A major challenge to fabricating molecular electronic circuits 1 is the difficulty of simultaneously chemically bonding molecular components to two metal electrodes. This can be accomplished by adjusting the electrode separation to match the molecular dimensions using break junctions 2-5 or by using a sharp tip to vary the electrode-surface spacing. 6 Such approaches provide detailed information on molecular conduction, but are not easily extended to planar systems required for a realistic circuit. 7Molecularly linked nanoparticles have been synthesized in solution and deposited onto surfaces 7,8 but the location of the nanoparticles in the circuit is dictated by the cross-linking structure. Ordered assemblies have been formed from functionalized nanoparticles but they are often not covalently connected. Finally, the length of the molecular linker can be matched to the nanoparticle spacing but requires the molecular size to be tailored to the separation of the nanoparticles. 10An alternative strategy is proposed based on recent observations that molecules that bind strongly to metals with low cohesive energies such as gold or copper can oligomerize by extracting metal atoms from the substrate.11-14 An example of this is the lateral self-assembly of 1,4-phenylene diisocyanide (PDI) on Au(111) that forms -(Au-PDI) n -oligomers comprising long, one-dimensional chains by extracting low-coordination gold atoms from surface defect sites. [15][16][17] The relatively short (B1.1 nm) repeat distance between gold atoms in the oligomer suggests the possibility of being able to chemically bond between gold nanoparticles with various separations by incorporating a number of repeat units until the gap is bridged. PDI has been previously proposed as a prototypical molecular electronic component, 4,6,[18][19][20][21] and theory suggests that PDI is a suitable candidate for device applications. 22This lateral self-assembly is explored by measuring the conductivity of a gold nanoparticle film on mica that has been exposed to PDI. Evaporating gold films on mica (and other insulating substrates)23-28 provides a simple method for growing isolated nanoparticles with different spacings merely by ensuring that the gold film thickness remains below a critical value, above which a continuous film is formed. The success of this approach relies on the oligomers being sufficiently mobile to bridge between nanoparticles. This mobility is illustrated in Fig. 1, which displays a typical series of 15 consecutive STM images (taken 53 seconds apart) of a saturated layer of Au-PDI chains on Au (111) showing the repeated lateral motion of an entire chain, where a line is drawn to highlight the chain motion, showing nine hopping events corresponding

The pathways for the spontaneous self-assembly of one-dimensional oligomeric chains from the adsorption of 1,4-phenylene diisocyanide (PDI) on Au(111) surface are explored using density functional theory. It has been shown previously that the chain comprises repeating −(Au−PDI)− structures. The results show that the chains form from mobile Au−PDI adatom complexes and that chains propagate by the adatom complex coupling to a terminal isocyanide group which lies close to parallel to the surface and the activation barrier for this propagation step is ∼28 kJ/mol. It is also found that the Au−PDI adatom complex is attracted to the terminal isocyanide, thereby facilitating the oligomerization process. The insights into the oligomerization pathway are used to explore whether an external electric field applied to diisocyanide functionalized molecules that contain a dipole moment can be used to align them. It is found that molecules with dipole moments of ∼1 D show significant alignment with an electric field of ∼10 8 V/m and almost complete alignment when the electric field reaches ∼10 9 V/m. This suggests that the selfassembly chemistry of dipolar diisocyanides can be used to create oriented systems.

The structure of the 1-D oligomer chains that form on a Au(111) surface following adsorption of 1,4-phenylene diisocyanide (PDI) is explored using reflection-absorption infrared spectroscopy and scanning tunneling microscopy (STM). The experimental work is complemented by first-principles density functional theory calculations, which indicate that the previously proposed gold-PDI oligomer chains in which the PDI molecule bridged gold adatoms are thermodynamically stable. In addition, the calculated vibrational modes for this structure are in excellent agreement with the experimental infrared data. The linkage of the PDI units by gold adatoms is confirmed by comparing STM images collected as a function of tip bias with images for the calculated structure by the Bardeen method.

Lubrication conditions have significant influences on the formation of tribofilms and then affect tribological behavior. In this work, the influence of tribofilm formation on the tribological behavior of textured surfaces with oval shapes was measured using a pin-on-plate tribometer. The results show that, under full lubrication, the adsorbed oil film controlled the friction and wear behavior of steel/steel tribopairs but under starved lubrication, the formation of a tribofilm significantly influenced the tribological behavior. The appropriate textured surfaces with oval-shaped dimples contributes to obtaining excellent antifriction and antiwear behavior. However, excessively high ratios of the major to the minor axis of the oval can result in high contact stresses which can destroy the tribofilm.