Photoemission spectroscopy is commonly applied to study the band structure of solids by measuring the kinetic energy versus angular distribution of the photoemitted electrons. Here, we apply this experimental technique to characterize discrete orbitals of large pi-conjugated molecules. By measuring the photoemission intensity from a constant initial-state energy over a hemispherical region, we generate reciprocal space maps of the emitting orbital density. We demonstrate that the real-space electron distribution of molecular orbitals in both a crystalline pentacene film and a chemisorbed p-sexiphenyl monolayer can be obtained from a simple Fourier transform of the measurement data. The results are in good agreement with density functional calculations.

Single-wall carbon nanotubes are severely restricted by the fact that they exist in bundles. In addition, their interaction with other materials is poorly understood. In this work a new spectroscopic method is described to measure the ratio of free polymer to nanotube-bound polymer in SWNT/polymer solutions. This ratio is highly nonlinear and can be described by a model based on polymer−nanotube adsorption/desorption kinetics. In combination with the experimental data, this model shows that the nanotube bundles decrease in size as the concentration is reduced. Individual nanotubes are stable at low concentration, as supported by atomic force microscopy data. In addition, the model allows the indirect measurement of the polymer−nanotube binding energy at 1.1 eV per molecule. In principle, this method is generic and can be used to monitor dispersions of any metallic nanomaterials in suitable, luminescent organic solutions.

The growth of epitaxial MnO(100) and MnO(111) layers on Pd(100) surface has been investigated by spot-profile analysis low-energy electron diffraction, dynamic atomic force microscopy, photoemission and high-resolution electron energy loss spectroscopy, and density functional theory. We have found that despite the large lattice mismatch to the Pd(100) substrate, the MnO(100) layers are kinetically stabilized at low temperatures (<= 350 degrees C) and at oxygen pressures between 2x10(-7) and 5x10(-7) mbar. Annealing in ultrahigh vacuum at 650 degrees C or, alternatively, deposition of manganese metal in oxygen pressure < 1x10(-7) mbar causes the transformation of the MnO(100) to a polar MnO(111) surface, which is decorated by triangular pyramids with (100) side facets. It is suggested that the growth of MnO(111) layers is energetically preferred over MnO(100) due to the epitaxial stabilization at the metal-oxide interface

The low, medium, and high concentration luminescence and luminescence-excitation spectra for alkyl substituted hexa-peri-hexabenzocoronene (HBC-C 8,2 ) and hexa(4-n-dodecylphenyl) substituted hexa-perihexabenzocoronene (HBC-PhC 12 ) are presented. A study of the concentration dependence of the optical properties of these self-assembling molecular nanowires, in the low to medium concentration regime, associates the spectrum at ∼10 -13 M with the isolated molecule and indicates that previously published spectra of HBC's by others were the product of aggregation phenomena. The insertion of an exo-phenyl group between the HBC core and the alkyl side chains, as in HBC-PhC 12 , was found not to extend the conjugation but did increase the inhomogeneous broadening of the isolated molecule luminescence. The continued presence of HBC-PhC 12 isolated molecules, at high concentration, implies that HBC-C 8,2 aggregates are thermodynamically more stable than HBC-PhC 12 aggregates. This is further supported by the calculated values for the Coulombic ground-state binding energy (W), the Coulombic excited state-ground-state interaction energy (W′) and the resonance interaction energy (β) for the aggregates of both derivatives (HBC-C 8,2 : W ≈ 0 eV, W′ ≈ 0.16 eV, and β ) 0.27 ( 0.02 eV; HBC-PhC 12 : W ≈ 0 eV, W′ ≈ 0 eV, and β ) 0.23 ( 0.02 eV). In the excited state, the exo-phenyl groups of HBC-PhC 12 were found to enhance the aggregate intermolecular vibronic coupling despite sterically hindering the full aggregation in the ground state. In conclusion, the spectroscopic properties of both derivatives were found to be very sensitive to aggregation at low concentration and strongly correlated to the observed macroscopic physical properties.

The deposition in an ultrahigh vacuum of prototypical linear para-sexiphenyl (6P) molecules onto the anisotropic reconstructed surface of Cu(110)2 × 1-O presents an ideal system with reduced symmetry for investigation. A dynamic photoemission electron microscopy (PEEM) study of the nucleation and growth of 6P, combined with data obtained from static techniques, is shown to facilitate our understanding of the requirements for 6P nuclei formation and self-assembly into long anisotropic needles. High-rate image acquisitions in PEEM are shown to reveal dynamic phenomena, such as meta-stable layer de-wetting and nanostructure growth in real time, that are the result of nucleation and self-assembly processes. Furthermore, time dependent studies of the relaxation of the meta-stable layer give insights into the molecular diffusion kinetics, whereas temperature dependent studies allow nucleation energies and molecular binding energies to be quantitatively measured. The deposition of the first monolayer of material is found to assemble without the formation of islands until full coverage (1 ML) is achieved. The second layer fills homogeneously and remains in a liquid smectic phase until a total deposition of 1.95 ± 0.07 ML is reached, whereupon critical nuclei of 6P crystallize out of the 2D liquid layer. The maximum of the diffusion coefficient is estimated to be 2 × 10(-9) cm(2) s(-1). The resulting de-wetting of the meta-stable second layer rapidly increases the size of the nuclei while maintaining the anisotropic needle nanostructure shape. Probing the de-wetting layer reveals that 6P diffusion is 1D up to 100 °C. The nucleation energy and intermolecular binding energy are measured to be 675 meV and 2.1 eV, respectively.