UB scientists demonstrate wafer-scale, combinatorial synthesis of heteroepitaxial films with rapid in-situ, structural and chemical characterization

BUFFALO, N.Y. – A University at Buffalo study published on March 7 in Nature’s Scientific Reports describes how a new materials development technique can help meet the goals of the Materials Genome Initiative (MGI).

The White House’s Office of Science and Technology Policy launched MGI in 2011 to “discover, develop, manufacture, and deploy advanced materials at least twice as fast as possible today, and at a fraction of the cost.” The initiative seeks to combine advances in computer technology, computation materials science and data science or materials informatics to design and develop new materials.

Significant advances in computation materials science and data science have since been realized. However, these fields only predict a “window of materials space” where excellent functional properties can be obtained, says the study’s senior author, Amit Goyal, PhD, SUNY Distinguished Professor and SUNY Empire Innovation Professor in the Department of Chemical and Biological Engineering.

There is still a need to investigate and probe within this window of materials space, he says, using some kind of combinatorial synthesis and high-throughput characterization to determine the optimal compositions and synthesis conditions.

As such, a research team led by Goyal employed combinatorial synthesis (in which multiple elements are combined in different ratios to yield compounds with different compositions in an automated manner) and high-throughput characterization (which consists of methods to quickly analyze many samples) to determine the optimal compositions and synthesis conditions of potential materials.

“In this study, we demonstrate a pulsed laser deposition-based, combinatorial synthesis of heteroepitaxial functional films via sequential, layer-by-layer deposition utilizing an in-situ, high-throughput, wafer-scale, structural and compositional analysis,” says Goyal.

Pulsed laser deposition is a process that delivers a fast, atomic-scale growth building process. Heteroepitaxial means that all the atoms in the grown multi-cation film are oriented in the same manner as the atomic arrangements in the substrate on which the film is grown.

“We report on the combination of two in-situ techniques. One involves reflection high-energy electron diffraction for heteroepitaxial characterization. The other is a new compositional analysis technique known as low-angle X-ray spectroscopy,” says Goyal. “Both methods help map the chemical composition profile of combinatorial heteroepitaxial complex oxide films.”

Reflection high-energy electron diffraction, or RHEED, uses an electron gun to send high-energy electrons to the substrate.

Goyal explains: “After undergoing diffraction, the electrons interfere constructively at specific angles according to the crystal structure and spacing of the atoms at the sample surface and the wavelength of the incident electrons. A fraction of these electrons collide with a phosphorescent detector, creating specific diffraction patterns according to the surface features of the sample.”

He adds: “The diffraction patterns reveal the quality of heteroepitaxy and other structural aspects of the grown film. Low-angle X-ray spectroscopy measures the characteristic X-rays emitted from a solid sample by the electron beam of a reflection high-energy electron diffraction already present in pulsed laser deposition/molecular beam epitaxy growth systems.”

The team’s technique can produce material libraries of “functional complex oxide films using lateral thickness gradients across wafer-scale substrates by sub-monolayer sequential deposition of the different constituents under precisely controlled growth parameters followed by interdiffusion between the sub-monolayers,” says Goyal.

The technique has the potential to impact the development of new advanced electronic, electromagnetic and other functional materials to help reach the goal of the MGI initiative.

The lead author of the paper, “Combinatorial synthesis of heteroepitaxial, multi‑cation, thin‑films via pulsed laser deposition coupled with in‑situ, chemical and structural characterization,” is Eun Ju Moon, PhD, a former research assistant professor in the Laboratory for Heteroepitaxial Growth of Functional Materials and Devices in the UB Department of Chemical and Biological Engineering. Moon, who also held an appointment in the RENEW Institute, left UB for an industry position last December.

Goyal is a member of the National Academies of Sciences, Engineering and Medicine ad hoc Committee on “Advising NSF on its Efforts to Achieve the Nation’s Vision for the Materials Genome Initiative.” Goyal is also a member of the National Materials and Manufacturing Board. He was the founding director of UB’s RENEW Institute from January 2015 to July 2021. He received the UB President’s Medal in recognition of extraordinary service to the university in 2019.

He is a member of the National Academy of Engineering and an elected Fellow of 10 professional societies: the National Academy of Inventors, the American Association for the Advancement of Science, the Materials Research Society, the Institute of Electrical and Electronics Engineers, the American Physical Society, the American Society of Metals, the American Ceramic Society, the Institute of Physics, the World Innovation Foundation, and the World Technology Network.