We present a method for mapping the electromagnetic field distribution in the vicinity of noble metal nanoparticles able to sustain localised surface plasmon resonance (LSPR). The field distribution is coded by topographic change in a self-developing photosensitive polymer (PMMA-DR1). Metallic nanostructures are fabricated by e-beam lithography and optically characterised by extinction spectroscopy. Photoinduced topographic changes are checked by means of atomic force microscopy (AFM). The dipolar character of the surface modification around the particles agrees qualitatively with theoretical predictions and a strong correlation between LSPR position and the relief depth is found.
In a classical multilayer organic light emitting diode (OLED) structure, almost 80% of the light emitted happens to be lost following guiding through the different layers. Patterning of the OLEDs structure was already proposed and reported as an interesting solution towards the optimization of an OLED external efficiency. As an alternative to classical lithographic patterning methods which appear to be quite complex, we propose here the implementation of a quite direct and easy-to-set light-induced patterning method using azo-dye polymers. When a polymer film containing azobenzene dyes is irradiated by an interference pattern between polarized laser beams at a wavelength near the chromophore absorption band, the film surface undergoes a direct, reversible and controlled topographic modification. More surprisingly, we have recently experimentally evidenced that uniform irradiation of an azo-dye polymer using a single laser beam with normal incidence onto the polymer film surface could lead to a self structuration process resulting in the formation of a quasi hexagonal surface-relief grating. After a description of the main features related to light-induced surface relief gratings, we show here that this original patterning process offers an interesting solution for control and optimisation of optoelectronic devices such as OLEDs. The guiding properties of both 1D and 2D structures have been studied and their effects on the light emission properties of a patterned electroluminescent polymer have been characterized and compared after angle dependent measurement of the photoluminescence spectrum. Quite efficient decoupling is evidenced.
It is now well established that, in azo-dye polymers repeated trans-cis-trans isomerization cycles induces molecular reorientation leading to quasi-permanent birefringence and dichroism. More recently, it has been shown that irradiation of an azo-polymer thin film with an interference pattern between polarized laser beams can lead to a direct and reversible topographic modification of the polymer film surface resulting in the induction of surface relief gratings in conjunction with the light interference pattern. Here, we provide experimental evidence of an original spontaneous light-assisted submicrometer patterning process. We show that uniform irradiation of an azo-dye polymer using a single collimated laser beam with normal incidence leads to the formation of organized hexagonal patterns. These structures geometry depends on the laser beam polarization : their period is about the irradiation wavelength and their modulation amplitude can reach one hundred nanometers. Possible origin of such process is discussed. Although showing similar features with models or experiments already described in the literature, the origin of light-assisted spontaneous patterning in azo-polymers is still unclear and further complementary investigations are needed. Indeed, accurate determination of the relevant parameters at the origin of such process should enable a full control of the process together with further possible generation of more complex structures.
During the last decade, large effort has been dedicated towards the miniaturization of devices for photonic applications. One of the key points towards this objective is structurization at the nanoscale level. Recently, one-step photoinscription of surface relief gratings onto azo-polymers was demonstrated: when a polymer film containing azobenzene dyes is irradiated by an interference pattern between polarizaed laser beams at a wavelength near the chromophore absorption band, the film surface undergoes a direct, reversible and controlled topographic modification. Grating modulation amplitudes as large as the film thickness can be obtained. In this work we provide experimental evidence of a new spontaneous light-assisted submicrometer hexagonal patterning process. More particularly, we show that uniform irradaiton of an azo-dye polymer using a singel laser beam wtih normal incidence onto the polymer film surface leads to a self structurization process resulting in the formation of a quasi hexagonal grating. The influence of parameters such as the laser intensity, the irradiation time, the thickness of the polymer film but also the irradiation wavelength is studied towards a better understanding of the process. Full control of the mechanisms at the origin of such process could further permit a complete manipulation of the molecular order and thus enable the generation of other spontaneous complex structures opening the way to the development of new easy-to-set micro and nano-structuration technqiues.
AEROSPATIALE Corporate Research Center conducts since 1989 experimental works on the interaction of lasers on optical materials. Those works are part of an approach to understand physical mechanisms leading to the observed damages. Several means of diagnostic have been developed to study the pulse duration and wavelength dependence of those processes. The damages observed in the nanosecond and the millisecond regime can be explained by a change in the mechanism. This observation is based on morphological examinations of the damage and on measured pulse duration and wavelength dependence. Furthermore, a numerical analysis of the temperature in the samples has been computed to strengthen this observation.