For decades, silicon has been the industry’s material of choice for the billions of tiny on-off switches that power our computers. To pack more power on smaller devices, developers are shrinking these switches towards the atomic scale. But when silicon approaches its physical limits, defects at the semiconductor surface begin to impede electron flow and waste energy.
Two-dimensional transition metal dichalcogenides (2D TMDs) are widely considered leading candidates to replace silicon. Their ultra-thin, atom-thick structure allows for faster electron flow and minimal power loss, promising a future of more energy-efficient electronics—at least in theory. In practice, however, 2D TMD devices have consistently fallen short of their predicted performance.
“It has been a persistent mystery in the field,” said Aaron Lau, Pillar Director at the A*STAR Quantum Innovation Centre (A*STAR Q.InC) and Johnson Goh, a Senior Principal Scientist at A*STAR Institute of Materials Research and Engineering (A*STAR IMRE). “For over two decades, the performance of these materials in the laboratory has consistently lagged behind what theory predicted.”
Lau, Goh and colleagues at A*STAR Q.InC and A*STAR IMRE suspected that environmental factors might be responsible, even though previous studies had largely assumed that TMDs were stable under ambient conditions. Together with Yee Sin Ang and his team at the Singapore University of Technology and Design, the researchers investigated whether non-dissociative chemisorption—where oxygen molecules bind strongly to a material’s surface—could explain the performance gap.
To catch the culprit, the team developed a rigorous oxygen-free fabrication method, handling the materials within carefully controlled environments to prevent any contact with the atmosphere. The difference was staggering: TMDs produced via the oxygen-free route outperformed those exposed to air by more than tenfold. These results showed that the TMDs’ persistent underperformance was not due to flaws in the underlying physics, but rather to environmental contamination.
“The biggest surprise was just how extensive and permanent the effect of oxygen exposure actually was,” said Goh, adding that even brief exposure to air allows oxygen molecules to attach to microscopic surface imperfections in the TMDs. “This was not just a surface stain we could wipe off; it’s an irreversible process that alters the material’s electronic properties.”
While the researchers built a specialised facility to minimise oxygen exposure during fabrication, they emphasised that controlling the manufacturing environment is an engineering challenge the semiconductor industry must address. “Our work can provide an instruction manual for the industry. If we want the best-performing 2D chips, we must maintain strict environmental hygiene,” Lau said.
The team now hopes to harness the unique physics of these 2D materials to develop new devices, aiming to improve both power and control in next-generation quantum technologies.
The A*STAR-affiliated researchers contributing to this research are from the A*STAR Quantum Innovation Centre (A*STAR Q.InC) and A*STAR Institute of Materials Research and Engineering (A*STAR IMRE).
