Fabrication of Hybrid Layered Films of MoS2 and an Amphiphilic Ammonium Cation Using the Langmuir−Blodgett Technique

Abstract

Inorganic/organic hybrid ultrathin films of MoS2 and a cationic amphiphile, dihexadecyldimethylammonium bromide (DHA+Br-), were prepared using the Langmuir−Blodgett (LB) technique. The surface pressure−area isotherms of DHA+Br- changed by introducing exfoliated MoS2 particles into the subphase. On the other hand, the isotherms of icosanoic acid in the presence and absence of MoS2 particles in the subphase were essentially the same. The UV/vis reflection spectra of DHA+(Br-) monolayers on MoS2 suspension showed a broad absorption band assignable to MoS2, whereas that of icosanoic acid did not show any appreciable band. These results suggest the formation of hybrid monolayers consisting of DHA+ and MoS2. The hybrid monolayers were transferred successfully onto substrates using a horizontal lifting method to form LB films. That was confirmed by the infrared and UV/vis absorption spectroscopies and AFM, although the transfer ratios were not determined. The X-ray diffraction patterns of the LB films showed the layered structure in which organic and inorganic sheets are stacked alternately. The AFM image of a single-layer LB film of DHA+ and MoS2 showed flat, plate-like particles with diameters in the submicrometer region. The structure of the hybrid LB films depended strongly on the MoS2 concentration in the subphase for the preparation of the hybrid monolayers. The number of DHA+ molecules per unit area of the LB film increased with increasing MoS2 concentration in the subphase while the amount of MoS2 in the LB film remained unchanged. Further, the tilt angle of the hydrocarbons of DHA+ was large and the interlayer spacing of the LB film was small when the MoS2 concentration in the subphase was large. A model of the formation of the hybrid film was proposed.