Dendrite Growth in Amorphous Films of HfO2 Under Electron-Beam Irradiation "In Situ"

Abstract

The morphology and kinetics of dendrites growth at the electron-beam crystallization of amorphous HfO₂ films have been studied with transmission electron microscopy using video recording. Amorphous films were obtained by pulsed laser sputtering of Hf in an oxygen atmosphere. Studies have shown that dendrite polymorph crystallization takes place. It can be either one-stage or two-stage in nature. In first case, four trunk non-crystallographic dendrite branches of the first order grow from one center. Their lateral surfaces (basal surfaces), bordering with amorphous phase, are places of formation of dendrite branches of the second order, which in turn can form branches of the third order. Branches are formed from a number of randomly oriented crystals in the process of geometric selection. The direction of its highest growth rate forms an acute angle with the basal surface. In the second case, the size-phase effect takes place, consisting in the fact, that when the disk-shaped HfO₂ crystal of the orthorhombic modification reaches a critical size (∼0.2 μm), it splits into domains, containing monoclinic crystal lattices. Subsequently they form non-crystallographic branches of the dendrite. After transformation the growth rate of dendrite sharply increases (∼4 times) in comparison with the growth rate of the disk-shaped crystal and remain constant at a fixed electron flux density through the sample. The analogy between Stranski–Krastanov growth mode of a crystal from the vapor phase and dendrite polymorphic crystallization of amorphous HfO₂ phase is looked through.