Thin-film Solidification Research Articles

Investigation of the Effect of 3D Meniscus Geometry on Fluid Dynamics and Crystallization via In Situ Optical Microscopy-Assisted Mathematical Modeling.

Solution-based thin-film solidification is a complex process involving various transport phenomena that are intricately dependent on multiple experimental parameters. The difficulty of analyzing this process experimentally or conducting exact numerical simulation make it challenging to understand, predict, and control the solidification process. In this work, a simple and effective technique to analyze the thin-film solidification process during solution shearing, based on 3D geometrical model of the meniscus, is proposed. The 3D meniscus geometry, which changes depending on the experimental parameters, is attained using high-speed side-view and top-view in situ microscopy. Thereafter, mass and momentum transport mathematical models are applied to obtain numerical solutions of transport phenomena within the meniscus. Utilizing these results, the underlying mechanism of dendritic growth of small molecule organic semiconductor is elucidated, which has previously been unknown. The 3D meniscus modeling is particularly important for this analysis, as dendrite formation is strongly dependent on the meniscus geometry near the contact line and mass transport variation perpendicular to the coating direction. This technique enables the study of complex relationship between experimental parameters and solidification process, which is widely applicable to various materials and coating systems; whereby, better understanding of thin-film growth and device performance optimization is possible.

Understanding the facet formation mechanisms of Si thin-film solidification through three-dimensional phase-field modeling

Adaptive phase field modeling is used in order to model the formation mechanism of a silicon faceted interface in three dimensions. We investigate the faceting condition for equilibrium shapes and dynamic situations. In this study, we propose a new anisotropic function of surface energy for the phase-field simulations in three-dimension, and negative stiffness is further considered. The morphological evolutions are presented and compare well with experimental findings. The growth mechanism is further discussed.

Morphological Transitions of Shallow Cells during Thin-Film Solidification of an Alloy: Phase Field Modeling & Experimental Observation

The morphological transitions of shallow cells near the onset of Mullins-Sekerka instability during the thin-film directional solidification of a succinonitrile/acetone alloy have been simulated quantitatively by means of phase field modeling for the first time. Long time/length scale experiments at a constant pulling speed were performed for the purpose of comparison. The simulation results show good agreement with classic theories in the planar and λ(subscript c)↔λ(subscript c)/2 cellular bifurcation regions, where λ(subscript c) is the critical wavelength. At a higher pulling speed, V, an anti-trapping current was introduced to maintain the local equilibrium, and the region for Vλ^2~constant was found. Finally, multiplets appeared when λ was close to λ(subscript c)/4. In the experiments, due to slow solute accumulation in the molten zone, morphological transitions were also revealed. Some interesting nonlinear phenomena, such as tip splitting, coarsening, pinch-off, and asymmetric cells, were also confirmed through both simulations and experiments.

Measurement of the onset of two-dimensional cellular solidification in the succinonitrile—acetone binary alloy

The onset of cellular solidification in a thin-film solidification system using dilute acetone in succinonitrile is experimentally determined by independent measurements of the crystal growth rate, temperature gradient, and acetone concentration. The temperature gradient is measured by thermocouples placed on the solidification cell, the growth rate is measured directly from the motion of the sample and the acetone concentration is measured by fourier transform infrared (FT-IR) spectroscopy by calibrating the magnitude of the spectral peak at 1700–1720 cm −1 with the concentration of acetone in the sample. Experimental results for a range of acetone concentrations and temperature gradients agree well with simple constitutional supercooling criteria and with the more exact morphological stability theory.

Addendum to “steady state thin film solidification as a well-posed Stefan problem”

Addendum to “steady state thin film solidification as a well-posed Stefan problem”

Spatiotemporal chaos near the onset of cellular growth during thin-film solidification of a binary alloy

Thin-film solidification experiments with a succinonitrile-acetone alloy are used to observe the long time-scale dynamics of cellular crystal growth at growth rates only slightly above the critical value V = V cλ c for the onset of morphological instability Under these conditions only very small amplitude cells are observed with wavelengths near the value predicted by linear stability theory λ = λ c. At long times, microstructures with wavelengths significantly finer than λ c form by nucleation at defects across the interface. These interfaces do not have a unique microstructure, but seem to exhibit spatiotemporal chaos on a long time scale caused by the continual birth and death of cells by tip splitting and cell annihilation in grooves.

Heat transfer at spherical thin film solidification

A mathematical model for the solidification process of a melted film coating a spherical particle plunged in an immobile fluid is presented. This model may be used in order to determine temperature distribution in the vicinity of the particle. The results obtained using a melted sulphur thin film cooled with air are consistent with the data available in literature.