January 9, 2006

Nanomaterials bloom

Much of today's nanotechnology is the result of materials science research, and materials science, in turn, is a cross-disciplinary combination of chemistry, physics and engineering. The ability to control the composition of materials at the nanoscale makes it possible to produce materials that have very specific electrical, optical, magnetic and chemical properties.

Researchers from IBM Research, Columbia University and the University of Michigan have found that a technique for engineering materials at the nanoscale, dubbed binary nanoparticle superlattices, has a considerably greater range of possibilities than previously thought. They produced dozens of materials by arranging two types of nanoparticles that differ by composition and size into various crystal structures.

Previous simulations that treated nanoparticles as simple spheres showed limited potential for the technique, but the the laws of physics for particles of various substances in the 1 to 10 nanometer range proved otherwise. The researchers produced 11 different crystal structures, for instance, by changing the arrangement of 6.2 nanometer lead selenium nanoparticles with 3 nanometer palladium nanoparticles.

The materials could eventually be used to make inexpensive computer chips, photonic crystals, data storage devices and chemical catalysts.

(Structural Diversity in Binary Nanoparticle Superlattices, Nature, January 5, 2006)

Nano gives solar 2-for-1

There are two ways to make solar cells more practical: decrease their prices and increase their efficiency. The lion's share of solar cell advances have been in the former camp -- making solar cells less expensive by making them from inexpensive materials like like plastics and zinc oxide. A couple of recent developments, however, show that there's a lot of potential for boosting the amount of electricity the average solar cell produces.

Solar cell's work by converting sunlight's photons into electrons that can be put to practical use as electricity.

Los Alamos National Laboratory researchers have shown that it is possible to produce two or more electrons from a single photon using many kinds of semiconductor materials, not just the more exotic lead selenium of initial carrier multiplication experiments. (See Solar crystals get 2-for-1, TRN, May 19/26, 2004)

The researchers' tests show that many kinds of semiconductor nanocrystals can be used to coax more than one electron from a photon, and that the size of the minuscule particles rather than their composition is key to the phenomenon.

Solar cells made with semiconductor nanocrystals could use carrier multiplication to boost solar efficiency to 60 percent, according to the researchers. Today's state-of-the-art solar cells are less than 40 percent efficient.

(Effect of Electronic Structure on Carrier Multiplication Efficiency: Comparative Study of PbSe and CdSe Nanocrystals, Applied Physics Letters, December 19, 2005)

Email shows it's who you know

Social networks are notoriously difficult to study. Fortunately, computer networks are changing that.

Columbia University researchers studied more than 14 million email messages generated by more than 43,000 members of a large university over the course of a year. The study tracked pairs of email correspondents based on attributes like gender, age, departmental affiliation, status, and years in the community, and classes taught or attended.

The study looked at the factors that influence whether strangers form a connection via mutual acquaintances. As it turns out, key factors are the strength of ties to mutual acquaintances, number of mutual acquaintances, and having shared classes, while individual attributes don't have a significant influence in forming connections.

Shared friends and shared activities win out over shared characteristics, at least in universities.

(Empirical Analysis of an Evolving Social Network, Science, January 6, 2006)

Sensor sees spark of life

Increasingly, and in many ways, computer chip technology is proving invaluable to the life sciences.

Researchers from the University of Manchester in England and the Institute for Microelectronics Technology in Russia have made an electric field sensor that detects the electric charge of a single electron, and does so at room temperature rather than less practical cryogenic temperatures.

The sensor is a semiconductor device that can measure electric fields in spaces as small as 100 nanometers, which is about one tenth the size of an E. coli bacterium.

The researchers used the sensor to measure the electrical responses of individual yeast cells to changes in their environment. The sensor could be used in biochips and laboratory equipment that monitors biological activity.

(Submicron Sensors of Local Electric Field with Single-Electron Resolution at Room Temperature, Applied Physics Letters, January 2, 2006)

Bits and pieces

A microfluidic device measures subtle changes in pressure like when a cell membrane ruptures, an infrared camera system aligns images of organs projected onto human bodies, a test with a spacecraft nearly 15 million miles from Earth shows the potential for interplanetary laser-based communications.