Nanoparticles drive display

Over the past decade researchers have moved closer to the goal of electronic paper -- a computer screen that combines the data manipulation abilities of computers with the high contrast and physical flexibility of paper.

Researchers from the Hong Kong University of Science and Technology in China and the Polytechnic School in France have advanced the field with a technology that has the potential to provide inexpensive, low-power, color electronic paper.

Like existing electronic paper schemes, the researchers' method involves manipulating tiny particles dispersed in liquid. Existing schemes move negatively charged black particles and positively charged white particles to the back or front of a tiny chamber depending on the polarity of an applied electric field. The new scheme, however, uses neutral rather than charged particles.

The researchers' neutral particles gain electric charges -- negative at one end and positive at the other -- in the presence of an electric field. When this happens, the particles connect to each other like magnets, forming chains between pairs of electrodes.

Particles floating in liquid allow light through, while particles that have formed chains do not. The chains remain in place for several hours after the electric field is switched off. Given a white background and black particles, the display looks like paper.

The particles are made from barium titanium oxalato surrounded by a urea shell, and average 50 nanometers in diameter. A nanometer is one millionth of a millimeter.

The researchers' next steps are to modify the nanoparticles to provide color and reduce the power needed to form chains.

The display could be ready for commercial use in five to ten years, according to the researchers. The work appeared in the March 1, 2005 issue of Nanotechnology (Neutral Nanoparticle-Based Display).