Electronic, vibrational, and structural properties of thin and ultrathin films of carbon and bismuth.

摘要

number of techniques, including Raman scattering spectroscopy, high resolution electron energy loss spectroscopy (HREELS), transmission electron microscopy (TEM), Auger electron and x-ray photoemission spectroscopies (AES and XPS), were employed to investigate the electronic, vibrational, and structural properties of nanocrystalline carbon and liquid bismuth clusters, as well as diamondlike amorphous carbon films.;Hydrogen-free, diamondlike amorphous carbon thin films with a wide range of tetrahedral bonding were studied using HREELS and Raman scattering in the visible and ultraviolet. The measurements provided direct evidence for the presence of sp;HREELS studies of two dimensional, grahite-like carbon clusters were performed and indicated a semimetal to semiconductor transition as a function of particle size. The formation of an energy gap was observed for nanocrystallites smaller than ;While a large number of elemental and compound semiconductors in bulk form become metallic upon melting due to changes in local atomic structure of the liquid state, in situ IERS studies of liquid Bi clusters suggested that for very small sizes this atomic structure transition does not occur. Changes in the vibrational spectra with the liquid cluster size have been correlated with ex situ transmission electron microscopy to estimate a critical size of