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To: ~digs who wrote (170)	6/17/2001 6:14:22 AM
From: ~digs	Read Replies (1) \| Respond to of 6763

physics: Tiny minds nature.com by: PHILIP BALL Researchers have developed prototype computer memories in which information is recorded, read and erased by molecular switches. Computer memories that store information in single molecules could be far more powerful than those of today's machines. Mark Reed of Yale University in New Haven, Connecticut, and colleagues built molecular switches consisting of rod-like organic (carbon-based) molecules that carry a current between two gold electrodes. The molecules are like tiny wires, each more than a thousand times smaller than the miniaturized transistors used as switches in silicon chips. Initially the molecules don't conduct electricity very well. But by applying a voltage pulse to one of the electrodes, the molecules can be kicked into another state in which their electrons are arranged differently. This new state is a better conductor. These high- and low-conductivity states are like the 'on' and 'off' positions of a switch. An array of molecules can store information by using the on and off states to represent the 1's and 0's used by computers to store information. Subsequent voltage pulses can read the stored information by determining whether a molecule is on or off. Information can be erased by applying a negative voltage pulse, which transforms the molecules back to their low-conductivity (off) state. So the device can function like a random-access memory (RAM), which can be repeatedly written and erased. At present, Reed and colleagues make their memory devices by sandwiching the molecules between a flat upper electrode and a dome-shaped lower electrode. These electrodes make contact over a roughly circular area 30–50 millionths of a millimetre wide, which contains about a thousand molecules. All of the molecules are switched together by the voltage pulses applied to the electrodes. So each bit of information is stored in a thousand molecules. This already makes for a smaller memory device than a transistor. But the researchers say that, if molecules could be wired up individually rather than in groups, there is no reason why each could not be switched independently, so that each molecule encodes a bit. To make these memories practical, however, the team will also have to worry about issues such as switching speed and long-term stability. © Macmillan Magazines Ltd 2001 - NATURE NEWS SERVICE