Uranium Oxide as a Highly Reflective Coating from 2.7 to 11.6 Nanometers
Abstract
We present the measured reflectances (Beamline 6.3.2, ALS at LBNL) of naturally oxidized and reactively sputtered uranium as compared to nickel, gold, and iridium thin films from 2.7 to 11.6 nm at 5, 10, and 15 degrees grazing incidence. These show that uranium, as UO2, can fulfill its promise as the highest known single surface reflector for this portion of the soft x-ray region, being nearly twice as reflective as nickel in the 5-10 nm region. This is due to its large index of refraction coupled with low absorption. Nickel, gold, and iridium are commonly used in soft x-ray applications in astronomy and synchrotrons. (The reflectance of nickel at 10 degrees exceeds that of gold and iridium for most of this range.) We prepared uranium thin films via DC-magnetron sputtering of a depleted U target. The nickel, gold, and iridium thin films were prepared with resistive heating evaporation. For the naturally oxidized uranium, ambient oxidation quickly brought the U sample to UO2 (total thickness about 30 nm). For reactively sputtered uranium, oxygen was back filled into the evacuated chamber with argon to sputter uranium oxide. The nickel sample (50 nm) also acquired a thin native oxide coating (<2nm). Though the density of U in UO2 is only half of the metal, its reflectance is high and it is relatively stable against further changes. There are important discrepancies between the actual reflectance of UO2 and those predicted by the atomic scattering factor model indicative of the need to determine the actual constants of UO2.
- Publication:
-
APS Four Corners Section Meeting Abstracts
- Pub Date:
- October 2003
- Bibcode:
- 2003APS..4CF.S9006S