Abstract
Hierarchical Si/ZnO trunk-branch nanostructures (NSs) have been synthesized by hot wire assisted chemical vapor deposition method for trunk Si nanowires (NWs) on indium tin oxide (ITO) substrate and followed by the vapor transport condensation (VTC) method for zinc oxide (ZnO) nanorods (NRs) which was laterally grown from each Si nanowires (NWs). A spin coating method has been used for zinc oxide (ZnO) seeding. This method is better compared with other group where they used sputtering method for the same process. The sputtering method only results in the growth of ZnO NRs on top of the Si trunk. Our method shows improvement by having the growth evenly distributed on the lateral sides and caps of the Si trunks, resulting in pine-leave-like NSs. Field emission scanning electron microscope image shows the hierarchical nanostructures resembling the shape of the leaves of pine trees. Single crystalline structure for the ZnO branch grown laterally from the crystalline Si trunk has been identified by using a lattice-resolved transmission electron microscope. A preliminary photoelectrochemical (PEC) cell testing has been setup to characterize the photocurrent of sole array of ZnO NR growth by both hydrothermal-grown (HTG) method and VTC method on ITO substrates. VTC-grown ZnO NRs showed greater photocurrent effect due to its better structural properties. The measured photocurrent was also compared with the array of hierarchical Si/ZnO trunk-branch NSs. The cell with the array of Si/ZnO trunk-branch NSs revealed four-fold magnitude enhancement in photocurrent density compared with the sole array of ZnO NRs obtain from VTC processes.
Highlights
Homo- and hetero-hierarchical nanostructures (NSs) consist of two or more materials in the family of nanostructures have become one of the most intensively studied topics in the field of nanotechnology
Our results are comparable to the photocurrent density of the vapor transport condensation (VTC)-grown zinc oxide (ZnO) NWs (0.01 to 0.07 mA/cm2) [19] and HTG prepared-nitrogen-doped ZnO NRs [20] reported by other groups
The reason of the higher photocurrent effect for VTC-grown ZnO NRs could be due to the high temperature growth process, resulted in the less structure defects in the ZnO NRs
Summary
Homo- and hetero-hierarchical nanostructures (NSs) consist of two or more materials in the family of nanostructures have become one of the most intensively studied topics in the field of nanotechnology. The level of study based on hierarchical NSs is the combination/integration of more than one type of fundamental building blocks as mentioned above which may consist of more than one material. Hierarchical core-shell or trunk-branch NSs are expected to give better performance to the photocurrent. Si as a group IV semiconductor material, is well-established due to its compatibility with CMOS process. Hierarchical NS for a Si/ZnO trunk-branch array was fabricated and its initial photoactivity namely photocurrent was tested under one sun light irradiation
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