In this blog post, I will briefly explain the principles and applications of nanoparticle patterning using the electrospray method.
We live in an era of rapid scientific and technological advancement, and you have likely come across the term “nano” at least once in newspapers or online.
I would like to briefly introduce one method in the field of nanotechnology, where active research is currently underway.
To create nano-scale devices based on nanoparticles, “nanoparticle patterning” technology—which involves attaching and arranging nanoparticles in specific locations—is essential. Technological development in this field is urgent, and globally, it is still in its early stages.
As part of this effort, a research lab in the Department of Mechanical and Aerospace Engineering at Seoul National University has developed a nanoparticle patterning technology utilizing the electrospray phenomenon, and in-depth research on this topic is currently underway.
To understand this technology, we can break it down into two main processes. The first involves spraying nanoparticles dispersed in water into the air to create fine particles, and the second involves attaching and arranging the resulting nanoparticles onto a desired substrate in specific patterns.
First, regarding the process of spraying nanoparticles dispersed in a solution into the air: a solution containing nanoparticles is placed in a syringe, and as it is extruded at a constant rate, a high voltage of about 6–7 kV is applied to the tip of the syringe needle. Unlike when there is no voltage, the liquid does not drip but is ejected from the needle tip in the shape of a sharp cone. This phenomenon is known as the Taylor cone effect.
In the Taylor cone state, the liquid is sprayed as fine droplets at a constant angle in the direction of the needle. These small droplets have a large surface area, allowing water molecules to evaporate easily; as a result, the solute that was dissolved in the solution remains and is distributed in the air in the form of nanoparticles.
Next, let’s examine how these dispersed nanoparticles are arranged into the desired shape on a substrate. Fundamentally, this process utilizes electrical properties. It leverages the electrical principle that like charges repel each other, while opposite charges attract. However, since it is difficult to create the desired shape using electrical forces alone, a “mask” is required.
The mask is a thin, electrically insulating film, roughly the same size as the substrate, with holes punched in it to match the desired pattern for the nanoparticles. The sprayed nanoparticles carry a positive (+) charge, and a negative (−) voltage is applied to the substrate. Initially, particles land both in the holes of the substrate and on the mask; however, particles that come into contact with the substrate lose their positive charge due to the substrate’s negative charge and become neutral, while those remaining on the mask retain their positive charge.
As the positive charge accumulated on the mask increases, repulsive forces arise between nanoparticles of the same charge, pushing the particles on the mask toward the holes in the substrate. Through this process, the desired pattern is formed on the substrate. Related studies have demonstrated that nanoparticles can be patterned in parallel using this electrodynamic focusing.
Additionally, reported results indicate that even though the width of the mask holes was 230 nm, the actual thickness of the formed nanoparticle pattern was approximately 50 nm, meaning the particles were deposited in a thinner layer. In other words, this suggests that patterns with thicknesses smaller than the mask holes can be obtained, enabling nanopatterning on a smaller scale.
We have briefly reviewed the basic principles and operating mechanisms of nanoparticle patterning via electrospray. As this is a relatively newly developed method, research is ongoing, and various experiments are being conducted for applications in fields such as gas sensors and protein devices.
