▲(From left) Professor Man Soo Choi of the Department of Mechanical Engineering at Seoul National University, Professor Junsuk Rho of the Department of Mechanical Engineering at Pohang University of Science and Technology, Postdoctoral Researcher Wooik Jung graduate student Yoon-Ho Jung of the Department of Mechanical Engineering at Seoul National University

Seoul National University College of Engineering (Dean Kookheon Char) announced that a 3D nanoprinting technology that can produce 100 nanometer three-dimensional structures was developed through a joint research by Professor Man Soo Choi's team of the Department of Mechanical Engineering and with Professor Junseok NohJunsuk Rho's team at Pohang University of Science and Technology and was published online on April 1 in the world renown journal 'Nature'.
 
The research team has succeeded in developing a practical technology that can produce thousands of three-dimensional nanostructures simultaneously, which is less than 1/100 of the size of structures that can be produced with existing technologies. Its differential point is that no polymer or ink is used and it is possible to produce ultra-high purity structures with minimal impurities by assembling after generating metal nano aerosols using a dry method. The inclusion of impurities makes a difference in the conductivity or physical properties of the metal and thus is greatly important in fields of applications that are based on the properties of the metal.
 
The current three-dimensional printing technology is a key element of the fourth industrial revolution and is causing a major change in industrial manufacturing technology, however, this study is expected to reach beyond its limitations to revolutionize industrial manufacturing technology as it can even practically produce three-dimensional nanometallic structures.
 
The 3D nano-printing technology can dramatically improve the performance of existing devices by making it possible to manufacture 3D nano-sensors with high sensitivity and 3D nano-electronic devices that can maximize the degree of integration. In the case of the 3D nano gas sensors, it is calculated that the sensitivity can be increased by more than twice when compared to the existing 2D film type.
 
In addition, it even makes it possible to implement new devices that do not exist. For example, in the manufacturing of metamaterials that artificially design and implement physical properties that do not exist in nature, it is essential to make an array of sophisticated 3D nanostructures, which can be implemented using the 3D nano-printing technology that was developed by the research team.
 
It has been shown that the commercialization of metamaterials, a new material in the future, can be accelerated by fabricating an array of 3D nanometal structures of a specific shape using the 3D nano-printing technology that was announced, after which the desired artificial magnetic properties can be implemented.
 
The production process is as follows. When charged nanoparticles and ions are injected into the deposition chamber in which the non-conductive mask has micrometer-sized holes aligned and the silicon substrate is separated horizontally, the ions first accumulate above the mask to form electrostatic lenses for each micrometer-sized hole. The principle of concentrating such charged nanoparticles arriving through the electrostatic lens to the center of the hole and concentrating them into an aerosol jet at the level of 100 nanometers was used in a new 3D printing technology.
 
If the 3-dimensional transfer of the silicon substrate occurs at the same time as the attachment of nanoparticles, it is possible to produce thousands of 3D nanostructures of the desired shape at once, and if the mask hole is made smaller, the research team believes that it would be possible to produce 3D nanostructures that are smaller than tens of nanometers or less.
 
"I am pleased to see the fruitful results of having worked with the graduate students for the past 10 years to develop the 3D nano-printing technology using aerosol technology and I am looking forward to the innovative development of Korea's industrial manufacturing technology through this research," said Professor Man Soo Choi of Seoul National University, the research director.
 
“This three-dimensional nano-printing technology is an innovative production technology that can create nanometer-level arbitrary shape three-dimensional structures that were the biggest challenges in the field of metamaterials that became known as negative refractive index, superlens, and transparent cloak technology,” said the co-corresponding author Professor Junsuk Rho of POSTECH.
 
The results of this research were accomplished through the participation of Seoul National University, Pohang University of Science and Technology, the Institute of Physical and Chemical Research (RIKEN) of Japan, the Global Frontier Multiscale Energy System Research Group and the Wave Energy Extreme Control Research Group supported by the Ministry of Science and ICT, the Korea Research Foundation's Mid-sized Researcher Support Project and the Leading Regional Innovation Research Center.
 
 
[About the Research Paper]
Title Three-dimensional Nanoprinting via Charged Aerosol Jets
Journal: Nature (Published online on April 1 DOI: 10.1038/s41586-021-03353-1)
Author:
Research Director and Corresponding Author: Professor Man Soo Choi (Seoul National University)
Co-corresponding author: Professor Junsuk Rho (POSTECH)
Co-corresponding author: Dr. Wooik Jung (Seoul National University), Yoon-Ho Jung (Seoul National University Ph.D. candidate)
 
All the authors: Wooik Jung (Seoul National University), Yoon-Ho Jung (Seoul National University), Peter V. Pikhitsa (Seoul National University), Jicheng Feng (Seoul National University), Younghwan Yang (POSTECH), Minkyung Kim (POSTECH), Hao-Yuan Tsai (RIKEN), Takuo Tanaka (RIKEN), Jooyeon Shin (Seoul National University), Kwang-Yeong Kim (Seoul National University), Ho Seob Choi (Seoul National University), Junsuk Rho (POSTECH), Man Soo Choi (Seoul National University)

 

▲ A three-dimensional nano-printing structure that can produce thousands of three-dimensional nanostructures simultaneously using aerosol technology

A 3D nano-stage in which an electrode and a conductive silicon substrate are combined is placed in a deposition chamber in an atmospheric pressure environment and a non-conductive silicon nitride (SiNx) mask aligned with thousands of holes that are of several micrometers in size is separated by several micrometers on the substrate.
 
Through this arrangement, the substrate bonded to the 3D nano-stage can move freely without touching the mask to provide an environment in which a 3D nanostructure can be manufactured. Subsequently, a negative voltage is applied to the electrode and the substrate with a power supply to form an electric field inside the deposition chamber.
 
Positively charged nanoparticles and cations generated by spark discharge enter the deposition chamber through the injection port along the nitrogen gas, after which they follow the electric field inside the chamber to the mask surface. As ions having a smaller mass than the charged nanoparticles first accumulate on the mask surface, a flat equipotential surface is distorted in a convex shape for each mask hole to form an electrostatic lens.
 
Charged nanoparticle aerosol jets that follow through the electrostatic lens can be collected into the center of a few micro-sized pores and become focused at the level of 100 nanometers and the aerosol jets passing through the mask holes are stacked continuously on the substrate, resulting in thousands of 3-dimensional nanostructures that can be produced simultaneously (at atmospheric pressure) in an array on the same substrate.
 
In particular, since structures can be produced through electrostatic lenses regardless of the type of charged nanoparticles' substance, three-dimensional nano-structure arrays can be produced by minimizing impurities as they do not use any polymer or ink.

By moving three-dimensional nano-stages, it is possible to produce three-dimensional nano-structure arrays of various shapes in "growth mode" and "writing mode" by controlling the shape of the inferior nanoparticle aerosol jet. In "growth mode," a three-dimensional nano-structure array, such as vertical nano-columns, tilted nano-columns or spiral nano-structures rotated by more than one revolution was produced by slowly moving or stopping the three -dimensional nano-stage. In addition, after producing the nanostructure array, the substrate was moved to the empty space between the structures and the same printing was repeated again to increase the density of the structure array.

In "writing mode", the three -dimensional nano-stage is moved at high speed to continuously point the inferior nanoparticle aerosol jet to the substrate surface, which is written like a letter on the substrate surface along the movement of the three-dimensional nano-stage.

Both modes were used to produce a vertical split ring resonator array, one of the three-dimensional metamaterial structures that is difficult to make using conventional methods and to confirm its applicability to metamaterials by demonstrating the strong magnetic resonance at certain wavelengths of light.
 
[Expected Benefits]
Since it is possible to easily produce an array of nanometer-sized 3D nanostructures simultaneously - something that was difficult to manufacture using the existing 3D printing technology – it is expected that there will be a breakthrough in the industrial fields that require nano-processing such as 3D nano-sensors that have higher sensitivity than before or 3D nano-electronic devices that are smaller and higher in intensity.
 
In addition, in fields such as that of metamaterials that have physical properties that did not exist in the natural world, it is expected that the use of this technology will allow the manufacturing and development of 3D nanostructures with new physical properties that did not exist before.