Dissertation Defenses

Doctoral Dissertation Announcement

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Candidate: Chaminda Nalaka Kodituwakku

Degree of: Doctor of Philosophy

Department: Physics

Title: Inelastic X-Ray Scattering Studies on Organic Semiconductors and Organic Superconductors

Committee:
Dr. Clement Burns, Chair
Dr. Harald Sinn
Dr. Thomas Gorczyca
Dr. Lisa Paulius

Date: Wednesday, March 28, 2007 2:00 p.m. – 4:00 p.m.
2202 Everett Tower

Abstract:
We present studies of x-ray inelastic scattering measurements on the organic semiconductor copper phthalocyanine (β−CuPc) and organic superconductor k−(BEDT-TTF)2Cu(NCN)2.  We have measured electronic excitations and excitons in CuPc polycrystalline and single crystals samples. Measurements on a polycrystalline sample were done with 300 meV resolution and measurements on a single crystal were done using 120 meV resolution. TD-DFT calculations were done on CuPc molecule to understand the electronic excitations in this system.

Several interesting features were observed on this organic semiconductor system. Lower energy excitons were observed in a single crystal. These excitons are visible only along the major axis (b) of the crystal and moreover exist only over a limited region of momentum transfer. Higher energy excitations are consistent with the TD-DFT calculations.

Phonon measurements were done above and below of superconducting transition temperature on organic superconductor k−(BEDT-TTF)2Cu(NCN)2. Measurements were very challenging but we managed to see phonon shifts above and below the superconducting phase transition.  Finally, a preparation procedure of medium energy resolution (120 meV) Ge (733) inelastic x-ray scattering analyzer will be discussed.