In most micro/nano-engineered systems, multiple materials are in intimate contact with each other while being subjected to extreme thermal, mechanical and electrical loads. This results in unique scale-sensitive near-interface phenomena, such as diffusional transport along interfaces, driven by a combination of stress, thermal and electric fields. In solid materials, this causes interfacial sliding, which may cause migration of features embedded within a device, causing interfacial strain incompatibilities and potential failure. At liquid-solid interfaces, the application of an electric field can result in movement of the liquid relative to the solid via liquid electromigration (L-EM), which has potential applications in micro-fluidics, conformal coating of circuitry in micro-systems, and tip-based nano-lithography. This proposal has four objectives: (1) obtain mechanistic insight and develop a constitutive model for sliding at solid hetero-interfaces under a combination of stress, electric field and thermal gradient; (2) understand and model diffusional liquid transport at liquid-solid interfaces under a combination of electric field and thermal gradient; (3) correlate the kinetics of diffusion along solid-solid and liquid-solid interfaces to interfacial and near-interface structure and chemistry; and (4) utilize the models and insights generated to simulate the combined impact of shear stress, electromigration and thermomigration on interfacial sliding in solid-solid and liquid-solid systems of practical importance. As such, the insights obtained will be valuable for reliability of micro/nano-electronic devices, as well as for novel applications involving micro/nano-scale liquid-motion, such as tip-based nanolithography and micro-fluidics.
NON-TECHNICAL SUMMARY: Micro and nano-scale devices such as those used in electronics have numerous boundaries between disparate materials that are packed very closely together. The materials within these devices are subjected to mechanical, electrical and thermal loads, causing transport of material to occur along the internal boundaries. This can cause severe reliability problems in electronics. Occasionally, when one of the materials undergoes melting due to excessive heating, the same phenomenon also causes flow of the liquid relative to the solid. This presents opportunities to exploit this phenomenon in new technologies like advanced lithography and microfluidics. In the proposed work, mechanistic insight and models for transport along both solid-solid and solid-liquid boundaries will be developed. If successful, the work will have direct impact on the reliability of next-generation electronics, as well as on the development of new manufacturing technologies such as tip-based nanolithography, thus influencing US competitiveness. The project will involve a graduate student and a postdoctoral associate in research and education, undergraduate students through Research Experience for Undergraduates, and outreach to high-school students through a science competition summer program. It will also involve international collaboration with India and collaborative activities with a national laboratory and industry. Results of the project will be broadly disseminated through faculty and student participation at meetings of learned societies.
