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Fatema, R. (2009). Helium Atom Scattering Study of the Surface Structure and Dynamics of KCl(001) and Potassium Tantalate (KTaO₃) Doped with
Lithium and Niobium. Retrieved from http://purl.flvc.org/fsu/fd/FSU_migr_etd-4495
The structure and dynamics of the (001) surface of potassium tantalate (KTaO3), doped with lithium (KTL) and niobium (KTN) have been investigated using high resolution helium atom diffraction and single-phonon creation and annihilation, inelastic scattering experiments. This work is the first to investigate the surface structure and dynamics of KTL samples. These experiments are an extension of earlier work done with pure KTaO3 and KTN crystals. As in the previous experiments broad half-order diffraction peaks were observed in the <100> azimuth, which may be related to the formation of polar nanoregions that have been reported for bulk KTaO3. However, the condition for the formation of these regions differ somewhat from those reported previously. Drift spectra for these samples, which reveal the step-height distribution of terraces at the surface, show the expected oscillatory behavior for lightly doped KTaO3. Significantly, they also confirm the unusual behavior reported in earlier experiments for the 30% KTN samples. Surface dispersion curves in the two high symmetry directions, namely, <100> and <110>, have been obtained for both KTL and KTN samples. This work compares the above phenomena observed in KTL and KTN to similar phenomena previously observed in pure KTaO3 and KTN. Surface dynamics of KCl(001) is also investigated in this work and compared with reported model calculations. The agreement is generally good for the low-energy Rayleigh mode and for a crossing mode. However, a high energy dispersionless mode, found in the <100> high symmetry direction lies in the region of a shear-horizontal Lucas mode, that cannot in theory be observed by helium atom scattering in our experimental configuration. This disagreement between theory and experiment suggests that further theoretical work is necessary to understand the dynamics of simple ionic-insulator systems like KCl.
Phonon, Lattice Dynamics, Surface Structure, Helium Atom Scattering, Dispersion
Date of Defense
March 24, 2009.
Submitted Note
A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Bibliography Note
Includes bibliographical references.
Advisory Committee
David H. Van Winkle, Professor Directing Dissertation; Sanford A. Safron, Outside Committee Member; Francis A. Flaherty, Committee Member; Efstratios Manousakis, Committee Member; Grigory Rogachev, Committee Member.
Publisher
Florida State University
Identifier
FSU_migr_etd-4495
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Fatema, R. (2009). Helium Atom Scattering Study of the Surface Structure and Dynamics of KCl(001) and Potassium Tantalate (KTaO₃) Doped with
Lithium and Niobium. Retrieved from http://purl.flvc.org/fsu/fd/FSU_migr_etd-4495
