Guzelturk Burak, Utterback James K, Coropceanu Igor, Kamysbayev Vladislav, Janke Eric M, Zajac Marc, Yazdani Nuri, Cotts Benjamin L, Park Suji, Sood Aditya, Lin Ming-Fu, Reid Alexander H, Kozina Michael E, Shen Xiaozhe, Weathersby Stephen P, Wood Vanessa, Salleo Alberto, Wang Xijie, Talapin Dmitri V, Ginsberg Naomi S, Lindenberg Aaron M
Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States.
Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California 94025 United States.
ACS Nano. 2020 Apr 28;14(4):4792-4804. doi: 10.1021/acsnano.0c00673. Epub 2020 Mar 30.
Metal nanocrystals exhibit important optoelectronic and photocatalytic functionalities in response to light. These dynamic energy conversion processes have been commonly studied by transient optical probes to date, but an understanding of the atomistic response following photoexcitation has remained elusive. Here, we use femtosecond resolution electron diffraction to investigate transient lattice responses in optically excited colloidal gold nanocrystals, revealing the effects of nanocrystal size and surface ligands on the electron-phonon coupling and thermal relaxation dynamics. First, we uncover a strong size effect on the electron-phonon coupling, which arises from reduced dielectric screening at the nanocrystal surfaces and prevails independent of the optical excitation mechanism ( inter- and intraband). Second, we find that surface ligands act as a tuning parameter for hot carrier cooling. Particularly, gold nanocrystals with thiol-based ligands show significantly slower carrier cooling as compared to amine-based ligands under intraband optical excitation due to electronic coupling at the nanocrystal/ligand interfaces. Finally, we spatiotemporally resolve thermal transport and heat dissipation in photoexcited nanocrystal films by combining electron diffraction with stroboscopic elastic scattering microscopy. Taken together, we resolve the distinct thermal relaxation time scales ranging from 1 ps to 100 ns associated with the multiple interfaces through which heat flows at the nanoscale. Our findings provide insights into optimization of gold nanocrystals and their thin films for photocatalysis and thermoelectric applications.
金属纳米晶体在光照下展现出重要的光电和光催化功能。到目前为止，这些动态能量转换过程通常通过瞬态光学探针进行研究，但对光激发后的原子响应的理解仍然难以捉摸。在这里，我们使用飞秒分辨率电子衍射来研究光激发的胶体金纳米晶体中的瞬态晶格响应，揭示纳米晶体尺寸和表面配体对电子-声子耦合和热弛豫动力学的影响。首先，我们发现电子-声子耦合存在强烈的尺寸效应，这是由于纳米晶体表面的介电屏蔽减弱所致，且与光激发机制（带间和带内）无关。其次，我们发现表面配体充当热载流子冷却的调节参数。特别是，在带内光激发下，与基于胺的配体相比，具有硫醇基配体的金纳米晶体由于纳米晶体/配体界面处的电子耦合而表现出明显较慢的载流子冷却。最后，我们通过将电子衍射与频闪弹性散射显微镜相结合，在时空上解析了光激发纳米晶体薄膜中的热传输和热耗散。综合来看，我们解析了与热在纳米尺度上流动所经过的多个界面相关的从1皮秒到100纳秒的不同热弛豫时间尺度。我们的研究结果为优化用于光催化和热电应用的金纳米晶体及其薄膜提供了见解。
