Toward Technologically Relevant Single-Molecule Junctions: New Metals, New Interfaces, New Functionality

Nontechnical description Improvements in computing and data storage over the past six decades have largely been driven by shrinking the electronic components used in integrated circuits. However, it is becoming increasingly difficult to make these conventional silicon-based circuits even smaller. As a result, new approaches are needed to continue improving the performance and energy efficiency of future electronic devices. The field of molecular electronics seeks to address this challenge by using individual molecules as electronic circuit elements. However, most studies in this field rely on gold, an electrode material that is incompatible with modern silicon chip fabrication. This makes it difficult to integrate molecular electronic circuits with existing chip technologies, a step widely thought to be essential to their practical realization. In this project, the research team seeks to identify new methods to form and study molecular circuits using a wider range of technologically relevant electrode materials. A major goal is to understand how different electrode materials influence circuit performance. This research aims to develop circuits that are highly conducting, chemically stable, and provide a well-defined electrical response. Together, this knowledge will help guide the development of future hybrid technologies that combine molecular and silicon-based electronics. Graduate and undergraduate students involved with this project will receive broad training in materials science, chemistry, and computational modeling. This project will also provide paid summer research positions to community-college students. These experiences will strengthen pathways into four-year undergraduate degrees, graduate programs, and STEM careers. The research team will also continue work on the Molecular Junction Database, a free search tool that organizes thousands of published studies for use by students and researchers across the world. Technical description In this project, the research team explores how electrode metal and interfacial chemistry control charge transport through single molecules connected between atomic-sized electrodes. Most studies to date have used inert gold electrodes and air-stable molecules, limiting understanding of how more technologically relevant electrode metals and unconventional contact chemistries may influence junction properties. To expand the range of chemical systems that can be studied, this project develops and applies air-free methods for scanning tunneling microscope-based break-junction studies. Such methods enable reliable conductance measurements with readily oxidized electrode metals and reactive molecules that cannot easily be studied in the presence of water and oxygen. New families of precursors are used to create distinct electrode-molecule bonding motifs that form robust, well-defined junctions with enhanced electronic coupling. Systematic studies probe the relationships between electrode metal, interfacial bonding, junction conductance, and stability. Such investigations establish the core design principles that link junction structure and composition with electronic performance. Experimental measurements are combined with computational modeling to establish the mechanisms governing charge transport. These advances lay the foundation for next-generation molecular electronic circuits while also providing new insights into the chemistry and electronic properties of metal-solution interfaces relevant to catalysis, sensing, and energy conversion. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.