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

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 我们建议用相干X射线衍射法对单个银纳米线(AgNW)的结构进行成像，并对超快激光脉冲激发后这种结构的变化进行时间分辨测量。这些测量将在BioCARS/14区进行，利用其激光泵浦X射线探测器的能力。 纳米尺度物体中的热力学过程具有重要的科学和技术意义。众所周知，在纳米尺度上控制热能耗散的过程与在宏观长度尺度上的过程有很大不同，管理这些过程对于例如集成电路、光电子器件(如光伏和固态照明)和能源生成系统中的热管理是必不可少的。随着物体的尺寸从块状缩小到纳米尺度，熔化温度特别是一段时间以来一直被认为是显著下降的。在甚至低于这些压低的纳米级熔点的温度下，人们认为会发生无序或预熔过程，但人们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，并使用时间分辨的x射线衍射来观察其结构的后续变化，将有可能获得关于这些纳米级熔化过程的机制信息，这是以前无法获得的。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的影响。 实验的第一个目标将是演示单个银纳米线的相干X射线衍射。获得的关于单纳米粒子衍射的定量信息将对我们更大的研究项目的进展至关重要，该研究项目的目标是测量单个金属纳米粒子的X射线衍射，这些纳米粒子被捕获并排列在激光镊子设备中。一旦我们演示了单个AgNW的衍射，我们将测量在超快激光脉冲激励下纳米线的衍射图的变化。计算将用于将衍射图的变化与导线的结构变化相关联。这将是第一次对单个纳米颗粒进行时间分辨熔融测量，并将提供有关激光加热后结构变化的关键信息，否则无法获得这些信息。

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 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. The first goal of the experiments will be to demonstrate coherent x-ray diffraction from individual silver nanowires. The quantitative information obtained about single-nanoparticle diffraction 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 measure changes in the diffraction pattern after the nanowire has been excited with an ultrafast laser pulse. Calculations will be used to correlate changes in the diffraction pattern to structural changes in the wire. 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.