Abstract
Films from congo red (CR) alternated with poly(allylamine hydrochloride), PAH, were prepared by layer-by-layer and alternative spray techniques. In order to investigate the change of roughness induced by laser light irradiation (532 nm), both kinds of films were characterized by using UV-visible spectroscopy and atomic force microscopy (AFM). At dif- ferent irradiation times, layer-by-layer, LbL, films showed small changes in the roughness and irregular behavior, whereas spray films exhibited higher and a regular decreasing of roughness with increasing irradiation time. The higher roughness of spray films as compared with the LbL ones was attributed to different formation mechanisms of the films. The decreasing of the roughness as a function of the irradiation time (exhibited by the spray films) was associated to surface relaxation due to the interplay between photoisomerization of congo red dye and the heating of the sample during the laser light irradiation. The results suggested that the alternative spray technique is the best choose to control of roughness of the films by using light irradiation.
Highlights
Molecules able to exhibit geometric isomerization by the action of light, such as azobenzene and their derivatives are promising because they have characteristics suitable for application in memory devices, optical switches and modulators [1]
In order to investigate the change of roughness induced by laser light irradiation (532 nm), both kinds of films were characterized by using UV-visible spectroscopy and atomic force microscopy (AFM)
We have investigated the effect of laser irradiation on roughness of layerby-layer and films prepared by alternative spray technique, alternating poly, poly(allylamine hydrochloride) (PAH), and congo red dye, CR
Summary
Molecules able to exhibit geometric isomerization (change of geometric shape in space) by the action of light, such as azobenzene and their derivatives are promising because they have characteristics suitable for application in memory devices, optical switches and modulators [1]. After some time of light irradiation, which occur during the trans photoisomerization cycles trans cis trans, comes an excess of molecules oriented perpendicular to the axis of the dipole electric field optical excitation, providing the optical birefringence and dichroism in films [4]. Another important property of azobenzene derivatives, which comes from the molecular photoisomerization, is the change of surface morphology of films [5] producing surface relief grades. Layers of material are alternated by spraying their solutions by controlled time [12]
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