Featured Research

from universities, journals, and other organizations

Killer Pulses Help Characterize Special Surfaces

Date:
August 1, 2008
Source:
University of Illinois at Urbana-Champaign
Summary:
Detecting deadly fumes in subways, toxic gases in chemical spills, and hidden explosives in baggage is becoming easier and more efficient with a measurement technique called surface-enhanced Raman scattering. Researchers have now devised a method to evaluate substrate surfaces by using a series of killer laser pulses.

Researchers led by chemistry professor Dana Dlott, center, have improved the sensititvity of a measurement technique that helps in detecting deadly fumes, chemical spills or hidden explosives. Other members of the team are graduate student Ying Fang, left, and postdoctoral research associate Nak-Hyun Seong.
Credit: Photo by L. Brian Stauffer

Detecting deadly fumes in subways, toxic gases in chemical spills, and hidden explosives in baggage is becoming easier and more efficient with a measurement technique called surface-enhanced Raman scattering. To further improve the technique's sensitivity, scientists must design better scattering surfaces, and more effective ways of evaluating them.

Researchers at the University of Illinois, led by chemistry professor Dana Dlott, have devised a method to evaluate substrate surfaces by using a series of killer laser pulses. They describe the method and report measurements for a commonly used substrate in the July 18 issue of the journal Science.

Surface-enhanced Raman scattering, which functions by adsorbing molecules of interest onto rough metal surfaces, typically enhances the Raman spectrum a million times. Hot spots can occur, however, where the electric field enhancement can be a billion or more.

Current surface characterization techniques cannot tell hot spots from cold spots, and create an average value across the entire substrate surface.

"Looking at a spectrum, you can't tell if it's the result of a small number of molecules in hot spots or a large number of molecules in cold spots," Dlott said. "Two materials could have the same average spectrum, but behave quite differently."

Dlott, graduate student Ying Fang and postdoctoral research associate Nak-Hyun Seong came up with a way to measure the distribution of site enhancements on the substrate surface. Using killer laser pulses, their technique can count how many molecules are sitting in the hottest spots, how many are sitting in the coldest spots, and how many are sitting between the two extremes.

The killer pulse is a short duration laser pulse with a variable electric field. When the electric field is strong enough, it rips a molecule apart, "killing" it.

"If a molecule is in a very hot spot on the substrate, where the electric field enhancement is really big, it takes only a weak pulse to kill it," Dlott said. "If the molecule is in a very cold spot, then it takes a really big laser pulse to kill it."

Dlott, Fang and Seong demonstrated their technique by measuring the distribution of local enhancements for benzenethiolate molecules on a substrate of silver-coated nanospheres 330 nanometers in diameter.

To characterize the surface, the researchers first measured the initial Raman intensity. Then they put in a weak killer pulse, which destroyed the molecules in the hottest spots. After measuring the new Raman intensity, they put in a bigger pulse and destroyed the molecules in slightly colder spots. The researchers continued with bigger and bigger pulses until all the benzenethiolate molecules were destroyed.

"We found the hottest spots comprised just 63 molecules per million, but contributed 24 percent of the overall Raman intensity," Dlott said. "We also found the coldest spots contained 61 percent of the molecules, but contributed only 4 percent of the overall intensity."

Measurements like these, of the distribution of local site enhancements, will help researchers design better scattering surfaces for sensor applications.

Prior to this work, no one knew if the Raman intensity was dominated by a small number of hot molecules or a large number of cold ones. Dlott, Fang and Seong have answered that important scientific question; not just with a yes or no, but with a full determination of exactly how many molecules there are in each level of hot or cold.

"Now, when evaluating a new surface-enhanced Raman material, instead of knowing just the average intensity, we know the highest, the lowest, and everything in between," Dlott said.

Funding was provided by the National Science Foundation, the Air Force Office of Scientific Research, and the Army Research Office. Electron microscopy was carried out in the university's Center for Microanalysis of Materials, which is supported by the U.S. Department of Energy.


Story Source:

The above story is based on materials provided by University of Illinois at Urbana-Champaign. Note: Materials may be edited for content and length.


Cite This Page:

University of Illinois at Urbana-Champaign. "Killer Pulses Help Characterize Special Surfaces." ScienceDaily. ScienceDaily, 1 August 2008. <www.sciencedaily.com/releases/2008/07/080729133531.htm>.
University of Illinois at Urbana-Champaign. (2008, August 1). Killer Pulses Help Characterize Special Surfaces. ScienceDaily. Retrieved September 20, 2014 from www.sciencedaily.com/releases/2008/07/080729133531.htm
University of Illinois at Urbana-Champaign. "Killer Pulses Help Characterize Special Surfaces." ScienceDaily. www.sciencedaily.com/releases/2008/07/080729133531.htm (accessed September 20, 2014).

Share This



More Matter & Energy News

Saturday, September 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

What This MIT Sensor Could Mean For The Future Of Robotics

What This MIT Sensor Could Mean For The Future Of Robotics

Newsy (Sep. 20, 2014) MIT researchers developed a light-based sensor that gives robots 100 times the sensitivity of a human finger, allowing for "unprecedented dexterity." Video provided by Newsy
Powered by NewsLook.com
MIT BioSuit A New Take On Traditional Spacesuits

MIT BioSuit A New Take On Traditional Spacesuits

Newsy (Sep. 19, 2014) The MIT BioSuit could be an alternative to big, bulky traditional spacesuits, but the concept needs some work. Video provided by Newsy
Powered by NewsLook.com
New Music With Recycled Instruments at Colombia Fest

New Music With Recycled Instruments at Colombia Fest

AFP (Sep. 19, 2014) Jars, bottles, caps and even a pizza box, recovered from the trash, were the elements used by four musical groups at the "RSFEST2014 Sonorities Recycling Festival", in Colombian city of Cali. Duration: 00:49 Video provided by AFP
Powered by NewsLook.com
Virtual Reality Headsets Unveiled at Tokyo Game Show

Virtual Reality Headsets Unveiled at Tokyo Game Show

AFP (Sep. 18, 2014) Several companies unveiled virtual reality headsets at the Tokyo Game Show, Asia's largest digital entertainment exhibition. Duration: 00:48 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins