Seed/catalyst-free vertical growth of high-density electrodeposited zinc oxide nanostructures on a single-layer graphene

Abstract

We report the seed/catalyst-free vertical growth of high-density electrodeposited ZnO nanostructures on a single-layer graphene. The absence of hexamethylenetetramine (HMTA) and heat has resulted in the formation of nanoflake-like ZnO structure. The results show that HMTA and heat are needed to promote the formation of hexagonal ZnO nanostructures. The applied current density plays important role in inducing the growth of ZnO on graphene as well as in controlling the shape, size, and density of ZnO nanostructures. High density of vertically aligned ZnO nanorods comparable to other methods was obtained. The quality of the ZnO nanostructures also depended strongly on the applied current density. The growth mechanism was proposed. According to the growth timing chart, the growth seems to involve two stages which are the formation of ZnO nucleation and the enhancement of the vertical growth of nanorods. ZnO/graphene hybrid structure provides several potential applications in electronics and optoelectronics such as photovoltaic devices, sensing devices, optical devices, and photodetectors.

Effect of Annealing Temperature on ECD Grown Hexagonal-Plane Zinc Oxide

“…The overall reaction for nucleation was dependent on the deposition process to the cathode surface. Hence, considering the primary growth reaction of ZnO via ECD with Zn(NO 3 ) 2 ($\mathrm{Zn}{\left({\mathrm{NO}}_3\right)}_{2}6{\mathrm{H}}_2\mathrm{normalO}$) and KCl as reagents, they can be broken down in the chemical reactions listed below [45,46,47,48]:$\mathrm{Zn}{({\mathrm{NO}}_3)}_2+2\mathrm{KCl}\leftrightharpoons {\mathrm{ZnCl}}_2+2{\mathrm{KNO}}_3$…”

Shape controlled growth of ZnO nanorods and fabrication of ZnO/CuO heterojunctions by chemical bath deposition using zinc nitrate hexahydrate and copper (III) nitrate trihydrate

“…Up to now, we have reported the shape controllability of vertically aligned ZnO NRs prepared by the CBD techniques using zinc chloride (ZnCl 2 ) and zinc acetate dihydrate [Zn(CH 3 COO) 2 · 2H 2 O] as source materials and their photoluminescence (PL) properties [29]. We have also reported the successful growth of vertically aligned ZnO NRs on graphene/glass substrates by ED [30]. It was also confirmed that the optical properties and diameters of the NRs can be effectively controlled by the current density during the deposition process [31].…”

High electron mobility and low carrier concentration of hydrothermally grown ZnO thin films on seeded a-plane sapphire at low temperature

“…Li et al reported on the synthesis of ZnO nanoparticles on Si substrates with and without an Au catalyst [16]. Recently, we report the growth of ZnO nanostructures on seed/ catalyst-free substrates by introducing graphene as the template layer using both electrochemical and hydrothermal processes [14,23,26]. Up to date, there is no report on the formation of a ZnO continuous film structure on a ZnO-seeded substrate using liquid-phase methods.…”

“…Liquid-phase techniques such as hydrothermal and electrochemical processes have been widely used to grow ZnO structures on ZnO-seeded substrates [7,11,17,[19][20][21], catalyzed substrates [22], or seed/catalyst-free substrates [14,19,21,23]. Generally, the grown ZnO structures on the ZnO-seeded substrates are mostly in the form of onedimensional (1D) nanostructures [7,9,20,21,24,25] due to the nature of chemical reaction of liquid-phase techniques and also due to the small grains and rough surfaces of ZnO seed layers prepared by the sputtering method [7,20,21] or other deposition techniques [9,24,25].…”