Nucleation, Growth, and Relaxation of Thin Films:  Metal(100) Homoepitaxial Systems

Thiel, Patricia A.; Evans, James W.

doi:10.1021/jp9933471

Cited by 41 publications

(45 citation statements)

References 91 publications

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“…Moreover, BCS values are also compared to experimental results [16,54,69,[71][72][73][74][75][76][77][78], as well as barriers obtained from our nudged-elasticband (NEB) calculations using an embedded atom method interatomic potential [79]. Activation barriers for selected processes are listed in Table I.…”

Section: Theory and Computational Detailsmentioning

confidence: 99%

Formation and morphological evolution of self-similar 3D nanostructures on weakly interacting substrates

Lü

Almyras

Gervilla

et al. 2018

Phys. Rev. Materials

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Vapor condensation on weakly interacting substrates leads to the formation of three-dimensional (3D) nanoscale islands (i.e., nanostructures). While it is widely accepted that this process is driven by minimization of the total film/substrate surface and interface energy, current film-growth theory cannot fully explain the atomic-scale mechanisms and pathways by which 3D island formation and morphological evolution occurs. Here, we use kinetic Monte Carlo simulations to describe the dynamic evolution of single-island shapes during deposition of Ag on weakly interacting substrates. The results show that 3D island shapes evolve in a self-similar manner, exhibiting a constant height-to-radius aspect ratio, which is a function of the growth temperature. Furthermore, our results reveal the following chain of atomic-scale events that lead to compact 3D island shapes: 3D nuclei are first formed due to facile adatom ascent at single-layer island steps, followed by the development of sidewall facets bounding the islands, which in turn facilitates upward diffusion from the base to the top of the islands. The limiting atomic process which determines the island height, for a given number of deposited atoms, is the temperature-dependent rate at which adatoms cross from sidewall facets to the island top. The overall findings of this study provide insights into the directed growth of metal nanostructures with controlled shapes on weakly interacting substrates, including two-dimensional crystals, for use in catalytic and nanoelectronic applications.

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Section: Theory and Computational Detailsmentioning

confidence: 99%

Formation and morphological evolution of self-similar 3D nanostructures on weakly interacting substrates

Lü

Almyras

Gervilla

et al. 2018

Phys. Rev. Materials

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“…These low-barrier processes consist of diffusion from the low coordination sites that are created as a result of the RDF deposition dynamics. Our motivation for this model comes from consideration of the Ag/Ag͑100͒ system, where the barrier for diffusion across ͕100͖ terraces equals E d (100) Ϸ0.4 eV, 23 so this process is inactive below about 130 K. However, the barrier for diffusion across ͕111͖ micofacets of E d (111) Ϸ0.1 eV ͑Ref. 24͒ is much lower, leading to activation of this process around 40 K. Atoms landing on the side of pyramidal microprotrusions are, in actuality, landing on ͕111͖ facets, so their diffusion leads to interlayer transport potentially smoothing the film above 40 K. In the rest of this section, we present results of the kinetic Monte Carlo ͑KMC͒ simulations, in which we incorporate certain low-barrier diffusion processes into our previously described RDF models in 1ϩ1d and 2ϩ1d.…”

Section: Growth At Low Temperatures: Low-barrier Interlayer Diffumentioning

confidence: 99%

Metal homoepitaxial growth at very low temperatures: Lattice-gas models with restricted downward funneling

Caspersen

Evans

2001

Phys. Rev. B

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We develop and analyze 1+1-and 2+1-dimensional (d) models for multilayer homoepitaxial growth of metal films at low temperatures (T), where intralayer terrace diffusion is inoperative. This work is motivated by recent variable-temperature scanning tunneling microscopy studies of Ag/Ag(100) homoepitaxy down to 50 K. Adsorption sites are bridge sites in our 1+1d models, and fourfold hollow sites in our 2+1d models for fcc(100) or bcc(100) surfaces. For growth at 0 K, we introduce a "restricted downward funneling" model, wherein deposited atoms can be trapped on the sides of steep nanoprotrusions rather than always funneling down to lower adsorption sites. This leads to the formation of overhangs and internal defects (or voids), and associated "rough" growth. Upon increasing T, we propose that a series of interlayer diffusion processes become operative, with activation barriers below that for terrace diffusion. This leads to "smooth" growth of the film for higherT (but still within the regime where terrace diffusion is absent), similar to that observed in models incorporating "complete downward funneling. " Disciplines Chemistry | Mathematics | Physical Chemistry CommentsThis article is from Physical Review B 64 (2001) We develop and analyze 1ϩ1-and 2ϩ1-dimensional ͑d͒ models for multilayer homoepitaxial growth of metal films at low temperatures (T), where intralayer terrace diffusion is inoperative. This work is motivated by recent variable-temperature scanning tunneling microscopy studies of Ag/Ag͑100͒ homoepitaxy down to 50 K. Adsorption sites are bridge sites in our 1ϩ1d models, and fourfold hollow sites in our 2ϩ1d models for fcc͑100͒ or bcc͑100͒ surfaces. For growth at 0 K, we introduce a ''restricted downward funneling'' model, wherein deposited atoms can be trapped on the sides of steep nanoprotrusions rather than always funneling down to lower adsorption sites. This leads to the formation of overhangs and internal defects ͑or voids͒, and associated ''rough'' growth. Upon increasing T, we propose that a series of interlayer diffusion processes become operative, with activation barriers below that for terrace diffusion. This leads to ''smooth'' growth of the film for higher T ͑but still within the regime where terrace diffusion is absent͒, similar to that observed in models incorporating ''complete downward funneling.''

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“…This has been shown by the large body of work on crystalline substrates and films. 18 For this purpose, scanning tunneling microscopy ͑STM͒ provides invaluable detailed insight. This is because the spatial characteristics of films at low coverages, such as the island density, reflect the kinetics of nonequilibrium adlayer evolution during deposition.…”

Section: Introductionmentioning

confidence: 99%

Nucleation and growth of Ag islands on fivefold Al-Pd-Mn quasicrystal surfaces: Dependence of island density on temperature and flux

et al. 2007

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Scanning tunneling microscopy (STM) has been used to investigate the nucleation and growth of Ag islands on the fivefold surface of an icosahedral Al-Pd-Mn quasicrystal. Analysis of the data as a function of deposition temperature, from 127 K to 300 K, reveals that island density is constant, while at higher temperature it decreases. To model this behavior, we first show that the potential energy surface describing bonding of Ag at various locations on the surface is complex, with a few sites acting as traps for clusters of adatoms. We then develop a rate equation model which incorporates enhanced nucleation at trap sites relative to nucleation at regular sites on terraces. It recovers the temperature dependence of the island density, plus previous flux-scaling data. Our model suggests that the critical size for both types of nucleation sites is large-corresponding to stable clusters of at least 6 Ag atoms-and that binding between atoms at trap sites is significantly stronger than at free terrace sites. The data and the model, combined, provide guidance about the conditions of temperature and flux under which saturation of trap sites can be expected. This, in turn, provides a general indicator of the conditions that may favor localized pseudomorphic growth at low coverage, here and in other systems. Scanning tunneling microscopy ͑STM͒ has been used to investigate the nucleation and growth of Ag islands on the fivefold surface of an icosahedral Al-Pd-Mn quasicrystal. Analysis of the data as a function of deposition temperature, from 127 K to 300 K, reveals that island density is constant, while at higher temperature it decreases. To model this behavior, we first show that the potential energy surface describing bonding of Ag at various locations on the surface is complex, with a few sites acting as traps for clusters of adatoms. We then develop a rate equation model which incorporates enhanced nucleation at trap sites relative to nucleation at regular sites on terraces. It recovers the temperature dependence of the island density, plus previous fluxscaling data. Our model suggests that the critical size for both types of nucleation sites is large-corresponding to stable clusters of at least 6 Ag atoms-and that binding between atoms at trap sites is significantly stronger than at free terrace sites. The data and the model, combined, provide guidance about the conditions of temperature and flux under which saturation of trap sites can be expected. This, in turn, provides a general indicator of the conditions that may favor localized pseudomorphic growth at low coverage, here and in other systems.

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Nucleation, Growth, and Relaxation of Thin Films: Metal(100) Homoepitaxial Systems

Cited by 41 publications

References 91 publications

Formation and morphological evolution of self-similar 3D nanostructures on weakly interacting substrates

Formation and morphological evolution of self-similar 3D nanostructures on weakly interacting substrates

Metal homoepitaxial growth at very low temperatures: Lattice-gas models with restricted downward funneling

Nucleation and growth of Ag islands on fivefold Al-Pd-Mn quasicrystal surfaces: Dependence of island density on temperature and flux

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