US 2752882 A
Description (OCR text may contain errors)
July 3, 1956 w. HElMANN 2,752,882
APPARATUS FOR EVAPORATION OF CHEMICAL COMPOUNDS Filed Oct. 15, 1954 INVENTOR. WALT EH H EIMAIN N APPARATUS FOR EVAPORATION OF CHEMICAL CGMPOUNDS Walter Heimann, Wiesbaden-Dotzheim, Germany Application October 15, 1954, Serial No. 462,576
6 Claims. (Cl. 118- 49) This invention relates to apparatus for applying coating to articles by evaporation of chemical compounds and is particularly directed to such apparatus for applying coatings of binary compounds of a metal and a nonmetal in an evacuated chamber.
When evaporating certain such compounds, as for example a metal sulfide, dissociation of the compound takes place to an extent dependent on the particular composition of the metal sulfide. As a result, with conventional method and apparatus for applying such coatings to articles undesired strong local concentrations of the dissociated metal occurs in portions of the coating. Hence the ratio of the metal to the sulfide in the coating is in excess of the stoichiometric ratio and further treatment is necessary for example to bring the coating as close as possible to the stoichiometric condition.
An object or this invention comprises the provision of a novel apparatus for avoiding the aforementioned difiiculties resulting from the dissociation of the compound being evaporated. A still further object of the invention comprises the provision of novel apparatus utilizing an electric field to avoid said ditiiculties. As used herein the term electric field is intended to be sufficiently broad to include both electrostatic and magnetic fields.
in accordance with the invention, when a coating is applied to an article by evaporating a chemical compound, the particles on evaporation are subjected to an electric field formed between positive and negative poles. Due to the fact that at least some of said evaporated particles are electrically charged the electric field is effective to modify the composition of the coating on said article. it has been found, for example, when a metal sulfide is being evaporated within such a field a concentration of dissociated metal particles is deposited on the negative pole and the deposit on the positive pole shows a surplus of the non-metallic or sulfur portion of the compound. Accordingly by proper selection of the field intensity and of the shape and arrangement of the field poles the percentage of the elements in the composition of the coating deposited on the article can be varied, Within limits, as desired.
Other objects of the invention will become apparent upon reading the annexed detailed description in con nection with the drawing in which:
Fig. 1 is a schematic view of apparatus embodying the invention;
Fig. 2 is a view taken along line 2-2 of Fig. l; and
Figs. 3, 4, 5, 6 and 7 are views similar to Fig. l illustrating modifications of the invention.
Referring first to Figs. 1 and 2 of the drawing, a bell jar id is mounted on a support 12 which is provided with means including a conduit 14 for evacuating the jar it to the desired extent to provide an evacuated chamber. A container or cup-like vessel 16 is supported in the jar or chamber and support means, schematically indicated at 18, is provided for supporting articles, such as nite States Patent 6 2,752,882 hatenterl July 3, 1956 Ice the plates 24), above the container 16. Means are also provided for heating a chemical compound within the container 1 6 for, evaporating the compound so as to form a coating of the compound on the plates 20. As is conventional, the wall of the container 16 may comprise an electric resistance heating element to which a source of alternating electric currentis connected, as indicated by the wires 22, for heating and evaporating the chemical compound within said container. Semi-conductors, such as sulfides of lead, Zinc and cadmium are examples of chemical compounds which may be evaporated toapply a coating to an article in this manner. The apparatus and method so far described isconventional.
in accordance with the invention a strong steady electric field is provided in the evacuated chamber 10 by means of electrodes or poles 24 and 26. In Figs. 1 and 2 the field is an electrostatic field and the pole 24 is the positive pole or anode and the pole 26 is the negative pole or cathode. Also, as illustrated, the poles 24 and 26 are disposed on opposite sides of the container 16 and part way between the container and the plates 26 so that the evaporated particles traveling from said container to the plates 2t} must pass across the condenser type field between said poles before reaching said plates. The voltage applied across the plates 24 and 26 may be of. the order of 1000 to 1500 volts. With this method and apparatus the electric field exerts a force on the charged particles evaporated from the container 16 to modify the composition of the coating deposited on the plates 20 whereby, for example, a stoichiometric deposit may be obtained.
In Figs. 1 and 2 the poles 24 and 26 are disposed on opposite sides of the container 16 and each pole has an arcuate shape which is similar and parallel to that of the adjacent side or" the container. The poles may have various other shapes and arrangements as illustrated in Figs. 3-7.
Fig. 3 illustrates a further modification in which the poles 24b and 26b are formed as co-axial rings of equal diameterand are disposed so that the axis of said rings extends from the center of the container 16 to the center of the group of plates 20 or other article or articles to be coated. With this ring-type pole construction the field is similar to that provided by an electronic or ionic lens and causes separation of the paths of the charged evaporated particles. Either of said rings may be the positive pole with the other the negative pole. "in addition the ring disposed adjacent to the container for the compound to be evaporated may have the smaller diameter. This latter arrangement is illustrated in Figs. 4 and 5. In Fig. 4 the smaller diameter pole is the negative pole Ztic while in Fig. 5 the smaller diameter pole is the positive pole 24d. I
Still another modification is illustrated in Fig. 6 Where the negative pole 262 has a screen-type construction disposed adjacent to and in front of the plates 202 so that the positively charged metal particles readily collect on this pole before reaching the plates 20s.
The modification illustrated by Fig. 7 shows the positive ring-type pole 24 disposed between the negative pole 26), of screen-type construction, and plates 29].
Except for the above discussed differences, the up paratus of Figs. 3-7 are like that of Figs. 1 and 2 and for ease of understanding the parts of Figs. 3-7 have been designated by the same reference numerals as the corresponding parts of Figs. 1 and 2 except subscripts b, c, d, e, and f have been added to the reference numbers of Fig. 3, Fig. 4, Fig. 5, Fig. 6 and Fig. 7 respectively. Accordingly no further description of Figs. 3-7 appears necessary.
While I have described my invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. I aim in the appended claims to cover all such modifications.
I claim as my invention:
1. Apparatus for depositing a coating on the surface of an article; said apparatus comprising a chamber; means for evacuating said chamber; container means in said chamber for supporting a compound to be evaporated therein; means for supporting an article in said chamber at a point spaced from said container means so that upon evaporation of said compound said article becomes coated thereby; and pole-means disposed between said article supporting means and container means for providing an electric field therebetween, said pole means including positive and negative poles symmetrically surrounding the mean path between said supporting means and said container means.
2. Apparatus as recited in claim 1 in which said pole means includes a negative pole of screen-type construction disposed across the path of travel of evaporated particles from said container means to said article, and a positive pole of ring-type construction surrounding the said path of travel.
3. Apparatus for depositing a coating on the surface of an article; said apparatus comprising a chamber; means for evacuating said chamber; container means in said chamber for supporting a compound to be evaporated therein; means for supporting an article in said chamber at a point spaced from said container means so that upon evaporation of said compound said article becomes coated thereby; and a positive pole and a negative pole, said poles having the forms of complete figures of rotation and being disposed substantially symmetrically with respect to the shortest path between said article supporting means and container means for providing an electric field therebetween.
4, Apparatus as recited in claim 3 in which each of said poles has a ring-like shape.
5. Apparatus as recited in claim 3 in which each of said poles has a ring-like shape with one of said poles having a diameter smaller than that of the other and with said smaller diameter polebeing disposed closest to said container means.
6. Apparatus as recited in claim 4 in which the negative pole has a screen-type construction and is closer to said container means than the positive pole.
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