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We have fabricated organic thin-film transistors and integrated circuits based on the small-molecule organic semiconductors α,α'-didecylquaterthiophene, α,α'-didecylquinquethiophene, and α,α'-didecylsexithiophene. The organic semiconductors were deposited by thermal evaporation, with solution-processed and cross linked poly-4-vinylphenol serving as the gate dielectric layer. We have found that bottom-contact devices based on these materials have better electrical performance than top-contact devices, presumably due to more efficient carrier injection from bottom contacts due to the presence of the relatively long alkyl chains substituted at the α- and ω-positions of the oligothiophene molecules. Bottom-contact transistors have carrier mobility as large as 0.5 cm²/V s and on/off current ratio as large as 10[sup 5], and ring oscillators fabricated using bottom-contact transistors and α,α'-didecylsexithiophene as the organic active layer have signal propagation delay as low as 30 µs per stage. [ABSTRACT FROM AUTHOR]

We have fabricated pentacene organic thin film transistors with spin-coated polymer gate dielectric layers, including cross-linked polyvinylphenol and a polyvinylphenol-based copolymer, and obtained devices with excellent electrical characteristics, including carrier mobility as large as 3 cm[SUP2]/V s, subthreshold swing as low as 1.2 V/decade, and on/off current ratio of 10[SUP5]. For comparison, we have also fabricated pentacene transistors using thermally grown silicon dioxide as the gate dielectric and obtained carrier mobilities as large as 1 cm[SUP2]/V s and subthreshold swing as low as 0.5 V/decade. [ABSTRACT FROM AUTHOR]

We propose a stability criterion applicable to eigenstates of approximate Hamiltonians. We define a ‘‘robustness’’ of the physical properties of the underlying system under a variety of internal and external conditions that can be deduced from stability properties of the eigenstates of the approximate Hamiltonian. Stability properties are assigned to an ensemble of eigenstates according to the statistics of its response to an ensemble of random perturbations of given magnitude. The stability criterion is explicitly formulated for the eigenstates of polyatomic molecules exhibiting a normal to local mode transition. As an example, a stability analysis for the water molecule is carried out and experiments in the low density gas phase (rotational energy transfer), high density gas phase (collision-induced spectra), and condensed phase are suggested. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We argue that the physical significance of the normal to local mode transition in triatomic molecules AB2 lies in an enhanced susceptibility of eigenstates to symmetry breaking perturbations. States of local character have higher susceptibilities than states of normal character. The quantum mechanical condition for the normal to local mode transition is formulated. The issue of stability is addressed from a classical, semiclassical, and quantum mechanical point of view. The question of instability of the unperturbed quantum system is decided individually for each eigenstate. The relevance for experiments is outlined. [ABSTRACT FROM AUTHOR]

We have fabricated organic thin-film transistors and ring oscillators on paper and on flexible polyetherether ketone film using small-molecule hydrocarbon pentacene as the semiconductor and solution-processed polyvinylphenol as the gate dielectric. Transistors on paper have a carrier mobility of 0.2 cm2/V s and an on/off current ratio of 106, similar to devices on polyetherether ketone. A signal propagation delay of 22 μs per stage was measured for pentacene ring oscillators on polyetherether ketone film, and a signal delay of 12 ms was obtained for ring oscillators on paper. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrate the usage of caesium phosphate (Cs3PO4) as a low-cost n-dopant for conductivity enhancements of the electron transport layer in organic light-emitting diodes (OLEDs). Up to 9 orders of magnitude, reaching 2.3 × 10-5 S/cm with only 10% dopant concentration in 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline single-carrier devices, were achieved. Luminance current voltage and impedance spectroscopy measurements confirmed the increased conductivities of the single carrier devices in green light-emitting diodes. Constant operation voltages of below 4 V were realized independently of the electron transport layer (ETL) thickness, which was varied from 50-150 nm. Dielectric constants were modeled by usage of the least squares method. Measured and calculated capacitances based on the geometric properties and modeled dielectric constants varied by less than 1.3% for doped OLEDs, confirming the highly conductive nature of Cs3PO4-doped ETLs and demonstrating that a highly conductive electron transport layer can be understood as an extended cathode. [ABSTRACT FROM AUTHOR]

We have fabricated organic thin film transistors, inverters, and ring oscillators on glass and on flexible polyethylene naphthalate, using the small-molecule hydrocarbon pentacene as the semiconductor and solution-processed polyvinylphenol as the gate dielectric. Depending on the choice of substrate, the transistors have a carrier mobility between 0.3 and 0.7 cm[SUP2]/V s, an on/off current ratio between 10[SUP5] and 10[SUP6], and a subthreshold swing between 0.9 and 1.6 V/decade. To account for the positive switch-on voltage of the transistors, circuits were designed to operate with integrated level shifting. Depending on the type of substrate, ring oscillators have a signal propagation delay as low as 15 μs per stage. [ABSTRACT FROM AUTHOR]