Improved uniformity of deposited metallic layer on hybrid micro/nano-structured Si substrates fabricated by two-step laser ablation for SERS application

复合激光烧蚀制备微纳结构硅基底表面的金属沉积层匀化及SERS性能研究

Surface-enhanced Raman scattering(SERS) has been widely used as an effective technique for lowconcentration molecules detections in the past decades. This work proposes a rapid and accessible process to fabricate SERS-active substrates with high uniformity and controllability based on two-step laser ablation. Laser beams directly ablate the surface of Si, concurrently creating microstructures and ejecting molten materials caused by the thermal effect that nucleate in ambient air. The nuclei grow into nanoparticles and deposit over the surface. These nanoparticles,together with microstructures, improve the light collection efficiency of the SERS-active substrates. Especially after Au thin film deposition, these nanoparticles can provide nanogaps as hotspots for SERS. By orthogonal experiment design,laser processing parameters for better performances are determined. Compared with substrates fabricated by single 1064 nm master oscillator power amplifier(MOPA) laser ablation, substrates ablated by the primary 1064 nm MOPA laser and secondary UV pulsed laser show more uniform nanoparticles’ deposition over the surface. The optimized largearea substrate has a SERS detection limit of 10^(-8)mol/L for 4-aminothiophenol(4-ATP), indicating the potential realworld applications for trace detection.

近几十年来,表面增强拉曼散射(SERS)作为一种有效的低浓度分子检测技术得到了广泛应用。本文提出了一种基于1064 nm MOPA脉冲光纤激光和紫外脉冲激光的两步激光烧蚀成形法,以提升SERS活性衬底的硅基表面多尺度微纳结构的均匀性和可控性。利用激光束直接烧蚀硅表面并形成微结构,在此过程中硅材料因为光热效应产生的热影响区而逐渐熔融,并向四周喷射出而形成等离子体羽,这些高速离子在空气中冷却成核,然后重新沉积回微结构表面上而形成多尺度结构,进一步提高了基底的光收集效率,随后沉积的Au薄膜中的纳米颗粒可以提供纳米间隙作为SERS的热点。本研究通过正交试验设计确定了优化的激光加工参数,与仅使用MOPA激光烧蚀加工相比,1064 nm MOPA激光和紫外激光的两步复合激光烧蚀可以使硅纳米颗粒分布更加均匀,从而提升沉积金属层的表面均匀性。经过试验,所加工的大面积SERS基底对4-ATP的SERS检测极限可以达到10^(-8) mol/L,表明其在痕量物质检测方面具有很好的应用前景。