Ambipolar charge carrier transport in mixed organic layers of phthalocyanine and fullerene

Mixed layers of copper-phthalocyanine (p-conductive) and fullerene (n-conductive) are used for the fabrication of organic field-effect transistors (OFETs) and inverters. Regarding the electrical characteristics of these donor-acceptor blends they show ambipolar charge carrier transport, whereas devices made from only one of the materials show unipolar behavior. Such mixed films are model systems for ambipolar transport with adjustable field-effect mobilities for electrons and holes. By variation of the mixing ratio it is possible to balance the transport of both charge-carrier types. In this paper we discuss the variation of mobility and threshold voltage with the mixing ratio and demonstrate ambipolar inverters as a leadoff application. The gained results were analyzed by simulations using an analytical model for ambipolar transistors and subsequently compared to complementary inverters

Differences of interface and bulk transport properties in polymer field-effect devices

The influence of substrate treatment with self-assembled monolayers and thermal annealing was analysed by electrical and structural measurements on field-effect transistors (FETs) and metal-insulator-semiconductor (MIS) diodes using poly(3-hexylthiophene) (P3HT) as a semiconducting polymer and Si/SiO2 wafers as a substrate. It is found that surface treatment using silanising agents like hexamethyldisilazane (HMDS) and octadecyltrichlorosi-lane (OTS) can increase the field-effect mobility by up to a factor of 50, reaching values in saturation of more than 4E-2 cm^2/Vs at room temperature. While there is a clear correlation between the obtained field-effect mobility and the contact angle of water on the treated substrates, X-ray diffraction and capacitance measurements on MIS diodes show that structural and electrical properties in the bulk of the P3HT films are not influenced by the surface treatment. On the other hand, thermal annealing is found to cause an increase of grain size, bulk relaxation frequency and thereby of the mobility perpendicular to the SiO2/P3HT interface, but has very little influence on the field-effect mobility. Temperature dependent investigations on MIS diodes and FETs show that the transport perpendicular to the substrate plane is thermally activated and can be described by hopping in a Gaussian density of states, whereas the field-effect mobility in the substrate plane is almost temperature independent over a wide range. This investigations reveal significant differ-ences between interface and bulk transport properties in polymer field-effect devices.Comment: accepted at Organic electronic

Nanofriction mechanisms derived from the dependence of friction on load and sliding velocity from air to UHV on hydrophilic silicon

This paper examines friction as a function of the sliding velocity and applied normal load from air to UHV in a scanning force microscope (SFM) experiment in which a sharp silicon tip slides against a flat Si(100) sample. Under ambient conditions, both surfaces are covered by a native oxide, which is hydrophilic. During pump-down in the vacuum chamber housing the SFM, the behavior of friction as a function of the applied normal load and the sliding velocity undergoes a change. By analyzing these changes it is possible to identify three distinct friction regimes with corresponding contact properties: (a) friction dominated by the additional normal forces induced by capillarity due to the presence of thick water films, (b) higher drag force from ordering effects present in thin water layers and (c) low friction due to direct solid-solid contact for the sample with the counterbody. Depending on environmental conditions and the applied normal load, all three mechanisms may be present at one time. Their individual contributions can be identified by investigating the dependence of friction on the applied normal load as well as on the sliding velocity in different pressure regimes, thus providing information about nanoscale friction mechanisms

The influence of distraction on speech processing: How selective is selective attention?

-* indicates shared first authorship - The present study investigated the effects of selective attention on the processing of morphosyntactic errors in unattended parts of speech. Two groups of German native (L1) speakers participated in the present study. Participants listened to sentences in which irregular verbs were manipulated in three different conditions (correct, incorrect but attested ablaut pattern, incorrect and crosslinguistically unattested ablaut pattern). In order to track fast dynamic neural reactions to the stimuli, electroencephalography was used. After each sentence, participants in Experiment 1 performed a semantic judgement task, which deliberately distracted the participants from the syntactic manipulations and directed their attention to the semantic content of the sentence. In Experiment 2, participants carried out a syntactic judgement task, which put their attention on the critical stimuli. The use of two different attentional tasks allowed for investigating the impact of selective attention on speech processing and whether morphosyntactic processing steps are performed automatically. In Experiment 2, the incorrect attested condition elicited a larger N400 component compared to the correct condition, whereas in Experiment 1 no differences between conditions were found. These results suggest that the processing of morphosyntactic violations in irregular verbs is not entirely automatic but seems to be strongly affected by selective attention

Применение программного продукта Eclipse для оптимизации разработки нефтяных месторождений Западно-Сибирского региона

Применение программного продукта Eclipse для оптимизации разработки нефтяных месторождений Западно-Сибирского регионаApplication software Eclipse to optimize the development of oil fields of West Siberi

Transport properties of copper phthalocyanine based organic electronic devices

Ambipolar charge carrier transport in Copper phthalocyanine (CuPc) is studied experimentally in field-effect transistors and metal-insulator-semiconductor diodes at various temperatures. The electronic structure and the transport properties of CuPc attached to leads are calculated using density functional theory and scattering theory at the non-equilibrium Green's function level. We discuss, in particular, the electronic structure of CuPc molecules attached to gold chains in different geometries to mimic the different experimental setups. The combined experimental and theoretical analysis explains the dependence of the mobilityand the transmission coefficient on the charge carrier type (electrons or holes) and on the contact geometry. We demonstrate the correspondence between our experimental results on thick films and our theoretical studies of single molecule contacts. Preliminary results for fluorinated CuPc are discussed.Comment: 18 pages, 16 figures; to be published in Eur. Phys. J. Special Topic

Transcriptional repression of Hox genes by C. elegans HP1/HPL and H1/HIS-24.

Elucidation of the biological role of linker histone (H1) and heterochromatin protein 1 (HP1) in mammals has been difficult owing to the existence of a least 11 distinct H1 and three HP1 subtypes in mice. Caenorhabditis elegans possesses two HP1 homologues (HPL-1 and HPL-2) and eight H1 variants. Remarkably, one of eight H1 variants, HIS-24, is important for C. elegans development. Therefore we decided to analyse in parallel the transcriptional profiles of HIS-24, HPL-1/-2 deficient animals, and their phenotype, since hpl-1, hpl-2, and his-24 deficient nematodes are viable. Global transcriptional analysis of the double and triple mutants revealed that HPL proteins and HIS-24 play gene-specific roles, rather than a general repressive function. We showed that HIS-24 acts synergistically with HPL to allow normal reproduction, somatic gonad development, and vulval cell fate decision. Furthermore, the hpl-2; his-24 double mutant animals displayed abnormal development of the male tail and ectopic expression of C. elegans HOM-C/Hox genes (egl-5 and mab-5), which are involved in the developmental patterning of male mating structures. We found that HPL-2 and the methylated form of HIS-24 specifically interact with the histone H3 K27 region in the trimethylated state, and HIS-24 associates with the egl-5 and mab-5 genes. Our results establish the interplay between HPL-1/-2 and HIS-24 proteins in the regulation of positional identity in C. elegans males

Using airborne LiDAR Survey to explore historic-era archaeological landscapes of Montserrat in the eastern Caribbean

This article describes what appears to be the first archaeological application of airborne LiDAR survey to historic-era landscapes in the Caribbean archipelago, on the island of Montserrat. LiDAR is proving invaluable in extending the reach of traditional pedestrian survey into less favorable areas, such as those covered by dense neotropical forest and by ashfall from the past two decades of active eruptions by the Soufrière Hills volcano, and to sites in localities that are inaccessible on account of volcanic dangers. Emphasis is placed on two aspects of the research: first, the importance of ongoing, real-time interaction between the LiDAR analyst and the archaeological team in the field; and second, the advantages of exploiting the full potential of the three-dimensional LiDAR point cloud data for purposes of the visualization of archaeological sites and features