Large-Area Fabrication of Laser-Induced Periodic Surface Structures on Fused Silica Using Thin Gold Layers.

Clemens Kunz,Sebastian Engel,Frank Müller,Stephan Gräf

doi:10.3390/nano10061187

Clemens Kunz, Sebastian Engel + Show 2 more

Open Access

https://doi.org/10.3390/nano10061187

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Abstract

Despite intensive research activities in the field of laser-induced periodic surface structures (LIPSS), the large-area nanostructuring of glasses is still a challenging problem, which is mainly caused by the strongly non-linear absorption of the laser radiation by the dielectric material. Therefore, most investigations are limited to single-spot experiments on different types of glasses. Here, we report the homogeneous generation of LIPSS on large-area surfaces of fused silica using thin gold layers and a fs-laser with a wavelength λ = 1025 nm, a pulse duration τ = 300 fs, and a repetition frequency frep = 100 kHz as radiation source. For this purpose, single-spot experiments are performed to study the LIPSS formation process as a function of laser parameters and gold layer thickness. Based on these results, the generation of large-area homogenous LIPSS pattern was investigated by unidirectional scanning of the fs-laser beam across the sample surface using different line spacing. The nanostructures are characterized by a spatial period of about 360 nm and a modulation depth of around 160 nm. Chemical surface analysis by Raman spectroscopy confirms a complete ablation of the gold film by the fs-laser irradiation. The characterization of the functional properties shows an increased transmission of the nanostructured samples accompanied by a noticeable change in the wetting properties, which can be additionally modified within a wide range by silanization. The presented approach enables the reproducible LIPSS-based laser direct-writing of sub-wavelength nanostructures on glasses and thus provides a versatile and flexible tool for novel applications in the fields of optics, microfluidics, and biomaterials.

Highlights

The advantageous mechanical, physical, and chemical properties of technical and optical glasses, such as borosilicate glass, soda-lime-silicate glass, and fused silica, make them the material of choice for a large variety of applications in the fields of optics, microfluidics, photovoltaics, and biomaterials
The nanostructured surfaces were subsequently analyzed with regard to their topography and surface chemistry and characterized with respect to selected functional properties that might open up new applications in fields such as optics, microfluidics, and photovoltaics
In order to evaluate the impact of the thin gold layer on laser-induced periodic surface structures (LIPSS) formation, the layer thickness t was varied from 20 to 300 nm and compared to the LIPSS formation on the initial fused silica surface as reference

Summary

Introduction

The advantageous mechanical, physical, and chemical properties of technical and optical glasses, such as borosilicate glass, soda-lime-silicate glass, and fused silica, make them the material of choice for a large variety of applications in the fields of optics, microfluidics, photovoltaics, and biomaterials. Rudenko et al recently performed numerical studies for fused silica suggesting that the formation of both LIPSS types is driven by the interference of the incident laser field with the scattered (non-radiative) near-field (HSFL) and the (radiative) far-field (LSFL), respectively, below the surface [16]. This requires the presence of initial inhomogeneities, electron defects, or scattering centers. The low number of studies is caused by some challenges during LIPSS formation on glasses, which are mainly related to their amorphous chemical structure and the relatively large band gap energy, when compared to metals and semiconductors The latter results in strongly non-linear (multi-photon) absorption processes at the typical laser wavelengths. The nanostructured surfaces were subsequently analyzed with regard to their topography and surface chemistry and characterized with respect to selected functional properties that might open up new applications in fields such as optics, microfluidics, and photovoltaics

Sample Preparation

Characterization

Single-Spot Investigation

Large-Area Fabrication of HSFL