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Kinetic Monte-Carlo studies of island shape evolution on weakly-interacting substrates
Linköping University, Department of Physics, Chemistry and Biology.
2018 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Metal thin films deposited on weakly-interacting substrates constitute an essential element of numerous microelectronic, catalytic, and optical devices. However, the natural tendency of metal atoms to agglomerate, upon condensation on a weakly-interacting surface, in dispersed three-dimensional (3D) islands affects negatively the performance of the above-mentioned devices. The aim of this thesis is to investigate one of the mechanisms governing silver (Ag) 3D island growth on weakly-interacting substrates, i.e. the nucleation of a new layer on the island top. Kinetic Monte Carlo (KMC) simulations are employed to calculate the top island-layer critical radius Rrequired for nucleating a new layer in the out-of-plane direction. Single-island simulations are performed for growth temperatures T in the range 250 to 500 K and ratios of the pairwise adatom/substrate atom bond strength EB,sub to the corresponding adatom/adatom value EB,film in the range 0.5 to 0.75. We find that for T values below 250 K the islands exhibit a 2D morphology for all EB,sub/EB,film ratios. In contrast, for T values above 300 K there exists a range of relatively small EB,sub/EB,film values, where 2D morphology dominates. To calculate Rfor each island layer as the island shape evolves, a subroutine is developed and implemented in an existing KMC algorithm. Rvalues are computed for 3D island growth at EB,sub/EB,film = 0.5 in the T range 300−500 K and the results show that Rdecreases monotonously from 17.3 to 6.0 Å and saturates approximately at 375 K. This trend is opposite to the typical behavior of islands grown under homoepitaxial conditions, for which the enhancement of downward inter-layer diffusion caused by an increase of T leads to lower atomic densities on the top, i.e. to a lower nucleation probability, and thus to an increase of Rc. This work contributes to the understanding of the physical processes that control thin-film morphological evolution; which is paramount for controlling and manipulating film growth for specific applications.

Place, publisher, year, edition, pages
2018. , p. 45
Keywords [en]
Kinetic Monte Carlo, thin film, metal, weakly interacting substrates
National Category
Nano Technology
Identifiers
URN: urn:nbn:se:liu:diva-150984ISRN: LITH-IFM-A-EX—18/3574—SEOAI: oai:DiVA.org:liu-150984DiVA, id: diva2:1246495
Subject / course
Physics
Supervisors
Examiners
Available from: 2018-09-25 Created: 2018-09-07 Last updated: 2018-09-25Bibliographically approved

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Citation style
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