G. Hemakanthi et al., Formation of nickelhydroxy sulfide precursor and nickel sulfide in Langmuir and Langmuir-Blodgett films of a nickel complex of octadecylsuccinic acid, THIN SOL FI, 384(2), 2001, pp. 206-211
The influence of parameters on size of NiS particles formed at ambient temp
eratures by reacting Na2S with the nickel salt of octadecylsuccinic acid (O
DSA) at the air/water interface and in Langmuir-Blodgett films was investig
ated by changes in surface pressure-molecular area (pi -A) and surface pote
ntial-molecular area (DeltaV-A) isotherms. The contraction in area of ODSA
on Ni2+ subphase is indicative of a strong interaction of the dibasic acid
with Ni2+ leading to a monodentate complex of Ni2+ with ODSA. The Langmuir
monolayers of the nickel complex of ODSA were analysed using Brewster angle
microscopy (BAM). In the absence of nickel in the subphase, ODSA exhibited
no domains in BAM. The sulfidation reaction on ODSA/Ni2+ complex at the ai
r/water interface shows two steps as seen in the surface potential vs. time
plot corresponding to formation of Ni(OH)S initially which then changes to
NiS. The domain size seen with NiS formation increased with time and surfa
ce pressure indicating the growth of a two-dimensional solid complex in the
monolayer at the air/water interface. The Langmuir-Blodgett (LB) films of
ODSA/Ni2+ on sulfidation transferred onto solid substrates from the two ste
ps in the reaction were characterized using diffuse reflectance UV-visible
spectroscopy (DIR-UV-vis) and X-ray photoemission spectroscopy. These exper
iments confirmed the reduction process involved in the above reaction. Atom
ic force microscopy experiments on these LB films indicated that there is a
variation in the structural organization in the monolayers and in the morp
hology of the LB film, depending on the initial Ni(OH)S formation which ult
imately leads to NiS. The results show that the average particle size which
varies between 2 and 3.5 nm depends on the nature of the nickel complexes
formed at the air/water interface. (C) 2001 Elsevier Science B.V. All right
s reserved.