Power/Performance Bits: Dec. 27

Tiny diamond radio

Researchers at Harvard built the world’s smallest radio receiver, built out of an assembly of atomic-scale defects in pink diamonds.

The radio uses tiny imperfections in diamonds called nitrogen-vacancy (NV) centers. To make NV centers, researchers replace one carbon atom in a diamond crystal with a nitrogen atom and remove a neighboring atom — creating a system that is essentially a nitrogen atom with a hole next to it. NV centers can be used to emit single photons or detect very weak magnetic fields. They have photoluminescent properties, making them promising systems for quantum computing, phontonics and sensing.

In this radio, electrons in diamond NV centers are powered, or pumped, by green light emitted from a laser. These electrons are sensitive to electromagnetic fields. When NV center receives radio waves it converts them and emits the audio signal as red light. A common photodiode converts that light into a current, which is then converted to sound through a simple speaker or headphone.

An electromagnet creates a strong magnetic field around the diamond, which can be used to change the radio station, tuning the receiving frequency of the NV centers.

This tiny radio, whose building blocks are the size of two atoms, can withstand extremely harsh environments and is biocompatible, meaning it could work anywhere from a probe on Venus to a pacemaker in a human heart. (Source: Eliza Grinnell/Harvard SEAS)

The team used billions of NV centers in order to boost the signal, but the radio works with a single NV center, emitting one photon at a time, rather than a stream of light.

The radio is extremely resilient, thanks to the inherent strength of diamond. The team successfully played music at 350 degrees Celsius, or about 660 Fahrenheit. “Diamonds have these unique properties,” said Marko Loncar, professor of electrical engineering at Harvard. “This radio would be able to operate in space, in harsh environments and even the human body, as diamonds are biocompatible.”

Solid-state batteries

Researchers at the University of Maryland made a key advance in solid-state battery technology, inserting a layer of ultra-thin aluminum oxide between lithium electrodes and a solid non-flammable ceramic electrolyte known as garnet. One stumbling block for garnet-based solid-state batteries is high impedance, limiting the flow of energy and decreasing the battery’s ability to charge and discharge.

The team focused on solving the problem of high impedance between the electrolyte and electrode materials with the layer of ultrathin aluminum oxide, which decreased the impedance 300 fold. This virtually eliminates the barrier to electricity flow within the battery, allowing for efficient charging and discharging of the stored energy.

“Our garnet-based solid-state battery is a triple threat, solving the typical problems that trouble existing lithium-ion batteries: safety, performance, and cost,” said Liangbing Hu, associate professor of materials science and engineering at UMD.

The garnet-based solid-state electrolyte is non-flammable, eliminating the risk of fire, and allow the use of metallic lithium anodes, which contain the greatest possible theoretical energy density. Combined with high-capacity sulfur cathodes, the team expects it to offer a potentially unmatched energy density and outperform any lithium-ion battery currently on the market.