Scattering of atoms and molecules off a barium zirconate surface

Neutral particle imaging in the low-energy range will, when employed in fut ure spacecraft missions. potentially contribute to enlarging our knowledge about the origin and evolution of our universe. The main difficulty for a n eutral particle detector in this energy range is that the incoming neutrals must first be ionized such that they can be mass- and energy-analyzed by c onventional methods. In this paper. we report on the first observation of t he formation of negatively charged ions upon reflection from a barium zirco nate surface, Experiments were performed at two different setups, one of th em including a time-of-flight (TOF) measurement of the specularly reflected particles, the other one allows position-resolved detection. We measured h igh fractions (22-35%) of negative ions and no positive ions when scatterin g O-, O-0, O-2(+) and O-2(0) at 500-3000 eV primary energy per atom off a B aZrO3, surface. When scattering H-, H-2(+) and H-2(0) at 300-1500 eV per at om off the BaZrO3 surface, 3-5% of the particles were converted into negati ve ions and 2-8% into positive ions. Our results suggest a complete memory loss of the incident charge state. Scattered molecules dissociated almost c ompletely. The mean energy loss was proportional to the incident particle e nergy. BaZrO3 therefore meets the most important requirements for applicati on on a space platform. (C) 2001 Elsevier Science B.V. All rights reserved.