Abstract

The effects of annealing temperature on the structural, surface morphological and nanomechanical properties of Cu-doped (Cu-10 at %) NiO thin films grown on glass substrates by radio-frequency magnetron sputtering are investigated in this study. The X-ray diffraction (XRD) results indicated that the as-deposited Cu-doped NiO (CNO) thin films predominantly consisted of highly defective (200)-oriented grains, as revealed by the broadened diffraction peaks. Progressively increasing the annealing temperature from 300 to 500 °C appeared to drive the films into a more equiaxed polycrystalline structure with enhanced film crystallinity, as manifested by the increased intensities and narrower peak widths of (111), (200) and even (220) diffraction peaks. The changes in the film microstructure appeared to result in significant effects on the surface energy, in particular the wettability of the films as revealed by the X-ray photoelectron spectroscopy and the contact angle of the water droplets on the film surface. The nanoindentation tests further revealed that both the hardness and Young’s modulus of the CNO thin films increased with the annealing temperature, suggesting that the strain state and/or grain boundaries may have played a prominent role in determining the film’s nanomechanical characterizations.

Highlights

  • NiO is a p-type semitransparent conducting oxide with reported bandgap ranging from 3.6 to 4.0 eV [1]

  • The Cu-doped NiO (CNO) films used in the present study were deposited on glass substrates at ambient temperature by radio frequency magnetron sputtering method

  • We conducted a comprehensive investigation on the effects of post-annealing on the microstructure, surface, and nanomechanical properties of CNO thin films deposited on glass the microstructure, surface, and nanomechanical properties of CNO thin films deposited on glass substrates by the rf-sputtering method

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Summary

Introduction

NiO is a p-type semitransparent conducting oxide with reported bandgap ranging from 3.6 to 4.0 eV [1]. It was demonstrated that by doping metallic elements, such as Li [10,11], Na [12], K [13,14] and Cu [15,16,17], the optical and electrical properties of the obtained NiO thin films could be enhanced/improved substantially. In addition to improving the optoelectronic properties of NiO-based thin films, the mechanical properties are of critical importance when designing and fabricating the practical devices. Understanding the correlations between the mechanical properties and microstructure of NiO-based films has been of great interest.

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