Fabrication of thermally stable multilayer thin films and their device application

Abstract

Organic/inorganic thin films composed of poly-4-vinylpyridine (PVP) and cadmium selenide (CdSe) were prepared with dip and spin self-assembly (SA) method and their structures were investigated by X-ray reflectivity and AFM. The hydrogen bonding interaction between PVP and CdSe was employed to assemble multilayer structure. In AFM experiment, the surface roughness of multilayer thin films by spin SA show smoother surface than that by dip SA. In the X-ray reflectivity experiment, the multilayer thin films by spin SA shows more ordered internal structure than that of dip SA but thickness of two multilayer thin films is almost same. When the temperature of the thin film increases, the multilayer thin films by spin SA preserve its ordered structure up to 200° C in in-situ X-ray reflectivity experiment. On further heating, however, the multilayer thin films to lose ordered structure and finally the fully collapsed structures are observed around 300°C. In addition, we demonstrate that the dip and spin SA films having same internal sequence of multilayers can have remarkably different electrical characteristics owing to their structural difference. For the diodes, ultrathin films of poly(phenylene vinylene) (PPV) and poly(styrene sulfonate) (PSS) were fabricated by spin SA method as hole conductors (p-type). As electron conductors (n-type), multilayers of poly(4-vinylpyridine) (PVP) and CdSe were self-assembled by the dip or spin SA method. The relative thickness of respective layers in thin film devices could be easily controlled by the spin self-assembly. The device of ITO/(PPV/PSS)7/(PAH/PAA)/(PVP/CdSe)5/Al showed asymmetry in the I-V curve, which is the indicative of a diode behavior and the turn-on voltage of the diode was controlled by the thickness variation of the n-type multilayer.