Diffusion bonding of ductile single crystals for strain‐free mounting

A technique has been developed, utilizing high-temperature diffusion, to bond nearly-perfect single crystals of copper to a metal backing. The motivation for this work is the study of interfaces between metals. The structure of the interface formed by deposition onto a single-crystal substrate is affected by the degree of perfection of the substrate surface. Local inhomogeneities, defects and strains will obscure the nature of the interface region. These single crystals of ductile metals are extremely susceptible to damage during handling and it is a serious problem to find a way to secure them without introducing strain or deformation. Many methods have been investigated, including glues, epoxies, tapes and mechanical devices. Most of these techniques induce strains or cause permanent deformation of the crystal. For laboratory inspection of crystals a rubber-based double-stick tape* has been successful. However, this tape is not compatible with the high-vacuum environment and ion bombardment for surface cleaning necessary to form a high-quality interface. This note reports another technique that will secure the crystal to a thick metallic backing without introducing deformation or strain. The technique is based on material transport resulting from the diffusion of metals that occurs at elevated temperature. Copper was chosen as the single-crystal material because it is most susceptible to deformation. Thin copper crystals, 0.5-1-0 mm thick, 15 mm diameter, were prepared by acid sawing and acid polishing from a boule grown by the Czochralski method (Kuriyama, Early & Burdette, 1974; Kuriyama, Boettinger & Burdette, 1978). The surface normal was parallel to the [111] direction. The crystals were annealed for 10 d at 1270 K in hydrogen and their perfection was verified by X-ray topography using anomalous transmission from an asymmetric (111) diffraction. A polycrystalline oxygen-free copper backing, 21 x 19 x 15 mm with an 11 mm