LIPSS for SERS: Metal Coated Direct Laser Written Periodic Nanostructures for Surface Enhanced Raman Spectroscopy

Abstract

molecular identification technique that originates from the marriage of the high molecular specificity of Raman spectra and the ultra-high signal amplification property of plasmonic metal nanostructures. [1][2][3][4][5][6][7][8] SERS technique shows great promise in a wide variety of fields including biosensing, gas phase chemical detection, and single molecule detection. [9][10][11][12][13][14][15] Besides the high and spatially uniform enhancement factor (EF); chemical stability, reproducibility, precision, and fast fabrication in large areas with less debris are demanded for ideal SERS substrates. [16,17] Even though metallic nanoparticles exhibit high SERS EFs, they do not offer proper particle stability, and use in large areas. [18][19][20] Femtosecond laserbased techniques offer the fabrication of highly sensitive SERS substrates with low detection limits. [21][22][23] On the contrary to wet chemical synthesis procedures, uniformity, robustness, and reproducibility are provided by laser-assisted periodic nanostructures. Without any lithographic processes, the number of processes to fabricate highly sensitive SERS sensing devices is also reduced. [24][25][26] Generation of laser-induced periodic surface structuring (LIPSS) by using the direct laser writing technique with ultrafast (femtosecond -fs) laser sources [27] is a fast and low-cost method compared to other well-established techniques such as laser interference lithography, [28] photolithography, electron beam lithography, and nanoimprint lithography. [29] Controlling the irradiation wavelength, the number of pulses on the spot, the polarization direction of the beam, repetition rate, the fluence of the ultrafast laser, and the scanning speed leads to the formation of the nano ripples on semiconductors and metals. [30][31][32][33][34] Nanoripples formed by an fs-laser can be classified into two, Low Spatial Frequency LIPSS (LSFL) and High Spatial Frequency LIPSS (HSFL). [35] Furthermore, both types of structures, formed on metal and semiconductor surfaces, have potential benefits as a SERS substrate as well. [36][37][38][39][40][41] LSFL structures exhibit periods close to irradiation wavelength, meanwhile; HSFL structures have periods smaller than half of the irradiation wavelength. [35,[42][43][44][45][46] The formation mechanism of LSFL structures was first introduced by Sipe theory in 1982. [47] With the appropriate energy exposure and the high number of free carriers on the surface, the dielectric A novel method of fabricating large-area, low-cost surface-enhanced Raman spectroscopy (SERS) substrates is introduced which yields densely nanostructured surfaces utilizing laser-induced periodic surface structuring (LIPSS) of crystalline silicon (Si). Two different interaction regimes yield low spatial frequency (LSFL) and high spatial frequency (HSFL) LIPSS patterns. Nanostructuring of Si surface is followed by deposition of a thin noble metal layer to complete the fabrication procedure. A 50-70 nm thick Ag layer is shown to maximize the SERS perform...

Ag Nanoparticles@Au Nanograting Array as a 3D Flexible and Effective Surface-Enhanced Raman Scattering Substrate

“…After nanoimprinting, the color of the PVC sheet changed from transparent to rainbow (Figure S1). The rainbow color can be ascribed to the dispersion of light that occurred on the surface of the grating structure, , indicating that the complementary nanograting structure of the DVD template was patterned on the surface of the PVC sheet in a large area of 2 × 2 cm 2 . As shown in the corresponding SEM and AFM images (Figure d–f), the 3D periodic structures on the imprinted PVC sheet exhibit a similar periodicity and height as those of the DVD template.…”

Laser-based bionic manufacturing

“…This ultrafast laser is well-suited for a wide range of solid materials, making them particularly effective for manufacturing brittle, hard materials, or any material with unfavorable thermal properties. Figure 4 illustrates the main methods for achieving bionic micro/nano structural surfaces using laser direct ablation [40], laser-induced [41], and laser template methods [42].…”

Laser Micro/Nano‐Structuring Pushes Forward Smart Sensing: Opportunities and Challenges

“…After the deposition of a thin noble metal layer of 50-70 nm, the SERS substrates are found to be capable of detecting a Raman analyte down to 10 −11 m. Both LSFL and HSFL surfaces with 70 nm thick Ag exhibited the strongest SERS with Raman EFs as high as 10 9 . [160] Considering the importance of a hybrid nanostructure for improving the sensing performance, Zhang et al incorporated Au NPs to decorate ZnO nanospheres by laser irradiation-induced heating-melting-evaporating processes (355 nm, 40 mJ) (Figure 8b). [161] The as-formed Au-ZnO nanospheres with an average size of 40-65 nm showed significantly enhanced gas sensing properties compared with those of pure ZnO nanospheres, with response values of 252 to 100 ppm ethanol (Figure 8b).…”