Pukyong National University

Technology Developed to Create Ultrafine Surface Features Below 50 Nanometers―Approximately One-Thousandth the Thickness of a Human Hair―Using Commercial 3D Printers

― Pukyong National University Joint Research Team Overcomes the Resolution Limits of Commercial SLA 3D Printers with ‘Nano-Seed’ Technology

A “Nano-Seed-Assisted Stereolithography (SLA) Technology” has been developed that enables ultrafine surface patterns measuring less than 50 nanometers (nm, one-billionth of a meter)―previously difficult to achieve using commercial stereolithography 3D printers alone―to be formed on complex, free-form three-dimensional structures.

The achievement is the result of a joint study led by Professor Woon-Ik Park of the Department of Materials Science and Engineering at Pukyong National University. The research team included Dr. Tae-Wan Park of Northwestern University, doctoral student Eun-Bin Kang of Ulsan National Institute of Science and Technology (UNIST), and master’s graduate Young-Rim Kang of Pukyong National University, in collaboration with Professor Min-Sun Lee’s research team at Daegu Gyeongbuk Institute of Science and Technology (DGIST) and Dr. Diana Jung’s research team at Stanford University in the United States.

The research team successfully created nanopatterns even on the hair and forehead of a Buddha sculpture with a complex geometry, demonstrating that ultrafine surface structures can be integrated with free-form 3D printing in a single process.

Stereolithography (SLA) is a widely used 3D printing technology that creates three-dimensional structures by curing liquid resin with light. Although it offers the advantages of smooth surfaces and highly precise geometries, directly producing ultrafine surface structures at the nanometer scale has remained difficult because of light diffraction and the diffusion of photopolymerization reactions within the resin.

In practice, the commercial SLA 3D printer used in the study could reliably produce lines only as narrow as approximately 250 micrometers (μm, one-millionth of a meter) without the Nano-Seed technology. By applying the technology, however, the researchers successfully produced ultrafine lines measuring less than 50 nanometers. This represents structures approximately 5,000 times finer than the resolution limit of the commercial printer, equivalent to about one-thousandth the thickness of a human hair.

The researchers devised a method in which a “Nano-Seed,” created by replicating nanopatterns from a silicon (Si) master mold onto a thin polymethyl methacrylate (PMMA) film, is attached to the 3D printer’s build plate. An ultrathin inorganic barrier layer approximately 30 nanometers (nm) thick is then formed over the Nano-Seed. This barrier prevents the resin from mixing with the Nano-Seed and confines the photocuring reaction to the interface, allowing the nanopatterns to be transferred with high precision.

Using this method, the researchers precisely produced a variety of nanopatterns―including dots, holes, waves, and cross-shaped structures―ranging in size from 250 nanometers to 2 micrometers. They also successfully created ultrafine line patterns measuring less than 50 nanometers. In addition, the nanopatterns were formed uniformly over areas as large as 45 by 75 millimeters (mm), nearly the size of a business card, demonstrating the technology’s potential for large-area processing.

The research team further validated the practicality of the technology by applying it to actual 3D-printed structures. While it has traditionally been difficult to fabricate nanometer-scale surface features on complex three-dimensional objects with free-form curved surfaces, the researchers successfully created nanopatterns on the hair and forehead of a Buddha sculpture using the newly developed technique. They demonstrated not only the fabrication of a separate nanopatterned component that could be assembled onto the sculpture, but also the direct production of a fully integrated Buddha sculpture containing nanopatterns during the printing process without any additional assembly. This achievement demonstrates that nanopatterns, which previously required post-processing or separate assembly, can now be incorporated directly into the 3D printing process. The technology therefore integrates nanometer-scale surface patterning and the fabrication of complex three-dimensional structures into a single manufacturing process.

This study represents a successful integration of nanopatterning and 3D printing technologies, highlighting its potential applications in a wide range of fields, including surfaces with optical properties, anti-counterfeiting security markings, and biomimetic surfaces designed to control adhesion and fluid behavior.

Professor Woon-Ik Park said, “This study is significant because it demonstrates that nanometer-scale surface structures can be produced by precisely controlling the printing interface without modifying the optical components of a commercial 3D printer. We expect the technology to be applied to the fabrication of optical and photonic surfaces, anti-counterfeiting markings, biomimetic structures, and various functional 3D-printed components.”

Dr. Tae-Wan Park, doctoral student Eun-Bin Kang, and master’s graduate Young-Rim Kang contributed equally to the study as co-first authors. The co-authors included master’s student Yu-Na Kim, undergraduate student Yu-Jin Kang, Professor Kang-Jun Baek, and Professor Sung-Dae Kim of Pukyong National University; Professor Hoo-Young Jung of UNIST; and Professor Seung-Sae Hong of the University of California, Davis (UC Davis). Corresponding author Professor Woon-Ik Park is jointly affiliated with Pukyong National University, UC Davis, and RANO-M Co., Ltd.

The study was conducted as part of a research project funded by the Ministry of Science and ICT and administered by the National Research Foundation of Korea. The findings were recently published online in the international academic journal 『Small Structures』 under the title ‘Sub-50 nm Surface Nanopatterning via Nano-Seed Assisted Stereolithography.’ <Pukyong Today>