Electronic and optical properties at the nanoscale studied by STM

Resumen

This thesis reports on the electronic properties of surface state (SS) electrons near one-dimension gratings; and the opto-electronic properties of metallic systems, and molecular emitters, inside the plasmonic nano-cavity of a Low-Temperature (LT) Scanning Tunneling Microscope (STM) in Ultra-High-Vacuum (UHV) conditions. The thesis can be divided in three blocks. First, the scattering of Cu(111) surface state (SS) electrons near the edges of TCNQ molecule islands is investigated. By means of Quasi Particle Interference (QPI), and 1D Fourier-Transform of dI/dV spectra, it is found that the band structure of the quasi-free Cu(111) SS electrons, follows a discrete set of energy bands, originating from Bragg diffraction at the edges of the molecule islands. Second, the light emission of noble metal surfaces, is studied as a function of the tunneling parameters. We have focused on the interpretation of the slow decay of the light intensity towards the quantum cut-off for 1e􀀀���� processes, the overbias emission, and the quenching of luminescence after the maximum of the photon yield. Also, the effects on the light emission properties due to the adsorption of ultrathin layers, on top of noble metal surfaces, are studied for two cases: Au islands on Ag(111), and NaCl bi-layers on Au(111). Third, the luminescence of electronically decoupled C60 nanocrystals is characterized. At positive bias above a certain threshold voltage, the spectral distribution of the emitted light is dominated by a series of sharp resonances, that are unambiguously identified with molecular fluorescence of C60 molecules. We show that the emission type can be switched in a controlled way from plasmonic to molecular with the tunneling parameters, in a fixed excitation position. As a general remark, the results presented in this thesis contribute to the better understanding of the opto-electronic properties of model systems, at the atomic and molecular level