The objective of this research is to develop an atomic force microscope based cyber-physical system that can enable automated, robust and efficient assembly of nanoscale components such as nanoparticles, carbon nanotubes, nanowires and DNAs into nanodevices. The approach in this project is based on the premise that automated, robust and efficient nanoassembly can be achieved through tip based pushing in an atomic force microscope with intermittent local scanning of nanoscale components. In particular, in order to resolve temporally and spatially continuous movement of nanoscale components under tip pushing, the research is exploring the combination of intermittent local scanning and interval non-uniform rational B-spline based isogeometric analysis in this research.
Successful completion of this research is expected to lead to foundational theories and algorithmic infrastructures for effective integration of physical operations (pushing and scanning) and computation (planning and simulation) for robust, efficient and automated nanoassembly. The resulting theories and algorithms will also be applicable to a broader set of cyber physical systems.
If successful, this research will lead to leap progress in nanoscale assembly, from prototype demonstration to large-scale manufacturing. Through its integrated research, education and outreach activities, this project is providing experiences and understanding in cyber-physical systems and nanoassembly for students from high schools to graduate schools. The goal is to increase interest in science and engineering among domestic students and therefore strengthen our competitiveness in the global workforce.
In recent years, quasi one-dimensional nanostructures have been widely implemented in a variety of nanoscale electronic devices because of their unique geometries and exceptional electrical properties. As nanowires and nanotubes can be synthesized routinely through different kinds of techniques, the key challenge of fabricating nanowires or nanotubes based devices is to effectively manipulate those one-dimensional nanostructures to desired locations. Dielectrophoresis (DEP), generated by an electric filed, provides an effective way to align nanowires with high throughput. Unfortunately, the DEP assisted nanoassembly is very difficult to control and it is almost impossible to guarantee the uniformity of the devices. Atomic force microscope (AFM), an instrument nanoscale imaging, is able to directly interact with nanosize objects through nanomanipulation. However, the AFM based nanomanipulation has low throughput because of its sequential process nature. By combining AFM based nanomanipulation and DEP assisted nanoassembly, a nano-robotic system, taking the advantages from both AFM based nanomanipulation and DEP assisted nanoassembly, is expected to enable automated, robust and efficient assembly of nanoscale components such as nanoparticles, carbon nanotubes, nanowires and DNAs into nanodevices with high throughput and high precision. The goal of this project is to achieve high throughput of deterministic assembly of nanodevices by combination of DEP assisted nanoassembly and AFM based nanomanipulation. Through study of DEP assisted nanoassembly and AFM based nanomanipulation, we have made several significant findings and developed several techniques that can further advance the technologies of DEP assisted nanoassembly and AFM based nanomanipulation, thus paved the road for the integration of these two technologies for high throughput fabrication of nanowires and nanotubes based nanodevices. During the research of this project, we first solved the notorious problem of thermal drift in AFM based nanomanipulation, which has been the main hurdle for high throughput of AFM based manipulation. By developing a local scan strategy to remove drift contamination of AFM images and also to compensate the thermal drift during nanomanipulation in real-time, we are able to completely eliminate the effect of thermal drift during AFM based manipulation. Based on the drift free technology, we have developed a drift-resistant augmented reality system for AFM based nanomanipulation. The system builds a foundation for automated nanomanipulation with extremely high throughput. Such high throughput nanomanipulation system will be a practicable tool for assembling nanodevices by manipulating nanoscale objects such as nanoparticles and nanowires. We then further studied the DEP assisted nanoassembly though modeling, simulation, and experimental verification. We developed the accurate model for DEP assisted nanoassembly. Using the accurate model, we have developed simulation software that can simulate the motion behavior of nanowires under DEP assisted nanoassembly and predict the final alignment of nanowires after DEP assisted nanoassembly. The alignment of nanowires is critically important for the throughput of fabrication of nanowires based devices. We have discovered the principle of how the nanowires are aligned during DEP assisted nanoassembly. Our finding suggests that the nanowire tends to align with the direction of gradient of electric field when it is close to the center of electrodes, whereas it is more likely to align with the direction of electric field as it attaches farther from the center. As a result, the gap size, the length of the nanowire, and the contact position determine whether the nanowire has the ability to bridge the electrodes. The findings from the study of the alignment of nanowires in DEP assisted nanoassembly have a significant impact among the society for fabrication of nanowire based devices. The exact alignment of nanowires in DEP assembly has puzzled the society for many years without a clue why the nanowires align in a specific manner. The findings from this study provide reasonable explanation and useful guidance in the fabrication of nanowire based devices.
