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On-surface synthesis (Ullmann-type coupling) of functionalised DPP monomers on Au(111); STM characterisation reveals alkyl chains drive alignment of molecular wires.

Alginate hydrogel beads were loaded with bimetallic NiPt nanoparticles by in situ reduction of the respective polymer matrix containing precursor metallic ions using a NaBH

Lithium iron phosphate (LiFePO4, LFP) is the most promising cathode material for use in safe electric vehicles (EVs), due to its long cycle stability, low cost, and low toxicity, but it suffers from low conductivity and ion diffusion. In this work, we present a simple method to obtain LFP/carbon (LFP/C) composites with different types of NC: cellulose nanocrystal (CNC) and cellulose nanofiber (CNF). Microwave-assisted hydrothermal synthesis was used to obtain LFP with nanocellulose inside the vessel, and the final LFP/C composite was achieved by heating the mixture under a N2 atmosphere. The resulting LFP/C indicated that the NC in the reaction medium not only acts as the reducing agent that aqueous iron solutions need (avoiding the use of other chemicals), but also as a stabiliser of the nanoparticles produced in the hydrothermal synthesis, obtaining fewer agglomerated particles compared to synthesis without NC. The sample with the best coating—and, therefore, the best electrochemical response—was the sample with 12.6% carbon derived from CNF in the composite instead of CNC, due to its homogeneous coating. The utilisation of CNF in the reaction medium could be a promising method to obtain LFP/C in a simple, rapid, and low-cost way, avoiding the waste of unnecessary chemicals.

Bimetallic CuPt alloyed nanoparticles were conveniently synthesized on biohydrogels and were capable of carrying out hydrogen release from ammonium borane hydrolysis. The biohydrogel consisted of bead-shaped alginate chains crosslinked by calcium ions, which were used as support material to synthesize and stabilize the bimetallic nanoparticles, employing adsorption and coreduction strategy steps. The as-prepared nanoparticles exhibited light absorption in the visible range (580 nm) resulting from the surface plasmon resonance (SPR) phenomenon ascribed to the presence of copper in the alloyed system. On the other hand, the presence of platinum atoms in these nanoalloys endows them with a notable catalytic performance toward ammonia borane hydrolysis as a hydrogen release reaction, reaching kr values from 0.32 x 10-4 to 2.23 x 10-4 mol L-1 min-1 as the Pt content increases. Finally, by taking advantage of the SPR light absorption shown by CuPt 1:1, it was demonstrated that these entities could be successfully employed as photocatalysts for the hydrogen generation reaction, boosting its activity by almost 2.06 times compared to its performance in dark conditions. This catalytic enhancement was mainly ascribed to the plasmonic-derived light-harvesting properties and the specimen's metallic composition.

Photocathodes have a wide range of applications, and different materials can be used depending on the incident photon wavelength. The structure and composition of a crystalline material can strongly affect the electronic properties such as the electron affinity and the work function. Molecular beam epitaxy (MBE) provides much improved control over the composition and synthesis of a photocathode versus traditional manufacturing methods, which allows these electrical and optical properties to be optimized for a particular application. In this article, we use density functional theory (DFT) through commercially available MedeA-VASP simulation software to identify the available parameter space of electron affinity and absorption coefficient by varying the stoichiometry and crystallinity. We identify trends to motivate the manufacture of new dicesium telluride- and gallium arsenide-like materials via MBE to optimize photocathode performance for a particular application.

A set of AuNPs-L-TiO2NP nanoaggregates which showed efficient covering of the semiconductor's surface by AuNPs, as well as appropriate AuNP sizes for effective sensibilization were used as photocatalysts for the hydrogen evolution reaction (HER). Three aliphatic short-chain linkers: 3-mercaptopropionic acid (MPA), thioglycolic acid (TGA) and thiolactic acid (TLA) were used as stabilizing agents. The slight structure variations of the linkers did not produce differences in the AuNP size and morphology. However, it was interesting to show how the photocatalytic performance of the nanoaggregates is dependent on the linker present, as well as to determine the influence of the Au/TiO2 ratio. It was found that TGA gave the best performance at a longer irradiation time, though high amounts of H2 were also obtained for the other two linkers. Furthermore, for all samples large amounts of hydrogen were obtained, which are significantly higher than that usually obtained with plasmon-sensitized TiO2 nanostructures. In addition, high amounts of H2 were obtained after five catalytic cycles for all samples, showing the suitability of these nanoaggregates for the photoinduced HER.

The development of water electrolysis devices is crucial for the sustainable production of green hydrogen fuel. However, the slow kinetics and high overpotential are key shortfalls for hydrogen production during the half-cell hydrogen evolution reaction (HER) and significantly reduce the overall efficiency. Here we fabricated two micro-and mesoprorous cobalt MOFs [Co(BDC)(DMSO)(DMF)]n and [Co(NH2-BDC)(DMSO)(DMF)]n (labeled Co-1 and Co-2, respectively) by using a benezenedicarboxylic acid (H2BDC) linker and its amine-derivative (H2N-BDC). The chemical functionalization of organic linkers in MOFs enhances catalytic activity by providing Lewis acidity or basicity, potentially enhancing electrocatalytic activity. Co-1 MOF ([Co(BDC)(DMSO)]n) had a rod-like morphology, while Co-2 MOF ([Co(NH2-BDC)(DMSO)]n) was in the form of two-dimensional sheets. After characterizing the materials using PXRD, SEM-EDX, XPS, TGA, FTIR, and gas sorption, we explored the electrocatalytic activity of the MOFs for hydrogen evolution reaction (HER). The presence of surface amino functions slightly improved HER activity of Cobalt MOFs in terms of overpotential (? from 0.217 V to 0.215 V @ 25mAcm2-) and Tafel slope (from 95mVdec-1 to 91mVdec-1). However, Co-2 showed better stability and high Faradic efficiency (97 %), which we attribute to morphological features, mesoporosity, and the presence of basic surface functionalities.

We present a thorough soft x-ray photoelectron spectroscopy (XPS) study of a mesoporous titanium dioxide electrode sensitized with the dye 4-(diphenylamino)phenylcyanoacrylic acid, referred to as “L0.” Supported by calculations, the suite of XPS, x-ray absorption spectroscopy, and resonant photoelectron spectroscopy allows us to examine bonding interactions between the dye and the surface and the frontier electronic structure at the molecule–oxide interface. While placing these measurements in the context of existing literature, this paper is intended as a useful reference for further studies of more complex triphenylamine based sensitizers.

We present the synthesis of metal nanowires in a multiplexed device configuration using single-walled carbon nanotubes (SWNTs) as nanoscale vector templates. The SWNT templates control the dimensionality of the wires, allowing precise control of their size, shape, and orientation; moreover, a solution-processable approach enables their linear deposition between specific electrode pairs in electronic devices. Electrical characterization demonstrated the successful fabrication of metal nanowire electronic devices, while multiscale characterization of the different fabrication steps revealed details of the structure and charge transfer between the material encapsulated and the carbon nanotube. Overall the strategy presented allows facile, low-cost, and direct synthesis of multiplexed metal nanowire devices for nanoelectronic applications.

Converting solar energy directly into electricity as a clean and renewable energy resource is immensely important to solving the energy crisis and environmental pollution problems induced by the consumption of fossil fuels. Dye-sensitized solar cells (DSSCs) provide a technically and economically credible alternative that could challenge the dominance of conventional p-n junction photovoltaic devices in the solar energy market. DSSCs use dye molecules adsorbed at the surface of nanocrystalline oxide semiconductors such as TiO2 to collect sunlight. These thin films require a large surface area, to adsorb many dye molecules, and mesoporous channels so the electrolyte can permeate the film and regenerate the dye molecules. This favourable morphology is traditionally achieved by the random assembly of a network of nanoparticles by the sintering process. Two-photon polymerization is a 3D printing technique used to fabricate structures with feature resolutions down to 100 nm. We use this technique to fabricate TiO¬2 thin films of optimised 3D micro-design for use in DSSCs. Our films have a considerable advantage over the conventional (random assembly) films as it allows the implementation of light scattering designs which are shown to significantly enhance photocurrent in the cell by up to ~25%.

We present a series of three studies investigating the potential application of high vacuum electrospray deposition to construct molecular electronic devices. Through the use of time of flight secondary ion mass spectrometry we explore the use of this novel deposition technique to fabricating multilayer structures using materials that are compatible with the same solvents and films containing a mixture of molecules from orthogonal solvents. Using X-ray photoelectron spectroscopy we study the deposition of a polymer blend using electrospray and find evidence of preferential deposition of one of the components.

Despite important advances in the synthesis of inorganic perovskite nanocrystals (NCs), the long-term instability and degradation of their quantum yield (QY) over time need to be addressed to enable the further development and exploitation of these nanomaterials. Here we report stable CsPbI3 perovskite NCs and their use in hybrid light emitting diodes (LEDs), which combine in one system the NCs and a blue GaN-based LED. Nanocrystals with improved morphological and optical properties are obtained by optimizing the post-synthesis replacement of oleic acid ligands with iminodibenzoic acid: the NCs have a long shelf-life (>2 months), stability under different environmental conditions, and a high QY, of up to 90%, in the visible spectral range. Ligand replacement enables the engineering of the morphological and optical properties of the NCs. Furthermore, the NCs can be used to coat the surface of a GaN-LED to realize a stable diode where they are excited by blue light from the LED under low current injection conditions, resulting in emissions at distinct wavelengths in the visible range. The high QY and fluorescence lifetime in the nanosecond range are key parameters for visible light communication, an emerging technology that requires high-performance visible light sources for secure, fast energy-efficient wireless transmission.

Windows integrated with semi-transparent photovoltaics (PVs) such as Dye-Sensitized Solar Cells (DSSCs) show good potential in improving building performance, in terms of providing daylight, reducing unnecessary solar heat gain and also generating electricity onsite. However, low cell efficiency remains an obstacle for their applications in windows. Using light trapping structures in DSSCs shows the potential to improve solar to electrical conversion efficiency. In this work, different pyramid-patterned titanium dioxide (TiO2) geometries are designed to enhance the photon absorption in DSSCs, and characterised using a Monte-Carlo algorithm based 3D ray-tracing simulation. Various studies were carried out under average irradiation, spectrum dependent irradiation and different solar incidental angles, respectively. The simulation results at the average irradiation wavelength (540 nm) were compared to those from a previous study using Scanning Photocurrent Microscopy (SPCM) and a reasonable agreement has been achieved. It was found that the structure based on the pyramid array of side wall angle 54.7° can significantly enhance light absorption by up to ~25% and the maximum achievable photocurrent density (MAPD) by up to ~45% across the spectrum of 380–800 nm, when compared to a planar control counterpart.

Ultra-thin aluminium oxide was grown on a rutile titanium dioxide surface by atomic layer deposition using trimethylaluminium and water precursors. This process, carried out using realistic temperatures and pressures (1 mbar, 450 K), was monitored in situ using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). This provides insight into the surface chemistry at the interface between the two oxide layers - specifically the reduction of titanium atoms from Ti4+ to Ti3+ upon dosing of trimethylaluminium. These defect states become locked into the heterojunction's interface, with implications to its electronic structure, and can act as an indicator as to when complete coverage of the rutile substrate is achieved.

Monolayers of C60 and the functionalised fullerene phenyl-C61-butyric acid methyl ester (PCBM) have been prepared on Au(1 1 1) by in situ electrospray deposition. The observation of super-spectator/super-Auger decay in resonant photoemission spectroscopy (RPES) of C60 confirms monolayers prepared using electrospray undergo ultra-fast charge transfer as per previous studies of C60 monolayers on Au(1 1 1) prepared by sublimation. For PCBM, X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) show the lowest unoccupied molecular orbital (LUMO) of the molecule overlaps the Fermi-level of the metal surface. Despite this, no evidence of ultra-fast charge transfer is observed in the RPES of PCBM.

Two-dimensional resonant inelastic x-ray scattering (RIXS) and resonant photoelectron spectroscopy (RPES) maps are presented for multilayer and monolayer coverages of an aromatic molecule (bi-isonicotinic acid) on the rutile TiO

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.

The study of electron delocalisation in oxygen atom segregated zones in graphene, aided by the first-principles density functional theory, has revealed extra energy bands of ≥2 eV wide around the Fermi level, predicting Faradaic charge storage occurring in a wide range of potentials, which disagrees with Nernst's law but accounts well for the so called pseudocapacitance of heteroatom-modified graphene based electrode materials in supercapacitors.

The adsorption and charge transfer dynamics of the organic molecule bi-isonicotinic acid (4,4?-dicarboxy-2,2?-bipyridine) on single crystal Ag(111) has been studied using synchrotron radiation-based photoemission, x-ray absorption and resonant core spectroscopies. Measurements for multilayer and monolayer coverage are used to determine the nature of the molecule-surface interactions and the molecular orientation. An experimental density of states for the monolayer with respect to the underlying metal surface is obtained by combining x-ray absorption spectroscopy at the N 1s edge and valence photoemission to measure the unoccupied and occupied valence states, respectively. This shows that the lowest unoccupied molecular orbital in the core-excited state lies energetically below the Fermi level of the surface allowing charge transfer from the metal into this orbital. Resonant photoelectron spectroscopy was used to probe this charge transfer in the context of super-spectator and super-Auger electron transitions. The results presented provide a novel interpretation of resonant core-level spectroscopy to explore ultra-fast charge transfer between an adsorbed organic molecule and a metal surface through the observation of electrons from the metal surface playing a direct role in the core-hole decay of the core-excited molecule.

Charge transfer interactions between C60 and the metal surfaces of Ag(111), Cu(111), Au(111) and Pt(111) have been studied using synchrotron-based photoemission, resonant photoemission and X-ray absorption spectroscopies. By placing the X-ray absorption and valence band spectra on a common binding energy scale, the energetic overlap of the unoccupied molecular orbitals with the density of states of the underlying metal surface have been assessed in the context of possible charge transfer pathways. Resonant photoemission and resonant Auger data, measuring the valence region as a function of photon energy for C60 adsorbed on Au(111) reveals three constant high kinetic energy features associated with Auger-like core-hole decay involving an electron transferred from the surface to the LUMO of the molecule and electrons from the three highest occupied molecular orbitals, respectively and in the presence of ultra-fast charge transfer of the originally photoexcited molecule to the surface. Data for the C60/Ag(111) surface reveals an additional Auger-like feature arising from a core-hole decay process involving more than one electron transferred from the surface into the LUMO. An analysis of the relative abundance of these core-hole decay channels estimates that on average 2.4 $\pm$ 0.3 electrons are transferred from the Ag(111) surface into the LUMO. A core-hole clock analysis has also been applied to assess the charge transfer coupling in the other direction, from the molecule to the Au(111) and Ag(111) surfaces. Resonant photoemission and resonant Auger data for C60 molecules adsorbed on the Pt(111) and Cu(111) surfaces are shown to exhibit no super-Auger features, which is attributed to the strong modification of the unoccupied molecular orbitals arising from stronger chemical coupling of the molecule to the surface.

Vernier templating exploits a mismatch between the number of binding sites in a template and a reactant to direct the formation of a product that is large enough to bind several template units. Here, we present a detailed study of the Vernier-templated synthesis of a 12-porphyrin nanoring. NMR and small-angle X-ray scattering (SAXS) analyses show that Vernier complexes are formed as intermediates in the cyclo-oligomerization reaction. UV/Vis/NIR titrations show that the three-component assembly of the 12-porphyrin nanoring figure-of-eight template complex displays high allosteric cooperativity and chelate cooperativity. This nanoring–template 1:2 complex is among the largest synthetic molecules to have been characterized by single-crystal analysis. It crystallizes as a racemate, with an angle of 27° between the planes of the two template units. The crystal structure reveals many unexpected intramolecular C[BOND]H⋅⋅⋅N contacts involving the tert-butyl side chains. Scanning tunneling microscopy (STM) experiments show that molecules of the 12-porphyrin template complex can remain intact on the gold surface, although the majority of the material unfolds into the free nanoring during electrospray deposition.

N 1s Resonant Inelastic X-ray Scattering (RIXS) was used to probe the molecular electronic structure of the ruthenium photosensitizer complex cis-bis(isothiocyanato) bis(2,2'-bipyridyl-4,4'-dicarboxylato) ruthenium(II), known as "N3." In order to interpret these data, crystalline powder samples of the bipyridine-dicarboxylic acid ligand ("bi-isonicotinic acid") and the single ring analog "isonicotinic acid" were studied separately using the same method. Clear evidence for intermolecular hydrogen bonding is observed for each of these crystalline powders, along with clear vibronic coupling features. For bi-isonicotinic acid, these results are compared to those of a physisorbed multilayer, where no hydrogen bonding is observed. The RIXS of the "N3" dye, again prepared as a bulk powder sample, is interpreted in terms of the orbital contributions of the bi-isonicotinic acid and thiocyanate ligands by considering the two different nitrogen species. This allows direct comparison with the isolated ligand molecules where we highlight the impact of the central Ru atom on the electronic structure of the ligand. Further interpretation is provided through complementary resonant photoemission spectroscopy and density functional theory calculations. This combination of techniques allows us to confirm the localization and relative coupling of the frontier orbitals and associated vibrational losses.

Solvent-induced aggregates of nanoring cyclic polymers may be transferred by electrospray deposition to a surface where they adsorb as three-dimensional columnar stacks. The observed stack height varies from single rings to four stacked rings with a layer spacing of 0.32 ± 0.04 nm as measured using scanning tunneling microscopy. The flexibility of the nanorings results in distortions from a circular shape, and we show, through a comparison with Monte Carlo simulations, that the bending stiffness increases linearly with the stack height. Our results show that noncovalent interactions may be used to control the shape and mechanical properties of artificial macromolecular aggregates offering a new route to solvent-induced control of two-dimensional supramolecular organization.

Chemists use template-directed synthesis to position molecular components so that they can be covalently linked into complex molecules that are not readily accessible by classical synthetic methods. But as larger structures are targeted, the synthesis of the templates themselves becomes challenging. O'Sullivan et al. now show that 'molecular Verniers', based on the principle of moire pattern formation, can solve this problem. Using a Vernier template with six binding sites and molecular building blocks with four porphyrins acting as binding sites, the authors create a 12-porphyrin nano-ring with a diameter of 4.7 nanometres. The ease and efficiency of this synthesis establishes Vernier templating as a powerful new strategy for producing large monodisperse macromolecules. Templates are widely used to arrange molecular components so they can be covalently linked into complex molecules that are not readily accessible by classical synthetic methods. But, as larger structures are targeted, the synthesis of the templates themselves becomes challenging. It is now shown that 'molecular Verniers' can solve this problem: using a template with six binding sites and molecular building blocks with four porphyrins acting as binding sites, a 12-porphyrin nano-ring with a diameter of 4.7 nm is created. The ease and efficiency of this synthesis establishes Vernier templating as a powerful new strategy for producing large monodisperse macromolecules. Templates are widely used to arrange molecular components so they can be covalently linked into complex molecules that are not readily accessible by classical synthetic methods1,2,3,4,5,6,7. Nature uses sophisticated templates such as the ribosome, whereas chemists use simple ions or small molecules. But as we tackle the synthesis of larger targets, we require larger templates—which themselves become synthetically challenging. Here we show that Vernier complexes can solve this problem: if the number of binding sites on the template, nT, is not a multiple of the number of binding sites on the molecular building blocks, nB, then small templates can direct the assembly of relatively large Vernier complexes where the number of binding sites in the product, nP, is the lowest common multiple of nB and nT (refs 8, 9). We illustrate the value of this concept for the covalent synthesis of challenging targets by using a simple six-site template to direct the synthesis of a 12-porphyrin nano-ring with a diameter of 4.7 nm, thus establishing Vernier templating as a powerful new strategy for the synthesis of large monodisperse macromolecules.

Stacked layers of cyclic porphyrin nanorings constitute nanoscale receptacles with variable height and diameter which preferentially adsorb sublimed molecules. Using scanning tunnelling microscopy we determine the filling capacity of these nanoring traps, and the dependence of adsorbate capture on stack height and diameter.

The adsorption of two ruthenium-based dye complexes containing dipyrrin-based ligands has been studied on the rutile TiO2(110) surface using synchrotron-based electron spectroscopy. The dye complexes studied were bis(5-(4-carboxyphenyl)-4,6-dipyrrin)bis(dimethyl sulfoxide)ruthenium(II) and bis(5-(4-carboxyphenyl)-4,6-dipyrrin)(2,2′-bipyridine)ruthenium(II). The dye molecules were deposited using in situ electrospray deposition, which allows for the deposition of thermally fragile molecules in ultrahigh vacuum. Photoemission studies were used to provide experimental data on the bonding geometry of the dye complexes to the rutile TiO2(110) substrate and to provide data on molecular orbitals involved in the charge transfer process. DFT calculations of the molecules adsorbed onto the rutile TiO2(110) surface have also been performed to identify the most energetically favorable bonding geometry.

Many hands make light work: Small templates working together have directed the formation of a giant π-conjugated macrocycle with a diameter of 10 nm-larger than many enzymes. The 24 porphyrin subunits of the nanoring are well resolved in the STM image. The conformation of the nanoring can be controlled by self-assembly of a stable 2:24 double-strand sandwich complex with 1,4-diazabicyclo[2.2.2]octane (DABCO). Copyright © 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim.

Two-dimensional resonant inelastic x-ray scattering (RIXS) and resonant photoelectron spectroscopy (RPES) maps are presented for multilayer and monolayer coverages of an aromatic molecule (biisonicotinic acid) on the rutile TiO2(110) single crystal surface. The data reveal ultra-fast intramolecular vibronic coupling upon core excitation from the N 1s orbital into the lowest unoccupied molecular orbital (LUMO) derived resonance. In the RIXS measurements, this results in the splitting of the participator decay channel into a purely elastic line which disperses linearly with excitation energy and a vibronic coupling channel at constant emission energy. In the RPES measurements, the vibronic coupling results in a linear shift in binding energy of the participator channel as the excitation is tuned over the LUMO-derived resonance. Localisation of the vibrations on the molecule on the femtosecond time scale results in predominantly inelastic scattering from the core-excited state in both the physisorbed multilayer and the chemisorbed monolayer. Published by AIP Publishing.

The adsorption of perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) on Au(1 1 1) has been studied using synchrotron-based X-ray photoelectron spectroscopy and in situ scanning tunnelling microscopy. Direct topographic and surface coverage information provided by the scanning probe measurements have enabled us to correlate peaks in the relatively complex carbon core-level photoemission to interactions of the surface with different parts of the PTCDI molecule. A strong interaction between the imide ends of the molecule with the underlying gold substrate is evidenced by a large chemical shift in the imide carbon peaks, which is observed only for the first adsorbed layer.

Here we present the characteristic signatures in X-ray absorption and photoemission spectroscopy for molecular damage in adsorbed monolayers of bi-isonicotinic acid on a rutile TiO2(1 1 0) surface. Bi-isonicotinic acid is the anchor ligand through which many important inorganic complexes are bound to the surface of TiO2 in dye-sensitized solar cells. The nature of the damage caused by excessive heating of the adsorbed monolayer is consistent with splitting the molecule into two adsorbed isonicotinic acid molecular fragments. The effect on the lowest unoccupied molecular orbitals (involved in electron transfer in the molecule) can be understood in terms of the adsorption geometry of the reaction products and their nearest neighbor interactions.

An electrospray technique has been successfully used to deposit C60 onto a hydrogen-bonded supramolecular template held in an ultrahigh vacuum environment. Characterization of the surface by in situ scanning tunneling microscopy shows the size-selective trapping of C60 dimers and heptamers within a 3,4,9,10-perylene tetracarboxylic diimide (PTCDI)/melamine network. We demonstrate that ultrahigh vacuum electrospray deposition (UHV-ESD), where energetic molecules impact onto a substrate, is compatible with surfaces which have been functionalized through the incorporation of hydrogen-bonded templates.

The "core-hole clock" implementation of resonant photoemission has been used to investigate the charge-transfer dynamics of bi-isonicotinic acid molecules (4,4'-dicarboxy-2,2'-bipyridine) adsorbed on a rutile TiO2(110) surface containing varying densities of gold islands. In the presence of, nominally, a few monolayers of gold there exists a strong coupling between the adsorbed molecules and the surface. This is derived from the measurement of a

Advances in template-directed synthesis make it possible to create artificial molecules with protein-like dimensions, directly from simple components. These synthetic macromolecules have a proclivity for self-organization that is reminiscent of biopolymers. Here, we report the synthesis of monodisperse cyclic porphyrin polymers, with diameters of up to 21 nm (750 C–C bonds). The ratio of the intrinsic viscosities for cyclic and linear topologies is 0.72, indicating that these polymers behave as almost ideal flexible chains in solution. When deposited on ​gold surfaces, the cyclic polymers display a new mode of two-dimensional supramolecular organization, combining encapsulation and nesting; one nanoring adopts a near-circular conformation, thus allowing a second nanoring to be captured within its perimeter, in a tightly folded conformation. Scanning tunnelling microscopy reveals that nesting occurs in combination with stacking when nanorings are deposited under vacuum, whereas when they are deposited directly from solution under ambient conditions there is stacking or nesting, but not a combination of both.

We have used the established technique of electrospray in developing a portable vacuum electrospray system which can deposit, in vacuo, dissolved molecules onto a sample which may then be analysed by UHV techniques. As an initial test of the system we have analysed silicon samples with an electrosprayed layer of poly(ethylene) oxide (PEO) using atomic force microscopy (AFM). The polymer forms different structures depending on the voltage applied to the emitter, and solution composition. The system is part of our ongoing effort to deposit other materials such as nanoparticles, and large dye molecules for developing molecular dye sensitised solar cells.

In this study, metal-free phthalocyanine has been deposited on a conducting glass surface by two methods: by spreading the molecular powder directly on the substrate in air and by vapor sublimation under ultra-high vacuum conditions (evaporation). The films have been characterized by means of core level X-ray Photoemission Spectroscopy, X-ray Absorption Spectroscopy (XAS) and Ultra Violet and Visible absorption spectroscopy (UV-Vis). Our results show that the two deposition methods produce molecular overlayers in different polymorphic phases; the UV-Vis measurements indicate that the film obtained by powder deposition is of x-phase type whereas sublimation leads to an α-polymorph structure. The XAS results show that in the powder deposited film the molecules are mainly oriented parallel to the surface. This is opposite to the case of the vapor deposited film, where the molecules mainly are oriented orthogonal to the surface.

We have investigated the ordered phases of the perylene derivatives perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) and the imide analogue PTCDI on the Ag-Si(111)square root(3) x square root(3)R30 degrees surface using scanning tunneling microscopy. We find that PTCDA forms square, hexagonal, and herringbone phases, which coexist on the surface. The existence of a square phase on a hexagonal surface is of particular interest and is a result of a near commensurability between the molecular dimensions and the surface lattice. Contrast variations across the square islands arise from PTCDA molecules binding to different sites on the surface. PTCDI on Ag-Si(111)square root(3) x square root(3)R30 degrees forms extended rows, as well as two-dimensional islands, both of which are stabilized by hydrogen bonding mediated by the presence of imide groups. We present models for the molecular arrangements in all these phases and highlight the role of hydrogen bonding in controlling this order.

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.

Resonant core spectroscopies are applied to a study of the excited electron transfer dynamics on a low-femtosecond time scale in systems of aromatic molecules (isonicotinic acid and bi-isonicotinic acid) adsorbed on a rutile TiO 2 (110) semiconductor surface. Depending on which adsorbate state is excited, the electron is either localized on the adsorbate in an excitonic effect, or delocalizes rapidly into the substrate in less than 5 fs (3 fs) for isonicotinic acid (bi-isonicotinic acid). The results are obtained by the application of a variant of resonant photoemission spectroscopy.

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. (C) 2003 Elsevier B.V. All rights reserved. (Less)

We present for the first time two-dimensional resonant inelastic x-ray scattering (RIXS) maps of multilayer and monolayer bi-isonicotinic acid adsorbed on the rutile TiO2(110) single crystal surface. This enables the elastic channel to be followed over the lowest unoccupied molecular orbitals resonantly excited at the N 1s absorption edge. The data also reveal ultra-fast intramolecular vibronic coupling, particularly during excitation into the lowest unoccupied molecular orbital-derived resonance. Both elastic scattering and the vibronic coupling loss features are expected to contain the channel in which the originally excited electron is directly involved in the core-hole decay process. This allows RIXS data for a molecule coupled to a wide bandgap semiconductor to be considered in the same way as the core-hole clock implementation of resonant photoemission spectroscopy (RPES). However, contrary to RPES measurements, we find no evidence for the depletion of the participator channel under the conditions of ultra-fast charge transfer from the molecule to the substrate densities of states, on the time scale of the core-hole lifetime. These results suggest that the radiative core-hole decay processes in RIXS are not significantly modified by charge transfer on the femtosecond time scale in this system.

The interaction of the dye molecule N3 (cis-bis(isothiocyanato)bis(2,2-bipyridyl-4,4'-dicarboxylato)-ruthenium(II)) with the ultra-thin oxide layer on a AlNi(110) substrate, has been studied using synchrotron radiation based photoelectron spectroscopy, resonant photoemission spectroscopy (RPES) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). Calibrated X-ray absorption and valence band spectra of the monolayer and multilayer coverages reveal that charge transfer is possible from the molecule to the AlNi(110) substrate via tunnelling through the ultra-thin oxide layer and into the conduction band edge of the substrate. This charge transfer mechanism is possible from the LUMO+2&3 in the excited state but not from the LUMO, therefore enabling core-hole clock analysis, which gives an upper limit of $6.0\pm$2.5fs for the transfer time. This indicates that ultra-thin oxide layers are a viable material for use in dye-sensitized solar cells (DSSC), which may lead to reduced recombination effects and improved efficiencies of future devices.

We show that Cr subcoatings in beamline optical elements can introduce an additional structure in C K-edge X-ray absorption measurements, which somewhat resembles the well-known losses produced by carbon contamination. The photon throughput variations induced by Cr and C require different treatments when correcting absorption spectra. The potential difficulties in unravelling the two effects could be avoided with efficient filtration of higher-order light.

The interaction of lithium, sodium and potassium with an oxidised Ni(110) single crystal surface has been investigated using X-ray photoelectron spectroscopy (XPS). Incorporation of the alkali metal into the oxide layer at room temperature results in the suppression of the intrinsic Ni(2p) satellite structure of stoichiometric NiO, confirming its origin in an inter-site screening process in accordance with a recent theoretical model. In addition, the reaction of the alkali metal with NiO at higher temperatures gives rise to a divalent or trivalent nickelate species. The effect of water vapour on nickelate formation and the reactivity of the nickelate to carbon monoxide is also investigated.

We have developed an experimental setup for the study of small mass-selected clusters delivered by soft landing to a model oxide support. An automated deposition system to achieve accurately quantified homogeneous surfaces is described which also overcomes beam instability. Finally we present some recent photoelectron spectroscopic data from the analysis of mass-selected Agn+ clusters deposited on a Xe covered Al2O3 surface. Large core-level binding energy shifts are observed as a function of deposited cluster size and diffusion/agglomeration within the noble gas layer.