Jason I. Henderson

Self-Assembly of a Two-Dimensional Superlattice of Molecularly Linked Metal Clusters

Close-packed planar arrays of nanometer-diameter metal clusters that are covalently linked to each other by rigid, double-ended organic molecules have been self-assembled. Gold nanocrystals, each encapsulated by a monolayer of alkyl thiol molecules, were cast froma colloidal solution onto a flat substrate to form a close-packed cluster monolayer. Organic interconnects (aryl dithiols or aryl di-isonitriles) displaced the alkyl thiol molecules and covalently linked adjacent clusters in the monolayer to form a two-dimensional superlattice of metal quantum dots coupled by uniform tunnel junctions. Electrical conductance through such a superlattice of 3.7-nanometer-diameter gold clusters, deposited on a SiO2 substrate in the gap between two gold contacts and linked by an aryl di-isonitrile [1,4-di(4-isocyanophenylethynyl)-2-ethylbenzene], exhibited nonlinear Coulomb charging behavior.

Coulomb Staircase at Room Temperature in a Self-Assembled Molecular Nanostructure

Double-ended aryl dithiols [α,α′-xylyldithiol (XYL) and 4,4′-biphenyldithiol] formed self-assembled monolayers (SAMs) on gold(111) substrates and were used to tether nanometer-sized gold clusters deposited from a cluster beam. An ultrahigh-vacuum scanning tunneling microscope was used to image these nanostructures and to measure their current-voltage characteristics as a function of the separation between the probe tip and the metal cluster. At room temperature, when the tip was positioned over a cluster bonded to the XYL SAM, the current-voltage data showed “Coulomb staircase” behavior. These data are in good agreement with semiclassical predictions for correlated single-electron tunneling and permit estimation of the electrical resistance of a single XYL molecule (∼18 ± 12 megohms).

CONDUCTANCE SPECTRA OF MOLECULAR WIRES

A relatively simple and straightforward procedure for characterizing molecular wires is to measure the conductance spectrum by forming a self-assembled ordered monolayer (SAM) on a metallic surface and using a high scanning-tunneling microscope resolution (STM) tip as the other contact. We find that the conductance spectrum (dI/dV vs. V) can be understood fairly well in terms of a relatively simple model, provided the spatial profile of the electrostatic potential under bias is properly accounted for. The effect of the potential profile is particularly striking and can convert a symmetric conductor into a rectifier and vice versa. The purpose of this paper is to (1) describe the theoretical model in detail, (2) identify the important parameters that influence the spectra and show how these parameters can be deduced directly from the conductance spectrum, and (3) compare the theoretical prediction with experimentally measured conductance spectra for xylyl dithiol and phenyl dithiol.

Negative differential resistance in the scanning-tunneling spectroscopy of organic molecules

In the interpretation of scanning-tunneling spectroscopy data on molecular nanostructures the tunneling conductance is often assumed to be proportional to the local density of states of the molecule. This precludes the possibility of observing negative differential resistance (NDR). We report here the observation of NDR in the current-voltage

Synthesis of neutral nickel catalysts for ethylene polymerization ? the influence of ligand size on catalyst stabilityElectronic supplementary information (ESI) available: experimental protocol for (tmeda)Ni(Me)2 and compounds 3,4,7,8,9 and 10 and 1H-NMR magnetization transfer data for compound 7. See http://www.rsc.org/suppdata/cc/b3/b306701g/

(I\ensuremath{-}V)

Self-assembled monolayers of dithiols, diisocyanides, and isocyanothiols on gold: ‘chemically sticky’ surfaces for covalent attachment of metal clusters and studies of interfacial electron transfer

characteristics of a self-assembled monolayer of

Room temperature Coulomb blockade and Coulomb staircase from self‐assembled nanostructures

4\ensuremath{-}p\ensuremath{-}\mathrm{terphenylthiol}

Resistance of molecular nanostructures

molecules on the Au(111) surface measured using a platinum tip. We argue that the NDR arises from narrow features in the local density of states of the tip apex atom and show that depending on the electrostatic potential profile across the system, NDR could be observed in one or both bias directions.

Synthesis of nanoscale arrays of coupled metal dots

A facile synthesis of nickel salicylaldimine complexes with labile dissociating ligands is described. In addition to producing highly active ethylene polymerization catalysts, important insights into the effect of ligand size on catalyst stability and information on the mechanism of polymerization are provided.

DiPyMe in SDS Micelles: Artifacts and Their Implications in the Interpretation of Micellar Properties

Abstract The preparation of self-assembled monolayers (SAMs) of the double-ended dithiols 4,4−biphenyldithiol, and αα- p -xylidithiol, the double-ended diisocyanides 1,4-phenylenediisocyanide, 4,4′-biphenyldiisocyanide, 4,4′- p -terphenyldiisocyanide, 1,6-hexanediisocyanide, 1,12-dodecanediisocyanide, and 1,4-di(4-isocyano-phenylethynyl)-2-ethylbenzene, and the 4-sulfido phenyl isocyanide capped trinuclear nickel cluster 4-( μ 3 -iodo-tris(bis(diphenylphosphino)methane)-trinickel-(isocyano)phenylenesulfide by direct adsorption or by displacement of a pre-existing SAM of 1-octadecanethiol on gold is reported. The SAMs were characterized using reflection-absorption infrared spectroscopy (RAIR), optical ellipsometry, and advancing contact-angle ( θ a ) measurements. The substitution chemistry of SAMs was found to be irreversible. The dithiols and aryl diisocyanides were found to form SAMs with only one functional group attached to the surface. The SAMs of dithiols were used to covalently attach nanometer scale gold clusters to the exposed thiol surface of the SAM. Scanning tunneling microscopy (STM) was used to image these immobilized gold clusters. The diisocyanides have been used to covalently anchor trinuclear nickel clusters. The SAM of the 4-sulfido phenyl isocyanide capped trinuclear nickel cluster 4-( μ 3 -iodo-tris(bis(diphenylphosphino)methane)-trinickel-(isocyano)-phenylenesulfide, was studied by cyclic voltammetry. The electron acceptors methylviologen (MV 2+ ) and the methyl ester of cobaltocenium [MeCOOCpCp] + [PF 6 ] − were used to demonstrate rectification in the interfacial electron transfer from nickel cluster SAM modified gold electrodes to the electron acceptors.