Effects of Polyethylenimine and Its Molecular Weight on the Chemical Bath Deposition of ZnO Nanowires

Abstract

The addition of polyethylenimine (PEI) in the standard chemical bath deposition (CBD) of ZnO nanowires has received an increasing interest for monitoring their aspect ratio, but the physicochemical processes at work are still under debate. To address this issue, the effects of PEI are disentangled from the effects of ammonia and investigated over a broad range of molecular weight (i.e., chain length) and concentration, varying from 1300 to 750 000 and from 1.5 to 10 mM, respectively. It is shown that the addition of PEI strongly favors the elongation of ZnO nanowires by suppressing the homogeneous growth at the benefit of the heterogeneous growth as well as by changing the supersaturation level through a pH modification. PEI is further found to inhibit the development of the sidewalls of ZnO nanowires by adsorbing on their nonpolar m -planes, as supported by Raman scattering analysis. The inhibition proceeds even in the low pH range, which somehow rules out the present involvement of electrostatic interactions as the dominant mechanism for the adsorption. Furthermore, it is revealed that PEI drastically affects the nucleation process of ZnO nanowires on the polycrystalline ZnO seed layer by presumably adsorbing on the nanoparticles oriented with the m -planes parallel to the surface, reducing in turn their nucleation rate as well as inducing a significant vertical misalignment. These findings, specifically showing the effects of the PEI molecular weight and concentration, cast light onto its multiple roles in the CBD of ZnO nanowires.

Synthesis of Vertically Aligned ZnO Nanorods Using Sol-gel Seeding and Colloidal Lithography Patterning

“…The ZnO NP sol-gel solution was prepared according to [ 22 ] by dissolving 8.25 g of zinc acetate (Zn(CH 3 COO) 2 ·2H 2 O) and 2.26 ml of monoethanolamine (ethanolamine) in 100 ml of pure ethanol with final concentrations of 375 mM. The solution was stirred on a hotplate at 60 °C for 10 h and then at room temperature overnight.…”

“…A sol-gel technique, described in [ 22 ], can be used to prepare a highly uniform, dense and thin seed layer of polycrystalline ZnO NPs on virtually any substrate, including Si or glass. In contrast to the spin-coating of a ZnO NP dispersion on a substrate, which usually leads to non-continuous dispersed islands of NP clusters [ 23 ], the sol-gel method results in a thin (tens of nm) continuous and highly uniform layer of ZnO NPs.…”

Chemical Bath Deposition of ZnO Nanowires Using Copper Nitrate as an Additive for Compensating Doping

“…5 Many efforts have been devoted to controlling the morphology of ZnO NWs by optimizing the structural properties of polycrystalline ZnO and Au seed layers and by tailoring the CBD conditions. 6 In addition to the zinc salt and hexamethylenetetramine (HMTA) typically used as a source of Zn(II) species and HOions, 7 respectively, chemical additives including polyethylenimine, 8 ethylenediamine, 9 chlorine and citrate ions, 10,11 have also been used to control the aspect ratio of ZnO NWs.…”

Synthesis and Characterization of ZnO/Graphene Nanostructures for Electronics and Photocatalysis

“…To improve the uniformity and the smoothness of the seed layers, a sol-gel solution of 8.25 g of zinc acetate and 2.26 ml of monoethanolamine 13 (ethanolamine), with an equimolar final concentration of 375 mM, in 100 ml of pure ethanol was prepared [75,76]. The solution was stirred at 60 ˚C for 10 h and then at room temperature overnight.…”