Studying the atomic structure of quasicrystalline surfaces is a challenging task due to the lack of translational symmetry characteristic of conventional crystals. In this paper, we present the results of a study of the five-fold surface of an Al–Cu–Fe quasicrystal using scanning tunneling microscopy (STM) and dynamic Raman spectroscopy.
High-resolution STM images of the atomic structure of the surface were obtained, demonstrating the presence of characteristic quasi-periodic patterns. Regions with different local atomic configurations are observed, reflecting the complexity and heterogeneity of the quasi-crystalline structure. Analysis of STM images revealed dominant structural motifs, such as pentagons and rhombuses, arranged in accordance with icosahedral symmetry.
Using scanning tunneling microscopy (STM) and a specialized technique of dynamic low-energy electron diffraction (DLED), we study the atomic structure of the quintuple surface of the icosahedral Al–Cu–Fe alloy. STM data indicate that the step heights predominantly take two values in the ratio τ characteristic of quasicrystals. However, the spatial distribution of these values does not obey the Fibonacci sequence, indicating violations of the ideal volumetric order of the quasicrystalline layers oriented perpendicular to the surface. Observations in STM images confirm the presence of an imperfect quasicrystalline structure.
At the same time, the local probing method, which demonstrated its efficiency in the study of Al–Pd–Mn in the previous work, is successfully applied to Al–Cu–Fe. Similar structural characteristics, including interlayer relaxations and types of surface terminations, were revealed in both materials. Despite the absence of strict periodicity in the structure, clear atomic planes are observed in the bulk of the material, some of which form repeating motifs.
In both alloys, the surface tends to form between these grouped layers. For Al–Cu–Fe, the step heights obtained by STM correspond to the thickness of the grouped layers identified by the local probing method. The results obtained suggest that the five-fold Al–Cu–Fe surface has a quasi-crystalline layered structure, but with stacking faults.
Dynamic Raman spectroscopy provided information on the lattice vibrational modes and their relationship to the surface atomic structure. Raman spectra demonstrate broad bands reflecting the disorder of the quasicrystal atomic structure. Polarization analysis of the Raman spectra allowed us to determine the symmetry of the vibrational modes and their contribution to the thermal properties of the material.
Comparison of STM and Raman spectroscopy data allowed us to establish a relationship between the atomic structure of the surface and its vibrational properties. It was found that regions with different atomic configurations are characterized by different frequencies and intensities of vibrational modes. The results obtained provide valuable information for understanding the physical properties of quasi-crystalline surfaces and their potential application in various fields of science and technology.
Author: T. Caia, F. Shi, Z. Shen, M. Gierer, A. I. Goldman, M. J. Kramer, C. J. Jenks, T. A. Lograsso, D. W. Delaney, P. A. Thiel, M. A. Van Hove
Institute: Department of Chemistry and Ames Laboratory, Iowa State University, Ames, IA 50011-3111, USA, Division of Materials Science, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, USA, Institute of Crystallography and Mineralogy, University of Munich, Theresienstrasse 41, 80333 Munich, Germany