Computation of Electrostatic Field near Three-Dimensional Corners and Edges

Theoretically, the electric field becomes infinite at corners of two and three dimensions and edges of three dimensions. Conventional finite-element and boundary element methods do not yield satisfactory results at close proximity to these singular locations. In this paper, we describe the application of a fast and accurate BEM solver (which usesexact analytic expressions to compute the effect of source distributions on flatsurfaces) to compute the electric field near three-dimensional corners and edges. Results have been obtained for distances as close as 1$\mu m$ near the corner/edge and good agreement has been observed between the present results and existing analytical solutions.Comment: Presented in International Conference on Computational and Experimental Engineering and Sciences held at IIT Madras, Chennai, India, during 1-6 December, 200

Mapping Orientational Order of Charge-Probed Domains in a Semiconducting Polymer

Structure–property relationships are of fundamental importance to develop quantitative models describing charge transport in organic semiconductor based electronic devices, which are among the best candidates for future portable and lightweight electronic applications. While microstructural investigations, such as those based on X-rays, electron microscopy, or polarized optical probes, provide necessary information for the rationalization of transport in macromolecular solids, a general model predicting how charge accommodates within structural maps is not yet available. Therefore, techniques capable of directly monitoring how charge is distributed when injected into a polymer film and how it correlates to structural domains can help fill this gap. Supported by density functional theory calculations, here we show that polarized charge modulation microscopy (p-CMM) can unambiguously and selectively map the orientational order of the only conjugated segments that are probed by mobile charge in the few nanometer thick accumulation layer of a high-mobility polymer-based field-effect transistor . Depending on the specific solvent-induced microstructure within the accumulation layer, we show that p-CMM can image charge-probed domains that extend from submicrometer to tens of micrometers size, with markedly different degrees of alignment. Wider and more ordered p-CMM domains are associated with improved carrier mobility, as extracted from device characteristics. This observation evidences the unprecedented opportunity to correlate, directly in a working device, electronic properties with structural information on those conjugated segments involved in charge transport at the buried semiconductor–dielectric interface of a field-effect device

Light-Controlled Resistance Modulation in a Photochromic Diarylethene\u2013Carbon Nanotube Blend

Photochromic molecules are part of a large class of materials in which light stimulus not only induces a color variation but also affects other physicochemical properties. However, the change of bulk electrical properties (e.g., electrical conductivity) via light excitation remains difficult to control because the intrinsically switchable molecules may lose their functionality when wired with conductive electrodes. In contrast with previous work based on single molecules, here we demonstrate a facile and accessible \u201cwet-chemical\u201d method to produce light-induced electrical switching. The electrical conductivity of a photochromic blend composed of diarylethene polymer and single-walled carbon nanotubes (SWNTs) is reversibly tuned according with UV 12vis excitation. The devices present good thermal stability and remarkable fatigue resistance under ambient conditions. Supported by electrical and spectroscopic evidence, we show that the intertube electrical coupling, mediated by the light-induced electrocyclization of the diarylethene unit, is the mechanism responsible for the modulation