Laser-induced periodic surface structures (LIPSS) of polymers produced by pulsed UV lasers have been reported. This study was attempted to extend such laser induced surface structures of polyimide to near UV or visible ranges by the presence of dyes as dopants. Although no LIPSS was formed with second harmonic irradiation, ripple structures of spacing 400 ⁺_- 50 nm was successfully developed on polyimide surface with pulsed Nd:YAG laser irradiation at third harmonic generation (355 nm). The periodicity γ of polymers studied follows γ = λ/(n - sinθ) relationship. The effect of laser dosage, angle of incidence, presence of oxygen and dopant additions on LIPSS were investigated. Dopants, enhanced the absorption of polyimide both at 355 nm and 532 nm, were shown to moderately increase the ra...[ Read more ]

Laser-induced periodic surface structures (LIPSS) of polymers produced by pulsed UV lasers have been reported. This study was attempted to extend such laser induced surface structures of polyimide to near UV or visible ranges by the presence of dyes as dopants. Although no LIPSS was formed with second harmonic irradiation, ripple structures of spacing 400 ⁺_- 50 nm was successfully developed on polyimide surface with pulsed Nd:YAG laser irradiation at third harmonic generation (355 nm). The periodicity γ of polymers studied follows γ = λ/(n - sinθ) relationship. The effect of laser dosage, angle of incidence, presence of oxygen and dopant additions on LIPSS were investigated. Dopants, enhanced the absorption of polyimide both at 355 nm and 532 nm, were shown to moderately increase the rate of forming ripples and deepen the ripple amplitude by about 20%. Moreover, addition of dopant gives some insights of the surface melting process of LIPSS. All these results were supported by scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray photon spectroscopy (XPS) and static secondary ion mass spectroscopy (SSIMS).

Secondly, the infrared dichroism on LIPSS of polymers, poly(ethylene terephthalate) (PET), polystyrene (PS), polysulfone (PSu) and polyimide (PI) were characterized by polarized reflection infrared spectroscopy using specular angle approach. The dichroism of C=O and C-H stretchings of PET increases with respect to the periodic lines in parallel and perpendicular directions respectively. This suggests an induced alignment of carbonyl groups in the LIPSS areas of PET under the influence of polarized electric field during pulsed laser irradiation. The similar molecular alignment study was carried out on PS, PSu and PI. Their degree of orientation is less distinguished. The cause of this difference may be due to dipole moment, crystallinity, glass transition temperature and others.