Place: 4274 Chamberlin (Refreshments will be served)
Speaker: Song Jin, UW Department of Chemistry
Abstract: I will discuss some complex "Christmas Tree" like nanowire structures spontaneously formed through chemical reactions. These fascinating nanostructures demonstrate a ?new? nanowire formation mechanism that is completely different from the well-known metal catalyzed vapor-liquid-solid (VLS) mechanism. The screw component of an axial dislocation provides the self-perpetuating steps to enable 1-dimensional crystal growth, unlike previously understood mechanisms that require metal catalysts. This mechanism was found in hierarchical nanostructures of lead sulfide (PbS) nanowires resembling ?pine trees? that were synthesized via chemical vapor deposition. Structural characterization reveals a screw-like dislocation in the nanowire trunks with helically rotating epitaxial branch nanowires. The rotating trunks and branches are the consequence of the Eshelby twist of screw dislocations. We suggest that screw dislocation growth is overlooked and underappreciated in modern literature on one-dimensional nanomaterials. The proposed nanowire growth mechanism will be general to many materials and enable more complex nanostructures to be synthesized in the future to enable diverse applications.