New ultra-thin insulator may lead to smaller and faster devices

Scientists have created an insulator film just 25 atoms thick that may help develop smaller, faster and more energy-efficient electronic devices. Topological insulators (TI) have tantalising pontential in the field of electronics.

Researchers from University of California Riverside and Massachusetts Institute of Technology (MIT) in the US created a TI film just 25 atoms thick that adheres to an insulating magnetic film, creating a "heterostructure." This heterostructure makes TI surfaces magnetic at room temperatures and higher to above 126 degrees Celsius.

The surfaces of TI are only a few atoms thick and need little power to conduct electricity. If TI surfaces are made magnetic, current only flows along the edges of the devices, requiring even less energy.

This is called the quantum anomalous Hall effect (QAHE), which lead to smaller devices with more long-lasting batteries, said Jing Shi, a professor at the University of California, Riverside. Topological insulators are the only materials right now that can achieve the coveted QAHE, but only after they are magnetised. However, TI surfaces are not naturally magnetic. In 2015, Shi's lab first created heterostructures of magnetic films and one-atom-thick graphene materials by using a technique called laser molecular beam epitaxy.

The same atomically flat magnetic insulator films are critical for both graphene and topological insulators. "The materials have to be in intimate contact for TI to acquire magnetism," Shi said. "If the surface is rough, there won't be good contact. 

We're good at making this magnetic film atomically flat, so no extra atoms are sticking out," he said. Researchers used molecular beam epitaxy to build 25 atomic TI layers on top of the magnetic sheets, creating the heterostructures, which were then used for device fabrication and measurements.

More research is needed to make TI show the quantum anomalous Hall effect (QAHE) at high temperatures, and then make the materials available for miniaturisation in electronics, Shi said. However, the findings show that by taking the heterostructures approach, TI surfaces can be made magnetic and robust at normal temperatures. Making smaller, faster devices operate at the same or higher levels of efficiency as their larger, slower predecessors "doesn't happen naturally," Shi said.

The study was published in the journal Science Advances.