Showing papers by "Peter H. Beton published in 2003"

Controlling molecular deposition and layer structure with supramolecular surface assemblies

Abstract: Selective non-covalent interactions have been widely exploited in solution-based chemistry to direct the assembly of molecules into nanometre-sized functional structures such as capsules, switches and prototype machines1,2,3,4,5. More recently, the concepts of supramolecular organization have also been applied to two-dimensional assemblies on surfaces6,7 stabilized by hydrogen bonding8,9,10,11,12,13,14, dipolar coupling15,16,17 or metal co-ordination18. Structures realized to date include isolated rows8,13,14,15, clusters9,10,18 and extended networks10,11,12,17, as well as more complex multi-component arrangements16. Another approach to controlling surface structures uses adsorbed molecular monolayers to create preferential binding sites that accommodate individual target molecules19,20. Here we combine these approaches, by using hydrogen bonding to guide the assembly of two types of molecules into a two-dimensional open honeycomb network that then controls and templates new surface phases formed by subsequently deposited fullerene molecules. We find that the open network acts as a two-dimensional array of large pores of sufficient capacity to accommodate several large guest molecules, with the network itself also serving as a template for the formation of a fullerene layer.

Assembly and Processing of Hydrogen Bond Induced Supramolecular Nanostructures

Abstract: The adsorption of a diimide derivative (NTCDI) of naphthalene tetracarboxylic dianhydride (NTCDA) on the Ag/Si(111)-√3 × √3R30° surface has been investigated using ultrahigh vacuum (UHV) scanning tunneling microscopy (STM). Hydrogen bonding, mediated by the imide groups, controls the ordering of adsorbed molecules, resulting in extended rows up to 20 nm in length with an intermolecular separation of 1.5 lattice constants. A near-identical row motif is observed in the molecular packing of crystalline NTCDI. Tip-adsorbate interactions lead to modification and repositioning of supramolecular nanostructures.

High mobility organic transistors fabricated from single pentacene microcrystals grown on a polymer film

Abstract: Isolated multilayer, bilayer, and monolayer crystals of pentacene are grown on polymer thin films. Source and drain contacts are formed to individual crystallites and transistor operation, based on the formation of an inversion layer at the pentacene/polymer interface is demonstrated for multilayers, trilayers, and bilayers. Hole inversion layers are formed with mobilities up to 1.2 cm2/V s for multilayer crystals, while a reduced mobility is observed for trilayers and bilayers.

Adsorption and manipulation of endohedral and higher fullerenes on Si ( 100 ) − 2 × 1

Abstract: The adsorption of the endohedral fullerene, $\mathrm{La}@{\mathrm{C}}_{82},$ and the higher fullerene, ${\mathrm{C}}_{84},$ on $\mathrm{Si}(100)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1$ is investigated using a scanning tunneling microscope (STM) operating in ultrahigh vacuum. Both molecules are found to adsorb directly above the dimer rows that are formed on the $\mathrm{Si}(100)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1$ surface, as well as in trough sites midway between dimer rows. Adsorption above dimer rows, not observed for ${\mathrm{C}}_{60},$ is attributed to the larger radius of curvature of these fullerene cages. The response of $\mathrm{La}@{\mathrm{C}}_{82}$ to manipulation by the tip of the STM is also investigated. Molecules in either adsorption site may be manipulated with a threshold gap impedance \ensuremath{\sim}1.0 G\ensuremath{\Omega}. Owing to a near-commensurability between the molecular diameter of $\mathrm{La}@{\mathrm{C}}_{82}$ and the lattice constant of the Si(100) surface, close-packed arrangements of molecules may be formed.

Competing interactions of noble metals and fullerenes with the Si(111)7×7 surface

Abstract: Synchrotron-based photoelectron spectroscopy (PES) has been used to investigate the interaction of atomic gold and silver with a covalently bound C60-monolayer adsorbed on Si(111)7×7. In contrast to the relatively benign interaction of silver with the C60/Si(111)7×7 surface, core-level photoemission data reveal a strong interaction of gold with the underlying silicon despite the presence of a chemisorbed fullerene monolayer. The Si 2p PES data exhibit dramatic changes consistent with the formation of a gold silicide, which is also evident from the corresponding Au 4f spectra. Valence band photoemission also reveals the absence of any density of states at the Fermi level following the adsorption of either metal, indicating a negligible transfer of electrons from the adsorbed metal to the C60 cage.