Colloidal crystals with complex hierarchical architectures possess unique optical, electrical, thermal, and mechanical properties that differ from the properties of their individual building blocks. These metamaterials are playing an increasingly important role in various emerging technologies ranging from energy conversion (photovoltaic cells) to microelectronics to medicine to defense (stealth technology). While a large library of nanocrystals with various properties and functionalizations is available, understanding colloidal crystal formation and process kinetics remains a challenge. Tools that are currently available to the experimenter include light scattering, which provides information on ensemble averages, and transmission electron microscopy of ?frozen? samples taken at discrete times during the assembly process (typically at the end of the process), which do not reveal process dynamics. To enable the development of new processes and new materials, it is highly desirable to observe the self and controlled assembly of nanocrystals in real time as a function of various process conditions.
Intellectual Merit: This project studies colloidal crystal formation with a novel imaging tool dubbed the nanoaquarium. The device consists of a thin reactor, ranging in height from tens to hundreds of nanometers, sandwiched between two thin (electron-transparent) silicon nitride membranes. The nanoaquarium will accommodate multistreams of liquids and suspensions, will retain the liquids for hours in the high vacuum environment of the electron microscope without any leaks, and will allow the tracking of individual particles, their rotation, and interactions in real time. Although preliminary experiments demonstrating the utility of the nanoaquarium for studying the aggregation of monodisperse particles have successfully been completed, it is desirable to improve the device to allow the mixing of multiple liquid streams and equip the device with embedded resistors for temperature measurement and control and with electrodes for the induction of electric fields for actuation and sensing. In close collaboration with chemists and material scientists, the device will be used to study the formation of binary and ternary superlattices. Such superlattices are predicted to have properties that significantly differ from those of the individual components and that may be optimal for photovoltaic cells and microelectronics. The nanoaquarium provides a ?programmable? environment to study colloidal self and controlled assembly in real time as a function of particles? geometries, functionalization, and concentrations; solvent composition, pH, and temperature; and electric fields. Despite their potential importance, little is known about these crystals? nucleation and growth processes.
Broader Impact: The nanoaquarium has broad applicability for in-situ electron microscope imaging of processes in liquid media such as nano particle self and controlled assembly, study of nanoparticle toxicology (migration of particles on membranes), electrochemical material deposition, contact line motion, nucleation processes, and biological processes. Since the device facilitates new experiments, it is likely to provide new insights and enable discoveries in a variety of disciplines. Additionally, the nanoaquarium has potential for commercialization. Many researchers have expressed an interest in using the device in their studies. The results of the proposed study and the videos obtained with the nanoaquarium will be incorporated into instructional material in courses on materials science, colloidal science, interfacial phenomena, and nanotechnology offered to engineering, physics, and chemistry majors. In-situ electron microscopy video footage obtained with the nanoaquarium conveys information about dynamical nanoscale phenomena that is vivid, accessible, and exciting to scientists and non-scientists alike. Narrated videos will be posted on the web, prepared for high school students and teachers, undergraduate students, and the public to convey the excitement of discovery and promote interest in science and engineering. The project will engage undergraduate researchers and high school teachers in device development, imaging, and image analysis.
