A sample of depleted uranium was abraded with 1200 grid SiC paper and subsequently polished with 3µm and 1µm diamond to a mirror finish. Areas 20µmx20µm wide that included uranium carbide inclusions were ion-etched with 30 keV Gallim ions with a current of 2.8 nA, for up to 5 minutes. The depths of the “craters” thus generated were measured by electron microscopy and by profilometry and the ratio of the number of uranium atoms removed and the ion fluence was used to determine the sputtering yield for both uranium and uranium carbide.

We show the results in SEM images of sputtered areas and depth measurements on "craters" that include uranium carbide inclusions.

The same procedure was used to determine the sputtering yield of 16keV Cesium ions bombarding uranium. At their respective energies the depth of penetration of Gallium and Cesium (109Å and 50Å, respectively, as calculated by the TRIM[1] code) is much smaller than the crater depths. The measured depth increases represent therefore the sputtering yields of the Uranium-Gallium and Uranium-Cesium alloys created by ion implantation, since sputtered atoms originate almost inclusively from the first atomic layers of the substrate[2] . Comparison of the measured sputtering yields with those of pure U using Matsunami’s equation[3] demonstrates the effect of alloying on sputtering yield.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

[1] Sputtering by Particle Bombardment. Behrisch, R. Ed. Springer Verlag GmbH., 2007.

[2] Burnett, J.W. et al., Journal of Vac. Science & Technology A., 6, 3, 2064-2068, 1988.

[3] Matsunami, N. et al., Atomic Data and Nuclear Data Tables, 31, 1-80, 1984.