Spectroscopy and dynamics of nanometer-sized noble metal particles
Spectroscopy and dynamics of nanometer-sized noble metal particles
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DOI：
10.1021/jp9809787
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发表时间：
1998-09-03
影响因子：
3.3
通讯作者：
Hartland, GV
中科院分区：
文献类型：
--
作者：
Hodak, JH;Martini, I;Hartland, GV
11 +/- nm 直径 Au 颗粒以及 10 +/- 3 nm 和 50 +/- 10 nm Ag 颗粒中的电子-声子耦合已通过超快泵浦探针光谱进行了检查。观察到的弛豫时间很大程度上取决于泵浦激光功率。在使用最低泵浦功率时，弛豫时间常数对于 11 nm Au 颗粒为 0.8 +/- 0.1 ps，对于 10 nm Ag 颗粒为 1.1 +/- 0.1 ps，对于 50 nm Ag 颗粒为 1.0 +/- 0.1 ps。测量的弛豫时间与块体金属的弛豫时间相似，这意味着在此尺寸区域内的颗粒动力学不存在尺寸依赖性效应。使用 Rosei 等人开发的理论对颗粒的瞬态吸收/漂白恢复信号进行建模。 （冲浪科学 1973, 37, 689）。这些计算产生作为电子分布温度的函数的瞬态吸收光谱。使用电子-声子耦合的二温度模型计算了泵浦激光激发后电子温度的时间依赖性。然后通过结合这两种计算来模拟选定波长下的实验信号与时间的关系。模拟结果与实验结果半定量一致。特别是，模型计算正确预测了低功率弛豫时间。在非常高的泵浦激光功率 (>5 mJ/cm(2)) 下，Ag 的瞬态漂白信号显示出异常的 10 ps 增长。这种增长归因于由于颗粒的传热或热诱导的吸附分子的解离而导致周围介质介电常数的变化。
Electron-phonon coupling in 11 +/- nm diameter Au particles and 10 +/- 3 nm and 50 +/- 10 nm Ag particles has been examined by ultrafast pump-probe spectroscopy. The observed relaxation times are strongly dependent on the pump laser power. At the lowest pump powers used, the time constants for relaxation are 0.8 +/- 0.1 ps for the 11 nm Au particles, 1.1 +/- 0.1 ps for the 10 nm Ag particles, and 1.0 +/- 0.1 ps for the 50 nm Ag particles. The measured relaxation times are similar to those for bulk metals, which implies that there are no size-dependent effects in the dynamics for particles in this size region. The transient absorption/ bleach recovery signals for the particles were modeled using the theory developed by Rosei et al. (Surf. Sci. 1973, 37, 689). These calculations yield the transient absorption spectrum as a function of the temperature of the electron distribution. The time dependence of the electronic temperature after pump laser excitation was calculated using the two-temperature model for electron-phonon coupling. The experimental signal versus time traces at selected wavelengths were then simulated by combining the two calculations. The results from the simulations are in semiquantitative agreement with the experimental results. In particular, the low-power relaxation times are correctly predicted by the model calculations. At very high pump laser power(>5 mJ/cm(2)) the transient bleach signal for Ag shows an unusual 10 ps growth. This growth is attributed to either a change in the dielectric constant of the surrounding medium due to heat transfer from the particles or thermally induced dissociation of adsorbed molecules.