Long-Term Stability at High Temperatures for Birefringence in PAZO/PAH Layer-by-Layer Films

Optical memories with long-term stability at high temperatures have long been pursued in azopolymers with photoinduced birefringence. In this study, we show that the residual birefringence in layer-by-layer (LbL) films made with poly[1-[4-(3-carboxy-4 hydroxyphenylazo)benzene sulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) alternated with poly(allylamine hydrochloride) (PAH) can be tuned by varying the extent of electrostatic interactions with film fabrication at different pHs for PAH. The dynamics of both writing and relaxation processes could be explained with a two-stage mechanism involving the orientation of the chromophores per se and the chain movement. Upon calculating the activation energies for these processes, we demonstrate semiquantitatively that reduced electrostatic interactions in films prepared at higher pH, for which PAH is less charged, are responsible for the longer stability at high temperatures. This is attributed to orientation of PAZO chromophores via cooperative aggregation, where the presence of counterions hindered relaxation.

Photoinduced orientation in natural rubber

Azobenzene molecules and their derivatives have been widely investigated for their potential applications in optical and electrooptical devices. We have prepared a new guest-host system from natural rubber (NR) impregnated with azobenzene derivative Sudan Red B (SRB). The effects of stretching and immersion time on photoinduced orientation were investigated by birefringence signal measurements. We have found that the molecular orientation increase when the samples are stretched and decrease with the increase of immersion time. The first behavior was explained by using the random coil model and the latter was attributed to increase of the aggregation of SRB into NR matrix. (C) 2012 Published by Elsevier B.V.

Focusing surface plasmons on Er3+ ions through gold planar plasmonic lenses

Gold plasmonic lenses consisting of a planar concentric rings-groove with different periods were milled with a focused gallium ion beam on a gold thin film deposited onto an Er3+-doped tellurite glass. The plasmonic lenses were vertically illuminated with an argon ion laser highly focused by means of a 50x objective lens. The focusing mechanism of the plasmonic lenses is explained using a coherent interference model of surface plasmon-polariton (SPP) generation on the circular grating due to the incident field. As a result, phase modulation can be accomplished by the groove gap, similar to a nanoslit array with different widths. This focusing allows a high confinement of SPPs that can excite the Er3+ ions of the glass. The Er3+ luminescence spectra were measured in the far-field (500-750 nm wavelength range), where we could verify the excitation yield via the plasmonic lens on the Er3+ ions. We analyze the influence of the geometrical parameters on the luminescence spectra. The variation of these parameters results in considerable changes of the luminescence spectra.

Effects of cryogenic and stress relief treatments on temper carbide precipitation in AISI D2 tool steel

The effects of cryogenic and stress relief treatments on temper carbide precipitation in the cold work tool steel AISI D2 were studied. For the cryogenic treatment the temperature was −196°C and the holding time was 2, 24 or 30 h. The stress relief heat treatment was carried at 130°C/90 min, when applied. All specimens were compared to a standard thermal cycle. Specimens were studied using metallographic characterisation, X-ray diffraction and thermoelectric power measurements. The metallographic characterisation used SEM (scanning electron microscopy) and SEM-FEG (SEM with field emission gun), besides OM (optical microscopy). No variation in the secondary carbides (micrometre sized) precipitation was found. The temper secondary carbides (nanosized) were found to be more finely dispersed in the matrix of the specimens with cryogenic treatment and without stress relief. The refinement of the temper secondary carbides was attributed to a possible in situ carbide precipitation during tempering.