We report on in situ studies of the vibrational properties of ultra-thin Si layers grown by dc magnetron sputtering in ultrahigh vacuum on amorphous MgO and Ag buffer layers. The average thickness of the Si layers ranged from monolayer coverage up to 200 Å. The interference enhanced Raman scattering technique has been used to study changes in the phonon spectra of Si nanoparticles during the crystallization process. Marked size-dependencies in the phonon density of states of the Si quantum dots and the relaxation of the k-vector conservation condition with decrease in size of the Si nanoparticles have been detected. Electron energy loss spectra have been collected for amorphous and crystallized Si nanoparticles on SiO 2 buffer layers and the difference in the onset of the electronic transitions have been found.

In situ Raman scattering, UPS and HREELS measurements have been used to study the fee to orthorhombie phase transition in RbCeo thin films. Large changes in the Raman spectra are interpreted in terms of increased interfullerene coupling in the orthorhombie phase. However, the data do not support the proposed polymer model for this phase. Photoemission measurements indicate only small differences in the electronic states between the two phases in contrast with photopolymerized Ceo where additional states are observed. Low energy metallic-like excitations and screening of intramolecular vibrations are observed in HREELS.

Oxide thin films have been studied for frequency and phase agile electronics. The electric-field tuning of microwave devices employs ferroelectrics, while the Magnetic-field tuning uses ferrites. The critical material parameters for ferroelectric thin films are the tunability of the dielectric constant and the dielectric loss. This paper describes the current understanding of the fundamental mechanisms of these properties and the research efforts to improve them in ferroelectric thin films.

We report on in situ studies of the vibrational properties of Si nanoparticles and ultrathin layers grown by dc magnetron sputtering in ultrahigh vacuum on amorphous MgO and Ag buffer layers. The average thickness of the Si layers ranged from monolayer coverage up to 200Å. Transmission electron microscopy has been used to determine size and shape of the Si nanoparticles. Changes in the phonon spectra of Si nanoparticles during the crystallization process have been studied by interference enhanced Raman scattering technique. Marked size-dependences in the phonon density of states and the relaxation of the k-vector conservation with decrease in size of the Si nanoparticles have been detected. The transition between crystalline- and amorphous-like behavior takes place in the particles with an average number of Si atoms equal to (7±2)×102.

We have studied lattice dynamic properties of SrTiO3 thin films from 5 to 300 K using metal-oxide bilayer Raman scattering. First-order zone-center optical phonons, symmetry forbidden in single crystals, have been observed in the thin films, indicating strain-induced lowering of symmetry. The asymmetric line shape of the TO2 phonon is interpreted as evidence for micropolar regions in the thin films, likely due to oxygen vacancies. The optical phonon lines and the asymmetry persist up to room temperature. [S0031-9007(99)09277-7].

We have used a metal–oxide bilayer Raman scattering technique to study lattice dynamics in SrTiO3 thin films. The SrTiO3 thin films were epitaxially grown on a conducting metal–oxide layer which reflects the exciting laser beam so that it does not enter the LaAlO3 substrate. Raman scattering from the SrTiO3 thin films was clearly observed, including the first-order Raman peaks forbidden by the cubic symmetry in single crystals. We suggest that strain exists in the films, which changes the crystal symmetry and will affect the dielectric properties of the SrTiO3 thin films.

Pair distribution functions (PDFs), obtained from powder neutron diffraction measurements have been used to construct structural models for the body centered orthorhombic (bco) and fcc phases of RbC60. The PDF exhibits small differences, primarily due to the shortened inter-fullerene distance in the bco phase. The bco-RbC60 system is well fit to a model derived from first-principles quantum molecular dynamics in which the C-C interfullerene distance is 1.57 Å. While the geometry of the interfullerene linkages is similar to a previously proposed model, the present results imply less distortion of the C60 molecules and larger interfullerene distances. The PDF analysis also indicates significant orientational disorder between chains of linked molecules.

The body centered orthorhombic (bco) phase of RbC60 has attracted considerable interest due to the proposal of intermolecular bond formation. In the present work, the structure, vibrational and electronic states of the RbC60 compound have been investigated with a variety of techniques. Raman scattering through the fcc to orthorhombic phase transition exhibits substantial changes attributed to increased intermolecular interactions. Corresponding modifications of the electronic states, measured by valence band photoemission and electron energy loss spectroscopy, are considerably smaller. Comparison of the measurements of bco RbC60 with observations on laser modified C-60, for which there is strong evidence of interfullerene bonding, indicates stronger perturbations of the molecular symmetry in the fatter. A structural study, employing a pair distribution function analysis of neutron diffraction data, suggests a model with a C-C interfullerene distance of 1.57 Angstrom, considerably larger than previously proposed. Improved agreement with the neutron data is achieved by considering a two-ball per cell Jahn-Teller distortion, suggested by the quantum molecular dynamics calculations of Adams and Page.

Substantial changes in the electronic and vibrational properties of crystalline C-60 modified by laser irradiation are reported. Ultraviolet photoemission identifies new states relative to C-60. Electron energy loss spectra indicate broadening of interband transitions with the gap remaining unchanged upon laser modification. Intermolecular Raman scattering exhibits one strong mode at 115 cm(-1) and two previously unreported weaker bands centered at 85 and 140 cm(-1). Comparison of the observed vibrational and electronic states with calculations for dimers and infinite chains indicate the laser modified films consist primarily of dimers.

In situ Raman scattering, ultraviolet-photoemission-spectroscopy (UPS), and electron-energy-loss-spectroscopy (EELS) measurements have been performed on crystalline films of ${\mathrm{RbC}}_{60}$ through the fcc-to-orthorhombic structural phase transition. The Raman spectra exhibit large changes in intensity of modes not active for isolated icosahedra, including ungerade vibrations. This is attributed to a substantial increase in interfullerene coupling in the presence of ${\mathrm{C}}_{60}$ merohedral disorder. UPS measurements indicate a finite density of states at the Fermi energy for both phases with small changes in the ${\mathrm{C}}_{60}$ derived states through the transition. Low-energy metalliclike excitations are observed in EELS.