Driving forces for self-organization in thin metal films during their partial ablation with a cylindrically focused laser beam

Abstract

Articles you may be interested inSimple formula for the interspaces of periodic grating structures self-organized on metal surfaces by femtosecond laser ablation Appl. Phys. Lett. 102, 174106 (2013); 10.1063/1.4803940Self-organized, gratinglike nanostructures in polymer films with embedded metal nanoparticles induced by femtosecond laser irradiation J. Appl. Phys. 108, 073114 (2010); 10.1063/1.3490191 Patterning polycrystalline thin films by defocused ion beam: The influence of initial morphology on the evolution of self-organized nanostructures Abstract. Metal films on transparent substrates are widely used in industry for mask production, and lasers are frequently applied for their patterning. The quality of patterning is limited by fundamental phenomena taking place close to edges of the laser ablated area. We investigated transformations in metal films experimentally and numerically during their irradiation with the laser beam with fluences above the ablation threshold. The beam of a nanosecond pulse laser tightly focused by aspheric cylindrical lens to a stripe (2.5 μm × 2.5 mm) was applied for the back-side ablation of the chromium thin film on a glass substrate. Two phases, the initiation and growth of periodical structures in a thin metal film, were distinguished. The prolonged holes were ablated with a single laser pulse. Ridges of the resolidified metal with increased but not uniform thickness were always present on edges of the cleaned area. Instabilities during the ablation process forced the molten metal in the ridges to agglomerate into droplets with the predictable periodicity. The average ratio of the droplet formation period to the radius of the resolidified ridge was found to be close to 9.0, which was a clear evidence of the Rayleigh-Plateau instability along the molten ridge. Use of overlapping laser pulses to extend the cleaned area initiated self-organization of chromium on the glass substrate. The droplets on ridges were starting points for formation of ripples from the metal film by irradiation with partially overlapping laser pulses. Growth of a highly periodical structure of metal on glass was observed in a certain range of process parameters, depending on the pulse energy and the beam overlap. The ripples were located with a period of 2.5-4 m parallel to the direction of the laser spot shift. The initial droplets and later the ripples were acting as heat sinks that cooled down the metal in their close proximity. The COMSOL finite element modeling revealed that temperature modulation along the laser irradiation spot was high enough to initiate the Marangoni effect which resulted in movement of the molten metal from hot to colder areas. After each laser pulse the process lasted as long as the liquid phase existed. The time when chromium remained in liquid phase was estimated to be as long as 100 ns. The distance that chromium in molten film traveled because of Marangoni convection before it solidified has been evaluated by multiplying Marangoni speed and lifetime of the liquid phase and i...

Hierarchical Micro-/Nano-Structures on Polycarbonate via UV Pulsed Laser Processing

“…At a somewhat higher fluence level of 2.90 mJ/cm 2 , the DLIP ridges start to separate into chains of larger micro-droplets. Similar results were found when processing LSFL on top of LSFL on polyethersulfone, when the sample was rotated by 90 • [57] and when processing LIPSS on a chromium thin film [58]. This phenomenon can be related to the Plateau-Rayleigh instability [58].…”

“…Similar results were found when processing LSFL on top of LSFL on polyethersulfone, when the sample was rotated by 90 • [57] and when processing LIPSS on a chromium thin film [58]. This phenomenon can be related to the Plateau-Rayleigh instability [58]. In brief, the surface energy in a stationary fluid in cylindrical form is larger than the effect of gravity and, hence, changes the shape of the cylinder into droplets in order to reduce the total surface energy.…”

Laser-Induced Periodic Surface Structures (LIPSS)

“…They were oriented orthogonally to the line focus, i.e., parallel to the movement of the focused laser beam. The authors estimated the lifetime of the molten Cr to be in the order of 100 ns and proposed a six-stage thermophysical model based on the Marangoni effect and the Plateau-Rayleigh instability (Gedvilas et al 2012).…”

Impact of capillarity forces on the steady-state self-organization in the thin chromium film on glass under laser irradiation

“…Formation of regular diffraction gratings was experimentally implemented by using the above-mentioned technique [16]. The Rayleigh-Plateau instability was introduced as an initiator of the self-organization of a flat metal film into parallel metal lines [17][18][19]. The physical phenomenon responsible for the steady continuation of the self-organization of the chromium thin film on the glass substrate into the regular structures was still unknown.…”