Switching from Electron to Hole Transport in Solution-Processed Organic Blend Field-Effect Transistors

Organic electronics became an attractive alternative for practical applications in complementary logic circuits due to the unique features of organic semiconductors such as solution processability and ease of large-area manufacturing. Bulk heterojunctions (BHJ), consisting of a blend of two organic semiconductors of different electronic affinities, allow fabrication of a broad range of devices such as light-emitting transistors, light-emitting diodes, photovoltaics, photodetectors, ambipolar transistors and sensors. In this work, the charge carrier transport of BHJ films in field-effect transistors is switched from electron to hole domination upon processing and post-treatment. Low molecular weight n-type N,N′-bis(n-octyl)-(1,7&1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI8-CN2) was blended with p-type poly[2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene] (PBTTT-C14) and deposited by spin-coating to form BHJ films. Systematic investigation of the role of rotation speed, solution temperature, and thermal annealing on thin film morphology was performed using atomic force microscopy, scanning electron microscopy, and grazing incidence wide-angle X-ray scattering. It has been determined that upon thermal annealing the BHJ morphology is modified from small interconnected PDI8-CN2 crystals uniformly distributed in the polymer fraction to large planar PDI8-CN2 crystal domains on top of the blend film, leading to the switch from electron to hole transport in field-effect transistors

Anatomy of Malicious Singularities

As well known, the b-boundaries of the closed Friedman world model and of Schwarzschild solution consist of a single point. We study this phenomenon in a broader context of differential and structured spaces. We show that it is an equivalence relation $\rho$, defined on the Cauchy completed total space $\bar{E}$ of the frame bundle over a given space-time, that is responsible for this pathology. A singularity is called malicious if the equivalence class $[p_0]$ related to the singularity remains in close contact with all other equivalence classes, i.e., if $p_0 \in \mathrm{cl}[p]$ for every $p \in E$. We formulate conditions for which such a situation occurs. The differential structure of any space-time with malicious singularities consists only of constant functions which means that, from the topological point of view, everything collapses to a single point. It was noncommutative geometry that was especially devised to deal with such situations. A noncommutative algebra on $\bar{E}$, which turns out to be a von Neumann algebra of random operators, allows us to study probabilistic properties (in a generalized sense) of malicious singularities. Our main result is that, in the noncommutative regime, even the strongest singularities are probabilistically irrelevant.Comment: 16 pages in LaTe

Hyperfine interactions of 57Fe in Pt3Fe in Pt 3Fe - Ab initio and Mossbauer effect studies

The Mossbauer effect and ab initio investigations of an electric ¯eld gradient at 57Fe nuclei in Pt3Fe compound are presented. It is shown that nonzero 57Fe electric ¯eld gradient exists in the cubic Pt3Fe. Ab initio study of Pt3Fe in antiferromagnetic state con¯rms the presence of electric ¯eld gradient at 57Fe nuclei. Lattice, local valence electron (3d, 4p) and weakly bound 3p core electron contributions to electric ¯eld gradient are separated out and discussed in the context of the electronic structure changes upon the antiferromagnetic phase transition

On the Crystal and Magnetic Behavior of ScFe4Al8 Single Crystal

Nuclear and magnetic properties of the ScFe4Al8 single crystal were found to exhibit unparalleled complexity of nuclear and magnetic structures. Our previous neutron measurements revealed presence of two modulation vectors, both along [", ", 0], however with dfferent critical temperatures. Recent experiments forced us to revise our knowledge of the structural ordering in the sample. So far, the crystal structure of this alloy, being of ThMn12-type, has never been questioned

Self-Aligned Bilayers for Flexible Free-Standing Organic Field-Effect Transistors

[Image: see text] Free-standing and flexible field-effect transistors based on 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene)/polystyrene bilayers are obtained by well-controlled phase separation of both components. The phase separation is induced by solvent vapor annealing of initially amorphous blend films, leading to crystallization of TIPS-pentacene as the top layer. The crystallinity and blend morphology strongly depend on the molecular weight of polystyrene, and under optimized conditions, distinct phase separation with a well-defined and trap-free interface between both fractions is achieved. Due to the distinct bilayer morphology, the resulting flexible field-effect transistors reveal similar charge carrier mobilities as rigid devices and additionally pronounced environmental and bias stress stabilities. The performance of the flexible transistors remains stable up to a strain of 1.8%, while above this deformation, a close relation between current and strain is observed that is required for applications in strain sensors

Role of oxygen within end group substituents on film morphology and charge carrier transport in thiophene/phenylene small-molecule semiconductors

In this study, the end group polarity of (5,5′)-biphenyl-(2,2’)-bithiophenes (PTTPs) was systematically varied from alkyl (1) to alkoxy (2) with one oxygen atom to glycol (3) with two oxygen atoms while the overall length of the end groups is kept constant. Thin films of the three compounds were sublimated at different substrate temperatures and their morphology, crystallinity and charge carrier transport in field-effect transistors was investigated to draw structure-property relationships for the PTTP derivatives. For all three compounds, the effective charge carrier mobility is improved with higher substrate temperatures at which films with higher crystallinity and larger grains are formed. The effective mobility decreases with higher polarity of the end groups from alkyl to alkoxy and glycol. The reliability factor of the alkyl (1) and alkoxy (2) substituted PTTPs decreases with higher substrate temperature, but at the same time this value is enhanced for the glycol substituted molecules (3). The transistors of 3 prepared at higher substrate temperatures also show a reduced threshold voltage and smaller hysteresis in the transfer characteristics. These insights are important for the understanding of the impact of oxygen incorporation into side chain/end group substituents of organic semiconductors and their implementation in organic electrochemical transistors, thermoelectrics and photovoltaics

Efficacy and Safety of Polymer-Free Ultrathin Strut Sirolimus-Probucol Coated Drug-Eluting Stents for Chronic Total Occlusions: Insights from the Coroflex ISAR 2000 Worldwide Registry

Objective. Coronary revascularization in chronic total occlusion (CTO) is associated with improved clinical outcomes. The choice of the coronary stent is crucial in maintaining long-term vessel patency after CTO revascularization. We investigated the efficacy and safety of polymer-free ultrathin strut sirolimus-probucol coated drug-eluting stents (PF-SES) for CTO lesions. Methods. Patients with CTO lesions treated with PF-SES were identified from the prospective multicenter international ISAR 2000 registry. The primary endpoint was clinically driven target lesion revascularization (TLR) at 9 months. Secondary endpoints were 9-month major adverse cardiac events (death, myocardial infarction, or TLR) (MACE) and the occurrence of stent thrombosis. Results. A total of 111 patients with CTO lesions (n=127) were available for analysis. The 9-month clinical follow-up rate was 91%. The mean reference vessel diameter and lesion length were 2.76 mm ± 0.40 and 26.8 mm ± 13.1, respectively. The overall DAPT duration was 9.7 ± 2.8 months. Only one (1%) in-hospital MI was reported. The TLR and MACE rates at 9 months were 2% (2/101) and 5.9% (6/101), respectively. The 9-month accumulated rates of definite or probable stent thrombosis was 0% (0/101). Conclusion. Revascularizations for CTO with PF-SES are associated with low rates of TLR and MACE at 9 months with no stent thrombosis. These initial findings need to be compared with results of other new generation DES of larger studies