PNNL

The Science

In oriented attachment, already formed nanoscale crystals come together to create a larger single crystal—a process that significantly differs from classic crystal growth. Despite being observed in many materials systems, the fundamental forces that govern oriented attachment are still overall poorly understood. Researchers from the Ion Dynamics in Radioactive Environments and Materials (IDREAM) Energy Frontier Research Center studied the formation of gibbsite crystals through the oriented attachment of nanoplatelets. The team observed the sliding motion in real time using transmission electron microscopy (TEM), which showed how the nanoplatelets shifted and moved as they attached together. Combining this observation with simulations, the researchers determined that a staggered arrangement of platelets is the lowest energy option, leading to the structure of the observed larger crystals.

The Impact

Gibbsite is an aluminum-based material found in legacy nuclear waste within the United States. Understanding how gibbsite nanomaterials behave has implications for the management of this legacy nuclear waste. Beyond waste processing, this work provides important details about the forces behind oriented attachment. This knowledge can be used to help develop models that predict oriented attachment and material stability in both gibbsite and other systems. 

Summary

Oriented attachment is a critical, yet poorly understood, pathway in which larger crystals grow through the self-assembly of nanocrystals. In oriented attachment, particles separated by solvent align and join via precise rotation and translation, driven by atomic-scale forces. In particular, the forces that facilitate observed uniform stacking and superlattice formation remain unclear. IDREAM researchers showed how macroscopic gibbsite mesocrystals form through the directional sliding of nanoplates. TEM and X-ray scattering data support the formation of a monoclinic superlattice structure based on nanoplate stacking with a uniform ≈50-degree stagger along the gibbsite [010] direction. In situ liquid-cell TEM captured preferential sliding along the gibbsite [010] direction, which slows as particle overlap increases. Molecular dynamics simulations highlight that the staggered arrangement corresponds to a global free-energy minimum. The simulations also confirm that sliding along the [010] direction is energetically favored, providing insight into the role of interfacial water in achieving long-range ordered assemblies. These insights highlight the energy landscape’s role in oriented attachment, with implications for material synthesis and hierarchical structures in nature.

Contact

Xiaoxu Li, Pacific Northwest National Laboratory, xiaoxu.li@pnnl.gov

Xin Zhang, Pacific Northwest National Laboratory, xin.zhang@pnnl.gov

Kevin M. Rosso, Pacific Northwest National Laboratory, kevin.rosso@pnnl.gov 

Carolyn Pearce, Pacific Northwest National Laboratory, carolyn.pearce@pnnl.gov 

Funding

This material is based on work supported by the IDREAM program, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science (SC), Basic Energy Sciences (BES) FWP 68932. X.L., C.P., D.J.J., K.M.R., and X.Z. also acknowledge support from the DOE, SC, BES, Chemical Sciences, Geosciences, and Biosciences Division through its Geosciences Program at Pacific Northwest National Laboratory (PNNL) (FWP 56674). T.A.H. acknowledges support from the DOE, SC, BES, Chemical Sciences, Geosciences, and Biosciences Division through its Geosciences Program at Sandia National Laboratories (FWP 24- 015452). This article was authored by an employee of National Technology & Engineering Solutions of Sandia, LLC, under contract no. DENA0003525 with DOE. This research also utilized the Complex Materials Scattering (CMS, 11-BM) beamline of the National Synchrotron Light Source II, a DOE SC user facility operated by DOE SC at Brookhaven National Laboratory under contract no. DE-SC0012704. A portion of the work was carried out in the Environmental and Molecular Sciences Laboratory, a DOE SC user facility at PNNL sponsored by DOE SC Biological and Environmental Research, under user proposals 10.46936/lser.proj.2020.51382/60000186 and 10.46936/lser.-proj.2021.51922/60000373.