Power/Performance Bits: April 5

DNA diodes

Researchers at the University of Georgia and at Ben-Gurion University in Israel created nanoscale electronic components from single DNA molecules.

“For 50 years, we have been able to place more and more computing power onto smaller and smaller chips, but we are now pushing the physical limits of silicon,” said Bingqian Xu, an associate professor in the UGA College of Engineering. “If silicon-based chips become much smaller, their performance will become unstable and unpredictable.”

The team isolated a specifically designed single duplex DNA of 11 base pairs and connected it to an electronic circuit only a few nanometers in size. After the measured current showed no special behavior, the team site-specifically intercalated a small molecule named coralyne into the DNA. They found the current flowing through the DNA was 15 times stronger for negative voltages than for positive voltages.

Illustration of the coralyne-intercalated DNA junction used to create a single-molecule diode, which can be used as an active element in future nanoscale circuits. (Source: University of Georgia and Ben-Gurion University)

“This finding is quite counterintuitive because the molecular structure is still seemingly symmetrical after coralyne intercalation,” Xu said. “Our discovery can lead to progress in the design and construction of nanoscale electronic elements that are at least 1,000 times smaller than current components.”

The research team plans to continue its work, with the goal of constructing additional molecular devices and enhancing the performance of the molecular diode.

Paperlike electrode

A research team at Kansas State University developed a new battery electrode using silicon oxycarbide-glass and graphene. Made of low-cost materials that are byproducts of the silicone industry, the battery is capable of functioning at temperatures as low as minus 15 degrees C, which gives it numerous aerial and space applications.

It has been difficult to incorporate graphene and silicon into practical batteries because of challenges that arise at high mass loadings, such as low capacity per volume, poor cycling efficiency and chemical-mechanical instability.

The team tackled these challenges by manufacturing a self-supporting and ready-to-go electrode that consists of a glassy ceramic called silicon oxycarbide sandwiched between large platelets of chemically modified graphene, or CMG. The electrode has a high capacity of approximately 600 miliampere-hours per gram — 400 miliampere-hours per cubic centimeter — that is derived from silicon oxycarbide. The paperlike design is made of 20% chemically modified graphene platelets.

(Source: Gurpreet Singh/Kansas State University)

“The paperlike design is markedly different from the electrodes used in present day batteries because it eliminates the metal foil support and polymeric glue — both of which do not contribute toward capacity of the battery,” said Gurpreet Singh, associate professor of mechanical and nuclear engineering, a development that saved approximately 10% of the cell’s total weight. The result is a lightweight electrode capable of storing lithium-ion and electrons with near 100% cycling efficiency for more than 1000 charge discharge cycles.

Moving forward, Singh’s goal is to produce this electrode material at even larger dimensions. For example, present-day pencil-cell batteries use graphite-coated copper foil electrodes that are more than one foot in length. The team also would like to perform mechanical bending tests to see how they affect performance parameters.