SrZnO nanostructures grown on templated &amp;lt;0001&amp;gt; Al2O3 substrates by pulsed laser deposition

Joselito P Labis,Hamad A Albrithen,Hussein Elsayed Elafifi,Anwar Q Alanazi,Osama M Abaza,Ahmed Mohamed El-Toni,Mahmoud Hezam

doi:10.1063/1.4996812

Abstract

The parameters of pulsed laser deposition (PLD) have been optimized to design different nanostructures of Strontium-alloyed zinc oxide (SrZnO). In this work, SrZnO nanostructures are grown on &lt;0001&gt;Al2O3 substrates via two-step templating/seeding approach. In the temperature range between 300 - 750 oC and O2 background pressures between 0.01 and 10 Torr, the growth conditions have been tailored to grow unique pointed leaf-like- and pitted olive-like nanostructures. Prior to the growth of the nanostructures, a thin SrZnO layer that serves as seed layer/template is first deposited on the Al2O3 substrates at ∼300oC and background oxygen pressure of 10 mTorr. The optical properties of the nanostructures were examined by UV/Vis spectroscopy and photoluminescence (PL), while the structures/morphologies were examined by SEM, TEM, and XRD. The alloyed SrZnO nanostructures, grown by ablating ZnO targets with 5, 10, 25% SrO contents, have in common a single-crystal hexagonal nanostructure with (0002) preferential orientation and have shown remarkable changes in the morphological and optical properties of the materials. To date, this is the only reported work on optimization of laser ablation parameters to design novel SrZnO nanostructures in the 5-25% alloying range, as most related Sr-doped ZnO studies were done below 7% doping. Although the physical properties of ZnO are modified via Sr doping, the mechanism remains unclear. The PLD-grown SrZnO nanostructures were directly grown onto the Al2O3 substrates; thus making these nanomaterials very promising for potential applications in biosensors, love-wave filters, solar cells, and ultrasonic oscillators.

Highlights

ZnO is a remarkable semiconductor with a wide and direct bandgap of 3.37 eV
The formed Strontium-alloyed zinc oxide (SrZnO) nanostructures were characterized by UV/Vis spectrometry, photoluminescence (PL), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and X-ray diffraction (XRD)
The morphological features of the grown SrZnO nanostructures were characterized by HighResolution Transmission Electron Microscopy (JEOL-2100 HRTEM, Japan) operated at 200 kV, Scanning Electron Microscopy (JEOL-7600F SEM), and X-ray Diffraction (Xpert PRO PANanalytical XRD), while their electronic properties were observed by UV/Vis spectroscopy (Shimadzu UV-2550) and Photoluminescence (Horiba iHR 320 PL)

Summary

INTRODUCTION

Das et al doped ZnO with Sr (up to 3%) using solid state reaction with resulting modifications in the structure, bandgap, conductivity, and photocatalytic activity of the SrZnO nanostructures.[12] Very recently, using spray-pyrolysis technique, Raghavendra et al reported an enhancement of up to 250 % in the UV emission at RT due to improvement in surface morphology at higher concentration of Sr atoms in the ZnO wurtzite structures resulting from oxygen vacancies induced by Sr doping.[21] In all these reported growths of SrZnO, there seem to be a consensus that the applicability of Sr-doped ZnO is dependent on the kind and shapes of the formed nanostructures and on the synthesis method used. The formed SrZnO nanostructures were characterized by UV/Vis spectrometry, photoluminescence (PL), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and X-ray diffraction (XRD)

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

SUMMARY AND CONCLUSIONS