Investigating Structure Property Relationships in Electroactive Molecules via Scanning Tunneling Microscopy

Abstract

This dissertation will discuss issues related to determining structure property relationships that are relevant to molecular electronics. More specifically, an STM will be used to compare electronic measurements over insulating n-alkanethiolate SAMs and electroactive SAMs composed of ferrocenyl- terminated thiols and viologen terminated thiols, as well as multilayer SAMs created by alternating a metal dication and a thiolate. The surface characterization of these SAMs will be discussed. Current — voltage (I-V) measurements on the SAMs will be discussed as they pertain to the non-linear current voltage behavior of negative differential resistance (NDR). A mechanism for the nature of NDR will be discussed as well as the need to understand how the junctions used to measure I-V curves influence NDR. The attenuation of the apparent tunneling barrier of ferrocenyl-terminated thiolates via non-covalent binding of β-cyclodextrin will be shown. This attenuation will be shown to influence the peak to valley ratio of NDR Stochastic variation in electroactive molecules inserted into an insulating n-alkanethiolate background SAM was observed and is believed to be a general phenomenon. In this dissertation it will also be shown that the electric field generated by the STM tip increases the rate of replacement of electroactive molecules in to the background SAM.