1. An apparatus comprising: a body defining a plurality of apertures, wherein each of the plurality of apertures defines a first opening and a second opening, wherein each of the plurality of apertures is conically-shaped, and wherein the first opening is smaller than the second opening; a plurality of conductive elements, each of the plurality of conductive elements disposed within a respective one of the plurality of apertures; an ionizable material disposed within each of the plurality of apertures; and a device coupled to each of the plurality of conductive elements and to associate charge received from each of the plurality of conductive elements with one or more respective image pixels.