Abstract
The structure of metallic glasses is a long-standing question because the lack of long-range order makes diffraction based techniques difficult to be applied. Here, we used scanning tunneling microscopy with large tunneling resistance of 6 GΩ at low temperature in order to minimize forces between probe and sample and reduce thermal fluctuations of metastable structures. Under these extremely gentle conditions, atomic structures of Ni40Ta60 metallic glasses are revealed with unprecedented lateral resolution. In agreement with previous models and experiments, icosahedral-like clusters are observed. The clusters show a high degree of mobility, which explains the need of low temperatures for stable imaging. In addition to icosahedrons, chain-like structures are resolved and comparative density functional theory (DFT) calculations confirm that these structures are meta-stable. The co-existence of icosahedral and chain-like structures might be an key ingredient for the understanding of the mechanical properties of metallic glasses.
Highlights
The structure of metallic glasses is a long-standing question because the lack of long-range order makes diffraction based techniques difficult to be applied
It is worth mentioning that Ni40Ta60 is considered as a high temperature Metallic glasses (MG) meaning that its glass temperature Tg is relatively high compared to other metallic glasses (≈ 1080 K)[27,28]
All of the samples were found completely amorphous by means of X-ray diffraction and scanning tunneling microscopy (STM) overviews after preparations
Summary
The structure of metallic glasses is a long-standing question because the lack of long-range order makes diffraction based techniques difficult to be applied. We used scanning tunneling microscopy with large tunneling resistance of 6 GΩ at low temperature in order to minimize forces between probe and sample and reduce thermal fluctuations of metastable structures Under these extremely gentle conditions, atomic structures of Ni40Ta60 metallic glasses are revealed with unprecedented lateral resolution. Combined theoretical calculations and nano-beam diffraction[14,15] have experimentally observed icosahedral-like diffraction patterns in MG, always accompanied by large distortions giving rise to face-cubic centered (fcc) and hexagonal closed packed (hcp) configurations These results confirmed the existence of icosahedral clusters, the restriction to the reciprocal space hinders to conclude whether the clusters have complex hybrid hetero-structures[15] or several metastable structures coexist in the MG as recently suggested[16,17,18]. We systematically performed real-space investigations of the Ni40Ta60 metallic glass surface by means of STM at low temperature in combination with X-Ray Diffraction (XRD) and X-ray Photo-electron Spectroscopy (XPS) to shed light on the atomic-scale structural characteristics of metallic glass
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