Synthesis of Vertically Aligned ZnO Nanorods on Ni-Based Buffer Layers Using a Thermal Evaporation Process

Abstract

Uniform, vertically aligned ZnO nanorods have been grown mainly on Au-coated and ZnO-coated sapphire substrates, ZnO-and GaN-coated substrates, or self-catalyzing substrates. Conventionally, Ni-coated substrates have resulted in thick rods with diameter more than 250 nm, rods with nonuniform distribution in diameter, or rods with an alignment problem. In the best result in this paper, slender, uniform, vertically aligned, solely UV-emitting ZnO nanorods with diameter of 110 ± 25 nm and length of 30 ± 10 lm have been successfully grown at 700°C for 2 h on sapphire substrates covered with Nibased buffer layers by using metallic zinc and oxygen as reactants. Scanning electron microscopy and room-temperature photoluminescence have been used to investigate the effects of process conditions on the slenderness and vertical alignment of the ZnO rods. To develop the desired ZnO nanorods, etched sapphire substrates, a second metallic Sn buffer layer on top of a spin-coated nickel oxide layer, polyvinyl alcohol binder at 10% concentration in solution of iron nitrate, and pyrolysis and reduction reactions were involved. Defect photoemission for thick ZnO rods is attributed to insufficient oxygen supply during the growth process with fixed oxygen flow rate.

Micromechanism and Kinetic Formulation of Vertically Aligned ZnO Nanorods Grown on Catalytic Bilayers

“…The systematical dimension measurements at different durations for kinetic understanding are our major approach to probe the growth kinetic problems. This work is totally different from our previous work on the developments of aligned and well-controlled ZnO rods, but they provide the basis for our progress in kinetics [8][9][10][11].…”

“…In order to understand the growth micromechanisms, we ever used Au-containing bilayer catalysts of Au/Al, Au/Ni, and Au/In to grow randomly oriented ZnO rods on silicon wafer substrates with diameters of ∼100, 400, and 800 nm, respectively [8]. To make a further progress in order to grow well-aligned ZnO nanorods instead of micrometer sized and randomly oriented ZnO rods on the bilayer catalyst-covered substrates without using Au as a catalyst, we had investigated different unilayer or bilayer configurations made by mixed-solution coating, sputtering, polymer dispersant in coating solution, substrate etching techniques [9][10][11]. The one with the promising result is the ZnO rods grown on the Fe-covered [9] and Sn/Ni bilayer substrates [11].…”

“…To make a further progress in order to grow well-aligned ZnO nanorods instead of micrometer sized and randomly oriented ZnO rods on the bilayer catalyst-covered substrates without using Au as a catalyst, we had investigated different unilayer or bilayer configurations made by mixed-solution coating, sputtering, polymer dispersant in coating solution, substrate etching techniques [9][10][11]. The one with the promising result is the ZnO rods grown on the Fe-covered [9] and Sn/Ni bilayer substrates [11]. We have continued efforts on the growth of ZnO nanorods by using the bilayer configurations.…”

A Review on Synthesis and Optoelectronic Applications of Nanostructured ZnO

“…Pneumatic spray pyrolysis technique with precursors: ZnCl 2 and thiocarbamide has been established and leads to the formation of thinner ZnO nanorods (Dedova et al, 2007). A thermal evaporation process on a patterned Si wafer (110) which has silver (Ag) is a template for growth (Panda and Jacob, 2009), at 700°C for 2 h on Nickel based buffer layer (Sputtered layer and Spin coated) on Silicon wafer and sapphire substrate (Kuo et al, 2012). Chemical Vapor Deposition, for growth of ZnO nanorods has also been established using ZnSe particles as the seed layer (Guo et al, 2006).…”