Tailoring the molecular structure to suppress extrinsic disorder in organic transistors

In organic field-effect transistors, the structure of the constituent molecules can be tailored to minimize the disorder experienced by charge carriers. Experiments on two perylene derivatives show that disorder can be suppressed by attaching longer core substituents - thereby reducing potential fluctuations in the transistor channel and increasing the mobility at low temperature - without altering the intrinsic transport properties

Description of a Sarcoptic Mange Outbreak in Alpine Chamois Using an Enhanced Surveillance Approach

Since 1995, the Alpine chamois (Rupicapra r. rupicapra) population of the Dolomites has been affected by sarcoptic mange with considerable management concerns. In this study, 15 years (2006–2020) of passive surveillance and demographic data were analyzed in order to describe a mange outbreak. Furthermore, an enhanced passive surveillance protocol was implemented in order to evaluate the efficiency of ordinary vs. enhanced surveillance protocol in identifying dead chamois in the field and in reaching a correct diagnosis. Our results confirm the role of mange as a determining factor for chamois mortality, while stressing the importance of a wider view on the factors affecting population dynamics. The enhanced passive surveillance protocol increased the probability of carcass retrieval and identification of the cause of death; however, its adoption may be too costly if applied for long periods on a wide scale. Passive surveillance, in both ordinary and enhanced surveillance protocol, should encompass the use of other strategies in the future to study the eco-epidemiology of the disease in wild Caprinae

Electronic structure of few-layer black phosphorus from μ\mu-ARPES

Black phosphorus (BP) stands out among two-dimensional (2D) semiconductors because of its high mobility and thickness dependent direct band gap. However, the quasiparticle band structure of ultrathin BP has remained inaccessible to experiment thus far. Here we use a recently developed laser-based micro-focus angle resolved photoemission ($\mu$-ARPES) system to establish the electronic structure of 2-9 layer BP from experiment. Our measurements unveil ladders of anisotropic, quantized subbands at energies that deviate from the scaling observed in conventional semiconductor quantum wells. We quantify the anisotropy of the effective masses and determine universal tight-binding parameters which provide an accurate description of the electronic structure for all thicknesses.Comment: Supporting Information available upon reques

The mechanism of NO and N2O decomposition catalyzed by short-distance Cu(I) pairs in Cu-ZSM-5: A DFT study on the possible role of NO and NO2in the [Cu–O–Cu]2+active site reduction

The reactivity between NO and the oxidized form of a short-distance dinuclear Cu-ZSM-5 catalyst (ZCu2O) was investigated. ZCu2O, which contains the [Cu–O–Cu]2+bridge coordinated at the opposite T11 positions of the M6 ring of ZSM-5, is obtained by the spin-forbidden decomposition of N2O on the reduced form of the catalyst, ZCu2, with an activation energy of about 18 kcal mol−1. The further addition of NO to the [Cu–O–Cu]2+unit of ZCu2O occurs in the doublet state without activation energy and gives NO2. After desorption, which requires 39.9 kcal mol−1, NO2decomposes on a second ZCu2O site, giving NO again and O2. Three reaction paths were defined for the latter reaction, with activation energies ranging from about 30 to 42–43 kcal mol−1. Final O2desorption is endothermic. The effect of enthalpy and Gibbs free energy contributions at 298.15 and at 773 K was also shown and discussed. According to the present calculations, the [Cu–O–Cu]2+bridge can easily be broken by reaction with NO but the desorption and further decomposition of NO2are characterized by energetics which make the above mechanism slower than the spin-allowed decomposition of N2O on similar sites, already reported in the literature. The above conclusions were based on a kinetic analysis according to the Energetic Span Model

A DFT study on the mechanism of NO decomposition catalyzed by short-distance Cu(I) pairs in Cu-ZSM-5

The complete NO decomposition catalyzed by short-distance Cu+ pairs in Cu-ZSM-5 was studied by means of DFT calculations. After adsorption of two NO molecules, an hyponitrite species is formed. Further decomposition of hyponitrite occurs with activation energies ranging from about 4 to 24 kcal mol−1, depending on the initial geometry of the substrate-catalyst complex. An oxidized form of the catalyst, [Cu[sbnd]O[sbnd]Cu]2+ and a copper-coordinating N2O molecule are obtained. Further N2O decomposition may occur with oxygen transfer from N2O to [Cu[sbnd]O[sbnd]Cu]2+ and formation of N2 and O2, both adsorbed on the catalyst. Three different kinds of transition states were identified for the latter step, which appears to be rate-determining due to activation energies ranging from 39–40, to 44–45, and to 50–52 kcal mol−1, respectively. After this, N2 desorption occurs easily, whereas O2 desorption is endothermic (from 28.8 to 36.5 kcal mol−1), the highest value being associated to reductive O2 desorption from a peroxide-like complex. It turned out that the best way for N2O elimination is the direct, spin-forbidden decomposition on a reduced Cu+⋯Cu+ pair, with formation of [Cu[sbnd]O[sbnd]Cu]2+ and N2, as already suggested in the literature. The problem of how the reduced catalyst may be regenerated is left open. © 2017 Elsevier B.V

A theoretical study of hydrogen bonding, proton transfer and kinetic isotope effects in the dimers of 2-tetrahydropyranol and in the 2-tetrahydropyranol-H2O adducts

The epimerization process of the model sugar 2-tetrahydropyranol was studied by means of ab initio calculations. The results suggest that the rate limiting step of sugar ring opening involves a high-energy intramolecular proton transfer reaction or a low-energy process in which the proton transfer is mediated by a catalyst molecule, formic acid in the case investigated. The catalyzed process is an asynchronous concerted double proton transfer reaction, where both protons are transferred within the same elementary step but one of them is transferred much earlier than the other one along the reaction coordinate. The motion of both protons in the transition state of the catalyzed process is strongly coupled with the breaking of the C-O bond of the sugar ring. Geometry optimization at the B3LYP/6-31G* level, with additional p polarization functions located on the hydrogen atoms involved in proton transfer, appears to be suitable for further MP2/6-31G** single point energy calculations, as it provides hydrogen bond and activation energies in good agreement with those obtained from geometry optimization at the full MP2 level of theor

The epimerisation of 2-tetrahydropyranol catalysed by the tautomeric couples 2-pyridone/2-hydroxypyridine and formamide/formamidic acid as a model for the sugar's mutarotation: a theoretical study

In the present computational study a complete reaction mechanism for the sugar's mutarotation promoted by tautomeric catalysts in vacuum is outlined. The rate determining step of the process consists in the breaking of the C-O bond of the sugar ring which occurs by a concerted double proton transfer between the substrate and the catalyst. After ring opening, the -CHO group of the substrate rotates around the C2-C3 bond without dissociation of the substrate catalyst adduct. Theactivation energy of this step is generally less than 8-9 kcal mol(-1). Alternative reaction paths which require the dissociation of the substrate catalyst complex are less favourable for both probability and energetic reasons. When the mutarotation is catalysed by the 2-pyridone/2-hydroxypyridine (PD/HP) tautomeric couple, the process may be promoted by either PD or HP derived from the dissociation of the (PD)(2), (HP)(2) or PD-HP dimers. According to B3LYP and MP4 (SDQ) calculations the HP-promoted reaction path should be faster than the PD-promoted one. When the process is catalysed by the formamide/formamidic acid (F/FA) tautomeric couple, the reaction path promoted by FA, which is derived from the dissociation of the F-FA dimer, should be the most favourable, according to B3LYP, MP2 and MP4(SDQ) calculations. Solvent effects in benzene, calculated by the PCM method, did not affect to a relevant extent the mechanism outlined in vacuum. The present study suggests, differing from the hypothesis formulated in many experimental studies, that the sugar's mutarotation process is more efficiently catalysed by the less stable tautomer or catalyst dimer rather than by the more stable one of both the PD/HP and F/FA couples