System Bits: July 19

Using carbon nanotubes to leapfrog today’s silicon chips
According to Stanford University’s Subhasish Mitra, associate professor of electrical engineering and of computer science, and H.-S. Philip Wong, professor of electrical engineering, the future of supercomputing might actually be really, really small. With support from the National Science Foundation, the two are working with IBM and other collaborators to develop a new generation of computers that have processors based on carbon nanotubes (CNTs).

They believe CNTs could be the foundation for a new generation of electronics designed to deliver supercomputer performance on something as small and battery-efficient as a smartphone, and that chips based on carbon nanotube designs could eventually complement or replace the current generation of silicon-based electronics.

To make this a reality, Mitra and Wong are working to create multi-layered chips with carbon nanotube transistors and memory devices stacked on top of each other like an urban skyscraper because this architecture could boost computing speed and performance into the future.

Carbon nanotubes could be the foundation for a new generation of electronics. (Source: Stanford University)

Even though CNTs might be the perfect material to make the perfect transistor, Wong explained that the main engineering challenge right now is actually trying to figure out how to make this technology on a large scale. Last December, this technology was named N3XT, which stands for Nano-Engineering Computing Systems Technology.

Smart thread collects diagnostic data when sutured into tissue
In an advance that could pave way for new generation of implantable and wearable diagnostics, Tufts University researchers have integrated nano-scale sensors, electronics and microfluidics into threads – ranging from simple cotton to sophisticated synthetics – that can be sutured through multiple layers of tissue to gather diagnostic data wirelessly in real time.

Their research suggests that the thread-based diagnostic platform could be an effective substrate for a new generation of implantable diagnostic devices and smart wearable systems.

Threads penetrate multiple layers of tissue to sample interstitial fluid and direct it to sensing threads that collect data, such as pH and glucose levels. Conductive threads deliver the data to a flexible wireless transmitter sitting on top of the skin. (Source: Tufts University)

Until now, the researchers noted that the structure of substrates for implantable devices has essentially been two-dimensional, limiting their usefulness to flat tissue such as skin, according to the paper. Additionally, the materials in those substrates are expensive and require specialized processing. By contrast, thread is abundant, inexpensive, thin and flexible, and can be easily manipulated into complex shapes.

Enabling new sensors, light-emitting devices
In a development that could open up new areas of technology based on types of light emission that had been thought to be “forbidden,” or at least so unlikely as to be practically unattainable, MIT researchers have developed an approach that could cause certain kinds of interactions between light and matter.

Interestingly, these interactions, which would normally take billions of years to happen, could take place instead within billionths of a second, under certain special conditions, the researchers pointed out.

The findings are based on a theoretical analysis by the MIT team.

Interactions between light and matter, described by the laws of quantum electrodynamics, are the basis of a wide range of technologies, including lasers, LEDs, and atomic clocks. But from a theoretical standpoint, most light-matter interaction processes are forbidden by electronic selection rules, which limits the number of transitions between energy levels we have access to.

Now, the researchers have demonstrated theoretically that these constraints can be lifted using confined waves within atomically thin, 2-D materials, and they show that some of the transitions which normally take the age of the universe to happen could be made to happen within nanoseconds. And because of this, many of the dark regions of a spectrogram become bright once an atom is placed near a 2-D material.

They said the key to enabling a whole range of interactions, specifically transitions in atomic states that relate to absorbing or emitting light, is the use of 2D graphene, in which light can interact with matter in the form of plasmons, a type of electromagnetic oscillation in the material.

This method can enable the simultaneous emission of two photons that are “entangled,” meaning they share the same quantum state even when separated, and such generation of entangled photons is an important element in quantum devices, such as those that might be used for cryptography.

Emission spectra are a widely used method for identifying chemical compounds; the bright lines reveal the different frequencies of light that can be emitted by an atom. Here, a normal emission spectrum for an atom in a high-energy state (top) is compared to the emission from the same atom placed just a few nanometers (billionths of a meter) away from graphene that has been doped with charge carriers (bottom). For each energy-level transition, an orange line (or purple cloud) appears if that transition is estimated to be faster than one per microsecond — making it frequent enough to be observed. (Source: MIT)

Beyond its scientific implications, the team said the study has possible applications across multiple disciplines, since in principle it has potential to enable the full use of the periodic table for optical applications, possibly leading to applications in spectroscopy and sensing devices, ultrathin solar cells, new kinds of materials to absorb solar energy, organic LEDs with higher efficiencies, and photon sources for possible quantum computing devices.

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