Novel dual-scale structures were obtained by femtosecond double pulse train (subpulse delay Delta t > 0 ps) one-step irradiating silicon in water. The dual-scale structures consist of microspikes of similar to 2 mu m width and similar to 0.5 mu m height, and nanoripples with a mean period of 146 nm or nanoparticles with a mean diameter of 90 nm which entirely cover on the microspikes, for linearly polarized or circularly polarized femtosecond laser respectively. The formation of dual-scale structures involves the following processes: (1) Continuously laser energy deposited at femtosecond to picosecond timescales within silicon surfaces and central regions, will result in enhanced capillary waves and thinner melted silicon layers. Hence, the microspikes can be induced at laser fluences below ablation threshold; (2) Later (> 500-800 pulses), a mass of debris and bubbles produced will lead to the remarkably and uniformly scattering or shielding of subsequent incident laser energy. Hence, the nanostructures can be induced. The novel structures exhibit high-sensitive surface enhanced Raman scattering with an enhancement factor of 10(8) for Rhodamine 6G detecting. Besides, the novel structures have application potentials in improving the silicon hydrophobicity, antireflection, etc. (C) 2017 Elsevier B.V. All rights reserved.