Organic thin-film devices are of interest for a variety of forthcoming ubiquitous electronic applications. [1,2] In order to take full advantage of the potential of organic semiconductors, the improvement of crystallinity is indispensable. Unfortunately, promising organic molecules that have a large overlap of p-orbitals between the molecules cannot migrate freely on a substrate [3] because of the stronger cohesion between the molecules than the interaction between the molecule and the substrate. Therefore, enhancement of the molecule-substrate interaction, that is, the 'molecular wettability' should promote crystallization. Here, we show that the use of a substrate covered with an atomically flat pentacene (C 22 H 14 ) monomolecular layer can drastically increase the crystallinity of C 60 films and increase the field-effect mobilities of C 60 transistors to 2.0-4.9 cm 2 V -1 s -1 , which is a four-to fivefold improvement over C 60 films grown without a pentacene buffer. The observation of the initial growth stages indicates that control of the molecular wettability of the substrate by an atomically flat pentacene buffer caused the improvement of crystallinity in the C 60 films. Molecular-wetting-controlled substrates can thus offer a general solution to the fabrication of high-performance crystalline plastic and molecular-electronic applications. In order to fabricate complex electronic devices such as field-effect transistors (FETs), for ubiquitous electronics, organic thin films need to be grown on many different substrate materials to fit the requirements of particular applications.However, most organic compounds grown on such practical substrates as oxide dielectrics show a poor crystallinity. Because poor crystallinity of the active layers suppresses the device performance markedly, crystalline organic films that have good crystallinity and few grain boundaries are required for a high-performance operation. The molecular wettability of a substrate controls the distance of the lateral migration of the molecules at the film growth front and thus largely determines the morphology of the growing film. The wettability on a substrate surface is determined by the ratio of the cohesion strength among the molecules and the adhesion of the molecules to the substrate surface, as shown in Figure 1a. If the balance between the cohesion and adhesion forces could be controlled by inserting a thin buffer layer, we would expect to obtain organic films with improved crystallinity. Surface modification of a substrate by self-assembled monolayers (SAMs) has been used for the suppression of disorder in organic films near electrodes, [4] and for controlling the carrier density in organic FETs.
Gastrointestinal stromal tumor (GIST), as well as the hyperplastic lesions of intestinal neural tissue and its supporting structures, is a gastrointestinal complication of type 1 neurofibromatosis (NF1) (von Recklinghausen's disease). In the present study, we analyzed the histologic and immunohistochemical features, and the c-kit and PDGFRA gene mutations of 36 GISTs derived from 9 NF1 patients. Distinctively, multiple GISTs arose preferentially in the small intestine. The histologic features of NF1-associated GISTs are almost similar to those of non-NF1 GISTs, but characteristically most of the NF1-associated GISTs contained skeinoid fibers. Thirty-three GISTs (92%) showed immunoreactivity for KIT, and 23 tumors (64%) showed diffuse or mosaic-like immunoreactivity for S-100 protein. Hyperplasic lesions, which may be the hyperplasia of interstitial cells of Cajal, were observed around some GISTs. Exons 9, 11, 13, and 17 of the c-kit gene and exons 12 and 18 of the PDGFRA gene were amplified and directly sequenced. Point mutations of c-kit gene or PDGFRA gene were identified only in three (8%) and two (6%) tumors, respectively. NF1-associated GISTs, showing the dual differentiation of interstitial cells of Cajal and Schwann cells, develop in close association with the myenteric nerve structure of gastrointestinal tract of NF1 patients. The point mutations of c-kit and PDGFRA gene may play a limited role in the tumorigenesis of NF1-associated GISTs.
Aromatic ring-condensed TTF derivatives exhibited excellent p-type FET performances in thin films. Introduction of fused benzene and pyrazine rings to the TTF skeleton was effective to enhance the intermolecular interactions and stability to oxygen. Ordered molecular alignment was confirmed by XRD studies. A pi-stacking structure was observed in the single crystal of diquinoxalinoTTF.
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