Quantum materials, batteries and water might not seem like natural partners, but UChicago Pritzker School of Molecular Engineering (PME) experts in these three respective research fields have broken through a major barrier in creating new quantum devices.
“This is the perfect example of interdisciplinary research,” said PME Prof. Y. Shirley Meng, whose team contributed to the research.
One of the most common ways to build semiconductors, transistors, diodes and nanotechnology devices from the molecule up is a process called molecular-beam epitaxy (MBE). Researchers grow microscopically thin films of material on single crystal wafers called substrates.
The films can be sliced, diced and stacked in novel formations to create new devices on the microscopic level. The problem is that the valuable films are still stuck on – and stuck with – the substrates.
“Once the film is grown, it's permanently bonded to the substrate,” said PME Asst. Prof. Shuolong Yang, whose lab led the interdisciplinary team. “This puts some very strong limitations on how creative you can be in processing the material.”
In a paper published in Nano Letters, an interdisciplinary team from three PME labs has shown how MBE-grown films can be “liberated” from the substrates and still maintain their delicate quantum physics – an engineering triumph at the molecular level.
Peeling the tape
The ultrathin membranes created through MBE are the building blocks of exotic quantum materials. Researchers seeking to use these films to create new, innovative and better quantum devices came to see the substrates as an unavoidable burden, something that comes with the territory.
When an undergraduate student – Chi Ian Jess Ip, the new paper’s first author – approached Yang about potential research opportunities a few years ago, he presented this challenge and outlined the exciting future research opportunities if such a barrier could be overcome.
“She found a way to robustly separate topological insulator products, a form of material which is great for low-dissipation, low-power electronics,” Yang said.
Ip’s method, which is outlined in the paper, chemically removes the film where quantum properties previously deemed too delicate to survive being ripped off the substrate survived.
“We used an acid to selectively eat away the top few layers of atoms on the substrate, leaving the film floating on the acid and ready to be fished out by any other substrate or devices,” said Ip, now at MIT.