Synthesis, characterization and photoluminescence of well-ordered ZnO micropillars grown on ZnO buffer layers

Abstract

Using ZnO buffer layers prepared by simply thermal oxidation of ion beam sputtered Zn films, highly oriented and uniformly aligned single-crystalline ZnO micropillars arrays have been synthesized by thermal evaporation of Zn powder with free catalysts at low temperature of 430 ℃. The ZnO micropillars show sharp hexagonal umbrella-like tips with thin ZnO nanowire grown on the tips. The umbrella-like tips grow in a layer-by-layer mode along the direction of [001]. The growth mechanism has been discussed. The formation of the micropillars basically depends on the gradually decreasing Zn vapor pressure and subsequently cooling process. The photoluminescence (PL) spectrum indicates a moderately good crystal quality of the ZnO micropillars. Our results may reinforce the understanding of the formation mechanism of different ZnO nano/microstructures. This kind of complex microstructures may find potential applications in multifunctional microdevices, optoelectronic and field emission devices.One-dimensional wide band-gap nanowires have attracted much interest because of their remarkable physical properties and their potential applications in constructing nanoscale electronic and optoelectronic devices. Hence, the synthesis of semiconducting nanostructures with different controllable dimension and morphology is very important and challenging [1] . ZnO is one of promising semiconducting materials for potential applications due to its wide band gap (3.37 eV) and large exciton binding energy (60 meV). Over the past few years, a number of different nanostructure morphologies have been reported. Obtained morphologies include nanowires, tubes, rings [2] , nails [3] , screws [4] , and so on. Recently, considerable effort has also been made to fabricate well-ordered ZnO nanoarrays. An ordered one-dimensional structure of ZnO nanoarrays are highly interesting in laser emission, gas sensor, and field emission devices. Wang et al and Liu et al fabricated well-aligned ZnO nanowires using porous alumina and porous silica membranes respectively [5,6] , but the applications of nanowire arrays were limited by the difficulties in separating nanowires from the templates introduced in the synthesis. Jie et al also demonstrated that aligned ZnO nanowires could be formed on ZnO substrate [7] . Unfortunately, the prepared nanowires were rather thick and the used substrates were c-oriented ZnO film grown on expensive sapphire.

Influence of variation in the concentration of ammonium hydroxide on the size of ZnO crystal obtained by Microwave Chemical Bath Deposition

“…The significance of the ZnO films is such that various techniques have been employed to obtain it, such as RF magnetron sputtering at various temperatures [1], thermal oxidation of Zn ion beam sputtered films [2] Zn-vapor release in argon atmosphere and subsequent oxidation in air [3], vapordeposition method (PVD) [4], chemical vapor deposition (CVD) [5], etc. It has also been reported the synthesis of nanoparticles of ZnO in aqueous medium under microwave irradiation conditions, deposited on different substrates from zinc salts and various solvents [6].…”