Growth behavior and field emission property of ZnO nanowire arrays on Au and Ag films

Abstract

We propose a facile method to control the growth and areal density of zinc-oxide (ZnO) nanowire arrays using gold or silver films deposited on aluminum-doped ZnO (AZO) layers coated on glass substrates. Nanowires exceeding 5 μm in length grew on both the glass/AZO-layer and on the glass/AZO-layer/Au-film where the areal array density was controlled primarily by changing the annealing temperature. In contrast, the nanowire arrays grew only on the AZO surface but not on the Ag film owing to the formation of an Ag-oxide layer. We fabricated field emitter devices with density controlled ZnO nanowire arrays and low turn-on electric field of ∼6 V/μm and a field enhancement factor of up to 1188 were obtained with density controlled ZnO nanowire arrays

Effect of Ti and Au buffer layers on controlling the density and wettability of well-aligned ZnO nanorod arrays grown on different substrates

“…It should be noted that the length of NRs slightly decreases with an increase of Au lm thickness from 12.0 to 16.0 nm attributed to an increase in lattice mismatch with the substrate, which veries the strong inuence of AZO surface morphology 64,65. The obtained results (TablesS1 and S2†) are in good agreement with the reports,[66][67][68][69][70] where ZnO NRAs were grown on AZO/Au. The length of NRs increases up to a thickness of 8.0 nm for Au and 0.5 nm for Ti in the case of AZO and AZO/ZnO, aer which the length decreases due to increase in buffer layer thickness (∼750 nm of AZO), which is a limiting factor of AZO and AZO/ ZnO (Fig.4).…”

“…It is also seen that the tips of several NRs touched and/or crossed each other when the density (samples: Au (12.0 nm)/ZnO/FTO, Au (16.0 nm)/ZnO/ITO) is much lower, which could be due to the piezoelectric properties of ZnO NRs and/or the slightly tilted growth at the initial stage, which lead to an increase in the diameter of the NRs. 70 In the EDX spectrum (inset Fig. 2 ), only Zn and O atoms are detected.…”

“…When the seed layers were coated with Au and Ti buffer layers the density of ZnO NRAs decreased with an increase of Ti and Au thickness, which might inhibit the growth of ZnO NRs. 69,70 According to ref. 68, the lateral growth is not as effectively suppressed at lower nucleation density, resulting in larger diameter NRs.…”

“…40) and further increasing the contact angle requires increasing the surface roughness and/or surface free energy. 85 The ZnO NR arrays grow faster along the (002) plane due to their lower surface free energy 69,70 and the roughness is associated with the ZnO NRA density. The variation of the water contact angle for a smooth surface can be described by Young's model as 86 cos θ y = ( γ sv − γ sl )/ γ lv where γ lv , γ sl and γ sv are the surface tension of liquid–vapour, solid–liquid, and solid–vapour, respectively.…”

“…An effective growth approach and a facile control of distribution, alignment and density of ZnO NRAs are prerequisites for their applications. 21 Over the past few years, various methods have been used to synthesize one dimensional (1D) ZnO nanostructures such as thermal decomposition of precursors, 52 different chemical vapor deposition processes, 53 pulsed laser deposition, 54 molecular beam epitaxy, 49 vapor phase transport technique, 55 magnetron sputtering, 56 oxidation of zinc metal 57 and metal–organic vapor phase. 58 These methods are expensive, require moderate to high temperature, stringent experimental conditions and sometimes dangerous chemicals are also used to grow NRAs on a commercial scale.…”