Negative ion surface production through sputtering in hydrogen plasma

Abstract

A graphite sample is negatively biased in a hydrogen plasma. ${\text{H}}^{-}$ ions created on the surface are accelerated by the sheath toward a mass spectrometer where they are detected according to their energy. The ion distribution function shows two contributions: a main peak followed by an energetic tail. It was previously proven backscattering of positive ions as negative ions is responsible for the high energy tail. In this paper we demonstrate 75% of negative ion surface production is coming from sputtering of adsorbed hydrogen atoms as negative ions. The positive ion energy threshold for this mechanism is around 20 eV and its maximum around 70 eV.