The liquid-solid interface plays an essential role in many phenomena encountered in biological, chemical, and physical processes relevant to both fundamental and applied science. However, study of the hydrated materials such corroded interfaces or hydrated proteins is challenging as liquid water is generally incompatible with many analytical imaging techniques that require high to ultrahigh vacuum conditions. One strategy to probe hydrated materials is to cryogenically freeze the liquid into solid form to preserve local ionic chemistry gradients and surface composition within a solid structure, making it more amendable to vacuum-based analyses such as Atom Probe Tomography (APT). Nevertheless, the regular application of APT to cryogenic specimens is lacking due to challenges in preparing the necessary nanoscale needle-shape morphology using a FIB-SEM and the subsequent environmentally protected transfer of the frozen specimens to the APT instrument for analysis. Motivated by the prospect to map ionic and macromolecular gradients in hydrated biological systems, I will walk you through my journey to develop unique hardware and protocols that enable the exploration of new science within environmentally sensitive materials. Specifically, I will discuss the development of a FIB-based site-specific liftout and attachment scheme of cryogenically cooled specimens involving a combination of redeposition and overcoating of organic and organometallic molecules. A modified commercially-available specimen suitcase shuttle device and an environmental transfer hub vacuum chamber at PNNL is used to facilitate environmentally protected specimen transfer between the cryo FIB and the APT tool, allowing for the first time, APT analysis of a water/solid interface to reveal ionic distributions and the complex nanoscale water-filled porous network of corroded glass. I will end this presentation focused on the unique 3D nanoscale analysis of proteins in an aqueous suspension, where with the aid of deep learning, macromolecular structure may be directly mapped and provide a complementary approach to single particle cryo-EM. This talk will provide some perspective regarding the challenges as well as the unique insight this experimental approach can offer.

Daniel Perea
Senior Staff Scientist
Pacific Northwest National Laboratory

Danny Perea is a Senior Staff Scientist at the Environmental Molecular Sciences Laboratory national user facility at the Pacific Northwest National Laboratory. He received his Ph.D. in Materials Science & Engineering from Northwestern University, where he established the application of APT to quantitatively map 3D dopant impurity distributions in low-dimensional semiconductor nanostructures. His current interests at PNNL include developing unique cryogenic-based techniques and protocols to pioneer the use of APT to probe the composition and structure of environmentally sensitive materials related to energy and the environment.