High performance of low band gap polymer-based ambipolar transistor using single-layer graphene electrodes.

Bottom-contact bottom-gate organic field-effect transistors (OFETs) are fabricated using a low band gap pDTTDPP-DT polymer as a channel material and single-layer graphene (SLG) or Au source/drain electrodes. The SLG-based ambipolar OFETs significantly outperform the Au-based ambipolar OFETs, and thermal annealing effectively improves the carrier mobilities of the pDTTDPP-DT films. The difference is attributed to the following facts: (i) the thermally annealed pDTTDPP-DT chains on the SLG assume more crystalline features with an edge-on orientation as compared to the polymer chains on the Au, (ii) the morphological features of the thermally annealed pDTTDPP-DT films on the SLG electrodes are closer to the features of those on the gate dielectric layer, and (iii) the SLG electrode provides a flatter, more hydrophobic surface that is favorable for the polymer crystallization than the Au. In addition, the preferred carrier transport in each electrode-based OFET is associated with the HOMO/LUMO alignment relative to the Fermi level of the employed electrode. All of these experimental results consistently explain why the carrier mobilities of the SLG-based OFET are more than 10 times higher than those of the Au-based OTFT. This work demonstrates the strong dependence of ambipolar carrier transport on the source/drain electrode and annealing temperature.

Nanoscopic management of molecular packing and orientation of small molecules by a combination of linear and branched alkyl side chains.

We synthesized a series of acceptor-donor-acceptor-type small molecules (SIDPP-EE, SIDPP-EO, SIDPP-OE, and SIDPP-OO) consisting of a dithienosilole (SI) electron-donating moiety and two diketopyrrolopyrrole (DPP) electron-withdrawing moieties each bearing linear n-octyl (O) and/or branched 2-ethylhexyl (E) alkyl side chains. X-ray diffraction patterns revealed that SIDPP-EE and SIDPP-EO films were highly crystalline with pronounced edge-on orientation, whereas SIDPP-OE and SIDPP-OO films were less crystalline with a radial distribution of molecular orientations. Near-edge X-ray absorption fine structure spectroscopy disclosed an edge-on orientation with a molecular backbone tilt angle of ∼22° for both SIDPP-EE and SIDPP-EO. Our analysis of the molecular packing and orientation indicated that the shorter 2-ethylhexyl groups on the SI core promote tight π-π stacking of the molecular backbone, whereas n-octyl groups on the SI core hinder close π-π stacking to some degree. Conversely, the longer linear n-octyl groups on the DPP arms facilitate close intermolecular packing via octyl-octyl interdigitation. Quantum mechanics/molecular mechanics molecular dynamics simulations determined the optimal three-dimensional positions of the flexible alkyl side chains of the SI and DPP units, which elucidates the structural cause of the molecular packing and orientation explicitly. The alkyl-chain-dependent molecular stacking significantly affected the electrical properties of the molecular films. The edge-on oriented molecules showed high hole mobilities in organic field-effect transistors, while the radially oriented molecules exhibited high photovoltaic properties in organic photovoltaic cells. These results demonstrate that appropriate positioning of alkyl side chains can modulate crystallinity and molecular orientation in SIDPP films, which ultimately have a profound impact on carrier transport and photovoltaic performance.

Application of helical tomotherapy for two cases of advanced hepatocellular carcinoma.

The role of radiotherapy in the treatment of hepatocellular carcinoma (HCC) has been limited to date, because the liver has a low tolerance to radiation. However, reconstructing tumors and surrounding organs via a three-dimensional conformal planning system can avoid excess radiotherapy exposure to the rest of the liver and adjacent organs. Recently, the concept of "adaptive radiotherapy," such as with helical tomotherapy, has been introduced for treating HCC. Helical tomotherapy obtains an image from the computed tomography component, which allows targeted regions to be visualized prior to, during, and immediately after each treatment and delivers intensity-modulated radiation therapy. We report two patients with advanced HCC who underwent tomotherapy treatment. One was a patient afflicted with advanced HCC and a portal vein tumor thrombus, which was treated with tomotherapy combined with transarterial chemolipiodolization. The other was a patient afflicted with multiple pulmonary metastases treated with tomotherapy followed by systemic chemotherapy.

Percutaneous transhepatic biliary drainage may serve as a successful rescue procedure in failed cases of endoscopic therapy for a post-living donor liver transplantation biliary stricture.

BACKGROUND: Although a biliary stricture is one of the most important complications that develop after living donor liver transplantation (LDLT), a standard approach has not yet been established. OBJECTIVE: The aim of this study was to evaluate the usefulness of nonoperative management in repairing a post-LDLT biliary stricture. DESIGN: A total of 60 patients were referred, from July 2004 to July 2007, for management of a post-LDLT biliary stricture. The patients had ERCP if the hepatic arterial flow was patent on a Doppler sonography. If endoscopic therapy failed, then percutaneous transhepatic drainage (PTBD) was performed to dilate the stricture. If the percutaneous approach also failed, then a repeated PTBD was performed after a 3-dimensional abdominal CT (3D-CT). SETTING: Division of Gastroenterology, Department of Internal Medicine, Yongdong Severance Hospital. PATIENTS: Sixty patients were referred from Catholic University Hospital of Korea for ERCP. RESULTS: ERCP was performed on all 60 patients, and 38 (63%) were successfully treated. When the shape of the distal side of the bile-duct anastomosis was classified into 3 categories (pouched, triangular, and intermediate), the pouched shape showed the lowest success rate of endoscopic therapy (25% [4/16]). Fifteen of 22 patients in whom endoscopic therapy failed were treated by using PTBD. Nine of the 15 patients were successfully managed in the first PTBD attempt, and 4 of the 6 patients in whom the first attempt of PTBD failed had repeated PTBD after a 3D-CT. Four patients were successfully treated with repeated PTBD of the alternative branch approach after a 3D-CT. CONCLUSIONS: ERCP is a feasible first modality in the treatment of a post-LDLT biliary stricture, but, in failed cases, especially in the pouched shape, PTBD can be attempted. When initial PTBD trial fails, a biliary-tract examination, such as a 3D-CT, can be useful for a repeated PTBD trial.