STEM builds structures atom by atom
STEM image of silicon cluster within graphene [Ondrej Dyck/Oak Ridge National Laboratory, U.S. Dept. of Energy].
US-based researchers have used scanning transmission electron microscopy to manipulate and assemble atom structures.
Ondrej Dyck and colleagues from the Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, used an atomically focused electron beam to introduce silicon substitutional defects into graphene.
They then manipulated these defects to form dimers, trimers and even more complex structures, capturing the process dynamics at atomic resolution.
As Dyck writes in Small: "Our studies suggest that control of the e-beam-induced local processes offers the next step toward atom-by-atom nanofabrication."
"[This provides] a tool to study atomic-scale chemistry in 2D materials and fabricate predefined structures and defects with atomic specificity," he adds.
STEM video: trimer rotation [ORNL]
While researchers have been racing to build materials with atoms, the only platform that has enabled single-atom manipulation has been scanning tunnelling microscopy.
However, using STEM, Dyck and colleagues have now introduced silicon atoms into a single-atom-thick sheet of graphene.
As the electron beam scans across the material, its energy disrupts the graphene's molecular structure and creates room for a nearby silicon atom to swap places with a carbon atom.
"We observed an electron beam-assisted chemical reaction induced at a single atom and chemical bond level, and each step has been captured by the microscope, which is rare," highlights Dyck.
Using this process, the scientists were further able to bring two, three and four silicon atoms together to build clusters and rotate these structures within the graphene layer.
Ondrej Dyck of Oak Ridge National Laboratory used a STEM to move single atoms in a 2D layer of graphene, an approach that could be used to build nanoscale devices from the atomic level up for quantum-based applications. [Carlos Jones/Oak Ridge National Laboratory, U.S. Dept. of Energy]
According to Dyck, he selected graphene for this work as "it is robust against a 60-kilovolt electron beam."
"We can look at graphene for long periods of time without damaging the sample, compared with other 2D materials such as transition metal dichalcogenide monolayers, which tend to fall apart more easily under the electron beam," he adds.
Dyck and colleagues will now try to introduce other atoms such as phosphorus into the graphene structure.
"Phosphorus has potential because it contains one extra electron compared to carbon," says Dyck. "This would be ideal for building a quantum bit, or qubit, which is the basis for quantum-based devices."
The researchers' goal is to eventually build a device prototype in the STEM but as Dyck cautions, while building a qubit from phosphorus-doped graphene is on the horizon, how the material would behave at ambient temperatures, outside the STEM or a cryogenic environment, remains unknown.
Given this the researchers will continue to experiment with ways to keep the material stable in non-laboratory environments, which is important to the future success of STEM-built atomically precise structures.
Dyck and ORNL colleagues' work supports the ORNL-led initiative, 'The Atomic Forge', which encourages the microscopy community to reimagine STEM as a method to build materials from scratch.
Research is published in Small.