Studying the growth and stability of Al-Cu-Fe quasicrystalline thin films (QCTF) is an important task in materials science due to the unique properties of these aperiodic structures. Direct observation of these processes is critical for understanding the formation mechanisms and optimizing the characteristics of QCTF. This work is devoted to the analysis of the growth and stability of Al-Cu-Fe QCTF using a set of methods that provide in-situ monitoring of the structure and composition.
Al-Cu-Fe based films with quasi-crystalline structure demonstrate exceptional surface characteristics and mechanical properties. In order to study in depth the formation processes of such films, we conducted a study of the direct growth of quasi-crystals formed in multilayer Al-Cu-Fe films by heat treatment. In the experiments, we used in situ synchrotron X-ray diffraction and in situ transmission electron microscopy, which allow us to observe changes during heating and cooling.
The results obtained using these two techniques demonstrate that the ternary phase is more stable thermodynamically than the binary phases at temperatures above 470 °C during heating. The quasi-crystalline structure is formed during cooling, especially at 660 °C, after the material has become liquid.
To differentiate quasicrystals from approximating crystalline structures in the obtained samples, high-resolution X-ray diffraction analysis was performed at room temperature. A monotonic increase in the peak width along the two-, three-, and five-fold symmetry axes with increasing scattering vector is observed, while there is no systematic dependence on the pulse phase. This allows us to conclude that the obtained thin films are indeed quasicrystals, not approximating crystals, and are practically unaffected by phase stresses. This study provides a comprehensive understanding of the growth mechanism of Al-Cu-Fe quasicrystalline films, which is critical for the development of various applications of quasicrystals.
The films were deposited by magnetron sputtering on various substrates, with careful control of temperature and deposition rate. In-situ scanning tunneling microscopy (STM) allowed observation of the atomic structure of the surface in real time, revealing the stages of nucleation, island growth and formation of a continuous film. STM data were supplemented by high-energy electron diffraction (RHEED) data, providing information on the crystal structure as a whole and allowing identification of the phase composition.
The observations revealed complex growth processes characterized by competition between different quasicrystalline and crystalline phases. The substrate temperature turned out to be a key parameter determining the morphology and phase composition of the film. At low temperatures, amorphous growth prevailed, while at higher temperatures, the formation of quasicrystalline islands was observed. The stability of the formed CCFTs was studied by long-term annealing at different temperatures. It was shown that under certain conditions, a phase transition to more stable, but less desirable crystalline structures occurs.
The obtained results provide valuable information for optimizing the deposition and heat treatment conditions of Al-Cu-Fe CCFTs in order to obtain high-quality quasi-crystalline films with desired properties. Further studies are aimed at studying the influence of alloying elements and creating multilayer structures to improve the stability and functional characteristics of CCFTs.
Author: Hadi Parsamehr, Chun-Liang Yang, Wei-Ting Liu, Shi-Wei Chen, Shou-Yi Chang, Lih-Juann Chen, An Pang Tsai, Chih-Huang Lai
Institute:
Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, 30013, Taiwan
National Synchrotron Radiation Research Center, Hsinchu, Taiwan 30076
Institute for Advanced Materials Interdisciplinary Research, Tohoku University, Sendai, 980-8577, Japan
National Institute of Materials Science, 305-0047, Tsukuba, Japan