  In this work negative-ion production on the surface of a sample negatively DC
biased in a hydrogen plasma is studied. The negative ions created under the
positive ion bombardment are accelerated towards the plasma, self-extracted and
detected according to their energy and mass, by a mass spectrometer placed in
front of the sample. The use of a pulsed bias allows applying a quasi-DC bias
on insulating material during a short period of time and offers the possibility
to extend the measurement method to nonconductive samples. The pulsed-bias
tests were performed first with Highly Oriented Pyrolitic Graphite (HOPG), a
conductive material, to demonstrate the feasibility of the method. By changing
the pulsed-bias frequency it was possible to obtain HOPG material with
different hydrogen surface coverages and hence different surface states leading
to an increase of negative-ion production by up to 30-50% as compared to the
continuous bias case. To establish a protocol for insulating materials, charge
accumulation on the surface during the bias pulse and influence of the bias
duration and frequency were explored using microcrystalline diamond (MCD) thin
layers. By using a pulse short enough (10 $\mu$s) at 1 kHz frequency, it has
been possible to measure negative-ions on MCD sample at a quasi-constant
surface bias of 130 V, with only 1 V variation during the measurement.
Negative-ion surface production on MCD has been studied in pulsed mode with
surface temperature from room temperature to 800{\textdegree}C. It is shown
that pulsing the bias and increasing the temperature allows limiting defect
creation on MCD which is favorable for negative-ion production. Consequently,
at 400{\textdegree}C the yield on MCD in pulsed mode is one order of magnitude
higher than the yield on HOPG in continuous mode at room temperature.
