US2131187A - Method of producing finely divided metallic layers - Google Patents

Description

Sept. 27, 1938. G. LIEBMANN v 2,131,187

METHOD OF PRODUCING FINELJY DIVIL'EE) METALL IC LAYERS File d May 28, 1955 717 yen for I WIEMMM ATENT orrics v METHQD F PRODUCING FINELY DIVIDE METALLIC LAYERS Gerhmd Liebmann, Berlin, Germany Application May 28, 1935, Serial No. 23,845

- In Germany May 31, 1934 9 Claims. (01. 91-701) The present invention relates to a methodof producing metallic layers on insulating materials, such, for example, as mica or the like, whereby the metallic layer consists of the finest particles,

which are insulated against each other, and represents in a manner of speaking a mosaic screen composed of single particles of metal. A screen of this nature may be employed more particularly in certain television image recording methods, in

in which the images to be transmitted are recorded with the assistance of an Ikonoscope camera. After corresponding treatment the mosaic screen represents a surface collection of elementary photo-cells, which produce electrical charges corld responding with the particular exposure. These charges may then further be employed for controlling the transmitter in suitable fashion.

The production oi the layer consisting of finest particles of metal is accompanied by considerable 2o dimcultles, both as regards selection of the mate-1 rial for the intermediate insulating layer as well as the method of insulation.

It is possible to employ mica for the intermediate insulating layer. 95 when employing a heating process for dividing the case of chemical treatment 'it is impossible in numerous cases, owing to the smallpowers. of

adhesion, to produce a metallic layer in equal I Y replaced to a. certain extent by a suitable temdistribution.

5 The methods set forth in the present invention are devoid of these disadvantages.

According to the invention, there are employed as intermediate dielectric layers, sheets of mica or other suitable bases, for example, ceramicmagig terial, certain kinds of glass, etc., the surface of this base preferably being made smooth by polish ing. On this base there is produced in suitable fashion a metallic coating, for example a silver, copper or the like coating. A metallic coating as of this nature may be produced, for example, chemically by cathode atomization or by thermal application in vapour form. The metallized plates are then heated to a high temperature in an atmosphere 0;? indifierent gas or in a vacuum. so If the metallic coating is of a certain thickness (no longer transparent), the temperature is required to be very high, for example in the case of silver to about 100W, in order to obtain a brief fusing of the layer of silver, whereby the surface s5 is then converted from the previously unitary The use of thismaterial v I An, additional metho fo insular formation a metallic layer into single elementary parts isconfronted by diificulties owing to the inconstancy structureless metallic surface into a very even mosaic consisting of small drops of metal of negligible diameter and insulated against each other. According to the invention, this heating is performed extremely rapidly, preferably bymeans of perature constancy of mice. is of advantage when,

employing-a materialof this kind; Whenuslng other materials, such as ceramic substances, glass or the like, the surface ofithe base; is preferably 'madesmooth by polishing, in order to accelerate the insular formation during the heating process.

According to the'invention,' it isalso possible to deposit the metallic layerlon a heated base, so that small globules ,1 are likewise formed right from the commencemenitj ,When using mica, however, the method-Jo jdepositedmetal f subsequently heating the Srl in preferred.

resides according to 1th: invention in the fact the above is to be that s. thin layer of silvendeposited, for example,

sure (approximately 1 mm. mercury). Theolternate oxidation and reduction might also be ture is thereupon again lowered, etc. In the case 40 of the glow discharge method the silver layer to "on mica is altemately-oxidi'zedand reduced. This method is performed in the mostfconvenient form by glow discharge in anatmosphere of alternately "introduced oxygen and hydmg'enjat suitable presbe granulated is in the most convenient form the layer than at other points. As final stage of the process, after production of the discrete particles of silver, there is conveniently performed a light oxidation, as in this man'nerit is possible to obtain a layer which is advantageously suited v for photo sensitization.

The drawing shows-diagrammatically how to carry out the method according to the invention. In the drawing Fig. 1 shows the indirect heating by means of a heating plate I, which heats by radiation the layer of silver I mounted on the supporting material 3, for example mica. Since this heating is required to commence instantaneously. the heating is preferably performed by eddy currents, which is represented diagrammatically by the high-frequency coil 4.

Fig. 2 shows the arrangement for carrying out the glow discharge process. In the same there is provided an electrode 5, which is connected up as anode and is situated opposite to a grid-like cathode I. The metallic layer 1 to be granulated is arranged within reach of the glow discharge which develops in the case of a suitable filling of gas. '1 is the metallic layer on the base 0. In

Figs. 3 and 4 there is illustrated by way of example the finishedproduct. In these I is the intermediate di-electric'layer, which acts for the coatings l0 and H. The coating ll represents,

the thin layer of metal divided up into finest elementary particles, whilst I I is intended as capac-' itative counter-coating for the photocell arrangement.

The following special embodiments of the present invention have been proved useful:

A well-cleaned mica plate with all grease removed is coated by the thermal vaporization of silver with a silver layer ofapproximately liq-A 0 1 in thickness. A thickness of the layer approximately midway of the stated range, 1. e., approximately $5 to H w produced the best results. The application of the layer by vaporization performed in a suitable vessel from which the air has been removed, the distance between the mica plate to be treated and the evaporation furnace being of such extent that a very even coating is obtained. Insulation edges-of a desired kind may be allowed to remain by selective screening. After the application 'of the silver layerby vaporization has been completed a certain amoimt of air or oxygen is allowed to enter the vessel, and the part of the vessel in which the plate is situated, is heatedto a temperature below 500 C.

I approximately 400-450 C. This latter operation extends over a period of approximately 15 to 30 minutes. After cooling-it will be noticed that the coating on the plate has been divided into single well-separated crystals of about In in size.

It has been'found that to obtain this effect it is necessary v 1. To adhere to the above stated range as regards the thickness of the layer, and 2. To employ a suitable gas atmosphere. If the initial layer is made thinner, a granula tion" of any kind is not to be determined with the usual optical means available. If thelayer is too thick, there is certainly a granulation up to a certain point, but the particles are situated so close together that the requisite insulation may be not I obtained. If on-the other hand the layeris still thicker (completely opaque), a distribution according to the described process may be not ac-.

1,000 (7.), andconsiderable difiiculties are then 1 encountered in preventing the mica from becoming entirely useless. The size of the formed particles is also a wholly different one in the last mentioned case. Further, it has been found that even with suitable layers a separation does not take place when the process is performed in an extremely high vacum (higher than 10- mm. Hg). The presence of a certain gas atmosphere (presumably oxygen) is accordingly necessary for the saparation at the low temperature stated.

Mica plates of this kind, which are furnished with a silver screen in the manner stated, may then be employed in the known fashion, by silvering the rear side and by oxidation and sensitization of the front screen surface, as lightsensitive mosaic electrodes in television transmission tubes, more particularly tubes known'under the name of Ikonoscope.

I claim: a

1. A process of producing a finely subdivided metallic layer on an insulating base comprising the steps of coating said base with silver, of interrupting coating actionwhen a layer of 0.01 to 0.1 -thickness has been formed, and of subjecting the coated base to a thermal treatment in a gas atmosphere containing oxygen at a temperature of at least about 400 centigrade and below 500 centigrade.

2. A process of producing a finely subdivided metallic layer on an insulating base comprisin the steps of coating said base with silver, of interrupting this coating action when a layer of 0.01 to 0.1 a thickness has been formed, and of subjecting the coated base to a thermal treatment in a gas atmosphere containing oxygen at a temperature of at least about 400 centigrade and below 600 centigrade during 15 to 30 minutes 3. A process of .producing a finely subdivided metallic layer on an insulating base comprising a temperature of 400 to 450 centigrade.

4. A process of producing a finely subdivided metallic layer 'on an insulating base comprising the steps of coating said base with sliver, of interrupting this coating action when a layer of 0.01 to 0.1 a thickness has been formed, and of subjecting the coated base to a thermal treat-' ment in a gas atmosphere containing oxygen at 'a temperature ofat least about 400 centigrade and below 500 centigrade by causing the radiation of a plate heated by eddy currents to act on said coated base. 4

5. A process of producing a finely subdivided metallic layer on a mica base comprising the steps of coating said base with sliver, of interrupting this coating action when a layer of 0.01 to 0.1 a thickness has been formed, and of subiecting the coated base to a thermal treatment in a gas atmosphere containing oxygen at a temperature of at least about 400 centigrade and below 500 centigrade.

8. A process of producing a-finely subdividedmetallic layer on a glass base comprising the steps of coating said base with sliver, of interrupting this coating action when a layer of 0.01 to 0.1 thickness has been formed, and of sub- Jecting the coated base to a thermal treatment in a gas atmosphere containing oxygen at a temperature of at least about 400 centigrade and below 500' centigrade.

. 7. A process of producing a finely subdivided I metallic layer on a base of a'ceramic material comprising the steps of coating said base withsilver, of interrupting this coating action when I.

a layer oi 0.01 to 0.1 a thickness has been formed. and of subjecting the coated base to a thermal treatment in a gas atmosphere containing oxygen at a temperature oi at least about 400 centigrade and below 500' centigrade.

8. A process of producing a finely subdivided metallic layer on a glass base comprising the steps 01' polishing the surface of said base. of coating the poiished-suriace oi. said base with silver, of interrupting this coating action when a layer of 0.01 to 0.1 a thickness has been formed, and of subjecting the coated base to a thermal treatment in a gas atmosphere containing oxygen at a temperature or at least about 400' centigrade and below 500 centigrade.

9. A process of producing a finely subdivided metallic layer on a base of ceramic material comprising the steps 01 polishing the surface of said base, oi coating the polished surface of said base with silver, 01 interrupting this coating action when a layer of 0.01 to 0.1 a thickness has been formed, and 0t subjecting the coated base to a thermal treatment in a gas atmosphere containing oxygen at a temperature of at least about 400 centigrade and below 500 centigrade.

GERHARD LIEBMANN.

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