Rutile TiO Flocculent Ripples with High Antireflectivity and Superhydrophobicity on the Surface of Titanium under 10 ns Laser Irradiation without Focusing.

We report on the formation of rutile TiO flocculent laser-induced periodic surface structures (LIPSSs) with high antireflectivity and superhydrophobicity on the surface of titanium under 10 ns 1064 nm laser irradiation without focusing. The center part of the Gaussian laser beam is used to deposit flocculent structure and the edge part used to produce LIPSSs. The melt and modification thresholds of titanium were determined first, and then, the melt and modification spot-overlap numbers, several responsible for the formation of flocculent structure and LIPSSs, were introduced. It is found that both the melt and modification spot-overlap numbers increase with an increase in laser fluence and spot-overlap number, contributing to the production of flocculent LIPSSs. LIPSSs are obtained with the modification spot-overlap number above 300, and the amount of flocculent structures increases with an increase in the peak laser fluence and spot-overlap number. Then, considering that the fine adjustment of the melt and modification spot-overlop numbers in one-time line scanning is quite difficult, the composite structure, of which both LIPSSs and flocculent structures are distinct, was optimized using laser line scanning twice. On this basis, a characterization test shows the sample full of the flocculent LIPSSs represents best antireflectivity with the value around 10% in the waveband between 260 and 2600 nm (advance 5 times in infrared wavelengths compared to the initial titanium surface), and shows the no-stick hydrophobicity with the contact angle of 160° and roll-off angle of 25° because of the pure rutile phase of TiO.