July 23, 2011

by Benjamin White

At the SPIRE workshop in Hamburg, Germany on June 30, NQPI director Dr. Arthur Smith and recent Ohio University physics graduate Daniel Bergman were proud to present a talk on OU's new spin-polarized scanning tunneling microscope (SP-STM) and its new material growth systems.
Smith began the presentation with an overview of the SP-STM, which cost roughly half a million dollars and was designed by NQPI researchers. Bergman continued the talk by explaining the state-of-the-art material deposition systems contained in the unit.

The new SP-STM is capable of creating materials using two techniques: molecular beam epitaxy (MBE) and pulsed laser epitaxy (PLE). MBE, the only method OU researchers could use in the past, works by shooting the material in a gas form out of a tube like a can of spray paint. The newer system, PLE, works by firing a laser at targeted particles. The super-powerful laser forms a particle plume – forming gas straight from the solid state of the material – which is deposited on a substrate, forming a much more even and controllable surface than the MBE method. Up to five elements can be used for a single sample in rapid succession to form complex substrates that will help researchers experiment with new materials that could be used in future quantum computing.

The machine even has a wheel with ten spots where different materials can be placed. After the laser deposits one material, the wheel can quickly be turned and the process can be repeated, making multi-material creation easier and faster.

“Surprisingly, it's a lot harder to get together than you would think,” said Bergman.

At first, the SP-STM experimenters experienced noise problems – sound waves in the lab's ancient building (through both the air and the floor) created vibrations that interfered with the machines precise readings. To fix this, NQPI scientists and engineers mounted the entire microscope and material depositing system on pneumatic legs, making super-effective shocks which solved the sound vibrations from the building. To fix the acoustic vibrations (those traveling through the air), they rigged a box lined with vinyl, cotton and aluminum around the sensitive area. These materials blocked sound waves and preserved the sensitivity of the behemoth machine.

Currently, the researchers are experiencing problems with the PLE laser but engineers hope to get the machine up and running in the near future.

The new SP-STM opens many doors for NQPI researchers. New, more complex substrates can be made much more easily and quickly, and, since the machine performs at very low temperatures, researchers can now define single atoms, a feat which proved difficult with the old equipment which performed at room temperature.

“It's definitely given me a new look on performing research,” said Bergman.

Bergman is currently studying at the University of Hamburg, where the SPIRE workshop took place. The school, which is much bigger than Ohio University, has almost a dozen STMs, and Bergman's job is to help run research with one of them. He will be attending the University of Toledo as a graduate physics student in the fall.
“It's a sweet place to study abroad,” he said. “Everyone is here to help you.”