Power/Performance Bits: March 17

Artificial photosynthesis: leaves of nickel

Inspired by a chemical process found in leaves, Caltech scientists developed an electrically conductive film that could help pave the way for devices capable of harnessing sunlight to split water into hydrogen fuel.

When applied to semiconducting materials (it’s been tested with silicon, indium phosphide, and cadmium telluride), the team’s film of nickel oxide prevents rust buildup and facilitates an important chemical process in the solar-driven production of fuels such as methane or hydrogen.

The development could lead to safe, efficient artificial photosynthetic systems—also called solar-fuel generators or “artificial leaves”—that replicate the natural process of photosynthesis that plants use to convert sunlight, water, and carbon dioxide into oxygen and fuel in the form of carbohydrates, or sugars.

The artificial leaf consists of three main components: two electrodes—a photoanode and a photocathode—and a membrane. The photoanode uses sunlight to oxidize water molecules to generate oxygen gas, protons, and electrons, while the photocathode recombines the protons and electrons to form hydrogen gas. The membrane, which is typically made of plastic, keeps the two gases separate in order to eliminate any possibility of an explosion, and lets the gas be collected under pressure to safely push it into a pipeline.

Ke Sun, a Caltech postdoc in the lab of George L. Argyros Professor and Professor of Chemistry Nate Lewis, peers into a sample of a new, protective film that he helped develop to aid in the process of harnessing sunlight to generate fuels. (Source: Lance Hayashida/Caltech Marcomm)

While there have been many experiments to create a protective coatings for the electrodes, all previous attempts have failed for various reasons. “You want the coating to be many things: chemically compatible with the semiconductor it’s trying to protect, impermeable to water, electrically conductive, highly transparent to incoming light, and highly catalytic for the reaction to make oxygen and fuels,” says Nate Lewis, professor of chemistry at Caltech. “Creating a protective layer that displayed any one of these attributes would be a significant leap forward, but what we’ve now discovered is a material that can do all of these things at once.”

The team is working on a photocathode, but Lewis cautions that they are still a long way off from developing a commercial product that can convert sunlight into fuel. “What we have to do is combine both of these elements together and show that the entire system works. That will not be easy, but we now have one of the missing key pieces that has eluded the field for the past half-century.”

Doubling RF data capacity

At the International Solid-State Circuits Conference in February, a team from Columbia University demonstrated what was thought to be impossible: an integrated circuit that can simultaneously transmit and receive at the same frequency in a wireless radio.

While the theoretical feasibility of the technology—full-duplex radio integrated circuits that can be implemented in nanoscale CMOS—has been demonstrated, no one had yet been able to build nanoscale ICs with this capability.

CoSMIC (Columbia high-Speed and Mm-wave IC) Lab full-duplex transceiver IC that can be implemented in nanoscale CMOS to enable simultaneous transmission and reception at the same frequency in a wireless radio. (Source: Jin Zhou and Harish Krishnaswamy/Columbia Engineering)

“Our work is the first to demonstrate an IC that can receive and transmit simultaneously,” said Harish Krishnaswamy, associate professor of electrical engineering at Columbia. “Doing this in an IC is critical if we are to have widespread impact and bring this functionality to handheld devices such as cellular handsets, mobile devices such as tablets for WiFi, and in cellular and WiFi base stations to support full duplex communications.”

Having overcome their biggest challenge of canceling out transmitter echo, the researchers’ next step is to test a number of full-duplex nodes to understand what the gains are at the network level.

Play me a tune, nano piano

Researchers at the University of Illinois presented the first-ever recording of optically encoded audio onto a non-magnetic plasmonic nanostructure.

The nanostructure, an array of novel gold, pillar-supported bowtie nanoantennas (pBNAs), exhibited photographic film properties in the team’s previous investigations—a feature they were able to exploit to store sound and audio files.

“Data storage is one interesting area to think about,” said Kimani Toussaint, associate professor of mechanical science and engineering at the University of Illinois. “For example, one can consider applying this type of nanotechnology to enhancing the niche, but still important, analog technology used in the area of archival storage such as using microfiche. In addition, our work holds potential for on-chip, plasmonic-based information processing.”

The researchers demonstrated the ability of pBNAs to store sound information either as a temporally varying intensity waveform or a frequency varying intensity waveform. Eight basic musical notes were stored on a pBNA chip and then retrieved and played back in a desired order to make a tune.

Hear the first piece performed on the nano piano: “Twinkle, Twinkle, Little Star”

Nano piano concept: An experimental setup (left) for an array of gold, pillar-supported bowtie nanoantennas (bottom center) which can be used to record distinct musical notes, as shown in the experimentally obtained dark-field microscopy images (bottom right). These particular notes were used to compose ‘Twinkle, Twinkle, Little Star.’ (Source: University of Illinois at Urbana-Champaign)

“Our approach is analogous to the method of ‘optical sound,’ which was developed circa 1920s as part of the effort to make ‘talking’ motion pictures,” the team said in a paper published in Nature’s Scientific Reports. The researchers recorded audio signals by using a microscope to scan a sound-modulated laser beam directly on their nanostructures. Retrieval and subsequent playback was achieved by using the same microscope to image the recorded waveform onto a digital camera, whereby simple signal processing can be performed.