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.
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.
“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.
James E. Kloeppel | University of Illinois
Building a brain, cell by cell: Researchers make a mini neuron network (of two)
23.05.2018 | Institute of Industrial Science, The University of Tokyo
Research reveals how order first appears in liquid crystals
23.05.2018 | Brown University
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
The historic first detection of gravitational waves from colliding black holes far outside our galaxy opened a new window to understanding the universe. A...
A team led by Austrian experimental physicist Rainer Blatt has succeeded in characterizing the quantum entanglement of two spatially separated atoms by observing their light emission. This fundamental demonstration could lead to the development of highly sensitive optical gradiometers for the precise measurement of the gravitational field or the earth's magnetic field.
The age of quantum technology has long been heralded. Decades of research into the quantum world have led to the development of methods that make it possible...
02.05.2018 | Event News
13.04.2018 | Event News
12.04.2018 | Event News
23.05.2018 | Life Sciences
23.05.2018 | Life Sciences
23.05.2018 | Physics and Astronomy