Influence of Oxygen Vacancies on the Frictional Properties of Nanocrystalline Zinc Oxide Thin Films in Ambient Conditions

Huan Pu Chang, En De Chu, Yu Ting Yeh, Yueh Chun Wu, Fang Yuh Lo, Wei Hua Wang, Ming Yau Chern, Hsiang Chih Chiu

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Oxygen vacancy is the most studied point defect and has been found to significantly influence the physical properties of zinc oxide (ZnO). By using atomic force microscopy (AFM), we show that the frictional properties on the ZnO surface at the nanoscale greatly depend on the amount of oxygen vacancies present in the surface layer and the ambient humidity. The photocatalytic effect (PCE) is used to qualitatively control the amount of oxygen vacancies in the surface layer of ZnO and reversibly switch the surface wettability between hydrophobic and superhydrophilic states. Because oxygen vacancies in the ZnO surface can attract ambient water molecules, during the AFM friction measurement, water meniscus can form between the asperities at the AFM tip-ZnO contact due to the capillary condensation, leading to negative dependence of friction on the logarithm of tip sliding velocity. Such dependence is found to be a strong function of relative humidity and can be reversibly manipulated by the PCE. Our results indicate that it is possible to control the frictional properties of ZnO surface at the nanoscale using optical approaches.

Original languageEnglish
Pages (from-to)8362-8371
Number of pages10
JournalLangmuir
Volume33
Issue number34
DOIs
Publication statusPublished - 2017 Aug 29

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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