Crystallization of GeO2 thin films into alpha-quartz: from spherulites to single crystals

TL;DR

This study demonstrates the controlled crystallization of amorphous GeO2 thin films into quartz, revealing the growth mechanisms and enabling the synthesis of single crystalline quartz for industrial and scientific applications.

Contribution

It provides new insights into the nucleation and growth processes of quartz from GeO2 thin films and achieves controlled synthesis of single crystalline quartz.

Findings

Crystallization occurs via spherulitic growth at low temperatures.

Higher temperatures lead to the formation of quartz crystals.

Edges facilitate nucleation and inward growth of crystals.

Abstract

Piezoelectric quartz SiO2 crystals are widely used in industry as oscillators. As a natural mineral, quartz and its relevant silicates are also of interest of geoscience and mineralogy. However, the nucleation and growth of quartz crystals is difficult to control and not fully understood. Here we report successful solid state crystallization of thin film of amorphous GeO2 into quartz on various substrates including Al2O3, MgAl2O4, MgO, LaAlO3 and SrTiO3. At relatively low annealing temperatures, the crystallization process is spherulitic: with fibers growing radially from the nucleation centers and the crystal lattice rotating along the growth direction with a linear dependence between the rotation angle and the distance to the core. For increasingly higher annealing temperatures, quartz crystals begin to form. The edges of the sample play an important role facilitating nucleation followed by growth sweeping inward until the whole film is crystallized. Control of the growth allows single crystalline quartz to be synthesized. Our study reveals the complexity of the nucleation and growth process of quartz and provides insight for further studies.