Spectroscopic ellipsometric investigation of the clean and oxygen exposed Ni(110) surface

Abstract

Dynamical ellipsometric investigationsof the initial oxidation of the Ni(ll0) surface have been performed.Ellipsometry appears to be well suited to distinguish between chemisorbed oxygen and nickel oxide on the surface. Annealing at 740 K causes the nucleation of nickel oxide to proceed faster than at 570 K. After equal exposures however, the nucleation is slower with an oxygen pressure of 2X10W7 Torr than with a pressure of 1.3X IO-' Torr. Spectroscopic elhpsometric measurements (400-800 nm) have been performed on clean and oxygen-exposed (at saturation) Ni(ll0)surfaces. The complex dielectric function of the clean surface has been determined. To explain the results of the oxygen exposed surface a model is discussed -a surface layer with a thickness of 6 A and a mixture of 90% NiO and 10% Ni -in which changes with substrate optical properties are taken into account.

On the kinetics of oxidation of austenitic stainless steels AISI 304 and incoloy 800H

“…the ellipsometric parameters A and 4 showed a small decrease. This was of the same order of magnitude (6A = 0.2") 81) = 0.02" ), and had a similar relaxation time (t = 45 min) as reported for Ni(ll0) [23]. This decrease in A and J/ is caused by the segregation of oxygen towards the surface.…”

“…A 3 ML coverage has also been reported for Ni(ll0) [23] and Ni(lOO) [6,7]. Mitchel et al [8] reported that the oxidation is strongly influenced by the amount of carbon present at the surface prior to oxidation.…”

“…The subsequent oxidations, indicated by the change in SA -St) curves, agreed, in all cases, within experimental error. Hanekamp et al [23] reported that no difference could be found, for Ni(llO), between initial oxidations performed without oxygen or with 5 at% oxygen present prior to oxidation. They explained this behaviour by suggesting that the 5 at% oxygen present at the surface, was dissolved oxygen in the layer just below the Ni(ll0) surface.…”

“…The length of this saturation period depends on the anneal temperature of the crystal prior to oxidation. Hanekamp et al [23] have shown for a Ni(ll0) crystal that the length of this saturation period could be changed from 0 to 2 L by lowering the anneal temperature from 740 to 570 K. The nucleation stage is inversely related to the sample temperature, thus increasing temperature leads to a decrease in nucleation rate. The oxidation of stainless steels, however, shows a temperature independent part up to a 3 ML coverage.…”

Spectroscopic ellipsometric investigation of the clean and oxygen exposed Ni(110) surface

“…TDP's were also observed with nickel [8] at the same energy values as reported by Becker and Hagstrum [9]. At 740 K the TDP's were totally absent, except for a small shoulder around 200 eV.…”