The interaction of dislocations with precipitates is an essential strengthening mechanism in metals, as exemplified by the superior high-temperature strength of Ni-base superalloys. Here we use atomistic simulation samples generated from atom probe tomography data of a single crystal superalloy to study the interactions of matrix dislocations with a γ precipitate in molecular dynamics simulations. It is shown that the precipitate morphology, in particular its local curvature, and the local chemical composition significantly alter both, the misfit dislocation network which forms at the precipitate interface, and the core structure of the misfit dislocations. Simulated tensile tests reveal the atomic scale details of many experimentally observed dislocation-precipitate interaction mechanisms, which cannot be reproduced by idealized simulation setups with planar interfaces. We thus demonstrate the need to include interface curvature in the study of semicoherent precipitates and introduce as an enabling method atom probe tomography-informed atomistic simulations.

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Transient electroluminescence (EL) from polymer light emitting diodes is investigated by measurements of the response to short voltage pulses. The carrier mobility is derived from the delay time between the electrical pulse and the onset of EL, μ≈3×10−4 cm2/V s. Bilayer devices with a polyethylene-dioxythiophene (PEDOT), hole injection layer are also studied. The delay time between the electrical pulse and the onset of EL is independent of the thickness of the injection layer, implying that the conducting PEDOT functions as a part of the electrode. When a dc forward bias is applied to the device, the delay time decreases, probably as a result of the shift of the emission zone towards the anode. The EL turn-on depends on the amplitude of the voltage pulse. The data are modeled by an equivalent circuit with a fixed capacitance connected in parallel with a nonlinear resistance. The solution of the differential equation depends on the exact form of the device’s I–V curve. Two analytical solutions are provided, and an analysis based on space-charge-limited current is presented. By applying a dc forward bias in advance to precharge the space-charge capacitance, the turn-on response time is reduced to 12 ns. The EL decay consists of two components with time constants of 15 ns and 1 μs. The decay does not depend on either the amplitude of the voltage pulse or the prebias.

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