Vacancies in solids and the stability of surface morphology

McCarty, K. F.; Nobel, J. A.; Bartelt, N. C.

doi:10.1038/35088026

Cited by 107 publications

(74 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The observation of stationary substrate steps suggests that the steps are not a major source of Al atoms in the initial oxidation of NiAl (110), that is, the oxide growth involves Al atoms from another source (i.e., the NiAl bulk). Indeed, McCarty and coworkers (22,23) have shown that mass transport between the NiAl(110) surface and the bulk can be very efficient at elevated temperatures (750-1,000°C). For clean NiAl(110) in vacuum, surface Al atoms supplied from the bulk attach to steps, thus inducing step migration (22,23).…”

Section: Resultsmentioning

confidence: 99%

“…Indeed, McCarty and coworkers (22,23) have shown that mass transport between the NiAl(110) surface and the bulk can be very efficient at elevated temperatures (750-1,000°C). For clean NiAl(110) in vacuum, surface Al atoms supplied from the bulk attach to steps, thus inducing step migration (22,23). However, under oxidizing conditions it is thermodynamically more favorable for Al atoms supplied from the bulk to be incorporated in the growing oxide rather than steps.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Oxidation-driven surface dynamics on NiAl(100)

Qin

Chen

et al. 2014

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

View full text Add to dashboard Cite

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...

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Oxidation-driven surface dynamics on NiAl(100)

Qin

Chen

et al. 2014

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

View full text Add to dashboard Cite

show abstract

“…One example is the diffusion of transition metal atoms into bulk Si, which may actually be more efficient than diffusion on the surface [1]. Surface morphology changes mediated by bulk vacancy transport [2] and vacancy mediated surface diffusion [3] have also been discussed recently for metals. In this Letter, we discuss a growth mechanism in which the surface transport involves adatom diffusion below a metallic adlayer on a semiconductor surface.…”

mentioning

confidence: 99%

Adatom Kinetics On and Below the Surface: The Existence of a New Diffusion Channel

et al. 2003

View full text Add to dashboard Cite

Employing density-functional theory in combination with scanning tunneling microscopy, we demonstrate that a thin metallic film on a semiconductor surface may open an efficient and hitherto not expected diffusion channel for lateral adatom transport: adatoms may prefer diffusion within this metallic layer rather than on top of the surface. Based on this concept, we interpret recent experiments: We explain why and when In acts as a surfactant on GaN surfaces, why Ga acts as an autosurfactant, and how this mechanism can be used to optimize group-III nitride growth. DOI: 10.1103/PhysRevLett.90.056101 PACS numbers: 68.35.Fx, 68.37.Ef, 81.15.Aa Most known transport mechanisms on semiconductor surfaces have rather high activation temperatures: typically a ratio between activation and melting temperature well above 0.5 is found (T act =T melt > 0:5). Growing at lower temperature typically results in a rough surface morphology. Recently, a number of interesting transport mechanisms having low activation energies have been discussed. One example is the diffusion of transition metal atoms into bulk Si, which may actually be more efficient than diffusion on the surface [1]. Surface morphology changes mediated by bulk vacancy transport [2] and vacancy mediated surface diffusion [3] have also been discussed recently for metals. In this Letter, we discuss a growth mechanism in which the surface transport involves adatom diffusion below a metallic adlayer on a semiconductor surface. Employing state-of-the art first principles calculations and scanning tunneling microscopy, we demonstrate that adatoms may prefer to incorporate and diffuse between the adlayer and the substrate. This mechanism, which we call adlayer enhanced lateral diffusion (AELD) becomes activated already at rather low temperatures, thereby enabling the growth of materials having a high melting temperature even at modest temperatures.The materials system for which this mechanism is demonstrated are the group-III nitrides (GaN, InN, AlN, and their alloys). The members of this technologically important class of materials are strongly bonded and exhibit high melting temperatures. For example [4], GaN has a melting temperature of 2791 K and so the optimum growth temperature is expected to be higher than 1400 K. However, since GaN decomposes in vacuum when the temperature exceeds 1200 K, low pressure growth methods such as molecular beam epitaxy (MBE) can be performed only at temperatures well below the decomposition temperature. One might therefore expect that MBE growth results in a poor surface morphology and indeed, this is found for a large range of possible growth conditions. Only under extreme Ga-rich conditions, close to the onset of Ga-droplet formation, can smooth surfaces be achieved [5,6]. Recent experimental studies indicate that the presence of an In adlayer also leads to a smooth surface morphology and a better crystal quality [7][8][9][10].In order to understand why the presence of In or excess Ga leads to smoother surfaces, it is essential to k...

show abstract

“…In case the observed decay of Ga droplets is due to diffusion of Ga into the bulk of the sample or evaporation into vacuum, all of the droplets would decrease in size. [33][34][35][36] We find that droplets B-I exhibit decay while the size of droplet A remains nearly constant at all t. Moreover, the rates of changes in droplet size are not the same for all the droplets. For example, the sizes of smaller droplets F and G decrease continuously, while the sizes of larger droplets B and C change little initially and decrease at later times.…”

Section: Fig 2 Typical Bright-field Xtemmentioning

confidence: 76%

Kinetics of Ga droplet decay on thin carbon films

Kodambaka

Ngo

Pališaitis

et al. 2013

Applied Physics Letters

View full text Add to dashboard Cite

Using in situ transmission electron microscopy, we investigated the kinetics of liquid Ga droplet decay on thin amorphous carbon films during annealing at 773 K. The transmission electron microscopy images reveal that liquid Ga forms spherical droplets and undergo coarsening/decay with increasing time. We find that the droplet volumes change non-linearly with time and the volume decay rates depend on their local environment. By comparing the late-stage decay behavior of the droplets with the classical mean-field theory model for Ostwald ripening, we determine that the decay of Ga droplets occurs in the surface diffusion limited regime.

Funding Agencies|AFOSR|FA9550-10-1-0496|STINT||Swedish Foundation for International Cooperation in Research and Higher Education||Swedish Research Council||Austrian Science Fund FWF, START project|Y371|Knut and Alice Wallenberg Foundation||

show abstract

Vacancies in solids and the stability of surface morphology

Cited by 107 publications

References 18 publications

Oxidation-driven surface dynamics on NiAl(100)

Oxidation-driven surface dynamics on NiAl(100)

Adatom Kinetics On and Below the Surface: The Existence of a New Diffusion Channel

Kinetics of Ga droplet decay on thin carbon films

Contact Info

Product

Resources

About