Statistical assessment of order within systems of nanoparticles: Determining the efficacy of patterned substrates to facilitate ordering within nanoparticle monolayers fabricated through electrophoretic deposition

Abstract

The degree of order within nanoparticle monolayers deposited through electrophoretic deposition on lithographically patterned and unpatterned substrates was analyzed using four complementary measures of order: Voronoi-cell edge-fraction entropy, local bond-orientation order parameter, translational order parameter, and anisotropy order parameter. From these measures of order, we determined that the pattern had an influence on some aspects of the ordering within the nanoparticle monolayer but had no effect on others. The Voronoi-cell edge-fraction entropy did not measurably change due to the pattern, indicating that the pattern has no effect on the number of defects present. The translational order parameter also had no change due to the pattern. The local bond-orientation order parameter had a measurable change, indicating the pattern increased the bond ordering slightly. Also, the anisotropy order parameter developed herein indicated an increase in order. The direction of the increased order corresponded with the direction of the anisotropy designed on the patterned substrate, strongly suggesting that the pattern drives the particles to become more ordered.

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

“…Figure 3d shows the same image with Voronoi tessellations only for those particles considered well-ordered. 20 In this figure, the color indicates the orientation of the hexagonal cell. From these two images, only small clusters of well-ordered iron oxide NPs were visible.…”

“…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

“…This effect is quantified as FRET efficiency e ¼ 1 À s FA =s SA (Ref. 25), where s FA and s SA are the acceptor dot recombination times in the film and in solution, respectively. In A-ML, the maximum e calculated for the shortest wavelength is 84.5%, which remains almost unchanged in the 120 min photo-excitation period.…”

Quantifying disorder in colloidal films spin-coated onto patterned substrates

“…Although there exist several methods for characterizing colloidal structures in real space [27][28][29][30], these translational-and orientational-order-based methods are more suited to homogeneous structures of reasonably high crystallinity. For example, a recent comparison of various * ayethiraj@mun.ca † wens@unav.es different methods for making colloidal crystals [30,31] uses bond-orientational order parameters that can sensitively distinguish crystals for which 0.8 < 6 < 1.…”