Molecules in 2D h-BN

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NON-TECHNICAL SUMMARY With this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, Professor Michael Arnold and his research group at the University of Wisconsin will investigate the creation of ultrathin, sheet-like materials that are only one atom thick. The materials will be created from an electrical insulator, containing the elements boron and nitrogen. Embedded and bonded within the sheets will be ultrasmall islands of carbon atoms. These islands will be as small as molecules, and, like normal molecules, these islands will have an exactly defined number of atoms and precisely defined shapes. The carbon islands will also mimic the electrical and optical properties of normal molecules but be seamlessly integrated and lie flat within the boron-nitrogen sheets. Materials like these, with this precision, have never been created previously. This project will address the challenge of synthesizing these materials and develop the fundamental understanding needed to create them. Atomically well-defined structures like these have the potential to be employed as next-generation filter-like materials with record-efficiency because of the materialsˈ extreme thinness and thus promise to impact applications of societal importance pertaining to the purification of air and water. The resulting materials moreover promise to possess properties needed for next-generation electronics and quantum electronics technologies, important for national defense and prosperity. The impact of the supported research and science, and of research and science in general, will be communicated to the public by the researchers through planned outreach activities, for example via the University of Wisconsin’s Badger Talks initiative. TECHNICAL SUMMARY Molecules are the ultimate nanostructures. Their size, shape, and composition can be nearly infinitely tuned, and exact replicas can be created on a massively parallel scale. Moleculesˈ physical, electrical, and optical properties can be vastly tailored – to realize insulating, semiconducting, and metallic behaviors and manipulate photons from the ultraviolet to the infrared. In this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, we will create and explore analogs to molecules – specifically analogs to polycyclic aromatic hydrocarbon (PAH) molecules – that are not free but covalently embedded, in-plane, in crystalline monolayer sheets of insulating hexagonal boron nitride (h-BN). While nanoscale domains of carbon have been fabricated from the top-down in h-BN previously, these domains have been relatively large and/or disordered in shape and size, and none have been defined with molecular precision. Here, atomically precise carbon domains will be realized, from the bottom-up, by using PAH molecules themselves to create them. The embedded PAHs will offer the exactness and tunablility of conventional molecules but in a planar, immobilized, and atomically thin form. Molecularly embedded h-BN sheets promise phenomena not previously possible – including exceptionally thin materials with exact pores of widely tunable size and shape (through selective carbon etching) for molecular sequencing or sieving applications, h-BN sheets (conventionally insulating) with functional semiconducting dopants, and immobilized single molecules that are individually addressable.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.