Bonding techniques for the fabrication of internally cooled X-ray monochromators

At CHESS, 2500 W total are absorbed by the first crystal of the double bounce monochromators located on the A2 and F2 wiggler beamlines. In order to dissipate this absorbed power and deliver the highest X-ray flux to an end station, we have explored the technique of internally cooling the silicon first crystals with water channels. This technique brings with it the need for reliable mechanical joints between the silicon diffracting surface and a glass or silicon water manifold. The joint must have structural strength to resist the internal water pressure and the cyclic heat load, be vacuum leak tight for operation in UHV, and not act as a source of residual strain in the crystal lattice of the diffracting surface. We have explored four bonding techniques which have been tested for their suitability to monochromator fabrication: direct silicon to silicon bonding, anodic glass to silicon bonding, a variety of ceramic and die attach adhesives (alumina, zirconia, silica/silver) and metallic diffusion bonding/brazing. In this paper, we characterize each method with respect to the requirements of structural integrity (bond tensile strength), residual strain (minimal effect on diffraction quality) and vacuum compatibility.