Genesis Sample Surface Contamination Study using Total-reflection X-Ray Fluorescence (TXRF)

We have used synchrotron-based Total-reflection X-Ray Fluorescence (TXRF) to measure the surface and near-surface contamination of Genesis flight spare material as well as one piece of sapphire which flew on the mission. Flight spare samples included uncoated, Al-coated and Au-coated sapphire wafers and diamond-like carbon (DLC) on silicon. These studies were performed to determine the suitability of TXRF for the study of Genesis materials. The technique is optimally suited and highly surface sensitive for elements between Na and Br with sensitivities ranging from 1e9 to 1e12 atoms/cm2. By changing the x-ray angle of incidence one can vary the sampling depth from ~ 100 Å to several thousand Å. We found that the level of contamination of the flight-spare material varied widely. For the case of the returned piece of sapphire there were concentrations of Ge on the surface approaching monolayer coverage.