Limiting Intersystem Crossing in Conjugated Polymers by Molecular Design
✍ Scribed by A.J. Cadby; C. Yang; S. Holdcroft; D.D.C. Bradley; P.A. Lane
- Publisher
- John Wiley and Sons
- Year
- 2002
- Tongue
- English
- Weight
- 216 KB
- Volume
- 14
- Category
- Article
- ISSN
- 0935-9648
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✦ Synopsis
could be obtained from the image by fitting the measured data to this equation. The inset in Figure 3 is a plot of the angle between the (001) normal and the grain boundary plane as a function of distance from the boundary for two different regions of the nanocrystal shown. As can be seen in the figure, the boundary showed a transition from wide to narrow at a constant boundary angle. At the bottom of the grain boundary the width was 2.4 nm, and at the top it was 0.4 nm, a value on the order of the size of one unit cell.
The fringes were out of registry in the upper part of the boundary, which was consistent with the assertion that contact between the conducting layers was not maintained there. Previous work has shown that high-angle grain boundaries in crystalline organics act as deep traps for carriers. The ability to transport charge and maintain mechanical strength across grain boundaries in polydiacetylene bicrystals was lost for misorientation angles greater than 15. [17] The pentacene nanocrystal in Figure 3 showed a transition from continuous bending over an extended range to a localized grain boundary at a constant boundary angle ( 40). The ability of the pentacene lattice to locally bend may increase charge transport across grains as well as overall mechanical strength. [22] We have investigated the crystal microstructure and related defects in pentacene nanocrystals using optical microscopy, XRD, and HREM. Thin samples of pentacene were produced by mechanical disruption of the bulk powder. Our results confirm that the nanocrystals contained only the bulk phase of pentacene, and no reorganization of the material was seen near crystal surfaces or in the thinnest crystals. Lattice defects such as grain boundaries and dislocations were imaged, and variations in the way the pentacene (001) layers accommodated the distortions by lattice bending were discussed.