Alex J. Krejci

Evolution of Ordering in Iron Oxide Nanoparticle Monolayers Using Electrophoretic Deposition

Iron-oxide nanoparticle monolayers and multilayers were assembled using dc electrophoretic deposition. The rate of deposition and the total particle deposition were controlled by varying the concentration of nanoparticles and the deposition time, respectively. Using scanning electron microscopy, we performed a time-resolved study that demonstrated the growth of the monolayer from a single isolated nanoparticle to a nearly complete layer. We observed tight, hexagonal packing of the nanoparticles indicating strong particle-particle interaction. Multilayer growth was assessed using scanning electron microscopy and atomic force microscopy, revealing a monolayer-by-monolayer growth process.

Patterned substrates to facilitate long-range ordering in the formation of nanoparticle monolayers by electrophoretic deposition

Nanoparticle submonolayer and monolayer films were deposited using electrophoretic deposition onto silicon substrates that were patterned with arrays of hexagonally ordered polymeric structural elements. Line structures of four different lengths were fabricated on the substrates by electron-beam lithography. Scanning electron microscopy, used to analyze the deposited nanoparticle films, confirmed that the particles tended to align along the faceted edges of these structures. Such phenomena appeared to promote correlations among the nanoparticles that facilitated ordered arrangements within the monolayers and sub-monolayers.

Using Voronoi tessellations to assess nanoparticle-nanoparticle interactions and ordering in monolayer films formed through electrophoretic deposition.

Monolayers of iron oxide nanoparticles of two different sizes, 9.6 nm and 16.5 nm, were fabricated through electrophoretic deposition. The arrangements of nanoparticles within the films were analyzed using the technique of Voronoi tessellations. These analyses indicated that the films possessed equivalent degrees of ordering, and that the films were uniform over centimeter length scales. Precise measurements of the interparticle spacing were obtained, and the magnitudes of magnetic dipole interactions were calculated. The dipole-dipole interaction among the larger nanoparticles was 14 times larger than that of the smaller nanoparticles, indicating that magnetic coupling interactions could not have been the lone source of ordering in the system.

X-ray scattering as a liquid and solid phase probe of ordering within sub-monolayers of iron oxide nanoparticles fabricated by electrophoretic deposition

Order within sub-monolayers of nanoparticles, fabricated by electrophoretic deposition, was assessed during nanoparticle deposition in a liquid suspension and after the films had dried by grazing-incidence small-angle X-ray scattering. Experiments were performed in a custom-made, liquid-phase cell. The results indicated that ordering occurred during the drying event.

Kinetics of monolayer and bilayer nanoparticle film formation during electrophoretic deposition

Abstract The kinetics of electrophoretic deposition are studied for the growth of monolayers and bilayers of ∼10 nm iron oxide nanoparticles. The net deposited nanoparticle film is measured as a function of time for five voltages through analysis of scanning electron microcopy images of the films. The collected data suggest that films deposited at different voltages have different kinetic behaviours. Additionally, we observe monolayer and bilayer growth separately, from which we assert that the initiation of the bilayer may be the source of variation in kinetic behaviour.

Selective Deposition of TiO2 during Monolayer Formation of TiO2 and Iron Oxide Nanocrystals by Electrophoretic Deposition in Non-Polar Solvents

The electrophoretic deposition of TiO2 iron oxide nanocrystal monolayers from stable, mixed colloidal suspensions by electrophoretic deposition using non polar solvents is reported. The selective deposition of TiO2 was accomplished by controlling the mobility of the nanocrystals and the voltage during electrophoretic deposition. The effect of the electrophoretic deposition processing parameters (voltage and particle mobility) on the promotion and suppression of nanocrystal deposition was investigated.

Current Measurements as a Direct Diagnostic for Sub-Monolayer Growth of Nanoparticle Films in Non-Polar Electrophoretic Deposition

Electrophoretic current densities and nanoparticle densities were measured during and after the electrophoretic deposition of iron oxide nanoparticles and were compared to infer the relationship between the quantity of deposited nanoparticles and the measured current. This information led to an assessment of the primary contributors to the measured current during non-polar solvent-based electrophoretic deposition. Such information was employed to monitor and to control sub-monolayer growth of nanoparticle films. Subsequently, the average charge magnitude of each suspended colloidal nanoparticle was calculated to be ±3.2 ± 0.3 electron charges.