Most present-day semiconductor devices use inorganic crystalline materials, with single-crystalline silicon dominating other materials like GaAs by about a factor of 1000. Despite the advantages of single-crystalline inorganic semiconductors like high room-temperature mobility (up to 1000 cm2/(V s)) and high stability, these materials are less suitable for low-cost and large-area applications. Additionally, silicon is an indirect semiconductor and therefore is not well suited for optoelectronic applications like light-emitting diodes. Solar cells from silicon are expensive and require a large amount of energy for their fabrication, leading to a long energy payback time. As an alternative, organic semiconductors have recently gained much attention (for review articles, see refs 1 -3 (OLEDs), ref 4 (organic electronics in general), and refs 5 and 6 (organic solar cells)). Originally, much of the research concentrated on single crystals, which can have mobilities of a few cm2/(V s) at room temperature and even much higher values at low temperature, as shown in the pioneering work of Karl et al.7 However, for practical applications, thinfilm organic semiconductors with disordered morphology, such as evaporated small-molecule compounds or polymers processed from solution, are prevailing. Organic semiconductors are already broadly applied as photoconductors for copiers and laser printers. * Corresponding author. E-mail: leo@iapp.de. Web address: www.iapp.de. 1233 Chem. Rev. 2007, 107, 1233−1271

Highly efficient organic devices based on electrically doped transport layers.

Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with reference to the latest literature reports in these areas. Two case studies on the deactivation mechanisms of catalysts used for cobalt Fischer-Tropsch and selective catalytic reduction are considered to provide additional depth in the topics of sintering, coking, poisoning, and fouling. Regeneration considerations and options are also briefly discussed for each deactivation mechanism.

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Heterogeneous Catalyst Deactivation and Regeneration: A Review

Organometallic Polymers with Transition Metals in the Main Chain.

The efforts to produce photocatalysts operating efficiently under visible light have led to a number of plasmonic photocatalysts, in which noble metal nanoparticles are deposited on the surface of polar semiconductor or insulator particles. In the metal–semiconductor composite photocatalysts, the noble metal nanoparticles act as a major component for harvesting visible light due to their surface plasmon resonance while the metal–semiconductor interface efficiently separates the photogenerated electrons and holes. In this article, we survey various plasmonic photocatalysts that have been prepared and characterized in recent years.

Plasmonic photocatalysts: harvesting visible light with noble metal nanoparticles

Ordered anion adlayers on metal electrode surfaces.

The electronic structure of poly(tetrafluoroethylene) (PTFE) was studied by UPS, VUV absorption, and ab-initio MO calculations. The UPS spectra give a photoemission threshold energy of 10.6eV, with deeper valence band features consistent with the reported XPS and the oligomer vapour UPS spectra. The UPS spectra are also consistent with the density of states derived from the calculated band structure, which indicates that the uppermost part of the valence band is formed from the C and F 2p orbitals with C-C bonding and C-F antibonding combinations. The VUV absorption spectrum shows an intense peak at 7.7eV, which most probably corresponds to the valence excitation from the top of the valence band to the bottom of the conduction band. With these data, the structure of the occupied and vacant states are deduced.

https://iopscience.iop.org/article/10.1088/0031-8949/41/1/041/pdf

Electronic structure of poly(tetrafluoroethylene) studied by UPS, VUV absorption, and band calculations

A new method is proposed for the determination of anharmonic interatomic potentials of fcc metals (Cu, Pd, Ag and Au) and metal halides (AgBr and CuBr). Structural parameters given by the temperature-dependent EXAFS (extended X-ray absorption fine structure) analysis allow us to estimate an interatomic potential if a certain analytical potential function such as Morse or Mardelung potential is assumed. The derived parameters as dissociation energies, thermal expansion coefficients and Mardelung constants (only for Mardelung potentials) are compared with the data in the literature.

https://iopscience.iop.org/article/10.1143/JJAP.28.1905/pdf

Anharmonic Interatomic Potentials of Metals and Metal Bromides Determined by EXAFS

The gas-phase X-ray photoelectron spectra were observed on benzene and its eight mono-substituted derivatives; C6H5X, X=H, CH3, NH2, OH, F, Cl, Br, NO2 and CN. Binding energies of core levels were determined from the observed spectra by using the spectrum simulation technique, and they were compared with the chemical shift predicted from the CNDO/2 charge densities on the basis of the electrostatic potential model. It is shown that the Cls binding energies of benzene derivatives can be generally correlated with atomic charges, qj, by the following equation;E_i(Cls)=290.2+22.67q_i+\undersetj\eweqi∑(q_j/R_ij) eV.By using this relation and the observed Cls binding energies, the atomic charge analysis is carried out. Satellite bands were observed in the Cls spectra as well as in some other core-electron spectra of benzene derivatives. Theoretical calculations are carried out on the energies and probabilities of shake-up transitions. It is concluded that the observed satellites are mainly due to the shake-up p...

Core-electron Spectra of Mono-substituted Benzenes Obtained by the Gas-phase X-Ray Photoelectron Spectroscopy

X-Ray photoelectron spectra of p-benzoquinone, chloranil, bromanil, iodanil, hydroquinone, tetrachlorohydroquinone and chloranilic acid were observed by using the samples freshly deposited in the high vacuum of the spectrometer. The chemical shifts of C ls and O ls levels determined from the XPS spectra are compared with the chemical shifts predicted according to the electrostatic potential model by use of the charge distributions calculated by CNDO/2 method. The charge distributions in the quinone derivatives are successfully estimated by using the observed binding energies of C ls and O ls levels.

X-Ray Photoelectron Spectroscopy of p-Benzoquinone, Hydroquinone and Their Halogen-Substituted Derivatives

The electronic structure of dye/AgBr interfaces has been studied by UV photoelectron spectroscopy for several merocyanine dye films vacuum deposited on AgBr films. With these results energy diagrams of interfaces were obtained, which include the vacuum level, Fermi level, top of the valence band, and bottom of the conduction band of AgBr, and the energy levels of the highest occupied molecular orbital and the lowest unoccupied molecular orbital of the dyes. These energy diagrams were consistent with the trend in the measured abilities of these dyes for spectral sensitization in the framework of the electron-transfer mechanism. The vacuum level of AgBr was found to be significantly lowered by dye deposition. We discuss the factors determining the electronic structure, including the origin of the electric double layer at the interface, which gives rise to the shift of the vacuum level.

Toshiaki Ohta

Papers

Electronic structure of poly(tetrafluoroethylene) studied by UPS, VUV absorption, and band calculations

Anharmonic Interatomic Potentials of Metals and Metal Bromides Determined by EXAFS

Core-electron Spectra of Mono-substituted Benzenes Obtained by the Gas-phase X-Ray Photoelectron Spectroscopy

X-Ray Photoelectron Spectroscopy of p-Benzoquinone, Hydroquinone and Their Halogen-Substituted Derivatives

UV photoemission study of dye/AgBr interfaces in relation to spectral sensitization