The research objective of this award is increase rate and yield of microscale self-assembly processes. In self-assembly, components are designed to spontaneously bond when brought together as by mixing or agitation. The rate of component assembly and the process yield depend on the characteristics of the interaction processes. The research approach will first validate and refine force and energy models of individual self-assembly bonds. These bond models will provide key inputs into a stochastic process models that relate controllable process parameters to process rate and yield. The models will be experimentally validated through assembly of a function microsystem?a micro thermoelectric cooler. The micro thermoelectric cooler will be assembled from high performance nanostructured thermoelectric materials to validate the predictive capabilities of the models. Deliverables include capillary bond models, general self-assembly process models, experimental model validation, process of generating models of related processes, documentation of results, and educational outreach to K-12 students.
If successful, the results of this research will enable large scale integration of components too small to effectively pick up and manipulate using current assembly techniques. This will improve performance of microsystems by enabling integration of new materials and devices. For example, smaller thermoelectric elements can be integrated for more efficient cooling of electronic and photonic equipment and lower cost recovery of waste heat. The models and the methods for building them developed through this project can be adapted to self-assembly using other bond types and at other size scales. Examples from this work will be incorporated into presentations to K-6 students to teach important concepts about energy and to increase students? recognition of the role science and engineering play in their lives. High school demonstrations will be used to recruit students for hands-on lab work on the project during the summers. Advances from this project will also be integrated into graduate and undergraduate courses.
Modern technology, particularly in the medical and electronics industry has seen a continuing trend toward the fabrication of smaller devices. While these are sometimes made in one piece, there is often a requirement to assemble key components. Assembly has traditionally been done by physically grasping and positioning each piece by hand or with a tool such as a robot. As component sizes continue to shrink, this is increasingly problematic. Alternatively, the components can be designed to bond spontaneously when they come together. While this creates many challenges for the component design, the assembly process can be significantly simplified. Robots are replaced by simple circulating baths in which many assemblies can occur in parallel. This process has been successfully used to create a wide range of functional assemblies in the laboratory. However, most of these assemblies require careful management and there is no proven theories for scaling the self-assembly process from a laboratory scale to production scale. The objective of this project was to test the accuracy of parameterized models based on theories from chemical reaction rates to efficiently predict how assembly rates will change as the process parameters change. This progress developed a set of parameters and a model based on these parameters. This model was tested by carefully controlling many of the parameters that vary stochastically during self-assembly. The outcomes of these assembly tests were compared to the model predictions to verify key aspects of the model. As a result of this project, researchers now have key information to guide the development of self-assembly processes for production. This includes the sensitivity to assembly success of several key parameters, strategies for designing self-assembled systems to increase yield and to decrease sensitivity to process errors. This information will support efforts to create highly functional systems from consumer electronics to life saving medical devices from small components. These results could also be used to integrate functional blocks into parts produced by additive manufacturing (3D Printing). One promising application studied in this project is in the fabrication of small thermoelectric devices. Thermoelectric devices can convert electrical energy to thermal energy or vice versa. They have applications from cooling electronics to recovering waste heat to improve energy efficiency. In cooling applications, small elements are most efficient. This project demonstrated several approaches to improving the effectiveness of self-assembly for these applications. This research also supported the education of many students both graduate and undergraduate students. Approximately half of the students were from groups that are traditionally under-represented in the Science, Technology, Engineering, and Math fields. Through this project they learned about advanced manufacturing processes, characterization tools, problem solving, and communications. The graduate students received multiple poster awards from poster presentations of their work on this project. Examples from this project were used to teach about energy conversion and manufacturing to hundreds of students in local schools.
