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Chain-like structure elements in Ni40Ta60 metallic glasses observed by scanning tunneling microscopy.

Pawlak R, Marot L, Sadeghi A, Kawai S, Glatzel T, Reimann P, Goedecker S, Güntherodt HJ, Meyer E - Sci Rep (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, University of Basel, Klingelbergstr. 82, 4056 Basel, Switzerland.

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.

No MeSH data available.


Related in: MedlinePlus

Amorphous nature and bonding character of the Ni40Ta60 metallic glass.(a) Typical large-scale STM overview of the Ni40Ta60 metallic glass surface, (500 × 500) nm2; I = 10 pA, Vt = 50 mV). (b) Typical XRD pattern of the amorphous metal. (c) normalized XPS spectra of Ni 2p and, (d) Ta 4f of the metallic glass with respect to the preparation cycles. The gray curves in both spectra correspond to the pure Ni and Ta metals respectively. As received samples always show a surface Ta-rich oxide layer which can be removed with preparations. After oxide removal, both Ni 2p and Ta 4f metal spectra are shifted to higher binding energies compared to their metal analogue as a consequence of their preferential bonding in the metallic glass.
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f1: Amorphous nature and bonding character of the Ni40Ta60 metallic glass.(a) Typical large-scale STM overview of the Ni40Ta60 metallic glass surface, (500 × 500) nm2; I = 10 pA, Vt = 50 mV). (b) Typical XRD pattern of the amorphous metal. (c) normalized XPS spectra of Ni 2p and, (d) Ta 4f of the metallic glass with respect to the preparation cycles. The gray curves in both spectra correspond to the pure Ni and Ta metals respectively. As received samples always show a surface Ta-rich oxide layer which can be removed with preparations. After oxide removal, both Ni 2p and Ta 4f metal spectra are shifted to higher binding energies compared to their metal analogue as a consequence of their preferential bonding in the metallic glass.

Mentions: The Ni40Ta60 metallic glass used in our study were quenched in a home-built apparatus by the crucible free splat-cooling method (10 m.s−1) corresponding to a quench rate of ≈107 K/s. Prior to measurements in ultra-high vacuum, the sample was cleaned by a few cycles of sputtering (Ar+, 2.5 keV, up to 210 min) and subsequent annealing at 650 K. It is worth mentioning that Ni40Ta60 is considered as a high temperature MG meaning that its glass temperature Tg is relatively high compared to other metallic glasses (≈1080 K)2728. The annealing temperature is 430 K below Tg thus re-crystallization of the glass is not expected. Additionally, all of the samples were found completely amorphous by means of X-ray diffraction and STM overviews after preparations. A typical large-scale constant-current STM image shown in Fig. 1a reveals the lack of long-range order in accordance with the amorphous state of the material, i.e. no crystalline domains, steps and grain boundaries are observed at the surface. Fig. 1b shows a typical XRD pattern of the sample which further confirms the absence of long-range order in the bulk of the material. Therefore, atomic-scale arrangements in whatsoever structures are not spatially extended at both surface and bulk of the material.


Chain-like structure elements in Ni40Ta60 metallic glasses observed by scanning tunneling microscopy.

Pawlak R, Marot L, Sadeghi A, Kawai S, Glatzel T, Reimann P, Goedecker S, Güntherodt HJ, Meyer E - Sci Rep (2015)

Amorphous nature and bonding character of the Ni40Ta60 metallic glass.(a) Typical large-scale STM overview of the Ni40Ta60 metallic glass surface, (500 × 500) nm2; I = 10 pA, Vt = 50 mV). (b) Typical XRD pattern of the amorphous metal. (c) normalized XPS spectra of Ni 2p and, (d) Ta 4f of the metallic glass with respect to the preparation cycles. The gray curves in both spectra correspond to the pure Ni and Ta metals respectively. As received samples always show a surface Ta-rich oxide layer which can be removed with preparations. After oxide removal, both Ni 2p and Ta 4f metal spectra are shifted to higher binding energies compared to their metal analogue as a consequence of their preferential bonding in the metallic glass.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4542518&req=5

f1: Amorphous nature and bonding character of the Ni40Ta60 metallic glass.(a) Typical large-scale STM overview of the Ni40Ta60 metallic glass surface, (500 × 500) nm2; I = 10 pA, Vt = 50 mV). (b) Typical XRD pattern of the amorphous metal. (c) normalized XPS spectra of Ni 2p and, (d) Ta 4f of the metallic glass with respect to the preparation cycles. The gray curves in both spectra correspond to the pure Ni and Ta metals respectively. As received samples always show a surface Ta-rich oxide layer which can be removed with preparations. After oxide removal, both Ni 2p and Ta 4f metal spectra are shifted to higher binding energies compared to their metal analogue as a consequence of their preferential bonding in the metallic glass.
Mentions: The Ni40Ta60 metallic glass used in our study were quenched in a home-built apparatus by the crucible free splat-cooling method (10 m.s−1) corresponding to a quench rate of ≈107 K/s. Prior to measurements in ultra-high vacuum, the sample was cleaned by a few cycles of sputtering (Ar+, 2.5 keV, up to 210 min) and subsequent annealing at 650 K. It is worth mentioning that Ni40Ta60 is considered as a high temperature MG meaning that its glass temperature Tg is relatively high compared to other metallic glasses (≈1080 K)2728. The annealing temperature is 430 K below Tg thus re-crystallization of the glass is not expected. Additionally, all of the samples were found completely amorphous by means of X-ray diffraction and STM overviews after preparations. A typical large-scale constant-current STM image shown in Fig. 1a reveals the lack of long-range order in accordance with the amorphous state of the material, i.e. no crystalline domains, steps and grain boundaries are observed at the surface. Fig. 1b shows a typical XRD pattern of the sample which further confirms the absence of long-range order in the bulk of the material. Therefore, atomic-scale arrangements in whatsoever structures are not spatially extended at both surface and bulk of the material.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, University of Basel, Klingelbergstr. 82, 4056 Basel, Switzerland.

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.

No MeSH data available.


Related in: MedlinePlus