Indium
tin oxide (ITO) nanoparticles (NPs) with protrusions on
their surfaces have been successfully obtained by solvothermal synthesis
under high In3+ and Cl– concentrations.
High-resolution transmission electron microscopy (HR-TEM) observations
revealed that the ITO NPs with protrusions consisted of not a polycrystalline
but a single-crystalline structure. The results suggested that the
unique shape was produced by heterogeneous epitaxial nucleation on
the growing surfaces of the ITO NPs in the presence of tetramethylammonium
hydroxide (TMAH). Inhibition of homogeneous particle growth by adsorption
of a large excess amount of Cl– ions on the surfaces
of growing ITO NPs might play a critical role in the evolution of
the unique protrusions. Compared to single-crystalline ITO NPs with
a cubic shape, the ITO NPs thus obtained showed a high specific surface
area and a low resistivity. Furthermore, the ITO NPs with protrusions
exhibited an unprecedented high dispersion stability in water for
a long period without the use of any dispersant. 1H nuclear
magnetic resonance (NMR) relaxation (T
2) measurements revealed that such high dispersion stability could
be due to the shape-triggered increase in the hydrophilicity of the
surfaces of the ITO NPs. The resulting ITO NP dispersions in water
could be applied to prepare ITO thin films with low resistivity on
a glass substrate. The behavior has great potential for application
as sustainable coating materials to fabricate transparent conductive
ITO thin films on flexible substrates under mild atmospheric conditions
without usage of expensive production systems and harmful and environmentally
undesirable chemicals.
Gallium-doped zinc
oxide (GZO) nanoparticles (NPs) have been synthesized
by a solvothermal synthesis method using gallium chloride and zinc
chloride as precursors in anhydrous methanol along with bases. Systematic
investigations have revealed that H2O, formed through the
condensation of metal hydroxides to obtain GZO NPs, not only enhances
the production of layered compounds as byproducts but also accelerates
Ostwald ripening to reduce the amount of doped gallium ions. To overcome
H2O generation during NP growth, we first applied sodium
methoxide (NaOMe) as a base for the synthesis of GZO NPs. As a result,
high-performance GZO NPs were successfully obtained in a single phase,
and the mean particle size of the GZO NPs was controlled from 10 to
35 nm by changing the molar ratio of the sodium hydroxide (NaOH) and
NaOMe in the reaction mixture. We further applied the obtained GZO
NPs to prepare GZO NP-based transparent conductive metal oxide (TCO)
films using an NP-mist deposition strategy as our developed NP-coating
method on substrates. The resistivity and transparency of the deposited
GZO thin films were compared with those of conventional thin films
prepared by a dispersion coating method, showing that NP-mist deposition
is a promising method for fabricating high-performance GZO NP-based
TCO thin films on substrates under mild atmospheric conditions.
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