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Light scattering from acoustic vibrational modes in confined structures

Bandhu, Rudra Shyam
http://rave.ohiolink.edu/etdc/view?acc_num=osu1101838395

Abstract Details

2004, Doctor of Philosophy, Ohio State University, Physics.
The acoustic vibrational modes and their light scattering intensities in confined structures such as supported films, double layer free-standing membrane and sub-micron sized wires on a free-standing membrane have been studied using Brillouin Light Scattering (BLS). Standing wave type acoustic phonons were recently observed in supported thin films of silicon oxy-nitride. We build upon this finding to study the acoustic modes in thin zinc selenide (ZnSe) films on gallium arsenide (GaAs). The surprising behaviour of the Brillouin intensities of the standing wave modes in ZnSe are explained in terms of interference of the elasto-optic scattering amplitudes from the film and substrate. Numerical calculations of the scattering cross-section, which takes into account ripple and elasto-optic scattering mechanism, agrees well with the experimental data. Light scattering studies of standing wave type modes in free-standing polymethyl methacrylate (PMMA) layer on Si 3 N 4 were carried out. In these bilayer structures PMMA is much softer than Si 3 N 4 , a property that leads to confinement of low frequency modes associated with the PMMA layer to within its boundaries. In addition, the flexural and the dilatational modes from the Si 3 N 4 layer are observed and are found to hybridize with the standing wave modes from the PMMA layer. Our study of phonon modes in PMMA wires supported on a free-standing Si 3 N 4 membrane extends our work on free-standing double layer membranes. In recent years there is much interest in the study of phonon modes in nano-scale structures such as wires or dots. Although much theoretical work has been carried out in this direction, no experiments exist that explore the dispersion of the phonon modes in such structures. Brillouin Light scattering is ideally suited for studying phonons in such reduced dimensions and our work represents the first effort in this direction. The spectra reveal modes which are quantized both along the width, as well along the thickness of the wires. In addition torsional, shear and dliatational modes of the PMMA wires are observed. The mode amplitudes are analyzed by the use of xyz algorithm.
R Sooryakumar (Advisor)
Physics, Acoustics
Brillouin light scattering; ; acoustic phonons; ; confined; ; membranes; phonons in quantum wires; phonons in free-standing membrane

Recommended Citations

Citations

  • Bandhu, R. S. (2004). Light scattering from acoustic vibrational modes in confined structures [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1101838395

    APA Style (7th edition)

  • Bandhu, Rudra. Light scattering from acoustic vibrational modes in confined structures. 2004. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1101838395.

    MLA Style (8th edition)

  • Bandhu, Rudra. "Light scattering from acoustic vibrational modes in confined structures." Doctoral dissertation, Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1101838395

    Chicago Manual of Style (17th edition)

osu1101838395
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© 2004, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.