James N. O’Shea

Structural study of adsorption of isonicotinic acid and related molecules on rutile TiO2(110) I: XAS and STM

The adsorption of monolayers of the pyridine-carboxylic acid monomers (isonicotinic acid, nicotinic acid, and picolinic acid) on rutile TiO2(1 1 0) has been studied by means of X-ray photoemission spectroscopy. An investigation of the O 1s spectra shows that the molecular carboxylic groups are deprotonated and, hence, that the molecules bind to the surface in a bidentate mode. Moreover, the binding energy of those core levels that are related to the pyridine ring atoms shift as a function of molecule relative to the substrate O 1s and Ti 3p levels, while the position of the core levels related to emission from the carboxylic group are constant relative to the substrate levels. The molecule-dependent shifts are attributed to local intermolecular interactions that determine the proximity of adjacent molecular rings and thus the core-hole screening response of the neighbouring molecules. We propose a simple molecular arrangement for each case which satisfies the known constraints

Electrospray deposition of fullerenes in ultra-high vacuum: in situ scanning tunneling microscopy and photoemission spectroscopy

Electrospray deposition of fullerenes on gold has been successfully observed by in situ room temperature scanning tunneling microscopy and photoemission spectroscopy. Step-edge decoration and hexagonal close-packed islands with a periodicity of 1 nm are observed at low and multilayer coverages respectively, in agreement with thermal evaporation studies. Photoemission spectroscopy shows that fullerenes are being deposited in high purity and are coupling to the gold surface as for thermal evaporation. These results open a new route for the deposition of thermally labile molecules under ultra-high vacuum conditions for a range of high resolution surface science techniques.

Electrospray deposition of carbon nanotubes in vacuum

Here we report on a novel and effective technique for the deposition of carbon nanotubes onto surfaces in vacuum directly from a liquid suspension. The technique, based on in-vacuum electrospray ionization, has the potential to bridge the gap between high resolution techniques requiring ultra-high vacuum conditions, and non-volatile molecules and nanostructures such as carbon nanotubes. Atomic force microscopy of double-walled nanotubes deposited onto silicon surfaces in vacuum show individual nanotubes and low density bundles.

Single molecule magnets on a gold surface: in situ electrospray deposition, x-ray absorption and photoemission

Single molecule magnets based on the dodecamanganese (III, IV) cluster with two different types of ligand (acetate and benzoate) have been studied on the Au(111) surface. Due to the non-volatile and fragile nature of the molecules, we have used ultra-high vacuum electrospray deposition to produce a series of surface coverages from a fraction of a monolayer to multilayer films in both cases. Synchrotron radiation based electron spectroscopy has been used to study the adsorption of the molecules on the Au(111) surface and the effect that this has on the oxidation states of the manganese atoms in the core. In both cases, reduction of the core is observed due to the interaction with the surface, to essentially the same extent despite substantial differences in the size and nature of the ligand shell.

Colloidal particle foams: Templates for Au nanowire networks?

Spin coating a dilute solution of thiol-passivated Au nanoparticles onto silicon produces nanostructured cellular networks. Photoemission measurements, coupled with atomic force microscopy imaging and a statistical crystallography analysis, show that although annealing in the 500–600 K range removes the thiol surfactants surrounding the nanoparticles, the cellular morphology of the nanocrystal foam is preserved following annealing. Thus, self-assembled nanocrystal arrays may be exploited as templates for (bare) Au nanostructures on Si. Although appreciable particle diffusion during annealing does not occur, significant sintering of Au nanocrystals within the cellular network branches is observed.

Single molecule magnets with protective ligand shells on gold and titanium dioxide surfaces: In situ electrospray deposition and x-ray absorption spectroscopy

Two single molecule magnets based on the dodecamanganese (III, IV) cluster with either benzoate or terphenyl-4-carboxylate ligands, have been studied on the Au(111) and rutile TiO2(110) surfaces. We have used in situ electrospray deposition to produce a series of surface coverages from a fraction of a monolayer to multilayer films in both cases. X-ray absorption spectroscopy measured at the Mn L-edge (Mn 2p) has been used to study the effect of adsorption on the oxidation states of the manganese atoms in the core. In the case of the benzoate-functionalised complex reduction of the manganese metal centres is observed due to the interaction of the manganese core with the underlying surface. In the case of terphenyl-4-carboxylate, the presence of this much larger ligand prevents the magnetic core from interacting with either the gold or the titanium dioxide surfaces and the characteristic Mn(3+) and Mn(4+) oxidation states necessary for magnetic behaviour are preserved.

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

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.

Electrospray deposition in vacuum as method to create functionally active protein immobilization on polymeric substrates

We demonstrate in this work the deposition of a large biological molecule (fibronectin) on polymeric substrates in a high vacuum environment using an electrospray deposition system. Fibronectin was deposited and its distribution and structure investigated and retention of function (ability to promote cell adhesion) on return to liquid environment is shown. AFM was used to monitor changes in the morphology of the surface before and after fibronectin deposition, whilst the biological activity of the deposited protein is assessed through a quantitative analysis of the biomolecular adhesion and migration of fibroblast cells to the modified surfaces. For the first time we have demonstrated that using high vacuum electrospray deposition it is possible to deposit large protein molecules on polymeric surfaces whilst maintaining the protein activity. The deposition of biological molecules such as proteins with the retention of their activity onto clean well-controlled surfaces under vacuum condition, offers the possibility for future studies utilizing high resolution vacuum based techniques at the atomic and molecular scale providing a greater understanding of protein-surface interface behaviour of relevance to a wide range of applications such as in sensors, diagnostics and tissue engineering.

Insulating surface layer on single crystal K3C60

Abstract.Using angle-dependent photoemission spectra of core and valence levels we show that metallic, single crystal K3C60 is terminated by an insulating or weakly-conducting surface layer. We attribute this to the effects of strong intermolecular correlations combined with the average surface charge state. Several controversies on the electronic structure are thereby resolved.

Angle-dependent valence photoemission study of pure phase K3C60

We have carried out angle-dependent PES measurements of pure phase K3C60 films prepared in UHV. The shape of the valence spectrum shows a quite strong angle-dependence which was unobserved in previous studies. We attribute this to the important role of the light polarization. We show that there is a strong bulk contribution at the Fermi level.