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Materials 2018, 11(6), 949; https://doi.org/10.3390/ma11060949

A Study of Quantum Confinement Effects in Ultrathin NiO Films Performed by Experiment and Theory

1
Department of Materials Science, University of Patras, 26504 Patras, Greece
2
Department of Mechanical Engineering, Technological Educational Institute (T.E.I.) of Western Greece, M. Alexandrou 1, 26504 Patras, Greece
*
Author to whom correspondence should be addressed.
Received: 5 March 2018 / Revised: 18 May 2018 / Accepted: 1 June 2018 / Published: 4 June 2018
(This article belongs to the Special Issue Advanced Functional Nanomaterials and Their Applications)
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Abstract

Ultrathin NiO films in the thickness range between 1 and 27 nm have been deposited on high-quality quartz substrates by direct magnetron sputtering under a rough vacuum with a base pressure of 2 × 10−2 mbar. The sputtering target was metallic Ni; however, due to the rough vacuum a precursor material was grown in which most of Ni was already oxidized. Subsequent short annealing at temperatures of about 600 °C in a furnace in air resulted in NiO with high crystallinity quality, as atomic force microscopy revealed. The images of surface morphology showed that the NiO films were continuous and follow a normal grain growth mode. UV-Vis light absorption spectroscopy experiments have revealed a blue shift of the direct band gap of NiO. The band gap was determined either by Tauc plots (onset) or by the derivative method (highest rate of absorbance increase just after the onset). The experimental results are interpreted as evidences of quantum confinement effects. Theoretical calculations based on Hartree Fock approximation as applied for an electron-hole system, in the framework of effective mass approximation were carried out. The agreement between theory and experiment supports the quantum confinement interpretation. View Full-Text
Keywords: thin films; semiconductor oxides; grain growth; optical properties; quantum confinement; potential morphing method thin films; semiconductor oxides; grain growth; optical properties; quantum confinement; potential morphing method
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Garoufalis, C.S.; Barnasas, A.; Stamatelatos, A.; Karoutsos, V.; Grammatikopoulos, S.; Poulopoulos, P.; Baskoutas, S. A Study of Quantum Confinement Effects in Ultrathin NiO Films Performed by Experiment and Theory. Materials 2018, 11, 949.

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