By combining scanning probe microscopy and femtosecond laser techniques, a team of American researchers was able to take snapshots of the movement of molecules in a billionth of a second. The researchers said this is a significant advance in surface science, which studies phenomena such as the formation of crystals and the activity of catalysts that transform pollutants into benign gasses. Their next step will be to shoot real-time, real-space movies of molecular motions.
A team of researchers including University of California, Riverside (UCR) Assistant Professor of Chemistry, Ludwig Bartels has developed a technique to take extremely fast snapshots of molecular and atomic movement. The development is considered a significant advance in surface science, the study of chemical reactions taking place on the surface of solids.
"It was possible to identify the individual site-to-site displacements of molecules undergoing ultra-fast dynamics induced by femtosecond laser pulses," Bartels said, characterizing the technique as a way of getting something akin to snapshots of the molecules' movements.
Here are Bartels's explanations about this new technique.
Scanning probe microscopy has the capability of reaching directly down to the natural spatial scale of atoms and molecules," Bartels said. "While femtosecond laser techniques have the capability of reaching down to the time scale of atomic events.
"There has been considerable interest in the very challenging problem of combining these two capabilities," he added. "While we have not yet achieved the ultimate goal of a real-time, real-space movies, the current paper reports what we believe to be a very significant advance in combining the two very powerful techniques."
||Here is an illustration of the process of using femtosecond laser pulses to measure molecular movement of carbon monoxide on a copper substrate (Credit: UCR).|
What can we do with this new technique? Here is an example about the activities of a catalyst.
A small portion of the catalyst surface can transform the pollutant into benign gasses while the rest of the surface supports these active sites. Understanding how carbon monoxide moves across a catalyst surface to find the active sites may ultimately allow the design of more efficient catalysts. The article's findings offer a new way of studying the very fast movement of carbon monoxide on surfaces.
The research work has been published by Science. Here is a link to the abstract of the paper named "Real-Space Observation of Molecular Motion Induced by Femtosecond Laser Pulses."
Femtosecond laser irradiation is used to excite adsorbed CO molecules on a Cu(110) surface; the ensuing motion of individual molecules across the surface is characterized on a site-to-site basis by in situ scanning tunneling microscopy. Adsorbate motion both along and perpendicular to the rows of the Cu(110) surface occurs readily, in marked contrast to the behavior seen for equilibrium diffusion processes. The experimental findings for the probability and direction of the molecular motion can be understood as a manifestation of strong coupling between the adsorbates' lateral degrees of freedom and the substrate electronic excitation produced by the femtosecond laser radiation.
For more information about femtosecond lasers, you can read several previous entries.
Sources: UCR news release, via EurekAlert!, August 4, 2004; Science, Vol. 305, Issue 5684, 648-651, July 30, 2004