Femtosecond laser induced surface melting and nanojoining for plasmonic circuits A. Hu* a,b , G. L. Deng b , S. Courvoisier b , O. Reshef b , C. C. Evans b , E. Mazur b , Y. Zhou a a Department of Mechanical and Mechatronics Engineering and Centre of Advance Materials of Joining, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, N2L 3G1, Canada b School of Engineering and Applied Science, Harvard University, 9 Oxford Street, Cambridage, Massachusetts, 02138 USA ABSTRACT Femtosecond laser induced nonthermal processing is an emerging nanofabrication technique for delicate plasmonic devices. In this work we present a detailed investigation on the interaction between ultra-short pulses and silver nanomaterials, both experimentally and theoretically. We systematically study the laser-silver interaction at a laser fluent from 1 J/m 2 to 1 MJ/m 2 . The optimal processing window for welding of silver nanowires occurs at fluences of 200–450 J/m 2 . The femtosecond laser-induced surface melting allows precise welding of silver nanowires for “T” and “X” shape circuits. These welded plasmonic circuits are successfully applied for routining light propagation. Keywords: Femtosecond laser, silver nanomaterials, nano-thermal processing, plasmonic circuits 1. INTRODUCTION Nanofabrication based on the nanojoining method has attracted extensive interests since the E-beam lithography has limitations to develop nano-circuitry and nanoelectronics [1-4]. Not only E-beam lithography is difficult to write a nanowire with a single crystal structure and the atomic flatted surface, it is also challenge to fabricate nanodevices with 3 dimensional structure and hybrid materials using E-beam lithography [5]. Current E-beam lithography involves many steps including thin film deposition, resist masking, E-beam writing, etching, lift-up, it is almost impossible to develop an atomic flatter surface [5]. For a nanoscale light waveguide, single crystal structure and ultra-smooth surface is required to reducing the dissipation [3]. For basic nanoelectronics, the assembly of an architecture based on different building blocks is critical for proper functions and applications [6]. Sintering is a basic joining manufacturing which results in a density-controlled material starting from powder materials. At a microscale, sintering is a thermal activated mass transfer procedure driven by the surface energy and total curvature of two neighboring particles. At a nanoscale, due to a higher surface and the size effect, the solid state diffusion can occur at very low temperatures, even at room temperature [7,8]. However, a liquid phase sintering is expected as a more time-effective procedure than a solid state sintering since a liquid phase sintering takes place at a higher temperature than a solid state sintering. Recently, our theoretical study based on molecular dynamics simulation unveiled that a surface melting can occur at a rather lower temperature than the particle melting temperature [9] although the particle melting is lower than the bulk melting temperature due to the size effect [10]. This clearly shows that the melting and thereby the liquid phase sintering are the significant factors to be considered during nano-manufacturing. For the joining at a nanoscale, the activated energy should be highly localized to avoid the negative effect on the building blocks. Various energy sources have been employed for nanojoining. Nanosoldering in heated liquid medium is one of popular but less controlled joining methods [11]. A tip-style solder carrier can transfer pico-letre solder and implement microscopic interconnection on a hotplate with the aid of optical microscope [12]. A microscale ultrasonic * a2hu@uwaterloo.ca; phone 1 519 888-4567; fax 1 519 885-5892; uwaterloo.ca Plasmonics: Metallic Nanostructures and Their Optical Properties XI, edited by Mark I. Stockman, Proc. of SPIE Vol. 8809, 880907 · © 2013 SPIE · CCC code: 0277-786X/13/$18 · doi: 10.1117/12.2022482 Proc. of SPIE Vol. 8809 880907-1