Optoelectronic Manipulation, Assembly, and Patterning of Nanoparticles

Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission. The synthesis of nanostructures has advanced in the last decade to a point where a vast range of insulating, semiconducting, and metallic materials are available in a variety of forms and shapes such as wires, tubes, ribbons, sheets, and spheres. These nanostructures display exceptional physical properties that can be used to realize novel devices such as high-speed electronics, efficient photovoltaics and thermoelectrics, sensitive chemical and biological sensors, nano-light sources such as lasers and light-emitting diodes, and high-frequency resonators. However, a persistent challenge has been the development of a general strategy for manipulation and heterogeneous integration of individual nanostructures with arbitrary shapes and compositions. Development of such methods is essential in transforming nano-sciences into successful nano-technologies that can ultimately affect the society. Several techniques such as microcontact printing, microfluidics, Langmuir-Blodgett, mechanical nano-manipulators, optical tweezers, and fixed-electrode dielectrophoresis have been developed to address this challenge. However, these techniques either lack the capability to manipulate single nanostructures or are unable to do so in a dynamic and large-scale fashion. Optoelectronic tweezers (OET) has emerged as a powerful tool for massively parallel manipulation of polymer-beads and living cells at micron length-scales via optically-induced dielectrophoresis. By combining the optical and electrical trapping capabilities, OET is able to manipulate particles with much lower optical intensities than optical tweezers and unlike fixed electrode dielectrophoresis, OET is capable of dynamic manipulation of single particles over large areas. In this dissertation, we will first introduce OET as an optofluidic platform and characterize the various electrokinetic forces that can be generated in the OET device. Next, we will use these forces for manipulation, sorting, assembly, and patterning of various nanostructures such as semiconducting and metallic nanowires, carbon nanotubes, and metallic spherical nanocrystals. Though the initial demonstrations of OET were limited to manipulation of microscale objects, 2 here, we will explore the capabilities of OET for manipulation of nanoscale particles, establishing it as an important tool for post-synthesis organization and heterogeneous integration of nanostructures.