Charge Transport through Single Molecules with Mechanically Controlled Break Junctions

Abstract

Single molecule-based devices represent the ultimate limit in device design, with promising applications in next-generation electronic and optoelectronic devices. A lack of fundamental understanding of the electronic structure resulting from the interface of an organic molecule and the two metal electrodes has prevented developments of such devices. This missing understanding is driven by a dearth of experimental data directly probing the energy level alignment between the energy levels of organic molecules bound between metal contacts. The work presented here aims to develop an experimental platform which can probe the interfacial energy level alignment along with investigating several key variables proposed to affect the energy level alignment.

This thesis provides a discussion of the developed mechanically controlled break junction platform, as well as attempts to control the energy level alignment with systematic molecular design. The construction, development, and improvements made to the experimental platform are detailed, including the development of novel instrumentation and statistical analysis methods. The developed platform is applied to the study of atomic nanowires, where distinct sub-features not previously seen are unambiguously identified. Furthermore, investigations into different binding group chemistries delineate the importance of environmental control for molecular transport. Finally, studies using molecular systems with intrinsic dipole moments demonstrate the complicated interfacial physics occurring at the molecular-metal interface. Overall, the work presented here demonstrates the power of the developed experimental platform in studying the interfacial electronic structure of single molecule systems.