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  • 1.
    Elofsson, Viktor
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Almyras, Georgios
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Lü, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Garbrecht, Magnus
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Boyd, Robert
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska fakulteten.
    Sarakinos, Kostas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Structure formation in Ag-X (X = Au, Cu) alloys synthesized far-from-equilibrium2018Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 123, nr 16Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We employ sub-monolayer, pulsed Ag and Au vapor fluxes, along with deterministic growth simulations, and nanoscale probes to study structure formation in miscible Ag-Au films synthesized under far-from-equilibrium conditions. Our results show that nanoscale atomic arrangement is primarily determined by roughness build up at the film growth front, whereby larger roughness leads to increased intermixing between Ag and Au. These findings suggest a different structure formation pathway as compared to the immiscible Ag-Cu system for which the present study, in combination with previously published data, reveals that no significant roughness is developed, and the local atomic structure is predominantly determined by the tendency of Ag and Cu to phase-separate.

  • 2.
    Lü, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska högskolan.
    Dynamics of the Early Stages in Metal-on-Insulator Thin Film Deposition2014Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 3.
    Lü, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Nano- and mesoscale morphology evolution of metal films on weakly-interacting surfaces2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Thin films are structures consisting of one or several nanoscale atomic layers of material that are used to either functionalize a surface or constitute components in more complex devices. Many properties of a film are closely related to its microstructure, which allows films to be tailored to meet specific technological requirements. Atom-by-atom film growth from the vapor phase involves a multitude of atomic processes that may not be easily studied experimentally in real-time because they occur in small length- (≤ Å) and timescales (≤ ns). Therefore, different types of computer simulation methods have been developed in order to test theoretical models of thin film growth and unravel what experiments cannot show. In order to compare simulated and experimental results, the simulations must be able to model events on experimental time-scales, i.e. on the order of microseconds to seconds. This is achievable with the kinetic Monte Carlo (kMC) method.

    In this work, the initial growth stages of metal deposition on weakly-interacting substrates is studied using both kMC simulations as well as experiments whereby growth was monitored using in situ probes. Such film/substrate material combinations are widely encountered in technological applications including low-emissivity window coatings to parts of microelectronics components. In the first part of this work, a kMC algorithm was developed to model the growth processes of island nucleation, growth and coalescence when these are functions of deposition parameters such as the vapor deposition rate and substrate temperature. The dynamic interplay between these growth processes was studied in terms of the scaling behavior of the film thickness at the elongation transition, for both continuous and pulsed deposition fluxes, and revealed in both cases two distinct growth regimes in which coalescence is either active or frozen out during deposition. These growth regimes were subsequently confirmed in growth experiments of Ag on SiO2, again for both pulsed and continuous deposition, by measuring the percolation thickness as well as the continuous film formation thickness. However, quantitative agreement with regards to scaling exponents in the two growth regimes was not found between simulations and experiments, and this prompted the development of a method to determine the elongation transition thickness experimentally. Using this method, the elongation transition of Ag on SiO2 was measured, with scaling exponents found in much better agreement with the simulation results. Further, these measurement data also allowed the calculation of surface properties such as the terrace diffusion barrier of Ag on SiO2 and the average island coalescence rate.

    In the second part of this thesis, pioneering work is done to develop a fully atomistic, on-lattice model which describes the growth of Ag on weakly-interacting substrates. Simulations performed using this model revealed several key atomic-scale processes occurring at the film/substrate interface and on islands which govern island shape evolution, thereby contributing to a better understanding of how 3D island growth occurs at the atomic scale for a wide class of materials. The latter provides insights into the directed growth of metal nanostructures with controlled shapes on weakly-interacting substrates, including twodimensional crystals for use in catalytic and nano-electronic applications.

  • 4.
    Lü, Bo
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Almyras, Georgios
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Gervilla Palomar, Victor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Greene, Joseph E
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten. Univ Illinois, IL 61801 USA; Univ Illinois, IL 61801 USA.
    Sarakinos, Kostas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Formation and morphological evolution of self-similar 3D nanostructures on weakly interacting substrates2018Ingår i: PHYSICAL REVIEW MATERIALS, ISSN 2475-9953, Vol. 2, nr 6, artikel-id 063401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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.

  • 5.
    Lü, Bo
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska högskolan.
    Elofsson, Viktor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska högskolan.
    Münger, Peter
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Sarakinos, Kostas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska högskolan.
    Dynamic competition between island growth and coalescence in metal-on-insulator deposition2014Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, nr 16, s. 163107-1-163107-5Artikel i tidskrift (Refereegranskat)
    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.

  • 6.
    Lü, Bo
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska högskolan.
    Münger, E. Peter
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska högskolan.
    Sarakinos, Kostas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska högskolan.
    Growth regimes during metal-on-insulator deposition using pulsed vapor fluxes2014Manuskript (preprint) (Övrigt vetenskapligt)
    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.

  • 7.
    Lü, Bo
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Münger, Peter
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Sarakinos, Kostas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Coalescence-controlled and coalescence-free growth regimes during deposition of pulsed metal vapor fluxes on insulating surfaces2015Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, nr 13, artikel-id 134304Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The morphology and physical properties of thin films deposited by vapor condensation on solid surfaces are predominantly set by the processes of island nucleation, 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. These regimes can be accessed by tuning deposition conditions; however, 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 to control microstructure evolution and thus access a larger palette of film morphological features. Recently, we derived the quantitative criterion to stop coalescence during continuous metal vapor flux deposition on insulating surfaceswhich typically yields 3-dimensional growthby describing analytically the competition between island growth by atomic incorporation and the coalescence rate of islands [Lu et al., Appl. Phys. Lett. 105, 163107 (2014)]. Here, we develop the analytical framework for entering a coalescence-free growth regime for metal vapor deposition on insulating substrates using pulsed vapor fluxes, showing that there exist three distinct criteria for suppressing coalescence that correspond 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 atomistic nucleation theory for pulsed vapor deposition to control morphology of thin films beyond the point of island density saturation. (C) 2015 AIP Publishing LLC.

  • 8.
    Lü, Bo
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Souqui, Laurent
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Tunnfilmsfysik. Linköpings universitet, Tekniska fakulteten.
    Elofsson, Viktor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Sarakinos, Kostas
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Nanodesign. Linköpings universitet, Tekniska fakulteten.
    Scaling of elongation transition thickness during thin-film growth on weakly interacting substrates2017Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 111, nr 8, artikel-id 084101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The elongation transition thickness (hElong) is a central concept in the theoretical description of thin-film growth dynamics on weakly interacting substrates via scaling relations of hElong with respect to rates of key atomistic film-forming processes. To date, these scaling laws have only been confirmed quantitatively by simulations, while experimental proof has been left ambiguous as it has not been possible to measure hElong. Here, we present a method for determining experimentally hElong for Ag films growing on amorphous SiO2: an archetypical weakly interacting film/substrate system. Our results confirm the theoretically predicted hElong scaling behavior, which then allow us to calculate the rates of adatom diffusion and island coalescence completion, in good agreement with the literature. The methodology presented herein casts the foundation for studying growth dynamics and cataloging atomistic-process rates for a wide range of weakly interacting film/substrate systems. This may provide insights into directed growth of metal films with a well-controlled morphology and interfacial structure on 2D crystals-including graphene and MoS2-for catalytic and nanoelectronic applications. Published by AIP Publishing.

  • 9.
    Sarakinos, Kostas
    et al.
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska högskolan.
    Magnfält, Daniel
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska högskolan.
    Elofsson, Viktor
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska högskolan.
    Lü, Bo
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Plasma och beläggningsfysik. Linköpings universitet, Tekniska högskolan.
    Atomistic view on thin film nucleation and growth by using highly ionized and pulsed vapour fluxes2014Ingår i: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 257, s. 326-332Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a brief review on the use of ionized and pulsed vapour fluxes, primarily generated by high power impulse magnetron sputtering (HiPIMS) discharges, as tools to gain atomistic understanding on film nucleation and growth. Two case studies are considered; the first case study concerns stress generation in polycrystalline films. It is highlighted that by using vapour fluxes of well-controlled ion content and ion energy and by studying the film microstructure and intrinsic stresses one can obtain experimental evidence for stress generation by insertion of film forming species in the grain boundaries. In the second case study it is discussed how the use of pulsed vapour fluxes with well controlled time domain can facilitate understanding of growth dynamics and microstructural evolution in thin films grown in three-dimensional (i.e., Volmer-Weber) fashion. Broader implications of the described research strategies for the surface science and surface engineering communities are highlighted and discussed.

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