Charge redistribution at heterogeneous interfaces is a fundamental aspect of surface chemistry. Manipulating the amount of charges and the magnitude of dipole moments at the interface in a controlled way has attracted tremendous attention for its potential to modify the activity of heterogeneous catalysts in catalyst design. Two-dimensional ultrathin silica films with well-defined atomic structures have been recently synthesized and proposed as model systems for heterogeneous catalysts studies. R. Wlodarczyk et al. (Phys. Rev. B, 85, 085403 (2012)) have demonstrated that the electronic structure of silica/ Ru(0001) can be reversibly tuned by changing the amount of interfacial chemisorbed oxygen. Here we carried out systematic investigations to understand the underlying mechanism through which the electronic structure at the silica/Ru(0001) interface can be tuned. As corroborated by both in situ X-ray photoelectron spectroscopy and density functional theory calculations, the observed interface energy level alignments strongly depend on the surface and interfacial charge transfer induced dipoles at the silica/ Ru(0001) heterojunction. These observations may help to understand variations in catalytic performance of the model system from the viewpoint of the electronic properties at the confined space between the silica bilayer and the Ru(0001) surface. The same behavior is observed for the aluminosilicate bilayer, which has been previously proposed as a model system for zeolites.Jian-Qiang Zhong and Mengen Wang contributed equally to this work.

The adsorption of CO on a saturated overlayer of 1,4-phenylene diisocyanide (PDI) adsorbed on a Au(111) surface at 300 K is studied using scanning tunneling microscopy (STM), density functional theory (DFT) calculations and reflection absorption infrared spectroscopy (RAIRS). The PDI forms closed-packed rows of gold-PDI chains by extracting gold atoms from the Au(111) substrate. They are imaged by STM and the structure calculated by DFT. The adsorption of CO is studied on the low-coordination gold sites formed on the PDI-covered surface where it adsorbs exhibiting a CO stretching frequency of 2004 cm -1 , consistent with adsorption on an atop site. It is found that CO is stable on heating the sample to *150 K and is only removed from the surface by heating to *180 K. Since low-coordination gold atoms are suggested to be the active catalytic sites on supported gold nanoclusters, ''embossing'' the surface to form similar lowcoordination sites using PDI might offer a strategy for tailoring the catalytic activity of gold.

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.

The confinement of noble gases on nanostructured surfaces, in contrast to bulk materials, at non-cryogenic temperatures represents a formidable challenge. In this work, individual Ar atoms are trapped at 300 K in nano-cages consisting of (alumino)silicate hexagonal prisms forming a two-dimensional array on a planar surface. The trapping of Ar atoms is detected in situ using synchrotron-based ambient pressure X-ray photoelectron spectroscopy. The atoms remain in the cages upon heating to 400 K. The trapping and release of Ar is studied combining surface science methods and density functional theory calculations. While the frameworks stay intact with the inclusion of Ar atoms, the permeability of gasses (for example, CO) through them is significantly affected, making these structures also interesting candidates for tunable atomic and molecular sieves. These findings enable the study of individually confined noble gas atoms using surface science methods, opening up new opportunities for fundamental research.

The oxidation and reduction of Ru(0001) surfaces at the confined space between two-dimensional nanoporous silica frameworks and Ru(0001) have been investigated using synchrotron-based ambient pressure X-ray photoelectron spectroscopy (AP-XPS). The porous nature of the frameworks and the weak interaction between the silica and the ruthenium substrate allow oxygen and hydrogen molecules to go through the nanopores and react with the metal at the interface between the silica framework and the metal surface. In this work, three types of two-dimensional silica frameworks have been used to study their influence in the oxidation and reduction of the ruthenium surface at elevated pressures and temperatures. These frameworks are bilayer silica (0.5 nm thick), bilayer aluminosilicate (0.5 nm thick), and zeolite MFI nanosheets (3 nm thick). It is found that the silica frameworks stay essentially intact under these conditions, but they strongly affect the oxidation of ruthenium, with the 0.5 nm thick aluminosilicate bilayer completely inhibiting the oxidation. The latter is believed to be related to the lower chemisorbed oxygen content arising from electrostatic interactions between the negatively charged aluminosilicate framework and the Ru(0001) substrate.

Infiltration synthesis, the atomic-layer-deposition-based organic-inorganic material hybridization technique that enables unique hybrid composites with improved material properties and inorganic nanostructures replicated from polymer templates, is shown to be driven by the binding reaction between reactive chemical groups of polymers and perfusing vapor-phase material precursors. Here, we discover that residual solvent molecules from polymer processing can react with infiltrating material precursors enabling the infiltration synthesis of metal oxides in a non-reactive polymer. The systematic study, combining in-situ quartz crystal microgravimetry, polarization-modulated infrared reflection-absorption spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, shows that the ZnO infiltration synthesis in nominally non-reactive SU-8 polymer is mediated by residual processing solvent cyclopentanone, a cyclic ketone whose Lewis-basic terminal carbonyl group can react with the infiltrating Lewis-acidic Zn precursor diethylzinc (DEZ). In addition, we find favorable roles of residual epoxy rings in the SU-8 film in further assisting the infiltration synthesis of ZnO. The discovered rationale not only improves the understanding of infiltration synthesis mechanism but also potentially expands its application to more diverse polymer systems for the generation of unique functional organic-inorganic hybrids and inorganic nanostructures.