Kinetics of volume and surface driven crystallization in thin films

Abstract

A mathematical model of the crystallization process in a thin film is presented with the purpose to overcome the limitations of Kolmogorov-Johnson-Mehl-Avrami theory regarding finite-size systems. Two ways of nucleation are taken into account: at the film boundaries and in the bulk. The solution is obtained in terms of crystallization probability, which is the probability of a point inside the film to be included in the crystal at a given moment of time. It is shown that the characteristic feature of crystallization in finite-size systems is a non-uniform distribution of crystalline fraction.

Artificial Anisotropy in Ge2Sb2Te5 Thin Films after Femtosecond Laser Irradiation

“…This allows us to define the activation energy value E a via the approximation of the line slope in the semi-logarithmic scale. The calculated value of the activation energy for the initial sample is 0.41 ± 0.01 eV, which agrees with the previous data [ 39 ]. The activation energy for the conductivity in direction 1–1 orthogonal to the scanlines is 0.40 ± 0.01 eV and does not differ dramatically from the activation energy of the unirradiated sample.…”

“…Thus, the observed Raman spectra transformation most likely indicates a transition from an amorphous to a face-centered cubic (fcc) crystalline structure [ 30 , 37 ] after laser treatment. The observed laser-induced crystallization of GST225 thin films can be described by the nucleation processes, with subsequent nanocrystal growth [ 38 , 39 ]. In particular, the forming nuclei may be needle-shaped crystal particles aligned along the applied laser field [ 29 ].…”

Periodic Relief Fabrication and Reversible Phase Transitions in Amorphous Ge2Sb2Te5 Thin Films upon Multi-Pulse Femtosecond Irradiation

“…Therefore, it might be assumed that the observed behavior is related to the appearance and increase of the crystalline fraction in GST225 [7]. The crystallization can be described by the simultaneous volume and surface nucleation processes [44]. In the case of Ns = 750, the Raman spectra showed that the intensity ratio of the 125 cm −1 line to the 110-200 cm −1 broadband maximum is smaller in the laser spot center than at the periphery area (Figure 4b).…”

“…Therefore, it might be assumed that the observed behavior is related to the appearance and increase of the crystalline fraction in GST225 [7]. The crystallization can be described by the simultaneous volume and surface nucleation processes [44].…”