PNU TEM Laboratory

The Koo Group

Research Highlights - We Illuminate the Unseen

through Multi-modal and in-situ Electron Microscopy

Facet Development of Nanocatalysts

Nanoparticles with high-index facets show great promise because these facets can boost catalytic activity. We study a ligand-free, solid-state method to create such nanoparticles using an alloying–dealloying process with volatile metals. By using gas-cell transmission electron microscopy, we watched platinum and bismuth salt change from small spheres into tetrahexahedral shapes in real time. Additional evidence from atom probe tomography and theoretical calculations helped us uncover the key steps in this transformation, paving the way for better synthesis of these advanced nanocatalysts.

Nature Communications, 14, 3790

Gas Phase Catalysis

Palladium catalysts are widely used to directly produce water from hydrogen oxidation at room temperature. This reaction is important both for practical water production and as a model for studying basic processes like gas adsorption and surface reactions. However, the detailed steps in the middle of the reaction remain unclear because of the complex mix of gas attachment, atomic movement, and changes in the catalyst structure. In our study, we used gas cell transmission electron microscopy to watch the reaction as it happened. We captured real-time images showing water formation along with reversible changes in palladium. Our results indicate that the order in which gases are introduced plays a crucial role in controlling the reaction rate, which is mainly limited by how well the gas molecules stick to the catalyst. These insights help us determine the best conditions for the reaction and may guide future research on similar metal-catalyzed processes.

Proceedings of the National Academy of Sciences USA (PNAS), 121, 40, e2408277121

Etching of Silicon Gate at FET

Modern semiconductor manufacturing faces challenges from physical and chemical limits. One major issue is the wet etching of dummy gate silicon, where material must be removed from spaces only a few nanometers wide. At this tiny scale, the chemical processes differ greatly from those in larger, bulk materials. Although factors like electrical double-layer formation, bubble entrapment, poor surface wettability, and insoluble particles have been suggested, the exact reasons for these difficulties are still unclear. In our study, we used liquid-phase transmission electron microscopy, 3D electron tomography, and theoretical calculations to examine how silicon etches with tetramethylammonium hydroxide at the nanoscale. We observed slower chemical reactions, unexpected resistance to stripping, and random etching behaviors that aren’t seen on a larger scale. These insights into the challenges at the nanoscale could help us develop better fabrication methods in the future.

Nano Letters, 24, 16, 4900-4907