Nanogenerators Grow Strong Enough To Power Small Conventional Electronics

Blinking numbers on a liquid-crystal display (LCD) often indicate that a device's clock needs resetting. But in the laboratory of Zhong Lin Wang at Georgia Tech, the blinking number on a small LCD signals the success of a five-year effort to power conventional electronic devices with nanoscale generators that harvest mechanical energy from the environment using an array of tiny nanowires.


In this case, the mechanical energy comes from compressing a nanogenerator between two fingers, but it could also come from a heartbeat, the pounding of a hiker's shoe on a trail, the rustling of a shirt, or the vibration of a heavy machine. While these nanogenerators will never produce large amounts of electricity for conventional purposes, they could be used to power nanoscale and microscale devices - and even to recharge pacemakers or iPods.


Wang's nanogenerators rely on the piezoelectric effect seen in crystalline materials such as zinc oxide, in which an electric charge potential is created when structures made from the material are flexed or compressed. By capturing and combining the charges from millions of these nanoscale zinc oxide wires, Wang and his research team can produce as much as three volts - and up to 300 nanoamps.

Nanopillar Light Collectors Solar Cells

Sunlight represents the cleanest, greenest and far and away most abundant of all energy sources, and yet its potential remains woefully under-utilized. High costs have been a major deterrant to the large-scale applications of silicon-based solar cells. Nanopillars - densely packed nanoscale arrays of optically active semiconductors - have shown potential for providing a next generation of relatively cheap and scalable solar cells, but have been hampered by efficiency issues. The nanopillar story, however, has taken a new twist and the future for these materials now looks brighter than ever.

"By tuning the shape and geometry of highly ordered nanopillar arrays of germanium or cadmium sulfide, we have been able to drastically enhance the optical absorption properties of our nanopillars," says Ali Javey, a chemist who holds joint appointments with the Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) at Berkeley.

Energy Efficient And Ultra-Small Displays

University of Michigan scientists using AFOSR-funding have created the smallest pixels available that will enable LED, projected and wearable displays to be more energy efficient with more light manipulation possible and all on a display that may eventually be as small as a postage stamp.

This latest nanostructuring technology for the Air Force developed by Dr. Jay Guo, associate professor in the Department of Electrical Engineering and Computer Science at the University of Michigan and his graduate student researchers, Ting Xu, Yi-Kuei Wu and collaborator Dr. Xiangang Luo includes a new color filter made of nano-thin sheets of metal-dielectric-metal stack, which have perfectly-shaped slits that act as resonators. They trap and transmit light and transform the pixels into effective color filtering elements.

The pixels created from this technology are ten times smaller than what are now on a computer monitor and eight times smaller than ones on a smart phone. They use existing light more effectively and make it unnecessary to use polarizing layers for liquid crystal displays (LCDs). They enable the backlighting on the LED to be used more efficiently. Prior to this technology, LCDs had two polarizing layers, a color filter sheet, two layers of electrode-laced glass and a liquid crystal layer, but only about five percent of the backlighting reached the viewer.

Nanosprings Offer Improved Performance In Biomedicine

Researchers at Oregon State University have reported the successful loading of biological molecules onto "nanosprings" - a type of nanostructure that has gained significant interest in recent years for its ability to maximize surface area in microreactors.

The findings, announced in the journal Biotechnology Progress, may open the door to important new nanotech applications in production of pharmaceuticals, biological sensors, biomedicine or other areas.

"Nanosprings are a fairly new concept in nanotechnology because they create a lot of surface area at the same time they allow easy movement of fluids," said Christine Kelly, an associate professor in the School of Chemical, Biological and Environmental Engineering at OSU.

"They're a little like a miniature version of an old-fashioned, curled-up phone cord," Kelly said. "They make a great support on which to place reactive catalysts, and there are a variety of potential applications."

Artificial Skin Out of Nanowires

Engineers at the University of California, Berkeley, have developed a pressure-sensitive electronic material from semiconductor nanowires that could one day give new meaning to the term "thin-skinned."

The artificial skin, dubbed "e-skin" by the UC Berkeley researchers, is described in a Sept. 12 paper in the advanced online publication of the journal Nature Materials. It is the first such material made out of inorganic single crystalline semiconductors.

A touch-sensitive artificial skin would help overcome a key challenge in robotics: adapting the amount of force needed to hold and manipulate a wide range of objects.

For the e-skin, the engineers printed the nanowires onto an 18-by-19 pixel square matrix measuring 7 centimeters on each side. Each pixel contained a transistor made up of hundreds of semiconductor nanowires. Nanowire transistors were then integrated with a pressure sensitive rubber on top to provide the sensing functionality. The matrix required less than 5 volts of power to operate and maintained its robustness after being subjected to more than 2,000 bending cycles.

The researchers demonstrated the ability of the e-skin to detect pressure from 0 to 15 kilopascals, a range comparable to the force used for such daily activities as typing on a keyboard or holding an object. In a nod to their home institution, the researchers successfully mapped out the letter C in Cal.

Nanoribbons for Graphene Transistors

In the recent issue of Nature, scientists from Empa and the Max Planck Institute for Polymer Research report how they have managed for the first time to grow graphene ribbons that are just a few nanometers wide using a simple surface-based chemical method. Graphene ribbons are considered to be «hot candidates» for future electronics applications as their properties can be adjusted through width and edge shape.

Transistors on the basis of graphene are considered to be potential successors for the silicon components currently in use. Graphene consists of two-dimensional carbon layers and possesses a number of outstanding properties: it is not only harder than diamond, extremely tear-resistant and impermeable to gases, but it is also an excellent electrical and thermal conductor. However, as graphene is a semi-metal it lacks, in contrast to silicon, an electronic band gap and therefore has no switching capability which is essential for electronics applications. Scientists from Empa, the Max Planck Institute for Polymer Research in Mainz (Germany), ETH Zürich and the Universities of Zürich und Bern have now developed a new method for creating graphene ribbons with band gaps.