Intrinsic and Extrinsic Losses in Nanoelectromechanical Systems

标题：纳米机电系统中的本征和外在损耗项目目标：对纳米结构中的能量损耗有一个基本的了解，并利用这一知识来提高纳米结构的性能非技术摘要：纳米机电系统(NEMS)因其具有高频率和品质因数(Q)而引起人们的极大兴趣。然而，最近的许多实验研究发现，NEMS的机械品质因数Q(单位周期内储存的能量与损失的能量之比)远低于理论预测值。这种差异可以归因于出现在纳米尺度上的新物理学，而经典理论中没有解释这种差异。NEMS中可获得的频率与声子频率相当，这可能会引入新的本征耗散源，如Akhiezer衰减，这可以显著降低品质因数。此外，由于纳米尺度下的表面体积比更高，表面作为一个额外的耗散源降低了Q值。为了充分发挥NEMS的潜力，重要的是在纳米尺度上发展对所有耗散机制的全面物理理解。通过这些知识，可以设计出高Q值的纳米结构。由于经典理论不能很好地描述纳米尺度上的耗散，本项目的重点是发展原子论和多尺度的方法来理解纳米结构中的耗散。本项目将提供跨学科的研究，教育和培训研究生和本科生，研究成果将被广泛传播，以产生更广泛的影响。技术摘要：将考虑和理解两种类型的机械损失，即内在和外在损失。固有损耗或能量耗散机制是纳米结构所固有的。常见的本征损耗来源有Akhiezer损耗、热弹性损耗、表面损耗、缺陷等。大多数纳米结构都是在流体介质中工作的，因此除了本征损耗外，还需要考虑由流体引起的损耗。该项目的主要目标是(I)开发原子学和多尺度计算方法，以了解各种一维和二维纳米结构中的固有损失。将开发用于模拟Akhiezer、热弹性、缺陷、表面和其他本征耗散源的综合理论。(2)发展原子论和多尺度计算方法，以了解外部损失。为了确定外部损失，流体和结构耦合分析是必要的。为了计算作用在纳米结构上的流体力，将开发一种综合的多尺度方法。流体分析的多尺度方法将与纳米结构分析的多尺度方法相结合，以确定外部损失。(3)通过将计算的品质因数与实验数据进行比较，确定计算方法的有效性。此外，还将寻求NEMS的各种应用，如高频谐振器、能量收集和质量传感。

Title: Intrinsic and Extrinsic Losses in Nanoelectromechanical SystemsProject Goals:To develop a fundamental understanding of energy losses in nanostructures and to exploit this knowledge for enhanced performance of nanostructuresNontechnical Abstract: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.Technical Abstract: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.