Evrim Yazgin
Cosmos science journalist
In some very neat science, electron imaging has captured the atomic structure of the outermost layer of electrons on a material’s surface.
Understanding the structure of surface atoms is useful for engineers and chemists.
The research could aid in fabrication, growth, and controlling electronic and mechanical properties of nano-scale materials.
The imaging of atomic structure is fascinating.
Some materials have “surface reconstruction” where the atoms on the material’s surface have a different structure to those in its interior.
Understanding the structure of surface atoms is useful for engineers and chemists.
Scanning electron microscopy (SEM) uses a focused electron beam to release and capture secondary electrons (SEs) emitted from the surface of the material.
SEs tend to come from a shallow depth just beneath the surface – about 1 nanometre deep. This can make it difficult to observe surface reconstruction, especially if the sample is only a single-atomic layer.
The new research, published in the journal Microscopy, tackles this issue.
The researchers from Japan’s Nagoya University note that previous research has observed SEs in silicon crystal from a depth of just 0.2nm. The Nagoya experiment takes this a step further, investigating the thinnest system with a surface layer sitting on a substrate – a double layer of the compound molybdenum disulphide (MoS2).
They found high surface sensitivity in their tests. The intensity of the SEs from the surface layer was about 3 times higher than from the second layer.
“This result suggests that the surface layer absorbs or scatters SEs from the second layer,” says lead author Koh Saitoh from Nagoya’s Institute of Materials and Systems Sustainability. “This absorption contributes to the method’s depth sensitivity.”
The SE images revealed stunning honeycomb-like structures on the surface layer, composed of molybdenum and sulphur atoms. It also showed overlapping patterns, indicating a distinct atomic arrangement in the surface and second layer.
