Ag cubes of uniform size (70nm) and self-assembled into two dimensional arrays are formed by physical vapor deposition. The formation of the Ag cubes depends critically on the substrate composition. While heat dissipation can control the crystallization of Ag islands on surfaces, the thermal conductivity and infrared optical property of the substrate can be tuned by a suitable substrate composition. While evaporation on native SiO₂ on a Si waver leads to the formation of flat islands, the evaporation on a thick SiO ₂/Ag/Si substrate leads to the formation of oriented Ag cubes of narrow size distribution (80-100nm).