Surface patterning by ripples using femtosecond laser for sensing and opto-fluidics

Ripples on silicon have been fabricated by femtosecond laser ablation to minimize Si removal and to achieve a flat (not a groove-like) coverage of extended millimeter size areas for nano-/micro-fluidic applications. Such flat ripple-covered regions were found to control flow and wetting properties of water. Depending on orientation of ripples the flow speed of a 1 µl water droplet can be changed from 1.6 to 9.1 mm/s. Gold-coated ripples on sapphire are demonstrated as an excellent SERS substrate with more than one order-of-magnitude larger sensitivity and superior reproducibility a,.., compared to the commercial SER.S substrates; SERS signal on the ripples was more than 15 times higher and more than 2 times more uniform as compared to Klarite substrate at 633 mn excitation wavelength. It was shown that ripples can also be fabricated on thin transparent conducting indium tin oxide (ITO) coatings of 45 mn thickness. The electrical resistance can be controlled by orientation and area fraction of ripples. Applications on miniaturized heaters for incubation and micro-chemistry chambers on lab-on-chip and electrowetting are discussed along with potential applications in orientational flows, self-assembly of micro-chips, and sensing.