[en] Diamond amplifiers demonstrably are an electron source with the potential to support high-brightness, high-average-current emission into a vacuum. We recently developed a reliable hydrogenation procedure for the diamond amplifier. The systematic study of hydrogenation resulted in the reproducible fabrication of high gain diamond amplifier. Furthermore, we measured the emission probability of diamond amplifier as a function of the external field and modelled the process with resulting changes in the vacuum level due to the Schottky effect. We demonstrated that the decrease in the secondary electrons average emission gain was a function of the pulse width and related this to the trapping of electrons by the effective NEA surface. The findings from the model agree well with our experimental measurements. As an application of the model, the energy spread of secondary electrons inside the diamond was estimated from the measured emission.