We use a two-dimensional hybrid simulation (particle ions and Boltzmann ele
ctrons) to study sheath and ion dynamics around a small round hole in a fla
t, conducting plate following the application of a large, negative voltage
pulse, such as might be encountered during plasma-based ion implantation. R
esults for hole radii of an eighth and half the ion-matrix overlap length a
nd for depths of one, two and four times the radius are reported. For all t
hese cases, it is found that the hole represents a small perturbation to a
planar sheath since the sheath width is always greater than the hole radius
. Consequently, most of the ions that enter the hole impact on its bottom a
t near normal angles; only a small fraction impact on the sidewall obliquel
y.