In this work, two orthogonally polarized femtosecond laser beams are employed to irradiate a p-doped silicon wafer with an electrical resistivity of 0.008 Ω·cm. It is interesting to find that 2D compound structures composed of sub-wavelength periodic ripples and deep sub-wavelength nanodot array can be produced when proper laser fluence and time delay between the dual laser beams are used. The formation of the periodic ripples can be explained by the interference between the preceding incident laser and it induced surface plasmon polaritons (SPPs). The periodic nanodot array has a period down to ∼200 nm and the radius of the nanodot is ∼30 nm, most of which appear at the boundary between the ditch and ridge of the ripple. During the ripples’ formation, the residual melting silicon is most probably located at the boundary between the ditch and ridge of the ripple. Furthermore, the period of the nanodot array is roughly equal to the perimeter of the nanodot. Therefore, it is considered that the dot array may be generated due to the Rayleigh-Taylor instability of the melting silicon. It is also noted that these nanodots are all uniformly arranged along vertical lines, indicating that the subsequent incident laser may break the stochastic characteristic of the Rayleigh-Taylor instability and produce the 2D periodic dot array. The thermo-hydrodynamical process combined with the interference effect between SPPs and the incident laser can benefit the formation of complex surface structures with versatile functions.

在这项工作中，采用两束正交偏振的飞秒激光束照射电阻率为0.008 Ω·cm的p掺杂硅片。有趣的是，当使用适当的激光注量和双激光束之间的时间延迟时，可以产生由亚波长周期性波纹和深亚波长纳米点阵列组成的二维复合结构。周期性波纹的形成可以通过前面的入射激光与其诱导的表面等离子体之间的干涉来解释极化子（SPP）。周期性纳米点阵列的周期低至~200 nm，纳米点的半径为~30 nm，大部分出现在波纹的沟和脊之间的边界处。在波纹形成过程中，残留的熔融硅很可能位于波纹的沟和脊之间的边界处。此外，纳米点阵列的周期大致等于纳米点的周长。因此，认为点阵列可能是由于熔融硅的瑞利-泰勒不稳定性而产生的。还值得注意的是，这些纳米点均沿垂直线均匀排列，表明随后的入射激光可能会打破瑞利-泰勒不稳定性的随机特性并产生二维周期性点阵列。