title: A stable, quasi-2D modification of silver: optical, electronic, vibrational and mechanical properties, and first principles calculations.
abstract: We report the optical, electronic, vibrational and mechanical properties of a stable, anisotropic, hexagonal (4H) form of silver. First principles calculations based on density functional theory were used to simulate the phonon dispersion curves and electronic band structure of 4H-Ag. The phonon dispersion data at 0 K do not contain unstable phonon modes, thereby confirming that it is a locally stable structure. The Fermi surface of the 4H phase differs in a subtle way from that of the cubic phase. Experimental measurements indicate that, when compared to the commonly known face-centered cubic (3C) form of silver, the 4H-Ag form shows a 130-fold higher, strongly anisotropic, in-plane resistivity and a much lower optical reflectance with a pronounced surface plasmon contribution that imparts a distinctive golden hue to the material. Unlike common silver, the lower symmetry of the 4H-Ag structure allows it to be Raman active. Mechanically, 4H-Ag is harder, more brittle and less malleable. Overall, this novel, poorly metallic, anisotropic, darker and harder crystallographic modification of silver bears little resemblance to its conventional counterpart.
authors.affiliation: Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Mumbai 400005, India.
authors.forename: Indrani
authors.initials: I
authors.lastname: Chakraborty
authors.forename: Sharmila N
authors.initials: SN
authors.lastname: Shirodkar
authors.forename: Smita
authors.initials: S
authors.lastname: Gohil
authors.forename: Umesh V
authors.initials: UV
authors.lastname: Waghmare
authors.forename: Pushan
authors.initials: P
authors.lastname: Ayyub