Researchers Develop Corrosion-Free Copper Thin Films

The copper thin film was grown using atomic sputtering epitaxy and then the mechanism behind its strong oxidation-resistance was revealed using theoretical models. Image courtesy of PRNewswire/Pusan National University.

Scientists from Pusan National University (PNU) (Busan, South Korea), Sungkyunkwan University (Seoul, South Korea), and Mississippi State University (Starkville, Mississippi, USA) have developed a new method to fabricate anatomically flat single-crystal copper (Cu) thin films with semi-permanent oxidation resistance designed to limit unwanted corrosion on Cu surfaces.

A team of researchers led by Prof. Se-Young Jeong from PNU detail their process of fabricating oxidation-resistant thin films of copper in Nature magazine.

“Oxidation-resistant Cu could potentially replace gold in semiconductor devices, which would help bring down their costs,” says Jeong. “Oxidation-resistant Cu could also replace electrical consumption, as well as increase the lifespan of devices with nanocircuitry.”

Previous studies have shown that Cu oxidation occurs due to microscopic “multi-steps” on the surface. These steps provide a source of Cu adatoms (adsorbed atoms), which interact with oxygen and allow 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,” explains Jeong. “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.”

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 [111] direction and had an almost flat surface with occasional mono-atomic steps. Next, they compared the single-crystal Cu (111) films (SCCFs) with other Cu films that had higher surface roughness and found that unlike with the other films, the SCCFs were oxidation-resistant, thereby making it 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 the researchers created.

“The novelty of our research lies in the realization of atomically flat surfaces, i.e., surfaces that are flat on the atomic level, as well as an elucidation of the oxidation-resistance mechanism of ultraflat metals,” says Jeong.

Source: PRNewswire,