Electrical Resistivity
of Assembled Transparent Inorganic
Oxide Nanoparticle Thin Layers: Influence of Silica, Insulating Impurities,
and Surfactant Layer Thickness
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Abstract
The electrical properties of transparent, conductive
layers prepared
from nanoparticle dispersions of doped oxides are highly sensitive
to impurities. Production of cost-effective thin conducting films
for consumer electronics often employs wet processing such as spin
and/or dip coating of surfactant-stabilized nanoparticle dispersions.
This inherently results in entrainment of organic and inorganic impurities
into the conducting layer leading to largely varying electrical conductivity.
Therefore, this study provides a systematic investigation on the effect
of insulating surfactants, small organic molecules and silica in terms
of pressure dependent electrical resistivity as a result of different
core/shell structures (layer thickness). Application of high temperature
flame synthesis gives access to antimony-doped tin oxide (ATO) nanoparticles
with high purity. This well-defined starting material was then subjected
to representative film preparation processes using organic additives.
In addition ATO nanoparticles were prepared with a homogeneous inorganic
silica layer (silica layer thickness from 0.7 to 2 nm). Testing both
organic and inorganic shell materials for the electronic transport
through the nanoparticle composite allowed a systematic study on the
influence of surface adsorbates (e.g., organic, insulating materials
on the conducting nanoparticle’s surface) in comparison to
well-known insulators such as silica. Insulating impurities or shells
revealed a dominant influence of a tunneling effect on the overall
layer resistance. Mechanical relaxation phenomena were found for 2
nm insulating shells for both large polymer surfactants and (inorganic)
SiO<sub>2</sub> shells