A sample called a field emitter tip is usually prepared by electrochemical polishing of a wire which is typically less than a few tenths of a millimeter in diameter. The apex of the tip provides the substrate for imaging and analysis. Since the size of the tip apex is smaller than the size of individual crystallites in most polycrystalline materials, a tip prepared from polycrystalline wire will usually be formed from a single, perfect crystal. (Occasionally, a tip will be formed from two or more single crystallites of the polycrystalline wire separated by one or more well defined grain boundaries. [58] Tip preparation using a Focussed Ion Beam (FIB) has also been used for sample preparation. [17]

As a result of the preparation technique, the surface of the tip apex may display many different crystal planes of low and high Miller indices, smoothly joined into an approximately hemispherical contour. Thermal annealing by resistive heating or electron bombardment can be used to increase the apex radius of the tip.