Periodic Reporting for period 1 - RAPID-AFM (Real Time 2D Polymerization studied using Atomic Force Microscopy)
Reporting period: 2024-07-01 to 2026-06-30
We are studying how tiny molecules join together directly on a surface to form sheets just a single layer thick, called two-dimensional polymers (2DPs) or 2D covalent organic frameworks (2D-COFs). Instead of making these materials separately and analysing them later, we watch them grow in real-time, in the liquid-solid interface where they are actually formed. This is a big leap forward compared to traditional material synthetic methods, which build the material first and examine its properties afterwards. To do this, we use a cutting-edge tool called high-speed atomic force microscopy (HS-AFM), which can record images at 45 frames per second, almost like filming a molecular movie. With this speed, we can track molecules, one by one, as they move, meet, and lock together into larger networks. By understanding how the molecules choose their pathways during polymerisation, we can control the process to create much larger, more perfect sheets with fewer defects. But, why does this matter? Just like a cracked windshield weakens a car, defects in a material weaken its performance. In advanced electronics and semiconductor devices, the tiniest imperfection can ruin performance. If we learn how to guide molecules into defect-free patterns, we can build stronger, more predictable materials for future nano-electronics.
Our project also looks at how these molecular sheets can grow on different solid surfaces, an ongoing challenge in research. We will look for multiple factors, including the effect of solvents, temperature and catalyst in obtaining the best 2DP in given conditions. Once we fully understand the forces between molecules and between molecules and surfaces, we can design materials to assemble anywhere we need them, which is a crucial step toward building devices directly at the nanoscale. Finally, we will test how these carefully made 2D polymers behave electronically and record carrier mobility of 2D-COF using FET device fabrication. By combining fundamental insight (watching how molecules grow) with practical application (measuring performance), we expect to unlock a pathway to create next-generation hybrid 2D materials with exceptional precision, ready to drive advances in nano-electronics and beyond.
Our project also looks at how these molecular sheets can grow on different solid surfaces, an ongoing challenge in research. We will look for multiple factors, including the effect of solvents, temperature and catalyst in obtaining the best 2DP in given conditions. Once we fully understand the forces between molecules and between molecules and surfaces, we can design materials to assemble anywhere we need them, which is a crucial step toward building devices directly at the nanoscale. Finally, we will test how these carefully made 2D polymers behave electronically and record carrier mobility of 2D-COF using FET device fabrication. By combining fundamental insight (watching how molecules grow) with practical application (measuring performance), we expect to unlock a pathway to create next-generation hybrid 2D materials with exceptional precision, ready to drive advances in nano-electronics and beyond.
We have completed benchmark investigations on the surface-assisted synthesis of two-dimensional polymers (2DPs) on highly oriented pyrolytic graphite (HOPG) using boronic acid and imine linkage monomers (aldehyde and amines). The studies employed scanning tunneling microscopy (STM) and high-speed atomic force microscopy (HS-AFM) to analyze and understand the growth dynamics at the liquid–solid interface. The synthesis protocol was initially validated with pyrene-2,7-diyldiboronic acid (2,7-PDBA) and subsequently extended to pyrene-1,6-diyldiboronic acid (1,6-PDBA) and naphthalene-2,6-diyldiboronic acid (NDBA). STM imaging confirmed large-area, uniform monolayer domains of boroxine-linked 2DPs featuring a well-resolved hexagonal porous lattice. In first step towards understanding the dynamics of 2DP growth, we successfully captured the real-time dynamics of the growth of 2DP from NDBA monomer using STM measurements. Correlative STM (electric field) and AFM (field-free) measurements establish a robust benchmark for assessing the influence of external fields on nucleation and domain propagation. The liquid-phase AFM imaging independently verified a lattice periodicity of ~2 nm for 2DP from 2,7-PDBA, consistent with STM-calibrated images, confirming that both techniques probe the same surface architecture. However, boroxine-linked frameworks exhibited a comparative reduced stability under AFM scanning, with tip–surface interactions degrading domain. For 1,6-PDBA, liquid phase AFM imaging revealed a lattice spacing of ~4.6 nm, attributed to a self-assembled monomer network (SAMN) rather than a covalently bonded boroxine polymer. To address these stability limitations, imine-linked 2DPs were synthesised via Schiff-base condensation of 1,3,5-tris(4′-aminophenyl)benzene (TAPB) and 1,3,5-tris(4′-formylphenyl)benzene (TFPB). High-resolution AFM imaging at the liquid-solid interface confirmed the formation of robust monolayer networks with a hexagonal lattice of ~2.3 nm periodicity, which is also consistent with the previously obtained calibrated STM images, demonstrating a superior resistance to tip-induced disruption compared to boroxine frameworks.
The combined use of STM (electric-field-assisted) and HS-AFM (field-free) provides, for the first time, a direct comparative framework for quantifying how external fields influence nucleation, domain propagation, and lattice stability in on-surface 2D polymerisation. Observing direct on-surface synthesis of 2DP and its molecular level visualisation using liquid phase AFM imaging and studying all the factors affecting the polymerisation in-situ, goes beyond the current state of the art techniques, which is not possible using STM due to the instrumental limitations. These benchmark results also demonstrate that boroxine-linked 2DPs are inherently less robust under field-free conditions, while imine-linked 2DPs exhibit superior structural integrity and imaging stability at the liquid–solid interface. Such insight enables rational selection of covalent chemistries optimised for real-time, high-resolution AFM studies of polymerisation dynamics - something previously unattainable at the scale of a single molecule.