Time-Resolved Single-Particle X-ray Scattering Reveals Electron-Density Gradients As Coherent Plasmonic-Nanoparticle-Oscillation Source
Dominik Hoeing, Robert Salzwedel, Lena Worbs, Yulong Zhuang, Amit Samanta, Jannik Lübke, Armando D. Estillore, Karol Długołęcki, Christopher Passow, Benjamin Erk, Nagitha Ekanayake, Daniel Ramm, Jonathan Correa, Christina C. Papadopoulou, A. Atia-Tul-Noor, Florian Schulz, Malte Selig, Andreas Knorr, Kartik Ayyer, Jochen Küpper, Holger Lange
Abstract
Dynamics of optically excited plasmonic nanoparticles are presently understood as a series of scattering events involving the initiation of nanoparticle breathing oscillations. According to established models, these are caused by statistical heat transfer from thermalized electrons to the lattice. An additional contribution by hot-electron pressure accounts for phase mismatches between theory and experimental observations. However, direct experimental studies resolving the breathing-oscillation excitation are still missing. We used optical transient-absorption spectroscopy and time-resolved single-particle X-ray diffractive imaging to access the electron system and lattice. The time-resolved single-particle imaging data provided structural information directly on the onset of the breathing oscillation and confirmed the need for an additional excitation mechanism for thermal expansion. We developed a new model that reproduces all of our experimental observations. We identified optically induced electron density gradients as the initial driving source.