title: Spin transition in arrays of gold nanoparticles and spin crossover molecules.
abstract: We investigate if the functionality of spin crossover molecules is preserved when they are assembled into an interfacial device structure. Specifically, we prepare and investigate gold nanoparticle arrays, into which room-temperature spin crossover molecules are introduced, more precisely, [Fe(AcS-BPP)2](ClO4)2, where AcS-BPP = (S)-(4-{[2,6-(dipyrazol-1-yl)pyrid-4-yl]ethynyl}phenyl)ethanethioate (in short, Fe(S-BPP)2). We combine three complementary experiments to characterize the molecule-nanoparticle structure in detail. Temperature-dependent Raman measurements provide direct evidence for a (partial) spin transition in the Fe(S-BPP)2-based arrays. This transition is qualitatively confirmed by magnetization measurements. Finally, charge transport measurements on the Fe(S-BPP)2-gold nanoparticle devices reveal a minimum in device resistance versus temperature, R(T), curves around 260-290 K. This is in contrast to similar networks containing passive molecules only that show monotonically decreasing R(T) characteristics. Backed by density functional theory calculations on single molecular conductance values for both spin states, we propose to relate the resistance minimum in R(T) to a spin transition under the hypothesis that (1) the molecular resistance of the high spin state is larger than that of the low spin state and (2) transport in the array is governed by a percolation model.
authors.affiliation: †Huygens-Kamerlingh Onnes Laboratory, Leiden Institute of Physics, Leiden University P.O. Box 9504, 2300 RA Leiden, The Netherlands.
authors.forename: Edwin J
authors.initials: EJ
authors.lastname: Devid
authors.affiliation: ‡Centro de Química e Bioquímica (CQB), Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal.|∥Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Paulo N
authors.initials: PN
authors.lastname: Martinho
authors.affiliation: §Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-41296 Göteborg, Sweden.
authors.forename: M Venkata
authors.initials: MV
authors.lastname: Kamalakar
authors.affiliation: ∥Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.|◊Department of Inorganic Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinskeho 9, SK-812 37, Bratislava, Slovakia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Šalitroš
authors.affiliation: ⊥School of Chemical Sciences, Dublin City University, Dublin 9, Ireland.
authors.forename: Úna
authors.initials: Ú
authors.lastname: Prendergast
authors.affiliation: #Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), CNRS UMR 7504, Laboratory NIE, Université de Strasbourg, 23 Rue du Loess, 67034 Strasbourg, France.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Dayen
authors.affiliation: ∥Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Velimir
authors.initials: V
authors.lastname: Meded
authors.affiliation: ⊥School of Chemical Sciences, Dublin City University, Dublin 9, Ireland.
authors.forename: Tibebe
authors.initials: T
authors.lastname: Lemma
authors.affiliation: ∥Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.|¶Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Ciudad Universitaria, E-28040 Madrid, Spain.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: González-Prieto
authors.affiliation: ∥Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.|△Institut für Theorie der Kondensierten Materie, Karlsruhe Institute of Technology (KIT), Wolfgang-Gaede-Straße 1, D-76128 Karlsruhe, Germany.
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Evers
authors.affiliation: ⊥School of Chemical Sciences, Dublin City University, Dublin 9, Ireland.
authors.forename: Tia E
authors.initials: TE
authors.lastname: Keyes
authors.affiliation: ∥Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.|#Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), CNRS UMR 7504, Laboratory NIE, Université de Strasbourg, 23 Rue du Loess, 67034 Strasbourg, France.
authors.forename: Mario
authors.initials: M
authors.lastname: Ruben
authors.affiliation: #Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), CNRS UMR 7504, Laboratory NIE, Université de Strasbourg, 23 Rue du Loess, 67034 Strasbourg, France.
authors.forename: Bernard
authors.initials: B
authors.lastname: Doudin
authors.affiliation: †Huygens-Kamerlingh Onnes Laboratory, Leiden Institute of Physics, Leiden University P.O. Box 9504, 2300 RA Leiden, The Netherlands.
authors.forename: Sense Jan
authors.initials: SJ
authors.lastname: van der Molen
keywords: gold nanoparticles; molecular charge transport devices; self-assembly; spin crossover molecules; two-dimensional arrays