H2O-induced instability of Al2O3/Ni3Al(110) and Al2O3/Ni3Al(111) thin films under non-UHV conditions

X‐ray photoelectron spectroscopy study of the interaction of ultra‐thin alumina films on NiAl alloys with NaCl solutions

“…2, Table 1). This peak, O 1s A , assigned to the oxide anions of the surface layer, is observed at high binding energy in agreement with previously reported data for thermal oxide films on Ni 3 Al, [19] NiAl [9,15 -18] and Al. [20] Based on our results obtained for oxides grown at room temperature and reported separately, this can be assigned to a charging effect induced by the growth of an anhydrous oxide film.…”

Reactivities of ultrathin alumina films exposed to intermediate pressures of H2O: Substrate-mediated mechanism for growth and loss of surface order

“…This overall result is contrary to the predictions of the CM model in the thin film limit and suggests that bulk-to-interface diffusion must be considered, even for films <20 Å average thickness. Further, the LEED and Auger data reported here provide an explanation of the previously reported [8][9][10] …”

“…Surprisingly, however, alumina thin films grown on Ni 3 Al(1 1 1) [8], Ni 3 Al(1 1 0) [8,9], and NiAl(0 0 1) [10] substrates are reactive towards H 2 O at intermediate pressures (roughly, 10 À7 -10 À1 Torr) and ambient temperatures. The pressure dependence of the reaction indicates a cooperative mechanism, even though the intermediate pressures involved result in average fractional H 2 O coverages (1 [11,12].…”

“…The pressure dependence of the reaction indicates a cooperative mechanism, even though the intermediate pressures involved result in average fractional H 2 O coverages (1 [11,12]. The nature of this reaction is not completely understood, but is marked by a rearrangement of the surface structure resulting in the eventual loss of long-range order and increased surface roughness [8][9][10]. Although the roughness observed by STM imaging has led to the suggestion of hydroxide formation [10], XPS measurements with polychromatic sources [8,10] show no evidence of the partially resolved shoulder in O(1s) spectra observed for hydroxide formation on thin film [2] and sapphire(0 0 0 1) surfaces [5,13].…”

“…The nature of this reaction is not completely understood, but is marked by a rearrangement of the surface structure resulting in the eventual loss of long-range order and increased surface roughness [8][9][10]. Although the roughness observed by STM imaging has led to the suggestion of hydroxide formation [10], XPS measurements with polychromatic sources [8,10] show no evidence of the partially resolved shoulder in O(1s) spectra observed for hydroxide formation on thin film [2] and sapphire(0 0 0 1) surfaces [5,13]. The oxide/vapor interface disorders at lower H 2 O exposures than the oxide/metal interface, and the disordering process appears to originate at localized surface defect sites, gradually encompassing the entire surface [9].…”