TIME-RESOLVED X-RAY MEASUREMENTS OF SINGLE SILVER NANOWIRE MELTING

这个子项目是许多利用资源的研究子项目之一 由NIH/NCRR资助的中心拨款提供。子项目的主要支持 而子项目的主要调查员可能是由其他来源提供的， 包括其它NIH来源。 列出的子项目总成本可能 代表子项目使用的中心基础设施的估计数量， 而不是由NCRR赠款提供给子项目或子项目工作人员的直接资金。 我们建议使用相干X射线衍射成像单个银纳米线（AgNWs）的结构，并在此结构中的变化进行初步的时间分辨测量激发的线与超快激光脉冲。 测量将在BioCARS / Sector 14进行，利用其激光泵浦X射线探针能力。 纳米级物体中的热力学过程具有重要的科学和技术意义。 在纳米尺度上控制热能耗散的过程与宏观尺度上的过程有很大的不同，管理这些过程对于集成电路、光电器件（如光电子器件和固态照明）和能量产生系统中的热管理至关重要。 一段时间以来，人们已经知道，随着物体的尺寸从大块减小到纳米级，熔化温度会显著下降。 在甚至低于这些降低的纳米级熔点的温度下，据信会发生无序或预熔融过程，但对这些结构变化知之甚少。 通过用短激光脉冲加热纳米结构并使用时间分辨X射线衍射来观察其结构的后续变化，将有可能获得有关这些纳米级熔化过程的机械信息，这些信息是以前无法获得的。 我们将使用化学合成的银纳米线作为模型系统，并对单个孤立的纳米线进行测量，以消除纳米线尺寸和结构不均匀性的影响。 这一快速获取建议将用于确定此类测量的可行性以及最佳实验条件。 第一个目标将是展示来自单个银纳米线的相干x射线衍射。 这将是一个重要的原理验证实验，它将确定所需的实验条件，以确定所需的X射线发射次数，从而获得分辨率良好的衍射图案并确定有关导线的结构信息。 所获得的定量信息将是必不可少的，我们的更大的研究项目的进展，其目的是在测量被困在一个激光镊子装置和对齐的单金属纳米粒子的X射线衍射。 一旦我们已经证明了从一个单一的AgNW衍射，我们将在纳米线已被激发与超快激光脉冲后，在衍射图案的变化进行初步测量。 这将是第一次对单个纳米颗粒进行时间分辨的熔化测量，并将提供有关激光加热后结构变化的关键信息，这些信息是无法通过其他方式获得的。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We propose to image the structure of individual silver nanowires (AgNWs) using coherent x-ray diffraction and to make preliminary time-resolved measurements of changes in this structure following excitation of the wires with ultrafast laser pulses. The measurements will be made at BioCARS / Sector 14 taking advantage of their laser-pump x-ray-probe capabilities. Thermodynamic processes in nanoscale objects are of significant scientific and technological importance. Processes governing the dissipation of thermal energy at the nanoscale are known to differ significantly from those on macroscopic length scales and managing these processes is essential for example for heat management in integrated circuits optoelectronic devices (such as photovoltaics and solid-state lighting) and energy-generation systems. Melting temperatures in particular have been known for some time to drop significantly as the dimensions of objects are reduced from the bulk to the nanometer scale. At temperatures even below these depressed nanoscale melting points disordering or premelting processes are believed to occur but little is known about these structural changes. By heating a nanostructure with a short laser pulse and using time-resolved x-ray diffraction to observe subsequent changes in its structure it will be possible to gain mechanistic information about these nanoscale melting processes that has not previously been accessible. We will use chemically synthesized silver nanowires as model systems and make measurements on individual isolated nanowires in order to eliminate the effects of inhomogeneities in nanowire size and structure. This rapid-access proposal will be used to determine the feasibility of such measurements as well as the optimal experimental conditions. The first goal will be to demonstrate coherent x-ray diffraction from individual silver nanowires. This will be an important proof-of-principle experiment that will determine the experimental conditions needed in order to determine the number of x-ray shots needed in order to obtain a well-resolved diffraction pattern and determine structural information about the wire. The quantitative information obtained will be essential for the progress of our larger research project which is aimed at measuring x-ray diffraction from single metal nanoparticles that are trapped and aligned in a laser-tweezers apparatus. Once we have demonstrated diffraction from a single AgNW we will make preliminary measurements of changes in the diffraction pattern after the nanowire has been excited with an ultrafast laser pulse. This will be the first time-resolved melting measurement of a single nanoparticle and will provide key information about the structural changes following laser heating that cannot be obtained otherwise.