Infrared spectroscopy of thin layers under ultra-high vacuumconditions

摘要

We summarize recent results from in-situ infrared spectroscopic studies of nanofilm growth. These studies, performed under ultra-high vacuum conditions with sub-monolayer sensitivity, exploited the relationship between morphology and structure on the one side and, on the other side, vibrational excitations and plasmonic ones. The studies were performed within various projects ranging from astronomy and high-energy physics to organic electronics and plasmonics. The results represent examples the description of which needs theoretical models beyond the use of Fresnel's formulae, the assumption of abrupt interfaces, and the use optical databases for bulk materials. For example, at the SiO-Si interface Si-O-Si bridges with Si-0 bonds longer than in the bulk are formed which can be identified via their special vibration signals at unusually low vibration frequencies. From a thickness of about 1 nm on, the infrared spectra show typical SiO-bulk features. The lowered vibrational frequencies are attributed to changes in the average distribution of Si-O bond length close to the interface. On the diamond (100) surface, during Cr deposition, we observed the formation of a conducting nanocrystalline fee phase of chromium. At a certain thickness, the nanocrystalline phase makes a phase transition to the typical bulk chromium phase. Cr is a preferred material for electric contacts in single-crystal diamond detectors the performance of which sensitively depends on the conductivity of the deposited Cr contact. On organic semiconductor layers metallization may be accompanied by an intermixing at the metal-semiconductor interface. Such intermixing can be observed as the appearance of new excitation features.