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Thin film transistors based on high-mobility organic semiconductors are prone to contact problems that complicate the interpretation of their electrical characteristics and the extraction of important material parameters such as the charge carrier mobility. Here we report on the gated van der Pauw method for the simple and accurate determination of the electrical characteristics of thin semiconducting films, independently from contact effects. We test our method on thin films of seven high-mobility organic semiconductors of both polarities: device fabrication is fully compatible with common transistor process flows and device measurements deliver consistent and precise values for the charge carrier mobility and threshold voltage in the high-charge carrier density regime that is representative of transistor operation. The gated van der Pauw method is broadly applicable to thin films of semiconductors and enables a simple and clean parameter extraction independent from contact effects.

The C‐13 NMR spectra of partly crystalline poly(phenylacetylene) (PPA) in CDCl3 CCl4 are rather well resolved and the peaks can be matched with those of 1, 3,5‐triphenylbenzene. A different, less‐well‐resolved C‐13 spectrum is characteristic of a disordered PPA obtained by heating. We conclude that crystalline PPA has the chain conformation of a cis‐cis‐oid helix. This interpretation is consistent with the proton NMR spectra and is supported by the fluorescence spectra, which can display two bands, one concluded to be characteristic of the cis‐cis‐oid conformation, the other of chain conjugation in the disordered polymer. Phase equilibria of PPA in the presence of chloroform were determined and are represented as those of the quasiternary mixture cis‐cis‐oid helix, disordered polymer, and chloroform.

To grow small molecule semiconductor thin films with domain size larger than modern-day device sizes, we evaporate the material through a dense array of small apertures, called a stencil nanosieve. The aperture size of 0.5 μm results in low nucleation density, whereas the aperture-to-aperture distance of 0.5 μm provides sufficient crosstalk between neighboring apertures through the diffusion of adsorbed molecules. By integrating the nanosieve in the channel area of a thin-film transistor mask, we show a route for patterning both the organic semiconductor and the metal contacts of thin-film transistors using one mask only and without mask realignment.

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SynopsisThe high-temperature (>12OoC) electron paramagnetic resonance (EPR) spectrum of solutions of polyphenylacetylene have been deconvoluted into the spectra of two separate radicals, a delocalized K radical, whose EPR spectrum consists of a single 15-G wide Gaussian line comprising about 90% of the total signal and a second, more localized K radical exhibiting complex hyperfine structure in its EPR spectrum. Some possible structures for the minor component radical are suggested and their hyperfine splitting constants calculated using molecular orbital theory.

Some solutions of polyphenylacetylene (PPA) were recently found to display high-resolution 13C NMR spectra.' These were assigned to the crystallizable form of PPA, which was concluded to assume a conformational structure consistent with a cis-cisoid helix. That assignment was based on the similarity of the '3c spectra with those of solutions of 1,3,5-triphenylbenzene. It was suggested that a cis-cisoid helix was also likely to be the characteristic molecular conformation in the solid-state crystal lattice of PPA, but evidence for this conjecture awaited the availability of high-resolution spectra of crystalline PPA. Such spectra have now been obtained.A purified sample of crystalline PPA can be obtained by repetitive exhaustive extraction of amorphous polymer with chloroform.' During most of the extraction process two fluid phases coexist and the polymer being purified goes from a solution phase through a gel phase to a polycrystalline phase.' Washing is continued until the chloroform extract is colorless. A t an initial polymer concentration of 10% by weight and an approximate fivefold dilution in each extraction, approximately 20 such steps are required.

1982) Electrical properties of thin films of polyphenylacetylene doped with iodine or arsenic pentafluoride, Molecular Crystals and Liquid Crystals, 83:1, 307-308,