Combined Experimental and Theoretical Study of Femtosecond Laser Based Micro/Nano Machining of Ultra Thin Metallic Films

Abstract

The effectiveness of ultra-short pulsed laser radiation for high-precision material processing and surface micro-modification, owing to the minimal thermal and mechanical damage, has been shown. Micro/Nano structuring of thin films is gaining widespread importance owing to ever-increasing applications in a variety of fields. The present study details femtosecond laser interaction with ultra thin metallic films at the micro and nano scales. Results of Microablation studies, carried out with an 800nm wavelength, 80fs pulse duration, femtosecond laser focused tightly using a long working distance objective lens, are discussed. A parametric study of single shot ablation and subsequent atomic force microscope characterization of the ablation craters is presented. The formation of elevated convex hillock structures at low laser pulse energies and considerable delamination at higher energies evinces a stress driven modification mechanism. Further, nanostructuring results on thin films carried out with femtosecond laser in conjunction with an atomic force microscope are presented. Various nanofeatures were machined with high spatial resolution (∼10–12nm), flexibility and repeatability by utilizing the local field enhancement in the near-field of the scanning probe tip irradiated with the laser beam. Attempting to understand the modification mechanism and the physics involved, numerical simulation studies were performed to evaluate the field enhancement underneath the tip and the ‘femtosecond laser–thin film’ interaction dynamics in general. Possible applications of thin film structuring may be in the areas of high-resolution nanolithography, controlled nanodeposition, ultra high-density data storage, high-resolution mask production and repair, nanoelectronics, nanophotonics and various nanobiotechnology related applications.