Electron dynamics in gold and gold-silver alloy nanoparticles: The influence of a nonequilibrium electron distribution and the size dependence of the electron-phonon relaxation
Electron dynamics in gold and gold-silver alloy nanoparticles: The influence of a nonequilibrium electron distribution and the size dependence of the electron-phonon relaxation
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DOI：
10.1063/1.479310
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发表时间：
1999-07-15
影响因子：
4.4
通讯作者：
El-Sayed, MA
中科院分区：
文献类型：
--
作者：
Link, S;Burda, C;El-Sayed, MA
利用飞秒瞬态吸收光谱研究了平均直径为9 ~ 48 nm的金纳米粒子中的电子动力学。在低功率激发后的等离子体漂白恢复之后，表明非费米电子分布通过在500 fs的时间尺度上的电子-电子弛豫热化为费米分布。这种效应仅在低激发功率下以及当电子分布通过与导带内的带内跃迁混合而被扰动时观察到（即，当激发波长为630或800 nm时）。然而，在400 nm处激发带间跃迁不允许遵循早期电子热化过程。电子热化与晶格的纳米粒子的电子-声子相互作用发生在1.7 ps在这些条件下，独立的激发波长。与实验一致，模拟的光学响应所产生的热化和nonthermalized电子分布表明，一个非费米电子分布导致等离子体激元吸收的较低强度漂白。此外，对于电子气的小温度变化（低激发功率），来自两个电子分布的响应之间的差异更大。对于直径在9和48 nm之间的金纳米颗粒，没有观察到电子热化动力学的尺寸依赖性。高分辨透射电子显微镜（HRTEM）显示，这些金纳米粒子具有缺陷结构。这对电子-声子弛豫过程的影响进行了讨论。将金摩尔分数为0.8的18 nm金-银合金纳米颗粒与15 nm金纳米颗粒进行比较。虽然混合银导致基态吸收光谱中的等离子体吸收蓝移，但在系统的飞秒动力学中没有观察到差异。(C)1999年美国物理学会。[S0021-9606（99）71427-3]。
Electron dynamics in gold nanoparticles with an average diameter between 9 and 48 nm have been studied by femtosecond transient absorption spectroscopy. Following the plasmon bleach recovery after low power excitation indicates that a non-Fermi electron distribution thermalizes by electron-electron relaxation on a time scale of 500 fs to a Fermi distribution. This effect is only observed at low excitation power and when the electron distribution is perturbed by mixing with the intraband transitions within the conduction band (i.e., when the excitation wavelength is 630 or 800 nm). However, exciting the interband transitions at 400 nm does not allow following the early electron thermalization process. Electron thermalization with the lattice of the nanoparticle by electron-phonon interactions occurs within 1.7 ps under these conditions, independent of the excitation wavelength. In agreement with the experiments, simulations of the optical response arising from thermalized and nonthermalized electron distributions show that a non-Fermi electron distribution leads to a less intense bleach of the plasmon absorption. Furthermore, the difference between the response from the two electron distributions is greater for small temperature changes of the electron gas (low excitation powers). No size dependence of the electron thermalization dynamics is observed for gold nanoparticles with diameters between 9 and 48 nm. High-resolution transmission electron microscopy (HRTEM) reveals that these gold nanoparticles possess defect structures. The effect of this on the electron-phonon relaxation processes is discussed. 18 nm gold-silver alloy nanoparticles with a gold mole fraction of 0.8 are compared to 15 nm gold nanoparticles. While mixing silver leads to a blue-shift of the plasmon absorption in the ground-state absorption spectrum, no difference is observed in the femtosecond dynamics of the system. (C) 1999 American Institute of Physics. [S0021-9606(99)71427-3].