The dramatic expansion of the electronics industry over the past 40 years has been based on the progressive reduction in size of the silicon-based semiconductor components of integrated circuits. The miniaturisation of semi-conductor circuits cannot, however, continue indefinitely, and we are rapidly approaching the stage where quantum effects will prevent further dramatic improvements in computer performance using existing technology. As a result, the field of molecular electronics, which seeks to identify and develop much smaller molecular analogues of the transistors that make up integrated circuits, has expanded rapidly over the past few years. Recent studies suggested that extended metal atom chains (EMAC) may have many potential applications in molecular electronics, but it is clear that this potential can only be realised if we establish a link between the fundamental electronic properties of these systems and the transport of electrons. For this reason the ultimate goal of this thesis is to relate the electronic structure of extended metal chains to their electron transport properties. We address the problem using non-equilibrium Green’s function, in conjugation with density functional theory. In the results sections of this thesis we present calculations on tricobalt, trichromium and trinickel chains. Our data suggested that in the trimetal chains, the dominant electron transport channel is the σ manifold, while the π systems establish the contact with the electrodes. The implication of this is that even when the highly polarized π channels are strongly rehybridised by the applied electric field, current flow is not affected. In the trichromium systems we find that the distortion of the chain away from the symmetric equilibrium structure does not perturb the current flow but rather enhances it. Our rather counter intuitive conclusion is therefore that ‘broken wires’ (highly unsymmetric) are more efficient conductors than their symmetric counterparts. We have performed calculation on longer penta- and heptacobalt structures chains to establish the extent to which longer structures attenuate the conductance. Our calculations show significant oscillations of the conductance due to development of a one-dimensional band structure about the Fermi level. The evolution of the electron transport properties in cobalt chains with different length is a complex one, but it is clear that narrowing the band gap in longer chains makes it increasingly likely that the Fermi level will be in resonance with one or more of the orbitals of the extended metal atom chain.

Thesis (Ph. D.)--Drexel University, 2004. / Includes abstract and vita. Includes bibliographical references (leaves 93-103).

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2006. / Dr. C. P. Wong, Committee Member ; Dr. C. David Sherrill, Committee Member ; Dr. Thomas M. Orlando, Committee Member ; Dr. Mostafa A. El-Sayed, Committee Member ; Dr. Robert M. Dickson, Committee Chair.

The anion-intercalation chemistries of graphite have the potential to construct batteries with promising energy and power breakthroughs. Here, we report the use of an ultrathin, positively charged two-dimensional poly(pyridinium salt) membrane (C2DP) as the graphite electrode skin to overcome the critical durability problem. Large-area C2DP enables the conformal coating on the graphite electrode, remarkably alleviating the electrolyte. Meanwhile, the dense face-on oriented single crystals with ultrathin thickness and cationic backbones allow C2DP with high anion-transport capability and selectivity. Such desirable anion-transport properties of C2DP prevent the cation/solvent co-intercalation into the graphite electrode and suppress the consequent structure collapse. An impressive PF6−-intercalation durability is demonstrated for the C2DP-covered graphite electrode, with capacity retention of 92.8% after 1000 cycles at 1 C and Coulombic efficiencies of > 99%. The feasibility of constructing artificial ion-regulating electrode skins with precisely customized two-dimensional polymers offers viable means to promote problematic battery chemistries.

Dans le cadre du concept de stockage de déchets radioactifs à vie longue en couche géologique profonde développé par l'Andra, l’IRSN mène une étude in situ sur la Station Expérimentale de Tournemire, en collaboration avec EDF afin de déterminer les interactions acier/argilite dans un contexte naturel. Au terme de 10 ans d’interaction, deux forages ont été sur-carottés afin de caractériser les transformations de l’argilite de Tournemire au contact d’aciers carbone et inoxydables et de comparer les phénomènes réactifs mis en évidence et ceux induits par des simulations numériques par des codes de calcul géochimique et couplant chimie-transport.Les échantillons argilite/acier carbone montrent une importante corrosion du disque d’acier. Le fer libéré sous la forme d’auréoles et dans les fissures de la roche perturbe l’argilite au contact entraînant des modifications minéralogiques et structurales. La précipitation d’oxydes de fer ainsi qu’une dissolution de la calcite et des feuillets smectitiques des interstratifiés I/S sont identifiés. Une zonation métal/métal corrodé/argilite perturbée/argilite saine est mise en évidence et des variations de porosité sont observées marquant les interfaces entre deux zones. Les simulations géochimiques montrent que l’essentiel des modifications est rapidement initié lors de la mise en place du système et que l’oxygène piégé à la fermeture du système est consommé par la corrosion des aciers mais surtout qu’il diffuse dans le matériau encaissant par gradient de concentration.Les échantillons argilite/acier inoxydable présentent une très faible corrosion par piqûration de l’acier. La minéralogie de l’argilite ne semble pas perturbée au cont / Within the framework of a long lived radioactive waste storage concept in deep geological layer developed by Andra, IRSN leads an in situ study on the Experimental Station of Tournemire, in association with EDF to determine the interactions steel/argillite in a natural context. After 10 years of interaction, two drillings overcoring performed to characterize the processings of the Tournemire argillite in contact with carbon and stainless steels and to compare reactive phenomena highlighted and those induced by simulations tools combining chemistry and transport.Argillite/carbon steel samples show a significant corrosion of steel disk. Iron released, in the form of rings and cracks in the rock, disrupts the argillite in contact resulting in mineralogical and structural changes. Iron oxides precipitation and a calcite and smectitic leaf of mixed-layers I/S dissolution are identified. A succession of areas: metal/metal corroded/argillite disturbed/argillite is highlighted and porosity variations are observed on the interfaces between two areas. Geochemical simulations show that major changes are initiated speedly during establishment of the system and the oxygen trapped in the closed system is consumed by the corrosion of steel but mostly it diffuses into the surrounding material through concentration gradient.Argillite/stainless steel samples have a very low pitting corrosion of steel disk. This does not seem to affect the mineralogy of the argillite in contact.