title: Electrum, the Gold-Silver Alloy, from the Bulk Scale to the Nanoscale: Synthesis, Properties, and Segregation Rules.
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.
authors.affiliation: Department of Physics & Astronomy, University of Texas at San Antonio , One UTSA Circle, San Antonio, Texas 78249, United States.
authors.forename: Grégory
authors.initials: G
authors.lastname: Guisbiers
authors.affiliation: Department of Physics & Astronomy, University of Texas at San Antonio , One UTSA Circle, San Antonio, Texas 78249, United States.|Institute of Physics, Universidad Nacional Autónoma de Mexico , A. P. 20-364 Distrito Federal C.P. 01000 Mexico City, Mexico.
authors.forename: Rubén
authors.initials: R
authors.lastname: Mendoza-Cruz
authors.affiliation: Department of Physics & Astronomy, University of Texas at San Antonio , One UTSA Circle, San Antonio, Texas 78249, United States.|Institute of Physics, Universidad Nacional Autónoma de Mexico , A. P. 20-364 Distrito Federal C.P. 01000 Mexico City, Mexico.
authors.forename: Lourdes
authors.initials: L
authors.lastname: Bazán-Díaz
authors.affiliation: Department of Physics & Astronomy, University of Texas at San Antonio , One UTSA Circle, San Antonio, Texas 78249, United States.
authors.forename: J Jesús
authors.initials: JJ
authors.lastname: Velázquez-Salazar
authors.affiliation: Department of Physics & Astronomy, University of Texas at San Antonio , One UTSA Circle, San Antonio, Texas 78249, United States.
authors.forename: Rafael
authors.initials: R
authors.lastname: Mendoza-Perez
authors.affiliation: Advanced Materials Department, IPICYT, A.C., Camino Presa San José 2055, Lomas 4a Secc. 78216 San Luis Potosi, Mexico.
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Robledo-Torres
authors.affiliation: Advanced Materials Department, IPICYT, A.C., Camino Presa San José 2055, Lomas 4a Secc. 78216 San Luis Potosi, Mexico.
authors.forename: José-Luis
authors.initials: JL
authors.lastname: Rodriguez-Lopez
authors.affiliation: Institute of Physics, Universidad Autónoma de San Luis Potosi , Alvaro Obregón 64000, Centro, San Luis Potosi Mexico.
authors.forename: Juan Martín
authors.initials: JM
authors.lastname: Montejano-Carrizales
authors.affiliation: Department of Physics & Astronomy, University of Texas at San Antonio , One UTSA Circle, San Antonio, Texas 78249, United States.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Whetten
authors.affiliation: Department of Physics & Astronomy, University of Texas at San Antonio , One UTSA Circle, San Antonio, Texas 78249, United States.
authors.forename: Miguel
authors.initials: M
authors.lastname: José-Yacamán
mesh_terms: D000497:Alloys / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D036103:Nanotechnology; D010316:Particle Size; D044367:Phase Transition; D012834:Silver / Q000737:chemistry*; D020349:Surface Plasmon Resonance; D013696:Temperature; D013816:Thermodynamics
chemical_list: D000497:Alloys; D012834:Silver; D006046:Gold
keywords: aberration corrected electron microscopy; nanothermodynamics; noble metals; optical properties; phase diagram; polyhedra; surface segregation; thermal properties