Interface engineering for organic electronics : manufacturing of hybrid inorganic-organic molecular crystal devices

Organic semiconductors are at the basis of Organic Electronics. Objective of this dissertation is “to fabricate high-quality organic molecular single-crystal devices”, to explore the intrinsic properties of organic semiconductors. To achieve this, the in situ fabrication of complete field-effect transistors by direct deposition of metal contacts and oxide gate\ud dielectrics on the surface of free-standing pentacene single-crystals at room temperature (with the ‘quasi-dynamic stencil deposition’ technique in pulsed laser deposition) is selected as main approach.\ud First, the structure of vapor-grown pentacene single-crystals is investigated. The observed morphology shows step flow is the dominant crystal growth mechanism. For pentacene, the most common oxidation product and largest impurity present is 6,13-pentacenequinone. It is observed that this quinone is preferentially located as a thin monolayer (partly) covering the crystal surface. In order to remove the quinones selectively, the partly-oxidized crystals are heated in vacuum at a fixed temperature overnight.\ud Next, the direct deposition of various materials through a stencil on the pentacene singlecrystal surface by PLD is investigated. By taking several precautions in the process, lowkinetic energy deposition or ‘soft-landing’ was achieved. Smooth and isolated patterns with a well-defined geometry were successfully deposited, without obvious destruction of the fragile substrate. The terraced structure of the underlying pentacene substrate is often still noticeable on top of the patterned features. A series of gold patterns is deposited on silicon oxide and pentacene single-crystals; the results show that the growth evolution of the surface roughness is similar on both kinds of substrates.\ud Finally, the influence of the deposition parameters applied in the device fabrication and performing a heat treatment on the electrical properties of pentacene single-crystals is investigated, by characterizing space-charge-limited current and field-effect transistor devices fabricated on the surface of pentacene single-crystals

How micropatterns and air pressure affect splashing on surfaces

We experimentally investigate the splashing mechanism of a millimeter-sized ethanol drop impinging on a structured solid surface, comprised of micro-pillars, through side-view and top-view high speed imaging. By increasing the impact velocity we can tune the impact outcome from a gentle deposition to a violent splash, at which tiny droplets are emitted as the liquid sheet spreads laterally. We measure the splashing threshold for different micropatterns and find that the arrangement of the pillars significantly affects the splashing outcome. In particular, directional splashing in direction in which air flow through pattern is possible. Our top-view observations of impact dynamics reveal that an trapped air is responsible for the splashing. Indeed by lowering the pressure of the surrounding air we show that we can suppress the splashing in the explored parameter regime.Comment: 7 pages, 9 figure

Efficient cloning system for construction of gene silencing vectors in Aspergillus niger

An approach based on Gateway recombination technology to efficiently construct silencing vectors was developed for use in the biotechnologically important fungus Aspergillus niger. The transcription activator of xylanolytic and cellulolytic genes XlnR of A. niger was chosen as target for gene silencing. Silencing was based on the expression vector pXLNRir that was constructed and used in co-transformation. From all the strains isolated (N = 77), nine showed poor xylan-degrading activities in two semi-quantitative plate assays testing different activities for xylan degradation. Upon induction on D-xylose, transcript levels of xlnR were decreased in the xlnR-silenced strains, compared to a wild-type background. Under these conditions, the transcript levels of xyrA and xynB (two genes regulated by XlnR) were also decreased for these xlnR-silenced strains. These results indicate that the newly developed system for rapid generation of silencing vectors is an effective tool for A. niger, and this can be used to generate strains with a tailored spectrum of enzyme activities or product formation by silencing specific genes encoding, e.g., regulators such as Xln

Peer evaluation: The effect of reciprocity and level of performance on evaluative feedback

The study was designed to examine the impact of reciprocal evaluation, a factor which differentiates the relational aspect of peer and supervisor evaluation contexts, and level of performance on the accuracy of performance ratings. One hundred and thirty-six undergraduate students evaluated standardized solutions on an \u27Organizational Problem Solving Task\u27 which demonstrated either a poor or a satisfactory level of performance, under one of two rating conditions. In one rating condition, participants were told that they would simply evaluate another person\u27s performance on the task (non-reciprocal rating condition). In the other rating condition, participants were informed that not only would they rate another person\u27s performance on the task, but that they would also complete the task themselves and be rated on it by the person whose performance they just rated (reciprocal rating condition). As hypothesized, participants in reciprocal evaluation conditions rated performance as significantly more positive than those in non-reciprocal evaluation conditions. Furthermore, an evaluation condition by performance level interaction revealed that participants in reciprocal rating conditions provided significantly more positive ratings than those in non-reciprocal rating conditions when the performance they rated was poor. However, there was no significant difference between the ratings of those in reciprocal and non-reciprocal rating conditions when the performance they rated was satisfactory. The results are discussed in relation to the effect of level of performance and reciprocal evaluation on performance ratings

Synthesis and characteristics of nanocrystalline 3Y-TZP and CuO powders for ceramic composites

A weakly agglomerated 3Y-TZP powder with 100% tetragonal crystal structure and a primary crystallite diameter of 8 nm was prepared by co-precipitation of metal chlorides in an ammonia solution, followed by extensive washing with ethanol, drying and calcining at 550 °C. Powder characteristics as function of thermal treatment are discussed. A copper oxalate precipitation for the preparation of nanocrystalline CuO powders was optimised in order to minimise aggregation and agglomeration. The influence of calcination procedure and synthesis medium on several powder characteristics of the CuO powders were investigated in detail. Oxalate precipitation in ethanol followed by sequential drying and calcination in air at 250 °C in an open tubular furnace with proper air-powder contact area was found to be the optimal procedure for producing nanocrystalline single-phase CuO powder with small aggregates and weak agglomerates. With this optimal procedure a CuO powder with crystallite diameter and BET equivalent particle diameter of respectively 12 and 20 nm was obtained