To our knowledge, only two methods have been reported on the growth of seedless ZnO nanostructures on graphene via low-temperature liquid phase method. The term ‘seedless’ refers to the omission of pre-deposition of the ZnO seed layer by other processes and metal catalysts. Kim et al. reported the growth of ZnO nanorods on graphene without any seed layer by hydrothermal method, but the obtained results show low density of nanostructures [15]. Xu et al. reported the seedless growth of ZnO nanotubes

and nanorods on graphene by electrochemical deposition [28, 29]. They reported the growth of highly dense ZnO nanostructures by using solely zinc nitrate as the electrolyte with the JQ-EZ-05 datasheet introduction of oxidation process of graphene prior to actual growth. They also find more reported that the diameter, length, and morphology of the nanostructures showed significant dependencies on the growth parameters such as current density, precursor concentration, and growth time. Several other reports also indicated that current density plays an important role in inducing the growth of ZnO nanostructures on the seedless substrate [30, 31]. Recently, Aziz et al. reported the electrodeposition of highly dense ZnO nanorods on single-layer (SL) graphene [30]. Furthermore, the distance between the electrodes and the molarity of electrolyte are also able to give significant effects

on the properties of the resulting nanostructures [32]. Generally, a change in distance between the two electrodes can change the rate of the electrolysis reaction due to the change in the level of current density. The shorter the distance between the electrodes, the higher the electric field and thus the higher current density will be applied [32]. In this paper, we report Unoprostone the seedless growth of highly dense ZnO flower-shaped structures on multilayer (ML) graphene by a single-step cathodic electrochemical deposition method. Methods Figure 1a shows the schematic of chemical vapor deposition (CVD)-grown ML graphene on a SiO2/Si substrate (Graphene Laboratories Inc., Calverton, NY, USA). The Nomarski optical image of ML graphene in Figure 1b

shows the visibility of graphene sheets on the SiO2/Si substrate with different numbers of layers [33] which is consistent with the measured Raman spectra shown in Figure 1c. Ferrari et al. reported that the two-dimensional (2D) peaks which occur at approximately 2,700 cm−1 for bulk graphite have much broader and upshifted 2D band which can be correlated to few-layer graphene [34]. Figure 1 CVD-grown ML graphene and electrochemical deposition. (a) Schematic of ML graphene substrate, (b) Nomarski image of ML graphene, (c) Raman spectra for as-received ML graphene (the measured regions were identified in the circles), (d) schematic of electrochemical deposition setup, and (e) time chart for electrochemical growth process.