Studies of interfacial phenomena: Alkanethiol adsorption and patterning on gold and the superconducting proximity effect in superconductor/semiconductor systems

Investigations of two interfacial systems are presented. The first system is that of alkanethiol monolayers on Au surfaces. The alkanethiol/Au system has been widely studied and thus was chosen as a model system to explore the feasibility of the use of alkanethiols as ultrathin resist materials. In order for alkanethiols to be effective resist materials, they must have low a real defect densities. This research reports initial investigations of the characterization of defect density. Full monolayers are formed and defects are intentionally introduced either electrochemically or by exposure to deep UV light in the presence of O₂. These defected monolayers are then examined using cyclic voltammetry to qualitatively determine the defect density. Additionally, the assembly process of alkanethiols on Au is explored as a function of substrate composition, solution concentration and assembly time. The structural evolution of the monolayer during the assembly process is monitored by infrared absorption spectroscopy, cyclic voltammetry and AC impedance spectroscopy. These investigations show monolayer structural evolution at least out to 10 days in assembly solution.; The second phenomenon studied is the superconducting proximity effect at Nb/InAs and NbN/InAs interfaces. Previous investigations of Nb/InGaAs show an excess conductance at low bias voltages when the system is superconducting. However, current models do not sufficiently explain this excess conductance. Raman spectroscopy is used in this research to overcome difficulties in performing electrical measurements on the high transmittance Nb/InAs interface. Materials processing issues in producing high quality, reproducible Nb/InAs interfaces are discussed, including the effects of passivation, dry etching and metal film deposition. Although several Nb/InAs and NbN/InAs samples exhibited evidence of a superconducting proximity effect, additional processing issues must be overcome before a conclusive determination of the excess conduction mechanism can be ascertained.