Direct Measurements of Fundamental Sintering Parameters in Nanoparticles

技术概述：本提案的智力优势集中在影响金属纳米颗粒（NPs）低温（300&#730；C）烧结的基本机制上。现有的模型不能准确预测NPs在低温下的烧结响应。最先进的处理和原位和非原位透射电子显微镜的协同组合将被用来研究NPs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。这是至关重要的，因为通常存在于NPs表面的有机分散剂会干扰NPs在低温下的固有烧结行为。其次，配备了用于原位烧结实验的新型加热阶段的最先进的像差校正TEM/STEM将用于实时测量颈部生长，颗粒间距离和边界迁移率的NPs。第三，将在NPs对上进行的研究与在厚膜中使用真实的三维粒子形态的研究之间建立相关性。这些实验将通过以下方式增加对金属纳米颗粒烧结的基本理解：1)确定颗粒尺寸、温度和颗粒几何形状如何影响NPs的烧结机制；2)测量颗粒尺寸、温度和颗粒几何形状对NPs表面或晶界扩散率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。4)确定电子束对原位TEM/STEM实验中测量的质量输运率的影响程度。非技术概述：厚膜材料目前在包括许多电子设备在内的各种应用中得到了广泛的应用。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 Review （Vol. 17, no . 2）。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&amp；#730；C，这严重限制了可以利用的材料，并大大提高了成本。此外，有许多新技术将受益于降低处理厚膜的温度，包括生物传感器和厚膜太阳能电池。这项研究的重点是了解在低于300℃的温度下加工金属纳米颗粒厚膜的基本机制。拟议的活动包括为失聪学生提供与拟议工作相关的研究机会的外展活动，失聪学生在科学和工程领域的代表性非常低。德克萨斯大学奥斯汀分校和德克萨斯聋人学校最近建立了合作伙伴关系，需要更多的研究项目，学生可以被安置在这些项目中，拟议的活动将提供大量的项目和学生，这将大大有利于这个项目。

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.