Pusan National University research team reveals the principle of copper oxidation and publishes it in Nature… Replacing Precious Metal Electrodes A Korean research team has succeeded in creating an ultra-smooth copper single-crystal thin film with a surface roughness of only one atom to create a surface that oxygen cannot penetrate. It was confirmed that it does not oxidize even if kept at room temperature for one year. The research team revealed that through this, the principle of copper oxidation was elucidated at the atomic level.
A research team led by Professors Jeong Se-young, Kim Young-min, and Kim Seong-gon produced a copper single-crystal thin film with a surface roughness equivalent to that of a monoatomic layer and published the research results on the principle of oxidation of copper using it, published in the international scientific journal Nature on the 17th.
Professor Sei-Young Jeong held a press conference in the briefing room of the Ministry of Science and ICT on the 15th and said, “This research result is the world’s first case to identify the origin of copper oxidation at the atomic level.”
Professor Jeong Se-young of Pusan National University is briefing on research results on the working principle of copper oxidation in the press room of the Ministry of Science and ICT in Sejong on the morning of the 15th. [Photo = Ministry of Science and ICT]
Professor Jeong said that although it is known that copper oxidation generally occurs in grain boundary defects or rough surfaces in polycrystalline materials made of many grains, the exact cause is not known. Oxidation is random and cannot be controlled. Our research team explained that they made a single crystal without grain boundaries and a copper thin film with a perfectly flat surface to fundamentally block oxidation and elucidate the principle.
The researchers built their own device to create an almost perfectly flat surface. The device, which the researchers named ASE, is a modification of the existing thin film growth device with its own technology. This device succeeded in achieving surface roughness of 0.21 nanometer level. This means that the height of the copper surface is only a maximum difference of one atom. The worlds highest level of surface roughness was about 1.5 nm.
According to the research team, the realization of a super-flat surface of copper in a thin film was a difficult topic to the extent that a paper titled that a nanocrystalline copper thin film can never become a flat surface was published in Science in 2017. Although the surface roughness of 1 nm has never been realized in the world, it is a very flat surface, but it also has a roughness of 4 atomic layers, which is a very rough surface from the point of view of atoms. So, he challenged the roughness of the first atomic layer and finally succeeded in growing a large-area copper thin film with an ultra-smooth surface of 0.2 nm.
Prof. Jeong developed his own equipment with domestic technology and developed a flat surface of this level, people are evaluating that it is quite like the State of the art in material engineering. It wasnt nearly perfect, it just boasted that it was perfect.
The ultra-flat copper thin film produced in this way did not oxidize even after being exposed to air for one year. As a result of observation using a high-resolution transmission electron microscope, etc., oxides such as copper oxide and copper dioxide generally observed on the copper surface did not appear at all.
The researchers confirmed this phenomenon in theory. As a result of calculating the energy change for oxygen to enter the inside of copper through the first principle calculation, when the surface roughness is two or more atomic layers, oxygen penetration into the copper easily proceeds as an exothermic reaction, whereas a perfectly flat surface or a monoatomic layer It was revealed that oxidation does not occur at room temperature because it requires a very large amount of energy for oxygen to penetrate into the inside of copper.
The research team also found that the oxygen ions present on the surface of the ultra-smooth thin film self-regulate the oxygen ion occupancy on the surface, and when 50% of the available oxygen sites are filled, it pushes out other oxygen from accessing it, thereby inhibiting oxidation. It was also revealed that there is Oxygen does not penetrate into the copper particles in the single crystal ultra-smooth thin film due to these two principles, so oxidation does not occur.
A schematic model for copper oxidation. It has been shown that oxygen does not permeate in an ultra-smooth surface, and oxygen can permeate in two or more layers of atomic steps. [Photo=Professor Jeong Se-young]
Copper is a material that conducts electricity well and is used throughout industry. However, due to the weakness caused by oxidation, expensive materials such as gold are used in circuits that require high reliability or ultra-precision materials. If copper is produced that does not rust, expensive precious metal electrodes can be replaced with copper with excellent conductivity. The electrical conductivity of copper is about 40% superior to that of gold, and if it becomes a single-crystal copper thin film with an ultra-smooth surface, it can increase the conductivity by more than 15% than that of general copper. there is.
The research team also expected that the self-developed thin film growth device could be replaced by reducing the expensive imported equipment costing hundreds of millions of won to 50 million won. The research team said that this device can be easily upgraded to the basic RF sputtering device, which is currently the most used, and can grow to a large area of 4 inches or more now, and continuous growth is possible if the equipment is modified.
◇Paper Title: Flat-surface-assisted and self-regulated oxidation resistance of Cu / Nature
◇Authors: Professor Se-Young Jeong, Professor Young-Min Kim, Professor Sung-Gon Kim, Dr. Su-Jae Kim, Yong-In Kim, Bipin Lamichhane, Young-Hoon Kim, Tae-Woo Ha, Professor Young-Hee Lee, Professor Lee Yu-Sil, Professor Chae-Yong Cho, Dr. Mi-Yeon Cheon, Professor Jong-Chan Kim, Professor Hu-Young Jung, Jeong-Dae Kim