The method, published in the May 4 issue of Nature Nanotechnology, enables more precise shaping of microchip components than what is possible with current technology. More precise component shapes could help manufacturers build smaller and better microchips, the key to more powerful computers and other devices.

“We are able to achieve a precision and improvement far beyond what was previously thought achievable,” said electrical engineer Stephen Chou, the Joseph C. Elgin Professor of Engineering, who developed the method along with graduate student Qiangfei Xia. Chou’s lab has previously pioneered a number of innovative chip making techniques, including a revolutionary method for making nanometer-scale patterns using imprinting.

Microchips work best when the structures fabricated on them are straight, thin and tall. Rough edges and other defects can degrade or even ruin chip performance in most applications. In integrated circuits, for instance, such flaws could cause current to leak and voltage to fluctuate. In optic devices, they could interfere with the transmission of light. In biological devices, they could impede the flow of DNA and other biomaterials.

“These chip defects pose serious roadblocks to future advances in many industries,” Chou said.

To deal with this problem, researchers try to improve the process used to make the microchips. However, Chou said such an approach works only to a point; eventually chip makers will run up against fundamental physical limits of current manufacturing techniques. In particular, the electrons and photons that are used like chisels to carve out the microscopic features on a chip always have some random behavior. This effect becomes pronounced at very small scales and limits the accuracy of component shapes.

“What we propose instead is a paradigm shift: Rather than struggle to improve fabrication methods, we could simply fix the defects after fabrication,” said Chou. ???And fixing the defects could be automatic — a process of self-perfection.???

Chou’s method, termed Self-Perfection by Liquefaction (SPEL), achieves this by melting the structures on a chip momentarily, and guiding the resulting flow of liquid so that it re-solidifies into the desired shapes. This is possible because natural forces acting on the molten structures, such as surface tension — the force that allows some insects to walk on water — smooth the structures into geometrically more accurate shapes. Lines, for instance, become straighter, and dots become rounder.

Simple melting by direct heating has previously been shown to smooth out the defects in plastic structures. This process can’t be applied to a microchip, for two reasons. First, the key structures on a chip are not made of plastic, which melts at temperatures close to the boiling point of water, but from semiconductors and metals, which have much higher melting points. Heating the chip to such temperatures would melt not just the structures, but nearly everything else on the chip. Secondly, the melting process would widen the structures and round off their top and side surfaces, all of which would be detrimental to the chip.

Chou’s team overcame the first obstacle by using a light pulse from so-called excimer laser, similar to those used in laser eye surgery, because it heats only a very thin surface layer of a material and causes no damage to the structures underneath. The researchers carefully designed the pulse so that it would melt only semiconductor and metal structures, and not damage other parts of the chip. The structures need to be melted for only a fraction of a millionth of a second, because molten metal and semiconductors can flow as easily as water and have high surface tension, which allows them to change shapes very quickly.

To overcome the second obstacle, Chou’s team placed a plate on top of the melting structures to guide the flow of liquid. The plate prevents a molten structure from widening, and keeps its top flat and sides vertical, Chou said. In one experiment, it made the edges of 70 nanometer-wide chromium lines more than five times smoother. The resulting line smoothness was far more precise than what semiconductor researchers believe to be attainable with existing technology.

The conventional approach to fixing chip defects is to measure the exact shape of each defect, and provide a correction precisely tailored to it — a slow and expensive process, Chou said. In contrast, Chou’s guided melting process fixes all defects on a chip in a single quick and inexpensive step. “Regardless of the shape of each defect, it always gets fixed precisely and with no need for individual shape measurement or tailored correction,” Chou said.

One of the big surprises from this work is observed when the guiding plate is placed not in direct contact with the molten structures, but at a distance above it. In this situation, the liquid material from the structures rises up and reaches the plate by itself, causing line structures to become taller and narrower — both highly desirable outcomes from a chip design perspective.

“The authors demonstrate improved edge roughness and dramatically altered aspect ratios in nanoscale features,” said Donald Tennant, director of operations at the NanoScale Science and Technology Facility at Cornell University. The techniques “may be a way forward when nanofabricators bump up against the limits of lithography and pattern transfer,” he said.

Next, Chou’s group plans to demonstrate this technique on large (8-inch) wafers. Several leading semiconductor manufacturers have expressed keen interest in the technique, Chou said.

[Steven Schultz @ Princeton University Engineering School]

Michelle Alfa and a team of scientists from Manitoba, Canada investigated the spread of so-called superbugs in hospitals. Hospital patients are thought to catch bugs like vancomycin resistant Enterococci (VRE), methicillin resistant Staphylococcus aureus (MRSA) and C. difficile because they are not eradicated from the hospital environment. These bugs may be transferred between patients through cross-contamination in the bathroom.

“Various studies have looked at the most effective cleaning agents, but none of these studies considered whether housekeeping staff were actually cleaning the toilets properly,” says Alfa. “It is impossible to assess the effectiveness of any action against these bacteria unless you can be sure that cleaners comply with protocols.”

Alfa’s toilet inspectors smeared the UV lotion under the seats of 20 toilets and commodes being used by patients with diarrhoea at a hospital in Winnipeg. Seven of these patients had C. difficile infection, while 13 others did not. The toilets and commodes were tested every weekday for six months and checked using UV light to determine how well they had been cleaned. In addition, samples were taken from toilet surfaces to determine whether C difficile spores were present.

The UV marker revealed that the commodes for the seven patients isolated with C. difficle infections had not been properly cleaned 72% of the time. The toilets fared slightly better, with half of the samples taken showing no residual UV lotion after cleaning. The 13 patients not on isolation had much cleaner toilets, with only 14% glowing brightly under UV light. Further assessments showed that differences in toilet cleaning were “ward dependent” and since specific cleaners work on different wards, the results likely reflect characteristics of the individual cleaning staff.

More worryingly, C. difficle was still detected in 40% of samples taken from the cleanest toilets (i.e. those with no detectable UV marker). “This suggests that both the physical cleaning action as well as the disinfectant/cleaning agent were ineffective for killing and/or removing C. difficile from toilets,” notes Alfa.

“Our data suggest that without an agent with some activity against C. difficile spores the physical action of cleaning alone cannot be relied upon to effectively eradicate this organism from the toilets of patients who are shedding this type of spore. Nevertheless, we would still recommend that monitoring with a UV marker becomes a routine part of a hospital’s housekeeping quality assurance programme.

[Charlotte Webber @ BioMed Central]

Engineers at Duke University believe that the results of feasibility studies conducted in their laboratory represent the first concrete steps toward achieving this space age vision of the future. Also, on a more immediate level, the technology developed by the engineers could make certain contemporary medical procedures safer for patients, they said.

For their experiments, the engineers started with a rudimentary tabletop robot whose “eyes” used a novel 3-D ultrasound technology developed in the Duke laboratories. An artificial intelligence program served as the robot’s “brain” by taking real-time 3-D information, processing it, and giving the robot specific commands to perform.

“In a number of tasks, the computer was able to direct the robot’s actions,” said Stephen Smith, director of the Duke University Ultrasound Transducer Group and senior member of the research team. “We believe that this is the first proof-of-concept for this approach. Given that we achieved these early results with a rudimentary robot and a basic artificial intelligence program, the technology will advance to the point where robots — without the guidance of the doctor — can someday operate on people.”

The results of a series of experiments on the robot system directing catheters inside synthetic blood vessels was published online in the journal IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. A second study, published in April in the journal Ultrasonic Imaging, demonstrated that the autonomous robot system could successfully perform a simulated needle biopsy.

Advances in ultrasound technology have made these latest experiments possible, the researchers said, by generating detailed, 3-D moving images in real-time.

The Duke laboratory has a long track record of modifying traditional 2-D ultrasound — like that used to image babies in utero — into the more advanced 3-D scans. After inventing the technique in 1991, the team also has shown its utility in developing specialized catheters and endoscopes for real-time imaging of blood vessels in the heart and brain.

In the latest experiment, the robot successfully performed its main task: directing a needle on the end of the robotic arm to touch the tip of another needle within a blood vessel graft. The robot’s needle was guided by a tiny 3-D ultrasound transducer, the “wand” that collects the 3-D images, attached to a catheter commonly used in angioplasty procedures.

“The robot was able to accurately direct needle probes to target needles based on the information sent by the catheter transducer,” said John Whitman, a senior engineering student in Smith’s laboratory and first author on both papers. “The ability of the robot to guide a probe within a vascular graft is a first step toward further testing the system in animal models.”

While the research will continue to refine the ability of robots to perform independent procedures, the new technology could also have more direct and immediate applications.

“Currently, cardiologists doing catheter-based procedures use fluoroscopy, which employs radiation, to guide their actions,” Smith said. “Putting a 3-D ultrasound transducer on the end of the catheter could provide clearer images to the physician and greatly reduce the need for patients to be exposed to radiation.”

In the earlier experiments, the tabletop robot arm successfully touched a needle on the arm to another needle in a water bath. Then it performed a simulated biopsy of a cyst, fashioned out of a liquid-filled balloon in a medium designed to simulate tissue.

“These experiments demonstrated the feasibility of autonomous robots accomplishing simulated tasks under the guidance of 3-D ultrasound, and we believe that it warrants additional study,” Whitman said.

The researchers said that adding this 3-D capability to more powerful and sophisticated surgical robots already in use at many hospitals could hasten the development of autonomous robots that could perform complex procedures on humans.

[Richard Merritt @ Duke University]

In a paper published today in Nature Biotechnology, researchers led by Los Alamos National Laboratory and the U.S. Department of Energy Joint Genome Institute announced that the genetic sequence of the fungus Tricoderma reesei has uncovered important clues about how the organism breaks down plant fibers into simple sugars. The finding could unlock possibilities for industrial processes that can more efficiently and cost effectively convert corn, switchgrass and even cellulose-based municipal waste into ethanol. Ethanol from waste products is a more-carbon-neutral alternative to gasoline.

The fungus T. reesei rose to dubious fame during World War II when military leaders discovered it was responsible for rapid deterioration of clothing and tents in the South Pacific. Named after Dr. Elwyn T. Reese, who, with colleagues, originally isolated the hungry fungus, T. reesei was later identified as a source of industrial enzymes and a role model for the conversion of cellulose and hemicellulose — plant fibers — into simple sugars.

The organism uses enzymes it creates to break down human-indigestible fibers of plants into the simplest form of sugar, known as a monosaccharide. The fungus then digests the sugars as food.

Researchers decoded the genetic sequence of T. reesei in an attempt to discover why the deep green fungus was so darned good at digesting plant cells. The sequence results were somewhat surprising. Contrary to what one might predict about the gene content of a fungus that can eat holes in tents, T. reesei had fewer genes dedicated to the production of cellulose-eating enzymes than its counterparts.

“We were aware of T. reesei’s reputation as producer of massive quantities of degrading enzymes, however we were surprised by how few enzyme types it produces, which suggested to us that its protein secretion system is exceptionally efficient,” said Los Alamos bioscientist Diego Martinez (also at the University of New Mexico), the study’s lead author. The researchers believe that T. reesei’s genome includes “clusters” of enzyme-producing genes, a strategy that may account for the organism’s efficiency at breaking down cellulose.

On an industrial scale, T. reesei could be employed to secrete enzymes that can be purified and added into an aqueous mixture of cellulose pulp and other materials to produce sugar. The sugar can then be fermented by yeast to produce ethanol.

“The sequencing of the Trichoderma reesei genome is a major step towards using renewable feedstocks for the production of fuels and chemicals,” said Joel Cherry, director of research activities in second-generation biofuels for Novozymes, a collaborating institution in the study. “The information contained in its genome will allow us to better understand how this organism degrades cellulose so efficiently and to understand how it produces the required enzymes so prodigiously. Using this information, it may be possible to improve both of these properties, decreasing the cost of converting cellulosic biomass to fuels and chemicals.”

[James E. Rickman @ DOE/Los Alamos National Laboratory]