Imagine a wire a thousand times thinner than a strand of hair. That’s the premise behind one-dimensional (1D) nanoribbons: strips of semiconducting material just a few atoms wide, but hundreds of times longer, which could shape faster, smaller, more precise and energy-efficient devices.
One promising base material for 1D nanoelectronics is titanium trisulfide (TiS₃), a layered crystal. “TiS₃ nanoribbons consist of long, loosely connected atomic chains that encourage electricity to flow lengthwise,” said Ivan Verzhbitskiy, a Senior Scientist at the A*STAR Quantum Innovation Centre (A*STAR Q.InC). “These chains act like multi-lane highways, allowing electrons to move smoothly in separate channels, which reduces scattering and overall energy loss from the current.”
However, TiS₃ nanoribbons can be tricky to incorporate in a circuit. Defects or ‘unfriendly’ interactions with certain metals can increase contact resistance, making it harder for electrons to flow between TiS₃ and other components. Even the process of depositing metal contacts onto TiS₃ nanoribbons can be harsh and potentially damaging.
“As nanoribbons are also very narrow, high contact resistance combined with ultra-low temperatures can severely limit electron flow, impeding their use in quantum technologies,” added Kuan Eng Johnson Goh, a Senior Principal Scientist at the A*STAR Institute of Materials Research and Engineering (A*STAR IMRE).
To address the contact resistance problem in 1D TiS₃ nanoribbons, Verzhbitskiy, Goh and A*STAR Q.InC colleagues recently collaborated with Yee Sin Ang’s team at the Singapore University of Technology and Design, and Goki Eda’s team at the National University of Singapore.
Together, the team ran models and simulations to identify an optimal metal to pair with TiS₃ nanoribbons. They found that indium (In) was an excellent candidate—it helps electrons in entering TiS₃, unlike many other metals which impede them. Its low melting temperature also enables gentler deposition onto fragile nanoribbons.
The team then developed a minimally damaging fabrication process for In-TiS₃ contacts using a specialised A*STAR ‘cleanbox’ system, which restricts ambient water and oxygen from reacting with and degrading the nanoribbons.
In-TiS₃ devices produced using this method demonstrated contact resistances as low as 2.7 kΩ*μm, and maintained contact resistances below 3 kΩ*μm across a temperature range of 5–300 K (or -268–27 °C). In comparison, conventional metal contacts such as gold show an order-of-magnitude higher contact resistance at low temperatures.
“We achieved one of the lowest contact resistances reported for semiconducting nanoribbons,” said Verzhbitskiy.
Encouraged by In-TiS₃’s performance even at ultra-low temperatures, the team also fabricated a tiny In-TiS₃ transistor with two extremely close metal contacts. “Thanks to indium’s efficient electron injection, the device could control currents with exceptional precision—down to the level of a single electron,” noted Goh. The team demonstrated efficient control of single-electron transport at ultra-low temperatures of 35 mK.
The team is eager to see In-TiS₃ nanoribbons applied to both existing and next-generation technologies. “Our low-power devices can be flexibly integrated as they’re not limited to a specific substrate,” said Verzhbitskiy. “They could serve as highly accurate current sources for quantum measurements, ultra-sensitive sensors, and compact transistors for ultra-low temperature settings where conventional technologies struggle.”
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).
