Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-12-28
2004-06-29
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S702000, C428S432000, C427S164000, C427S166000, C427S255320, C423S609000, C501S134000, C501S152000
Reexamination Certificate
active
06756137
ABSTRACT:
The invention relates to a vapor-deposition material for the production of high-refractive-index optical layers of titanium oxide, titanium and lanthanum oxide under reduced pressure, and to a process for the production of the vapor-deposition material.
Oxide layers are widely used in industry, in particular in optics, as protective layers or for optical functional purposes. They serve as protection against corrosion and mechanical damage or for coating the surfaces of optical components and instruments, such as lenses, mirrors, prisms, objectives and the like. Furthermore, the oxide layers are employed for the production of high-, medium- and low-refractive-index optical layers for increasing or reducing reflection. The most important areas of application are the production of antireflection layers on spectacle lenses and camera lenses, for binoculars and optical components and optics for laser technology. Further applications are the production of layers having a particular refractive index and/or certain optical absorption properties, for example for interference mirrors, beam splitters, heat filters and cold-light mirrors.
DE 42 08 811 A1 discloses a vapor-deposition material for the production of high-refractive-index optical layers by vapor deposition coating of substrates under reduced pressure. The material is a compound of the formula La
2
Ti
2
O
7-x
, where x=0.3 to 0.7, in particular a compound of the formula La
2
Ti
2
O
6.5
. Vapor-deposition materials of this type are produced by mixing oxides of lanthanum and titanium as well as metallic titanium in the corresponding stoichiometric ratio, and sintering the mixture below the melting point in a high vacuum.
German Patent 1 228 489 discloses a process for the production of thin oxide layers which are virtually absorption-free in the visible wavelength region for optical purposes, in particular on glass substrates, by vapor deposition of oxidic and/or oxidisable substances under reduced pressure. The vapor-deposition may, if desired, be carried out in the presence of an oxidising atmosphere. One or more elements and/or oxides from the group consisting of the rare earths, including yttrium, lanthanum and cerium, are vapor-deposited with the oxidic and/or oxidisable substances. The starting substances here are evaporated as a mixture or separately from one another. The oxidic and/or oxidisable substances used are, inter alia, titanium and/or titanium oxide.
For the production of high-refractive-index layers which have an optical refractive index of around the value 2, the choice of suitable starting materials is limited. Possible starting materials for this purpose are essentially the oxides of titanium, zirconium, hafnium and tantalum, as well as mixed system thereof. A preferred starting material for high-refractive-index layers is titanium dioxide.
Besides titanium oxide, the prior art furthermore uses compounds such as tantalum oxide, zirconium oxide, hafnium oxide and zinc sulfide, and mixtures of oxides, for example zirconium oxide and titanium oxide, titanium oxide and praseodymium oxide, and titanium oxide and lanthanum oxide.
These substances have advantages. Titanium dioxide, for example, has a high refractive index, and hafnium oxide and zirconium oxide have low absorption. The disadvantages of these known substances, for example, are vigorous gas evolution and spitting of the titanium dioxides, relatively high absorption in the case of tantalum oxide Ta
2
O
5
and a mixture of titanium oxide and praseodymium oxide, incomplete melting of zirconium oxide, hafnium dioxide and a mixture of zirconium oxide and titanium dioxide, and low hardness, for example, in the case of zinc sulfide. In a mixture of titanium oxide and lanthanum oxide, some of the advantages are, for example, low absorption, no gas evolution and spitting, and relatively good melting. However, the refractive index of a mixture of this type is significantly lower than in the case of titanium dioxide and zinc sulfide. From the practical processing point of view, it is also disadvantageous that these substances have high melting and boiling points, which in addition are relatively close to one another. In order to ensure a uniform and adequate evaporation rate, it is necessary for the vapor-deposition materials to be completely melted before commencement of significant evaporation. This condition is necessary in order for homogeneous and uniformly thick layers to form on the objects to be vapor deposition coated. However, this is not the case under use conditions for the oxides of zirconium and hafnium and in the case of titanium/zirconium mixed oxide systems. The said substances do not melt or do not melt completely under typical working conditions, they are difficult to evaporate completely, and thickness variations arise in the vapor-deposited layers. The aim in the prior art is to lower the melting points of the base materials by means of suitable additives, where these additives furthermore serve to vary the refractive index in the resultant layers within certain limits and to set the refractive index to a specific value. The choice of suitable additives for this purpose is restricted by the requirement for freedom from absorption. The only metal oxides suitable as corresponding additives are therefore those which have no absorptions in the visible spectral region as far as the near UV wavelength range, i.e. up to about 320 nm.
The said oxides have no or only slight absorption in the visible wavelength region, which is a basic prerequisite for optical applications. However, loss of oxygen and deposition of titanium oxide layers which are sub-stoichiometric with respect to the oxygen content occur during high-vacuum evaporation. This means that, the production of thin layers by vacuum evaporation with these materials results in layers having high absorption in the visible region without special precautionary measures. German Patent 1 228 489 addresses this problem by carrying out the evaporation in a vacuum with a certain residual oxygen pressure of from 5*10
−5
to <5*10
−4
mbar, whereby an oxidising atmosphere is established. Another approach for solving this problem consists in subjecting the resultant layers to post-conditioning in oxygen or air.
Even if the above-mentioned problems can be solved through a suitable choice of additives or the choice of corresponding substance mixtures, the use of mixed systems is not preferred per se in vacuum vapor-deposition technology. The reason is that mixed systems generally evaporate incongruently, i.e. they change their composition during the evaporation process, and the composition of the deposited layers also changes correspondingly. This can be avoided if the mixed systems comprise discrete chemical compounds which evaporate and re-condense without material change.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
The object of the invention is to provide a vapor-deposition material from which optical layers having the highest possible refractive index and low absorption can be produced, where the vapor-deposition material exhibits very good melting and evaporation behavior and can be evaporated with virtually no evolution of gas or spitting.
This object is achieved in accordance with the invention in that the material is a sintered mixture of the composition TiO
x
+z*La
2
O
3
, where x=1.5 to 1.8 and z=10 to 65%, e.g., 10 to 60%, by weight, based on the total weight of the mixture.
Titanium oxide, TiO
x
, for x=1.5 to 1.8 means titanium suboxide, i.e., a mixture with compounds having less oxygen than titanium dioxide, for example, but not limited to, Ti
3
O
5
or Ti
4
O
7
, but not Ti.
In an embodiment of the invention, the mixture comprises from 19 to 65% by weight of lanthanum oxide, from 38 to 74% by weight of titanium oxide and from 2 to 7% by weight of titanium. In two specific embodiments of the invention, the mixture consists of 58
Anthes Uwe
Friz Martin
Jones Deborah
Merck Patent GmbH
Millen White Zelano & Branigan P.C.
Xu Ling
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