To develop a fundamental understanding of energy losses in nanostructures and to exploit this knowledge for enhanced performance of nanostructures
Nanoelectromechanical systems (NEMS) have attracted significant interest as they promise high frequencies and quality factors (Q). However, many recent experimental studies have observed that the mechanical quality factor, Q, defined as the ratio of the energy stored to the energy lost per unit period, of NEMS is much lower than those from theoretical predictions. This discrepancy can be attributed to the novel physics that arises at the nanoscale and is not accounted for in the classical theory. The attainable frequencies in NEMS are comparable to the phonon frequencies and this can introduce new sources of intrinsic dissipation, such as Akhiezer damping, which can significantly reduce the quality factors. In addition, as the surface to volume ratio is higher at nanoscale, surfaces act as an additional source of dissipation reducing the Q. To realize the full potential of NEMS, it is important to develop a comprehensive physical understanding of all dissipation mechanisms at nanoscale. Through this knowledge, high Q nanostructures can be engineered. Since classical theories do not adequately describe dissipation at nanoscale, the focus of this project is to develop atomistic and multiscale approaches to understand dissipation in nanostructures.
This project will provide interdisciplinary research, education and training of graduate and undergraduate students and the research results will be widely disseminated for broader impact.
Two types of mechanical losses, namely intrinsic and extrinsic, will be considered and understood. Intrinsic losses or energy dissipation mechanisms are those that are inherent to the nanostructure. Popular sources of intrinsic dissipation are Akhiezer damping, thermo-elastic damping, surfaces, defects, etc. Most nanostructures operate in a fluid medium, so in addition to intrinsic losses, extrinsic losses, defined as the dissipation caused by the fluid, also needs to be taken into account. The key objectives of this project are to (i) Develop atomistic and multiscale computational approaches to understand intrinsic losses in a variety of one-dimensional and two-dimensional nanostructures. Comprehensive theories to model Akhiezer, thermo-elastic, defects, surfaces and other sources of intrinsic dissipation will be developed. (ii) Develop atomistic and multiscale computational approaches to understand extrinsic losses. To determine extrinsic losses, coupled fluidic and structural analysis is necessary. To compute fluidic forces acting on the nanostructure, a comprehensive multiscale approach will be developed. The multiscale approach for fluidic analysis will be coupled with a multiscale approach for nanostructural analysis to determine extrinsic losses. (iii) Establish validation of the computational approaches by comparing computed quality factors with experimental data. In addition, various applications of NEMS such as high frequency resonators, energy harvesting and mass sensing will be pursued.
