Tracking ultrafast hot-electron diffusion in space and time by ultrafast thermomodulation microscopy
Tracking ultrafast hot-electron diffusion in space and time by ultrafast thermomodulation microscopy
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DOI：
10.1126/sciadv.aav8965
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发表时间：
2019-05-01
期刊：
影响因子：
13.6
通讯作者：
van Hulst, N. F.
中科院分区：
文献类型：
--
作者：
Block, A.;Liebel, M.;van Hulst, N. F.
金属对光的超快响应受涉及激发电子和声子相互作用的有趣的非平衡动力学控制。它们之间的耦合导致了超短时间尺度上的非线性扩散行为。在这里，我们使用扫描超快热调制显微镜图像的时空热电子扩散在薄的金膜。通过跟踪局部瞬态反射率与20纳米的空间精度和0.25 ps的时间分辨率，我们揭示了两个不同的扩散制度：在最初的几皮秒的初始快速扩散，其次是约100倍的扩散较慢，在较长的时间。我们发现一个缓慢的初始扩散比以前预测的纯电子扩散。我们开发了一个全面的三维模型的基础上的两个温度模型和评估的热光响应，考虑到延迟效应的电子-声子耦合。我们的模拟很好地描述了所观察到的扩散动力学，让我们确定两个扩散制度热电子和声子限制的热扩散，分别。
The ultrafast response of metals to light is governed by intriguing nonequilibrium dynamics involving the interplay of excited electrons and phonons. The coupling between them leads to nonlinear diffusion behavior on ultrashort time scales. Here, we use scanning ultrafast thermomodulation microscopy to image the spatiotemporal hot-electron diffusion in thin gold films. By tracking local transient reflectivity with 20-nm spatial precision and 0.25-ps temporal resolution, we reveal two distinct diffusion regimes: an initial rapid diffusion during the first few picoseconds, followed by about 100-fold slower diffusion at longer times. We find a slower initial diffusion than previously predicted for purely electronic diffusion. We develop a comprehensive three-dimensional model based on a two-temperature model and evaluation of the thermo-optical response, taking into account the delaying effect of electron-phonon coupling. Our simulations describe well the observed diffusion dynamics and let us identify the two diffusion regimes as hot-electron and phononlimited thermal diffusion, respectively.