Arrays of hemispherical islands of cesium chloride are formed on an oxidized silicon wafer when a deposited thin film of CsCl is subsequently exposed to water vapor. High packing densities, P, and a wide, preselectable range of mean diameter, , can be obtained. Use of such arrays for nanoscale lithography is demonstrated. Silicon pillars and cones have been fabricated with CsCl used as resist in a fluorocarbon reactive ion etching scheme. Cones of tip angle 28 degrees and P = 0.18 and = 85 +/- 20 nm were made. The wall angle as a function of etching parameters was determined. CsCl arrays were used in a negative resist strategy, by coating the substrate and the hemispheres in aluminum and then lifting off the CsCl (with their Al coating). Wells were made in the exposed SiO2 on Si with = 920 +/-150 nm with a packing density of P = 35. Applications to field emission systems are noted.