Author : Jeremy D. Bergeson
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (137 download)
Book Synopsis Spin-dependent Transport Phenomena in Organic Semiconductors by : Jeremy D. Bergeson
Download or read book Spin-dependent Transport Phenomena in Organic Semiconductors written by Jeremy D. Bergeson and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: Thin-film organic semiconductor transport can have an anomalously high sensitivity to low magnetic fields. Such a response is unexpected considering that at a modest magnetic field of 100 Oe the ratio of thermal energy to the energy associated with the intrinsic spin of charge carriers is 104 at room temperature and 102 at liquid helium temperatures. Nevertheless, we report experimental characterization of (1) spin-dependent injection, detection and transport through organic semiconductors and (2) the influence of a magnetic field on the spin dynamics of recombination-limited transport. The first focus of this work is accomplished by fabricating basic spin-valve devices consisting of two magnetic layers spatially separated by a nonmagnetic organic semiconductor. The spin-valve effect is a change in electrical resistance due to the magnetizations of the magnetic layers changing from parallel to antiparallel alignment, or vice versa. Metallic and semiconductor conductivities differ by many orders of magnitude inhibiting spin injection from the magnet into the nonmagnet, however, we achieve a 20% spin-valve effect at cryogenic temperatures by inserting ultra-thin tunnel barriers at the metal/semiconductor interfaces. In a unique device we replace one metallic magnet with the organic-based magnetic semiconductor vanadium tetracyanoethylene (V[TCNE]2) and attain a spin-valve effect at 10 K. The second focus of this work is the bulk magnetoresistance (MR) of thin-film small molecule, oligomer and polymer organic semiconductor structures. At room temperature the resistance can change significantly (up to 8% at 100 Oe, 15% at 1000 Oe.) Depending on parameters such as temperature, layer thickness, or voltage, the resistance of these materials may increase or decrease as a function of field. A model, termed magnetoresistance by the interconversion of singlets and triplets (MIST), is developed to account for this anomalous behavior. The MIST mechanism predicts that increasing the spin-orbit coupling in the organic semiconductor should decrease the magnitude of the MR. In an experiment where the small molecule Alq3 is doped with strong spin-orbit coupling molecules the MR decreases by an order of magnitude or more, depending on the doping. In addition, we show the experimental observation of high-field MR in devices with and without magnetic contacts.