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首页> 外文会议>High-Power Laser Ablation VI pt.1 >Expansion-limited nanocluster growth in a plume formed by MHz-pulse-rate laser ablation
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Expansion-limited nanocluster growth in a plume formed by MHz-pulse-rate laser ablation

机译：由MHz脉冲速率激光烧蚀形成的羽流中的扩展受限的纳米簇生长

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摘要

We study the formation of carbon nanoclusters created by MHz repetition rate - picosecond laser pulses. We show that the average size of a nanocluster is determined exclusively by single laser pulse parameters and is largely independent of the gas fill (He, Ar, Kr, Xe) and pressure, in a range from 20 mTorr up to 200 Torr. We provide evidence of the formation of large clusters at higher pressures in excess of 400 Torr, where the gas fill density is comparable or higher to the density of carbons in the ablated plume, and use simple kinetic theory to estimate cluster sizes, which are in qualitative agreement with the experimental data. We conclude that at pressures well below 400 Torr, the role of the buffer gas is to induce a transition between thin solid film formation on the substrate and nanofoam formation by diffusing the clusters through the gas, with no significant effect upon the average cluster size. At the higher pressure the buffer gas serves as a confiner for the carbon plume, increasing the collision frequency between the carbon atoms and resulting in cluster size growth. We also introduce preliminary ICCD imaging results investigating the temporal evolution of the laser plume.
机译：我们研究了由MHz重复频率-皮秒激光脉冲产生的碳纳米团簇的形成。我们表明，纳米簇的平均尺寸仅由单个激光脉冲参数确定，并且在20 mTorr至200 Torr的范围内，很大程度上不受气体填充（He，Ar，Kr，Xe）和压力的影响。我们提供了在超过400托的高压下形成大团簇的证据，其中气体填充密度与烧蚀烟羽中的碳密度相当或更高，并使用简单的动力学理论来估算团簇大小，定性与实验数据吻合。我们得出的结论是，在远低于400 Torr的压力下，缓冲气体的作用是通过使团簇通过气体扩散，从而在基质上的固体薄膜形成与纳米泡沫的形成之间引起过渡，而对平均团簇大小没有明显影响。在较高的压力下，缓冲气体充当碳羽的约束者，从而增加了碳原子之间的碰撞频率，并导致簇尺寸增长。我们还介绍了初步的ICCD成像结果，以研究激光羽流的时间演变。

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