Imaging the domain structure of organic semiconductor films

State‐of‐the‐art solution‐processed organic field‐effect transistors typically use polycrystalline organic semiconductor thin films as the active layer. Although it is widely regarded that boundaries between polycrystalline domains are a likely source of charge trapping limiting charge carrier mobility, little is known about the detailed domain structure of such films. Furthermore, variations in local order particularly in conjugated polymer films are likely to further impede charge transport. In recent years a number of techniques have been exploited that are able to provide information regarding local domain orientation and molecular order in polycrystalline organic thin films. These techniques have provided new information regarding the nature of domain structure providing an opportunity to directly evaluate the influence of domain structure on device operation. This article aims to provide a timely review of the experimental approaches used to date and provide a perspective for future work. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

A study of mixed mode fracture by photoelasticity and digital image analysis

In this paper, the results from two experimental methodologies, photoelasticity aided by digital image processing and precision digital image correlation, are presented for a mixed mode fracture problem. The mixed mode fracture problem was a three-point-bend edge-crack specimen which was loaded at various off-crack-line locations between the crack line and the specimen support line. The estimations of K_I and K_II from both methodologies indicate that the crack tip stress field is strongly intensified by K_I but not K_II.     

Molecular structure of 2,4-dicarba-closo.heptaborane-7 by gas-phase electron diffraction

Gas phase electron diffraction patterns of 2,4-dicarba-closo-heptaborane were recorded at room temperature. Least squares analysis of the reduced intensity data show that the molecule is a pentagonal bipyramid and confirms the C_2v symmetry in the gas phase. The carbon atoms are located in the pentagonal belt and are separated by one boron atom. No significant departures from planarity of the pentagonal belt are indicated. The bond lengths in the belt are C(4)-B(3), 1.537 Å, C(4)-B(5), 1.558 Å, and B(5)-B(6), 1.659 Å. The distance from the apical B(l) atom to the B(3) is 1.852 Å, from the B(1) to the B(5) atom is 1.772 A, and from the B(1) to the C(2) atom is 1.717 Å. The bond angles in the pentagonal belt are C(2)B(3)C(4) = 100.5°, B(3)C(4)B(5) = 116.7° and C(4)B(5)B(6) = 103.0°. The angle between B(1)B(3)B(7) = 84.7°. Comparisons are made with structural data and moments of inertia determined by microwave spectroscopy.     

Thermal degradation of poly(vinyl bromide), vinyl bromide-methyl methacrylate copolymers,and poly(vinyl bromide)-poly(methyl methacrylate) blends

Degradation behavior has been compared for PVB, five VB-MMA copolymers which span the composition range, PMMA, and PVC by using thermogravimetry in dynamic nitrogen and thermal volatilization analysis (TVA) under vacuum for programmed heating at 10°C/min. Volatile products have been separated by subambient TVA and identified. PVB is substantially less stable than PVC but shows inmost respects analogous degradation behavior. The introduction of VB into the PMMA chain leads to intramolecular lactonization with release of methyl bromide at temperatures a little above 100°C; after this reaction is complete, however, the polymer is more stable toward volatilization than PMMA. Copolymers with moderate and high VB contents also lose hydrogen bromide. Carbon dioxide is a significant product at intermediate compositions. The variation of product distribution with copolymer composition is discussed in relation to the several reactions involved and comparisons are made with VC-MMA copolymers. PVB-PMMA blends snow some features of degradation behavior in common with the PVC-PMMA system but also very important differences. The effect of PVB is only to stabilize the PMMA; the mechanism is discussed. The role of PVB as an additive and VB as a comonomer for fire-retardant PMMA compositions is briefly considered in relation to earlier studies.     

Studies of the alpha decay of U

The decay of ²³³U through the first and second excited states of ²²⁹Th has been studied using a uranium oxide source. The half-life of the first excited state of ²²⁹Th was found to be less than 1.9 nsec; it decays by an almost pure M1 transition. The half-life of the second excited state of ²²⁹Th was found to be 0.5±0.2nsec; this level de-excites by E2 cross-over radiation in 96% of events. Contrary to expectations, an anisotropic alpha-gamma angular correlation was not found, and the probable reason for this is discussed.     

Two-proton neutron-hole yrast excitations in 66 147 Dy81

The level structure of theN=81 nucleus¹⁴⁷Dy has been studied byγ-ray spectroscopy following reactions of 230–250 MeV^58,60Ni beams on⁸⁹Y and^90,92Zr targets. Yrast and near-yrast levels in¹⁴⁷Dy above the known 59-s 11/2^? state are established up to ～3.7 MeV; they include isomeric levels at 2,681, 3,407 and 3,650 keV. Guided by the results of shell model calculations, we interpret most of the observed level as senioritythree states arising from the coupling ofs _1/2,d _3/2, andh _11/2 neutron holes withπh _11/2 ².     

The inhibition of factor inhibiting hypoxia-inducible factor (FIH) by beta-oxocarboxylic acids

Cyclic beta-oxocarboxylic acids inhibit factor inhibiting hypoxia-inducible factor via ligation to the active site iron.     

Pulse FT NMR of non-equilibrium states of half-integer spin quadrupolar nuclei in single crystals

For quadrupolar nuclei with spin quantum numbers equal to 3/2, 5/2 and 7/2, the intensities of the NMR transitions in a single crystal are examined as a function of the rf excitation flip angle. Single-quantum NMR intensities are calculated using density matrix theory beginning under various non-equilibrium conditions and are compared with those determined experimentally. As a representative spin-3/2 system, the flip-angle dependence of the ²³Na NMR intensities of a single crystal of NaNO₃ was investigated beginning with the inversion of the populations associated with one of the satellite transitions. Subsequently, the populations of both satellite transitions were inverted using highly frequency-selective hyperbolic secant pulses. Calculated and experimental intensities are in good agreement. As an example of a spin-5/2 system, the flip-angle dependence of the ²⁷Al NMR transition intensities was determined using a single crystal of sapphire, Al₂O₃, starting under different nuclear spin population conditions. The experimental trends mimicked those predicted by the density matrix calculations but the agreement was not as good as for the spin-3/2 case. Some SIMPSON simulations were also carried out to confirm the results generated by our density matrix calculations. The theoretical flip-angle behavior of the NMR transition intensities obtained from a spin-7/2 spin system is also discussed.