High-Density Regular Arrays of Nanometer-Scale Rods Formed on Silicon Surfaces via Femtosecond Laser Irradiation in Water

Abstract

We report on the formation of high-density regular arrays of nanometer-scale rods using femtosecond laser irradiation of a silicon surface immersed in water. The resulting surface exhibits both micrometer-scale and nanometer-scale structures. The micrometer-scale structure consists of spikes of 5-10 mum width, which are entirely covered by nanometer-scale rods that are roughly 50 nm wide and normal to the surface of the micrometer-scale spikes. The formation of the nanometer-scale rods involves several processes: refraction of laser light in highly excited silicon, interference of scattered and refracted light, rapid cooling in water, roughness-enhanced optical absorptance, and capillary instabilities.

Femtosecond laser irradiation-induced infrared absorption on silicon surfaces

“…The absorptance at wavelength of 1.5 µm of the structured silicon is about 50% that is much higher than that of unstructured silicon substrate. In visible wavelengths part, the absorptance increment is mainly originated from the effect of multiple reflections, i.e., the incident light is reflected multiple times on the micro/ nanostructured surface and is absorbed by the silicon [7][8][9][10][11]. In near-infrared (NIR) region, there is an obvious drop in wavelength around 1.1 μm for the unstructured silicon absorptance curve, which is corresponding to the silicon band gap.…”

“…If its wavelength is longer than 1.1 μm, i.e., its photon energy is less than the silicon band gap energy (1.1 eV), the light cannot be absorbed as it passes through silicon solid because the photon energy is not large enough to excite an electron to the conduction band from the valence band of the silicon solid. To improve the optical properties of silicon, femtosecond laser irradiation method has been applied to treat silicon surfaces [3,[7][8][9][10]. In order to increase the silicon absorption in the IR range, the microstructured silicon was formed with femtosecond laser irradiation on silicon surfaces in the presence of the background gas of SF 6 .…”

Passivation of all-angle black surfaces for silicon solar cells

“…For solar cells made from multicrystalline silicon wafers, where the random nature of the grain orientations precludes the formation of pyramids, acid texturing is instead used Whilst these methods are industry standards, new approaches have emerged to improve on optical absorption by utilizing nanoscale texturing. Examples include nano-textured surfaces formed via laser ablation [1,2], reactive ion etching [3,4], and wet chemical etching [5][6][7][8][9]. Several solar cells with nanowire AR structures have recently been reported with high power conversion efficiencies.…”

Reduction of Friction of Metals Using Laser-Induced Periodic Surface Nanostructures

“…With the development of laser technology, ripples can now be induced by different lasers with varied wavelengths and pulse widths. In general, LIPSS with periods close to the laser wavelength are called low spatial frequency LIPSS (LSFL), while LIPSS with periods much smaller than the laser wavelength are referred to as high spatial frequency LIPSS (HSFL) [20][21][22][23][24][25][26][27][28][29][30]. Several mechanisms have been proposed to explain the formation mechanisms of LIPSS, such as interference mechanisms [31], excitation of surface plasmon polaritons [32], self-organization [33], second harmonic generation [34], and Coulomb explosion [35].…”