Molecular film on liquid mercury reveals new properties

November 14, 2002

UPTON, NY -- A team of scientists from the U.S. Department of Energy's Brookhaven National Laboratory, Harvard University, and Bar-Ilan University in Israel have grown ultrathin films made of organic molecules on the surface of liquid mercury. The results, reported in the November 15, 2002, issue of Science, reveal a series of new molecular structures that could lead to novel applications in nanotechnology, which involves manipulating materials at the atomic scale.

Growing molecular films on liquid surfaces is part of an ongoing activity by Brookhaven scientists to create nanomaterials, which are a few billionths of a meter in thickness. Ultrathin films are becoming increasingly important for fast-developing applications, such as faster and smaller electronic and magnetic devices, advanced biotechnological membranes, and controlled drug release in the human body. The Brookhaven team is a leader in the field of liquid surface-supported film growth, with expertise gained over the past 20 years.

"When you grow a film on a solid surface, the molecules of the film tend to interlock with those of the underlying support," says Benjamin Ocko, the Brookhaven physicist who participated in the study. "But an underlying liquid surface is not ordered and provides an ideal setting for studying ultrathin states of matter without the complications of the solid support."

Ocko and his colleagues first filled a small tray with liquid mercury and then deposited on the surface a nanometer-thin film of stearic acid, an organic waxlike material that is a common component of cell membranes. Since stearic acid is not soluble in mercury, it floats on the surface.

To see how the molecules of the film organize on the surface, the scientists measured how x-rays produced by the National Synchrotron Light Source at Brookhaven scattered off the ultrathin molecular film. Key to the study was a unique instrument used for tilting the x-rays downward onto the liquid mercury surface, which was developed by Peter Pershan, a physicist at Harvard and one of the study's authors, along with the Brookhaven team.

The scientists discovered that, as the number of molecules deposited on the surface increased, they formed four distinct patterns. "First, when a few molecules are deposited, they tend to take as much space as they can, by lying on the surface," explains Henning Kraack, a physics Ph.D. student from Bar-Ilan and the study's lead author. "When more molecules are added, a second layer of molecules lies on top of the first one.

"Then, as even more molecules are deposited," Kraack continues, "they 'stand up' to leave more space to neighboring molecules, allowing them to densely pack in one layer. But even then, before standing up straight, the molecules are first tilted to the side, and stand up completely only when they are 'squeezed' by other molecules that 'elbow their way through.'"

These observations came as a surprise, since previous studies have shown that, when stearic molecules are deposited on water -- the only other liquid support studied so far -- they only stand up on the surface. "Patterns in which molecules lie flat on a liquid surface have never been observed before," Kraack says.

Moshe Deutsch, a physicist at Bar-Ilan and one of the authors of the study, notes that because the liquid mercury does not seem to influence too much the way the stearic molecules assemble, "growing films on a liquid surface is like growing them without support at all." It might be possible to choose a film pattern, he adds, simply by selecting the appropriate molecular coverage.

"This work shows that without an underlying lattice, we can control film growth," Deutsch says. "By growing other molecules on a liquid support, we will be able to control the size and properties of other films, and thus tailor them for different applications, in particular their use in nanoelectronics and nanosensor technology."
This work was funded by the U.S. Department of Energy, which supports basic research in a variety of scientific fields, the National Science Foundation, and the U.S.-Israel Binational Science Foundation in Jerusalem, Israel.

Visit Brookhaven Lab's electronic newsroom for links, news archives, graphics, and more:

The U.S. Department of Energy's Brookhaven National Laboratory ( conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies. Brookhaven also builds and operates major facilities available to university, industrial, and government scientists. The Laboratory is managed by Brookhaven Science Associates, a limited liability company founded by Stony Brook University and Battelle, a nonprofit applied science and technology organization.

Note to local editors: Ben Ocko lives in Stony Brook, New York.

DOE/Brookhaven National Laboratory

Related Mercury Articles from Brightsurf:

Mercury's 400 C heat may help it make its own ice
Despite Mercury's 400 C daytime heat, there is ice at its caps, and now a study shows how that Vulcan scorch probably helps the planet closest to the sun make some of that ice.

New potential cause of Minamata mercury poisoning identified
One of the world's most horrific environmental disasters--the 1950 and 60s mercury poisoning in Minamata, Japan--may have been caused by a previously unstudied form of mercury discharged directly from a chemical factory, research by the University of Saskatchewan (USask) has found.

New nanomaterial to replace mercury
Ultraviolet light is used to kill bacteria and viruses, but UV lamps contain toxic mercury.

Wildfire ash could trap mercury
In the summers of 2017 and 2018, heat waves and drought conditions spawned hundreds of wildfires in the western US and in November, two more devastating wildfires broke out in California, scorching thousands of acres of forest, destroying homes and even claiming lives.

Removing toxic mercury from contaminated water
Water which has been contaminated with mercury and other toxic heavy metals is a major cause of environmental damage and health problems worldwide.

Fish can detox too -- but not so well, when it comes to mercury
By examining the tissues at a subcellular level, the researchers discovered yelloweye rockfish were able to immobilize several potentially toxic elements within their liver tissues (cadmium, lead, and arsenic) thus preventing them from interacting with sensitive parts of the cell.

Chemists disproved the universal nature of the mercury test
The mercury test of catalysts that has been used and considered universal for 100 years, turned out to be ambiguous.

Mercury rising: Are the fish we eat toxic?
Canadian researchers say industrial sea fishing may be exposing people in coastal and island nations to excessively high levels of mercury.

New estimates of Mercury's thin, dense crust
Michael Sori, a planetary scientist at the University of Arizona, used careful mathematical calculations to determine the density of Mercury's crust, which is thinner than anyone thought.

Understanding Mercury's magnetic tail
Theoretical physicists used simulations to explain the unusual readings collected in 2009 by the Mercury Surface, Space Environment, Geochemistry, and Ranging mission.

Read More: Mercury News and Mercury Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to