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[Sandia Lab News]

Vol. 56, No. 8           April 16, 2004
[Sandia National Laboratories]

Albuquerque, New Mexico 87185-0165    ||   Livermore, California 94550-0969
Tonopah, Nevada; Nevada Test Site; Amarillo, Texas

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Sandia researcher brings Bell Labs technique to wiring molecules Combustion Research Facility team and partners measure car's particulate emissions driving on road



Sandia researcher brings Bell Labs technique to wiring molecules

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By Neal Singer

Attaching electrical wires to a chain of atoms is a lot harder than wiring a light bulb.

That may explain why Sandia researcher Julia Hsu's (1114) invited talk on creating electrical contacts for molecules attracted approximately 250 researchers at the American Physical Society's March Meeting in Montreal. The overflow crowd filled the seats and jammed the aisles of the too-small double room.

Single molecules could function as inexpensive, reliable chem/bio detectors, if an electrical signal could be made to flow through a molecule in a controlled manner. Such molecules can be designed to chemically bind to specific substances. Attachment of a target substance onto the molecule would then result in easily detectable variations in electrical output.

The American Institute of Physics' The Industrial Physicist magazine had briefly highlighted Julia in its December issue. The magazine noted that while "large changes in conductivity can be achieved with a single molecule," still "conductivity is profoundly affected by the way in which molecules are contacted." The article helped emphasize the need to return to pursuing more fundamental problems in molecular electronics after the journal Science had attacked the fledgling field in an article last year for claims of technological successes that the journal found dubious.

One problem was that earlier attempts to pass a current through a molecule foundered on the difficulty of attaching electrical nanocontact points to molecules. Electrical short-circuiting between the positive and negative contacts generally plagued device yields, and spurious electrical paths have often been misinterpreted as currents passing through the length of the signal molecule.

Julia's solution, brought with her from Bell Labs, uses a technique that resembles a child's printing set. It is called nanotransfer printing. The molecules she uses have a chain of carbon atoms anchored by sulfur atoms at each end. These molecules form a monolayer on a gallium-arsenide substrate with one of the sulfur ends binding to the gallium arsenide. The carbon chains and the other sulfur end groups elevate above the substrate like a field of wheat rising above the ground. To the top of this raised field, Julia applies a soft silicone stamp covered by a gold film. The gold film is able to chemically bond to the raised sulfur atoms while remaining strong enough to form an otherwise unsupported canopy (something like the way an umbrella's fabric does not need to be supported at every point to form a surface), rather than dripping down to the substrate and shorting out the device.

This gold canopy and the gallium arsenide substrate form positive and negative contacts for the attached field of molecules.

Her method boasts a 97 percent success rate, she says, compared to less than five percent successful yield in devices that involved merely evaporating metals onto the stand-up molecules.

"This is still basic science, not a useful device yet," Julia says. "It does not yet have features such as integration with silicon or a separate gate to make a transistor. There are many technical challenges to realize these goals and many researchers are tackling these questions. What I am doing is laying the basic scientific foundation for this very promising but still emerging technology."

More work remains to be done, she says, to establish parameters for different metals and varying temperatures and pressures. She is building collaborations with researchers in 1100, 1700, and 8700 to establish a research program in this area within Sandia.

Mark J. Cardillo, executive director at the Camille and Henry Dreyfus Foundation in New York, exited Julia's talk smiling. Asked why, he said it was an excellent talk and then volunteered that "I've never had a better postdoc for being unafraid to get to the core of an issue, and I have had some very good postdocs." Cardillo was a former executive at Bell Labs, from which Julia recently emigrated to Sandia.

Julia will co-chair the fall meeting of the Materials Research Society in 2004. -- Neal Singer

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Combustion Research Facility team and partners measure car's particulate emissions driving on road

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By Mike Janes

While on-board measurements of gaseous emissions are routine, real-time particulate measurements have been far more elusive, yet are essential for validating federal emissions guidelines for vehicle compliance.

Laser-induced incandescence

Pete Witze (8362) recently collaborated with Artium Technologies, Chevron Oronite, and the National Research Council (NRC) Canada to demonstrate the feasibility of obtaining on-board measurements of vehicle particulate emissions using laser-induced incandescence (LII) technology. LII is a nonintrusive diagnostic technology that can perform "real-time" measurements of particulate emissions produced by internal combustion engines.

Sandia, Artium Technologies, and the NRC have worked together to develop the portable version of LII instrumentation that was successfully applied during this recent trial. Consequently, this new method may alter the way in which the automotive industry effectively gauges particulate emissions.

During the past decade, CRF and NRC researchers honed the LII technique, discovered in the 1970s, with the NRC securing an important temperature-measurement patent that is key to the current measurement capability.

The most notable result during the recent tests, says Pete, was obtained during the coasting descent. "Although the vehicle speed and engine rpm were reasonably steady for the period from 470 to 600 seconds, the particulate emissions suggest that fuel injection cycled on and off intermittently," he says.

While the researchers believe the ideal fueling strategy would be to turn off injection for the entire descent, the vehicle is equipped with a catalyst that needs to be kept at its operating temperature.

The average particulate emissions measured by LII during this period were 8.4 ppb, as compared to 10-11 ppb during steady-state idle. This suggests that the engine control module has been programmed to minimize fuel consumption during a descent while maintaining idle-like particulate emission levels and an active catalyst.

Increasing environmental interest

The ability to measure on-board particulate tailpipe emissions is of growing environmental interest because of the desire to validate current US Environmental Protection Agency (EPA) vehicle certification procedures. These procedures, which have been the industry standard for more than 30 years, measure emissions using a chassis dynamometer and specify engine speed to be applied during testing. Because such tests do not replicate variables such as grade changes and weather encountered under actual driving conditions, the automotive industry expects dynamometer emissions testing to be supplemented with on-road measurements in the future.

In general, innovative new methods are needed to evaluate the effects of mobile source emissions -- both from off- and on-road sources -- on air quality, especially as the EPA and state agencies, such as the California Air Resources Board (CARB), update their mobile source emission models.

In conducting the tests, Artium's commercially available LII instrument and ancillary equipment were placed in the trunk and on one side of the rear seat of a 2002 Volkswagen Jetta with automatic transmission and a turbocharged direct-injection (TDI) diesel engine. An on-board diagnostics scan tool interface was used to access the vehicle and engine speeds for recording while the vehicle was driven on a test route in the Livermore valley.

These measurements were then time-matched with the LII measurements to obtain a synchronized data set correlating time-resolved particulate emissions with a variety of vehicle operating conditions that included city driving, freeway driving with entrance-acceleration and hill ascent, and coasting descent on a rural road.

Pete said another unique aspect of the LII measurement technique is that, unlike other systems, it does not require an operator to conduct the tests. For this and other reasons, he said engine manufacturers have proven to be "extremely interested" in LII.

Pete spoke on the topic of on-board particulate emissions at the Coordinating Research Council's 14th On-Road Vehicle Emissions Workshop on March 29 in San Diego. -- Mike Janes

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Last modified: April 14, 2004

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