Pulsed laser deposition growth of 3D ZnO nanowall network in nest-like structures by two-step approach
The mechanism for the growth of 3D ZnO nanowall networks in nest-like structure by a pulsed laser deposition (PLD) technique have been investigated for dye sensitized solar cells (DSSCs) and biosensor applications. As complex oxides shift towards large volume productions and practical applications, PLD offers a good advantage over other techniques due to the scalability of the produced film/structures, good adhesion between nanostructures and substrates, and preservation of stoichiometric ratio of the target material. In this study, a two-step temperature-pressure approach has been used to grow ZnO nanostructures on Si(100) using PLD. Optimizing this technique, we have structured a 3D ZnO nanowall networks with nest-like feature without any catalyst. Investigating the effect of substrate temperature from 300 degrees C to 750 degrees C and O-2 background from 10 mTorr to 10 Torr, we have grown the nanowall structures by first depositing a thin ZnO seed layer on Si(100) at a substrate temperature of similar to 300 degrees C and a background oxygen pressure of 10 mTorr, subsequently growing the nanowalls at similar to 550 degrees C and 500 mTorr background. The relationship of the PLD parameters and the morphology of the grown nanowalls were examined by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-ray Diffraction (XRD), Atomic Force Microscope (AFM), Photoluminescence (PL) and X-ray Photoemission Spectroscopy (XPS). The grown ZnO nanowall networks are single-crystals and highly-oriented on the c-axis. The nest-like structures initially grow on the thermodynamically active sites along the grain boundaries of randomly oriented Zn-rich ZnO (01 (1) over bar0) plane, which undergoes self-nucleation on the amorphous layer of the Si (100) substrates. The growth mechanisms for the synthesis of the ZnO nanowalls network can be explained by the vapor-solid (VS) model. The PLD-grown 3D ZnO nanowall network has a very high surface-to-volume ratio and appears to be denser than the previously reported ZnO nanowall structures grown by other techniques. This makes the PLD-grown ZnO nanowall a very promising material as photoanodes in DSSCs and an excellent matrix for biomolecule binding for potential applications in biosensors. (C) 2015 Elsevier B.V. All rights reserved.