  The p-type surface conductivity of H-terminated diamond (HD) has opened new
path ways to develop diamond based electronic devices, photo-catalysts,
chemical and bio-sensors. Herein, we report on the room temperature H2S
detection behaviour of pristine HD and the surface modified HD films with
partial O-termination (OHD) through ozonation. The response of the pristine HD
and partial OHD devices that are ozonated for 30, 60 and 90 s, is found to be ~
55, 1420, 810 and 95 % respectively, for exposing 900 ppb of H2S under ambient
atmosphere at room temperature. Here, the optimally partial OHD sensor displays
an enhanced sensitivity by about an order of magnitude due to the catalytic
activity of the sparsely populated O-functional groups on HD surface. Moreover,
the gas sensor response is found to be higher in wet background atmospheres
such as N2 and synthetic air as compared to their respective dry atmospheres.
Also, the response curve of these sensors exhibits a peculiar decrease in
resistance immediately after exposure to H2S under wet background atmosphere
while such oxidative behaviour is absent under dry atmospheres. Based on these
observations, the plausible sensing mechanism of these H-diamond based sensors
is proposed with the concept of humidity induced H2S hydrolyzation.
