Charge transport in low-dimensional solids and single molecule systems

A study of the low dimensional physics of 2D coupled Ag nanoparticle arrays and [2]Rotaxane single molecule transistors is presented. In the case of coupled Ag nanoparticle films, the tunable charge transport characteristics in a model system of an "artificial solid" are explored. Electronic properties of the Ag nanoparticle films are tuned with particle size, distance between particles, and temperature. The role of disorder in these 2D arrays is also probed with temperature dependent resistivity measurements, magnetoresistance (MR) measurements, and electric field effect measurements. Three regimes are evident in the temperature dependent resistivity measurements, a high temperature metallic-like behavior, an intermediate temperature regime which follows a simple activated process, and a low temperature variable range hopping regime. This is interpreted in terms of a mobility edge and localized states at the Fermi energy and leads to a classification of the system within the Mott insulator-Anderson Insulator regime. A localization length is calculated to be ∼100 nm and a threshold on the disorder for the quantum phase transition from insulator to metal is determined to be finite (∼3%). A small negative MR and a field dependent mobility further support the model of disorder induced domain localization in these films. Finally, a theoretical treatment of the physics of the systems probed is also presented with remarkable qualitative and quantitative agreement between experimental findings and the theoretical predictions.; Single electron transistors in the simple case of metallic grains and in the more complex case of [2]Rotaxane molecules are also presented in order to understand the device physics of a model system in molecular electronics. Electrical contact with single-to-few molecules is made with Pt electrodes and is probed with the addition of a gate. The nature of contact between molecule and electrode is varied through the incorporation of different linkage moieties. Differential conductance as a function of gate bias and source-drain bias is presented. It is determined that molecular composition plays a secondary role to the overwhelming role of the contact between molecule and electrode in the present case.