New process produces ‘unrealistic’ alloys

A multi-institutional team led by the US Department of Energy (DOE)'s National Renewable Energy Laboratory (NREL) has discovered a way to create new alloys that could form the basis for next-generation semiconductors.

Semiconductor alloys already exist – often made from a combination of materials with similar atomic arrangements – but until now researchers believed it was unrealistic to make alloys from certain constituents.

"Maybe in the past scientists looked at two materials and said I can't mix those two. What we're saying is think again," said Aaron Holder, a former NREL post-doctoral researcher who is now part of the research faculty at the University of Colorado Boulder. "There is a way to do it." Holder is corresponding author of a paper on this work in Science Advances.

Scientists connected to the Center for Next Generation of Materials by Design (CNGMD) made the breakthrough and took the idea from theory to reality. CNGMD is supported by the DOE's Office of Science and researchers from NREL, the Colorado School of Mines, Harvard University, Lawrence Berkeley National Laboratory, Massachusetts Institute of Technology, Oregon State University and SLAC National Accelerator Laboratory.

"It's a really nice example of what happens when you bring different institutions with different capabilities together," said Holder. His co-authors from NREL are Stephan Lany, Sebastian Siol, Paul Ndione, Haowei Peng, William Tumas, John Perkins, David Ginley and Andriy Zakutayev.

A mismatch between atomic arrangements previously thwarted the creation of certain alloys. Researchers with CNGMD have now been able to create an alloy of manganese oxide (MnO) and zinc oxide (ZnO), despite their atomic structures being very different. The new alloy can absorb a significant fraction of natural sunlight, even though neither MnO nor ZnO can on their own. "It's a very rewarding kind of research when you work as a team, predict a material computationally and make it happen in the lab," Lany said.

Blending a small percent of MnO with ZnO is already possible by applying heat, but reaching a 1:1 mix would require temperatures far greater than 1000°C (1832°F), and the materials would separate again as they cool.

Instead, the scientists deposited the MnO and ZnO as thin films using pulsed laser deposition and magnetron sputtering, which didn’t require such high temperatures; this process also allowed them to create an alloy of tin sulfide and calcium sulfide. "We show that commercial thin film deposition methods can be used to fabricate heterostructural alloys, opening a path to their use in real-world semiconductor applications," Zakutayev said.

The research also yielded a first look at the phase diagram for heterostructural alloys, revealing a route for predicting properties of other alloys along with a large area of metastability that keeps the elements combined. "The alloy persists across this entire space even though thermodynamically it should phase separate and decompose," Holder said.

This story is adapted from material from NREL, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.