Modification of photonic crystal effect from few monolayers prepared by convective deposition with and without vibrating assistance

Abstract

Photonic crystal effect can be observed in regular pattern thin film and an efficient inexpensive thin film fabrication method, which be able to control number of monolayers, is convective self-assembly. In this work, the film was prepared by polystyrene nanoparticle with particle sizes of 930, 500 and 310 nm. The few monolayer films were coated by convective deposition technique with fixed blade and slowly moving substrate with and without vibrating substrate. The optical properties of nanoparticle self-assembly were investigated by reflection spectrum analyzer embedded in microscope for nearly normal incident measurement. The spectrum angle depending on incidence and detector were also examined in co-rotational optical setting. The observed phenomena can be described by Bragg diffraction at various incident angle. The optical responses of self-assembly of 500 and 310 nm particles exhibited the photonic crystal effects in the green and blue color, respectively. It was found that the self-assembly nanoparticle usually provided a hexagonal closed packing. However in vibrational deposition, the polystyrene spheres can create the pattern of face centered cubic. This leads to the modification of photonic crystal effect shift on the thin film prepared with vibration. In addition, the self-assembly of 930 nm particles can show only the grating diffraction effect with various angle but the Bragg diffraction cannot be observed due to the detection limitation of visible light range.