High negative ion yield from light molecule scattering J.A. Scheer a, * , M. Wieser a , P. Wurz a , P. Bochsler a , E. Hertzberg b , S.A. Fuselier b , F.A. Koeck c , R.J. Nemanich c , M. Schleberger d a Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland b Lockheed Martin, Advanced Technology Center, 3251 Hanover St., Palo Alto, CA 94304, USA c Department of Physics, North Carolina State University, Raleigh, NC 27695-8202, USA d Institut fu ¨ r Experimentelle Physik, Universita ¨ t Duisburg-Essen, Universita ¨ tsstraße 5, 45117 Essen, Germany Abstract Molecular oxygen and hydrogen ions were scattered at grazing incidence from several diamond-like carbon (DLC) surfaces in the energy range from 190 eV to 2400 eV. Most surfaces were hydrogen terminated. For incident positive oxygen ions, scattered negative ion fractions of up to 33% were recorded, and for incident positive hydrogen ions, neg- ative ion fractions of more than 5% were measured. These values are among the highest ever reported, especially for oxygen. They have been matched only by results of scattering experiments using a hydrogen terminated surface of nat- ural diamond. Ó 2004 Elsevier B.V. All rights reserved. Keywords: Diamond like carbon (DLC); Neutral particle imaging; Particle scattering; Surface ionization; Tetrahedral amorphous carbon; ta-C 1. Introduction Interaction of atomic and molecular projectiles with insulating surfaces has gained considerable attention in recent years [1–9]. Reports of rela- tively high fractions of negative ions resulting from scattering of positive atomic and molecular ions off insulating surfaces were quite unexpected, but suggested possibilities for several new applications. Among these applications we propose to use this process for efficient detection of 5 eV to 2 keV neu- tral particles in interplanetary and interstellar space [10,12,13]. The proof of concept for this detection technique has already been demon- strated in space. The mass spectrograph on the IMAGE satellite mission, designed to detect low energy neutral atoms, uses a conversion surface of volatile adsorbates on a polished, poly-crystal- line W substrate to convert a fraction of incoming neutral atoms to negatively charged ions [11,14]. 0168-583X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2004.12.063 * Corresponding author. Fax: +41 31 631 4405. E-mail address: jscheer@phim.unibe.ch (J.A. Scheer). Nuclear Instruments and Methods in Physics Research B 230 (2005) 330–339 www.elsevier.com/locate/nimb