The emergent class of two-dimensional (2D) layered materials have gained considerable attention owing to their unique thickness-dependent properties and atomically thin structure. New applications rely on the assembly of heterolayers and ideally this is achieved via heteroepitaxial growth of the desired layers. This requires fundamental understanding of the growth mechanisms as well as thermal stability of the layers. Here, using in situ ultra-high vacuum variable-temperature (300 – 1000 K) scanning tunneling microscopy (UHV VT-STM), we investigated the hBN growth kinetics and high-temperature surface dynamics of hBN-covered Pd(111). We identify the mechanisms leading to 'carpet-like' growth of hBN monolayer across the Pd terraces. Interestingly, at higher deposition rate and lower temperature, we observe uphill growth via preferential attachment at the step edges while deposition at a lower rate and higher temperature leads to downhill growth via nucleation and growth of islands on Pd terraces. We attribute this unusual growth behavior to differences in temperature-dependent rates of hBN deposition at the steps vs. on the Pd terraces. We show that hBN-covered Pd(111) surfaces are thermally more stable than bare Pd(111). In situ VT-STM images reveal step-orientation dependent fluctuations and 2D Pd adatom island decay. Interestingly, we find that the hBN covered vacancy islands decay at significantly slower rates compared to adatom islands. We attribute our observations to suppression of adatom mobility under the hBN overlayer. Our results provide new, direct insights into the growth kinetics and the thermal stability of substrate-supported two-dimensional layered materials.

In situ high-temperature STM studies of hBN growth kinetics and surface dynamics

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.