C drive. Each fluorescent dot is about 300 nanometers wide and written using laser pulses in a derivative of phenolphthalein, a common pH indicator found in high school labs.

Memory That Sticks

Epoxy glues and their chemical relatives may join the next generation of high-density memory materials. New findings reveal that these inexpensive substances can store data in three dimensions at densities 10 or more times that of DVDs.

As impressive as the magnetic technology in a computer hard drive is, it can only store data in two dimensions. Researchers hoping to cram in more megabytes have grown increasingly interested in using lasers to encode and store data in three dimensions. One promising technology involves zapping certain types of materials with a tightly focused laser. At the spot where the laser is focused, the light kicks off a chemical alteration that causes the spot to fluoresce the next time it's exposed to the light. The process is known as multiphoton absorption because three photons are required to create a fluorescing spot. However, many materials used for such optical memory degrade when their data is read, or they require expensive, high-powered lasers.

Almost by accident, while studying supercooled liquids and glasses, physical chemist John Fourkas of Boston College and colleagues discovered that multiphoton absorption can be used to store data in cheap epoxies and other common materials. In the December issue of Nature Materials, the team reports that data encoded as fluorescent spots in these materials can be read more than a million times without degrading. The storage capacity of the half-dozen or so materials looked at so far is about 870 megabytes per square centimeter and requires laser pulses 1/500 to 1/1000 as intense as those used for previous multiphoton data storage techniques. Such optical memory can also break away from the mold of the disk shape and assume any form. And with refinements, Fourkas says the materials could encode up to 200 layers of data, dwarfing the one or two layers used in DVDs.

Despite these advantages, a serious limitation of this new technology is that data can now only be written one bit at a time instead of being stamped out all at once as with CD-pressing technology. Writing the equivalent of one double-sided DVD at the current rate would take about 3 weeks. Even so, applied physicist Eric Mazur of Harvard University says, "for large amounts of archival data such as with law firms or hospitals, this could prove useful." Fourkas adds that further improvements should speed up the process by lowering the amount of power required to write one spot and allowing multiple spots to be written simultaneously.

Related site
The Fourkas Lab

Posted in Math