Directing the synthesis and controllable assembly of nanostructures of different materials and dimensionalities in organized configurations is essential for harnessing them for device applications. This talk provides an overview of our recent works in directed synthesis, assembly, and properties of assemblies of carbon nanotubes, nanorods and nanoparticles of magnetic and thermoelectric materials, and molecular nanolayers. Our underlying goal is to develop a new toolbox of approaches for manipulating structure and chemistry across multiple length scales to realize novel properties for emerging applications in device wiring, data storage, sensing, power generation and refrigeration.

I will first describe the organized assembly and functionalization of carbon nanotube (CNT) mesoarchitectures by site-selective nucleation and growth of micron-sized CNT bundles of controllable lengths at desired locations in multiple orientations on planar and curved surfaces. Growth kinetics, scaling and electrical transport mechanisms in the CNT assemblies will be elucidated. I will then describe new scalable approaches to functionalize and derivatize CNTs using focused ion beam (FIB) irradiation, microwave stimulation and current injection. FIB modification can be used to functionalize CNT segments, and derivatize them with nanoparticles, amino-acids and proteins. Microwave stimulation allows the rapid functionalization, nanoparticle synthesis (e.g., Au, CdS, Cu2O), and anchoring -- all in a single step, while high electrical current densities are attractive to modify CNT networks. Key mechanisms of structural and chemical changes, and electrical properties and sensing responses, will be presented.

The second part of my talk will illustrate the synthesis and assembly of nanoparticles of magnetic and thermoelectric materials with control over crystal structure, shape and surface chemistry; and their subsequent organization into 1-D and 2-D assemblies. We have devised entirely new strategies to obtain high magnetic coercivity FePt-silica core-shell nanomagnets with simultaneous control over size, dispersity, composition, phase stability, by using non-ionic surfactant-stabilized water nanodroplets, and realize low temperature chemical ordering by doping. I will show the assembly of nanoparticle chains of desired length and diameter, or ordered films, by harnessing interactions between dibinding molecular couplers, polyelectrolytes, and substrate-nanoparticle interactions. I will illustrate the use of surfactant-mediated growth of single-crystal nanorods of bismuth telluride with control over surface chemistry and branching.

I will conclude with a remarkable example that demonstrates a use of a sub-nm-thick self-assembled molecular nanolayer to enhance the toughness of thin film interfaces by more than a factor of seven yielding values exceeding 28 Jm^-2. The toughening mechanism is explained based on electron spectroscopy of fracture surfaces and density functional theory calculations.

If you'd like to meet with Prof. Ramanath during his visit, please contact Prof. Michael Greenfield (greenfield at egr.uri.edu).