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From the Labs: Nanotechnology

New publications, experiments and breakthroughs in nanotechnology–and what they mean.
December 18, 2007

Terabyte Nonvolatile Memory
A Flash ­alternative ­could store a ­terabyte of data

Copper wires (small branching structures, above) grown by applying a voltage to copper-doped tungsten could be the key to a new type of ultradense memory.

Source: “Bipolar and Unipolar Resistive Switching in Cu-Doped SiO2
Christina Schindler et al.
IEEE Transactions on Electron Devices 54: 2762-2768

Results: Using silicon and copper, researchers have made a new type of ­memory that stores information by harnessing negative and positive charges to assemble and disassemble nanoscale metallic wires. Each ­memory cell consists of two electrodes separated by an electrolyte doped with copper ions. When a cell is in the off state, little current passes from one electrode to the other. When a “writing” voltage is applied, the ions line up and form a filament that bridges the electrodes, markedly increasing current. Reversing the voltage causes the filament to dissolve.

Why it matters: The technology could lead to memory devices that hold more information, since each binary bit could be stored in wires just a couple of atoms thick. The new memory devices could be used to replace flash memory, eventually making it possible to store a terabyte of data on a cell phone or music player. Similar ionic memory devices have been made before in the lab, but they relied on more exotic materials. Chip makers might be more likely to consider adopting this new type of memory if they could use materials common in semiconductor manufacturing.

Methods: The researchers used standard techniques to deposit and pattern a tungsten electrode, a layer of silicon dioxide, and a copper electrode. By heating the layers to more than 600 ºC, the researchers then caused copper ions from the electrodes to diffuse into the silicon dioxide, forming the copper-doped electrolyte.

Next steps: The researchers need to optimize the performance of the memory cells and determine how many read-write cycles they can survive. To reach terabyte densities, it will be necessary to fabricate multilayer memory devices and store multiple bits of information on each wire; both feats should be possible with the new technology.

Novel Drug Synthesis
A new catalyst could reduce waste and lead to new drugs based on natural products

Source: “A Predictably Selective Aliphatic C-H Oxidation Reaction for Complex Molecule Synthesis”
Mark S. Chen and M. Christina White
Science 318: 783-787

Results: A new iron-based cata­lyst developed by researchers at the University of Illinois at Urbana-Champaign enables researchers to predictably alter the cores of complex mole­cules by oxidizing specific ­carbon-hydrogen bonds.

Why it matters: Complex molecules produced by plants and other organisms are often good candidates for new drugs. But they frequently need to be chemically modified before they’re effective enough for therapeutic use. In the past, making the necessary modifications could require synthesizing the entire molecule from scratch, often a difficult process requiring multiple steps. The new catalyst makes these modifications easier.

Methods: The researchers synthesized a catalyst that was both relatively large and attracted to electrons. Then they derived a list of rules predicting precisely which bonds in complex molecules the catalyst would oxidize. They showed that in general it oxidized the carbon-hydrogen bond at the most electron-rich area of a complex molecule. If, however, the most electron-rich area was difficult to reach, the catalyst oxidized the most accessible C-H bond. Finally, if the molecule included a carboxylic acid group, the catalyst oxidized a bond a certain distance from the acid. The researchers confirmed that the rules allow chemists to predict exactly which bond will be modified.

Next steps: Researchers at other academic institutions and drug companies are beginning to use the catalyst in their work. The University of Illinois researchers are considering new catalysts that work on similar principles.

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