期刊
SCIENCE ADVANCES
卷 5, 期 5, 页码 -出版社
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/sciadv.aav8965
关键词
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资金
- International PhD fellowship program la Caixa-Severo Ochoa
- European Commission (ERC Advanced Grants) [670949-LightNet, 789104-eNANO]
- Spanish Ministry of Economy (Severo Ochoa program for Centres of Excellence in RD) [SEV-2015-0522, FIS2015-69258-P, MAT2017-88492-R, FIS2016-81740-REDC]
- Catalan AGAUR [2017SGR1369]
- Fundacio Privada Cellex
- Fundacio Privada Mir-Puig
- Generalitat de Catalunya through the CERCA program
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.
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