title: Thermoelectricity at the molecular scale: a large Seebeck effect in endohedral metallofullerenes.
abstract: Single molecule devices provide a unique system to study the thermoelectric energy conversion at an atomistic level and can provide valuable information for the design of organic thermoelectric materials. Here we present a comprehensive study of the thermoelectric transport properties of molecular junctions based on C(82), Gd@C(82), and Ce@C(82). We combine precise scanning tunneling microscope break-junction measurements of the thermopower and conductance with quantitatively accurate self-energy-corrected first-principles transport calculations. We find that all three fullerene derivatives give rise to a negative thermopower (n-conducting). The absolute value, however, is much larger for the Gd@C(82) and Ce@C(82) junctions. The conductance, on the other hand, remains comparable for all three systems. The power factor determined for the Gd@C(82) based junction is so far the highest obtained for a single-molecule device. Although the encapsulated metal atom does not directly contribute to the transport, we show that the observed enhancement of the thermopower for Gd@C(82) and Ce@C(82) is elucidated by the substantial changes in the electronic- and geometrical structure of the fullerene molecule induced by the encapsulated metal atom.
authors.affiliation: Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan. tada@molectronics.jp.
authors.forename: See Kei
authors.initials: SK
authors.lastname: Lee
authors.forename: Marius
authors.initials: M
authors.lastname: Buerkle
authors.forename: Ryo
authors.initials: R
authors.lastname: Yamada
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Asai
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Tada