Transport Limited Growth of Zinc Oxide Nanowires

Abstract

Vertical arrays of crystalline zinc oxide (ZnO) nanowires grown on various substrates find applications in dyesensitized and hybrid organic/inorganic bulk-heterojunction solar cells. The ability to grow dense nanowires at high rates and the fundamental understanding of the growth process are important for these applications. Herein, we show that heterogeneous growth of ZnO nanowires on substrates seeded with ZnO nanoparticles in an aqueous solution of methenamine and zinc nitrate is mass transport limited. Mass transport limited growth leads to an inverse relationship between the nanowire dimensions (height and diameter) and the nanowire number density. This mass transport limitation also leads to nonuniform growth near the boundaries between seeded and unseeded regions. Stirring the reaction solution increases the nanowire growth rate. Experimental results were interpreted within the framework of two simple but nontrivial models of the solution phase species transport and the nanowire growth. Additionally, it was determined that the anisotropic growth is due to the intrinsic growth kinetics of the (101 j 0) and (0001) surfaces of ZnO in zinc nitrate and methenamine and not due to the growth process being mass transport limited as previously suggested.

One-dimensional ZnO nanostructures: Solution growth and functional properties

“…The wavelength of the UV light, however, is normally hundreds of nanometers, and therefore the feature size of the pattern is limited to the micrometer range, which gives rise to very dense nanowire arrays growing out of one spot on seeded substrates [77,99]. On a patterned substrate, the growth rate of the nanowires was shown to be inversely proportional to the nanowire density [267,268], simply because the growth nutrient was shared between the competing nanowires. Also, the as-grown nanowires were not straight or uniformly oriented on seeded substrate [77], even though well-controlled ZnO nanowire arrays were grown on GaN substrates using photolithography with one or two nanowires growing out of one spot [269].…”

Highly ordered three‐dimensional ZnO nanorods for novel photonic devices

“…In the inner part of the array, however, the NRs are rather prismatic. The phenomenon can be ascribed to the transport limited growth as described by Boercker et al in [11]. The measured geometrical parameters are summarized in Table 1.…”

Fabrication of planar and curved polyimide membranes with a pattern transfer method using ZnO nanowire arrays as templates

“…These images show that the number density of the nanowires can be adjusted by changing the concentration of the ZnO seed solution. Boercker et al suggested two different growth models that can be identified by comparing the height (h) and diameter (R w ) of the ZnO nanowires as a function of their density [20]. The dimensionless Thiele modulus, Φ, which describes the relationship between the diffusion of the Zn precursor and the reaction occurring at the surface of the nanowires, is given by the following equation:…”