Femtosecond laser direct writing of monocrystalline hexagonal silver prisms

Abstract

Bottom-up growth methods and top-down patterning techniques are both used to fabricate metal nanostructures, each with a distinct advantage: One creates crystalline structures and the other offers precise positioning. Here, we present a technique that localizes the growth of metal crystals to the focal volume of a laser beam, combining advantages from both approaches. We report the fabrication of silver nanoprisms—hexagonal nanoscale silver crystals—through irradiation with focused femtosecond laser pulses. The growth of these nanoprisms is due to a nonlinear optical interaction between femtosecond laser pulses and a polyvinylpyrrolidone film doped with silver nitrate. The hexagonal nanoprisms have bases hundreds of nanometers in size and the crystal growth occurs over exposure times of less than 1 ms (8 orders of magnitude faster than traditional chemical techniques). Electron backscatter diffraction analysis shows that the hexagonal nanoprisms are monocrystalline. The fabrication method combines advantages from both wet chemistry and femtosecond laser direct-writing to grow silver crystals in targeted locations. The results presented in this letter offer an approach to directly positioning and growing silver crystals on a substrate, which can be used for plasmonic devices.

Substrate thermal conductivity controls the ability to manufacture microstructures via laser-induced direct write

“…Unfortunately, many investigations fail to provide concrete evidence of a diffusive thermal processes initiating and/or driving the laser writing process. For example, previous investigations involving laser direct write from silver nitrate solutions (AgNO 3 ) reference photoreduction [20], multiphoton absorption [16], and even non-equilibrium growth [21] as potential factors that ultimately lead to the formation of silver structures.…”