In situ studies of the electronic and vibrational properties of thin films and novel materials

The electronic and vibrational properties of several novel materials were investigated in an in situ ultra high vacuum (UHV) environment. The novel materials included thin films of laser-modified fullerenes, believed to be photopolymerized; rubidium fulleride, a fullerene polymer in a slow-cooled phase; the zinc selenide (100) surface which reconstructs into (2 x 1) and c(2 x 2) forms; and silicon nanoparticles which exhibit size-dependent effects. Interference enhanced Raman scattering (IERS) and high resolution electron energy loss spectroscopy (HREELS) in reflection were employed to study the vibrational spectra of the materials. Ultraviolet photoemission spectroscopy (UPS) and electron energy loss spectroscopy (EELS) provided spectral information related to the electronic states of these systems.; Ultra-thin layers of silicon were grown by dc magnetron sputtering in ultra high vacuum on amorphous MgO and Ag buffer layers. The average thickness of the layers ranged from monolayer coverage to 200 angstroms. Transmission electron microscopy (TEM) has been used to determine the size and shape of the silicon nanoparticles. Changes in the crystallization process have been studied by interference enhanced Raman scattering (IERS). Marked size dependences in the phonon spectra of amorphous silicon nanoparticles were detected. A relaxation of the k-vector conservation condition occurs in silicon nanocrystals as they decrease in size. The nanocrystal transition between crystalline-like and amorphous-like behavior takes place films with average thickness less than or equal to 10 angstroms. TEM micrographs indicate that the silicon nanoparticles exhibiting this transition have an average number of silicon atoms equal to 700 (+/−200). The electronic spectra as measured by EELS continue to be differentiable even at considerably thinner coverages.