Au Release Layer Development for High-Angular Resolution, Replicated Full-Shell X-ray Optics

The X-ray group at NASA Marshall Space Flight Center is developing replicated full-shell X-ray optics for future mission concepts with a goal of achieving sub-arcsecond angular resolution. One of the electroforming fabrication processes that may contribute significantly to resolution degradation of the mirror shell is the shell separation from the mandrel. Traditionally, a passivation layer has been used between the mandrel and the NiCo shell, resulting in the required medium angular resolution mirror shells. However, as resolution requirements become more stringent, improvements to this process must be investigated. To this end, we present the application of gold release layers for full-shell optics designed to improve the optic fabrication process and reduce azimuthal errors.

MSFC sputtered gold coatings are first optimized and characterized via X-ray reflectometry (XRR) measurements, atomic force microscopy (AFM), optical profilometry, and adhesion testing. Initial replication studies conducted on flat coupons made of the mandrel surface material are presented along with a comparison to other replicants fabricated using both passivation and evaporated Au layers. To validate the Au release layer for grazing incidence geometries, sputtered gold coatings were deposited onto a mandrel from which a full-shell optic was replicated. We report on the X-ray performance of this optic and compare the results to that of an identical optic fabricated with a passivation layer.