Using Voronoi Tessellations to Assess Nanoparticle–Nanoparticle Interactions and Ordering in Monolayer Films Formed through Electrophoretic Deposition

Abstract

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.

Comparing Highly Ordered Monolayers of Nanoparticles Fabricated Using Electrophoretic Deposition: Cobalt Ferrite Nanoparticles versus Iron Oxide Nanoparticles

“…Studies of iron oxide NPs suggest that limited mobility is still available, as ordering occurs after deposition. 19 Still, whether particles could traverse distances of >8 NP diameters (size of voids in the cobalt ferrite films) after interacting with the substrate remains uncertain. Additionally, if magnetic interactions are driving the ordering, the nanoparticles should have aligned crystal structures.…”

“…19 Iron oxide NPs behaved paramagnetically with a magnetic moment of 1800μ B per NP. In contrast, magnetic hysteresis measurements of cobalt ferrite NPs indicated ferromagnetic behavior of the NPs with a magnetic moment of ∼26,000μ B per NP (Figure 2).…”

“…In this light, recently developed statistical measurement tools have been demonstrated to be effective in quantifying the degree of ordering within monolayers of nanoparticles. 19,20 Motivated by this work, this article explores the application of these tools to two different systems (iron oxide and cobalt ferrite nanoparticles) and the observation of markedly different degrees of order in the systems. Based on physical measurements of the NP systems, the mechanisms behind the ordering in each system are deduced.…”

“…[10][11][12][13][14][15][16] A recently developed EPD technique has been able to create locally ordered monolayers of NPs. [16][17][18][19][20][21] Understanding the mechanisms that create the ordering could allow one to tune the ordering to create supercrystals using EPD. In this light, recently developed statistical measurement tools have been demonstrated to be effective in quantifying the degree of ordering within monolayers of nanoparticles.…”

Increased photo-stability of quantum dots in segregated bilayer films

“…[26][27][28][29][30] The details of how we calculated the primary peak values of the radial distribution function are described elsewhere. 31 The first peak in the RDF was fit to a Gaussian distribution in Fig. 4(b); the mean value of this peak corresponded to an inter-nanoparticle spacing of 9.1 6 0.6 nm.…”