Self-assembly and electronic transport properties of nanoparticle arrays

The tunneling mechanism in nanofabricated systems is largely determined by electron-electron interactions and energy differences between initial and final states. Electron hopping beyond nearest neighbor sites can take place in doped semiconductors with their sparse density of states; however, it is energetically unfavorable in close-packed metal nanoparticle arrays where the density of states is large. In such nanoparticle arrays, electron tunneling from one particle to another is the most likely scenario. Depending on the nature of the nearest-neighbor hops, either through direct or co-tunneling, different current-voltage (IV) characteristics arise. This thesis investigates the effects of inelastic cotunneling on the I-V characteristics and the temperature-dependent zero-bias conductance in dodecanethiol-ligated gold nanoparticle monolayers and multi-layers. So far, cotunneling has been explored primarily in small, linear arrays of a few junctions. The experiments discussed here are the first to be done in large nanoparticle arrays. For in-plane transport through multi-layered arrays with lateral size 65-70 particles between the electrodes it is shown that the resulting, power-law current-voltage characteristics as well as the temperature dependence of the conductance for small applied bias voltages are in line with recent predictions based on multiple inelastic cotunneling. The characteristic cotunneling length not only determines the power-law exponent of the low-bias current-voltage characteristics, but also the temperature dependence of the zero-bias conductance. In order to vary this length and to test the cotunneling scenario in more detail vertical transport through stacks of particle layers is investigated. Magnetic field measurements on the gold nanoparticle arrays indicate the absence of significant magnetoresistance, in contrast to results on films of semiconductor nanoparticles. In addition, results for cobalt monolayers and for modifications of the particles' ligand molecules are presented.