Collaborative Research: Tuning Graphene Nanoribbon Properties with Non-hexagonal Rings

With support from the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program of the Division of Chemistry, Professors Michael F. Crommie of the University of California at Berkeley and Colin Nuckolls of Columbia University are developing methods for the fabrication and characterization of new molecular structures that have the potential to enable faster, smaller, and more energy efficient electronic devices. Current high technology applications involve taking relatively large semiconductor crystals and embedding them with impurities as well as laboriously cutting them into very small shapes to control how they respond to electrical signals. In contrast, this collaborative research team will develop synthetic methods to create molecular analogs of wires and sheets having shapes and sizes that naturally facilitate the flow of electrons and enable their use as functional components in electronic devices. If successful, the new molecular materials that result from this project could eventually provide a cheaper, cleaner, and easier-to-mass-produce alternative to bulk semiconductors, and could also provide smaller and more efficient electrical devices (such as transistors, diodes, and solar cells) than is currently possible. During the course of conducting this project, students and postdoctoral researchers will gain valuable experience in the synthesis and characterization of new nanomaterials using cutting edge instrumental techniques. Several outreach activities targeting K12 students, underrepresented minorities, and the general public are planned. These include hosting laboratory open-house days, nanoscience poster sessions, and nanotechnology workshops; developing TikTok videos that highlight the blend of chemistry and physics that underpins the proposed research; and participating in several community-service programs, such as the Transfer to Excellence (TTE) REU, the Bay Area Scientists Inspiring Students (BASIS), and the Summer Math and Science Honors Academy (SMASH). The main goal of this project is to explore new graphene nanoribbon (GNR)-based systems whose electronic and magnetic properties can be tuned by embedding non-hexagonal carbon rings into the GNR backbone. Chemical synthesis and atomic-scale characterization will be combined to evaluate the utility of this new technique for controlling the electronic properties of bottom-up-fabricated GNRs. Chemical synthesis will be performed to develop new molecular precursors and polymers that enable the growth of GNRs with engineered ring structures on clean metal substrates via surface self-assembly and matrix-assisted-deposition (MAD). GNR local electronic and magnetic properties will be characterized using scanning tunneling microscopy (STM) and will be compared to theoretical predictions. Fundamental questions will be addressed such as the degree to which GNR radical states can be controlled by inserting simple non-hexagonal ring structures into molecular precursor building blocks. Competition between hybridization of adjacent radical states and on-site Coulomb repulsion within GNRs will be tuned with the aim of controlling GNR magnetic order, something never before accomplished. Other fundamental properties of new GNR systems will be evaluated, such as energy gaps, wavefunction distributions, electron hopping amplitudes, and spin-spin interaction strengths. If successful, this work could help build a foundation for the use of bottom-up fabricated GNRs as a new nanoelectronics platform. This could be transformative since GNRs have excellent electronic properties and can be synthesized in bulk quantities with high-fidelity and atomic precision from molecular starting materials. This could, in principle, allow quantum device densities much higher than other material platforms at very low cost, opening new possibilities for quantum device applications that would be beneficial to society.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.