Sub-10-nanometre metallic gaps for use in molecular electronics

Abstract

This thesis presents the development of a selective-etch fabrication process to create sub-10 nanometre metallic gaps and the subsequent use of the gaps to study the electronics of nanocrystals and molecules. A complete picture of the success of the process required both examination by scanning electron microscopy as well as probing the current response to an applied bias at low temperature. The empty gaps were fully characterised before self-assembling 7 nm CdSe nanocrystals onto the metal with the help of linker molecules. The I-V characteristics of the empty gaps showed a reduction of the tunnelling barrier height from the expected value (~5.1 eV, the work function of Au) when the results were fitted to the Simmons tunnelling model for a metal-insulator-metal system. Results indicate that after the barrier height is surpassed, a transition from direct to field-effect (Fowler-Nordheim) tunnelling occurs. After CdSe assembly, the collected I-V characteristics of the system at 77 K showed varied results. Many devices displayed conductance peaks at low voltages comparable to the results of the shadow evaporation process for 4.2 nm nanocrystals (also documented in this thesis). Several devices revealed switching between multiples of fundamental curves, suggesting conduction through multiples of nanocrystals.