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Dynamics of the Early Stages in Metal-on-Insulator Thin Film Deposition
Linköping University, Department of Physics, Chemistry and Biology, Plasma and Coating Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-0908-7187
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Thin films consist of nanoscale layers of material that are used in many technological applications to either functionalize a surface or serve as parts in miniaturized devices. The properties of a film are closely related to its microstructure, which in turn can be tuned during film preparation. Thin film growth involves a multitude of atomic-scale processes that cannot always be easily studied experimentally. Therefore, different types of computer simulations have been developed in order to test theoretical models of thin film growth in a highly controlled way. To be able to compare simulation and experimental results, the simulations must be able to model events on experimental time-scales, i.e. several seconds or minutes. This is achievable with the kinetic Monte Carlo method.

In this work, kinetic Monte Carlo simulations are used to model the initial growth stages of metal films on insulating, amorphous substrates. This includes the processes of island nucleation, three-dimensional island growth and island coalescence. Both continuous and pulsed vapor fluxes are investigated as deposition sources, and relations between deposition parameters and film morphology are formulated. Specifically, the film thickness at what is known as the “elongation transition” is studied as a function of the temporal profile of the vapor flux, adatom diffusivity and the coalescence rate. Since the elongation transition occurs due to hindrance of coalescence completion, two separate scaling behaviors of the elongation transition film thickness are found: one where coalescence occurs frequently and one where coalescence occurs infrequently. In the latter case, known nucleation behaviors can be used favorably to control the morphology of thin films, as these behaviors are not erased by island coalescence. Experimental results of Ag growth on amorphous SiO2 that confirm the existence of these two “growth regimes” are also presented for both pulsed and continuous deposition by magnetron sputtering. Knowledge of how to avoid coalescence for different deposition conditions allows nucleation for metal-on-insulator material systems to be studied and relevant physical quantities to be determined in a way not previously possible. This work also aids understanding of the growth evolution of polycrystalline films, which in conjunction with advanced deposition techniques allows thin films to be tailored to specific applications.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 54 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1687
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-112136DOI: 10.3384/lic.diva-112136ISBN: 978-91-7519-192-8 (print)OAI: oai:DiVA.org:liu-112136DiVA: diva2:763736
Supervisors
Available from: 2014-11-17 Created: 2014-11-17 Last updated: 2014-11-18Bibliographically approved
List of papers
1. Unravelling the Physical Mechanisms that Determine Microstructural Evolution of Ultrathin Volmer-Weber Films
Open this publication in new window or tab >>Unravelling the Physical Mechanisms that Determine Microstructural Evolution of Ultrathin Volmer-Weber Films
2014 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 4, 044302- p.Article in journal (Refereed) Published
Abstract [en]

The initial formation stages (i.e., island nucleation, island growth, and island coalescence) set characteristic length scales during growth of thin films from the vapour phase. They are, thus, decisive for morphological and microstructural features of films and nanostructures. Each of the initial formation stages has previously been well-investigated separately for the case of Volmer-Weber growth, but knowledge on how and to what extent each stage individually and all together affect the microstructural evolution is still lacking. Here we address this question using growth of Ag on SiO2 from pulsed vapour fluxes as a case study. By combining in situ growth monitoring, ex situ imaging and growth simulations we systematically study the growth evolution all the way from nucleation to formation of a continuous film and establish the effect of the vapour flux time domain on the scaling behaviour of characteristic growth transitions (elongation transition, percolation and continuous film formation). Our data reveal a pulsing frequency dependence for the characteristic film growth transitions, where the nominal transition thickness decreases with increasing pulsing frequency up to a certain value after which a steady-state behaviour is observed. The scaling behaviour is shown to result from differences in island sizes and densities, as dictated by the initial film formation stages. These differences are determined solely by the interplay between the characteristics of the vapour flux and time required for island coalescence to be completed. In particular, our data provide evidence that the steady-state scaling regime of the characteristic growth transitions is caused by island growth that hinders coalescence from being completed, leading to a coalescence-free growth regime.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-103920 (URN)10.1063/1.4890522 (DOI)000340710700078 ()
Available from: 2014-02-03 Created: 2014-02-03 Last updated: 2017-12-06
2. Dynamic competition between island growth and coalescence in metal-on-insulator deposition
Open this publication in new window or tab >>Dynamic competition between island growth and coalescence in metal-on-insulator deposition
2014 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, no 16, 163107-1-163107-5 p.Article in journal (Refereed) Published
Abstract [en]

The morphology of thin metal films and nanostructures synthesized from the vapor phase on insulating substrates is strongly influenced by the coalescence of islands. Here, we derive analytically the quantitative criterion for coalescence suppression by combining atomistic nucleation theory and a classical model of coalescence. Growth simulations show that using this criterion, a coalescence-free growth regime can be reached in which morphological evolution is solely determined by island nucleation, growth, and impingement. Experimental validation for the ability to control the rate of coalescence using this criterion and navigate between different growth regimes is provided by in situ monitoring of Ag deposition on SiO2. Our findings pave the way for creating thin films and nanostructures that exhibit a wide range of morphologies and physical attributes in a knowledge-based manner.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-112133 (URN)10.1063/1.4900575 (DOI)000344363000073 ()
Available from: 2014-11-17 Created: 2014-11-17 Last updated: 2017-12-05Bibliographically approved
3. Growth regimes during metal-on-insulator deposition using pulsed vapor fluxes
Open this publication in new window or tab >>Growth regimes during metal-on-insulator deposition using pulsed vapor fluxes
2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The morphology and physical properties of thin films deposited by vapor condensation on solid surfaces are predominantly set by the initial surface processes of nucleation, island growth and coalescence. When deposition is performed using pulsed vapor fluxes, three distinct nucleation regimes are known to exist depending on the temporal profile of the flux. While these regimes can be accessed by tuning deposition conditions, their effect on film microstructure becomes marginal when coalescence sets in and erases morphological features obtained during nucleation. By preventing coalescence from being completed, these nucleation regimes can be used in a straightforward manner to control microstructure evolution and thus access a larger palette of film morphological features. Recently, we proposed a mechanism and derived the quantitative criterion to stop coalescence during continuous vapor flux deposition, based on a competition between island growth by atomic incorporation and the coalescence rate of islands [Lü et al., Appl. Phys. Lett. 105, 163107 (2014)]. In the present study, we develop the analytical framework for entering a coalescence-free growth regime for thin film deposition using pulse vapor fluxes, showing that there exist three distinct criteria corresponding to the three nucleation regimes of pulsed vapor flux deposition. The theoretical framework developed herein is substantiated by kinetic Monte Carlo growth simulations. Our findings highlight the possibility of using classical nucleation theory for pulsed vapor deposition to design materials which have an inherent tendency to coalesce.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-112134 (URN)
Available from: 2014-11-17 Created: 2014-11-17 Last updated: 2014-11-17Bibliographically approved

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