Transient Nucleation in Ge–Sb–S Thin Films

Abstract

The crystal nucleation behavior and kinetics in Ge1.8Sb36.8S61.4 thin films were studied using optical microscopy coupled with a computer-controlled heating stage. The single-stage in situ heat treatment method was chosen for the study of nucleation. In-situ experiments were performed in the temperature range of 236–295 °C. The time evolution of the number of nuclei at various temperatures revealed transient behavior at low nucleation times. The transient nucleation data were described using the Shneidman equation to get values of steady-state nucleation rate, induction period, and time-lag of nucleation for the studied temperatures. On the basis of nucleation experiments, the temperature dependence of crystal–liquid surface energy and decoupling of nucleation rate and viscosity was assessed. The nucleation rate data obtained from microscopy measurements were discussed in terms of classical nucleation theory. It was found that the nucleation curve with the maximum at 288 °C and previously published growth curve with maximum at 309 °C overlap significantly.

Circumventing Thermodynamic Constraints in Nucleation-Controlled Crystallization of Al2TiO5-Based Chemical Vapor Deposition Coatings

“…At such low temperatures, the level of supercooling is extensive; therefore, the total driving force for nucleation (ΔG n ) becomes the dominating parameter influencing the entire crystallization process from a thermodynamic point of view. 59,76,77 This can be accentuated from an expression of the steady-state nucleation rate I st , which follows 76,78 i k j j j j j y { z z z z z…”

“…Also, W* represents the energetic barrier of nucleation, whereas ΔG D represents the kinetic ditto. By assuming the formation of a spherical nucleus having a critical radius r*, W* can be written into 76,78,79 W G…”

“…First, in terms of supercooling, all samples crystallized below half the melting points of their corresponding crystalline states. At such low temperatures, the level of supercooling is extensive; therefore, the total driving force for nucleation (Δ G n ) becomes the dominating parameter influencing the entire crystallization process from a thermodynamic point of view. ,, This can be accentuated from an expression of the steady-state nucleation rate I st , which follows , where I 0 is a pre-exponential factor, k B is Boltzmann’s constant, and T is the annealing temperature. Also, W * represents the energetic barrier of nucleation, whereas Δ G D represents the kinetic ditto.…”

“…Also, W * represents the energetic barrier of nucleation, whereas Δ G D represents the kinetic ditto. By assuming the formation of a spherical nucleus having a critical radius r *, W * can be written into ,, where γ denotes the crystal amorphous interfacial energy. In this equation, Δ G n represents the sum of all Gibbs free energy changes involved during nucleation.…”

“…Although the above expression is derived for amorphous bulk materials, 87 it is regularly assumed that the viscosity behavior is similar among thin films and coatings. 76,98 At intermediate annealing temperatures, where the untransformed amorphous state is left in an exorbitant energetic state (and the diffusion barrier is likewise), it becomes increasingly more viable for the transformation to continue through other possible, less-energy demanding routes. Such routes include, for instance, viscosity-driven structural relaxations.…”