  X-ray transmission windows for the low energy range, especially between 0.1
keV and 1 keV have been designed and fabricated based on graphenic carbon (GC)
with an integrated silicon frame. A hexagonal and a bar grid support structure
design have been evaluated. The bar grid design allows to substitute
polymer-based windows with the advantages of higher transmission, better
rejection of visible light and vacuum operability of the encapsulated silicon
drift detectors (SDD). In addition, the high mechanical resilience of graphenic
carbon is demonstrated by pressure cycle tests, yielding over 10 million cycles
without damage. The data are complemented by bulge tests to determine a Young`s
modulus for graphenic carbon of approximately 130 GPa. Additional
finite-element simulation and Raman studies reveal that the mechanical stress
is not homogeneously distributed, but reaches a maximum near the anchoring
points of the free standing graphenic carbon membrane.
