Laser-fluence dependence of microstructure formed on nickel by backward pulse laser deposition

Abstract In automotive components, there is a growing need for direct joining between resin and metal for the purpose of lightweighting, downsizing, and cost reduction. Microstructure formation on the metal surface has attracted attention as pretreatment for direct joining. To obtain strong adhesion, it is necessary to form microstructures with a high aspect ratio. Therefore, we used the backward pulse laser deposition method in air with a nanosecond pulsed laser to form microstructures on a nickel surface and studied the dependence of laser fluence on the surface morphology, such as width and pitch of microstructures. Deposition formed nano-columnar structures with aspect ratio and pitch of 3 to 4.6 and 6 nm to 66 nm, respectively. As the fluence increased, narrower columnar structures with a smaller pitch were formed, and eventually the structure changed from columnar structures to a flat layer. Thus, this study demonstrated that laser fluence controls the width and pitch of microstructures. In addition, it was suggested that the surface mobility of the ablation species after arrival on the substrate influences the width and pitch of the microstructures.