Study of nanostructure formation processes on thin film surfaces irradiated with femtosecond laser pulses and development of its physical model

由于使用女性econd（fs）激光器开发新的纳米技术的目标，本研究项目旨在为周期纳米结构形成清晰的实验条件和构建物理模型，以及在绑定结构中的选择性变化，我们最近发现了用fs激光脉冲辐射的硬薄膜。主要的结果都是按以下方式获得的。纳米结构尺寸观察到的激光波长度为λ/10 ~ λ/5，当激光脉冲在薄膜上辐射时，如TiN和金刚石样碳（DLC）在接近击穿阈值的低通量。我们展示了纳米结构，它的大小可能是由激光极化、波长和通量控制的。在补充中，我们找到了sp^3和sp^2的DLC组成，可以通过将sp^3的选择性过渡转换成纳米结构下的sp^3和sp^2几乎相同的实验条件。DLC电影表面的反射性被测量为荧光和激光脉冲拍摄的功能。结果表明，反射性变化与纳米结构密切相关，以及超植入的激光射击和结果孵化效应对纳米结构的主要贡献。DLC的反射性也是用泵和探测器技术来衡量的。结果显示，字符反射性的变化导致表面上的重力形成，以及从sp^3到sp^2的绑定结构中的选择性变化导致电影表面的大量产生。该测量方法被证明是这样的：DLC表面上的纳米结构是由绑定结构中的变化而精确地预测的。On the basis of the experimental results contained we have developing a physical model for the nanostructures，该model relies on a local field created in the interaction。

For the purposes of developing a new nanotechnology using femtosecond (fs) lasers, this research project was aiming at making clear experimental conditions and constructing a physical model for the periodic nanostructure formation and the selective change in bonding structure that we have recently found on hard thin films irradiated with fs laser pulses. The main results obtained are as follows.・The nanostructure size observed was λ/10〜λ/5 of the laser wavelength λ when fs laser pulses were irradiated on the thin films such as TiN and diamond-like carbon (DLC) at a low fluence near ablation threshold. We have shown that the nanostructure and its size could be controlled with the laser polarization, wavelength and fluence.・In addition, we have found that the DLC consisting of sp^3 and sp^2 can be modified into the conductive glassy carbon (GC) through the selective transition of sp^3 into sp^2 under almost the same experimental condition as for the nanostructure formation.・Reflectivity of DLC film surface was measured as a function of fluence and laser pulse shots. The results have shown that the reflectivity change is closely associated with the nanostructure formation, and that the superimposed laser shots and resulting incubation effect mainly contribute to the nanostructure formation.・The reflectivity of DLC was also measured using a pump and probe technique. The results have shown a characteristic reflectivity change due to the formation of a grating on the surface, where the selective change in the bonding structure from sp^3 to sp^2 induces a swelling of the film surface.・The measurements have demonstrated that the nanostructure formation on the DLC surface is certainly preceded by the change in the bonding structure.・On the basis of the experimental results obtained we have been developing a physical model for the nanostructure formation that relies on a localized field created in the interaction.