Search

We report thin-film morphology studies of inkjet-printed single-droplet organic thin-film transistors (OTFTs) using angle-dependent polarized Raman spectroscopy. We show this to be an effective technique to determine the degree of molecular order as well as to spatially resolve the orientation of the conjugated backbones of the 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene) molecules. The addition of an insulating polymer, polystyrene (PS), does not disrupt the π–π stacking of the TIPS-Pentacene molecules. Blending in fact improves the uniformity of the molecular morphology and the active layer coverage within the device and reduces the variation in molecular orientation between polycrystalline domains. For OTFT performance, blending enhances the saturation mobility from 0.22 ± 0.05 cm2/(V·s) (TIPS-Pentacene) to 0.72 ± 0.17 cm2/(V·s) (TIPS-Pentacene:PS) in addition to improving the quality of the interface between TIPS-Pentacene and the gate dielectric in the channel, resulting in threshold voltages of ∼0 V and steep subthreshold slopes.

Here, a new approach is introduced to prepare large single crystals of π‐conjugated organic molecules from solution. Utilizing the concept of azeotropism, single crystals of tri‐isopropylsilylethynyl pentacene (TIPS‐PEN) with dimensions up to millimeters are facilely self‐assembled from homogeneous solutions comprising two solvents with opposing polarities and a positive azeotropic point. At solvent compositions close to the azeotropic point, an abrupt transition of morphology from polycrystalline thin‐films to large single crystals is found. How to adjust the initial ratio of the binary solvents so that the change in solvent composition during evaporation favors the specific H‐aggregation and promotes an efficient self‐assembly of TIPS‐PEN is explained. The charge‐carrier (hole) mobilities are substantially enhanced by a factor of 4 from the morphology of thin‐films to large single crystals used as active layer in field‐effect transistors. Additionally, this approach is extended to other π–π stacked organic molecules to elucidate its broad applicability.

Liquid crystal (LC) concentrations in stratified holographic polymer-dispersed liquid crystal (PDLC) films have been quantified from depth profiles obtained by time-of-flight secondary ion mass spectrometry (SIMS). The volatile nature of the LCs was hindered during SIMS analysis by capping the PDLC samples with poly(vinyl alcohol) and cooling to cryogenic temperatures. It remains difficult to gain quantitative results from SIMS analysis due to matrix effects yielding complex SIMS fingerprint spectra. With the multivariate statistical method discriminant function analysis the LC contents in the stratified holographic PDLC films were quantified. The concentration of the LC-rich layers was determined to be 32.9 ± 3.4 wt % LC, and for the polymer-rich layers it was 28.8 ± 2.7 wt % LC. The low concentration difference was supported by imaging analysis and modeling results.

Abstract. γ-trace, a microprotein occurring in neuroendocrine cells, was demonstrated by immunohistochemical technique to be present in the calcitonin-producing C-cells of normal simian thyroid gland and of human medullary thyroid carcinoma. A comparatively high concentration of γ-trace was demonstrated in tissue extract of neoplastic C-cells. The immunoreactive protein found in the extract had a molecular weight and electrophoretic mobility characteristic for γ-trace.

The inside cover of this issue illustrates the solution‐phase self‐assembly of organic single crystals by using azeotropic binary solvent mixtures, described by X. Li et al. on page 3610, and is a snap‐shot taken during the self‐assembly of tri‐isopropylsilylethynyl pentacene single crystals from an azeotropic binary solvent mixture of isopropanol plus toluene, on a silicon substrate. These needle‐like crystals were growing with time while floating in the bulk of the solution during solvent evaporation, with bright colors showing their birefringence.