Effect of impurities on pentacene island nucleation

Pentacenequinone (PnQ) impurities have been introduced into a pentacene source material in a controlled manner to quantify the relative effects of the impurity content on grain boundary structure and thin film nucleation. Atomic force microscopy (AFM) has been employed to directly characterize films grown using 0.0-7.5% PnQ by weight in the source material. Analysis of the distribution of capture zones areas of submonolayer islands as a function of impurity content shows that for large PnQ content the critical nucleus size for forming a Pn island is smaller than for low PnQ content. This result indicates a favorable energy for formation of Pn-PnQ complexes, which in turn suggests that the primary effect of PnQ on Pn mobility may arise from homogeneous distribution of PnQ defects.Comment: 16 Pages, 5 figures, 1 Tabl

Effect of Impurities on Pentacene Thin Film Growth for Field-Effect Transistors

Pentacenequinone (PnQ) impurities have been introduced into a pentacene source material at number densities from 0.001 to 0.474 to quantify the relative effects of impurity content and grain boundary structure on transport in pentacene thin-film transistors. Atomic force microscopy (AFM) and electrical measurements of top-contact pentacene thin-film transistors have been employed to directly correlate initial structure and final film structures, with the device mobility as a function of added impurity content. The results reveal a factor four decrease in mobility without significant changes in film morphology for source PnQ number fractions below ~0.008. For these low concentrations, the impurity thus directly influences transport, either as homogeneously distributed defects or by concentration at the otherwise-unchanged grain boundaries. For larger impurity concentrations, the continuing strong decrease in mobility is correlated with decreasing grain size, indicating an impurity-induced increase in the nucleation of grains during early stages of film growth.Comment: 18 pages, 4 Figures, 1 Tabl

Chiral molecular tapes from novel tetra(thiafulvalene-crown-ether)-substituted phthalocyanine building blocks

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Immobilization of Zinc Porphyrin Complexes on Pyridine-Functionalized Glass Surfaces

To immobilize sublimable and fluorescent dye mols. on transparent surfaces for the detection of far field mol. interference expts., the authors study the potential of pyridine-functionalized glass substrates as coordination sites for the zinc complex of tetraphenylporphyrin (ZnTPP). Borosilicate glass is functionalized with 4-(6-(ethoxydimethylsilyl)hexyloxy)pyridine to cover the glass surface with pyridine subunits. ZnTPP mols. are deposited by sublimation through mech. masks of various sizes in a high-vacuum chamber. The resulting micropatterns are analyzed using epifluorescence microscopy which also allows one to define a measure for the quality of mol. immobilization. The authors observe a reduced mobility and an increased efficiency for the trapping of ZnTPP on pyridine-functionalized surfaces. [on SciFinder(R)

Chiral semiconductor phases : the optically pure D3[MIII(S,S-EDDS)]2(D = TTF, TSF) family

A new family of optically pure tetrathiafulvalenium and tetraselenafulvalenium salts, D3[MIII(S,S-EDDS)]2·nH2O (where D = TTF, TSF; M = Co, Fe, Cr; EDDS = ethylenediaminedisuccinato), were synthesized electrochemically. These phases are semiconductors with conductivities between 6.9 × 10−6 and 1.3 × 10−5 S·cm−1 (Eaca. 0.3 eV) for TTF and 2.8 × 10−4 to 2.8 × 10−5 S·cm−1 (Eaca. 0.1 eV) for TSF compounds. While some crystals suffer from twinning, other well resolved structures consist of TTF/TSF stacks which, under the influence of the chiral anion, exhibit a periodic undulation described by an elliptical helix. The crystallographic data, along with computational work, indicate charge localization in the semiconducting motifs