Laser-Induced Periodic Surface Structures Nanofabricated on Poly(trimethylene terephthalate) Spin-Coated Films

Abstract

Here we present a precise morphological description of laser-induced periodic surface structures (LIPSS) nanofabricated on spin-coated poly(trimethylene terephthalate) (PTT) films by irradiation with 266 nm, 6 ns laser pulses and by using a broad range of fluences and number of pulses. By accomplishing real and reciprocal space measurements by means of atomic force microscopy and grazing incidence wide- and small-angle X-ray scattering respectively on LIPSS samples, the range of optimum structural order has been established. For a given fluence, an increase in the number of pulses tends to improve LIPSS in PTT. However, as the pulse doses increase above a certain limit, a distortion of the structures is observed and a droplet-like morphology appears. It is proposed that this effect could be related to a plausible decrease of the molecular weight of PTT due to laser-induced chain photo-oxidation by irradiation with a high number of pulses. A concurrent decrease in viscosity enables destabilization of LIPSS by the formation of droplets in a process similar to surface-limited dewetting.

In Situ Monitoring of Laser-Induced Periodic Surface Structures Formation on Polymer Films by Grazing Incidence Small-Angle X-ray Scattering

“…The outer maxima are consecutive orders of the first one. 22 By comparing the intensity profiles for the samples irradiated at 2 and at 10 Hz, it is clear that a larger period is obtained for the sample irradiated at 10 Hz. This is corroborated by the analysis of the AFM images shown in Figure 1.…”

“…This model has been previously applied to LIPSS in films of different polymers including PTT. 15,22,41 In this way we can generate different GISAXS patterns, that can be compared to those obtained experimentally, by changing the value of the paracrystallinity parameter g. As an example, In the intensity profiles one can distinguish two different types of maxima. The sharper ones are associated to the lattice structure factor while the rounded ones are attributed to the form factor of the scatterer.…”

“…54 For polymer films in general, and for PTT in particular, it has been proposed that laser irradiation causes heating of the upper layer of the polymeric film. 15,21,22 The corresponding temperature increase can be estimated by solving the one-dimensional heat conduction equation, as previously reported. Additionally, for 10 Hz a much lower number of pulses (ca.…”

“…Heating provides enough polymer chain mobility to rearrange the material in the surface giving rise to the superficial height modulation. 15,22,23 However, the whole mechanism responsible for LIPSS formation is still not completely understood in polymers.…”

Nanostructuring Thin Polymer Films with Optical Near Fields

“…21 In particular, poly(trimethylene terephthalate) (PTT) is a semicrystalline aromatic polyester whose outstanding mechanical and optical properties, together with its low glass transition temperature T g ≈ 44°C, 22 make it an attractive material for the fiber industry 23 as well as for optoelectronic 24 and nanophotonic 25,26 applications. PTT has already shown interesting features when nanostructured by several different methods such as laser-induced periodic surface structuration (LIPSS) 27 and nanoimprint lithography (NIL). 28 In the present work we report nanofabrication of twodimensional near-field topographic patterns imprinted on polymeric thin films of PTT, resulting from interference between incident laser light and light scattered by dielectric microspheres placed at the film surface.…”