SCIENCE NOTEBOOK

Monday, February 25, 2008

IBM Solves Atomic Puzzle

You think Sisyphus had it bad, having to roll that boulder up a hill? Consider the opposite challenge faced by nano-engineers as they try to build microscopic electronic circuits. Using single atoms as building blocks, they need to push with barely measurable forces lest they send their Lilliputian Legos hurtling off the workbench. But how much force is just enough to move an atom?

Now scientists at IBM have become the first to find out, and the answer is little. Very little.

For years, chipmakers and materials scientists have been honing matter to ever smaller dimensions and etching increasingly finer circuits onto silicon. But at the smallest scales it makes sense to build circuits from the bottom up, an atom at a time.

The researchers used a tool that has at its heart a tiny quartz tuning fork vibrating thousands of times per second. By measuring how much those vibrations decreased as the tool was used to nudge individual atoms along a surface, the team was able to calculate how much force was required.

The answer depends on the atom. To push a cobalt atom over a copper surface, it turns out, takes 17 piconewtons, or about 0.000000002 (2 billionths) the amount of force it takes to lift a penny. By contrast, it takes 210 piconewtons to push a cobalt atom over a platinum surface, which bonds more strongly to cobalt.

The result "could pave the way for new data storage and memory devices," said Andreas J. Heinrich of the IBM Almaden Research Center in California, who helped lead the research with others from IBM and the University of Regensburg in Germany. Their work appeared in the Feb. 22 issue of Science.

-- Rick Weiss

'Devil Toad' Hints at Land Link

Scientists have discovered the remains of what appears to be the largest frog that ever lived: a predatory, 16-inch-long, 10-pound creature dubbed Beelzebufo, or Devil Toad, that hopped around Madagascar 65 million years ago.

David Krause of Stony Brook University and his colleagues first unearthed fossilized remains of the creature in northwestern Madagascar, the large island off Africa's southeastern coast, in 1993. Since then, the team has gathered some 75 fossilized fragments of the creature, enabling them to reconstruct its skeleton, including nearly the entire skull, they reported last week in the Proceedings of the National Academy of Sciences.

The creature appeared to have some type of armor or protective shield, an extremely wide mouth and powerful jaws, indicating it was capable of killing lizards and other small vertebrates -- perhaps even hatchling dinosaurs.

The biggest frog alive today is the Goliath frog of West Africa, which grows as long as 12.5 inches and can weigh 7.2 pounds.

Surprisingly, Beelzebufo appears to be closely related to smaller frogs that today live half a world away in South America. "We're asking ourselves, 'What's a "South American" frog doing halfway around the world in Madagascar?' " Krause said. One explanation may be that there was once a land connection between them, he said.

-- Rob Stein

Absinthe's Workings Still Unclear

Henri de Toulouse-Lautrec can rest easy. Absinthe remains a mystery.

Absinthe was the drink of choice in the seedy brothels and cafes depicted by the 19th-century French painter. It reputedly drove people mad and was eventually banned in many places.

The psychological effects aside, absinthe has an unusual property, one shared by Pernod, ouzo and other anise-flavored drinks. It turns cloudy when water is added.

A plant-derived oil responsible for the drink's distinctive flavor is fully dissolved in the undiluted liquor (which is at least 45 percent alcohol, the rest being water). When more water is added, the oil comes out of solution and forms little droplets. These make the drink cloudy.

Over time, the droplets get larger in size and fewer in number, causing the drink to become less cloudy. If left to stand for weeks, the liquid once again becomes clear, with the oil forming a thin layer on the surface.

In the current issue of Langmuir, a journal of the American Chemical Society, a team of Dutch chemists led by Erik van der Linden of Wageningen University explored the physics of this phenomenon.

Equations predict that the more watery the mixture, the longer the drink will remain cloudy. That is because it should be harder for the oil molecules to coalesce into large droplets. The equations also predict that the higher the water content, the longer it will take for the oil to "cream out" on the surface.

The Dutch experiments, however, showed just the opposite. The more alcoholic the mixture, the longer the cloudiness lasted and the slower the creaming.

What is known about molecular activity at the interface of oil droplets and water, the solubility of oil in the mixture, and the density issues involved is "not sufficient to explain the results for these unique three-component systems," the authors write.

-- David Brown