Tip Directed-Assembly of Nanoparticles via Surface Plasmon Excitation

Tip Directed-Assembly ofNanoparticles via Surface-Plasmon Excitation - Hastings, Menguc, and Hawes Project Summary Intellectual Merit: Controllable manufacturing of nanoscale structures is crucial for the future of nanotechnology. To meet this need, the proposers have recently developed a new approach to direct the assembly of nanoparticle building blocks. This research exploits the unique optical and thermal properties of metallic nanoparticles to selectively assemble them into more complex structures and eventually into active nanodevices. The approach relies on the optical excitation of particles under surface-plasmon resonance (SPR) conditions and then localizes additional energy via a nanoscale scanning probe to melt and fuse the particles together. Due to the unique thermal properties of metallic nanoparticles the surfaces of the particles will melt at temperatures dramatically lower than the bulk melting temperature to permit particle fusion. The nature of SPR allows the particles to be selectively excited based on size, geometry, material, and local microscopic environment, opening the door for an integrated process that permits multiple materials to be fused and patterned in the same time frame. Finally, targeted particles can be selectively evaporated or ablated providing both additive and subtractive modes of fabrication. The proposed effort intends to expand the theoretical and experimental foundation necessary to make this assembly process viable for nanomanufacturing. Pursuit of this goal will address fundamental questions in nanoscale electromagnetics and thermodynamics while developing a practical system for the assembly of nanoparticles into complex structures. Specifically, the proposed effort seeks to more fully understand (I) optical excitation, heating, and cooling of nanoparticle/nanoprobe systems; (2) melting, fusion, and evaporation of nanoparticles; and (3) critical factors involved in scaling up this process for manufacturing. Understanding of these areas will allow one to determine the optimal conditions for, ultimate limits of, and tradeoffs between resolution, selectivity, and throughput for tip-directed, surfaceplasmon assisted assembly. It will also establish the designs and requirements for tip arrays that can carry out this process in parallel for true manufacturing throughput levels. Broader Impact: The proposed investigation of nanoparticle-nanoprobe systems will have a far reaching impact on the understanding of nanoscale electromagnetics and thermal transport via radiation and conduction. The effort is likely to provide insight a a number of open questions about the optical excitation of nanoparticles and nanoprobes, the surface and bulk melting of nanoparticles at low temperatures, and the use of scanning probe techniques for nanoscale fabrication. As such it compliments many ongoing efforts in these areas. Establishing a framework for a new nanoscale assembly technique will also have broad impact by enabling new active nanodevices and by making nanoassembly technology more widely available. Participants in the program at the post-doctoral, graduate, and undergraduate level will receive extensive interdisciplinary training in nanoscale optics, thermal sciences, fabrication, microscopy, metrology, and modeling. The University of Kentucky has two Nanotechnology Programs: the Nanoscale Engineering Certificate Program (NECP) and the Honors program on Nanotechnology that introduce nanotechnology into the curriculum as early as the freshmen year. These programs promote active learning by understanding the processes and implications of nanotechnology and creating communication between engineering disciplines within the context of nanotechnology. The project will draw on students and researchers from within these communities. In addition, the project will provide a foundation for outreach efforts to high schools students in both urban and Appalachian regions of Kentucky.