While silicon has reached a performance limit, scientists have begun using smaller pieces of graphene as semiconductors used to make transistors.
In a recent study conducted at the Beckman Institute for Advanced Science and Technology at the University of Illinois and the Department of Chemistry at the University of Nebraska-Lincoln, researchers have used graphene, made of a single-atom thick sheet of carbon cut into smaller pieces called nanoribbons, as a faster and cooler material to make materials used to create the electronic components used to carry out logic operations in computing.
The recent study shows the first step toward integrating atomically precise graphene nanoribbons onto nonmetallic substrates.
Adrian Radocea, a doctoral student in Beckman’s Nanoelectronics and Nanomaterials Group, explained that under most scenarios nanoribbons are neither uniform nor narrow enough to exhibit the desired semiconductor properties.
“When you’re going from the top-down, it’s very hard to get control over the width,” Radocea said in a statement. “It turns out that if the width modulates by just an atom or two, the properties change significantly.”
However, the nanoribbons must be made from “the bottom up” from smaller molecules to create atomically precise nanoribbons with highly uniform electronic properties.
“It’s like molecular building blocks: kind of like snapping Legos together to building something,” Radocea said. “They lock in place and you end up with the exact control over the ribbon width.”
Nanoribbon stems are difficult to cleanly transfer from the high sensitivity to environmental contaminants.
Both solution-synthesized and surface-grown nanoribbons are exposed to chemicals during the transfer process that can affect the performance of graphene nanoribbons. However, scientists were able to use a dry transfer in an ultra-high vacuum environment.
The team used a fiberglass applicator coated in graphene nanoribbon powder that was heated to remove contaminants and solvent residue. The substance pressed onto a freshly prepared hydrogen-passivated silicon surface.
Members of Beckman’s Computational Multiscale Nanosystems Group, Tao Sun, a doctoral student, and Narayana Aluru, professor of mechanical science and engineering, provided expertise in computational modeling via density functional theory to investigate the properties of the nanoribbons.
“Density functional theory calculations provided a deeper understanding of the electronic properties of the integrated system and the interactions between graphene nanoribbons and the silicon substrate,” Sun said in a statement. “It was exciting that the computational results could help explain and confirm the experimental results and provided a coherent story.”
The study was published in Nano Letters.
