Laser-induced shape changes of colloidal gold nanorods using femtosecond and nanosecond laser pulses
Laser-induced shape changes of colloidal gold nanorods using femtosecond and nanosecond laser pulses
复制标题
DOI：
10.1021/jp000679t
复制
发表时间：
2000-07-06
影响因子：
3.3
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
金纳米棒被发现在强脉冲激光照射激发后会改变其形状。最终的辐照产物强烈地依赖于激光脉冲的能量以及其宽度。我们进行了一系列测量，其中激发功率在产生100 fs持续时间的脉冲的放大飞秒激光系统和具有7 ns脉冲宽度的纳秒光学参量振荡器（OPO）激光系统的输出功率的范围内变化。金纳米棒的形状转变通过两种技术进行：（1）通过监测金纳米颗粒的等离子体吸收带特征的变化的可见吸收光谱;（2）透射电子显微镜（TEM）以分析最终的形状和尺寸分布。虽然在高激光能量密度（类似于1 J cm（-2））下，金纳米颗粒碎裂，但当激光能量降低时，观察到纳米棒熔化成球形纳米颗粒（纳米点）。在降低激发脉冲的能量时，仅发生纳米棒的部分熔融。在最终分布中观察到较短但较宽的纳米棒以及具有奇怪形状（弯曲、扭曲、Φ形等）的较高丰度的颗粒。用飞秒激光脉冲完全熔化纳米棒的阈值约为0.01 J cm（-2）。比较使用两种不同类型的激发源（飞秒激光与纳秒激光）获得的结果，发现当使用纳秒激光脉冲时，将纳米棒完全熔化成纳米点的能量阈值比使用飞秒激光脉冲时高约2个数量级。这是解释在成功的竞争性冷却过程中的纳米棒时，使用纳秒激光脉冲。对于纳秒脉冲激发，由于纵向等离子体激元带的漂白，纳米棒的吸收在激光脉冲期间减小。此外，在100 ps的时间尺度上发生的晶格的冷却可以有效地竞争的吸收率的情况下的纳秒脉冲激发，但不是飞秒脉冲激发。当激发源是飞秒激光脉冲时，所涉及的进动（电子对光子的吸收（100 fs）、热电子与晶格之间的热传递（100 ps））在时间上被清楚地分离。
Gold nanorods have been found to change their shape after excitation with intense pulsed laser irradiation. The final irradiation products strongly depend on the energy of the laser pulse as well as on its width. We performed a series of measurements in which the excitation power was varied over the range of the output power of an amplified femtosecond laser system producing pulses of 100 fs duration and a nanosecond optical parametric oscillator (OPO) laser system having a pulse width of 7 ns. The shape transformations of the gold nanorods are followed by two techniques: (1) visible absorption spectroscopy by monitoring the changes in the plasmon absorption bands characteristic for gold nanoparticles; (2) transmission electron microscopy (TEM) in order to analyze the final shape and size distribution. While at high laser fluences (similar to 1 J cm(-2)) the gold nanoparticles fragment, a melting of the nanorods into spherical nanoparticles (nanodots) is observed when the laser energy is lowered. Upon decreasing the energy of the excitation pulse, only partial melting of the nanorods takes place. Shorter but wider nanorods are observed in the final distribution as well as a higher abundance of particles having odd shapes (bent, twisted, phi-shaped, etc.). The threshold for complete melting of the nanorods with femtosecond laser pulses is about 0.01 J cm(-2). Comparing the results obtained using the two different types of excitation sources (femtosecond vs nanosecond laser), it is found that the energy threshold for a complete melting of the nanorods into nanodots is about 2 orders of magnitude higher when using nanosecond laser pulses than with femtosecond laser pulses. This is explained in terms of the successful competitive cooling process of the nanorods when the nanosecond laser pulses are used. For nanosecond pulse excitation, the absorption of the nanorods decreases during the laser pulse because of the bleaching of the longitudinal plasmon band. In addition, the cooling of the lattice occurring on the 100 ps time scale can effectively compete with the rate of absorption in the case of the nanosecond pulse excitation but not for the femtosecond pulse excitation. When the excitation source is a femtosecond laser pulse, the involved precesses (absorption of the photons by the electrons (100 fs), heat transfer between the hot electrons and the lattice (100 ps) are clearly separated in time.