Plasmon Resonance Induced Localized Field Enhance Quantum Charge Transport In Metal Nanoparticle Arrays

The localized field enhancement is an important effect of suface plasmon resonance in noble metal nanoparticles. This enhanced localized electromagnetic field could lead to the third-order optical nonlinear effect of metal nanoparticles. In close-packed nanoparticle arrays, the nonradiative component of the extinction could provide energy to free electrons, which permit free electrons to cross the barrier between the particles. Thus localized surface plasmon resonance could induce the enhancement of quantum charge transport in metal nanoparticle arrays. This makes it possible to manufacturing photoelectric conversion devices below the diffraction limit and have very important applications in areas such as nano-scale ultra-fast optical switch, optical detectors, and photonic computer.The main work of this thesis is studying the enhancement of quantum charge transport under laser in close-packed Ag and Ag/Pd nanoparticle arrays; discussing the mechanism of enhanced quantum conductance and its relationship with the surface plasmon resonance in Ag nanoparticle, and manipulating the surface plasmon resonance of Ag nanoparticle arrays to achieve the maximum enhancement of the quantum conductances.Monodisperse Ag and Pd nanopaticles are prepared by the gas aggregation process. The conductance monitoring system is used to control the deposition of nanoparticles precisely. Two different close-packed nanoparticle arrays are prepared: Ag nanoparticle films with high coverage and Ag nanoparticle dotted Pd nanoparticle arrays with coverage near the percolation threshold. We analyzes the quantum charge transport variation with temperatures in these two samples. The result shows that:Ag nanoparticle films with high coverage exist Coulomb blockade effects at low temperatures. When the temperature is higher than266K, threshold voltage of current blocking is lower than zero indicating the disappearance of coulomb blockade effects. The decay of the localized field near Ag nanoparticles under laser makes electrons easier to cross the barrier between the particles, which weakens the influence of Coulomb blockade and decreases the threshold voltage. The enhancement factor of the transport current could be up to2.4times near threshold voltage at low temperatures. As the temperature rises Coulomb blockade effects become weak and the enhanced quantum charge transport caused by laser compete with thermal effects. It results the current enhancement decreases gradually and even disappear.For Ag nanoparticle dotted Pd nanoparticle arrays with coverage near the percolation threshold, the current blocking threshold voltage could be up to0.9V at low temperatures. The threshold voltage decreases drastically with temperature at low temperatures and transforms into slowly drop when temperature is higher than87K. Accordingly the photo quantum conductance enhancement factor increases rapidly with decreasing of temperature at low temperatures indicating that the rapidly reduced thermal activation of electron transport in nanoparticle arrays could be restored under laser. As the temperature rises, the enhancement of quantum conductance is induced by the energy provided by the decay of localized field and the heat produced by electron-phonon interaction. Optical third-order nonlinear effect will lead to electromagnetic fields anisotropy distribution in the spatial and the I-V curve performs highly asymmetric.On the other hand, if the plasmon resonance peak position of Ag nanoparticle matches the exciting wavelength, the maximum enhancement factor is reached. In order to achieve wavelength matching, we manipulating the morphology and surface plasmon resonance of Ag nanoparticle arrays with self-assembled SBS block copolymer templates.