Investigation and characterization of the nature of the electrical contacts in molecular electronic device constructions

by Daniel, Thomas Addison.

An overview of various molecular electronic device constructions that utilize selfassembly is given in chapter 1 with a more specific analysis of selected devices studied in later chapters. The second chapter details the use of CPAFM to probe the nature of the evolving interface and metal morphology arising from Au vapor deposition onto the surface of a SAM. The results show that the Au penetrates the ordered regions of the monolayer and forms a uniform layer at the thiol interface. However, filaments form at defect sites in the monolayer due to a higher diffusion rate through the monolayer. These results suggest that vapor deposition of Au is problematic for use in MEDs since no top contact is formed. The third chapter details the used of various applied techniques to probe the nature of the evolving interface chemistry and metal morphology arising from Ti vapor deposition onto the surface of a SAM. The results reveal a highly heterogeneous Ti overlayer forms, in which a large fraction of atoms do not stick to the bare SAM surface while the adsorbed atoms lead to a highly heterogeneous film. The data indicate that for applications such as molecular device contacts the use of Ti may be highly problematic. The fourth chapter inspects the growth of multilayer molecular films used as molecular resists. The actual performance of such a resist is dependent on the exact way that the multilayer stacks organize during the assembly, yet little is definitively known about the details. We have applied surface science techniques to unravel the mechanisms of multi-assembly. Our results differ significantly from previously proposed growth mechanisms, and point to improved ways to form multilayer films. The fifth chapter inspects SAMs of the isocyano derivative of OPE have been prepared in oxygenfree environments on smooth Pd surfaces. The SAMs show significant chemical iv instability when exposed to ambient conditions. Exposure results in a chemically degraded interface structure. CPAFM measurements show the conductance of the Pd SAMs diminish by ~2 orders of magnitude. The results underscore the importance of controlled assembly procedures for aromatic isocyanide SAMs. v