"Suddenly, almost every adatom started to move back and forth along the titanium row," said Lyubinetsky. "From theory and previous work, we expected to see this along the row."
Remarkably, the adatoms didn't just slide up and down the stripes. They also bounced out of them and landed in others, like pogoing dancers in a mosh pit.
"We saw quite unexpected things. We thought it was very strange -- we saw adatoms jump over the rows," Lyubinetsky said. "We just couldn't explain it."
Calculating how much energy it would take for the adatoms to move by themselves, much less hop over an oxygen row, the chemists suspected the adatoms were getting help -- most likely from the invisible water molecules.
The Unseen Enabler
To make sense of the dancing adatoms, the team calculated how much energy it would take to move adatoms with the help of water molecules. If a water molecule sits down next to an adatom, one of the water's hydrogen atoms can jump to the adatom, forming two oxygen-hydrogen pairs.
These pairs are known as hydroxyls and tend to steal atoms from other molecules, including each other. One of the thieving hydroxyls can then nab the other's hydrogen atom, turning back into a water molecule. The water molecule floats off, leaving behind an adatom. Half the time, that adatom is one spot over -- which makes the original appear to have moved.
The chemists determined that water can help the adatom jump a row as well: If a water molecule and an adatom are situated on either side of a raised oxygen row, a row oxygen can serve as the middleman, handing over a hydrogen from the water molecule to the adatom. Again, two hydroxyls form, one ultimately stealing both hydrogens (with the help of the middleman)
|Contact: Mary Beckman|
DOE/Pacific Northwest National Laboratory