title: Molecular design and control of fullerene-based bi-thermoelectric materials.
abstract: Molecular junctions are a versatile test bed for investigating nanoscale thermoelectricity and contribute to the design of new cost-effective environmentally friendly organic thermoelectric materials. It was suggested that transport resonances associated with discrete molecular levels could play a key role in thermoelectric performance, but no direct experimental evidence has been reported. Here we study single-molecule junctions of the endohedral fullerene Sc3N@C80 connected to gold electrodes using a scanning tunnelling microscope. We find that the magnitude and sign of the thermopower depend strongly on the orientation of the molecule and on applied pressure. Our calculations show that Sc3N inside the fullerene cage creates a sharp resonance near the Fermi level, whose energetic location, and hence the thermopower, can be tuned by applying pressure. These results reveal that Sc3N@C80 is a bi-thermoelectric material, exhibiting both positive and negative thermopower, and provide an unambiguous demonstration of the importance of transport resonances in molecular junctions.
authors.affiliation: Departamento de Física de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain.|Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia, E-28049 Madrid, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Rincón-García
authors.affiliation: Department of Physics, Lancaster University, Lancaster LA1 4YW, UK.|Department of Physics, College of Education for Pure Science, Tikrit University, Tikreet 34001, Iraq.
authors.forename: Ali K
authors.initials: AK
authors.lastname: Ismael
authors.affiliation: Departamento de Física de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain.
authors.forename: Charalambos
authors.initials: C
authors.lastname: Evangeli
authors.affiliation: Department of Physics, Lancaster University, Lancaster LA1 4YW, UK.
authors.forename: Iain
authors.initials: I
authors.lastname: Grace
authors.affiliation: Departamento de Física de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain.|Instituto Universitario de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, E-28049 Madrid, Spain.
authors.forename: Gabino
authors.initials: G
authors.lastname: Rubio-Bollinger
authors.affiliation: Department of Materials, University of Oxford, Oxford OX1 3PH, UK.
authors.forename: Kyriakos
authors.initials: K
authors.lastname: Porfyrakis
authors.affiliation: Departamento de Física de la Materia Condensada and Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049 Madrid, Spain.|Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia, E-28049 Madrid, Spain.|Instituto Universitario de Ciencia de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, E-28049 Madrid, Spain.
authors.forename: Nicolás
authors.identifier: http://orcid.org/0000-0003-4840-5851
authors.initials: N
authors.lastname: Agraït
authors.affiliation: Department of Physics, Lancaster University, Lancaster LA1 4YW, UK.
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Lambert
mesh_terms: D004553:Electric Conductivity; D004563:Electrochemistry; D004566:Electrodes; D037741:Fullerenes / Q000737:chemistry*; D006358:Hot Temperature; D008422:Materials Testing; D016252:Microscopy, Scanning Tunneling; D049329:Nanostructures; D012538:Scandium / Q000737:chemistry
chemical_list: D037741:Fullerenes; D012538:Scandium