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We report on a continuous flow microreactor for chemical bath deposition that enables rapid process characterization. The chemical bath flows through a submillimeter channel and material is deposited on a heated glass/silicon substrate that serves as one reactor wall. The microreactor operates in plug flow; bath composition changes as a function of distance down the reaction channel but the concentration profile is time-invariant. Spatially resolved characterization of the substrate enables rapid and direct correlation of material properties to growth conditions, which is not possible with a batch reactor where bath composition changes with time. We have used this microreactor to grow dense arrays of well-aligned, single-crystal ZnO nanowires. Slow flow rates result in nanowires whose lengths, growth mechanisms, and optical properties vary along the length of the substrate; fast flow rates produce nanowires that …