AVS 50th International Symposium
    Surface Science Friday Sessions
       Session SS2-FrM

Paper SS2-FrM8
Low Temperature Oxidation of Nitrided Surfaces

Friday, November 7, 2003, 10:40 am, Room 328

Session: Oxide Surfaces and Interfaces
Presenter: J. Torres, Johns Hopkins University
Authors: J. Torres, Johns Hopkins University
C.C. Perry, Johns Hopkins University
S.J. Bransfield, Johns Hopkins University
D.H. Fairbrother, Johns Hopkins University
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The oxidation of transition metal nitride coatings is an important process because the resultant oxidized interface plays a crucial role in determining the interfacial properties of these materials as well as their durability in extreme environments. The oxidation of iron nitrides, in particular, has received little attention despite its importance as a magnetic coating in the recording industry. In the present study, X-ray Photoelectron Spectroscopy (XPS), Reflection Absorption Infrared Spectroscopy (RAIRS) and Mass Spectrometry (MS) were used to probe the low temperature (< 150 K) oxidation of nitrided iron surfaces exposed to oxygen and water. By carrying out the reactions at these low reaction temperatures, new pathways and intermediates have been identified. During the exposure of nitrided iron surfaces to oxygen, iron oxynitride (Fe@sub x@N@sub y@O@sub z@), nitrosonium ions (NO@super +@) as well as nitrite(nitrito) and iron oxide(hydroxide) species were observed. Upon prolonged oxygen exposures, nitrate species were formed in the oxidized overlayer indicative of an O-insertion mechanism into the iron nitride lattice, a process that has not been observed in previous studies of nitride oxidation. In contrast to oxygen, the reactivity of nitrided iron surfaces towards water was limited to the production of adsorbed N-O species and iron oxide(hydroxide). No molecular nitrogen was produced during reactions with oxygen or water in contrast to oxidation studies on other transition metal nitrides. Upon annealing the oxidized overlayer from 150 K to 600 K, nitrogen desorbs exclusively as nitric oxide (NO) between 250-400 K, leaving a surface film of iron oxide on top of the iron nitride.