Highly Efficient Fabrication of Superhydrophilic Structures on Silicon Surface by the Interference of Two Femtosecond Laser Beams

Hybrid micro/nanostructures with an area of 10 mmx10 mm are fabricated in 30 s by using the two-beam interference of femtosecond laser combined with the cylindrical lens line scanning technique, which greatly improved the laser processing efficiency. The silicon surface structures contain long-periodic microstructures determined by two-beam interference and the periodic nanostructures induced by femtosecond laser. The hybrid micro/nanostructures greatly improve the surface roughness. Under the effect of capillarity,the ablated silicon surface shows superhydrophilicity in air,and the contact angle drops from 40 degrees to 0 degrees. The X-ray photoelectron spectra of the silicon surface shows that the content of Si-OH and H2O molecules increases by 22.3% and 13.6%,respectively,which further improves the hydrophilicity of silicon surface. With the increase of laser fluence and the decrease of scanning speed,the contact angle of the ablated silicon surface decreases gradually. This provides a new method for the efficient fabrication of large-area superhydrophilic structures,and has potential applications in the fields of heat conduction, biochip,etc.