Effects of Odd–Even Side Chain Length of Alkyl-Substituted Diphenylbithiophenes on First Monolayer Thin Film Packing Structure

Because of their preferential two-dimensional layer-by-layer growth in thin films, 5,5′bis(4-alkylphenyl)-2,2′-bithiophenes (P2TPs) are model compounds for studying the effects of systematic chemical structure variations on thin-film structure and morphology, which in turn, impact the charge transport in organic field-effect transistors. For the first time, we observed, by grazing incidence X-ray diffraction (GIXD), a strong change in molecular tilt angle in a monolayer of P2TP, depending on whether the alkyl chain on the P2TP molecules was of odd or even length. The monolayers were deposited on densely packed ultrasmooth self-assembled alkane silane modified $SiO_2$ surfaces. Our work shows that a subtle change in molecular structure can have a significant impact on the molecular packing structure in thin film, which in turn, will have a strong impact on charge transport of organic semiconductors. This was verified by quantum-chemical calculations that predict a corresponding odd–even effect in the strength of the intermolecular electronic coupling.Chemistry and Chemical BiologyEngineering and Applied Science

Towards molecular electronics with large-area molecular junctions

Electronic transport through single molecules has been studied extensively by academic(1-8) and industrial(9,10) research groups. Discrete tunnel junctions, or molecular diodes, have been reported using scanning probes(11,12), break junctions(13,14), metallic crossbars(6) and nanopores(8,15). For technological applications, molecular tunnel junctions must be reliable, stable and reproducible. The conductance per molecule, however, typically varies by many orders of magnitude(5). Self-assembled monolayers (SAMs) may offer a promising route to the fabrication of reliable devices, and charge transport through SAMs of alkanethiols within nanopores is well understood, with non-resonant tunnelling dominating the transport mechanism(8). Unfortunately, electrical shorts in SAMs are often formed upon vapour deposition of the top electrode(16-18), which limits the diameter of the nanopore diodes to about 45 nm. Here we demonstrate a method to manufacture molecular junctions with diameters up to 100 mu m with high yields (>95 per cent). The junctions show excellent stability and reproducibility, and the conductance per unit area is similar to that obtained for benchmark nanopore diodes. Our technique involves processing the molecular junctions in the holes of a lithographically patterned photoresist, and then inserting a conducting polymer interlayer between the SAM and the metal top electrode. This simple approach is potentially low-cost and could pave the way for practical molecular electronics

Electrical conduction through single molecules and self-assembled monolayers

Although research on molecular electronics has drawn increasingly more attention in the last decade, the large spread in obtained results for the conduction rescaled to a single molecule indicates a strong dependence of the measured data on the experimental testbed used. We subdivided a generalized metal–molecule–metal junction into different components and discuss their influence on electrical transport measurements of a single organic molecule or an assembly of molecules. By relating the advantages and disadvantages of different experimental testbeds to the more general view of a molecular junction, we strive to explain the discrepancies between the obtained results on molecular conduction. The reported results on molecular conduction of molecules with an alkane backbone can be categorized into three groups with different resistance values, depending on the device area of the molecular junction and the nature of the contacts.

Flexible a-IGZO TFT technology:new developments & applications

\u3cp\u3eWe present recent developments on flexible a-IGZO TFT technology scaling in terms of TFT channel length and operating voltage, as well as manufacturing cost optimization with a focus on R2R processing compatibility. We present progress on the relevant technology building blocks; (i) R2R compatible TFT architecture, (ii) (multilevel) nanoimprint lithography and (iii) S-ALD deposited TFT materials. Additionally, we show a developing application that drives scaling of the technology, namely a monolithically integrated flexible AMOLED display with in-display fingerprint detection.\u3c/p\u3

A high-resolution large-area detector for quality assurance in radiotherapy.

Hadron therapy is an advanced radiation modality for treating cancer, which currently uses protons and carbon ions. Hadrons allow for a highly conformal dose distribution to the tumour, minimising the detrimental side-effects due to radiation received by healthy tissues. Treatment with hadrons requires sub-millimetre spatial resolution and high dosimetric accuracy. This paper discusses the design, fabrication and performance tests of a detector based on Gas Electron Multipliers (GEM) coupled to a matrix of thin-film transistors (TFT), with an active area of 60 × 80 mm2 and 200 ppi resolution. The experimental results show that this novel detector is able to detect low-energy (40 kVp X-rays), high-energy (6 MeV) photons used in conventional radiation therapy and protons and carbon ions of clinical energies used in hadron therapy. The GEM-TFT is a compact, fully scalable, radiation-hard detector that measures secondary electrons produced by the GEMs with sub-millimetre spatial resolution and a linear response for proton currents from 18 pA to 0.7 nA. Correcting known detector defects may aid in future studies on dose uniformity, LET dependence, and different gas mixture evaluation, improving the accuracy of QA in radiotherapy

Aryl-Perfluoroaryl Substituted Tetracene: Induction of Face-to-Face pi-pi Stacking and Enhancement of Charge Carrier Properties

5-Perfluorophenyl-11-phenyltetracene (FPPT) having both aryl (Ar) and perfluoroaryl (FAr) groups has been designed and synthesized to obtain well-defined n-n stacking structure of the tetracene core. Single-crystal X-ray analyses as well as photoconductivity and hole mobility measurements revealed that this strategy is promising for enhancement of the charge carrier properties.close424

A high-resolution thin-film fingerprint sensor using a printed organic photodetector

Organic photodetectors (OPDs) have attracted much attention in recent years, due to their promise in large-area light sensing applications. Here, high-resolution slot-die-coated large-area bulk heterojunction organic photodiode (OPD) arrays are reported. The OPD uses a novel electron transport layer, indium gallium zinc oxide in combination with a molybdenum oxide top-electrode. Together, these effectively reduce dark current densities to very low levels of ≈10−7 mA cm−2 at −2 V. The OPDs show linear behavior in a wide range of light intensities and high detectivity values under reverse bias conditions. When coated on a 508 ppi TFT backplane, a high-quality optical fingerprint scanner capable of imaging in reflection is realized. The optical and electrical properties of the fingerprint sensor are characterized and high-resolution fingerprint images are obtained

A high-resolution thin-film fingerprint sensor using a printed organic photodetector

\u3cp\u3eOrganic photodetectors (OPDs) have attracted much attention in recent years, due to their promise in large-area light sensing applications. Here, high-resolution slot-die-coated large-area bulk heterojunction organic photodiode (OPD) arrays are reported. The OPD uses a novel electron transport layer, indium gallium zinc oxide in combination with a molybdenum oxide top-electrode. Together, these effectively reduce dark current densities to very low levels of ≈10\u3csup\u3e−7\u3c/sup\u3e mA cm\u3csup\u3e−2\u3c/sup\u3e at −2 V. The OPDs show linear behavior in a wide range of light intensities and high detectivity values under reverse bias conditions. When coated on a 508 ppi TFT backplane, a high-quality optical fingerprint scanner capable of imaging in reflection is realized. The optical and electrical properties of the fingerprint sensor are characterized and high-resolution fingerprint images are obtained.\u3c/p\u3

Stability of large-area molecular junctions

The stability of molecular junctions is crucial for any application of molecular electronics. Degradation of molecular junctions when exposed to ambient conditions is regularly observed. In this report the stability of large-area molecular junctions under ambient conditions for more than two years is presented. Furthermore, the thermal stability of molecular junctions at elevated temperatures is investigated. A transition temperature at 50 °C was observed for molecular junctions based on self-assembled monolayers of alkanedithiols, above which the resistance decreases exponentially with temperature. This transition temperature limits the process window during fabrication and the temperature window during operation.