1,343 research outputs found
Ballistic Electron Emission Microscopy on CoSi/Si(111) interfaces: band structure induced atomic-scale resolution and role of localized surface states
Applying a Keldysh Green`s function method it is shown that hot electrons
injected from a STM-tip into a CoSi/Si(111) system form a highly focused
beam due to the silicide band structure. This explains the atomic resolution
obtained in recent Ballistic Electron Emission Microscopy (BEEM) experiments.
Localized surface states in the -reconstruction are found to be
responsible for the also reported anticorrugation of the BEEM current. These
results clearly demonstrate the importance of bulk and surface band structure
effects for a detailed understanding of BEEM data.Comment: 5 pages, RevTex, 4 postscript figures,
http://www.icmm.csic.es/Pandres/pedro.ht
Accurate on-chip measurement of the Seebeck coefficient of high mobility small molecule organic semiconductors
We present measurements of the Seebeck coefficient in two high mobility organic small molecules, 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) and 2,9-didecyl-dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (C10-DNTT). The measurements are performed in a field effect transistor structure with high field effect mobilities of approximately 3 cm2/V s. This allows us to observe both the charge concentration and temperature dependence of the Seebeck coefficient. We find a strong logarithmic dependence upon charge concentration and a temperature dependence within the measurement uncertainty. Despite performing the measurements on highly polycrystalline evaporated films, we see an agreement in the Seebeck coefficient with modelled values from Shi et al. [Chem. Mater. 26, 2669 (2014)] at high charge concentrations. We attribute deviations from the model at lower charge concentrations to charge trapping.We gratefully acknowledge funding from the Engineering and Physical Sciences Research Council (EPSRC).This is the final version of the article. It first appeared from AIP Publishing via http://dx.doi.org/10.1063/1.493175
Charge trapping in polymer transistors probed by terahertz spectroscopy and scanning probe potentiometry
Terahertz time-domain spectroscopy and scanning probe potentiometry were used
to investigate charge trapping in polymer field-effect transistors fabricated
on a silicon gate. The hole density in the transistor channel was determined
from the reduction in the transmitted terahertz radiation under an applied gate
voltage. Prolonged device operation creates an exponential decay in the
differential terahertz transmission, compatible with an increase in the density
of trapped holes in the polymer channel. Taken in combination with scanning
probe potentionmetry measurements, these results indicate that device
degradation is largely a consequence of hole trapping, rather than of changes
to the mobility of free holes in the polymer.Comment: 4 pages, 3 figure
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Solution-based self-aligned hybrid organic/metal-oxide complementary logic with megahertz operation
We have developed a novel solution-based integration scheme featuring organic and metal-oxide semiconductors with a polymeric gate dielectric. The integration relies on a facile subtractive patterning technique for the semiconductors, which, through the selection of an appropriate etch stopper, leads to ideal transistor performance. We utilized this novel integration scheme to fabricate self-aligned transistors and logic circuits with a high-mobility p-type conjugated polymer and an n-type amorphous oxide semiconductor, along with a composite polymeric gate dielectric, all solution-deposited by spin coating. The resulting complementary logic gates are capable of rail-to-rail transitions, low-voltage operation down to a 3.5 V power supply, and ample noise margins. Thanks to the self-aligned-gate approach and the state-of-the-art balanced mobilities of the selected semiconductors, our logic gates achieve megahertz operation, thus demonstrating the strength of our hybrid integration scheme.We gratefully acknowledge Mike Hurhangee and Iain
McCulloch of Imperial College for supplying the IDT-BT conjugated
polymer. We also acknowledge financial support from the
European Commission through the POINTS project (FP7-NMP-
2010-Small-4).This is the author accepted manuscript. The final version is available via Elsevier at http://www.sciencedirect.com/science/article/pii/S1566119915000956
Molecular tuning of the magnetic response in organic semiconductors
The tunability of high-mobility organic semi-conductors (OSCs) holds great
promise for molecular spintronics. In this study, we show this extreme
variability - and therefore potential tunability - of the molecular
gyromagnetic coupling ("g-") tensor with respect to the geometric and
electronic structure in a much studied class of OSCs. Composed of a structural
theme of phenyl- and chalcogenophene (group XVI element containing,
five-membered) rings and alkyl functional groups, this class forms the basis of
several intensely studied high-mobility polymers and molecular OSCs. We show
how in this class the g-tensor shifts, , are determined by the
effective molecular spin-orbit coupling (SOC), defined by the overlap of the
atomic spin-density and the heavy atoms in the polymers. We explain the
dramatic variations in SOC with molecular geometry, chemical composition,
functionalization, and charge life-time using a first-principles theoretical
model based on atomic spin populations. Our approach gives a guide to tuning
the magnetic response of these OSCs by chemical synthesis
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Distinguishing spin pumping from spin rectification in lateral spin pumping device architectures based on doped organic semiconductors
Over the last two decades organic spintronics has developed into a striving
field with exciting reports of long spin diffusion lengths and spin relaxation
times in organic semiconductors (OSCs). Easily processed and inexpensive, OSCs
are considered a potential alternative to inorganic materials for use in
spintronic applications. Spin currents have been detected in a wide range of
materials, however, there is still uncertainty over the origin of the signals.
Recently, we explored spin transport through an organic semiconductor with
lateral spin injection and detection architectures, where the injected spin
current is detected non-locally via spin-to-charge conversion in an inorganic
detector. In this work we show that the widely-used control experiments like
linear power dependence and inversion of the signal with the magnetic field are
not sufficient evidence of spin transport and can lead to an incorrect
interpretation of the signal. Here, we use in-plane angular dependent
measurements to separate pure spin signal from parasitic effects arising from
spin rectification (SREs). Apart from well established anisotropic
magnetoresistance (AMR) and anomalous Hall effect (AHE), we observed a novel
effect which we call spurious inverse spin Hall effect (ISHE). It strongly
resembles ISHE behaviour, but arises in the ferromagnet rather than the
detector meaning this additional effect has to be considered in future work
Low voltage control of ferromagnetism in a semiconductor p-n junction
The concept of low-voltage depletion and accumulation of electron charge in
semiconductors, utilized in field-effect transistors (FETs), is one of the
cornerstones of current information processing technologies. Spintronics which
is based on manipulating the collective state of electron spins in a
ferromagnet provides complementary technologies for reading magnetic bits or
for the solid-state memories. The integration of these two distinct areas of
microelectronics in one physical element, with a potentially major impact on
the power consumption and scalability of future devices, requires to find
efficient means for controlling magnetization electrically. Current induced
magnetization switching phenomena represent a promising step towards this goal,
however, they relay on relatively large current densities. The direct approach
of controlling the magnetization by low-voltage charge depletion effects is
seemingly unfeasible as the two worlds of semiconductors and metal ferromagnets
are separated by many orders of magnitude in their typical carrier
concentrations. Here we demonstrate that this concept is viable by reporting
persistent magnetization switchings induced by short electrical pulses of a few
volts in an all-semiconductor, ferromagnetic p-n junction.Comment: 11 pages, 4 figure
Programmable logic circuits for functional integrated smart plastic systems
In this paper, we present a functional integrated plastic system. We have fabricated arrays of organic thin-film transistors (OTFTs) and printed electronic components driving an electrophoretic ink display up to 70mm by 70mm on a single flexible transparent plastic foil. Transistor arrays were quickly and reliably configured for different logic functions by an additional process step of inkjet printing conductive silver wires and poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) resistors between transistors or between logic blocks. Among the circuit functions and features demonstrated on the arrays are a 7-stage ring oscillator, a D-type ip-flop memory element, a 2:4 demultiplexer, a programmable array logic device (PAL), and printed wires and resistors. Touch input sensors were also printed, thus only external batteries were required for a complete electronic subsystem. The PAL featured 8 inputs, 8 outputs, 32 product terms, and had 1260 p-type polymer transistors in a 3-metal process using diode-load logic. To the best of our knowledge, this is the first time that a PAL concept with organic transistors has been demonstrated, and also the first time that organic transistors have been used as the control logic for a flexible display which have both been integrated on to a single plastic substrate. The versatility afforded by the additive inkjet printing process is well suited to organic programmable logic on plastic substrates, in effect, making flexible organic electronics more flexibleRCUK, OtherThis is the final published version. It is also available from Elsevier at http://www.sciencedirect.com/science/article/pii/S1566119914003607#
Multifunctional materials for OFETs, LEFETs and NIR PLEDs
The authors would like to thank the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no. 212311 of the ONE-P project, Chalmers Areas of Advance, Materials Science and the national research fund of Korea (2013R1A1A3011492, 2013K14A3055679) for funding
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