title: Electrical resistivity of assembled transparent inorganic oxide nanoparticle thin layers: influence of silica, insulating impurities, and surfactant layer thickness.
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(2) shells.
authors.affiliation: Functional Materials Laboratory, Institute for Chemical and Bioengineering, ETH Zurich, CH-8093 Zurich, Switzerland.
authors.forename: Stephanie B
authors.initials: SB
authors.lastname: Bubenhofer
authors.forename: Christoph M
authors.initials: CM
authors.lastname: Schumacher
authors.forename: Fabian M
authors.initials: FM
authors.lastname: Koehler
authors.forename: Norman A
authors.initials: NA
authors.lastname: Luechinger
authors.forename: Georgios A
authors.initials: GA
authors.lastname: Sotiriou
authors.forename: Robert N
authors.initials: RN
authors.lastname: Grass
authors.forename: Wendelin J
authors.initials: WJ
authors.lastname: Stark