Laser heating of thick layers through a backwards, self-sustained propagation of a steep, steady state thermal front

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Published on 05 January 2009

Presented paper reports on switching device based on reversible modulation of charge carrier mobility by photochromic additive distributed in polymer matrix. The light induced photochromic conversion of the additive is accompanied by significant increase of its dipole moment. The presence of the dipole moment induces change of electrostatic potential in its vicinity and shifts the site energies of individual polymer repeating units. Since the position and orientation of the photochromic additive with respect to the polymer chain are essentially random the effect results in broadening of the distribution of the transport states and consequently in the lowering of the charge carriers mobility. These notions suggested by quantum chemistry modeling are proved by experimental characterization of the optical and electrical switching properties of the suggested switch. The observed current-voltage characteristics showed reversible decrease of the currents after the photochromic switching of the additive to its metastable state with high dipole moment. This behaviour was explained on the basis of charge carrier mobility decrease due to the presence of charge traps. Impedance spectroscopy revealed a drop of the bulk conductivity when the polar state of the photochromic molecules was present. The induced conductivity decrease is proportional to the drop observed by current-voltage characterization.