University of Arkansas physicist Jak Chakhalian. Photo: University of Arkansas |
A University
of Arkansas physicist and
his colleagues have examined the challenges facing scientists building the next
generation of materials and innovative electronic devices and identified
opportunities for taking the rational material design in new directions.
Jak Chakhalian of the University of
Arkansas, A.J. Millis of Columbia University,
and J. Rondinelli of Drexel
University presented their
ideas in Nature.
“Where you see issues, there are opportunities,” Chakhalian said.
The researchers focus on complex oxide interfaces with strongly correlated
electrons, which are artificially created structures involving materials called
transition metal oxides. Oxide interfaces have the potential to revolutionize
materials and devices based on them the way that semiconductors once did, but
researchers find themselves hampered by several obstacles.
First, no one has developed a comprehensive theory of why oxide interfaces
behave as they do, which means that scientists cannot predict or often even
explain the materials’ properties. Second, scientists face challenges in
synthesizing these complex materials with atomic precision. Synthesizing
involves taking several chemical elements balanced very precisely and combining
them into intricate geometrical arrangements. On top of this, to create
interfaces, scientists must grow these very dissimilar materials together.
While these challenges may seem intimidating, Chakhalian and his colleagues
see two opportunities. The first is to grow materials in unusual directions.
Chakhalian has already demonstrated that an oxide interface grown along the
diagonal of a cube will crystallize into triangular and hexagonal atomic
patterns, while the same material grown on a conventional horizontal surface
will have a common cubic pattern.
“When grown along the diagonal, from the mechanical, electronic, and
magnetic properties point of view it becomes a new, exotic material,” he said.
By forcing materials to grow in directions that they would usually resist in
nature, Chakhalian suggests a way to find these novel exotic materials.
The second opportunity involves creating interfaces between oxide materials
and materials where oxygen is replaced by another element, which leads to
entirely new materials with novel electronic properties. For instance, nickel
oxide is an insulator but nickel sulfide is metallic. By alternating an oxide-based
layer with a non-oxide-based layer, scientists propose creating interfaces with
important properties for, among other things, energy savings and water
purification.
“If you want to talk about the next nanoelectronics revolution or real
solutions to the energy problem, these are some of the groundbreaking
directions we propose to take,” Chakhalian said.
