Electrum, the gold-silver alloy, from the bulk scale to the nanoscale: Synthesis, properties, and segregation rules

Grégory Guisbiers, Rubén Mendoza-Cruz, Lourdes Bazán-Díaz, J. Jesús Velázquez-Salazar, Rafael Mendoza-Perez, José Antonio Robledo-Torres, José Luis Rodriguez-Lopez, Juan Martín Montejano-Carrizales, Robert L. Whetten, Miguel José-Yacamán

Research output: Contribution to journalArticlepeer-review

126 Scopus citations

Abstract

The alloy Au-Ag system is an important noble bimetallic phase, both historically (as "Electrum") and now especially in nanotechnology, as it is applied in catalysis and nanomedicine. To comprehend the structural characteristics and the thermodynamic stability of this alloy, a knowledge of its phase diagram is required that considers explicitly its size and shape (morphology) dependence. However, as the experimental determination remains quite challenging at the nanoscale, theoretical guidance can provide significant advantages. Using a regular solution model within a nanothermodynamic approach to evaluate the size effect on all the parameters (melting temperature, melting enthalpy, and interaction parameters in both phases), the nanophase diagram is predicted. Besides an overall shift downward, there is a "tilting" effect on the solidus-liquidus curves for some particular shapes exposing the (100) and (110) facets (cube, rhombic dodecahedron, and cuboctahedron). The segregation calculation reveals the preferential presence of silver at the surface for all the polyhedral shapes considered, in excellent agreement with the latest transmission electron microscopy observations and energy dispersive spectroscopy analysis. By reviewing the nature of the surface segregated element of different bimetallic nanoalloys, two surface segregation rules, based on the melting temperatures and surface energies, are deduced. Finally, the optical properties of Au-Ag nanoparticles, calculated within the discrete dipole approximation, show the control that can be achieved in the tuning of the local surface plasmon resonance, depending of the alloy content, the chemical ordering, the morphology, the size of the nanoparticle, and the nature of the surrounding environment.

Original languageEnglish (US)
Pages (from-to)188-198
Number of pages11
JournalACS Nano
Volume10
Issue number1
DOIs
StatePublished - Jan 26 2016
Externally publishedYes

Keywords

  • Aberration corrected electron microscopy
  • Nanothermodynamics
  • Noble metals
  • Optical properties
  • Phase diagram
  • Polyhedral
  • Surface segregation
  • Thermal properties

ASJC Scopus subject areas

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

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