  In this letter, we report the effects of irradiating hydrogen-terminated
diamond surfaces with protons. We study the electrical behavior of the
two-dimensional hole gas that forms on the diamond surface as a result of
hydrogen-termination. Four diamond samples, two of which were passivated with
Al2O3 and the other two unpassivated, were irradiated with 2 MeV protons at two
fluences, 0.5x10^14 and 1.0x10^14 /cm^2. The hole conductivity degraded at a
higher proton fluence, which is attributed to the reduction of the mobility
caused by enhanced hole scattering. Both passivated and unpassivated samples
exhibited a reduction in the mobility, which can be explained by charging
effects of the Al2O3 (for the passivated samples) and degradation of the
hydrogen-terminated surface (for the unpassivated samples). To our knowledge,
this is the first reported data on 2 MeV proton tolerance of
hydrogen-terminated diamond surfaces.
