Transient Physicochemical Properties of Nanomaterials

当半导体粒子的尺寸缩小到几纳米时，它的许多特性就会改变。例如，这些纳米粒子发出的光的颜色可以简单地通过改变大小来改变。这种类型的尺寸可调性被用于许多现代电子设备，如高分辨率显示器和生物医学传感器。其他性质也会随颗粒大小而改变。例如，纳米颗粒的熔点随着其尺寸的减小而降低，这就给在制造过程中涉及大量加热的应用带来了问题。在这个由化学系大分子、超分子和纳米化学项目资助的项目中，西北大学的Richard Schaller教授正在研究突然引入能量后纳米颗粒的熔化。夏勒教授和他的学生一起使用非常短的激光脉冲来快速加热纳米粒子，使它们膨胀和融化。然后，研究小组采用了一系列超快实验方法来监测纳米粒子晶格的结构变化。从研究中获得的见解可能会影响从发光二极管（led）到太阳能电池等技术。这些见解可能有助于推进3D打印中的增材制造，这可能受益于颗粒的易熔化和生长成更大的固体。该项目还为研究生和本科生提供教育和培训机会。这项研究的结果被纳入西北大学的化学课程。Schaller教授和他的学生与芝加哥城市学院、STEMfest活动和anston 65区的k -8年级学生互动，通过现场课堂演示和客座讲座传播对科学的兴趣。本研究通过实验探讨了纳米粒子在高温和高温处理下的平衡和瞬态物理化学效应。这些活动的重点是推进对纳米粒子和表面化学的基本理解，从而开发出能够使单个纳米粒子在高温下保持其所需功能的策略（防止配体的损失，晶体相的变化或化学成分的演变）。这项工作实现了瞬态物理和光谱方法，包括高保真度、基于同步加速器的瞬态x射线衍射，以探测加热和相位行为，以及振动光谱。这项研究使人们能够深入了解配体的行为和局部化学，在这些重要的，但很少探索的条件下。目标系统的重点是形状控制半导体和含土丰富的半导体，如硅和Cu2ZnSnS4。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。

When the size of a semiconductor particle is reduced to just a few nanometers, many of its properties can change. For example, the colors of light emitted by these nanoparticles can be altered simply by changing the size. This type of size-tunability is exploited in many modern electronic devices, such as high-resolution displays and biomedical sensors. Other properties can also change with particle size. For example, the melting point of nanoparticles tend to decrease as their size is reduced, which presents problems for applications that involve significant heating during manufacturing. In this project, funded by the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, Professor Richard Schaller at Northwestern University is studying the melting of nanoparticles after the sudden introduction of energy. Working with his students, Professor Schaller uses very short pulses of laser light to rapidly heat nanoparticles, causing them to expand and melt. The team then employs a series of ultrafast experimental methods to monitor structural changes in the nanoparticle lattice. The insights gained from the research could impact technologies ranging from light-emitting-diodes (LEDs) to solar cells. These insights may help to advance additive manufacturing in 3D printing, which could benefit from facile melting and growth of particles into larger solids. The project also provides education and training opportunities for graduate and undergraduate students. The results from the research are incorporated into chemistry courses at Northwestern University. Professor Schaller and his students interact with the City Colleges of Chicago, STEMfest events, and K-8th grade students inEvanston's District 65, to spread interest in the sciences through on-site classroom demonstrations and guest lectures. This research experimentally probes equilibrium- and transient- physicochemical effects that underlie properties of nanoparticles at elevated temperature as well as in elevated temperature processing. The activities focus on advancing the fundamental understanding of both nanoparticle and surface chemistries, so as to develop strategies that can enable individual nanoparticles to maintain their desired function at elevated temperature (preventing the loss of ligands, change of crystal phases, or evolution of chemical composition). The effort implements transient physical and spectroscopic methods including high fidelity, synchrotron-based transient x-ray diffraction to probe heating and phase behavior, and vibrational spectroscopies. The research enables insight into ligand behavior and local chemistry, in these important, yet poorly explored conditions. The targeted systems focus on shape-controlled semiconductors and earth abundant semiconductors, such as silicon and Cu2ZnSnS4.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.