Scientists image 'magnetic semiconductors' on the nanoscale

Flatté notes that the team took a completely different approach toward seeing the magnetic interactions. Instead of trusting luck to help them find an arrangement of atoms, they placed the manganese atoms one at a time into a fresh, clean piece of gallium arsenide. "Using the tip of a scanning tunneling microscope, we can take out a single atom from the base material and replace it with a single metal that gives the semiconductor its magnetic properties," says Ali Yazdani, Princeton University physics professor and article co-author. He notes that the effort marks the first time that scientists have achieved this degree of control over the atomic-level structure of a semiconductor. In essence, the team used this unique capability to make a semiconductor magnetic, one atom at a time. "The ability to tailor semiconductors on the atomic scale is the holy grail of electronics, and this method may be the approach that is needed," says Yazdani.

Dale Kitchen, a researcher in Yazdani's lab, hit upon the solution while working with a high-tech tool used to explore complex materials called a scanning tunneling microscope, a device that operates very differently from a desktop optical microscope. The device has a finely-pointed electrical probe that passes over a surface in order to detect variations with a weak electric field. The team, however, found that the charged tip could also be used to eject a single gallium atom from the surface, replacing it with one of manganese that was waiting nearby.

By incorporating manganese atoms into the gallium arsenide semiconductor, the team has created an atomic-scale laboratory that can reveal what researchers have sought for decades: the precise interactions among atoms and electrons in chip materials. The team used their new technique to find the optimal arrangements for manganese atoms that enhance the magnetic properties of gallium manganese arsenide. These arrangements agreed with Flatté and Tang's predictions. "To predict how a material will behave, and then have that prediction dramatically confirmed, as in this experiment, is one of the most enjoyable experiences of research," says Flatté.

Flatté cautions that further advances will be required to translate the new research results into new chip technology and also that using a scanning tunneling microscope to grow large pieces of high quality gallium manganese arsenide may not be practical. However, he says, the lessons learned about optimal arrangements of magnetic atoms in semiconductors will be transferred to other semiconductor growth techniques and to other magnetic semiconductor materials.

The research project was funded in part by the National Science Foundation and the U.S. Army Research Office.

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