Metal Coated High Aspect Ratio Glass Capillary Arrays for X-Ray Collimation

X-Ray collimators based on MCPs (Micro Channel Plates) are composed of glass capillaries in a dense array. It is a known technology capable of producing large areas with high aspect-ratio holes; however, the choice of glass for the collimator material has some drawbacks. These collimator perform poorly at energies above >10 keV. We are developing MCPs for this energy range by adding a wall-coating that is comprised of a conformal several-micrometer-thick metal layer. All fabrication used techniques can be applied to large area glass capillary arrays. The main micro-fabrication challenge is that glass capillary arrays have extreme high aspect ratios, which requires that all fabrication methods have to be optimized for these aspect ratios. The fabrication sequence is a two-step process: (i) coating of array walls by metal ALD (atomic layer deposition) and (ii) metal (we use gold and copper) electroplating. We successfully develop homogenous Pt coating by ALD. Since ALD is an inherently slow process; depositing thick conducting films is extremely time-consuming. However, electroplating requires a good conducting film. A 200 nm thick highly conducting film can be plated within 20 min. Ni is a standard starting layer for gold or copper electroplating The combination of Pt ALD acting as a starting catalyst for the electroless nickel then enables to possibility of electroplating various thick metal coatings. Copper and gold films were electroplated onto the Ni conformally covering the MCP walls. One possible application of these metal coated MCPs would be the large area detector for the STROBE-X (Spectroscopic Time-Resolving Observatory for Broadband Energy X-rays) mission, a probe-class mission concept currently under consideration by NASAke.