the accompany drawings in which like reference numerals refer to like elements and in which:

Figure 1 is a perspective view of a channel electron multiplier of the prese invention; Figure 2 is a sectional view taken along lines 2-2 of the multiplier of Figu

1 showing additional support and electrical elements thereon;

Figure 3A is a perspective view of another channel electron multiplier according to the present invention having a tube-like body;

Figure 3B is a perspective view of yet another channel electron multiplier according to the present invention having a tube-like helical body;

Figure 4 is a perspective view of yet another channel electron multiplier o the present invention;

Figure 5 is a cross-sectional elevation view taken along line 5-5 of the dev of Figure 4; and Figure 6 is a sectional view of another embodiment of the channel electron multiplier of the present invention shown configured as a multiplier phototube.

Detailed Description of the Illustrated Embodiment

Figures 1 and 2 show a channel multiplier 10, constructed in accordance w the present invention. Multiplier 10 is comprised of a body 12 composed of an electrically insulating glass-ceramic composite material disposed about a curved central channel 16.

In the embodiment shown in Figures 1 and 2, the outer surface of monolit body 12 of the multiplier is cylindrical in shape. As will be further noted, one e of said body may be provided with a cone or funnel shaped entryway or entry po 14 which evolves to a hollow passageway or channel 16. The channel 16 defines curve which may be two dimensional and is preferably three dimensional and may have one or more turns therein which are continuous throughout the body 12 of the multiplier 10. Channel 16 exits the multiplier 10 at an exit port at the opposite end 18 of the cylinder shaped body from the entryport 14. In the embodiment of Figures 1 and 2, the lateral surfaces of body 12 are non-parallel with respect to the walls defining channel 16. The passage of the channel is curved particularly to avoid instability caused by "ion feedback".

Figure 2 shows a slightly modified version of Figure 1 , wherein an input collar 44 is press fit onto the monolithic body 12 and is used to make electrical contact with entry port 14. An output flange 46 is also pressed onto the monolithic body 12 and is used to position and hold a signal anode 48 and also to make electrical contact with exit port 18.

Monolithic body 12 is fabricated using "ceramic" techniques. In general, a preform in the configuration of the desired passageway 16 is surrounded with a composite material composed of a ceramic powder and an electrically non- conductive glass powder, and is then pressed at high pressure.

The body containing the composite and the preform is then processed using standard ceramic techniques such as bisquing and sintering. The preform has a low melting temperature compared to the glass powder and the ceramic powder, and the glass powder has a low melting temperature compared to the ceramic powder so the preform will melt or burn-off during the high temperature processing thereby leaving a passageway of the same configuration as the preform.

Also during high temperature processing, the glass powder will melt and diffuse through the ceramic matrix to form a layer of glass that covers the external surface of the body as well as the surface of channel 16. Finally, the ceramic powder sinters and forms a fused matrix which is encased in a glass coating. After cooling, the glass coating forms a gas impervious barrier that effectively reduces outgassing by sealing the body 12.

The monolithic glass-ceramic body of the multiplier of the present invention may be fabricated from a variety of different materials. Preferred ceramic materials are alumina. Preferred glass materials are lead silicate glasses. Preferably, the ceramic powder has a sintering melting temperate on the order of 2700°F, and an electrical conductivity, when fused, greater than 10¹⁰ ohm-cm. Preferably, the powder has a melting temperature in the range of 700-900°C, and an electrical conductivity greater than 10¹⁰ohm-cm. Preferably, the composite contains betw 5% and 30% glass, and between 95% and 70% ceramic. Preferably the glass- ceramic body is processed at a maximum temperature of approximately 2700 °F degrees for about 5 hours.

After cooling, the surfaces 20 of the funnel shaped entryway 14 and the hollow passageway 16 can be coated with a semiconducting material having goo secondary emitting properties, such as semiconducting glass. Said coating is hereinafter described as a dynode layer. Alternatively, the glass channel surface be reduced to result in a semi-conducting layer.

The materials chosen for the composite material are selected to be chemically, mechanically and thermally compatible with the dynode layer materi The composite material preferably has a high dielectric strength and behaves as electrical insulator between channel and exterior surfaces.

Figure 3A shows an alternate embodiment of a channel electron multiplie which may be described as a free form channel multiplier. In this configuration body 22 is formed from a monolithic glass-ceramic composite material, having tube-like body and an enlarged funnel-shaped head 24. In this embodiment the lateral surfaces of body 22 are substantially parallel to the walls defining channe

As with the embodiments of Figures 1 and 2, the surface 30 of the passageway and entrance way 28 are coated with a dynode layer.

Figure 3B shows yet another embodiment of a channel electron multiplie which is similar to the embodiment shown in Figure 3A, except that the body 2 defines a three dimensional helical curve.

Turning now to Figures 4 and 5, an alternative embodiment of the prese invention employing a plurality of hollow passageways or channels therein is sh generally at 60. Channel electron multiplier 60 is comprised of a unitary monol body 62 of glass-ceramic composite material with a multiplicity of hollow passa 64 interconnecting front and back surfaces 66, 68 of body 62. A layer of gas impervious non-conducting glass coats the walls of all hollow passages 64 as we front and back surfaces 66, 68. It will be appreciated that passages 64 may be straight, curved in two dimensions, or curved in three dimensions. Preferably, front and back surfaces 66, 68 are made conductive by metallizing them, while a dynode layer is coated on the passageways.

Figure 6 shows a phototube which incorporates a further embodiment of the channel electron multiplier of the present invention wherein the channel electron multiplier 10 has the same internal configuration as that shown in Figures 1 and 2, but has a different external configuration in that the body 32 is not in the form of a cylinder. Due to the above-described flexible method of manufacture of the monolithic body, almost any desired shape may be employed for said multiplier. Once the passageway has been coated with a dynode material and the aperture end and the output end have been metalized, the body may be fitted with various electrical and support connections as shown in Figure 6 such as an input collar or flange 35, a ceramic spacer ring 34, transparent faceplate 36 having a photoemission film on its inner surface, an output flange 38, and ceramic seal 40 with a signal anode 42 attached thereto. In such a configuration, the device functions as a phototube vacuum envelope electron multiplier.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

Claims: 1. An electron multiplier device having a predetermined outer surface conto comprising:

a monolithic electrically insulating body having at least one entrance port in said body and at least one exit port in said body, and having at least one hollow curv passageway through said body between said entrance port and said exit port, and wherein the walls defining said hollow passageways include a secondary-emissiv dynode material, and wherein said body is composed of a glass-ceramic composi material and has a gas impervious glass layer on said passageway walls and on s outer surface.

2. An electron multiplier device according to claim 1 , wherein said dynode material is a semiconducting glass.

3. An electron multiplier device according to claim 1, wherein said walls of passageway are non-parallel with respect to said predetermined outer surface contour.

4. An electron multiplier device according to claim 1 , wherein said hollow passageway has at least one turn therein.

5. An electron multiplier device according to claim 1, wherein said passage forms a two dimensional curve in said body.

6. An electron multiplier device according to claim 1 , wherein said passage forms a three dimensional curve in said body.

7. An electron multiplier device according to claim 6, wherein said three dimensional curve is a helix or spiral.

8. An electron multiplier device according to claim 1 , wherein said entrance port is funnel shaped.

9. An electron multiplier device according to claim 1 , wherein said passageway is seamless.

10. A method of fabricating a channel electron multiplier having a predetermined outer surface contour, and including a monolithic electrically insulating body, at least one entrance port in said body and at least one exit port in said body, at least one curved hollow passageway extending through said body between said entrance and exit ports, and wherein said outer surface contour and surfaces defining said passageway are impervious to gas flow therethrough, comprising the successive steps of: A. using a preform body of a preform material having a first melting temperature, said preform body having an outer surface in the shape of the desired contour of said passageway, B. surrounding said preform body with a composite material composed of a ceramic powder and a glass powder, said glass powder material having a second melting temperature higher than said first melting temperature, C. forming said composite material to establish a matrix disposed about said preform body, wherein the outer contour of said composite material substantially matches said predetermined outer surface contour, D. processing composite material said at a temperature higher than said second melting temperature, whereby said preform body initially melts and flows out of said matrix thereby leaving a passageway of the same shape as the preform body prior to said application of glass melting heat, and whereby said glass powder next melts and diffuses at least in part through said matrix to said outer surface contour and to the surface defining said passageway, and whereby finally said ceramic powder sinters thereby forming a fused matrix, and

E. cooling said fused matrix.

11. The method of claim 10 wherein said ceramic powder is characterized by:

a sintering point in the range 2700°F, and electrical conductivity, when fused, greater than 10¹⁰ohm-cm, and

wherein said glass powder is characterized by:

a melting point in the range 700-900°C, and electric conductivity greater than 10¹⁰ohm-cm

12. The method of claim 10 wherein said glass powder is a lead glass powder and comprising the substep of, following step D, reducing the melted glass as sai surface defining said passageway to establish a secondary emissive semi-conducti layer at said surface.

13. An electron multiplier device having a predetermined outer surface contou comprising:

a monolithic electrically insulating body having at least one entrance port in said body and at least one exit port in said body, and having at least one hollow passageway through said body between said entrance port and said exit port, and wherein the walls defining said hollow passageways include a secondary-emissive dynode material, and wherein said body is composed of a glass-ceramic composit material and has a gas impervious glass layer on said passageway walls and on sa outer surface.