US 3259782 A
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July 5, 1966 A. M. SHROFF 3,259,782
ELECTRON-EMISSIVE STRUCTURE Filed Oct. 25. 1962 INVENTOR HRvINo m. SHRoFF BY: 7 ml 7 HTTORNEY United States Patent 3,259,782 ELECTRON-EMISSIVE STRUCTURE Arvind M. Shroif, Paris, France, assignor to CSF-Compagnie Generale de Telegraphic Sans Fil, Paris, France Filed Oct. 25, 1962, Ser. No. 233,081 Claims priority, application France, Nov. 8, 1961, 878,265 6 Claims. '(Cl. 313-336) The present invention relates to a method for producing electron-emissive structures, and more particularly relates to a process for making point cathodes of the cold emission type as well as to the cold emission type cathode structures resulting from such method.
The most widely used form of a cold emission type electron emitter by extraction by means of a very intense electric field is the shape of a point having an extremely small radius of curvature. To obtain such a point, it is therefore necessary to have recourse to a pointing operation.
The known points are generally realized of tungsten, though other pure metals, such as platinum, molybdenum, or rhenium, have all been tested since all of these materials lend themselves with ease to the pointing operation, for example, by electro-chemical attack within an alkaline bath.
Nevertheless, it is of interest, and it has also already been proposed to realize these points of zirconium carbide, for this refractory material not only possesses a good conductivity but also possesses a working potential very much smaller than that of the afore-mentioned metals; consequently, the emission curve as a function of the applied field increases very rapidly, and, accordingly, a point made of zirconium carbide may form an electron emitter with very high current density.
However, the known manufacturing processes have proved to be incapable of producing points with sutficiently small radii of curvature. In these prior art processes, one either started with a block of zirconium carbide prefabricated by the usual methods, which did not lend itse f to the pointing operation, or one produced monocrystals of zirconium carbide which lend themselves well to the pointing operation by electrochemical attack within solutions, for example, of potassium fluoride within sulfuric acid, but these monocrystals are diflicult to prepare industrially.
The present invention essentially consists in a process for fabricating cold-emission-type electron emitters of zirconium carbide, which makes it possible to produce, in a simple manner, points of desired fineness, while avoiding at the same time the difliculties of the known methods and additionally permitting the simultaneous production of a large quantity of these points.
Accordingly, it is an object of the present invention to provide a process for producing point-like electron emitter structures of the type described hereinabove which effectively eliminates the shortcomings and drawbacks encountered with the prior art methods.
It is another object of the present invention to provide a method for producing cold emission electron emitter structures which may be manufactured with points of sufficiently small radius of curvature without great difficulties or expensive installations.
Still a further object of the present invention resides in the provision of a method for producing point-like cold cathode structures of zirconium carbide which assure, in operation, a very high current density.
Another object of the present invention resides in the provision of a method for producing cathode structures of the type mentioned hereinabove that lends itself readily to mass-production techniques.
Still another object of the present invention resides in the provision of a cold cathode structure made of zirconium carbide having a very small radius of curvature which is obtained with the method of manufacture in accordance with the present invention.
According to the present invention, there is produced a point of zirconium carbide by starting with a point made of base metal, such as tungsten, that is pointed to the desired degree by any known method or process, thereupon evaporating on this base metal zirconium, and thereafter carburizing the zirconium by any known method, in the presence, for example of a heavy organic product, such as naphthalene or benzene.
According to another characteristic of the present invention, these operations take place simultaneously with a series of points.
The present invention is also applicable to cathodes made of the carbide of refractory metals other than zirconium, if it proves of advantage to utilize such carbide by reason of its relatively small working potential or other characteristics which may be found advantageous.
Thus, while I have described a preferred process in connection with zirconium carbide, it is understood that the present invention is not limited thereto, but is sus ceptible of many changes and modifications Within the spirit and scope thereof, and I therefore do not wish to be limited to the details described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.
The accompanying drawing shows a cold emission cathode comprising a plurality of metal points, each having a tungsten core 1 carrying a very thin coating 2 of zirconium carbide.
1. A point-like cathode emitter, comprising a pointshaped tungsten support, and a thin layer of a zirconium carbide coating on said point-shaped support.
2. A point-like cathode emitter, comprising a pointshaped metallic support, and a thin layer of a zirconium carbide coating on said point-shaped support.
3. A process for making point cathodes having a high degree of field emission, comprising the steps of making a point-shaped support of tungsten, evaporating zirconium on said point-shaped tungsten support, and carburizing said zirconium in the presence of an organic atmosphere.
4. A process for mass-producing simultaneously a plurality of point cathodes having a high degree of field emission and utilizing a plurality of point-shaped tungsten supports, comprising the steps of simultaneously evaporating zirconium on said point-shaped supports, and thereafter simultaneously carburizing said zirconium in the presence of an organic atmosphere.
5. A process for making point cathodes having a high degree of field emission, comprising the steps of making a point-shaped support of a metal that can be easily pointed and selected from the group consisting of tungsten, platinum, molybdenum and rheniurn, evaporating zirconium on said point-shaped support, and carburizing said zirconium.
6. A process for making point cathodes having a high degree of field emission, comprising the steps of making a point-shaped support of a metal that can be easily pointed and selected from the group consisting of tungsten, platinum, molybdenum and rhenium, evaporating zirconium on said point-shaped support, and carburizing zirconium in the presence of an organic atmosphere.
References Cited by the Examiner UNITED STATES PATENTS JOHN W. HUCKERT, Primary Examiner.
said 10 JAMES KALLAM, Examiner.
R. F. POLISSACK, Assistant Examiner.