  This paper deals with a study of H-/D-negative ion surface production on
diamond in low pressure H2/D2 plasmas. A sample placed in the plasma is
negatively biased with respect to plasma potential. Upon positive ion impacts
on the sample, some negative ions are formed and detected according to their
mass and energy by a mass spectrometer placed in front of the sample. The
experimental methods developed to study negative ion surface production and
obtain negative ion energy and angle distribution functions are first
presented. Different diamond materials ranging from nanocrystalline to single
crystal layers, either doped with boron or intrinsic, are then investigated and
compared with graphite. The negative ion yields obtained are presented as a
function of different experimental parameters such as the exposure time, the
sample bias which determines the positive ion impact energy and the sample
surface temperature. It is concluded from these experiments that the electronic
properties of diamond materials, among them the negative electron affinity,
seem to be favourable for negative-ion surface production. However, the
negative ion yield decreases with the plasma induced defect density.
