3,373 research outputs found
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
Electrocatalysis of Lithium (Poly-) Sulfides in Organic Ether-Based Electrolytes
This work aims at identifying an effective electrocatalyst for polysulfide reactions to improve the electrode kinetics of the sulfur half-cell in liquid organic electrolytes for alkali-sulfur cells. To increase the charge and discharge rates and energy efficiency of the cell, functionalized electrocatalytic coatings have been prepared and their electrode kinetics have been measured. To the best of our knowledge, there is no extensive screening of electrocatalysts for the sulfur electrode in dimethoxyethane:1,3-dioxolane (DME:DOL) electrolytes. In order to identify a suitable electrocatalyst, apparent exchange current densities at various materials (Al, Co, Cr, Cu, Fe, Steel, glassy carbon, ITO, Ni, Pt, Ti, TiN, Zn) are evaluated in a polysulfide electrolyte using potentiodynamic measurements with a Butler-Volmer fit. The chemical stability and surface morphology changes after electrochemical measurements are assessed with X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The results show that cobalt is a promising candidate with appropriate electrocatalytic properties for polysulfide reactions while being stable in the electrochemical environment, followed by chromium in terms of catalytic activity and stability. Sputtered TiN was found to be a very stable material with very low catalytic activity, a possible current collector for the cell
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
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