UA PROFESSOR'S INNOVATION PAVES WAY FOR BETTER TELECOMMUNICATION

Above, individual atoms as seen by the University of Arkansas' Molecular Beam Epitaxy Machine.

FAYETTEVILLE, ARK. - University of Arkansas researchers and an international team have integrated a new light-dependent thermometer into a machine that will change the way the telecommunications industry looks at atoms and lead to better phones and faster computers.

The team consists of UA researchers Paul Thibado and Greg Salamo, Y. Baharav of CIU Systems Ltd., Israel and M. Ancilotti and P. Gerard of Riber, Inc., France.

The researchers use light, a foot-long bent quartz rod and a slender optical fiber bundle to measure surface temperatures in a Riber 32 Molecular Beam Epitaxy machine (MBE), which creates material atom by atom. The MBE generates a film of atoms that crystallize on a microscopic surface, forming new substances at an atomic level - growing "atomic sandwiches" layer by layer. These crystalline structures form the basis of transistors and lasers that fuel the growth of fiber-optic communications, cellular phones, direct broadcast satellite television and global positioning systems.

Until now, MBE machines have contained wire thermocouples to measure the surface temperatures of their substrates, the bottom layer of the atom sandwich. However, the thermocouple cannot touch the substrate without altering its temperature, so it hangs suspended behind the substrate - and gives readings frequently unrelated to the true sample temperature.

A few degrees too hot or too cool can cause atomic-level experiments to fail, Thibado said.

Furthermore, thermocouple measurements vary in each machine, so temperatures don’t translate well from one MBE to another, making it difficult for different research groups to replicate results.

To solve this problem, Thibado, Salamo, researchers at CI and at Riber, Inc. custom-built a system that measures light from the substrate. They shine light from a 20-Watt lamp and direct it behind the substrate using the fiber bundle and quartz rod. An instrument detects and measures the light that emerges on the other side.

"The optical properties are fundamental. When we know that temperature, we know it," Thibado said.

Thibado and his colleagues compared the results of the optical detector - that gave temperatures with 2-degree Celsius accuracy - with a thermocouple. They found that the thermocouple’s reading was sometimes as much as 15 degrees Celsius off.

The group’s work will be published in the January-February issue of the Journal of Vacuum Science and Technology. The results are already causing a stir in the telecommunications field.

Accurate temperature control becomes essential when developing theoretical models for MBE growth of compound semiconductors, the electronic components of the future, according to Mark Gyure of Hughes Research Laboratories. Without accurate temperatures scientists have no way to confirm their theories, he said.

Riber Inc. will offer the optical temperature device as an option with its customized machines.

And an NSF-funded partnership with the New Jersey-based Lucent Technologies Inc., inspired by the unique MBE facility, will foster exchange of researchers to hone research and development skills and help train the next generation of researchers.

The University of Arkansas also houses the only Scanning Tunneling Microscope attached to a phosphide MBE in the world. Click here to learn more.