Wuenschell J K, Helvajian H
Opt Express. 2019 Feb 18;27(4):5859-5873. doi: 10.1364/OE.27.005859.
Experimental evidence is presented that pulsed laser generated ultrasound can reduce the power necessary to phase convert a nm-scale amorphous film into the crystalline phase. The amount of energy carried by pulsed ultrasound is scant when compared to the CW laser power used to crystallize but the effect is substantial. The evidence points to the extra-ordinary effects possible when a small energy perturbation is applied at a critical juncture in dynamical systems. The candidate system is MoS (10 nm) sputtered on yttrium-stabilized zirconia single crystal substrate. A focused CW laser elevates the film - initially in a metastable disordered phase - to the order-disorder conversion (crystallization) temperature. Approximately 25 spot sizes removed from the heating source is a second, high repetition rate laser that induces ultrasonic excitation within the film/substrate via thermoelastic action. The processing is done on a moving stage with direct write patterning control. High resolution ex situ Raman spectroscopy, optical profilometry, and TEM are used to characterize the converted material. For this experimental configuration, we measure a 10% reduction in the heating power required to initiate crystalline formation. The measured phenomenon cannot be attributed to excess thermal energy supplied by the ultrasonic laser.
实验证据表明，脉冲激光产生的超声波可以降低将纳米级非晶薄膜相转化为晶相所需的功率。与用于结晶的连续波激光功率相比，脉冲超声波携带的能量很少，但效果却很显著。证据表明，在动态系统的关键时刻施加小能量扰动时可能会产生非凡的效果。候选系统是溅射在钇稳定氧化锆单晶衬底上的MoS（10纳米）。聚焦的连续波激光将最初处于亚稳态无序相的薄膜加热到有序-无序转变（结晶）温度。距离加热源大约25个光斑尺寸处是第二个高重复率激光，它通过热弹性作用在薄膜/衬底内引发超声激发。该处理在具有直接写入图案控制的移动平台上进行。高分辨率非原位拉曼光谱、光学轮廓测量和透射电子显微镜用于表征转化后的材料。对于这种实验配置，我们测量到启动晶体形成所需的加热功率降低了10%。所测量的现象不能归因于超声激光提供的多余热能。
