Domain walls may play an important role in future electronic devices, given their small size as well as the fact that their location can be controlled. Here, we report the observation of room-temperature electronic conductivity at ferroelectric domain walls in the insulating multiferroic BiFeO(3). The origin and nature of the observed conductivity are probed using a combination of conductive atomic force microscopy, high-resolution transmission electron microscopy and first-principles density functional computations. Our analyses indicate that the conductivity correlates with structurally driven changes in both the electrostatic potential and the local electronic structure, which shows a decrease in the bandgap at the domain wall. Additionally, we demonstrate the potential for device applications of such conducting nanoscale features.

We present a rst-principles density functional study of the structural, electronic and magnetic properties of the ferroelectric domain walls in multiferroic BiFeO3. We nd that domain walls in which the rotations of the oxygen octahedra do not change their phase when the polarization reorients are the most favorable, and of these the 109 • domain wall centered around the BiO plane has the lowest energy. The 109 • and 180 • walls have a signicant change in the component of their polarization perpendicular to the wall; the corresponding step in the electrostatic potential is consistent with a recent report of electrical conductivity at the domain walls. Finally, we show that changes in the Fe-O-Fe bond angles at the domain walls cause changes in the canting of the Fe magnetic moments which can enhance the local magnetization at the domain walls.

[3]-Radialene-based dopant CN6-CP studied herein, with its reduction potential of +0.8 versus Fc/Fc+ and the lowest unoccupied molecular orbital level of -5.87 eV, is the strongest molecular p-dopant reported in the open literature, so far. The efficient p-doping of the donor-acceptor dithienyl-diketopyrrolopyrrole-based copolymer having the highest unoccupied molecular orbital level of -5.49 eV is achieved. The doped films exhibit electrical conductivities up to 70 S cm(-1) .

Herein we present a molecular doping of a high mobility diketopyrrolopyrrole−dithienylthieno[3,2-b]thiophene donor−acceptor copolymer poly[3,6-thiophene], PDPP(6-DO) 2 TT, with the electron-deficient compound hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ). Despite a slightly negative HOMO donor −LUMO acceptor offset of −0.12 eV which may suggest a reduced driving force for the charge transfer (CT), a partial charge CT was experimentally observed in PDPP(6-DO) 2 TT:F6TCNNQ by absorption, vibrational, and electron paramagnetic resonance spectroscopies and predicted by density functional theory calculations. Despite the modest CT, PDPP(6-DO) 2 TT:F6TCNNQ films possess unexpectedly high conductivities up to 2 S/cm (comparable with the conductivities of the benchmark doped polymer system P3HT:F4TCNQ having a large positive offset). The observation of the high conductivity in doped PDPP(6-DO) 2 TT films can be explained by a high hole mobility in PDPP(6-DO) 2 TT blends which compensates a lowered (relatively to P3HT:F4TCNQ) concentration of free charge carriers. We also show that F6TCNNQ-doped P3HT, the system which has not been reported so far to the best of our knowledge, exhibits a conductivity up to 7 S/cm, which exceeds the conductivity of the benchmark P3HT:F4TCNQ system.