Investigation of the optical properties of Bi₂Sr₂Ca_n-1Cu_nO_y (n=1,2) by transmission electron energy loss spectroscopy

A high energy resolution transmission electron energy loss spectrometer was reassembled for this research project. The vacuum system, electron optical lenses, electronic control elements, and high voltage system were reconditioned. A CAMAC interface system was installed into the spectrometer, and a data collecting software package was developed which included a direct convolution method for removing the contributions of multiple scattering from the data. The spectrometer is running very well. Samples can be changed routinely without disturbing the performance of the spectrometer. The research conducted for this thesis was an investigation of the optical properties of the high temperature superconductors of Bi₂Sr₂Ca_{n - 1}Cu_nO₃(n = 1,2) by transmission electron energy loss spectroscopy. A thin film of Bi₂Sr₂CaCu₂O₈ was prepared by the flux method. A single crystal of Bi₂Sr₂CuO₆ also was grown from which a self-supporting thin film was prepared. The energy loss spectra of Bi₂Sr₂CaCu₂O₈ and Bi₂Sr₂CuO₆ materials were investigated, and the dielectric functions of these materials were derived by Kramers-Kronig analysis. A broad excitation centered at 2.7eV was identified as associated with the Cu — O₂ layer by comparing the spectrum of Bi₂Sr₂CaCu₂O₈ with that of Bi₂Sr₂CuO₆. A pseudo gap of 1.2eV in the spectrum of Bi₂Sr₂CuO₆ suggests that the one electron approximation for states derived from the hybridization of O 2p_σ and Cu3d_{x² - y²} orbital might not be valid. Two excitations at 3.6eV and 4.6eV were observed in both spectra. Comparing the spectrum of Bi₂Sr₂CaCu₂O₈ with that of Bi₂Sr₂CuO₆ suggests that the 3.6eV excitation is associated with the Bi — O layer. It was concluded that the 3.6eV and 4.6eV excitation are a spin-orbit doublet derived from the atomic bismuth 6p level. This identification is based on a comparison of Bi core level excitations from electron energy loss spectroscopy with X-ray photoemission measurements. A simplified atomic energy level picture of Bi in Bi₂Sr₂Ca_{n - 1}Cu_nO₃(n = 1, 2) is presented. A 1.0eV excitation in the energy loss spectrum of Bi₂Sr₂CaCu₂O₈ was observed, and its dispersion relationship with the momentum transfer q is presented. A Drude model was used to describe this controversial excitation.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Physics

Department dc:contributor.department

Physics

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

1990

Author dc:creator

• Wang, Yun-Yu

Chair dc:contributor.committeechair

• Ritter, Alfred "Jimmy"

Committee members dc:contributor.committeemember

• Zallen, Richard H.
• Lee, Ting-Kuo
• Long, J.
• Blecher, Marvin
• Schutt, D.

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

etd-07282008-135649

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/38983