New Technique Creates "Impossible" Reactions And New Electronic Materials In One Step

April 17, 1997

SAN FRANCISCO -- At temperatures far hotter than the sun's surface, University at Buffalo chemists are generating new coatings and then dramatically cooling them to, or even below, room temperature before depositing them on electronic devices.

By using such extremely high temperatures and then quenching the heat, the new technique solves one of the trickier problems in computer-chip fabrication: how to coat them while avoiding high temperatures that can cause computer chip samples to fail. This has been a serious drawback for fabricators of expensive chips for research-grade supercomputers, such as the Cray.

The technique -- utilizing an approach similar to that used in snow-making machines -- also is an improvement because the coatings it produces are always uniform and it removes from the fabrication process toxic precursors utilized in conventional methods.

The new method has applications in fabricating a wide range of thin films for use in electronic and opto-electronic materials and in fabricating uniform nanopowders for electronics applications, according to James F. Garvey, Ph.D., professor of chemistry and principal investigator.

Garvey discussed the technique here today (April 17, 1997) in an invited talk at the American Chemical Society's annual meeting. He conducted the work with Robert DeLeon, Ph.D., UB adjunct associate professor of chemistry.

Funding for the work is being provided by several Small Business Innovation Research grants, funded by Wright Patterson Air Force Base through the UB researchers' cooperative effort with Structured Materials Industries, Inc. (SMI) of Piscataway, N.J.

With the support of SMI, the UB scientists envision their technique and the apparatus they devised to implement it as eventually being marketed and sold as an accessory to expand the capabilities of molecular beam epitaxy machines, which are used widely in materials fabrication.

"We have developed a hybrid technique that marries the advantages of the two conventional fabrication methods -- laser ablation and molecular beam epitaxy -- and overcomes their disadvantages," said Garvey.

The new method, called Laser Assisted Molecular Beam Deposition (LAMBD), also takes the process for producing coatings for electronic devices a step further.

"Instead of simply sputtering a target material from point A to point B, we're chemically modifying it at the same time," Garvey said. "What's key about our fabrication method is that it causes chemical reactions that would be impossible to generate otherwise, and it does it all in one step. It provides us with a way to conduct novel, high-temperature chemistry."

Like laser ablation and molecular beam epitaxy, LAMBD uses extremely high heat to remove particles of a target material from one surface and transport it to another, creating a thin film.

"With our technique, molecules are ablated off the target material," said Garvey, "producing a plasma that is heated up to 20,000 degrees Kelvin."

What makes LAMBD different is that those molecules then collide with a pulse of gas, the identity of which is determined by the type of chemical product desired. For example, to create copper oxide, copper atoms that are ablated off a copper rod collide with oxygen.

The molecules are then pushed through a tiny nozzle, where they undergo a process that Garvey says is very similar to what happens when ice water is turned into snow in snow-making machines.

"When you pass ice water slurry through a hose, it's going from high pressure to low," he said. "That change in pressure causes the molecules to mix at a higher rate and to expand and cool, forming snow.

"In our system, the material that was ablated off the target mixes with the gas and expands as it passes through the nozzle, from high pressure to low pressure," he said. "When they get through the nozzle, the molecules physically separate, causing them to cool and to disperse into a spray, depositing material onto the substrate in a uniform layer."

Garvey noted that the technique removes from the fabrication process certain toxic precursors that otherwise are necessary in generating thin films.

For example, electronic wafers often must be coated with titanium nitride to act as a diffusion barrier. The process requires a very toxic precursor, requiring extensive safety and disposal equipment.

"With our technique, we simply blow nitrogen gas over a rod of titanium, depositing titanium nitride directly on the substrate," said Garvey. "The process results in a thin film of protective titanium nitrate without the use of toxic precursors."

So far, Garvey and DeLeon have produced a number of unique materials using LAMBD.

In collaboration with Paras Prasad, Ph.D., UB professor of chemistry, they have produced hybrid organic/inorganic films where an organic material with good optical characteristics was encapsulated in silica glass. These materials have photonics applications for new computer devices. The work was funded by the National Science Foundation's Division of Material Research.
-end-


University at Buffalo

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
Brightsurf.com 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 Amazon.com.