  We perform a computational study, based on the molecular dynamics method, of
the shape of Miram curves obtained from microscale planar diodes. We discuss
the smooth transition from the source-limited to space-charge-limited regime
due to the finite size of the emitter, i.e. the "knee" in the Miram curve. In
our model we find that the smoothing occurs mostly due to the increased
emission at the external edges of the emitting area, and that the knee becomes
softer when the size of the emitting area decreases. We relate this to the
recent work which has described how a heterogeneous work function similarly
affects the Miram curve.
