Korean researchers revealed the principle of copper oxidation at the atomic level A Korean research team has succeeded in elucidating the principle of the oxidation process of copper by making the worlds thinnest and smoothest copper thin film. The figure above shows that oxygen does not penetrate in an ultra-planar copper thin film at the level of an atom, and oxygen can penetrate in two or more layers of atoms. Provided by the Ministry of Science and ICT, Korean researchers have found that copper does not rust if it is made into a very thin film that is close to a monoatomic layer. Copper oxidizes when exposed to air for a long time, changing color and rusting. In the future, the researchers anticipate that this method will open the way to prevent corrosion of the surface of objects and to replace gold used in electrical circuits with copper.
On the 17th, a research team led by Professor Jeong Se-young of the Department of Optical Mechatronics Engineering at Pusan National University, Professor Kim Young-min of the Department of Energy Science at Sungkyunkwan University, and Professor Seong-gon Kim of the Department of Astrophysics at Mississippi State University in the US succeeded in making the worlds thinnest and smoothest ultra-planar single-crystal copper thin film with a thickness of only 4 nm and a roughness of only 0.2 nm. said.
Professor Jeong said at a research performance briefing held at the Ministry of Science and ICT on the 15th, “Electrons traveling on the rough surface of a material collide and scatter on the surface like a car traveling on a mountain road, and cannot move in a straight line.” “On the other hand, on a flat surface, electrons travel flat, changing the properties of matter. Professor Jeong explained that “the surface roughness of general materials is 30~50nm, but the worlds smoothest surface roughness record is about 1.5nm”.
In the academic community, the opinion that it was difficult to further improve the surface roughness was dominant. A joint research team from Ireland, the United States, and the United Kingdom published a paper titled ‘nanocrystalline copper thin film can never be a flat surface’ in the international scientific journal ‘Science’ also did
The research team made a single-crystal copper thin film with the smoothest surface using an atomic sputtering epitaxy device. A single crystal is a solid in which all atoms are aligned in one and the same direction. The research team succeeded in making an ultra-smooth single-crystal copper thin film with a thickness of 4 nm and a surface roughness of only 0.2 nm. Previously, the thinnest single-crystal copper thin film had a thickness of 30 nm. This device eliminates electrodynamic vibration and forms a single crystal thin film of 4 inches or more in a way that atoms are deposited and piled up on a substrate one by one. The research team made this device by directly modifying the existing radio frequency thin film growth device.
The research team exposed the ultra-flat single-crystal copper thin film to air for over a year and observed the oxidation process in which copper atoms and oxygen combine, and confirmed that oxidation did not occur on the surface. Copper oxide was not found on the surface of the copper thin film. As a result of calculating the change in energy required for oxygen to enter the inside of copper, the research team confirmed that oxygen penetrates into the inside of the copper atom when the surface roughness is two or more atomic layers, but oxidation does not occur when it is perfectly flat or monoatomic. This means that oxidation does not occur at room temperature because a very large endothermic reaction is required in the process of oxygen entering the copper layer.
The research team also confirmed that when oxygen ions occupy more than 50% of the surface of the ultra-smooth surface, additional energy is required for more oxygen ions to spread on the surface, so that oxygen is pushed out of the surface and has a self-regulating function.
The research team expected this development to be very useful industrially. It can be applied to replace gold used in electric circuits, prevent surface oxidation of copper, or to produce various colors.
Professor Jeong said, “The electrical resistance of copper is lower than that of gold, but the reason that copper could not be used was because of the problem of oxidation.” If you do, all of those problems will be solved.” Professor Jeong said, “The statue of liberty was initially copper, but now it is green because of oxidation.
Professor Jeong said, “When copper is oxidized, the color becomes mottled. If the oxidation is well controlled, it can be adjusted to the desired color among 1800 colors.”
