Scientists Land New Way To Modify Ultrasmall Surfaces

March 07, 1997

WEST LAFAYETTE, Ind. -- It sounds almost like a James Bond thriller -- tiny chemical structures are parachuted onto a surface for strategic safe-keeping, and then retrieved when duty calls.

Purdue University scientists have developed a way to bring chemical structures known as ions in for a "soft-landing" on surfaces, providing a new way to trap and study ions and modify the outermost layer of materials.

The new technique, outlined in today's (Friday, 3/7) issue of the journal Science , provides a way to alter surfaces of even the tiniest components, opening doors for new applications in computing, microelectronics and storing information at a nanoscale level.

"Many properties of materials depend on their surfaces for such traits as electrical conductivity and resistance to degradation," says R. Graham Cooks, the Henry Bohn Hass Distinguished Professor of Chemistry at Purdue.

"Our method differs from other deposition methods in that the ions do not react chemically with the surface on which they are being deposited. This not only allows us to preserve the ions for future use, but also allows us to modify the surface of a material in a way that is reversible."

Chemically modified surfaces are used in a variety of consumer items ranging from Saran Wrap to Post-it Notes. But traditional methods of modification rely on a limited range of chemicals that react after they are deposited on the surface, Cooks says.

His approach is done with a completely different chemical species, molecular ions, which can be selected on the basis of mass, allowing for a higher degree of chemical selection. Ions are electrically charged atoms or molecules, formed when an atom gains or loses an electron. Ions play a role in many everyday chemical reactions, such as those in electrical batteries.

To study ions, scientists use instruments called mass spectrometers, which generate the charged particles by turning neutral atoms or molecules into a gas, or vaporizing them, and passing them through a beam of high-speed electrons. Electrical and magnetic fields are used to control and measure the paths of the ions as they accelerate in the vacuum in the machine.

Though mass spectrometers make it possible to study ions, the particles are only stable while in flight. When they hit a surface, crash landings take a toll on the tiny structures, making it impossible to preserve them or deposit them onto a surface without destroying them, Cooks says. "Even the most successful instruments can trap ions for only a few seconds," he says.

Cooks and his students Scott Miller, now a researcher at Princeton University, and Hai Luo developed a way to "parachute" ions onto a surface and bring them in for a soft landing.

"Our study shows for the first time that polyatomic ions can be transferred from the gas phase to a surface and held there for periods of days," Cooks says.

They deposited ions onto gold surfaces covered with a single layer of organic molecules, which stood vertically like flagpoles from the surface and were strongly bonded to the gold. These molecules, called fluorocarbons, are inert compounds that resemble the chemicals that make up Teflon.

"These features of fluorocarbons may be why the ions can land on the surface without reacting with it," Cooks says.

Like tiny parachutes, bulky groups of trimethylsilicon molecules were attached to the end of each ion to slow its landing and ensure that it did not hit the gold surface. Instead, the ions wedged between the fluorocarbon structures. Once the ions landed, the fluorocarbons serve as shields to keep the chemically reactive particles from interacting with the gold surface or with molecules in the air.

The findings represent the first successful attempt to "soft-land" molecules onto a surface, and hold promise for new ways of modifying the outermost layer of surfaces, Cooks says.

"This experiment allows virtually any chemical species to be generated in a mass spectrometer as an ion, and injected into a surface," he says.

Using this method to deposit ions on a surface also will allow scientists to expand studies of isolated ions, Cooks says. "Because the fluorocarbon molecules keep the ions from reacting with other atoms and molecules, scientists can for the first time perform studies of isolated ions outside a mass spectrometer."

The method also allows scientists to trap undamaged ions on a surface for days at a time, then release them back into the mass spectrometer for further study.

"Our knowledge of ions can be greatly increased by the opportunity to study them at relative leisure while they are trapped and immobile in a surface," he says. "Such studies could boost progress in the many areas to which mass spectrometry is applied, from testing for drugs to determining the age of archaeological samples and monitoring environmental pollutants in the air and water."

The Purdue group collaborated with Steven J. Pachuta, a research scientist at the 3M Co. in St. Paul, Minn. The surfaces prepared with ions were first analyzed at Purdue and then sent to 3M for an independent analysis with a higher resolution instrument.

The study was funded by the National Science Foundation. Source: R. Graham Cooks, (765) 494-5263; e-mail,
Writer: Susan Gaidos, (765) 494-2081; e-mail,
Purdue News Service: (765) 494-2096; e-mail,

NOTE TO JOURNALISTS: Copies of the journal article are available from Purdue News Service.

Purdue University

Related Molecules Articles from Brightsurf:

Finally, a way to see molecules 'wobble'
Researchers at the University of Rochester and the Fresnel Institute in France have found a way to visualize those molecules in even greater detail, showing their position and orientation in 3D, and even how they wobble and oscillate.

Water molecules are gold for nanocatalysis
Nanocatalysts made of gold nanoparticles dispersed on metal oxides are very promising for the industrial, selective oxidation of compounds, including alcohols, into valuable chemicals.

Water molecules dance in three
An international team of scientists has been able to shed new light on the properties of water at the molecular level.

How molecules self-assemble into superstructures
Most technical functional units are built bit by bit according to a well-designed construction plan.

Breaking down stubborn molecules
Seawater is more than just saltwater. The ocean is a veritable soup of chemicals.

Shaping the rings of molecules
Canadian chemists discover a natural process to control the shape of 'macrocycles,' molecules of large rings of atoms, for use in pharmaceuticals and electronics.

The mysterious movement of water molecules
Water is all around us and essential for life. Nevertheless, research into its behaviour at the atomic level -- above all how it interacts with surfaces -- is thin on the ground.

Spectroscopy: A fine sense for molecules
Scientists at the Laboratory for Attosecond Physics have developed a unique laser technology for the analysis of the molecular composition of biological samples.

Looking at the good vibes of molecules
Label-free dynamic detection of biomolecules is a major challenge in live-cell microscopy.

Colliding molecules and antiparticles
A study by Marcos Barp and Felipe Arretche from Brazil published in EPJ D shows a model of the interaction between positrons and simple molecules that is in good agreement with experimental results.

Read More: Molecules News and Molecules 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