This is an orientation map of a spin-cast array of FePt nanoparticles. Most nanoparticles are enclosed by a hexagon of six neighboring nanoparticles. Each nanoparticle was color coded according to the angle (in degrees) of the hexagon’s orientation. Credit: North Carolina State Univ.
Researchers from North Carolina State Univ. have investigated the viability
of a technique called “spincasting” for creating thin films of nanoparticles on
an underlying substrate—an important step in the creation of materials with a
variety of uses, from optics to electronics.
Spincasting, which utilizes centrifugal force to distribute a liquid onto a
solid substrate, already has a variety of uses. For example, it is used in the
electronics industry to deposit organic thin films on silicon wafers to create
For this study, the researchers first dispersed magnetic nanoparticles
coated with ligands into a solution. The ligands, small organic molecules that
bond directly to metals, facilitate the even distribution of the nanoparticles
in the solution—and, later, on the substrate itself.
A drop of the solution was then placed on a silicon chip that had been
coated with a layer of silicon nitride. The chip was then rotated at high
speed, which spread the nanoparticle solution over the surface of the chip. As
the solution dried, a thin layer of nanoparticles was left on the surface of
Using this technique, the researchers were able to create an ordered layer
of nanoparticles on the substrate, over an area covering a few square microns. “The results are promising, and this approach definitely merits further
investigation,” says Dr. Joe Tracy, an assistant professor of materials science
and engineering at NC State and co-author of a paper describing the study.
explains that one benefit of spincasting is that it is a relatively quick way
to deposit a layer of nanoparticles. “It also has commercial potential as a
cost-effective way of creating nanoparticle thin films,” Tracy says.
However, the approach still faces several hurdles. Tracy notes that modifications to the
technique are needed, so that it can be used to coat a larger surface area with
nanoparticles. Additional research is also needed to learn how, or whether, the
technique can be modified to achieve a more even distribution of nanoparticles
over that surface area.
Analysis of the nanoparticle films created using spincasting led to another
development as well. The researchers adapted analytical tools to evaluate
transmission electron microscopy images of the films they created. One benefit
of using these graphical tools is their ability to identify and highlight
defects in the crystalline structure of the layer. “These methods for image
analysis allow us to gain a detailed understanding of how the nanoparticle size
and shape distributions affect packing into monolayers,” Tracy says.
The paper, “Formation and Grain Analysis of Spin Cast Magnetic Nanoparticle
Monolayers,” was published online by Langmuir. The paper was
co-authored by Tracy;
NC State PhD student Aaron Johnston-Peck; and former NC State post-doctoral
research associate Dr. Junwei Wang. The research was funded by the National
Science Foundation, the U.S. Department of Education, and Protochips, Inc.
NC State’s Department of Materials Science and Engineering is part of the