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

Inorganic/organic hybrid ultrathin films of MoS 2 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 MoS 2 particles into the subphase. On the other hand, the isotherms of icosanoic acid in the presence and absence of MoS 2 particles in the subphase were essentially the same. The UV/vis reflection spectra of DHA + (Br - ) monolayers on MoS 2 suspension showed a broad absorption band assignable to MoS 2, whereas that of icosanoic acid did not show any appreciable band. These results suggest the formation of hybrid monolayers consisting of DHA + and MoS 2 . 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 MoS 2 showed flat, plate-like particles with diameters in the submicrometer region. The structure of the hybrid LB films depended strongly on the MoS 2 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 MoS 2 concentration in the subphase while the amount of MoS 2 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 MoS 2 concentration in the subphase was large. A model of the formation of the hybrid film was proposed.