Direct Measurements of Fundamental Sintering Parameters in Nanoparticles

技术总结：这项建议的学术价值集中在影响金属纳米颗粒(NPs)低温(300℃)烧结的基本机制上。现有的模型不能准确地预测NPs在低温下的烧结响应。我们将采用最先进的工艺和原位和非原位电子显微镜相结合的方法来研究纳米颗粒的烧结。将生产不含分散剂的NPs对，以满足本研究所需的严格要求。这一点至关重要，因为通常存在于NPs表面的有机分散剂会干扰NPs在低温下的本征烧结行为。其次，将利用最先进的、具有像差校正的、配备了用于原位烧结实验的新型加热台的TEM/STEM实时测量颈长、颗粒间距离和边界迁移率的NPs。第三，将在对NPs进行的研究与使用真实的、厚膜中的三维颗粒形态的研究之间建立关联。这些实验将通过1)确定粒子尺寸、温度和粒子几何形状如何影响NPs的烧结机理，2)测量粒子尺寸、温度和粒子几何形状对NPs表面或晶界扩散系数和晶界迁移率的影响，3)确定缺陷，特别是孪晶对NPs烧结行为的作用，以及4)确定电子束对原位TEM/STEM实验中测量的传质速率的影响程度，从而增加对金属纳米粒子烧结的基本了解。非技术摘要：厚膜材料目前被用于包括许多电子设备在内的大量不同的应用中。这些设备的市场正在迅速增长，技术的改进对这些进步至关重要。例如，根据III-VS评论(第17卷，第2期，2004年3月，第7页)，厚膜市场在2008年估计为168亿美元，由于便携式电信设备的增加，未来可能会有显著增长。目前的技术要求加工温度高达800摄氏度，这严重限制了可利用的材料，并显著推高了成本。此外，许多新技术将受益于厚膜加工温度的降低，包括生物传感器和厚膜太阳能电池。拟议的研究侧重于了解允许在低于300℃的温度下处理金属纳米颗粒厚膜的基本机制。拟议的活动包括为在科学和工程领域严重不足的聋人学生提供与拟议工作相关的研究机会的外联活动。德克萨斯大学奥斯汀分校和德克萨斯聋人学校最近建立的合作伙伴关系需要更多的研究项目，学生可以被安置在其中，拟议的活动将提供大量的项目和学生，这些项目和学生将显著受益于该计划。

TECHNICAL SUMMARY: The intellectual merit of this proposal focuses on the fundamental mechanisms that influence the low temperature (300˚C) sintering of metallic nanoparticles (NPs). Existing models cannot accurately predict the sintering response of NPs at low temperatures. A synergistic combination of state-of-the art processing and in-situ and ex-situ transmission electron microscopy will be employed to investigate sintering of NPs. Pairs of NPs that are free of dispersants will be produced to meet the stringent requirements necessary for this study. This is crucial as the presence of organic dispersants that are typically present on the surfaces of NPs interfere with the intrinsic sintering behavior of the NPs at low temperatures. Second, a state-of-the-art, aberration-corrected TEM/STEM equipped with a novel heating stage for in-situ sintering experiments will be utilized to perform real-time measurements on NPs of neck growth, interparticle distance and boundary mobility. Third, correlations will be made between the studies performed on pairs of NPs with studies using realistic, three-dimensional particle morphologies in thick films. These experiments will increase fundamental understanding of sintering in metallic nanoparticles by 1) Determining how particle size, temperature, and particle geometry influence sintering mechanisms in NPs, 2) Measuring the influence of particle size, temperature, and particle geometry on surface or grain boundary diffusivity and grain boundary mobility in NPs, 3) Identifying the role of defects, particularly twins on the sintering behavior of NPs, and 4) Determining the extent to which the electron beam, influences the measured mass transport rates during in situ TEM/STEM experiments.NON-TECHNICAL SUMMARY: Thick film materials are currently used in a large number of diverse applications including many electronic devices. The market for these devices is growing rapidly and improvements in technologies are critical for these advancements. For example, according to III-Vs Review (Vol. 17, no 2. March 2004, pg 7.), the market for thick films was estimated at $16.8 billion in 2008 with significant growth likely in the future due to the increases in portable telecommunication devices. Current technologies require processing temperatures of up to 800˚C, which severely restricts the materials that can be utilized and drives up costs significantly. In addition, there are a number of new technologies that would benefit from reduced processing temperatures for thick films including biosensors and thick film solar cells. The proposed research focuses on understanding the fundamental mechanisms that would allow the processing of thick films of metallic nanoparticles at temperatures less than 300˚C. The proposed activities encompass outreach activities offering deaf students, who are highly underrepresented in science and engineering, research opportunities related to the proposed work. A recently established partnership between UT Austin and the Texas School for the Deaf is in need of additional research projects in which students can be placed and the proposed activities will provide a critical mass of projects and students that will significantly benefit this program.