Before submitting a sample, including a first material layered upon a substrate, to an ion milling process, whereby a second material is sputtered onto the surface of the first material and the sample is then submitted to an etching process, an irregularity is formed on the surface of the first material. The overall process results in the formation of cones, or micro-tip structures, which may then be layered with a layer of low work function material, such as amorphous diamond. The irregularity in the surface of the first material may be formed by polishing, sandblasting, photolithography, or mechanical means such as scratching.