DOI: 10.1021/cg900551f
ZnO Nanowires Grown by Chemical Bath Deposition in a Continuous Flow Microreactor
2009, Vol. 9 4538–4545
Kevin M. McPeak and Jason B. Baxter* Department of Chemical and Biological Engineering, Drexel University, Philadelphia, Pennsylvania 19104 Received May 22, 2009; Revised Manuscript Received July 23, 2009
ABSTRACT: 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, singlecrystal 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 are more spatially uniform. Spatially resolved characterization of a single substrate reveals that, along the direction of flow, nanowire lengths decreased, morphology changed from pyramidal tops to flat tops, growth mechanism transitioned from two-dimensional nuclei to spiral growth, and band gap blue-shifted because of compressive strain. The continuous flow microreactor, demonstrated here for ZnO, can also be used to deposit other oxide and chalcogenide nanowires and thin films.
Introduction Chemical bath deposition (CBD) has been widely used in the laboratory to deposit oxide and chalcogenide thin films and nanowire arrays. CBD also is used in industry for deposition of CdS buffer layers for thin film photovoltaics.1 In this method, material is deposited onto a substrate from a supersaturated solution of common aqueous precursors such as metal salts, complexing agents, and pH buffers. Advantages of CBD over high-temperature vapor-phase deposition techniques include its low cost, operation at low temperature (
