Search

In order to analyze the phenomenon of mold level hunching (MLH) during thin slab casting process, the variation of the mold level and the bulging of strand were measured and analyzed using Fast Fourier Transform (FFT) spectrum analysis. Both of mold level hunching and bulging had the same frequency and the specific frequency corresponded to the main roll pitch of the thin slab caster. The unsteady bulging was found to be a main reason of mold level hunching. The unsteady bulging profile through the full range of the caster and the height of mold level hunching were calculated using a heat transfer model and a continuous beam model. The effects of process variables on mold level hunching and the process condition of reducing mold level hunching were studied. The amount of mold level hunching increased as unsteady bulging increased due to the hunching of casting speed. An aperiodic roll pitch between segments could be effective in reducing mold level hunching.

Highly conducting thin films of C60 were deposited by thermal evaporation in high vacuum on single crystal silicon substrates. The microstructure of the films was characterized by using Atomic Force Microscopy, and laser Raman spectroscopy. The films were polymerized by uv irradiation. The dc electrical resistivities of the as-deposited and uv-polymerized films were measured as functions of temperature between 295 and 17K by the four-probe technique. We present results on the effects of uv-irradiation on the surface microstructure and the temperature dependence of the electrical resistivity of these films.

We present results from a study of the vibrational, structural, and electronic properties of three samples; C60 powder, thin films of C60and La-doped C60 We present Raman data for C60 powder subjected to pressures in a diamond anvil cell, ranging from 0.5 to 14.7 GPa. The material undergoes a structural phase transition between 9.1 and 14.7 GPa. Some of the frequencies of the Raman-active modes soften, while others harden with increasing pressure. The x-ray diffraction data show fee crystalline structure in the powder and Ladoped C60 films. The C60 film, however, appears disordered. The electronic valence bands of thin films were measured by photoemission spectroscopy. We observe a higher density of the electronic states in the doped sample.

We present results from a study of the vibrational, structural, and electronic properties of C60 powder and thin films. Raman spectroscopy and diamond anvil cell have been used to study pressure dependence of the Raman active modes of C60 powder. The material undergoes structural phase transition between 9 and 15 GPa. Some of the Raman modes soften, while others harden with increasing pressure. Thin films of C60 and La-doped C60 have also been studied by using Raman scattering, x-ray diffraction, x-ray photoelectron spectroscopy and uv photoemission spectroscopy. Whereas the powder and La-doped C60 films exhibit fcc crystalline structure, the C60 film appears disordered. Further, we observe a significant difference in the electronic valence bands of the doped and undoped films.

We have investigated interface effects in C60/Cu-oxide/Cu structures. C60 thin films were grown under high vacuum by thermal evaporation and the well-known “pentagonal pinch mode” of C60, Ag(2) band was examined by Raman spectroscopy. We observe Raman-active bands centered at 1420, 1448, 1455, and 1465 cm−1 in C60/Cu-oxide/Cu samples with a thin (∼40 nm) C60 overlayer. The 1420, 1448, and 1455 cm−1 Raman bands are not observed in the spectra of pristine C60 powder, copper-oxide substrate, and C60/Cu-oxide/Cu samples with thick (∼1.3 μm) C60 overlayer. We associate these new Raman-active bands with C60/copper-oxide interface.

We have used photoelectron spectroscopy to study possible modifications in the electronic valence band structures of thin films of C60 due to their deposition on single crystal silicon and polycrystalline copper. The C60 thin films were deposited by thermal evaporation under high vacuum and further characterized by using Raman spectroscopy. We observe significant differences in the valence band structures of C60 thin films deposited on these substrates and attribute them to interactions at the interface.