Hyungwoo Lee, a materials science and engineering postdoctoral researcher at the University of Wisconsin-Madison, looks inside a thin film deposition system during growth of an oxide thin film structure. Image: Renee Meiller.Lennon and McCartney. Abbott and Costello. Peanut butter and jelly. Think of one half of any famous duo, and the other half likely comes to mind. Not only do they complement each other, but they work better together.
The same is true in the burgeoning field of oxide electronics materials. Boasting a wide array of properties, including electronic, magnetic and superconducting, these multifunctional materials are poised to expand the way we think about the functions of traditional silicon-based electronic devices such as cell phones or computers.
Until recently, however, a critical aspect has been missing – one that complements the function of electrons in oxide electronics. A team led by materials scientist Chang-Beom Eom at the University of Wisconsin-Madison has now directly observed the missing second half of the duo required to move oxide electronics materials forward.
It's called a two-dimensional hole gas – a counterpart to something known as a two-dimensional electron gas. For more than a decade, researchers have recognized that the existence of a hole gas was possible, but haven't been able to create it experimentally. Now, in a paper in Nature Materials, Eom and his collaborators provide evidence of a hole gas co-existing with the electron gas. To obtain this evidence, they had to fabricate an ultrathin material known as a thin film structure.
"The 2D hole gas was not possible primarily because perfect-enough crystals could not be grown," says Eom, a professor of materials science and engineering. "Inside, there were defects that killed the hole gas."
Eom is a world expert in material growth, using techniques that allow him to meticulously build, or ‘grow’, each layer of a material with atomic precision. Using that expertise, combined with insight into the interaction between the layers in a thin-film structure, Eom was able to identify the elusive 2D hole gas.
"We were able to design the correct structure and make near-perfect crystals, all without defects that degrade the hole gas," Eom explains.
Also important for identifying the hole gas was the almost-symmetrical way in which Eom assembled the various layers of the thin-film structure– something like a club sandwich. While other researchers have made the material with a bi-layer structure, Eom designed a triple layer. He alternated layers of strontium oxide and titanium dioxide at the bottom, then deposited layers of lanthanum oxide and aluminum oxide, before adding additional layers of strontium oxide and titanium dioxide at the top.
As a result, the hole gas forms at the interface between the layers at the top, while the electron gas forms at the interface between the layers at the bottom -- the first demonstration of a very powerful complementary pair.
Just as people 50 years ago likely could not have envisioned communicating via wireless devices, this advance could lead to new concepts and applications that today remain beyond our wildest dreams.
"We're not just improving the performance of devices," says Eom. "So, not improving a cell phone, for example – but envisioning an entirely new device made possible by this advance. This is the beginning of an exciting new path."
This story is adapted from material from the University of Wisconsin-Madison, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.