Electronic Transport Properties of Pentacene Single Crystals upon Exposure to Air

We report the effect of air exposure on the electronic properties of pentacene single crystals. Air can diffuse reversibly in and out of the crystals and controls the physical properties. We discern two competing mechanisms that modulate the electronic transport. The presence of oxygen increases the hole conduction, as in dark four O2 molecules introduce one charge carrier. This effect is enhanced by the presence of visible light. Contrarily, water, present in ambient air, is incorporated in the crystal lattice and forms trapping sites for injected charges.Comment: 16 pages, 3 figure

Structure–function relations in diF-TES-ADT blend organic field effect transistors studied by scanning probe microscopy

We develop structure–property relations for organic field effect transistors using a polymer/small-molecule blend active layer. An array of bottom gate, bottom contact devices using a polymeric dielectric and a semiconductor layer of 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TES-ADT) is described and shown to have good device-to-device uniformity. We describe the nucleation and growth processes that lead to the formation of four structurally distinct regimes of the diF-TES-ADT semiconductor film, including evidence of layer-by-layer growth when spin-coated onto silver electrodes and an organic dielectric as part of a polymer blend. Devices exhibiting a maximum saturation mobility of 1.5 cm2 V−1 s−1 and maximum current modulation ratio (Ion/Ioff) of 1.20 × 105 are visualised by atomic force microscopy and appear to have excellent domain connectivity and aligned crystallography across the channel. In contrast, poorly performing devices tend to show a phase change in semiconductor crystallinity in the channel centre. These observations are enhanced by direct visualisation of the potential drop across the channel using Kelvin probe microscopy, which confirms the importance of large, well-aligned and well-connected semiconductor domains across the transistor channel

2,3-Butandiolproduktion mit GRAS Mikroorganismen – Screening, Kultivierung, Optimierung und Scale-up –

The objective of the present PhD thesis was the development of an efficient fermentative process for 2,3-butanediol (2,3-BD) production from wood hydrolysates using non-pathogenic microorganisms. In a first step, suitable non-pathogenic strains from different sources were screened for their potential to produce 2,3-BD and a strain improvement by random mutagenesis (UV light) was attempted. The best results were obtained with Paenibacillus polymyxa ATCC 12321 and Bacillus licheniformis DSM 8785. In the shake flask scale batch cultivations were carried out and optimized conditions were found with regard to the following parameters: C-/N-source and concentration, temperature, shaking rate, use of free/immobilized cells. Using the fed-batch cultivation mode and a stepwise addition of nutrients, 2,3-BD production could be increased up to 63.3 g/L (P. polymyxa) and 144.7 g/L (B. licheniformis). Cultivation results were similar on glucose medium, natural and artificial wood hydrolysates. Low amounts of the potential inhibitory compounds present in natural wood hydrolysates showed no negative effect on 2,3-BD production, while higher concentrations led to inhibiting effects. A scale-up to the 3.5 L bioreactor scale was carried out and optimal conditions for temperature, stirring speed and aeration rate were found. For P. polymyxa, an increase in productivity could be obtained using forced pH fluctuations. For B. licheniformis, 2,3-BD synthesis could be increased up to 78.9 g/L (batch) and 127.4 g/L (fed-batch) using 180 g/L initial glucose and 37°C. A successful scale-up to the 45 L bioreactor scale was obtained using the impeller tip speed as scale-up criterion, yielding up to 65.1 g/L 2,3-BD from 154 g/L glucose. The obtained results are the highest 2,3-BD concentrations reported so far using GRAS microorganisms and lie in the same range with data described for risk group 2 strains. B. licheniformis DSM 8785 is a suitable candidate for large scale 2,3-BD production processes.Das Ziel dieser Arbeit war die Entwicklung eines effizienten fermentativen Prozesses für die 2,3-Butandiol (2,3-BD) Bildung aus Holzhydrolysaten unter Einsatz nicht-pathogener Mikroorganismen. Die erste Aufgabe war das Screening nach geeigneten nicht-pathogenen Mikroorganismen aus unterschiedlichen Quellen und deren Untersuchung hinsichtlich 2,3-BD Bildung. Die besten Ergebnisse wurden mit Paenibacillus polymyxa ATCC 12321 und Bacillus licheniformis DSM 8785 erzielt. Während Batch-Kultivierungen im Schüttelkolbenmaßstab wurden Optimierungen hinsichtlich folgender Parameter vorgenommen: C-/N-Quelle und Konzentration, Schüttelgeschwindigkeit, Temperatur, Einsatz von freien/immobilisierten Zellen. Die 2,3-BD Produktion konnte durch Fed-Batch-Kultivierungen mit schrittweise Zugabe von Nährstoffen auf 63.3 g/L (P. polymyxa) bzw. 144.7 g/L (B. licheniformis) erhöht werden. Kultivierungen auf Glucose bzw. natürlichem/künstlichem Holzhydrolysat wiesen ähnliche Ergebnisse auf. Niedrige Mengen der Hemmstoffe zeigten keinen negativen Einfluss auf die 2,3-BD Produktion, während höhere Konzentrationen zu inhibierenden Effekten führten. Bei dem Scale-up der 2,3-BD Produktion zum 3,5 L Bioreaktormaßstab wurden optimale Bedingungen für Temperatur, Rührergeschwindigkeit und Belüftungsrate gesucht. Durch den Einsatz erzwungener pH-Shifts konnte ein Anstieg der Produktivität für P. polymyxa erreicht werden. Mit B. licheniformis wurden bis zu 78,9 g/L 2,3-BD (Batch) und 127,4 g/L (Fed-Batch) von 180 g/L Glucose bei 37°C erzielt. Unter Verwendung der Rührerspitzengeschwindigkeit als Scale-up Kriterium konnte ein gelungenes Scale-up zum 45 L Bioreaktormaßstab durchgeführt werden und die 2,3-BD Produktion konnte auf 65,1 g/L erhöht werden. Die Ergebnisse weisen die höchsten 2,3-BD Konzentrationen auf, die bisher mit GRAS Mikroorganismen erzielt wurden und in der Größenordnung der Risikoklasse 2 Stämme liegen. B. licheniformis DSM 8785 ist für die 2,3-BD Produktion im großen Maßstab geeignet

Low-Voltage Polymer/Small-Molecule Blend Organic Thin-Film Transistors and Circuits Fabricated via Spray Deposition

Organic thin-film electronics have long been considered an enticing candidate in achieving high-throughput manufacturing of low-power ubiquitous electronics. However, to achieve this goal, more work is required to reduce operating voltages and develop suitable mass-manufacture techniques. Here, we demonstrate low-voltage spray-cast organic thin-film transistors based on a semiconductor blend of 2,8-difluoro- 5,11-bis (triethylsilylethynyl) anthradithiophene and poly(triarylamine). Both semiconductor and dielectric films are deposited via successive spray deposition in ambient conditions (air with 40%–60% relative humidity) without any special precautions. Despite the simplicity of the deposition method, p-channel transistors with hole mobilities of \u3e1 cm2/Vs are realized at −4 V operation, and unipolar inverters operating at −6 V are demonstrated

Pentacene islands grown on ultra-thin SiO2

Ultra-thin oxide (UTO) films were grown on Si(111) in ultrahigh vacuum at room temperature and characterized by scanning tunneling microscopy. The ultra-thin oxide films were then used as substrates for room temperature growth of pentacene. The apparent height of the first layer is 1.57 +/- 0.05 nm, indicating standing up pentacene grains in the thin-film phase were formed. Pentacene is molecularly resolved in the second and subsequent molecular layers. The measured in-plane unit cell for the pentacene (001) plane (ab plane) is a=0.76+/-0.01 nm, b=0.59+/-0.01 nm, and gamma=87.5+/-0.4 degrees. The films are unperturbed by the UTO's short-range spatial variation in tunneling probability, and reduce its corresponding effective roughness and correlation exponent with increasing thickness. The pentacene surface morphology follows that of the UTO substrate, preserving step structure, the long range surface rms roughness of ~0.1 nm, and the structural correlation exponent of ~1.Comment: 15 pages, 4 figure

Suppressing Bias Stress Degradation in High Performance Solution Processed Organic Transistors Operating in Air

Solution processed organic field effect transistors can become ubiquitous in flexible optoelectronics. While progress in material and device design has been astonishing, low environmental and operational stabilities remain longstanding problems obstructing their immediate deployment in real world applications. Here, we introduce a strategy to identify the most probable and severe degradation pathways in organic transistors and then implement a method to eliminate the main sources of instabilities. Real time monitoring of the energetic distribution and transformation of electronic trap states during device operation, in conjunction with simulations, revealed the nature of traps responsible for performance degradation. With this information, we designed the most efficient encapsulation strategy for each device type, which resulted in fabrication of high performance, environmentally and operationally stable small molecule and polymeric transistors with consistent mobility and unparalleled threshold voltage shifts as low as 0.1 V under the application of high bias stress in air

Landslide Susceptibility Mapping in the Vrancea-Buzau Seismic Region, Southeast Romania

peer reviewedThis study presents the results of a landslide susceptibility analysis applied to the Vrancea- Buzau seismogenic region in the Carpathian Mountains, Romania. The target area is affected by a large diversity of landslide processes. Slopes are made-up of various types of rocks, climatic conditions can be classified as wet, and the area is a seismically active one. All this contributes to the observed high landslide hazard. The paper analyses the spatial component of the landslide hazard affecting the target area, the regional landslide susceptibility. First, an existing landslide inventory was completed to cover a wider area for the landslide susceptibility analysis. Second, two types of methods are applied, a purely statistical technique, based on correlations between landslide occurrence and local conditions, as well as the simplified spatial process-based Newmark Displacement analysis. Landslide susceptibility maps have been produced by applying both methods, the second one also allowing us to simulate different scenarios, based on various soil saturation rates and seismic inputs. Furthermore, landslide susceptibility was computed both for the landslide source and runout zones—the first providing information about areas where landslides are preferentially triggered and the second indicating where landslides preferentially move along the slope and accumulate. The analysis showed that any of the different methods applied produces reliable maps of landslide susceptibility. However, uncertainties were also outlined as validation is insufficient, especially in the northern area, where only a few landslides could be mapped due to the intense vegetation cover