All-carbon-nanotube transistor can be crumpled like a piece of paper

The researchers, Shinya Aikawa and coauthors from the University of Tokyo and the Tokyo University of Science, have published their study in a recent issue of Applied Physics Letters.

“The most important thing is that electronics might now be usable in places or situations that were previously not possible,” coauthor Shigeo Maruyama, a mechanical engineering professor at the University of Tokyo, told PhysOrg.com. “Since our device is so flexible and deformable it could potentially be stuck anywhere. This could lead to active electronic devices that are applied like a sticker or an adhesive bandage, as well as to wearable electronics.”

Unlike other field-effect transistors (FETs), the new FET is unique in that all channels and electrodes are made of carbon nanotubes (CNTs), while the substrate is made of highly flexible and transparent poly(vinyl alcohol) (PVA). Previously, the majority of flexible, transparent FETs have used gold or indium tin oxide as electrodes. However, gold decreases the devices’ transparency while brittle indium tin oxide limits the flexibility. A few recent FETs have been made that consist entirely of CNTs, but so far these devices have been built on thick plastic substrates, limiting their flexibility.

 The present device (1 mm curvature) is the most bendable CNT-FET to date without performance degradation. Image credit: Aikawa, et al. ©2012 American Institute of Physics

After patterning the components using standard photolithography and laminating the device with the PVA, the final thickness of the new all-CNT-FET was approximately 15 µm. This thinness made the device highly pliable, with tests showing that the finished transistor could withstand a 1-mm bending radius with almost no changes in electrical properties. Although other transistors have been developed with bendable radii as low as 0.1 mm, the new transistor is the most bendable that experiences no performance degradation. 

After subjecting the transistor to 100 wrinkling cycles, the researchers observed a slight decrease in maximum drain current, which may be due to some broken connections in the CNT network. However, the minimal decrease in maximum drain current, which stabilizes after about 30 cycles, does not affect the overall transconductance, which was not affected by the repeated bending. 

In addition to its flexibility, the all-CNT-FET also has an optical transmittance of more than 80%, which is sufficient to clearly see through the device. The researchers attribute the high flexibility to the inherent robustness of carbon nanotubes, and predict that they could increase the flexibility even further by optimizing the positions of the channels. Overall, the results demonstrate that flexible, transparent all-carbon electronics are coming closer to commercial reality.

“Ongoing topics are to control device properties and to integrate them,” Maruyama said. “If these issues can be resolved, we would like to realize flexible and transparent all-carbon working circuits.”

 

From physorg

Read More

Generating Power from Salty Water: Unique Salt Allows Energy Production to Move Inland

"We are taking two technologies, each having limitations, and putting them together," said Bruce E. Logan, Kappe Professor of Environmental Engineering. "Combined, they overcome the limitations of the individual technologies."

 Microbial reverse dialysis test cell. (Credit: Penn State, Dept of Public Information)

The technologies Logan refers to are microbial fuel cells (MFC) -- which use wastewater and naturally occurring bacteria to produce electricity -- and reverse electrodialysis (RED) -- which produces electricity directly from the salinity gradient between salty and fresh water. The combined technology creates a microbial reverse-electrodialysis cell (MRC). The researchers describe MRCs in  the March 1 edition of Science Express.

RED stacks extract energy from the ionic difference between fresh water and salt water. A stack consists of alternating ion exchange membranes -- positive and negative -- with each RED membrane pair contributing additively to the electrical output. Unfortunately, using only RED stacks to produce electricity is difficult because a large number of membranes is required when using water at the electrodes, due to the need for water electrolysis.

Using exoelectrogenic bacteria -- bacteria found in wastewater that consume organic material and produce an electric current -- reduces the number of stacks needed and increases electric production by the bacteria.

Logan, working with Roland Cusick, graduate student in environmental engineering, and postdoctoral fellow Younggy Kim, placed a RED stack between the electrodes of an MFC to form the MRC.

While the researchers previously showed that an MRC can work with natural seawater, the organic matter in water will foul the membranes without extensive precleaning and treatment of the water. Seawater use restricts MRC operation to coastal areas, but food waste, domestic waste and animal waste contain about 17 gigawatts of power throughout the U.S. One nuclear reactor typically produces 1 gigawatt.

Rather than rely on seawater, the researchers used ammonium bicarbonate, an unusual salt. An ammonium bicarbonate solution works similarly to seawater in the MRC and will not foul the membranes. The ammonium bicarbonate is also easily removed from the water above 110 degrees Fahrenheit. The ammonia and carbon dioxide that make up the salt boil out, and are recaptured and recombined for reuse.

"Waste heat makes up 7 to 17 percent of energy consumed in industrial processes," said Logan. "There is always a source of waste heat near where this process could take place and it usually goes unused."

The researchers tested their ammonium bicarbonate MRC and found that the initial production of electricity was greater than that from an MRC using seawater.

"The bacteria in the cell quickly used up all the dissolved organic material," said Logan. "This is the portion of wastewater that is usually the most difficult to remove and requires trickling filters, while the particulate portion which took longer for the bacteria to consume, is more easily removed."

The researchers tested the MRC only in a fill and empty mode, but eventually a stream of wastewater would be run through the cell. According to Logan, MRCs can be configured to produce electricity or hydrogen, making both without contributing to greenhouse gases such as carbon dioxide. The MRC tested produced 5.6 watts per square meter.

Logan also said not having to process wastewater would save about 60 gigawatts.

The King Abdullah University of Science and Technology supported this work.

From sciencedaily

Read More

Bacteria Communicate by Touch, New Research Suggests

The findings appeared recently in the journal Genes & Development.

Christopher Hayes, UCSB associate professor of molecular, cellular, and development biology, teamed with graduate students Elie Diner, Christina Beck, and Julia Webb to study uropathogenic E. coli (UPEC), which causes urinary tract infections in humans. They discovered a sibling-like link between cell systems that have largely been thought of as rivals.

 Associate professor Christopher Hayes and graduate student Christina Beck

The paper shows that bacteria expressing a contact--dependent growth inhibition system (CDI) can inhibit bacteria without such a system only if the target bacteria have CysK, a metabolic enzyme required for synthesis of the amino acid cysteine. CysK is shown to bind to the CDI toxin -- an enzyme that breaks RNA ó and activate it.

For a cell system typically thought of as existing only to kill other bacteria -- as CDIs have largely been -- the results are surprising, said Hayes, because they suggest that a CDI+ inhibitor cell has to get permission from its target in order to do the job.

"This is basically the inhibitor cell asking the target cell, 'Can I please inhibit you?'" he explained. "It makes no sense. Why add an extra layer of complexity? Why add a permissive factor? That's an unusual finding.

"We think now that the [CDI] system is not made solely because these cells want to go out and kill other cells," Hayes continued. "Our results suggest the possibility that these cells may use CDI to communicate as siblings and team up to work together; for example, in formation of a biofilm, which lends bacteria greater strength and better odds of survival."

The study points to the enzyme CysK as the potential catalyst to such bacterial communication -- like a secret handshake, or a password. In simpler terms, said Hayes, "If you have the right credentials, you're allowed into the club; otherwise you're turned away. There's a velvet rope, if you will, and if you're not one of the cool kids, you can't get in."

Although only UPEC was studied for this paper, Hayes said that the findings hold potential implications for pathogens from bacterial meningitis to the plague, as well as for plant-based bacteria that can devastate vegetation.

David Low, a UCSB professor of molecular, cellular, and developmental biology and secondary author on the paper, described the work by Hayes's laboratory as potentially groundbreaking for its insights into how bacteria communicate -- and the practical applications that could someday result.

"We are just starting to get some clues that bacteria may be talking to each other with a contact-dependent language," said Low. "They touch and respond to one another in different ways depending on the CDI systems and other genotypic factors. Our hope is that ultimately this work may aid the development of drugs that block or enhance touch-dependent communication, whether the bacteria is harmful or helpful."

The work was supported by grants from the National Institutes of Health and the National Science Foundation.

From sciencedaily

Read More