Charge Transfer in Potassium Doped Hydrocarbon Molecular Films and Pseudogap Effect in Metallic Thin Films

In this thesis, I mainly focus on two issues: charge transfer in potassium doped coronene films and pseudogap effect in metallic islands.;As a fundamental technology to improve the properties of organic devices, charge transfer in doped organic molecules has attracted prevailing interest. Especially, in alkali metal doped hydrocarbon molecules, a superconducting transition was discovered in 2010. For relative simple structures and high critical temperatures, the mechanism of the superconducting transition is very important for further research and is still ambiguous. However, the too low shielding fraction of the sample makes the experimental results via macroscopic methods less reliable. Strong debates exist on the electronic correlation effect in this system, based on the experimental results of photoemission spectra.;To overcome the disadvantage in previous experiments, we applied STM and STS to study the structure and electronic properties of potassium doped coronene films in the microscopic view. At first, well ordered coronene films are fabricated on gold, copper and graphite. STS of coronene films clearly demonstrates the electronic states in them. Comprehensively considering minimizing the influence of the substrates and the stability of coronene films, two layers coronene films on gold (111) are adopted to be doped by potassium atoms. The structures and electronic properties of coronene films after being doped by potassium atoms with various doping ratios are studied. As very different structures and electronic properties, the doping process can be separated into two ranges. In the low doping range, absorption of potassium atoms on two layers coronene film causes the alteration of molecular orientation from flat-lying to up-standing and the formation of a herringbone structure which remains unchanged in this doping range. With the increase of doping ratio the LUMO state gradually shifts to the Fermi level, as a result of charge transfer and the electrostatic effect. Further doping leads to KxCoronene phase turn back from the two-fold herringbone structure to a three-fold symmetric structure. Since the intermolecular hopping of electronic states is greatly suppressed, KxCoronene demonstrates obvious phase separation in the high doing range. Splitting of the LUMO state when is partially filled directly illustrates the presence of strongly correlated effect in this system. K3Coronene shows different phases varying not only in the topography but also in the strength of electronic correlation. With four electrons transferred to coronene, K4Coronene change to band insulating state. Our results demonstrate the interactions between coronene molecules and potassium atoms which are helpful to understand the mechanism of organic superconductors and different critical temperatures in K3Coronene.;For the work on pseudogap effect, we successfully extend the effect discovered in Pb islands as a common phenomenon in metallic thin films. By comparing the pseudogap in Pb, In, and Al islands, we find that the width of the pseudogap is strongly dependent on Debye energy. This result provides direct evidence that the pseudogap state is related to the electron-phonon interaction. Compared with other mechanisms proposed in other publications, our pseudogap theory possesses a particular advantage to interpret the alternation between the pseudogap and pseudopeak mediated by QWS, but is invalid in relation to explaining the size dependence. So, we develop the pseudogap theory by combining the dynamic coulomb blockade theory and the pseudogap theory which means adding an interface effect to the pseudogap theory. Therefore, the mechanism of the gap (or peak) feature in metallic thin films can be fully understood.