Fabrication of Radiation Entrance Windows with Optimized sub- 100 eV Transmission Properties
V-P. VIITANEN, S. SILANTO, AND M. BAVDAZ
ABSTRACT
A novel method for fabricating ultrathin metal membranes supported by a polymer mesh has been developed. The method utilizes a 200-nm-thick polyimide membrane supported by a photodefined polyimide grid as a substrate for subsequent metal sputtering and evaporation steps. Eventually, the thin polyimide membrane is etched off in oxygen plasma, leaving a metal membrane supported by a polyimide grid. Using this method, several batches of 150- to 400-nm-thick AI/Si, Nb and B/Ca membranes have been processed. The novel membranes transmit radiation at energies above 30 eV while reducing the transmission of IR, visible and UV photons to 10-4 - 10-7, depending on the membrane type. Atmospheric pressure-tolerant windows have been realized by stacking AI/Si or Nb layers with thin polyimide membranes and adding a metal mesh support. The Heleak rates of these windows are below 5 X 10-10 mbar liter s-1 cm-2. AI/Si and Nb (or Nb/polyimide) membranes form a complementary pair of filters; i.e., one material set has a good transmission where the other is absorbing. The calcium membrane has a good transmission over a very wide energy band, but due to the reactive nature of calcium, the lifetime of the foil is restricted if exposed to air, moisture, or other reactive gases.
Publication Source: Journal of X-Ray Science and Technology, ISSN: 0895-3996. Volume 8, Number 2, 1998. Pages: 130... Publisher:IOS Press - Amsterdam
