Compositionally-Driven Formation Mechanism of Hierarchical Morphologies in Co-Deposited Immiscible Alloy Thin Films

Abstract

Co-deposited, immiscible alloy systems form hierarchical microstructures under specific deposition conditions that accentuate the difference in constituent element mobility. The mechanism leading to the formation of these unique hierarchical morphologies during the deposition process is difficult to identify, since the characterization of these microstructures is typically carried out post-deposition. We employ phase-field modeling to study the evolution of microstructures during deposition combined with microscopy characterization of experimentally deposited thin films to reveal the origin of the formation mechanism of hierarchical morphologies in co-deposited, immiscible alloy thin films. Our results trace this back to the significant influence of a local compositional driving force that occurs near the surface of the growing thin film. We show that local variations in the concentration of the vapor phase near the surface, resulting in nuclei (i.e., a cluster of atoms) on the film’s surface with an inhomogeneous composition, can trigger the simultaneous evolution of multiple concentration modulations across multiple length scales, leading to hierarchical morphologies. We show that locally, the concentration must be above a certain threshold value in order to generate distinct hierarchical morphologies in a single domain.

Linking simulated polycrystalline thin film microstructures to physical vapor deposition conditions

“…However, they have limited predictive capability because they are inherently reductive. Predictive capabilities for directly relating growth conditions to the resulting film microstructure have been the focus of a few research studies including atomistic [10][11][12], kinetic Monte Carlo (kMC) [13][14][15] and phase-field [16][17][18][19][20][21][22] simulations. Although these studies have made advances in isolated aspects of the physical and microstructural processes occurring during PVD, such as surface diffusion, deposition incidence, and film/substrate interactions, or in understanding the roles of anisotropy or composition, and because they do not consider the vapor/film growth interactions in most of the cases, there is a need for a unified model to connect film microstructure and surface topographies with deposition conditions.…”

Inferring topological transitions in pattern-forming processes with self-supervised learning

“…When heated up, block copolymers thin films experience a smooth, thermally induced morphology transition from cylindrical to lamellar microdomains 6,7 . Similarly, the co-sputter deposition of immiscible elements results in a variety of self-organized microstructural patterns depending on processing conditions [8][9][10][11] .…”

Mathematical Modeling of Phase Separation and Branching Process of the Film Structure during Binary Thin Film Deposition

“…There have been many recent works dedicated to the simulation of the growth of nanostructured thin films [10][11][12][13][14][15][16][17][18][19][20][21]. Much attention has recently been given to the nanostructures observed in Cu-Mo thin films [10,11,14,21], where approaches based on the phase field theory have been used to simulate the growth of thin films, with the modeling data mostly compared to the experimental data observed in Cu-Mo thin films. Determining the influence of deposition rate and substrate temperature on the phase structure in the Cu-Mo system [10,11] were the main objective in [10,11].…”

“…A morphology map as a function of deposition rate and mobility obtained from simulation data is provided by Ankit et al in [11]. The influence of compositional variations within the vapor phase on the formation of hierarchical phase structures in co-deposited immiscible alloy thin films was investigated by Powers et al in [14], where it was discovered that certain vapor phase compositions promote the development of hierarchical structures during co-deposition of the alloy thin film. The effects of temperature-dependent surface and bulk diffusivities, temperaturedependent thermodynamic driving force for phase separation, and composition-dependent interfacial and surface energies on the phase structure of immiscible alloy thin films were investigated in [21].…”