Surface stability of WN ultrathin films under O2 and H2O exposure: A first-principles study

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Department of Physics


Recently developed tungsten nitride (WN) ultrathin films are reported to be potentially good diffusion barriers in electronic and protective coatings and have exceptional mechanical strength. However, the surface interactions with the impurities in ambient conditions may play a crucial role in their stability, modifying the electronic and mechanical properties. In this paper, we investigate the molecular and dissociative adsorptions of O2 and H2O on both polar and nonpolar WN surfaces using density functional theory. The results show that the nonpolar and the W-terminated polar surfaces are highly reactive to O2. On the other hand, the N-terminated surfaces are stable on which the O2 dissociation occurs with finite energy barriers. Moreover, H2O dissociation on WN surfaces is not spontaneous irrespective of the surface direction or termination. The results, therefore, suggest that experiments growing the energetically stable W-terminated ultrathin films should employ the controlled conditions to obtain defect-free surfaces that offer excellent mechanical strength.

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Applied Surface Science