Low-Temperature Phase Transitions in a Soluble Oligoacene and Their Effect on Device Performance and Stability

The use of organic semiconductors in high-performance organic field-effect transistors requires a thorough understanding of the effects that processing conditions, thermal, and bias-stress history have on device operation. Here, we evaluate the temperature dependence of the electrical properties of transistors fabricated with 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene, a material that has attracted much attention recently due to its exceptional electrical properties. We have discovered a phase transition at T = 205 K and discuss its implications on device performance and stability. We examined the impact of this low-temperature phase transition on the thermodynamic, electrical, and structural properties of both single crystals and thin films of this material. Our results show that while the changes to the crystal structure are reversible, the induced thermal stress yields irreversible degradation of the devices

The Halo Mass of Optically Luminous Quasars at z ,F≈ ,F1-2 Measured via Gravitational Deflection of the Cosmic Microwave Background

© 2019. The American Astronomical Society. All rights reserved.We measure the average deflection of cosmic microwave background photons by quasars at 〈Z〉= 1.7. Our sample is selected from the Sloan Digital Sky Survey to cover the redshift range 0.9 ≤z≤2.2 with absolute i-band magnitudes of M i ≤-24 (K-corrected to z = 2). A stack of nearly 200,000 targets reveals an 8δ detection of Planck's estimate of the lensing convergence toward the quasars. We fit the signal with a model comprising a Navarro-Frenk-White density profile and a two-halo term accounting for correlated large-scale structure, which dominates the observed signal. The best-fitting model is described by an average halo mass log 10 (M h h -1 M)12.6 ±0.2 = and linear bias b=2.7±0.3 at 〈Z 〉= 1.7, in excellent agreement with clustering studies. We also report a hint, at a 90% confidence level, of a correlation between the convergence amplitude and luminosity, indicating that quasars brighter than Mi≲ -26 reside in halos of typical mass M h ≈ 10 13 h -1 M, scaling roughly as M h ∞ L opt 3/4 at M i ≲-24 mag, in good agreement with physically motivated quasar demography models. Although we acknowledge that this luminosity dependence is a marginal result, the observed Mh-L opt relationship could be interpreted as a reflection of the cutoff in the distribution of black hole accretion rates toward high Eddington ratios: the weak trend of Mh with Lopt observed at low luminosity becomes stronger for the most powerful quasars, which tend to be accreting close to the Eddington limit.Peer reviewedFinal Accepted Versio

Quantitative Analysis of the Density of Trap States at the Semiconductor-Dielectric Interface in Organic Field-Effect Transistors

The electrical properties of organic field-effect transistors are governed by the quality of the constituting layers, and the resulting interfaces. We compare the properties of the same organic semiconductor film, 2,8-difluoro- 5,11-bis (triethylsilylethynyl) anthradithiophene, with bottom SiO2 dielectric and top Cytop dielectric and find a 10× increase in charge carrier mobility, from 0.17 ± 0.19 cm2 V−1 s−1 to 1.5 ± 0.70 cm2 V−1 s−1, when the polymer dielectric is used. This results from a significant reduction of the trap density of states in the semiconductor band-gap, and a decrease in the contact resistance

Charges and fluxes in Maxwell theory on compact manifolds with boundary

We investigate the charges and fluxes that can occur in higher-order Abelian gauge theories defined on compact space-time manifolds with boundary. The boundary is necessary to supply a destination to the electric lines of force emanating from brane sources, thus allowing non-zero net electric charges, but it also introduces new types of electric and magnetic flux. The resulting structure of currents, charges, and fluxes is studied and expressed in the language of relative homology and de Rham cohomology and the corresponding abelian groups. These can be organised in terms of a pair of exact sequences related by the Poincar\'e-Lefschetz isomorphism and by a weaker flip symmetry exchanging the ends of the sequences. It is shown how all this structure is brought into play by the imposition of the appropriately generalised Maxwell's equations. The requirement that these equations be integrable restricts the world-volume of a permitted brane (assumed closed) to be homologous to a cycle on the boundary of space-time. All electric charges and magnetic fluxes are quantised and satisfy the Dirac quantisation condition. But through some boundary cycles there may be unquantised electric fluxes associated with quantised magnetic fluxes and so dyonic in nature.Comment: 28 pages, plain Te

Influences of the 2010 Eyjafjallajökull volcanic plume on air quality in the northern Alpine region

A series of major eruptions of the Eyjafjallajökull volcano in Iceland started on 14 April 2010 and continued until the end of May 2010. The volcanic emissions moved over nearly the whole of Europe and were observed first on 16 April 2010 in Southern Germany with different remote sensing systems from the ground and space. Enhanced PM10 and SO2 concentrations were detected on 17 April at mountain stations (Zugspitze/Schneefernerhaus and Schauinsland) as well as in Innsbruck by in situ measurement devices. On 19 April intensive vertical mixing and advection along with clear-sky conditions facilitated the entrainment of volcanic material down to the ground. The subsequent formation of a stably stratified lower atmosphere with limited mixing near the ground during the evening of 19 April led to an additional enhancement of near-surface particle concentrations. Consequently, on 19 April and 20 April exceedances of the daily threshold value for particulate matter (PM10) were reported at nearly all monitoring stations of the North Alpine foothills as well as at mountain and valley stations in the northern Alps. The chemical analyses of ambient PM10 at monitoring stations of the North Alpine foothills yielded elevated Titanium concentrations on 19/20 April which prove the presence of volcanic plume material. Following this result the PM10 threshold exceedances are also associated with the volcanic plume. The entrainment of the volcanic plume material mainly affected the concentrations of coarse particles (>1 μm) – interpreted as volcanic ash – and ultrafine particles (<100 nm), while the concentrations of accumulation mode aerosol (0.1–1 μm) were not changed significantly. With regard to the occurrence of ultrafine particles, it is concluded that their formation was triggered by high sulphuric acid concentrations which are necessarily generated by the photochemical processes in a plume rich in sulphur dioxide under high solar irradiance. It became evident that during the course of several days, the Eyjafjallajökull volcanic emissions influenced the near-surface atmosphere and thus the ambient air quality. Although the volcanic plume contributed to the overall exposure of the population of the northern Alpine region on two days, only minor effects on the exacerbation of respiratory and cardiovascular symptoms can be expected

Freezing-in orientational disorder induces crossover from thermally-activated to temperature-independent transport in organic semiconductors

The crystalline structure of organic materials dictates their physical properties, but while significant research effort is geared towards understanding structure-property relationships in such materials, the details remain unclear. Many organic crystals exhibit transitions in their electrical properties as a function of temperature. One example is the 1:1 charge-transfer complex trans--stilbene-2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane. Here we show that the mobility and resistivity of this material undergo a transition from being thermally activated at temperatures above 235 K to being temperature independent at low temperatures. On the basis of our experimental and theoretical results, we attribute this behaviour to the presence of a glass-like transition and the accompanied freezing-in of orientational disorder of the stilbene molecule

Net grassland carbon flux over a subambient to superambient CO2 gradient

Increasing atmospheric CO2 concentrations may have a profound effect on the structure and function of plant communities. A previously grazed, central Texas grassland was exposed to a 200-µmol mol-1 to 550 µmol mol-1 CO2 gradient from March to mid-December in 1998 and 1999 using two, 60-m long, polyethylene-covered chambers built directly onto the site. One chamber was operated at subambient CO2 concentrations (200-360 µmol mol-1 daytime) and the other was regulated at superambient concentrations (360-550 µmol mol-1). Continuous CO2 gradients were maintained in each chamber by photosynthesis during the day and respiration at night. Net ecosystem CO2 flux and end-of-year biomass were measured in each of 10, 5-m long sections in each chamber. Net CO2 fluxes were maximal in late May (c. day 150) in 1998 and in late August in 1999 (c. day 240). In both years, fluxes were near zero and similar in both chambers at the beginning and end of the growing season. Average daily CO2 flux in 1998 was 13 g CO2 m-2 day-1 in the subambient chamber and 20 g CO2 m-2 day-1 in the superambient chamber; comparable averages were 15 and 26 g CO2 m-2 day-1 in 1999. Flux was positively and linearly correlated with end-of-year above-ground biomass but flux was not linearly correlated with CO2 concentration; a finding likely to be explained by inherent differences in vegetation. Because C3 plants were the dominant functional group, we adjusted average daily flux in each section by dividing the flux by the average percentage C3 cover. Adjusted fluxes were better correlated with CO2 concentration, although scatter remained. Our results indicate that after accounting for vegetation differences, CO2 flux increased linearly with CO2 concentration. This trend was more evident at subambient than superambient CO2 concentrations

Dynamical Boson Stars

The idea of stable, localized bundles of energy has strong appeal as a model for particles. In the 1950s John Wheeler envisioned such bundles as smooth configurations of electromagnetic energy that he called {\em geons}, but none were found. Instead, particle-like solutions were found in the late 1960s with the addition of a scalar field, and these were given the name {\em boson stars}. Since then, boson stars find use in a wide variety of models as sources of dark matter, as black hole mimickers, in simple models of binary systems, and as a tool in finding black holes in higher dimensions with only a single killing vector. We discuss important varieties of boson stars, their dynamic properties, and some of their uses, concentrating on recent efforts.Comment: 79 pages, 25 figures, invited review for Living Reviews in Relativity; major revision in 201

Macro-financial linkages and bank behaviour: evidence from the second-round effects of the global financial crisis on East Asia

This paper studies the link between macro-financial variability and bank behaviour, which justifies the second-round effects of the global financial crisis on East Asia. Following Gallego et al. (The impact of the global economic and financial crisis on Central Eastern and South Eastern Europe (CESEE) and Latin America, 2010), the second round effects are defined as the adverse feedback loop from the slumps in economic activities and sharp financial market deterioration, which may influence the financial performance of bank, inter alia via deteriorating credit quality, declining profitability and increasing problems in retaining necessary capitalization. Differentiating itself from other research, this study stresses adjustments in four dimensions of bank performance and behaviour: asset quality, profitability, capital adequacy, and lending behaviour, assuming that any change in a bank-specific characteristic is induced by endogenous adjustments of the others. The empirical results based on partial adjustment models and two-step system GMM estimation show that bank’s adjustment behaviour is subject to the variation in the macro-financial environment and the stress condition in the global financial market. There is no convincing evidence to support the effectiveness of policy rate cut to boots bank lending and to avoid a financial accelerator effect