For the first time, scientists have manipulated hydrogen atoms into stable sites beneath the surface of a palladium crystal, creating a structure predicted to be important in metal catalysts, in hydrogen storage, and in fuel cells. The research will be published in the 13 December 2005 issue of the journal
Proceedings of the National Academy of Science...
The researchers carried out the experiments in a low-temperature scanning tunneling microscope (STM) under ultrahigh vacuum by exposing the crystal to a hydrogen atmosphere. They removed excess hydrogen from the surface by cycles of exposure to heat and oxygen. After the surface had been cleaned, the researchers were able to use electrons from the STM tip to move hydrogen atoms that had been absorbed into the bulk metal up into the stable subsurface sites.
As the hydride formed underneath the surface of the material, Weiss and his team observed that the surface of the crystal distorted, the positive charge of palladium atoms above them increased, and interactions occurred with hydrogen atoms on the surface of the palladium crystal. "One of the most interesting aspects of the research was the ability to move atoms beneath the surface," Weiss says. "The observation of the effects of the populated sites, such as surface distortion, confirmed the existence of the stable sites and the theoretical predictions of the physical and electrical properties of the hydrides."....
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