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Vacancy segregation in the initial oxidation stages of the TiN(100) surface

: Zimmermann, J.; Finnis, M.W.; Ciacchi, L.C.

Fulltext urn:nbn:de:0011-n-947321 (1.6 MByte PDF)
MD5 Fingerprint: efd117b914cc85b808bc04f88193863d
Created on: 30.3.2012

The Journal of chemical physics 130 (2009), No.13, Art. 134714, 11 pp.
ISSN: 0021-9606
Journal Article, Electronic Publication
Fraunhofer IWM ()
Fraunhofer IFAM ()

The well-known corrosion resistance and biocompatibility of TiN depend on the structural and chemical properties of the stable oxide film that forms spontaneously on its surface after exposure to air. In the present work, we focus on the atomistic structure and stability of the TiN(100) surface in contact with an oxidizing atmosphere. The early oxidation stages of TiN(100) are investigated by means of first-principles molecular dynamics (FPMD). We observe selective oxidation of Ti atoms and formation of an ultrathin Ti oxide layer, while Ti vacancies are left behind at the metal/oxide interface. Within the formalism of ab initio thermodynamics we compute the segregation energies of vacancies and vacancy clusters at the metal/oxide interface, comparing the stability of the system obtained by FPMD simulations with ideally reconstructed models. We find that the localization of Ti vacancies in the thin oxide layer and at the TiN/oxide interface is thermodynamically stable and may account for the early removal of N atoms from the interface by segregation of N vacancies from the bulk reservoir. We suggest that superficial oxidation may proceed along two distinct possible pathways: a thermodynamically stable path along the potential energy minimum surface and a metastable, kinetically driven path that results from the high heat release during the dissociation of O-2.