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The synthesis of two new thieno(bis)imide (TBI, N) end functionalized oligothiophene semiconductors is reported. In particular, trimer (NT3N) and pentamer (NT5N) have been synthesized and characterized. Two different synthetic approaches for their preparation were tested and compared namely conventional Stille cross coupling and direct arylation reaction via C-H activation. Theoretical calculations, optical and electrochemical characterization allowed us to assess the role of the ?-conjugation extent, i.e., of the oligomer size on the optoelectronic properties of these materials. In both {TBI} ended compounds, due to the strong localization of the {LUMO} orbital on the {TBI} unit, the {LUMO} energy is almost insensitive to the oligomer size, this being crucial for the fine-tailoring of the energy and the distribution of the frontier orbitals. Surprisingly, despite its short size and contrarily to comparable TBI-free analogues, {NT3N} shows electron charge transport with mobility up to ?N = 10-4 cm2 V-1 s-1, while increasing the oligomer size to {NT5N} promotes ambipolar behavior and electroluminescence properties with mobility up to ?N = 0.14 cm2 V-1 s-1 and to ?P = 10-5 cm2 V-1 s-1.

We performed constant voltage stress on oligothiophene-based p- and n-type organic thin-film-transistors, in the accumulation regime. The stress induced charge trapping, mobility degradation and defect generation. The specific kinetics depends not only on the applied bias value and polarity, but also on the semiconductor type. Stress on PMMA capacitors (without the semiconductor film) revealed that most of the degradation is largely originated by the interaction with the semiconductor layer, which enhances charge injection. (C) 2013 Elsevier Ltd. All rights reserved.

Optoelectronic properties of light-emitting field-effect transistors (LETs) fabricated on bottom-contact transistor structures using a tetracene film as charge-transport and light-emitting material are investigated. Electroluminescence generation and transistor current are correlated, and the bias dependence of the LETs external quantum efficiency is determined. The device's performance degrade rapidly upon gate biasing. The effect is attributed to charge trapping, which can be prevented by operating the devices in pulsed mode. A model for the electron injection mechanism in a p-type organic transistor is proposed. On the basis of this model, electrical and optical characteristics, as well as the dependence of the external quantum efficiency on drain- and gate-bias, are well reproduced.

The interplay between atomic geometry and magnetic properties of Fe atoms at the Fe–Ni(1 1 1) interface was studied. To this end dichroic optical absorption and reflectivity (both in energy and θ–2θ angular scan mode) were carried out in the L 2 , 3 edge region of Fe in (Fe 6 A /Ni 24 A (1 1 1)) 10 multilayer while the atomic geometry of the Fe site at the interface was studied for 1 atomic layer of Fe on Ni(1 1 1) by photo-electron diffraction (in angular scan mode and back-scattering regime). The Fe atom was found to be chemisorbed in an fcc hollow site and to stack pseudomorphically to Ni(1 1 1). Its magnetic moment was found to be in the range 2.9±0.9–1.93±0.6 μ B . Possibility of surface anisotropy is discussed.

The atomic geometry and growth mechanism of Fe films (0.5-20 monolayers (ML)) epitaxially grown on Ni(001) have been investigated by a multitechnique approach with the twofold aim of assessing the reliability of quick structural techniques (primary-beam diffraction modulated electron emission (PDMEE), secondary electron imaging (SEI)), suitable for on-line monitoring of film growth, and studying the structural evolution of the Fe/Ni system. To this end, samples were analysed by PDMEE and SEI together with synchrotron radiation photoelectron diffraction (PD), and extended x-ray absorption fine structure (EXAFS). Results show the effectiveness of the approach by quick techniques. In the early stage of growth, Fe arranges in a strained fcc(001) structure. Transition to the bce phase occurs through nucleation of bcc(110) domains with the bce < 111 > //fcc < 110 > orientation. Quantitative analysis based on PD and EXAFS data is also presented.

We investigated the evolution during film growth of the electronic properties of Fe/Ni(111) ultrathin films with electron energy loss spectroscopy from the valence band and from the Fe L 2,3 ionization edges, relating them with structural modifications monitored with low energy electron diffraction. At ca. 4 monolayers of Fe a fcc to bcc phase transition was observed with the major changes in the electronic structure occurring in the 3d band region.