A periodic array of NaCl nanocrystals is prepared using a nanoreactor array, which consists of hemispherical nanowells of 800 nm in diameter fused side-by-side prepared by sputter deposition of Fe and Au layers over hexagonally close-packed 1-mu m polystyrene (PS) beads. The size of the nanocrystals can be controlled simply by changing the concentration of the precursor solution.