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]

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]

Developed by the creative team that brings you Make — the groundbreaking magazine devoted entirely to DIY technology — and authored by Matthew Weaver and Duane Wessels, this latest title presents clear, easy-to-follow instructions for making your own easily customizable geeky devices by learning how to build and customize small form factor PCs from scratch.

“We want to show you how they work, how they look (inside and outside), and how you can use them,” write Weaver and Wessels. “We’ve written this book for people who like to tinker with both computer hardware and software.”

The book is also written for those of us who think smaller is better when it comes to computers. As Wessels elaborates, “Nobody wants a large, noisy, 200-Watt computer sitting on their entertainment center. And why use a full-size computer for your network firewall when a much smaller computer gets the job done while using only 1/10th the power? We want people to see how easy and fun it is to turn a small form factor computer into something that you can use in your home or workplace.”

The projects devised by Weaver and Wessels include all the necessary details for building eight different systems, from the shoebox-sized Shuttle system down to the stick-of-gum sized gumstix.

Thorough illustrations and step-by-step instructions make creating these projects easy:

• Digital Jukebox. Play your music collection with this Mini-ITX system that will fit anywhere
• Digital Video Recorder. Record and watch live television using a Shuttle ST62k-based system
• Network Appliances. Create and configure your own router and network monitor using embedded computers from Soekris
• Wi-Fi Extender. Extend the range of your Wi-Fi network with the Access Cube
• Portable Firewall. Protect your computer from unknown networks with a USB-powered firewall based on the OpenBlockS
• Handheld Wi-Fi Console. Turn the ZipIt Wireless Messenger into a go-anywhere, text-only, wireless handheld
• Tiny Bluetooth gizmo. Use the Bluetooth-powered gumstix computer to talk to cell phones, PDAs, and more

Shoebox sized and smaller, small form factor PCs can pack as much computing muscle as everything from a PDA to a full-sized desktop computer. Even better, they consume less power, have few or no moving parts, and are very quiet. Whether you plan to use one as a standalone PC or want to embed it in your next hacking project, this new up-to-the-minute resource from Make Projects is a must.

What’s more, car owners are predicted to cut back on driving in order to save money. Together, these changes in consumer behaviour could make an important dent in the US contribution to global warming, reducing annual carbon dioxide emissions by tens of millions of tonnes per year. The impact will be dramatic, says Chris Knittel, an economist at the University of California, Davis, who was involved in one of the studies.

The changes are being driven by record fuel prices in the US, where, at the end of April, the average price of gasoline stood at $3.65 per gallon, 20 percent more than in January and treble the price of a decade ago. Until recently, these increases did not seem to be having a consistent effect on the car market and fuel use. Though sales of SUVs in the US have been falling over the past few years, this decline has come on the back of years of rapid growth, and overall gasoline consumption has been increasing every year since 1991.

That could be about to change. Knittel and colleagues looked at data on 1.4 million car purchases over the past 10 years, comparing sales patterns with gas prices. They found that sales of the least fuel-efficient cars, such as SUVs and pick-up trucks, fell by 13 percent for every $1 per gallon increase in the price of gasoline. The biggest SUVs suffered the most, with sales dropping by over 25 percent for every dollar by which the gas price rose. And for every $1 hike in gas prices there was a corresponding 17 percent sales boost for the most efficient vehicles, such as compact cars and hybrids. Knittel estimates that over about a decade, such changes in buying habits could cut the amount of gasoline used by US drivers by around 7 percent for every $1 increase in its price.

Knittel’s findings, presented last month at the University of California Energy Institute in Berkeley, are in broad agreement with those of economist Kenneth Small of the University of California, Irvine. Small looked at data on US fuel consumption and prices over the past 40 years, and projected last year that the recent doubling in fuel prices would quickly lead to a 4 percent drop in the total mileage covered on the roads. In the longer term, as drivers continue to react to rising prices, he projects the size of the reduction will grow to around 20 percent (The Energy Journal, vol 28, p 25).

This would lead to a substantial reduction in carbon emissions. Small says that a $1 per gallon rise in gasoline prices, roughly that seen over the past two years, will result in motorists using 14 percent less fuel in the long term. That would avoid the release of some tens of millions of tonnes of CO2 per year, equivalent to roughly 2 percent of the country’s greenhouse-gas emissions for 2006. That is a hugely significant drop, close to the level of cuts that some nations are required to make under the Kyoto protocol.

Small’s prediction comes with major caveats, however. Gasoline prices are not expected to return to the lows of a decade ago, but could fall by 10 or 20 percent in coming years. And any US economic recovery will boost fuel consumption, partly through raising incomes, which would dilute the pressure on motorists to drive less. So while expensive fuel will rein in consumption, Small and other economists question whether this will be enough to cause an overall fall in emissions from cars.

It is also possible that politics will intervene before any of these effects has a chance to kick in. Presidential hopefuls John McCain and Hillary Clinton have reacted to consumer protests over soaring fuel prices by declaring that they would suspend federal gasoline taxes. “It’s a fantastically stupid idea,” says Roberton Williams, an economist at the University of Texas at Austin.

“But people don’t like high gas taxes, so it’s popular.”

[Claire Bowles @ New Scientist]