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.

Stabilization of 1T-MoS2 Sheets by Imidazolium Molecules in Self-Assembling Hetero-layered Nanocrystals

“…[13][14][15][16][17] The 2H-1T transformation was recently found to involve gliding atomic planes of sulphur and/or molybdenum and proceeds via intermediate phases. 18 Such a transition was shown to switch the properties of the MoS 2 sheet from semiconducting to metallic [19][20][21] thus allowing, for instance, realization of electronic heterostructures within the parent structure, 17 preparation of highly-conductive films, 22 supercapacitor electrode materials 23 and efficient catalysts of hydrogen evolution reaction (HER). 24,25 The electron doping of the MoS 2 sheets provided by the electric double layer, in which the induced surface negative charge is balanced by the imidazolium or alkylammonium cations of the ionic liquid salt, was recently shown to result in metallic behavior of these sheets, providing excellent band transport characteristics in active FET channels 2,26,27 and even superconducting properties.…”

Shape and size selective separation of gold nanoclusters by competitive complexation with octadecylamine monolayers at the air–water interface

“…In a totally different approach, the growth of multilayer nanoparticle films by the LB technique was also shown to be possible through interaction of suitably derivatized colloidal particles from the sub phase with the polar group of the Langmuir monolayers [13][14][15]. Electrostatic interaction having a important role in biological and chemical processes [16] have only recently been investigated for the growth of multilayer of polyelectrolyte [17,18] and nanoparticle-polyelectrolyte films [19], as well as micron-sized objects [20]. Sastry's group has synthesized thin films of nanocomposites of surface-modified colloidal particles with fatty lipid molecules via selective electrostatic interaction both in Langmuir monolayers [21][22][23][24][25][26][27][28] and by diffusion in thermally evaporated films [29][30][31][32][33].…”

Langmuir and Langmuir-Blodgett Films of Organic Dye-Inorganic Nanosheet Hybrids

“…Inorganic nanosheets are ultrathin (~1 nm thick) and large (~1 m wide) ordered materials that are useful in constructing functional nanosystems [1,2]. Since most of the inorganic nanosheets are negatively charged, they can adsorb Langmuir films made of cationic surfactants spread on their aqueous colloidal suspensions [1].…”

“…Since most of the inorganic nanosheets are negatively charged, they can adsorb Langmuir films made of cationic surfactants spread on their aqueous colloidal suspensions [1].…”