title: Influence of molecular ordering on electrical and friction properties of ω-(trans-4-stilbene)alkylthiol self-assembled monolayers on Au(111).
abstract: The electrical and friction properties of ω-(trans-4-stilbene)alkylthiol self-assembled monolayers (SAMs) on Au(111) were investigated using atomic force microscopy (AFM) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). The sample surface was uniformly covered with a molecular film consisting of very small grains. Well-ordered and flat monolayer islands were formed after the sample was heated in nitrogen at 120 °C for 1 h. While lattice resolved AFM images revealed a crystalline phase in the islands, the area between islands showed no order. The islands exhibit substantial reduction (50%) in friction, supporting the existence of good ordering. NEXAFS measurements revealed an average upright molecular orientation in the film, both before and after heating, with a narrower tilt-angle distribution for the heated fim. Conductance-AFM measurements revealed a 2 orders of magnitude higher conductivity on the ordered islands than on the disordered phase. We propose that the conductance enhancement is a result of a better π-π stacking between the trans-stilbene molecular units as a result of improved ordering in islands.
authors.affiliation: Applied Science and Technology Graduate Group, University of California, Berkeley, California 94720, USA.
authors.forename: Yabing
authors.initials: Y
authors.lastname: Qi
authors.forename: Xiaosong
authors.initials: X
authors.lastname: Liu
authors.forename: B L M
authors.initials: BL
authors.lastname: Hendriksen
authors.forename: V
authors.initials: V
authors.lastname: Navarro
authors.forename: Jeong Y
authors.initials: JY
authors.lastname: Park
authors.forename: Imma
authors.initials: I
authors.lastname: Ratera
authors.forename: J M
authors.initials: JM
authors.lastname: Klopp
authors.forename: C
authors.initials: C
authors.lastname: Edder
authors.forename: Franz J
authors.initials: FJ
authors.lastname: Himpsel
authors.forename: J M J
authors.initials: JM
authors.lastname: Fréchet
authors.forename: Eugene E
authors.initials: EE
authors.lastname: Haller
authors.forename: Miquel
authors.initials: M
authors.lastname: Salmeron
mesh_terms: D004583:Electrons; D006046:Gold / Q000737:chemistry*; D008567:Membranes, Artificial; D010316:Particle Size; D013438:Sulfhydryl Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D008567:Membranes, Artificial; D013438:Sulfhydryl Compounds; D006046:Gold