Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – With material removal by etching – laser ablation – or...
C505S320000, C505S325000, C505S470000, C505S473000, C505S474000, C505S475000, C204S192340, C204S192350, C204S192110, C204S298040, C204S298360, C156S345390, C216S066000
The invention relates to ion texturing methods and articles.
Multi-layer articles can be used in a variety of applications. For example, superconductors, including oxide superconductors, can be formed of multi-layer articles. Typically, such superconductors include a layer of superconductor material and a layer, commonly referred to as a substrate, that can enhance the mechanical strength of the multi-layer article.
Generally, in addition to enhancing the strength of the multi-layer superconductor, the substrate should exhibit certain other properties. For example, the substrate should have a low Curie temperature so that the substrate is not ferromagnetic at the superconductor's application temperature. Furthermore, chemical species within the substrate should not be able to diffuse into the layer of superconductor material, and the coefficient of thermal expansion of the substrate should be about the same as the superconductor material. Moreover, if the substrate is used for an oxide superconductor, the substrate material should be relatively resistant to oxidation.
For some materials, such as yttrium-barium-copper-oxide (YBCO), the ability of the material to provide high transport current in its superconducting state depends upon the crystallographic orientation of the material. For example, such a material can exhibit a relatively high critical current density (Jc) when the surface of the material is biaxially textured.
As used herein, “biaxially textured” refers to a surface for which the crystal grains are in close alignment with a direction in the plane of the surface or in close alignment with both a direction in the plane of the surface and a direction perpendicular to the surface. One type of biaxially textured surface is a cube textured surface, in which the primary cubic axes of the crystal grains are in close alignment with a direction perpendicular to the surface and with the direction in the plane of the surface. Examples of cube textured surfaces include the (100) and (100) surfaces, and an example of a biaxially textured surface is the (113) surface.
For certain multi-layer superconductors, the layer of superconductor material is an epitaxial layer. As used herein, “epitaxial layer” refers to a layer of material whose crystallographic orientation is derived from the crystallographic orientation of the surface of a layer of material onto which the epitaxial layer is deposited. For example, for a multi-layer superconductor having an epitaxial layer of superconductor material deposited onto a substrate, the crystallographic orientation of the layer of superconductor material is derived from the crystallographic orientation of the substrate. Thus, in addition to the above discussed properties of a substrate, it can be also desirable for a substrate to have a biaxially textured surface or a cube textured surface.
Some substrates do not readily exhibit all the above-noted features, so one or more intermediate layers, commonly referred to as buffer layers, can be disposed between the substrate and the superconductor layer. The buffer layer(s) can be more resistant to oxidation than the substrate, and reduce the diffusion of chemical species between the substrate and the superconductor layer. Moreover, the buffer layer(s) can have a coefficient of thermal expansion that is well matched with the superconductor material.
In some instance, a buffer layer is an epitaxial layer, so its crystallographic orientation is derived from the crystallographic orientation of the surface onto which the buffer layer is deposited. For example, in a multi-layer superconductor having a substrate, an epitaxial buffer layer and an epitaxial layer of superconductor material, the crystallographic orientation of the surface of the buffer layer is derived from the crystallographic orientation of the surface of the substrate, and the crystallographic orientation of the layer of superconductor material is derived from the crystallographic orientation of the surface of the buffer layer. Therefore, the superconducting properties exhibited by a multi-layer superconductor having a buffer layer can depend upon the crystallographic orientation of the buffer layer surface.
In certain instances, a buffer layer is not an epitaxial layer but can be formed using ion beam assisted deposition. Typically, ion beam assisted deposition involves exposing a surface to ions directed at a specific angle relative to the surface while simultaneously depositing a material. In instances where ion beam assisted deposition is used to form a buffer layer, the crystallographic orientation of the surface of the buffer layer can be unrelated to the crystallographic orientation of the surface of the underlying layer (e.g., a substrate). Generally, however, the ion beam deposition parameters such as, for example, the ion energy and beam current, the temperature, the ratio of the number of atoms arriving at the surface relative to the number of ions coincidentally arriving at the surface, and the angle of incidence on the surface are selected so that the crystallographic orientation of the surface of the buffer layer provides an appropriate template for a layer that is deposited on the surface of the buffer layer (e.g., a layer of superconducting material).
The invention generally relates to ion texturing methods and articles.
In part, the invention relates to the realization that, by selecting the appropriate combination of parameters, multiple ion beams (e.g., two, three, four, etc.) can be used to increase the degree of texture of the surface (e.g, a noncrystalline surface) of a layer of material (e.g., a layer of an already deposited material, such as an already deposited buffer layer) so that the surface of the material has a predetermined crystallographic orientation. The crystallographic orientation of the ion textured surface can be different than the natural growth orientation of the layer of material.
The surface to be textured can be, for example, that of a substrate, a buffer layer, a protective layer or a layer of superconductor material. In certain embodiments, a multi-layer article (e.g., a multi-layer superconductor article, such as a coated superconductor article) can include more than one layer having an ion textured (or at least partially ion textured surface).
Materials that can be ion textured include, for example, metals, alloys, oxides of metals, nitrides of metals, oxides of alloys and nitrides of alloys. Such materials include, for example, nickel, nickel alloys, silver, MgO, titanium nitride, zirconia, zirconium nitride, TbO
, ceria (CeO
), yttria stabilized zirconia (YSZ), Y
, ruthenium oxide, barium titanate, lanthanum gallate, indium oxide and NdAlO
In some embodiments, the combination of appropriate parameters (e.g., the angle of the ion beams relative to the surface normal, the angle of the ion guns relative to each other and/or the crystal structure of the layer of material exposed to the ion beams) can be used to provide the predetermined crystallographic orientation of the surface in a relatively short period of time.
The multiple ion beams can be simultaneously active, or the multiple ion beams can be used in sequence. In some embodimnents, some or all of the ion beams can be simultaneously active for a portion of the ion bombardment, and some or all of the ion beams can be used sequentially for a portion of the ion bombardment.
In some embodiments, the multiple ion beams can provide an ion flux sufficiently high so that the sputtering rate of the noncrystalline surface would exceed the atom arrival rate during certain vapor deposition processes.
In certain embodiments, the process can provide a noncrystalline substrate having an ion textured surface.
In some embodiments, the process can provide a substrate with a noncrystalline layer deposited thereon. The surface of the noncrystalline layer can be ion textured.
Berdahl Paul H.
Fritzemeier Leslie G.
Reade Ronald P.
Russo Richard E.
McDonald Rodney G.
O'Banion John P.
The Regents of the University of California
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