M. S. Golden

Full characterization of the interface between the organic semiconductor copper phthalocyanine and gold

We present a study of the interface properties of the molecular organic semiconductor copper phthalocyanine (CuPC) on single crystalline as well as polycrystalline Au using photoemission spectroscopy. Despite the different orientation of the molecules on the two substrates, the observed energy level alignment is identical. We observe the formation of an interface dipole while band bending is very small. In addition, we have carried out complementary studies of the CuPC/GeS(001) interface to pin down photoemission final state effect contributions to the observed energy level shifts.

Order on disorder: Copper phthalocyanine thin films on technical substrates

We have studied the molecular orientation of the commonly used organic semiconductor copper phthalocyanine (CuPC) grown as thin films on the technically relevant substrates indium tin oxide, oxidized Si, and polycrystalline gold using polarization-dependent x-ray absorption spectroscopy, and compare the results with those obtained from single crystalline substrates [Au(110) and GeS(001)]. Surprisingly, the 20–50 nm thick CuPC films on the technical substrates are as highly ordered as on the single crystals. Importantly, however, the molecular orientation in the two cases is radically different: the CuPC molecules stand on the technical substrates and lie on the single crystalline substrates. The reasons for this and its consequences for our understanding of the behavior of CuPC films in devices are discussed.

Diameter grouping in bulk samples of single-walled carbon nanotubes from optical absorption spectroscopy

The influence of the synthesis parameters on the mean characteristics of single-wall carbon nanotubes in soot produced by the laser vaporization of graphite has been analyzed using optical absorption spectroscopy. The abundance and mean diameter of the nanotubes were found to be most influenced by the furnace temperature and the cobalt/nickel catalyst mixing ratio. Via an analysis of the fine structure in the optical spectra, the existence of preferred nanotube diameters has been established and their related fractional abundance could be determined. The results are consistent with nanotubes located mainly around the armchair axis.

Detailed analysis of the mean diameter and diameter distribution of single-wall carbonnanotubes from their optical response

We report a detailed analysis of the optical properties of single-wall carbon nanotubes (SWCNTs) with different mean diameters as produced by laser ablation. From a combined study of optical absorption, high-resolution electron energy-loss spectroscopy in transmission, and tight-binding calculations we were able to accurately determine the mean diameter and diameter distribution in bulk SWCNT samples. In general, the absorption response can be well described assuming a Gaussian distribution of nanotube diameters and the predicted inverse proportionality between the nanotube diameter and the energy of the absorption features. A detailed simulation enabled not only a determination of the mean diameter of the nanotubes, but also gives insight into the chirality distribution of the nanotubes. The best agreement between the simulation and experiment is observed when only nanotubes within

Electronic structure studies of BaFe2As2 by angle-resolved photoemission spectroscopy

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Electron energy-loss spectroscopy studies of single wall carbon nanotubes

of the armchair axis are considered. The mean diameters and diameter distributions from the optical simulations are in very good agreement with the values derived from other bulk sensitive methods such as electron diffraction, x-ray diffraction, and Raman scattering.

Anomalous Enhancement of the Coupling to the Magnetic Resonance Mode in Underdoped Pb-Bi2212

We report high resolution angle-resolved photoemission spectroscopy (ARPES) studies of the electronic structure of BaFe2As2, which is one of the parent compounds of the Fe-pnictide superconductors. ARPES measurements have been performed at 20 and 300 K, corresponding to the orthorhombic antiferromagnetic phase and the tetragonal paramagnetic phase, respectively. Photon energies between 30 and 175 eV and polarizations parallel and perpendicular to the scattering plane have been used. Measurements of the Fermi surface yield two hole pockets at the Γ point and an electron pocket at each of the X points. The topology of the pockets has been concluded from the dispersion of the spectral weight as a function of binding energy. Changes in the spectral weight at the Fermi level upon variation in the polarization of the incident photons yield important information on the orbital character of the states near the Fermi level. No differences in the electronic structure between 20 and 300 K could be resolved. The results are compared with density functional theory band structure calculations for the tetragonal paramagnetic phase.

Interface properties of organic/indium–tin oxide and organic/GeS(001) studied using photoemission spectroscopy

We have carried out momentum-dependent measurements of the density response function of bulk samples of purified single wall nanotubes using electron energy-loss spectroscopy. Carbon nanotubes support both excitations between delocalized and localized electronic states. The π-plasmon exhibits significant q-dependence, with a dispersion relation similar to that of the graphite plane, demonstrating the graphitic nature of the nanotube electron system along the tube axis. In contrast, the interband excitations observed at low energy have vanishingly small dispersion in q. These excitations between localized states are related to characteristic interband transitions between the singularities in the nanotube electronic density of states, and can thus be used to show that our samples contain significant quantities of both semiconducting and metallic single wall nanotubes.

The size of electron-hole pairs in p-conjugated systems

High-resolution angle-resolved photoemission with variable excitation energies is used to disentangle bilayer splitting effects and intrinsic (self-energy) effects in the electronic spectral function near the (

Studies of fullerenes by the excitation, emission, and scattering of electrons

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