S. Mulley et al., ORDERING AND MANIPULATION OF MOS2 PLATELETS ON DIFFERENTLY CHARGED MICAS BY ATOMIC-FORCE MICROSCOPY, Journal of materials chemistry, 6(4), 1996, pp. 661-666
Atomic force microscopy (AFM) has been used to investigate how dispers
ed MoS2 platelets (from colloidal suspensions) deposit onto three natu
ral(Muscovite) mica (001) surfaces. Different platelet arrangements ar
e observed, which are attributed to defects and charging effects of th
e mica (as well as the concentration of starting colloid). The provena
nce of the mica influences the self-organisation of the platelets into
long tape-like assemblies (South Dakota mica) or individual flakes (A
lps mica). Atomic scale imaging of the tapes reveals a distorted octah
edral (O-h)-based local structure, different from the trigonal prismat
ic structure found in the 2H-polytype of annealed MoS2, in agreement w
ith previous structural results on water-dispersed MoS2 platelets. The
buckling and susceptibility to stripping of the tapes is ascribed to
the presence of a water layer between the substrate mica and MoS2, and
after stripping by the tip, the platelets ultimately form small clust
ers. The ordering of these clusters depends not only on the defect and
charge structure of the mica, but also on complex hydration reactions
between the H2O layer associated with the MoS2 and K+ ions of the mic
a. Relatively symmetrical squares may be lifted out of the tapes, supp
orting the presence of weak bonding between tape and mica. Conversely,
Alps and Bihar micas give rise to separate platelets, which are resis
tent to tip manipulation, which is attributed to hydrophobic interacti
on between MoS2 platelets and the mica surface.