Thursday, April 2, 2009

How Snails Do It

By adjusting nine parameters in a single equation, a computer model can generate patterned shells (right example in each pair above) that closely resemble real mollusk shells. (Jump to original article in the link below for great animations.)

University of California, Berkeley, graduate student Alistair Boettiger has amassed a beautiful collection of seashells, but not by combing the beach. He created them in his computer.
A simple neural network model of seashell growth can generate realistic mollusk shells based on a simple principle discovered 140 years ago. He and George Oster, a UC Berkeley biophysicist, along with University of Pittsburgh mathematical neuroscientist Bard Ermentrout, have written a computer program that generates the complex patterns of seashells using simple principles developed to explain how the brain works and how memories are stored.
The "neural net" model explains how mollusks build their seashells based on the finding that the mollusk's tongue-like mantle, which overlaps the edge of the growing shell, senses or "tastes" the calcium carbonate layer laid down the day before in order to generate a new layer.
"The pattern on a seashell is the mollusk's memories," said Oster, a professor of environmental science, policy and management and of molecular and cell biology. "The shell is laid down in layers, so the mantle is sensing the history of the mollusk's 'thoughts' and extrapolating to the next layer, just like our brains project into the future."
The studies may help neuroscientists understand how neural networks work in the brain and throughout the body, where neural nets cover our skin and all internal organs.
The researchers' computer model can reproduce a wide variety of shell shapes, colors and patterns. The researchers' computer model, published this week in the early online edition of the journal Proceedings of the National Academy of Sciences, reproduces nearly all known shell shapes, ranging from scallops to whelks, and nearly all the shell patterns that make beachcombing so popular.
"The model gives us a remarkable ability to explain much of the dramatic diversity of both shape and pattern that we see in the natural world," Boettiger said.
Jump to the link for great animations.

Wednesday, February 25, 2009

Nanotube Bosch

A garden of (very small) earthly delights. Carbon nanotube arrays could be the basis of high-density energy storage devices and efficient chip cooling systems. The performance of such devices, however, depends on the quality of the nanotubes and the precise structure of the array. So researchers including Anastasios John Hart, assistant professor of mechanical engineering at the University of Michigan, are honing techniques for growing carefully structured forests of high-quality carbon nanotubes. Hart made these images with a scanning electron microscope; all show vertically grown nanotubes. This is a composite of many images of carbon nanotubes grown on silicon wafers or in cavities etched in the wafers. Each stalklike structure is made up of thousands of nanotubes or more. The catalyst that starts off the nanotubes’ growth is visible under some of them as a dark, shadowlike spot. Structures that appear withered were dipped in liquid after they grew; as the liquid evaporated, the nanotubes shriveled.

Friday, January 30, 2009

Super-Charged Metal Ion Generator

It is rare indeed that a justifiably "new" thin films deposition technique comes along. In my lifetime, I have not seen such a new technology, other than cathodic arc in the 1970s, that has the potential to significantly advance the field.
BERKELEY, CA – In the electronics industry, thin metal films are deposited on silicon wafers with a sputter gun, which uses ionized argon gas to knock the metal atoms off a target. Scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory have now developed a powerful new kind of sputter process that can deposit high-quality metal films in complex, three-dimensional nanoscale patterns at a rate that by one important measure is orders of magnitude greater than typical systems.
Called “self-sputtering far above the runaway threshold,” the new method “is an extraordinarily prolific generator of metal ions,” says Andre Anders, a senior scientist in Berkeley Lab’s Accelerator and Fusion Research Division, where he leads the Plasma Applications Group. Anders and his colleague Joakim Andersson, now at Uppsala University in Sweden, based their new "Self-Sputtering" method on the existing technique of High Power Impulse Magnetron Sputtering (HIPIMS). The new method uses much higher power in short pulses in order to keep the average power low enough to avoid overheating the sputtering target.
Self-sputtering occurs when target atoms that have themselves been ionized return to the target to knock out yet more target atoms. Some of the sputtered atoms remain neutral and may fly straight to the substrate; others are ionized and may return to the target, producing yet more ions and yet more free electrons (secondary electrons).
Once self-sputtering gets started, if enough new atoms get ionized and enough new ions return to the target, it becomes self-sustaining. The magnetic field lines near the target grow thick with spiraling electrons, the plasma is dominated by metal ions instead of gas, and the sheath becomes a potent source of a large flux of energetic electrons that produce still more “excess” plasma – the system runs away, until it finally reaches a new equilibrium at a much higher peak-power level than before.
Beyond the semiconductor industry Anders sees a wide range of applications for the efficient new process, some of which may sound exotic. Because a sustained, self-sputtering plasma can operate in pure vacuum, the new method could also be used for coating materials in space, or even for ion thrusters whose fuel consists of a low-cost, noncombustible metal target, making it unnecessary to carry bottled gases or liquids into space.
For now, Andersson and Anders’s demonstration of a 250-ampere current of copper ions to a substrate – far higher than any ever achieved in a magnetron system – stands as an achievement with the potential to revolutionize some of the semiconductor industry’s most important manufacturing processes.