Han Weina, Zhao Kang, Pan Changji, Yuan Yanping, Zhao Yan, Cheng Zhaochen, Wang Mengmeng
Opt Express. 2020 Aug 17;28(17):25250-25262. doi: 10.1364/OE.394093.
Femtosecond (fs) laser-thin film interaction is one of the most practical methods for fabricating functional nanostructures. However, the details of the interaction mechanism remain unclear. In this study, we demonstrate an abnormal ablation effect on nanofilms by using a tightly focused single fs laser pulse. After the irradiation of a single Gaussian-shaped femtosecond laser pulse, a molten micro/nanopatch at the irradiated central high-power zone is isolated from the surrounding film. The confined localized threshold effect is proposed as the main mechanism for the phase isolation. With this effect, the high refractive index dielectric GeSbTe crystal nanostructures can be fabricated by directed dewetting of the isolated molten micro/nanopatch on Si substrates. After the laser irradiation, the central isolated liquid through an amorphous GST film is transformed into a crystalline state after resolidification. The isolated central micro/nanopatch size can be controlled by the focused spot size and pulse energy, so that the morphologies (size, geometrical morphology, and distribution) of GST nanostructures can be flexibly modulated. Furthermore, separated solid and liquid phase states detected using spatial-temporal-resolved microscopy validates the crucial role of the confined-localized threshold effect in the dewetting effect based on the separated liquid phase.
飞秒（fs）激光与薄膜的相互作用是制备功能性纳米结构最实用的方法之一。然而，相互作用机制的细节仍不清楚。在本研究中，我们通过使用紧密聚焦的单个飞秒激光脉冲展示了对纳米薄膜的异常烧蚀效应。在单个高斯形状的飞秒激光脉冲照射后，在照射的中心高功率区域形成的熔融微/纳米斑与周围薄膜分离。提出受限局部阈值效应作为相分离的主要机制。利用这种效应，可以通过在硅衬底上对分离的熔融微/纳米斑进行定向去湿来制备高折射率介电GeSbTe晶体纳米结构。激光照射后，通过非晶GST薄膜的中心分离液体在重新凝固后转变为结晶态。分离的中心微/纳米斑尺寸可以通过聚焦光斑尺寸和脉冲能量来控制，从而可以灵活调节GST纳米结构的形态（尺寸、几何形态和分布）。此外，使用时空分辨显微镜检测到的分离的固相和液相状态验证了受限局部阈值效应在基于分离液相的去湿效应中的关键作用。
