Research Electronic & Optical Materials Material Growth Current Research
| Current Research |
Researchers at Chapel Hill, led by John Boland, associate professor of chemistry, use the scanning tunneling microscope to observe how hydrogen atoms behave and bond to surfaces at high temperature. They have seen a form of atomic Ping-Pong in which hydrogen atoms unpair, hop back and forth on the surface of silicon and sometimes even exchange partners. This research group was the first to witness the atoms hopping around the surfaces of silicon wafers - the raw material for making computer chips.
Each wafer is built from layers of silicon or other semiconductor material. The researchers bombarded tiny samples of silicon in a vacuum chamber with deuterium, or "heavy" hydrogen atoms. The dangling bonds of the silicon surface were almost entirely filled by the hydrogen. Then the chemists watched the surface through the STM. Instead of following the hydrogen atoms, the researchers tracked the bright spots made by the dangling bonds as they heated the surface to about 650 degrees farenheit. The research group confirmed that at relatively low temperatures, an individual dangling bond would hop from one silicon dimer to another. They also saw that at higher temperatures the bonds leap even further - even across a gap left by a missing dimer. Other researchers had predicted hydrogen hopping, however nobody had seen how the atoms interacted with a surface in such detail. Now the researchers are trying to find out why dangling bonds can pass over some defects but not others. This information should bring the chemists closer to the bigger goal of understanding how hydrogen comes off a silicon wafer's surface at even higher temperatures. |
