K. Xing

The electronic structure of poly(3,4-ethylene-dioxythiophene) : studied by XPS and UPS

Abstract The electronic structure of poly(3,4-ethylene-dioxythiophene) (PEDOT) has been investigated by X-ray and ultraviolet photoelectron spectroscopies as well as quantum chemical calculations. Significant differences have been observed in the photoelectron spectra between as-prepared chemically neutralized and anion-doped PEDOT thin films. The electronic structures of as-prepared neutral and doped PEDOT obtained from the photoelectron spectra are in good agreement with the results of new quantum chemical electronic structure calculations. No significant thermal-induced effects have been detected for either as-prepared neutral or doped PEDOT films. The concentration of anions on the polymer surface depends upon the size of the anion, with large anions, like polystyrene sulfonate (PSS − ) base, being much more likely to cover the surface of a PEDOT film than small anion, such as tosylate( p -methyl benzyl sulfonate). This surface concentration effect probably makes the large-anion-doped polymer a more suitable candidate as an electrode in polymer light-emitting diodes (LEDs) than the small-anion-doped polymer.

Polaron to bipolaron transition in a conjugated polymer. Rubidium-doped poly(p-phenylenevinylene)

Abstract Photoelectron spectroscopy has been used to study the evolution of the electronic structure induced by n-type doping of two π-conjugated systems: poly(p-phenylenevinylene), or PPV, and trans,trans-1,4-distyrylbenzene, a model molecule for PPV. Doping was carried out in UHV by physical vapor deposition of rubidium atoms. In both systems, two different doping regimes are observed. At low doping levels, for both materials, one new electronic state appears in the originally forbidden energy gap, and a finite density of states is observed at the Fermi level. Upon increased doping, the observed state moves to lower binding energy and a second state appears within the original energy gap. The evolution of the gap states, together with the appearance of a finite density of states at Fermi level at low doping levels, indicates a transition from polaron to bipolaron charge storage states in these conjugated systems. It should be stressed that these results constitute the first direct measurements of a polaron to bipolaron transition in a conjugated polymer using ultraviolet photoelectron spectroscopy.

A study of the ITO-on-PPV interface using photoelectron spectroscopy

Abstract Angle-dependent photoelectron spectroscopy has been used to study some details of the chemistry at the interface between indium-tinoxide, deposited by argon plasma sputtering, and poly( p -phenylene vinylene). We find chemical species corresponding to different oxidized states of poly( p -phenylene vinylene) and we discuss their assignment with reference to those produced in photo-oxidation experiments.

Resonant and nonresonant x-ray scattering spectra of some poly(phenylenevinylene)s

The electronic structure of some poly(phenylenevinylene)s have been investigated by resonant and nonresonant x-ray inelastic scattering spectroscopies. The nonresonant as well as all resonant spect ...

Electronic structure of pristine and sodium‐doped cyano‐substituted poly(2,5‐dihexyloxy‐p‐phenylenevinylene): A combined experimental and theoretical study

The electronic structure of cyano‐substituted poly(2,5‐dihexyloxy‐p‐phenylene‐vinylene), or CN‐PPV, has been studied in both pristine and doped states. Ultraviolet photoelectron spectroscopy (UPS) and x‐ray photoelectron spectroscopy (XPS), as well as optical absorption spectroscopy have been carried out under ultrahigh vacuum (UHV) conditions, and the results have been interpreted with the help of quantum‐chemical calculations. For the pristine polymer, the addition of cyano groups to the vinylene units does not affect the width of the π‐bands closest to the Fermi level; however, the positions of the flat parts of the upper π‐bands are shifted by approximately 0.4 eV towards higher binding energies relative to the Fermi energy, as compared with the corresponding bands of other alkoxy‐substituted poly(p‐phenylenevinylene)s. On the other hand, there are only marginal differences in the optical absorption spectra; the interband absorption onset is comparable to the values for alkoxy‐substituted poly(p‐pheny...

The electronic structure of neutral and alkali metal-doped poly[3-(4-octylphenyl)thiophene] studied by photoelectron spectroscopy

The electronic structure of poly [3-(4-octylphenyl)thiophene] (POPT) has been studied by ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS), as well as by quantum chemical calculations. Both temperature-dependent effects on the electronic structure of the neutral system, as well as the generation of new electronic states induced by doping with alkaline metals, have been observed. The experimental results are in good agreement with the results of the quantum chemical calculations.

Optical absorption studies of sodium doped poly(cyanoterephthalylidene)

The effects of doping poly(cyanoterephthalylidene) with sodium in ultrahighvacuum been studied by optical absorption spectroscopy. Upon doping, new optical transitions are observed within the bandgap; the characteristics of these transitions are consistent with the formation of bipolarons. The optical absorption results are confirmed by direct measurements of the doping-induced gap states using ultraviolet photoelectron spectroscopy.

The electronic and geometric structures of neutral and potassium-doped poly[3-(4-octylphenyl)thiophene] studied by photoelectron spectroscopy

The electronic and geometric structures of poly [3-(4-octylphenyl)thiophene] have been studied by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS, respectively). Thermochromic effects, and new charge induced states generated by potassium doping, have been observed by direct UPS measurements. The experimental results are in very good agreement with the results of theoretical quantum chemical calculations performed with the Austin Model 1 semi-empirical model and the valence-effective Hamiltonian pseudo-potential model.

Theoretical modeling of the interaction of water with poly-p-phenylene vinylene

Abstract The interaction of water with poly-p-phenylene vinylene is investigated theoretically by means of quantum-chemical calculations on molecular model systems. Water is found to form van der Waals complexes characterized by hydrogen-like bonds with the protons and/or the π system of the PPV chain. The formation of such complexes can lead to significant conformational changes which, in turn, affect the electronic properties of the conjugated polymer.

How the phenyle rings (benzene) act as building blocks in pi conjugated polymers

The Advanced Light Source (ALS), a national user facility located at Ernest Orlando Lawrence Berkeley National Laboratory of the University of California is available to researchers from academia, industry, and government laboratories. Operation of the ALS is funded by the Department of Energys Office of Basic Energy Sciences. This Compendium contains abstracts written by users summarizing research completed or in progress during 1997, ALS technical reports describing ongoing efforts related to improvement in machine operations and research and development projects, and information on ALS beamlines planned through 1998.Organic conjugated polymers have the electronic structure of semiconductors and can be doped to become good conductors (1). Conjugated polymers are now used as active materials in a wide variety of ...Conjugated polymers have been the subject of much interest owing to their unique electronic properties which can be technically exploited e.g., as doping induced electrical conductors and light emi ...