Invited Paper NS-MoM3
Peter Mark Memorial Award Lecture: Taking Control of the Nanoscale with Scanning Programming Microscopy
Monday, October 19, 2015, 9:00 am, Room 212B
Manipulation of single atoms and molecules is undoubtedly one of the most striking achievements of nanoscience. It has been repeatedly utilized to create clean model systems for surface physics, and it foretold the dream of atom-by-atom synthesis and atomic-scale control. However, it is also apparent that establishing atomic manipulation as a synthetic methodology for realistic materials faces major challenges. The first of these is scaling the complexity of atomic control – extending onto crystalline lattices, 3D objects, larger scales and increasingly complex chemical interactions. A related and equally potent challenge is increasing the energy scale of manipulation (and, conversely, the stability of manipulated matter), which necessitates control over chemical bond breaking. Essentially, we need to advance atomic manipulation toward the accuracy of macroscopic chemistry while retaining control over 1-100 nm length-scales. Over the last several years, we have explored the effects of large electric field, electronic current density and mechanical stress in progressively complex chemical reactions on surfaces and solid state materials with rich defect chemistry. Our goal is to peer into “pre-breakdown” window of material properties, that would normally be associated with destruction, desorption or amorphization. Quite on the contrary, using the unique capabilities of scanning probe microscopy, we have found this regime to be rich in chemical and electrochemical transformations, including reversible motion of oxygen vacancies in deep sub-surface volume of perovskite oxides (1-4) and delocalized chemical reactions involving rearrangements of chemical bond-order and strongly chemisorbed molecules (5-8. We established that local electrochemical control is key to understand and subsequently control specific phenomena, such as metal-insulator transitions in perovskite oxides in non-uniform stress and electric fields. Furthermore, hot-electron currents and electric fields can drive chemistry that is not thermally accessible, pointing toward novel catalytic and surface reactions. At the same time, many of these transformations exhibit memory, hysteresis and training. We therefore speculate that they provide a stepping stone to programmable materials, a distinct paradigm where the shape and function of the materials will be defined by a programmed protocol of excitation, relaxation and stresses. Programmable materials can be made adaptive and eventually even computing. Ultimately, we envision programmable metamaterials, wherein a “quilt” of nanoscale chemical compositions with distinct chemical boundaries produces a unique collective function.
Research supported in part by the Center for Nanophase Materials Sciences, sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.
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