The Crystallization of Amorphous Aluminum Oxide Thin Films Grown on <scp><scp>NiAl</scp></scp>(100)

Qin, Hailang; Sutter, Peter; Zhou, Guangwen

doi:10.1111/jace.13036

Cited by 29 publications

(21 citation statements)

References 26 publications

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“…LEED was used to verify the formation and structure of the oxide films formed from the in situ oxidation. The LEED patterns of the oxide films indicate a well-ordered (2 × 1, 1 × 2) structure (10,11), which is in accordance with the formation of θ-Al 2 O 3 films adopting the Bain epitaxy relationship between the fcc structure of the oxygen-sublattice and bcc structure of the NiAl substrate [i.e., (001) (7,(24)(25)(26).…”

Section: Methodssupporting

confidence: 64%

“…Low-energy electron microscopy (LEEM), capable of imaging surfaces in video rate during gas exposure and at elevated temperatures, has been used to visualize the initial oxidation of NiAl(110), revealing the formation of aluminum oxide stripes that can elongate from one substrate terrace to the next by overgrowing surface steps (1)(2)(3). A similar stripe morphology of aluminum oxide has also been observed in NiAl(100) oxidation, although a detailed explanation of the mechanisms of the oxide growth is lacking (4)(5)(6)(7)(8)(9)(10)(11). Here, we use in situ LEEM observations of the initial-stage oxidation of NiAl(100) at elevated temperatures to quantitatively relate the Al 2 O 3 growth to the mass transfer process on the NiAl(100) surface.…”

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confidence: 99%

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Oxidation-driven surface dynamics on NiAl(100)

Qin

Chen

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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Atomic steps, a defect common to all crystal surfaces, can play an important role in many physical and chemical processes. However, attempts to predict surface dynamics under nonequilibrium conditions are usually frustrated by poor knowledge of the atomic processes of surface motion arising from mass transport from/to surface steps. Using low-energy electron microscopy that spatially and temporally resolves oxide film growth during the oxidation of NiAl(100) we demonstrate that surface steps are impermeable to oxide film growth. The advancement of the oxide occurs exclusively on the same terrace and requires the coordinated migration of surface steps. The resulting piling up of surface steps ahead of the oxide growth front progressively impedes the oxide growth. This process is reversed during oxide decomposition. The migration of the substrate steps is found to be a surface-step version of the well-known Hele-Shaw problem, governed by detachment (attachment) of Al atoms at step edges induced by the oxide growth (decomposition). By comparing with the oxidation of NiAl(110) that exhibits unimpeded oxide film growth over substrate steps we suggest that whenever steps are the source of atoms used for oxide growth they limit the oxidation process; when atoms are supplied from the bulk, the oxidation rate is not limited by the motion of surface steps.oxidation | NiAl | surface steps S urface growth processes are often treated with a simplifying assumption that the substrate is immobile. The rationale behind this general belief is that the role of the rigid substrate is to serve as a structural template, guiding the arrangement of impinging atoms. However, many surface growth processes involve reaction with the substrate (i.e., require sources or sinks of substrate atoms). In such cases, the role of the metallic substrate goes far beyond that of a passive support because of its active participation in the growth process. Such surface growth processes are typified by the oxidation of metals, during which the interaction between oxygen and a metallic substrate results in oxide growth by consuming the substrate atoms. Although extensive interest in understanding surface oxidation has existed for decades owing to its critical role in many technological processes including high-temperature corrosion, heterogeneous catalysis, and thin film processing, many issues are still unresolved, particularly those concerning the early stages of oxidation. A detailed understanding of the initial oxidation processes of surfaces has always been complicated by overwhelming inhomogeneities owing to high density of defects. Atomic steps are present on virtually any crystalline material in any environment and serve as natural sources and sinks of substrate atoms owing to the reduced coordination of atoms at step sites. In this work we address oxidation-induced surface dynamics as a result of mass transfer from and to steps. This is a critical issue because it influences both the mechanism and kinetics of the surface physical and chemical pro...

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Section: Methodssupporting

confidence: 64%

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confidence: 99%

Oxidation-driven surface dynamics on NiAl(100)

Qin

Chen

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

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“…The larger thickness of the oxide film may facilitate the formation of γ-Al 2 O 3 as shown here, rather than the -Al 2 O 3 phase by UHV annealing of ultrathin aluminum oxide films 10,15,16 . In general, the magnitude of the binding energy shift is known to scale with the number of heterogeneous chemical bonds and a larger binding energy shift can be attributed to a larger coordination number.…”

Section: Oxidation By Molecular Oxygenmentioning

confidence: 81%

“…The thin aluminum oxide film grown by selective oxidation of Al in the NiAl alloy is widely used as one of the most important supports for dispersed metal catalysts. [1][2][3][4][5] Due to these important industrial applications and also the fundamental importance in understanding the degradation mechanism of intermetallic alloys, the initial-stage oxidation of single-crystal NiAl(100) has been extensively studied to address the atomistic mechanism of the formation of ultrathin aluminum oxide films using a wide range of surface science tools including low-energy electron diffraction (LEED) [6][7][8][9][10][11] , X-ray photoelectron spectroscopy (XPS) [11][12][13] , electron energy loss spectroscopy 6,7 , scanning tunneling microscopy (STM) [8][9][10][11][14][15][16] , and lowenergy electron microscopy (LEEM) 10,16 . These surface science studies of the oxidation of NiAl are performed mostly under ultrahigh vacuum (UHV) conditions with carefully dosing small amounts of oxygen gas.…”

Section: Introductionmentioning

confidence: 99%

Comparative Study of the Oxidation of NiAl(100) by Molecular Oxygen and Water Vapor Using Ambient-Pressure X-ray Photoelectron Spectroscopy

et al. 2016

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The oxidation behavior of NiAl(100) by molecular oxygen and water vapor under a near-ambient pressure of 0.2 Torr is monitored using ambient-pressure X-ray photoelectron spectroscopy. O exposure leads to the selective oxidation of Al at temperatures ranging from 40 to 500 °C. By contrast, HO exposure results in the selective oxidation of Al at 40 and 200 °C, and increasing the oxidation temperature above 300 °C leads to simultaneous formation of both Al and Ni oxides. These results demonstrate that the O oxidation forms a nearly stoichiometric AlO structure that provides improved protection to the metallic substrate by barring the outward diffusion of metals. By contrast, the HO oxidation results in the formation of a defective oxide layer that allows outward diffusion of Ni at elevated temperatures for simultaneous NiO formation.

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“…Al 2 O 3 is a popular support for catalysts; a thin Al 2 O 3 /NiAl(100) lm has been studied and used as a model system. 15,[32][33][34][35][36][37][38][39][40][41] We have performed simulations with alumina slabs of 1-5 atomic layers atop a NiAl(100) slab of 11 or 12 atomic layers. The alumina slabs have the structure of q-Al 2 O 3 and a surface termination of the (001) facet to match previous experimental results.…”

Section: Introductionmentioning

confidence: 99%