Though the synthesis of libraries of multicomponent metal oxide systems is prevalent using the combinatorial approach, the combinatorial approach has been rarely realized in studying simple metal oxides, especially applied to the atomic layer deposition (ALD) technique. In this literature, a novel combinatorial approach technique is utilized within an ALD grown simple metal oxide to synthesize a "spatially addressable combinatorial library". The two key factors in gradients were defined during the ALD process: (1) the process temperature and (2) a nonuniform flow of pulsed gases inside a cross-flow reactor. To validate the feasibility of our novel combinatorial approach, a case study of zinc oxide (ZnO), a simple metal oxide whose properties are well-known, is performed. Because of the induced gradient, the ZnO (002) crystallite size was found to gradually vary across a 100 mm wafer (∼10-20 nm) with a corresponding increase in the normalized Raman E2/A1 peak intensity ratio. The findings agree well with the visible grain size observed from scanning electron microscope. The novel combinatorial approach provides a means of systematical interpretation of the combined effect of the two gradients, especially in the analysis of the microstructure of ZnO crystals. Moreover, the combinatorial library reveals that the process temperature, rather than the crystal size, plays the most significant role in determining the electrical conductivity of ZnO.
Keywords: atomic layer deposition (ALD); combinatorial materials science; crystallinity; spatially addressable library; temperature gradient; zinc oxide (ZnO).