Study Of Fluorene Derivative In Raman Scattering And Electic Field Effect Of Tunneling Current

Compared to inorganic materials, the organic electroluminescent has become one of the forefronts and active areas of the optoelectronic information materials due to its advantages of wide energy gap, high luminous efficiency and the simplicity of preparation. The method of preparing molecular layers based on physical adsorption provides such a basic technique to create molecular device. These functional surface/interface molecular devices have potential applications in the fields of sensors, molecular recognition and nanoelectronic devices. In this dissertation, we systematically investigated the scattering light excited by incident light and the tunneling behavior when the derivatives exposed electric field. The response to incident light and the response to electric field were analyzed. Our research contents and main conclusions have been summarized as follows:1. Several of fluorene derivatives were purified through re-crystallization. The products were employed to study the absorption and scattering spectroscopy. The experiments showed that the variety of composition, structure and function group resulted in the change of molecular orbital, chemical bond and force constant. All the change was reflected in spectroscopy.2. The influence of frequency of incident light in scattering was studied. Under the condition of varying incident light frequency, the scattering spectra were measured to investigate the frequency dependence. Due to the periodicity and lattice vibration, the scattering of crystal is different from that of liquid or gas. The energy of photon decreases with the increase of wavelength of incident light, which result in the enhancement of low wavenumber vibration model. The main reason of the enhancement is lattice vibration.3. The resonance coupling in scattering spectra was studied further. The enhancement in low wavenumber, which based on lattice resonance, result in energy transfer either from one vibration model to another in a molecule or from one molecule to another molecule.4. We have systematically investigated the solution on scattering light. Solvent effect was exhibited obviously in Raman spectra. The difference of solvent leads to the change of scattering peaks. The concentrations of solution dominate the shape of scattering curve and have no influence on frequency shift of scattering peak. Furthermore, the tunneling current and tunneling conductance data presented electric field dependence. We predict that the study may deepen our understanding about the properties, which plays a major role in the application of the compound. 5. Our study firstly focus on BFBD molecule adsorbed on highly oriented pyrolytic graphite (HOPG) surface. X-ray photoelectron spectroscopy (XPS), contact angle measurement (CAM) and tunneling spectroscopy (TS) were employed to investigate the molecular layers of BFBD molecule adsorbed on HOPG surfaces at room temperature in air. XPS and CAM results have confirmed BFBD molecules adsorbed on an HOPG surface and formed surface/interface molecular device. The response to electric field was investigated by TS experiment under different electrode distance. The experiment results show that the tunneling behavior is of electric field dependence. The tunneling behavior is determined by both electrode potential and electrode separation. Under the condition of large electrode separation, the tunneling behavior can be described by the resonance between polaron and electron energy. With the decrease of electrode separation, the potential of tunneling conductance decrease. Under weak electic field, tunneling current is determined by elastic electron tunneling. However, tunneling current is composed of elastic and inelastic electron tunneling under strong electric field. The electric field, which results in the occurrence of inelastic tunneling, is related to the composition, structure and electron distribution of active organic layer, and keeps constant. These types of molecular layers provide a useful platform for the study of surface/interface phenomena. It is potentially useful for the molecular devices due to its properties of electric field response, the simplicity of the sample preparation and the stability of the interface in ambient conditions.