Collaborative Research: Thermal Investigation of Strain-Tuned Thermal Conductivities of Thin Films

应变纳米膜广泛应用于电子和光电子器件、微机电系统、光伏、发光二极管以及固态能量转换。然而，应变薄膜的热性能尚未得到系统的研究。该合作项目旨在研究高拉伸应变（根据薄膜厚度高达1-10%）对当前电子工业中技术重要材料的代表性薄膜热性能的影响。这项工作的结果可以特别有利于其广泛的工业应用，偏爱薄膜几何形状的器件制造。更广泛地说，所获得的知识可以潜在地推广到其他纳米结构材料的应变工程性质。这个项目可以通过博物馆展览的材料发现、两所大学跨学科教育和研究项目的发展以及为K-12和高中学生创造新的推广活动来造福公众。这项提议的工作将建立对？弹性应变工程？纳米膜，重点是沿拉伸应变和横向方向的热各向异性。通过结合最先进的超快泵探针实验技术和分子动力学（MD）模拟，将在单轴和等双轴拉伸应变下对具有代表性的薄膜进行一系列系统的温度相关热输运研究。将获得新的物理见解，特别是通常被忽视的横向声子输运。此外，通过调整泵浦探测实验中激光加热的光斑大小和频率，还可以重建平面内声子平均自由程（MFP）谱。这样的声子MFP谱将进一步用于应变薄膜的声子输运分析，与许多非应变块状材料的研究相比较。从薄膜研究中获得的知识可以潜在地扩展到其他纳米结构（例如，纳米线和二维材料）和纳米结构体材料（例如，在超高压力下热压的纳米复合材料）。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Strained nanofilms are widely used in electronic and optoelectronic devices, microelectromechanical systems, photovoltaics, light-emitting diodes, and for solid-state energy conversion. However, the thermal properties of a strained film have not yet been systematically investigated. This collaborative project aims to study the impact of a high tensile strain (up to 1-10% depending on the film thickness) on the thermal properties of representative thin films that are of technologically important materials in current electronic industry. Outcomes of this work can particularly benefit their broad industrial applications with the preference of thin-film geometry for device fabrication. More broadly, the obtained knowledge can be potentially generalized to other nanostructured materials for strain-engineered properties. This project can benefit a general public through materials discoveries at museum exhibitions, development of interdisciplinary education and research programs at two universities, and creation of new outreach activities to K-12 and high-school students. This proposed work will establish a comprehensive understanding on the thermal properties of ?elastic strain engineered? nanofilms, with an emphasis on the thermal anisotropy along both the tensile-strain and the transverse directions. A series of systematic temperature-dependent thermal transport studies will be carried out on representative thin films under uniaxial and equi-biaxial tensile strains, via the integration of the state-of-the-art ultrafast pump-probe experimental technique and molecular dynamics (MD) simulations. New physical insights will be gained, particularly, into the usually overlooked transverse-direction phonon transport. In addition, by tuning the spot sizes and frequencies of laser heating in the pump-probe experiments, the in-plane phonon mean-free-path (MFP) spectrum will also be reconstructed. Such a phonon MFP spectrum will be further used for the phonon transport analysis of strained films, in comparison with numerous studies on unstrained bulk materials. The knowledge gained from thin-film studies can be potentially extended to other nanostructures (e.g., nanowires and 2D materials) and nanostructured bulk materials (e.g., nanocomposites hot pressed under an ultrahigh pressure).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.