CAREER: Towards a Fundamental Understanding of Interface Strain-Driven Pseudomorphic Phase Transformation in Multilayered Nanocomposites

在适当的条件下，一种材料在另一种材料上的沉积可以呈现基底的结构，而不是过度生长的材料的通常结构。这种异常晶体结构中的过度生长被称为伪晶相。当作为多层沉积时，其中每个薄膜包含数千个过度生长的衬底组合，在环境温度和压力下，可以合成很大比例的薄膜体积来包含假晶相；以前，这种相变只有在极端压力或温度下才能实现。从结构和功能的角度来看，这些伪晶相具有很高的吸引力，并且在极端压力、温度和应变速率下表现出很高的稳定性。这个学院早期职业发展（Career）奖支持研究探索薄膜合成技术的进步，以获得对多层结构中伪晶相变和伪晶相的最终性质的基本理解。该项目将允许学生与国内和国际实验室合作，例如在瑞士联邦材料科学与技术实验室（EMPA）进行为期一个学期的国际实习，以便在实验室内开发新的科学和基础设施，并提高机构研究能力。该项目有三个主要目标：i)分别确定诱导相变所需的伪晶相和相邻衬底的最大和最小层厚，ii)在纳米层合材料合成过程中，通过使用合金元素和成分分级来最大化伪晶相的层厚，iii)通过界面应变工程获得合金伪晶相变形特性的基本理解。将系统地研究多个纳米层叠体系，即(1)立方到类立方的转化（Cu在Ni上，面心立方fcc到fcc， Ni在Cu上，fcc到面心四方效应），(2)六边形到立方（Mg在Nb上）和Zr在Nb上，依次进行。选择的顺序取决于伪晶相变的复杂性、合成/沉积的难度以及它们潜在的技术应用。该项目将利用集成的原子层和物理气相沉积平台，允许纳米层合材料的微观结构在原子尺度上精确定制。与工业伙伴的合作将促进这项研究的知识转移到工业应用。该项目是在工程理事会土木、机械和制造创新司（CMMI）的先进制造（AM）计划和数学和物理科学理事会（DMS）材料研究司（DMR）的金属和金属纳米结构（MMN）计划的支持下实现的。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。

Under the right conditions, deposits of one material on another can take on the structure of the substrate rather than the usual structure of the overgrowth material. Such overgrowths in the abnormal crystal structure are termed pseudomorphic phases. When deposited as a multilayer, where each film contains thousands of overgrowth-substrate combinations, a large proportion of the film volume can be synthesized to contain the pseudomorphic phase at ambient temperatures and pressures; previously such phase transformations were accessible only via extreme pressures or temperatures. These pseudomorphic phases can be highly attractive from both structural and functional viewpoints, and show high stability under extremes of pressure, temperature and strain rate. This Faculty Early Career Development (CAREER) award supports research to explore advancements to the thin film synthesis technique in order to obtain a fundamental understanding of the pseudomorphic phase transformation and the resultant properties of the pseudomorphic phases in a multilayered architecture. This project will allow students to collaborate with both national and international laboratories, such as semester-long international internships, at EMPA, the Swiss Federal Laboratories for Materials Science and Technology, in order to develop new science and infrastructure within the laboratories and increase the institutional research capacities. This project has three main objectives: i) To identify the largest and smallest layer thicknesses for the pseudomorphic phase and the adjoining substrate, respectively, required to induce the phase transformation, ii) To maximize the layer thickness of the pseudomorphic phases by use of alloying elements and compositional grading during the nanolaminate synthesis, and iii) To gain a fundamental understanding of the deformation properties of the alloyed pseudomorphic phases that are transformed by interface strain engineering. Multiple nanolaminate systems will be studied systematically, namely (1) cubic to cubic-like transformations (Cu on Ni, face centered cubic fcc to fcc, and Ni on Cu, fcc to face centered tetragonal fct), (2) hexagonal to cubic (Mg on Nb) and Zr on Nb, in that order. The order of selection is dictated by both the increasing degrees of complexity of the pseudomorphic phase transformation, their difficulties in the synthesis/deposition, and their potential technological applications. This project will utilize an integrated atomic layer and physical vapor deposition platform that allows the microstructure of nanolaminates to be precisely tailored at the atomic scale. Collaborations with industrial partners will promote knowledge transfer of this research to industrial applications.This project is made possible with the support of the Advanced Manufacturing (AM) program in the Division of Civil, Mechanical and Manufacturing Innovation (CMMI) of the Directorate for Engineering, and the Metals and Metallic Nanostructure (MMN) program in the Division of Materials Research (DMR) of the Directorate for Mathematical and Physical Sciences (DMS).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.