In a paper published in the journal Nature, the researchers said that previous studies have shown that Cu oxidation occurs due to microscopic “multi-steps” on the surface of copper. These steps provide a source of Cu adatoms (adsorbed atoms), which interact with oxygen and provide a place for oxides to grow. This is why single-crystalline Cu is resistant to oxidation.
“We used a method called atomic sputtering epitaxy to grow tightly coordinated flat single-crystal copper films. By using noise reduction systems to reduce electrical and mechanical noises, we were able to keep the Cu surfaces nearly defect-free and fabricate atomically flat films,” Jeong said.
The research team then used high-resolution transmission electron microscopy (HR-TEM) to study the Cu films. They found that the film grew in the  direction and had an almost flat surface with occasional mono-atomic steps. They then compared the single-crystal Cu (111) films (SCCFs) with other Cu films which had higher surface roughness and found that, unlike the other films, the SCCFs were oxidation-resistant, that is, it is very difficult for oxygen to penetrate the mono-atomic step edge.
The researchers then used a microscopic model of Cu oxidation based on “density functional theory” to investigate how the SCCF interacts with oxygen. They found that the surface of the SCCF was protected by oxygen itself, once 50% of its surface was covered with oxygen atoms. Additional absorption of oxygen atoms on the SCCF was suppressed by the high energy barrier they, themselves, created.
“The novelty of our research lies in the realization of atomically flat surfaces, that is, surfaces that are flat on the atomic level, as well as an elucidation of the oxidation-resistance mechanism of ultraflat metals,” Jeong said.
The findings of this study make major contributions not only to the electronics and semiconductor industry but also go a long way towards helping protect priceless bronze sculptures from damage.
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