Raman Scattering and Electronic States of Nanoscale Group 4 Materials

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9623315 Lannin The objectives of this work are to obtain basic information on the phonon states of ordered and disordered semiconducting nanoscale systems prepared and studied in ultrahigh vacuum. Basic studies of the phonons of group IV materials will be performed by interference enhanced Raman scattering (IERS) methods on ultrathin films of very small, 1-2nm, nanocrystallites and on ultrathin films epitaxial layers grown on selected crystalline oxides. The results will provide new information about the phonon states of very small crystallites, without chemisorbed species, and ultrathin crystalline semiconductor layers. For epitaxial layers the distinct surface geometry, such as the role of surface dimers and dangling bonds on Raman scattering are of interest. IERS will provide additional Information about interfacial bonding in semiconductor/oxide interfaces. The influence of adsorbate atoms on the phonon states of nanoscale systems will be studied. Raman scattering will be expanded as a tool for the study of surface and near surface atom dynamics and structure. Complementary specular, dipolar electron energy loss spectroscopy (EELS) research in Si, Ge and C nanoscale systems will provide information about interband electronic transitions with decreasing size or film thickness, about changes in the optical gap and subgap states, and the effects of chemisorbed species. Changes in the vibrational states of near surface atoms in amorphous diamond-like carbon materials prepared by pulsed laser deposition will be studied by high resolution EELS. These in situ measurements of diamond-like films will allow a means to increase 4-fold bonding in ultrathin and thin films. %%% As the size of condensed matter systems is reduced in one or more dimensions to nanoscale levels, surface and near surface atoms play an increasingly important role in determining physical and chemical properties. Thus electrons and phonon states, magnetic and optical properties are su bstantially influenced when dimensions decrease to a scale of 1-2nm. In such systems finite size quantum effects and the presence of new bonding geometries lead to very substantial changes in physical properties. Both basic scientific knowledge and potential technological applications of such small scale systems are thus of considerable current interest. Different classes of nanoscale systems will be studied to obtain information on the effects of finite size and near surface atoms on both the vibrational states and electronic interband transitions. These studies will involve the use and extension of new and developing experimental methods for studies of both ordered and disordered nanoscale systems. Improvements in bilayer interference enhanced Raman scattering (IERS) methods for ultrathin films in the form of nanocrystalline island particles and epitaxial layers will enhance Raman scattering as a surface science tool for ultrathin semiconductors and their interfaces. In addition, reflection electron energy loss spectroscopy (EELS) will be utilized for new interband electronic state studies of nanocrystalline, amorphous and epitaxial ultrathin films. These studies of ordered and disordered nanoscale semiconductors will employ ultrathin films deposited and studied in situ in a specialized uhv system. ***