Laser Induced Melting and Coalescence of Nanoparticle Clusters Captured with Ultrafast Transmission Electron Microscopy

Transmission electron microscopy (TEM) is an essential characterization method for obtaining information with high spatial resolution. Combining with <i>in situ </i>techniques, information during a dynamic process can be acquired in real time. Increasing the temporal resolution of these techniques allows for capturing ultrafast dynamics and reactions. Ultrafast TEM (UTEM) combines high spatial and temporal resolutions to capture nanoscale snapshots of the dynamics at well-defined delay times and has been applied to various materials and observable rapid dynamic processes [1–3]. The single shot pump probe scheme utilized in UTEM provides capabilities for observing irreversible processes such as laser induced interactions. Laser interactions with metal materials lead to complex heat transfer and transient events including melting, fusion, and other dynamic behaviors. Laser-based fabrication methods have become widespread in a variety of applications and industries and at various length scales [4]. Observing the dynamic behaviors at the nanoscale, temporally and spatially, allows for a more comprehensive understanding of the intricate processes involved in laser-material interactions. In this work, clusters of silver nanoparticles are irradiated by a single nanosecond laser pulse and imaged at precise delay times through single shot UTEM to investigate the dynamics and timescales of nanoparticle melting and coalescence. These dynamic events are shown to be manipulated through cluster location and size. Combined with electron microscopy and energy dispersive x-ray spectroscopy, substrate deformations and subsequent interactions are determined to strongly affect the exposed region and can influence the fusion process. This study provides valuable insights into laser-based fabrication behaviors of nanoparticle clusters for nanoscale structures.<br/> <br/>[1] O.-H. Kwon, B. Barwick, H.S. Park, J.S. Baskin, A.H. Zewail, 4D visualization of embryonic, structural crystallization by single-pulse microscopy, Proc Natl Acad Sci U S A 105 (2008) 8519–8524. https://doi.org/10.1073/pnas.0803344105.<br/>[2] H.S. Park, O.-H. Kwon, J.S. Baskin, B. Barwick, A.H. Zewail, Direct observation of martensitic phase-transformation dynamics in iron by 4D single-pulse electron microscopy, Nano Lett 9 (2009) 3954–3962. https://doi.org/10.1021/nl9032704.<br/>[3] T. LaGrange, M.R. Armstrong, K. Boyden, C.G. Brown, G.H. Campbell, J.D. Colvin, W.J. DeHope, A.M. Frank, D.J. Gibson, F.V. Hartemann, J.S. Kim, W.E. King, B.J. Pyke, B.W. Reed, M.D. Shirk, R.M. Shuttlesworth, B.C. Stuart, B.R. Torralva, N.D. Browning, Single-shot dynamic transmission electron microscopy, Applied Physics Letters 89 (2006) 044105. https://doi.org/10.1063/1.2236263.<br/>[4] A. Vafadar, F. Guzzomi, A. Rassau, K. Hayward, Advances in Metal Additive Manufacturing: A Review of Common Processes, Industrial Applications, and Current Challenges, Applied Sciences 11 (2021) 1213. https://doi.org/10.3390/app11031213.