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Ultrathin gold nanowires : atomic structure and self-assembly- Guillaume Viau

LPCNO - INSA Toulouse


Ultrathin gold nanowires (NWs), exhibiting a diameter below 2 nm and a micrometric length, have attracted expanding interests due to their unique properties, as high surface-to-volume ratio, mechanical flexibility and remarkable conductivity properties, with applications for electrical sensors or transparent electrodes [1]. In addition, under the effect of external stress (temperature, electron beam ...) nanowires fracture, leading to the formation of mono-atomic metal chains [2].

At the LPCNO ultrathin gold NWs are grown in organic solvents containing oleylamine. Their very small diameter, very high aspect ratio (>1000) and the great importance of the ligand shell organization both on their growth and stability make these fascinating objects intermediates between metal and 1D supramolecular organization (Fig. 1). A full description of their structure and growth mechanism requires to combine in situ studies using small angle X-ray scattering (SAXS), high energy-X-ray diffraction (HE-XRD) and X-ray absorption spectroscopy (XAS).

We have shown recently that the gold nanowires do not crystallize with the expected fcc structure but adopt a tetrahedrally close packed atomic structure (tcp) [3] that could be a compromise between high atomic packing density and surface effects due to a growth strongly confined by the organic molecules. Self-organization of oleylamine coating the wires as bi-layer during the growth was evidenced [4]. Gold speciation during the growth by XAS and evidence of the molecular precursor self-assembly in the reacting medium complete the study allowing a detailed sketch of the wires formation.

Finally, we have also shown that the interwire distance can be monitored in the range 2.5-10 nm thanks to ligand exchange at the wire surface, opening the way to a supramolecular coordination chemistry of ultrathin nanowires [5].

Figure 1. Transmission electron microscopy of Au nanowires (left) ; High resolution HAADF image and model deduced from the PDF analysis of in situ HE-XRD pattern of the nanowires (right) [3].

Références

  1. B. Ni et al., Adv. Mater. 2018, 1802031.
  2. L.-M. Lacroix, R. Arenal, G. Viau. J. Am. Chem. Soc. 2014, 136, 13075-13077.
  3. J. A. Vargas, V. Petkov, El Said Nouh, R. K. Ramaamorthy, L.-M. Lacroix, R. Poteau, G. Viau, P. Lecante, R. Arenal, ACS Nano 2018, 12, 9521-9531.
  4. A. Loubat, M. Impéror-Clerc, B. Pansu, F. Meneau, B. Raquet, G. Viau, L.-M. Lacroix, Langmuir 2014, 30, 4005-4012.
  5. El Said Nouh, E. Baquero, L.-M. Lacroix, F. Delpech, R. Poteau, G. Viau, Langmuir 2017, 33, 5456-5463.

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