Spray-Deposited Coral-Like ZnO Micro/Nano Thin Films on Glass Substrates
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https://doi.org/10.1007/s11837-020-04495-9 Ó 2020 The Minerals, Metals & Materials Society
ZINC OXIDE NANOTECHNOLOGY
Spray-Deposited Coral-Like ZnO Micro/Nano Thin Films on Glass Substrates SHADIA J. IKHMAYIES
1,2
1.—Jabal El-Hussain, Amman 11121, Jordan. 2.—e-mail: [email protected]
In this work, coral-like micro/nano zinc oxide (ZnO) thin films are synthesized onto glass substrates using the low-cost spray pyrolysis (SP) method without using a metal catalyst or surfactant. The films are prepared at substrate temperature Ts = 350 ± 3°C, using oxygen as the carrier gas. The structure, surface morphology, composition, and optical properties of the as-deposited thin films are characterized using x-ray diffraction (XRD), scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM–EDS), and UV– VIS spectroscopy, respectively. ImageJ software is used to produce the plot profiles and surface occupancy plots. The XRD diffractogram showed that the films are polycrystalline with hexagonal (wurtzite) structure. SEM observations revealed the formation of coral-like products of different shapes with a wide range of dimensions. The EDS spectrum showed that the films contain Cl in addition to Zn and O. Absorbance is used to infer the transmittance and to estimate the band gap energy, which is found to be Eg = 3.37 eV. The fourth derivative of the absorbance revealed the three free exciton peaks A, B, and C. In addition, a strong broad absorption band with several sharp lines is detected in the energy range 1.77–2.50 eV and a weaker absorption band in the energy range 2.48–2.80 eV. This non-catalyst production of coral-like ZnO micro/nano thin films on glass substrates may have potential applications in the industry of nanoelectronic and nanooptical devices, optoelectronics, sensors, nanoscale mechanics research, and solar cells.
INTRODUCTION The crystal structures of ZnO are wurtzite, zinc blende, and rock salt, but under ambient conditions, the wurtzite one is the thermodynamically stable phase. The wurtzite ZnO has the space group (C6mc) and lattice constants a =0.3296 nm and c =0.52065 nm. Hexagonal ZnO is described by a number of alternating planes of tetrahedrally coordinated O2 and Zn2+ ions, stacked alternately along the c-axis. An important characteristic of ZnO is its polar surfaces, where the most common polar surface of ZnO is the basal plane.1 Zinc oxide (ZnO) is a very important material that is used widely in various industries such as optoelectronic devices, photocatalysis, solar cells, and cosmetics.2 It is a wide-band-gap II-VI compound semiconductor, where the band gap energy of the wurtzite structure is 3.37 eV at room temperature. It has high electron mobility of 115–155 cm2 V1 s1 3,4
and high exciton binding energy of about 60 meV at room temperature, which makes it suitable for the optoelectronics industry. Nano-structured ZnO has a higher band gap and exciton binding energy due to quantum confinement, so it has received considerable attention. Due to the morphology-depend
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