Fast Decay of Adatom Islands and Mounds on Cu(111): A New Effective Channel for Interlayer Mass Transport

Giesen, Margret; Icking-Konert, G. Schulze; Ibach, H.

doi:10.1103/physrevlett.80.552

Cited by 106 publications

(63 citation statements)

References 24 publications

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“…The wiggles are therefore presumably caused by the random walk of the top layer island and the changing environment of the lower island. The acceleration of the decay of top layer islands as well as the constant TW in the late stages of the decay has been shown previously [18]. It was speculated that the increased decay rate of the top layer island may be caused by the formation of microscopic contacts between the island edges due to thermal edge fluctuations and the stochastic motion of the islands.…”

Section: Institut F üR Grenzflächenforschung Und Vakuumphysik Forschmentioning

confidence: 93%

“…1(a) would also match the experiment if a more moderate reduction of the ES barrier had been assumed. However, the rapid decay occasionally observed when the top layer islands accidentally comes very close to the boundary of the lower island [18] requires that the ES barrier vanishes more or less completely. We point out that the data cannot be described by assuming an enlarged diffusion constant on small terraces since the activation energy for diffusion is already small (about 0.05 eV [23,24]).…”

Section: Institut F üR Grenzflächenforschung Und Vakuumphysik Forschmentioning

confidence: 99%

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Interlayer Mass Transport and Quantum Confinement of Electronic States

1999

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A numerical analysis of the ripening of multilayer islands on Cu(111) shows that the EhrlichSchwoebel barrier for interlayer mass transport is independent of the terrace width w as long as w . w c 14 6 2 Å, but vanishes for w , w c . The critical width w c corresponds exactly to the terrace width below which the surface state is pushed above the Fermi level due to quantum confinement. The Ehrlich-Schwoebel barrier is therefore correlated with the occupation of surface states.[ S0031-9007(99)08912-7] PACS numbers: 68.35.Fx, 73.20.Dx The growth of atomically flat epitaxial films requires a facile mass transport across the step edges which separate terraces of different height. Diffusion across a step edge is frequently hindered by an activation barrier for interlayer mass transport (Ehrlich-Schwoebel barrier [1,2]). The existence of a significant EhrlichSchwoebel barrier (ES barrier) is well documented for the (111) surfaces of Pt, Rh, Ag,. In these and other experiments, merely an average ES barrier is typically determined. Total energy calculations based on the embedded atom model (EAM) [8][9][10] as well as recent ab initio calculations in the local density approximation [11] have shown that activation energies for mass transport across a step depend on the type of steps and involve an exchange of the adatom with a step atom. For the experimentally rather extensively studied Pt(111) surface Feibelman [11] has shown that the activation energy is practically zero (0.02 eV) for crossing the A step [displaying a (100) facet], but large (0.35 eV) for the B step [(111) facet]. This result is at variance with the large effective ES barrier observed in earlier experiments [3]. However, according to a recent study [12] the large ES barrier in earlier work was caused by preferential adsorption of CO on A steps from the residual gas. On clean Cu(111) surfaces on the other hand, a significant ES barrier was found experimentally also for the A type step [13]. EAM calculations have further revealed significant differences in the ES barrier on a straight step and at kink sites [9,10]. Whether the calculated differences are always significant for the interlayer mass transport depends on the preexponential factors which are presently not known and may (partly) compensate different activation barriers (see, e.g., [14]).Faced with the unpleasantly complex situation, both on the experimental and theoretical side, a better understanding as to why and when larger ES barriers exist, would be rather welcome. An attempt in that direction was made several years ago by Memmel and Bertel [15] who conjectures that the existence of an ES barrier on (111) oriented fcc surfaces is correlated with the nearly free electron surface state [16]. It was argued that the boundary condition for the surface state wave function at the steps leads to a reduction of the binding energy at steps and hence to an ES barrier. While the concept is appealing, convincing evidence for a correlation between the existence of surface states and the ES barrier ...

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Section: Institut F üR Grenzflächenforschung Und Vakuumphysik Forschmentioning

confidence: 93%

Section: Institut F üR Grenzflächenforschung Und Vakuumphysik Forschmentioning

confidence: 99%

Interlayer Mass Transport and Quantum Confinement of Electronic States

1999

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“…More recently, Giesen et al observed that the rates of Cu island decay on Cu(111) greatly increase when the separation distance, d, between island-and terrace-step edges is smaller than a critical value w c ≈ 14Å [10,11]. The effect was attributed to ES barriers becoming vanishingly small for d < w c , in accordance with theoretical models, which showed that quantum confinement of electronic surface states in metals occurs for terrace widths < w c = λ F / √ 2, where λ F is the Fermi-electron wavelength [12].…”

Section: Introductionmentioning

confidence: 99%

Effects of surface vibrations on interlayer mass transport: Ab initio molecular dynamics investigation of Ti adatom descent pathways and rates from TiN/TiN(001) islands

et al. 2018

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We carried out density-functional ab initio molecular dynamics (AIMD) simulations of Ti adatom (Ti ad ) migration on, and descent from, square TiN 100 epitaxial islands on TiN(001) at temperatures (T ) ranging from 1200 to 2400 K. Adatom-descent energy barriers determined via ab initio nudged-elastic-band calculations at 0 Kelvin suggest that Ti interlayer transport on TiN(001) occurs essentially exclusively via direct hopping onto a lower layer. However, AIMD simulations reveal comparable rates for Ti ad descent via direct hopping vs push-out/exchange with a Ti island-edge atom for T 1500 K. We demonstrate that this effect is due to surface vibrations, which yield considerably lower activation energies at finite temperatures by significantly modifying the adatom push-out/exchange reaction pathway.

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“…One of the widely used model systems for such investigations is the decay of two-dimensional ͑2D͒ metal islands on metal substrates. [2][3][4][5][6][7][8][9][10][11] The thermal decay of such islands was found to reduce the island area with time t proportional to (t 0 Ϫt) 2␤ , where t 0 is the time at which the island is fully dissolved. 12 The value of the exponent ␤ is a signature of the dominant microscopic mechanism governing the rate of decay.…”

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Decay characteristics of two-dimensional islands on strongly anisotropic surfaces

Yao

Ebert

et al. 2002

Phys. Rev. B

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We investigate analytically the decay characteristics of two-dimensional islands on strongly anisotropic surfaces. We show that a generic scaling law can always be established in describing the dynamical evolution of such islands, given by Lϰ(t 0 Ϫt) ␤ , where L is the island width, and t 0 is the lifetime of the islands. The value of the scaling exponent ␤ in the fast-decay direction is always 1/2 in the low-temperature regime where the decay is quasi-one-directional, irrespective of the specific dominant decaying mechanism involved. At higher temperatures where the decay proceeds effectively in both directions, ␤ is again a good measure of the dominant microscopic decaying mechanism involved, just like the isotropic case. We discuss these results in connection with recent experiments. There has been an overwhelming wealth of research activity on fabricating various nanostructures that may possess unique physical properties. Nevertheless, the stability of nanostructures, once formed, often poses a limiting factor for their practical applications. 1,2 Therefore, understanding the physical mechanisms involved in the stability and the dynamical evolution of nanostructures after their formation is both scientifically intriguing and technologically significant, and has been receiving increasing attention in recent years. One of the widely used model systems for such investigations is the decay of two-dimensional ͑2D͒ metal islands on metal substrates. [2][3][4][5][6][7][8][9][10][11] The thermal decay of such islands was found to reduce the island area with time t proportional to (t 0 Ϫt) 2␤ , where t 0 is the time at which the island is fully dissolved. 12 The value of the exponent ␤ is a signature of the dominant microscopic mechanism governing the rate of decay. In the case where attachment and detachment of atoms from the island edges dominate the rate of decay, ␤ equals 1/2 whereas for the diffusion-limited case, i.e., where diffusion of adatoms on the terrace limits the decay rate, ␤ is 1/3. These results very well describe the decay of islands on isotropic surfaces, which in fact has attracted most of the attention so far. However, the decay of islands on anisotropic substrates, i.e., surfaces with different energy barriers along the nonequivalent crystallographic directions, is expected to be more complex and may provide additional insight into the physical nature of island dissolution. Indeed the larger complexity was substantiated by the observation of a transition from a 2D decay mode at high temperatures to a quasi-onedimensional ͑1D͒ decay mode at low temperatures for the anisotropic system of Ag islands on Ag͑110͒. 11 Several more recent studies have also studied the evolution of islands and voids on other metal ͑110͒ surfaces, 13-15 but to date, the theoretical basis for description of island decay on anisotropic substrates is still lacking.In this paper we develop a comprehensive analytical description of the decay of two dimensional islands on highly anisotropic surfaces. We find that even for highl...

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Fast Decay of Adatom Islands and Mounds on Cu(111): A New Effective Channel for Interlayer Mass Transport

Cited by 106 publications

References 24 publications

Interlayer Mass Transport and Quantum Confinement of Electronic States

Interlayer Mass Transport and Quantum Confinement of Electronic States

Effects of surface vibrations on interlayer mass transport: Ab initio molecular dynamics investigation of Ti adatom descent pathways and rates from TiN/TiN(001) islands

Decay characteristics of two-dimensional islands on strongly anisotropic surfaces

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