국립 부경대학교

Joint research team of prof. Lee Seung-Hun from PKNU developed achromatic copper with preserving oxidation resistance

- joint research between PKNU, Busan national univ., Sungkyunkwan univ., and Mississippi state college

△ Representative images of the research (a) color control of porous nanostructured copper thin films, (b) Figure 3d shows achromatic copper and transmission electron microscopy of its nanostructured surface, (c) Wetting properties change process according to porosity of colorless copper

A joint research team with professor Lee Seung-Hun (dept. of physics) from Pukyong National University (President Jang Young-Soo) developed single-crystal copper that does not rust and can achieve continuous achromatic colors from gray to black.

The joint research team, which included researchers from Pukyong National University, Busan national university, Sungkyunkwan university, and Mississippi state college, identified the growth mechanism of colorless copper, the cause of oxidation resistance, and the specificity of the grown copper surface through theory and experiment.

The paper 'self-oxidation resistance of the curved surface of achromatic copper' containing the results of this research was introduced in the world-renowned academic journal <advanced materials> (IF: 29.4).

Last year, professor Jeong Se-Young (dept. Of optics and mechatronics)'s research team at Busan national university attracted attention by producing copper (Cu) with an atomic-level flat surface and suggesting a mechanism to prevent this copper from being oxidized. This time, the research team recently developed a copper growth technology that controls the growth conditions of thin copper films to achieve a variety of achromatic colors from light gray to complete black.

The joint research team suggested that the color of this achromatic copper is due to its nanostructure, and that it can have a variety of achromatic colors as the degree of light confinement varies depending on the density and size of pores within the nanostructure and the connectivity between pores.

Although colorless copper has a complex dendrite structure similar to the shape of tree branches or dendrites, oxidation does not occur. The research team found that the surface of the dendritic structure is made up of a series of single atomic layers, and that 2 to 3 surface layers made of atoms shrink to about 20 pm (picometre, one trillionth of a metre) due to surface tension, making it difficult for oxygen that causes oxidation to penetrate through the copper surface layer.

Professor Lee's research team paid intensive attention to the applicability that this colorless copper could have. He said, "Hydrophobicity refers to the property of not easily combining with water molecules, and refers to a property that is generally observed in organic substances. This characteristic is due to the fact that lotus leaves do not get wet easily and the car wax coating. We thought that nanostructures with many fine pores, such as colorless copper, could have high hydrophobic properties."

By investigating the wetting properties of achromatic copper, the Pukyong National University research team of professor Lee Seung-Hun, Nam Gi-Deuk in his master's program, and professor Park Sung-Heum confirmed that the wetting properties can be switched very stably and reversibly from superhydrophobicity to super hydrophile property through post-processing.

Through this study, they found that stable wettability switching properties were not possible with other coppers and were due to the unique structural properties of achromatic copper. The property of wettability switching can be utilized in microfluidic devices such as droplet pumps and tweezers, as well as fluid filters and microarray/library technologies. Various applications are expected in the future through synergy between the metallic properties of copper materials and the light-trapping properties of nanostructures that create achromatic colors.

Professor Lee said, "This is the result of efforts obtained through joint research by experts in various fields ranging from material production, analysis, and theory, and I believe it is a result that clearly shows the importance and interest of new materials."

△The researchers. (From left) Professor Lee Seung-Hun from Pukyong National University (co-first author), professor Jeong Se-Young from Busan national university (corresponding author), and professor Kim Young-Min from Sungkyunkwan university (corresponding author).