Steps on surfaces: experiment and theory

Jeong, Hyeong-Chai; Williams, Ellen D.

doi:10.1016/s0167-5729(98)00010-7

Cited by 682 publications

(742 citation statements)

References 296 publications

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“…This causes local chemical potential variations. The chemical potential differences lead to a mass flow and the net mass flux j can be expressed as j = −D S ∇μ, where μ is the local chemical potential and D S is the surface diffusivity of Al (14). Because the step motion can be considered as an incompressible flow, the velocity potential ϕ then satisfies the Laplace equation, ∇ 2 ϕ = 0.…”

Section: Resultsmentioning

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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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: Resultsmentioning

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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“…[1]. Formation of step/terrace structures is commonly observed on vicinal surfaces [4]. Technologically important substrates such as Si [5][6][7] and GaAs [8][9][10] have been studied, both for device applications and for the understanding of the basic surface physics such as step energetics and surface selfordering mechanisms.…”

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confidence: 99%

Self-Ordering of Nanofacets on Vicinal SiC Surfaces

2003

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Vicinal 4H and 6H-SiC 0001 surfaces have been investigated using atomic force microscopy and cross-sectional high-resolution transmission electron microscopy. We observed the characteristic selfordering of nanofacets on any surface, regardless of polytypes and vicinal angles, after gas etching at high temperature. Two facet planes are typically revealed: (0001) and high index 112n that are induced by equilibrium surface phase separation. A 112n plane may have a free energy minimum due to attractive step-step interactions. The differing ordering distances in 4H and 6H polytypes imply the existence of SiC polytypic dependence on nanofaceting. Thus, it should be possible to control SiC surface nanostructures by selecting a polytype, a vicinal angle, and an etching temperature.

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“…Many STM studies have been devoted to the mobility of surfaces. Most of these have focused on the motion of steps [1][2][3], islands [4], or adsorbates [5]. Recently it has been proposed that surface vacancies are responsible for mass transport between adatom islands on Cu(001) [6].…”

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confidence: 99%

Nothing Moves a Surface: Vacancy Mediated Surface Diffusion

et al. 2001

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We report scanning tunneling microscopy observations, which imply that all atoms in a Cu(001) surface move frequently, even at room temperature. Using a low density of embedded indium "tracer" atoms, we visualize the diffusive motion of surface atoms. Surprisingly, the indium atoms seem to make concerted, long jumps. Responsible for this motion is an ultralow density of surface vacancies, diffusing rapidly within the surface. This interpretation is supported by a detailed analysis of the displacement distribution of the indium atoms, which reveals a shape characteristic for the vacancy mediated diffusion mechanism that we propose.

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Steps on surfaces: experiment and theory

Cited by 682 publications

References 296 publications

Oxidation-driven surface dynamics on NiAl(100)

Oxidation-driven surface dynamics on NiAl(100)

Self-Ordering of Nanofacets on Vicinal SiC Surfaces

Nothing Moves a Surface: Vacancy Mediated Surface Diffusion

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